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CHEMISTRY (537 journals)                  1 2 3 4 5 6 | Last

2D Materials     Hybrid Journal   (Followers: 3)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 31)
ACS Catalysis     Full-text available via subscription   (Followers: 24)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 13)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 8)
ACS Macro Letters     Full-text available via subscription   (Followers: 17)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 25)
ACS Nano     Full-text available via subscription   (Followers: 270)
ACS Photonics     Full-text available via subscription   (Followers: 2)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 8)
Acta Chemica Iasi     Open Access  
Acta Chimica Sinica     Full-text available via subscription  
Acta Chimica Slovaca     Open Access   (Followers: 6)
Acta Chromatographica     Full-text available via subscription   (Followers: 10)
Acta Facultatis Medicae Naissensis     Open Access   (Followers: 1)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 4)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 3)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 4)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 8)
Advanced Functional Materials     Hybrid Journal   (Followers: 34)
Advances in Chemical Engineering and Science     Open Access   (Followers: 21)
Advances in Chemical Science     Open Access   (Followers: 8)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 13)
Advances in Drug Research     Full-text available via subscription   (Followers: 17)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 7)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 12)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 13)
Advances in Nanoparticles     Open Access   (Followers: 11)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Polymer Science     Hybrid Journal   (Followers: 38)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 10)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 4)
African Journal of Chemical Education     Open Access   (Followers: 1)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 4)
Afrique Science : Revue Internationale des Sciences et Technologie     Open Access  
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Alchemy     Open Access   (Followers: 3)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 4)
AMB Express     Open Access   (Followers: 1)
American Journal of Applied Sciences     Open Access   (Followers: 28)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 165)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 11)
American Journal of Chemistry     Open Access   (Followers: 17)
American Journal of Plant Physiology     Open Access   (Followers: 9)
American Mineralogist     Full-text available via subscription   (Followers: 2)
Analyst     Full-text available via subscription   (Followers: 35)
Angewandte Chemie     Hybrid Journal   (Followers: 16)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 213)
Annales UMCS, Chemia     Open Access   (Followers: 2)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 1)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 2)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 4)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 10)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 12)
Anti-Infective Agents     Hybrid Journal   (Followers: 1)
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 4)
Applied Spectroscopy     Full-text available via subscription   (Followers: 12)
Applied Surface Science     Hybrid Journal   (Followers: 14)
Arabian Journal of Chemistry     Full-text available via subscription   (Followers: 6)
ARKIVOC     Open Access   (Followers: 1)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 4)
Autophagy     Full-text available via subscription   (Followers: 1)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 6)
Biochemistry     Full-text available via subscription   (Followers: 205)
Biochemistry Insights     Open Access   (Followers: 4)
Biochemistry Research International     Open Access   (Followers: 4)
BioChip Journal     Hybrid Journal   (Followers: 1)
Bioinorganic Chemistry and Applications     Open Access   (Followers: 4)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 1)
Biointerphases     Open Access  
Biomacromolecules     Full-text available via subscription   (Followers: 17)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 5)
Biomedical Chromatography     Hybrid Journal   (Followers: 7)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 2)
BioNanoScience     Partially Free   (Followers: 4)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 30)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 24)
Bioorganic Chemistry     Hybrid Journal   (Followers: 5)
Biopolymers     Hybrid Journal   (Followers: 13)
Biosensors     Open Access   (Followers: 3)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 1)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 12)
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 3)
Canadian Journal of Chemistry     Full-text available via subscription   (Followers: 6)
Canadian Mineralogist     Full-text available via subscription   (Followers: 1)
Carbohydrate Research     Hybrid Journal   (Followers: 10)
Carbon     Hybrid Journal   (Followers: 38)
Catalysis for Sustainable Energy     Open Access   (Followers: 2)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 4)
Catalysis Science and Technology     Free   (Followers: 4)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 4)
Catalysts     Open Access   (Followers: 6)
Cellulose     Hybrid Journal   (Followers: 4)
Central European Journal of Chemistry     Hybrid Journal   (Followers: 5)

        1 2 3 4 5 6 | Last

Journal Cover Advanced Functional Materials
   Journal TOC RSS feeds Export to Zotero [36 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1616-301X - ISSN (Online) 1616-3028
     Published by John Wiley and Sons Homepage  [1604 journals]   [SJR: 4.862]   [H-I: 136]
  • Dipole‐field Sums, Lorentz Factors, and Dielectric Properties of
           Organic Molecular Films Modeled as Crystalline Arrays of Polarizable
    • Authors: Davide Vanzo; Benjamin J. Topham, Zoltán G. Soos
      Pages: n/a - n/a
      Abstract: The relative permittivity κ = ε/ε0 of thin films used in organic electronic devices is directly related to the structure and the molecular polarizability α when intermolecular overlap is small. Monolayer and multilayer films are modeled as lattices of polarizable points with induced dipoles μ = αF where the internal electric field F includes contributions from all induced dipoles. The polarization per unit volume is P = nμ for number density n. Dipole‐field sums are evaluated directly for atomic and molecular crystals and films through stacking of infinite layers. Lorentz factors in uniformly polarized crystals of less than cubic symmetry resolve completely the conditional convergence of dipole‐field sums in three dimensions. Thin films have equal P within layers but not at or near the surface. Surface effects are shown to increase with αn and sometimes to extend into films even though dipole fields are mainly due to adjacent layers. Simple and body‐centered tetragonal lattices illustrate polarizing or depolarizing interactions between layers that mimic molecules or oligomers tilted at angle Φ from normal to the surface in films or SAMs. Uniform P in molecular films refers to unit cells rather than to atoms and there are multiple ways to partition anisotropic molecular α among polarizable points. An illustrative analytical model based on polarizable points and dipole fields of adjacent layers is applied to oligophenyl films and to conjugated molecules in acene films. The relative permittivity κ = ε/ε0 of crystalline thin films is obtained in the limit of zero intermolecular overlap. Dipole‐field sums over polarizable points in applied field E are evaluated directly and combined with Lorentz factors to compute κ from monolayers to crystals, deviations from uniform polarization in surface layers, and dielectric properties in systems of lower than cubic symmetry.
      PubDate: 2014-10-22T12:11:03.916828-05:
      DOI: 10.1002/adfm.201402405
  • An Exciplex Forming Host for Highly Efficient Blue Organic Light Emitting
           Diodes with Low Driving Voltage
    • Authors: Jeong‐Hwan Lee; Shuo‐Hsien Cheng, Seung‐Jun Yoo, Hyun Shin, Jung‐Hung Chang, Chih‐I Wu, Ken‐Tsung Wong, Jang‐Joo Kim
      Pages: n/a - n/a
      Abstract: The exciplex forming co‐host with phosphorescent dopant system has potential to realize highly efficient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co‐host for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co‐host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO‐T2T, and a hole transporting material, N,N′‐dicarbazolyl‐3,5‐benzene (mCP). Photo‐physical analysis shows that the exciplexes are formed efficiently in the host and the energy transfer from the exciplex to blue phosphorescent dopant (iridium(III)bis[(4,6‐difluorophenyl)‐pyridinato‐N,C2′]picolinate; FIrpic) is also efficient, enabling the triplet harvest without energy loss. As a result, an unprecedented high performance blue PhOLED with the exciplex forming co‐host is demonstrated, showing a maximum external quantum efficiency (EQE) of 30.3%, a maximum power efficiency of 66 lm W−1, and low driving voltage of 2.75 at 100 cd m−2, 3.29 V at 1000 cd m−2, and 4.65 V at 10 000 cd m−2, respectively. The importance of the exciton confinement in the exciplex forming co‐host is further investigated which is directly related to the performance of PhOLEDs. A novel exciplex forming host, composed of mCP and PO‐T2T, is realized. Using the host and efficient energy transfer to FIrpic, unprecedented high performance blue phosphorescent OLED is demonstrated, showing a maximum EQE of 30.3%, power efficiency of 66 lm W−1, and extremely low operating voltages of 2.75 at 100 cd m−2, and 4.65 V at 10 000 cd m−2.
      PubDate: 2014-10-22T12:10:11.933815-05:
      DOI: 10.1002/adfm.201402707
  • Masthead: (Adv. Funct. Mater. 40/2014)
    • Pages: n/a - n/a
      PubDate: 2014-10-22T07:11:00.889783-05:
      DOI: 10.1002/adfm.201470265
  • Nanoconfined LiBH4 as a Fast Lithium Ion Conductor
    • Authors: Didier Blanchard; Angeloclaudio Nale, Dadi Sveinbjörnsson, Tamara M. Eggenhuisen, Margriet H. W. Verkuijlen, Suwarno, Tejs Vegge, Arno P. M. Kentgens, Petra E. de Jongh
      Pages: n/a - n/a
      Abstract: Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid‐state batteries. LiBH4 is a promising solid electrolyte for Li‐ion batteries. It displays high lithium mobility, although only above 110 °C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH4 in the pores of ordered mesoporous silica scaffolds leads to high Li+ conductivity (0.1 mS cm−1) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO2. Solid state 7Li NMR confirmed that the high conductivity can be attributed to a very high Li+ mobility in the solid phase at room temperature. Confinement of LiBH4 in the pores leads also to a lower solid‐solid phase transition temperature than for bulk LiBH4. However, the high ionic mobility is associated with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO2 pore walls. These results point to a new strategy to design low‐temperature ion conducting solids for application in all solid‐state lithium ion batteries, which could enable safe use of Li‐metal anodes. Confining LiBH 4 inside nanopores of mesoporous silica results in stable and high Li+ mobilities persisting to room temperature. The mobility is associated with a LiBH4 phase that does not undergo a structural phase transition, a phase probably located within 1.0 nanometer of the pore walls. This presents a new strategy to design efficient electrolytes for all solid‐state rechargeable lithium batteries.
      PubDate: 2014-10-22T04:54:11.288869-05:
      DOI: 10.1002/adfm.201402538
  • A Complete Separation of Hexane Isomers by a Functionalized Flexible Metal
           Organic Framework
    • Authors: Patricia A. P. Mendes; Patricia Horcajada, Sébastien Rives, Hong Ren, Alírio E. Rodrigues, Thomas Devic, Emmanuel Magnier, Philippe Trens, Hervé Jobic, Jacques Ollivier, Guillaume Maurin, Christian Serre, José A. C. Silva
      Pages: n/a - n/a
      Abstract: The separation ability of branched alkane isomers (nHEX, 3MP, 22DMB) of the flexible and functionalized microporous iron(III) dicarboxylate MIL‐53(Fe)‐(CF3)2 solid is evaluated through a combination of breakthrough experiments (binary or ternary mixtures), adsorption isotherms, X‐ray diffraction temperature analysis, quasi‐elastic neutron scattering measurements and molecular dynamics simulations. A kinetically controlled molecular sieve separation between the di‐branched isomer of hexane 22DMB from a mixture of paraffins is achieved. The reported total separation between mono‐ and di‐branched alkanes which was neither predicted nor observed so far in any class of porous solids is spectacular and paves the way towards a potential unprecedented upgrading of the RON of gasoline. A kinetically controlled molecular sieve separation between the 2,2‐Dimethyl‐Butane (22DMB) branched alkane isomer from a mixture of paraffins was achieved for the first time using the flexible and functionalized MIL‐53(Fe)‐(CF3)2 metal‐organic‐framework.
      PubDate: 2014-10-21T14:33:21.088049-05:
      DOI: 10.1002/adfm.201401974
  • Molecular‐Level Switching of Polymer/Nanocrystal Non‐Covalent
           Interactions and Application in Hybrid Solar Cells
    • Authors: Carlo Giansante; Rosanna Mastria, Giovanni Lerario, Luca Moretti, Ilka Kriegel, Francesco Scotognella, Guglielmo Lanzani, Sonia Carallo, Marco Esposito, Mariano Biasiucci, Aurora Rizzo, Giuseppe Gigli
      Pages: n/a - n/a
      Abstract: Hybrid composites obtained upon blending conjugated polymers and colloidal semiconductor nanocrystals are regarded as attractive photo­active materials for optoelectronic applications. Here it is demonstrated that tailoring nanocrystal surface chemistry permits to control non‐covalent and electronic interactions between organic and inorganic components. The pending moieties of organic ligands at the nanocrystal surface are shown to not merely confer colloidal stability while hindering charge separation and transport, but drastically impact morphology of hybrid composites during formation from blend solutions. The relevance of this approach to photovoltaic applications is demonstrated for composites based on poly(3‐hexylthiophene) and lead sulfide nanocrystals, considered as inadequate until this report, which enable the fabrication of hybrid solar cells displaying a power conversion efficiency that reaches 3%. By investigating (quasi)steady‐state and time‐resolved photo‐induced processes in the nanocomposites and their constituents, it is ascertained that electron transfer occurs at the hybrid interface yielding long‐lived separated charge carriers, whereas interfacial hole transfer appears hindered. Here a reliable alternative aiming to gain control over macroscopic optoelectronic properties of polymer/nanocrystal composites by mediating their non‐covalent interactions via ligands' pending moieties is provided, thus opening new possibilities towards efficient solution‐processed hybrid solar cells. Hybrid nanocomposites with switched morphology are obtained by mediating non‐covalent interactions between conjugated polymers and semiconductor nanocrystals via the pending moiety of organic ligands at the nanocrystal surface. Morphology switching deeply impacts the optoelectronic properties of polythiophene/PbS nanocrystal composites, as demonstrated by achieving unprecedented photovoltaic device performances for this blend material. Photo‐induced processes at the hybrid interface are investigated and discussed.
      PubDate: 2014-10-21T14:33:08.937597-05:
      DOI: 10.1002/adfm.201401841
  • Enhanced Optical Property with Tunable Band Gap of Cross‐linked
           PEDOT Copolymers via Oxidative Chemical Vapor Deposition
    • Authors: Sunghwan Lee; Karen K. Gleason
      Pages: n/a - n/a
      Abstract: Highoptical transmittance conjugated‐polymers with electrical conductivity are garnering much attention for the applications in organic optoelectronic devices including organic field‐effect‐transistors and solar cells. Polymers based on PEDOT are particularly promising candidates with high conductivity, uniform surface planarity and excellent ductility. In this work, homopolymer PEDOT deposited using oxidative chemical‐vapor‐deposition(oCVD) show the maximum conductivity of ≈3500 S/cm. However, their utility is limited due to the relatively low transmittance and abrupt decrease near the red edge in the visible regime. Here, the significantly improved optical properties achieved via tuning the bandgap of cross‐linked PEDOT copolymers using oCVD, offering a single‐step process for the synthesis and deposition of copolymer films, is reported. The cross‐linking monomers of biphenyl or anthracene are simultaneously evaporated with EDOT monomer and an oxidant(FeCl3) during the deposition. Poly(anthracene‐co‐EDOT)[p(ANTH‐co‐EDOT)] shows the superior transmittance (≈93%) to homopolymer PEDOT (≈80%) and poly(biphenyl‐co‐EDOT)[p(BPH‐co‐EDOT)] (≈88%). Additionally, copolymers show no transmission decay in the red edge regime unlike homopolymer PEDOT that presents an abrupt transmission falloff. An improvement in optical transmittance is in agreement with an increase in bandgap of materials (p(ANTH‐co‐EDOT), ≈2.3eV vs PEDOT, ≈1.8 eV). oCVD‐processed bandgap‐tunable PEDOT copolymers with enhanced transmittance may, therefore, have applications in organic optoelectronic devices that require high optical transparency. Band gap‐tuned PEDOT copolymers are successfully demonstrated using oCVD with the incorporation of cross‐linking monomers of anthracene or biphenyl. oCVD offers single‐step synthesis, deposition and doping of copolymers. oCVD copolymers show significantly improved visible‐regime transparency compared to homopolymer PEDOT, which is promising for many organic optoelectronic devices that require high optical transmittance with electrical conductivity.
      PubDate: 2014-10-20T10:44:56.928614-05:
      DOI: 10.1002/adfm.201402924
  • Blood Ties: Co3O4 Decorated Blood Derived Carbon as a Superior
           Bifunctional Electrocatalyst
    • Authors: Chao Zhang; Markus Antonietti, Tim‐Patrick Fellinger
      Pages: n/a - n/a
      Abstract: A simple, versatile and cheap synthetic route is demonstrated for the preparation of Co3O4 decorated blood powder derived heteroatom doped porous carbon (BDHC). The inorganic hybrid performs well as an advanced bifunctional non‐precious metal electrocatalyst. The hybridization of Co3O4 with the blood‐derived carbon results in improved activities not only towards the oxygen reduction reaction (ORR), but also in the reverse oxygen evolution reaction (OER). An improved ORR activity and a tuned four electron transfer selectivity can be assigned to a synergistic catalytic effect due the intimate contact between Co3O­4 particles and the highly conductive heteroatom doped carbon support, mediated by cobalt‐nitrogen or cobalt‐phosphorous coordination sites. This heterojunction may facilitate the electron transfer by preventing an accumulation of electron density within the Co3O­4 particles. The straight‐forward and cheap synthesis of the highly active and durable electrocatalyst make it a promising candidate for a next‐generation bifunctional electrocatalyst for applications such as reversible fuel cells/electrolyzers or metal air batteries. A simple, versatile and cheap synthetic route is developed for the preparation of Co3O4 decorated blood powder derived foam‐like heteroatom doped porous carbon (BDHC). The hybrid performs well as an advanced bifunctional non‐precious metal electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the alkaline medium.
      PubDate: 2014-10-18T05:20:17.650469-05:
      DOI: 10.1002/adfm.201402770
  • Multi‐Site Functionalization of Protein Scaffolds for Bimetallic
           Nanoparticle Templating
    • Authors: Kelly N. L. Huggins; Alia P. Schoen, Manickam Adhimoolam Arunagirinathan, Sarah C. Heilshorn
      Pages: n/a - n/a
      Abstract: The use of biological scaffolds to template inorganic material offers a strategy to synthesize precise composite nanostructures of different sizes and shapes. Proteins are unique biological scaffolds that consist of multiple binding regions or epitope sites that site‐specifically associate with conserved amino acid sequences within protein‐binding partners. These binding regions can be exploited as synthesis sites for multiple inorganic species within the same protein scaffold, resulting in bimetallic inorganic nanostructures. This strategy is demonstrated with the scaffold protein clathrin, which self‐assembles into spherical cages. Specifically, tether peptides that noncovalently associate with distinct clathrin epitope sites, while initiating simultaneous synthesis of two inorganic species within the assembled clathrin protein cage, are designed. The flexibility and diversity of this unique biotemplating strategy is demonstrated by synthesizing two types of composite structures (silver–gold mixed bimetallic and silver–gold core–shell nanostructures) from a single clathrin template. This noncovalent, Template Engineering Through Epitope Recognition, or TEThER, strategy can be readily applied to any protein system with known epitope sites to template a variety of bimetallic structures without the need for chemical or genetic mutations. A unique noncovalent biotemplating method is used to localize multiple inorganic species at specific nucleation sites on a single clathrin protein template. The data illustrate that this templating strategy facilitates the synthesis of two types of composite nanostructures based on the location of the nucleation sites: silver–gold mixed bimetallic and silver–gold core–shell nanostructures.
      PubDate: 2014-10-18T04:59:05.730423-05:
      DOI: 10.1002/adfm.201402049
  • Materials Meets Concepts in Molecule‐based Electronics
    • Authors: Frank Ortmann; K. Sebastian Radke, Alrun Günther, Daniel Kasemann, Karl Leo, Gianaurelio Cuniberti
      Pages: n/a - n/a
      Abstract: In this contribution, molecular materials are highlighted as an important topic in the diverse field of condensed matter physics, with focus on their particular electronic and transport properties. A better understanding of their performance in various applications and devices demands for an extension of basic theoretical approaches to describe charge transport in molecular materials, including the accurate description of electron–phonon coupling. Starting with the simplest case of a molecular junction and moving on to larger aggregates of bulk organic semiconductors, charge‐transport regimes from ballistic motion to incoherent hopping, which are frequently encountered in molecular systems under respective conditions, are discussed. Transport features of specific materials are described through ab initio material parameters whose determination is addressed. Molecular semiconductors are intriguing materials with applications in flexible electronics due to their potential low‐cost processing ability and chemical tunability. In addition, they are utile in fundamental studies of decoherence effects in single‐molecular junctions. Concepts of transport modeling for such systems are presented in this Feature Article, highlighting the unique transport properties of organic and molecular semiconductors.
      PubDate: 2014-10-14T11:32:31.870027-05:
      DOI: 10.1002/adfm.201402334
  • Effects of Delocalized Charge Carriers in Organic Solar Cells: Predicting
           Nanoscale Device Performance from Morphology
    • Authors: Adam G. Gagorik; Jacob W. Mohin, Tomasz Kowalewski, Geoffrey R. Hutchison
      Pages: n/a - n/a
      Abstract: Monte Carlo simulations of charge transport in organic solar cells are performed for ideal and isotropic bulk heterojunction morphologies while altering the delocalization length of charge carriers. Previous device simulations have either treated carriers as point charges or with a highly delocalized mean‐field treatment. This new model of charge delocalization leads to weakening of Coulomb interactions and more realistic predicted current and fill factors at moderate delocalization, relative to point charges. It is found that charge delocalization leads to significantly increased likelihood of escaping interface traps. In isotopic two‐phase morphologies, increasing the domain sizes leads to slight decreases in predicted device efficiencies. It was previously shown that tortuous pathways in systems with small domain sizes can decrease device performance in thin film systems. However, the diminishing effects of Coulomb interactions with delocalization and efficient separations of excitons by small domains make morphological effects less pronounced. The importance of delocalization, which has largely been ignored in past simulations, as a parameter to consider and optimize when choosing materials for organic solar cells is emphasized. The effects of charge delocalization on device efficiency is probed using mesoscale Monte Carlo simulations of charge transport in idealized and isotropic two‐phase morphologies. Interfacial charge trapping is drastically reduced when Coulomb interactions are weakened through moderate delocalization (1.0–2.0 nm). Morphological differences become less dominant as charges delocalize.
      PubDate: 2014-10-14T11:32:19.097764-05:
      DOI: 10.1002/adfm.201402332
  • Temperature‐Dependent Electrical Transport in Polymer‐Sorted
           Semiconducting Carbon Nanotube Networks
    • Authors: Jia Gao; Yueh‐Lin (Lynn) Loo
      Pages: n/a - n/a
      Abstract: The temperature dependence of the electrical characteristics of field‐effect transistors (FETs) based on polymer‐sorted, large‐diameter semiconducting carbon nanotube networks is investigated. The temperature dependences of both the carrier mobility and the source‐drain current in the range of 78 K to 293 K indicate thermally activated, but non‐Arrhenius, charge transport. The hysteresis in the transfer characteristics of FETs shows a simultaneous reduction with decreasing temperature. The hysteresis appears to stem from screening of charges that are transferred from the carbon nanotubes to traps at the surface of the gate dielectric. The temperature dependence of sheet resistance of the carbon nanotube networks, extracted from FET characteristics at constant carrier concentration, specifies fluctuation‐induced tunneling as the mechanism responsible for charge transport, with an activation energy that is dependent on film thickness. Our study indicates inter‐tube tunneling to be the bottleneck and implicates the role of the polymer coating in influencing charge transport in polymer‐sorted carbon nanotube networks. The temperature‐dependent electrical transport in polymer‐sorted semiconducting carbon nanotube networks is elucidated in this work. The source‐drain current and mobility in polymer‐sorted carbon nanotube network‐based field‐effect transistors decrease with decreasing temperature attributable to fluctuation‐induced tunneling. The barrier for charge transport inversely correlates with carbon nanotube network thickness, for the probability to sample conductive pathways with fewer inter‐tube junctions increases with increasing thickness.
      PubDate: 2014-10-14T11:31:33.854493-05:
      DOI: 10.1002/adfm.201402407
  • Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin
           Films of BiFe0.5Mn0.5O3
    • Authors: Eun‐Mi Choi; Thomas Fix, Ahmed Kursumovic, Christy J. Kinane, Darío Arena, Suman‐Lata Sahonta, Zhenxing Bi, Jie Xiong, Li Yan, Jun‐Sik Lee, Haiyan Wang, Sean Langridge, Yong‐Min Kim, Albina Y. Borisevich, Ian MacLaren, Quentin M. Ramasse, Mark G. Blamire, Quanxi Jia, Judith L. MacManus‐Driscoll
      Pages: n/a - n/a
      Abstract: Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X‐ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. A new window for designing multiferroic materials through epitaxial strain control: For the first time, coexistent ferrimagnetism and ferroelectricity is demonstrated at RT in BiFe0.5Mn0.5O3 (BFMO) by strain engineering. The most highly strained and crystalline films have a ferrimagnetic transition temperature of ∼600 K, which is 500 K higher than bulk BMO and a piezoresponse amplitude of 45 pm/V.
      PubDate: 2014-10-14T11:31:03.495917-05:
      DOI: 10.1002/adfm.201401464
  • From Chiral Islands to Smectic Layers: A Computational Journey Across
           Sexithiophene Morphologies on C60
    • Authors: Gabriele D'Avino; Luca Muccioli, Claudio Zannoni
      Pages: n/a - n/a
      Abstract: A theoretical investigation of the molecular organization at a sexithiophene (T6)‐C60 fullerene planar heterojunction, based on atomistic molecular dynamics, is presented, in which the effect of two different sample preparation processes on the resulting interface morphology is explored. First, the landing of T6 on C60(001) substrate is considered, which leads to crystalline layers of standing and tilted molecules, in accordance with experiments. The observation and the quantitative characterization of the nucleation and growth provide detailed insights on this out‐of‐equilibrium process, including the establishment of an epitaxial relationship between the substrate and the interfacial T6 layer, and the spontaneous formation of defective islands, characterized by chiral edges, during the growth of the second and third layers. It is then shown that molecular orientations can be radically changed upon annealing at 600 K, at which T6 forms a smectic phase with planar alignment, whose layers are perpendicular to the interface. The interfacial T6 morphologies are then analyzed in detail at room temperature and compared to the known bulk polymorphs. The morphology of sexithiophene thin films deposited over a C60 fullerene crystalline slab is investigated with an atomistic molecular dynamics technique. Simulations show that the nucleation and growth of vapor‐deposited sexithiophene leads to the formation of weakly correlated crystalline layers of standing molecules, while the orientation of sexithiophene molecules can be radically changed to planar upon thermal annealing.
      PubDate: 2014-10-14T11:30:58.115475-05:
      DOI: 10.1002/adfm.201402609
  • Strategy for Enhancing the Dielectric Constant of Organic Semiconductors
           Without Sacrificing Charge Carrier Mobility and Solubility
    • Authors: Solmaz Torabi; Fatemeh Jahani, Ineke Van Severen, Catherine Kanimozhi, Satish Patil, Remco W. A. Havenith, Ryan C. Chiechi, Laurence Lutsen, Dirk J. M. Vanderzande, Thomas J. Cleij, Jan C. Hummelen, L. Jan Anton Koster
      Pages: n/a - n/a
      Abstract: Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, ε r) in the range of 2–4. As a consequence, Coulombically bound electron‐hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance ε r of well‐known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of ε r together with poly(p‐phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of ε r with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl‐C61‐butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents. A synthetic strategy is presented for the dielectric constant enhancement of organic semiconductors. It is demonstrated that fullerene derivatives, DPP‐ and PPV‐based polymers show a marked increase of the relative dielectric constant when being functionalized with TEG side chains. Density functional theory calculations attribute such enhancements to the rapid reorientations of ethylene glycol ­dipoles on the side chains.
      PubDate: 2014-10-14T11:30:36.51344-05:0
      DOI: 10.1002/adfm.201402244
  • Plasmonic Janus‐Composite Photocatalyst Comprising Au and
           C–TiO2 for Enhanced Aerobic Oxidation over a Broad
           Visible‐Light Range
    • Authors: Lequan Liu; Thang Duy Dao, Rajesh Kodiyath, Qing Kang, Hideki Abe, Tadaaki Nagao, Jinhua Ye
      Pages: n/a - n/a
      Abstract: Asymmetric Janus nanostructures containing a gold nanocage (NC) and a carbon–titania hybrid nanocrystal (AuNC/(C–TiO2)) are prepared using a novel and facile microemulsion‐based approach that involves the assistance of ethanol. The localized surface plasmon resonance of the Au NC with a hollow interior and porous walls induce broadband visible‐light harvesting in the Janus AuNC/(C–TiO2). An acetone evolution rate of 6.3 μmol h−1 g−1 is obtained when the Janus nanostructure is used for the photocatalytic aerobic oxidation of iso‐propanol under visible light (λ = 480–910 nm); the rate is 3.2 times the value of that obtained with C–TiO2, and in photo‐electrochemical investigations an approximately fivefold enhancement is obtained. Moreover, when compared with the core–shell structure (AuNC@(C–TiO2) and a gold–carbon–titania system where Au sphere nanoparticles act as light‐harvesting antenna, Janus AuNC/(C–TiO2) exhibit superior plasmonic enhancement. Electromagnetic field simulation and electron paramagnetic resonance results suggest that the plasmon–photon coupling effect is dramatically amplified at the interface between the Au NC and C–TiO2, leading to enhanced generation of energetic hot electrons for photocatalysis. A novel and facile approach is developed for preparing asymmetric Janus nanostructures comprising a gold nanocage and carbon–titania hybrid nanoparticles. The microemulsion‐based preparation, results in composites with increased plasmon–photon coupling at the interface of the AuNC and C–TiO2 particle. The amplification of the plasmon–photon coupling leads to enhanced generation of energetic hot electrons for visible‐light photocatalysis.
      PubDate: 2014-10-14T11:28:39.121274-05:
      DOI: 10.1002/adfm.201402088
  • Organic Thin Film Transistors Based on Highly Dipolar Donor–Acceptor
           Polymethine Dyes
    • Authors: Andreas Liess; Lizhen Huang, Alhama Arjona‐Esteban, Aifeng Lv, Marcel Gsänger, Vladimir Stepanenko, Matthias Stolte, Frank Würthner
      Pages: n/a - n/a
      Abstract: Organic thin film transistors (OTFTs) of a series of twenty dipolar donor–acceptor‐substituted polymethine dyes (D–A dyes, dipole moments from 3–15 D) are investigated. The employed merocyanine dyes contain a dimethine bridge that is substituted with 1‐alkyl‐3,3‐dimethylindolin‐2‐ylidene (“Fischer base”), 3‐alkyl‐2,3‐dihydrobenzothiazol‐2‐ylidene or 1,3‐benzodithiole‐2‐ylidene, respectively, as electron‐donating unit and various acceptor heterocycles. These studies show that thin films formed by these D–A dyes upon deposition in high vacuum are all composed of antiparallel π‐stacked dimers. However, they are either amorphous, discontinuous or highly crystalline due to the interplay between molecule‐substrate and dimer–dimer interactions. With the help of single crystal X‐ray analysis, out‐of‐plane X‐ray studies (XRD), selected area electron diffraction (SAED), and atomic force microscopy (AFM), a correlation between the molecular structure, film ordering, and hole charge transport ability can be established. The mobility values are compared to Bässler's disorder charge transport theory and a film growth mechanism is proposed based on DFT calculations and single crystal structures. The results show that with carefully adjusted bulky substituents and high dipolarity an intimate centrosymmetric packing with a slipped, but tight π‐stacking arrangement could be realized. This provides two‐dimensional percolation pathways for holes and ultimately results in charge carrier mobilities up to 0.18 cm2 V−1 s−1. Twenty dipolar donor–acceptor‐substituted polymethine dyes (merocyanines) are investigated as active layer in organic thin film transistors. It is shown that the diverse performance of the devices can be attributed to either low or high dimensional ordering in the crystal structure which in the latter case leads to mobilities as high as 0.18 cm2 V−1 s−1.
      PubDate: 2014-10-13T12:17:06.207026-05:
      DOI: 10.1002/adfm.201402678
  • Significantly Enhanced Thermoelectric Performance in n‐type
           Heterogeneous BiAgSeS Composites
    • Authors: Di Wu; Yanling Pei, Zhe Wang, Haijun Wu, Li Huang, Li‐Dong Zhao, Jiaqing He
      Pages: n/a - n/a
      Abstract: High performance n‐type bulk BiAgSeS is successfully synthesized to construct heterogeneous composites which consist of mesoscale grains of both pristine BiAgSeS and doped BiAgSeS1‐xClx (x = 0.03 or 0.05). Without perceptibly deteriorating the Seebeck coefficient, a significant enhancement on electrical conductivity is obtained due to an anomalous increase of both carrier mobility and concentration; the enhanced carrier mobility is proven to be a direct result of modulation doping which relates to the band alignments, while the increased carrier concentration is attributed to the possible charge transfer from Cl rich nanoscale precipitates at the heterogeneous BiAgSeS/BiAgSeS1‐xClx grain boundaries. Eventually, an enhanced figure of merit ZT ≈ 1.23 at 773 K in the composite (BiAgSeS)0.5(BiAgSeS0.97Cl0.03)0.5 is achieved, indicating that heterogeneous composites ultilizing the mechanism of modulation doping shall be a promising means of boosting the performance of thermoelectric materials. This strategy should be very likely applicable to other thermoelectrics. Charge carriers swimming in matrix grains free of ionized impurites in undoped region in the notion of modulation doping leads to a significant enhancement on power factor over the uniformly doped counterpart.
      PubDate: 2014-10-13T12:15:40.19518-05:0
      DOI: 10.1002/adfm.201402211
  • Facile Photo‐Crosslinking of Azide‐Containing
           Hole‐Transporting Polymers for Highly Efficient,
           Solution‐Processed, Multilayer Organic Light Emitting Devices
    • Authors: Junwoo Park; Changyeon Lee, Jihye Jung, Hyunbum Kang, Ki‐Hyun Kim, Biwu Ma, Bumjoon J. Kim
      Pages: n/a - n/a
      Abstract: A novel framework of azide containing photo‐crosslinkable, conducting copolymer, that is, poly(azido‐styrene)‐random‐poly(triphenylamine) (X‐PTPA), is reported as a hole‐transporting material for efficient solution‐processed, multi‐layer, organic light emitting diodes (OLEDs). A facile and energy‐efficient crosslinking process is demonstrated with UV irradiation (254 nm, 2 mW/cm2) at a short exposure time (5 min). By careful design of X‐PTPA, in which 5 mol% of the photo‐crosslinkable poly(azido‐styrene) is copolymerized with hole‐transporting poly(triphenylamine) (X‐PTPA‐5), the adverse effect of the crosslinking of azide moieties is prevented to maximize the performances of X‐PTPA‐5. Since the photo‐crosslinking chemistry of azide molecules does not involve any photo‐initiators, superior hole‐transporting ability is achieved, producing efficient devices. To evaluate the performances of X‐PTPA‐5 as a hole‐transporting/electron‐blocking layer, Ir(ppy)3‐based, solution‐processable OLEDs are fabricated. The results show high EQE (11.8%), luminous efficiency (43.7 cd/A), and power efficiency (10.4 lm/W), which represent about twofold enhancement over the control device without X‐PTPA‐5 film. Furthermore, micro‐patterned OLEDs with the photo‐crosslinkable X‐PTPA‐5 can be fabricated through standard photolithography. The versatility of this approach is also demonstrated by introducing the same azide moiety into other hole‐transporting materials such as poly(carbazole) (X‐PBC). Photo‐crosslinkable azide (N3) containing X‐PTPA is used as a HTL/EBL layer for highly efficient, solution‐processed multi‐layer OLEDs. The X‐PTPA with 5 mol% of N3 group can be fully crosslinked via mild UV irradiation at short exposure time. A twofold enhancement of device performance is realized with X‐PTPA layer over the control device. This photo‐crosslinkable HTL/EBL layer also allows the fabrication of micro‐pixelated multi‐layer OLEDs by photolithography.
      PubDate: 2014-10-13T12:15:35.432484-05:
      DOI: 10.1002/adfm.201401958
  • Blue Aggregation‐Induced Emission Luminogens: High External Quantum
           Efficiencies Up to 3.99% in LED Device, and Restriction of the Conjugation
           Length through Rational Molecular Design
    • Authors: Jing Huang; Ning Sun, Jie Yang, Runli Tang, Qianqian Li, Dongge Ma, Zhen Li
      Pages: n/a - n/a
      Abstract: Great efforts have been devoted to seek novel approaches for constructing blue fluorescent materials, which is one of the most important prerequisites for the commercialization of OLEDs. In recent years, various outstanding luminogens with aggregation‐induced emission characteristic exhibit promising applications as emitters, but blue AIE fluorophores with excellent EL performance are still very scarce. Here, five hole‐dominated blue AIE molecules are demonstrated by adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, with the aim to restrict conjugation lengths without sacrificing good EL data. Device results show that the novel synthesized materials could be applied as bifunctional materials, namely blue light‐emitting and hole‐transporting materials, with comparable EL efficiencies, and the ηC,max and ηext,max are up to 8.03 cd A−1 and 3.99% respectively, which is among the best EL performance for blue AIE luminogens. Five hole‐dominated blue AIE molecules, constructed from TPA core and TPE derivatives peripheries, are successfully synthesized and served as hole‐transport layers and emitters for non‐doped blue OLEDs with current efficiencies up to 8.03 cd A−1. By adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, the conjugation lengths are effectively shortened for ensuring blue emission.
      PubDate: 2014-10-13T12:15:30.560198-05:
      DOI: 10.1002/adfm.201401867
  • pH‐Responsive Cyanine‐Grafted Graphene Oxide for Fluorescence
           Resonance Energy Transfer‐Enhanced Photothermal Therapy
    • Authors: Miao Guo; Jie Huang, Yibin Deng, He Shen, Yufei Ma, Mengxin Zhang, Aijun Zhu, Yanli Li, He Hui, Yangyun Wang, Xiangliang Yang, Zhijun Zhang, Huabing Chen
      Pages: n/a - n/a
      Abstract: Stimuli‐responsive anticancer agents are of particular interest in the field of cancer therapy. Nevertheless, so far stimuli‐responsive photothermal agents have been explored with limited success for cancer photothermal therapy (PTT). In this work, as a proof‐of‐concept, a pH‐responsive photothermal nanoconjugate for enhanced PTT efficacy, in which graphene oxide (GO) with broad NIR absorbance and effective photothermal conversion efficiency is selected as a typical model receptor of fluorescence resonance energy transfer (FRET), and grafted cyanine dye (e.g., Cypate) acts as the donor of near‐infrared fluorescence (NIRF), is reported for the first time. The conjugate of Cypate‐grafted GO exhibits different conformations in aqueous solutions at various pH, which can trigger pH‐dependent FRET effect between GO and Cypate and thus induce pH‐responsive photothermal effect of GO‐Cypate. GO‐Cypate exhibits severe cell damage owing to the enhanced photothermal effect in lysosomes, and thus generate synergistic PTT efficacy with tumor ablation upon photoirradiation after a single‐dose intravenous injection. The photothermal nanoconjugate with broad NIR absorbance as the effective receptor of FRET can smartly convert emitted NIRF energy from donor cyanine dye into additional photothermal effect for improving PTT. These results suggest that the smart nanoconjugate can act as a promising stimuli‐responsive photothermal nanoplatform for cancer therapy. A smart cyanine‐grafted GO nanoconjugate (GO‐Cypate) with pH‐dependent FRET effect, which triggers pH‐responsive photothermal effect and thus results in enhanced PTT efficacy with tumor ablation upon NIR irradiation after a single‐dose intravenous injection, is reported.
      PubDate: 2014-10-13T11:57:13.800737-05:
      DOI: 10.1002/adfm.201402762
  • Injectable Peptide Decorated Functional Nanofibrous Hollow Microspheres to
           Direct Stem Cell Differentiation and Tissue Regeneration
    • Authors: Zhanpeng Zhang; Melanie J. Gupte, Xiaobing Jin, Peter X. Ma
      Pages: n/a - n/a
      Abstract: Injectable microspheres are attractive stem cell carriers for minimally invasive procedures. For tissue regeneration, the microspheres need to present the critical cues to properly direct stem cell differentiation. In natural extracellular matrix (ECM), growth factors (GFs) and collagen nanofibers provide critical chemical and physical cues. However, there have been no reported technologies that integrate synthetic nanofibers and GFs into injectable microspheres. In this study, functional nanofibrous hollow microspheres (FNF‐HMS), which can covalently bind GF‐mimicking peptides, are synthesized. Two different GF‐mimicking peptides, Transforming Growth Factor‐β1 mimicking peptide Cytomodulin (CM) and Bone Morphogenetic Protein‐2 mimicking peptide P24, are separately conjugated onto the FNF‐HMS to induce distinct differentiation pathways of rabbit bone marrow‐derived mesenchymal stem cells (BMSCs). While no existing biomaterials are reported to successfully deliver CM to induce chondrogenesis, the developed FNF‐HMS are shown to effectively present CM to BMSCs and successfully induced their chondrogenesis for ­cartilage formation in both in vitro and in vivo studies. In addition, P24 is conjugated onto the newly developed FNF‐HMS and is capable of retaining its bioactivity and inducing ectopic bone formation in nude mice. These results demonstrate that the novel FNF‐HMS can effectively deliver GF‐mimicking peptides to modulate stem cell fate and tissue regeneration. Functional nano‐fibrous hollow microspheres (FNF‐HMS) are developed to deliver growth factor mimics to stem cells with enhanced efficacy. When a TGF‐β1 mimicking peptide is conjugated, FNF‐HMS can serve as injectable stem cell carriers and induce chondrogenesis and cartilage formation. FNF‐HMS can also deliver BMP‐2 mimicking peptide to induce stem cell osteogenesis and bone formation.
      PubDate: 2014-10-13T11:57:11.295319-05:
      DOI: 10.1002/adfm.201402618
  • Long Passage Times of Short ssDNA Molecules through Metallized Nanopores
           Fabricated by Controlled Breakdown
    • Authors: Harold Kwok; Matthew Waugh, José Bustamante, Kyle Briggs, Vincent Tabard‐Cossa
      Pages: n/a - n/a
      Abstract: The fabrication of individual nanopores in metallized dielectric membranes using controlled breakdown directly in solution is described. Nanopores as small as 1.5‐nm in diameter are fabricated in Au‐coated silicon nitride membranes immersed in 1 m KCl by subjecting them to high electric fields. The physical and electrical characteristics of nanopores produced with this method are presented. The translocation of short single‐stranded DNA molecules is demonstrated through such nanopore devices without further passivation of the metallic surface. Metallized nanopores can prolong the translocation times of 50‐nt ssDNA fragments by as much as two orders of magnitude, while the slowest events can reach an average speed as slow as 2 nucleotides per millisecond. The mechanism for the long dwell‐time distribution is differentiated from prior studies, which relied on friction to slow down DNA, and is attributed to nucleotide‐Au interactions. Controlled breakdown (CBD) is used to fabricate a single nanometer‐scale hole, or nanopore, in Au‐coated silicon nitride membranes immersed in 1 m KCl and subjected to high electric fields. These metallized nanopores can extend the dwell times of 50‐nt ssDNA fragments by as much as two orders of magnitude, by relying on nucleoside‐Au interactions.
      PubDate: 2014-10-13T11:55:47.213658-05:
      DOI: 10.1002/adfm.201402468
  • Achieving Outstanding Mechanical Performance in Reinforced Elastomeric
           Composite Fibers Using Large Sheets of Graphene Oxide
    • Authors: Mohammad Ziabari Seyedin; Joselito M. Razal, Peter C. Innis, Rouhollah Jalili, Gordon G. Wallace
      Pages: n/a - n/a
      Abstract: A simple fiber spinning method used to fabricate elastomeric composite fibers with outstanding mechanical performance is demonstrated. By taking advantage of the large size of as‐prepared graphene oxide sheets (in the order of tens of micrometers) and their liquid crystalline behavior, elastomeric composite fibers with outstanding low strain properties have been fabricated without compromising their high strain properties. For example, the modulus and yield stress of the parent elastomer improved by 80‐ and 40‐fold, respectively, while maintaining the high extensibility of ∼400% strain inherent to the parent elastomer. This outstanding mechanical performance was shown to be dependent upon the GO sheet size. Insights into how both the GO sheet size dimension and dispersion parameters influence the mechanical behavior at various applied strains are discussed. A straightforward approach to prepare liquid crystalline dispersions of poly­urethane/graphene oxide (PU/GO) formulations has enabled the fabrication of high performance elastomeric composite fibers. The PU/GO fibers containing large GO sheets display remarkable reinforcement in modulus and yield stress (low strain properties) without compromising the extensibility and stretchability (high strain properties) inherent to PU. These fibers are produced using a very simple, continuous and highly scalable fiber wet‐spinning process.
      PubDate: 2014-10-13T11:55:42.393484-05:
      DOI: 10.1002/adfm.201402167
  • Hierarchically CdS Decorated 1D ZnO Nanorods‐2D Graphene Hybrids:
           Low Temperature Synthesis and Enhanced Photocatalytic Performance
    • Authors: Chuang Han; Zhang Chen, Nan Zhang, Juan Carlos Colmenares, Yi‐Jun Xu
      Pages: n/a - n/a
      Abstract: A simple, low‐temperature synthesis approach is reported for planting CdS‐sensitized 1D ZnO nanorod arrays on the 2D graphene (GR) sheet to obtain the ternary hierarchical nanostructures, during which graphene oxide (GO) as the precursor of GR acts as a flexible substrate for the formation of ZnO nanorod arrays. The hierarchical CdS‐1D ZnO‐2D GR hybrids can serve as an efficient visible‐light‐driven photocatalyst for selective organic transformations. The fast electron transport of 1D ZnO nanorods, the well‐known electronic conductivity of 2D GR, the intense visible‐light absorption of CdS, the unique hierarchical structure, and the matched energy levels of CdS, ZnO and GR efficiently boost the photogenerated charge carriers separation and transfer across the interfacial domain of hierarchical CdS‐1D ZnO‐2D GR hybrids under visible light irradiation via three‐level electron transfer process. Furthermore, the superior reusability of ternary hybrids is achieved by controlling the reaction parameters, i.e., using visible light irradiation and holes scavenger to prevent ZnO and CdS from photocorrosion. This work demonstrates a facile way of fabricating hierarchical CdS‐1D ZnO‐2D GR hybrids in a controlled manner and highlights a promising scope of adopting integrative photosensitization and co‐catalyst strategy to design more efficient semiconductor‐based composite photocatalysts toward solar energy capture and conversion. A facile, low‐temperature synthesis approach is reported to fabricate hierarchical CdS‐1D ZnO nanorod arrays‐2D graphene (GR) hybrids in a finely tailored manner in pursuit of the integration of the fast electron transport of 1D ZnO, the electron conductive platform of 2D graphene and the desirable visible‐light absorption of CdS to efficiently harvest visible light and boost the separation and transfer of the photogenerated charge carriers for specific photocatalytic applications.
      PubDate: 2014-10-13T11:52:28.354328-05:
      DOI: 10.1002/adfm.201402443
  • Voltage‐Controlled Nonstoichiometry in Oxide Thin Films:
           Pr0.1Ce0.9O2−δ Case Study
    • Authors: Di Chen; Harry L. Tuller
      Pages: n/a - n/a
      Abstract: While the properties of functional oxide thin films often depend strongly on oxygen stoichiometry, there have been few means available for its control in a reliable and in situ fashion. This work describes the use of DC bias as a means of systematically controlling the stoichiometry of oxide thin films deposited onto yttria‐stabilized zirconia substrates. Impedance spectroscopy is performed on the electrochemical cell Pr0.1Ce0.9O2−δ (PCO)/YSZ/Ag for conditions: T = 550 to 700 °C, pO 2 = 10−4 to 1 atm, and ΔE = ‐100 to 100 mV. The DC bias ΔE is used to control the effective pO 2 or oxygen activity at the PCO/YSZ interface. The non‐stoichiometry (δ) of the PCO films is calculated from the measured chemical capacitance (Cchem ). These δ values, when plotted isothermally as a function of effective pO 2, established, either by the surrounding gas composition alone, or in combination with applied bias, agree well with each other and to predictions based on a previously determined defect model. These results confirm the suitability of using bias to precisely control δ of thin films in an in situ fashion and simultaneously monitor these changes by measurement of Cchem . Of further interest is the ability to reach effective pO 2s as high as 280 atm. The non‐stoichiometry of oxide thin films is systematically controlled by use of DC bias. The suitability of using bias across an electrochemical cell to conveniently and precisely control non‐stoichiometry of oxide thin films, in an in situ fashion, and simultaneously monitor these changes by measurement of the chemical capacitance, is confirmed.
      PubDate: 2014-10-09T12:32:06.794541-05:
      DOI: 10.1002/adfm.201402050
  • Quasi‐Three‐Dimensional Angle‐Tolerant Electromagnetic
           Illusion Using Ultrathin Metasruface Coatings
    • Authors: Zhi Hao Jiang; Douglas H. Werner
      Pages: n/a - n/a
      Abstract: Low‐profile and light‐weight coatings that offer comprehensive manipulation of the electromagnetic scattering for finite‐length objects are highly desirable, but not yet achieved, for applications including camouflaging, deceptive sensing, radar cognition control, and defense security. Here, for the first time, the theory, practical design, and experimental demonstration of quasi‐three‐dimensional and angle‐tolerant electromagnetic illusion coatings are presented which have been enabled by ultrathin single‐layer functional metasurfaces. By controlling the multiple Mie scattering coefficients using the tangential and non‐vanishing radial electromagnetic responses of the metasurface, the quasi‐two‐dimensional coating transforms the electromagnetic perception of one object to mimic that of another which has been pre‐selected by the designer. The illusion coating, which is homogeneous but anisotropic, is realized using hundreds of composite electric and magnetic sub‐wavelength unit cells operating at frequencies away from their resonance. Two different prototypes of the metasurface illusion coatings were fabricated and characterized, demonstrating very good camouflaging performance for finite‐length dielectric as well as conducting objects within a field‐of‐view up to ±10° off normal. This work paves the way for practical artificially engineered material coatings with exotic and versatile scattering control capabilities that would enable a wide range of applications throughout the entire electromagnetic spectrum. Quasi‐three‐dimensional and angle‐tolerant electromagnetic illusion coatings are proposed, designed, and demonstrated using ultrathin single‐layer functional metasurfaces with nonvanishing radial response. The quasi‐two‐dimensional metasurface coatings transform the electromagnetic perception of one object to mimic that of another which has been pre‐selected by the designer. The illusion coating is realized using hundreds of composite electric and magnetic sub‐wavelength unit cells.
      PubDate: 2014-10-09T12:32:01.637235-05:
      DOI: 10.1002/adfm.201401561
  • Self‐Powered Trajectory, Velocity, and Acceleration Tracking of a
           Moving Object/Body using a Triboelectric Sensor
    • Authors: Fang Yi; Long Lin, Simiao Niu, Jin Yang, Wenzhuo Wu, Sihong Wang, Qingliang Liao, Yue Zhang, Zhong Lin Wang
      Pages: n/a - n/a
      Abstract: Motion tracking is of great importance in a wide range of fields such as automation, robotics, security, sports and entertainment. Here, a self‐powered, single‐electrode‐based triboelectric sensor (TES) is reported to accurately detect the movement of a moving object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the movement of an object on the top surface of a polytetrafluoroethylene (PTFE) layer induces changes in the electrical potential of the patterned aluminum electrodes underneath. From the measurements of the output performance (open‐circuit voltage and short‐circuit current), the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values. Moreover, the TES can detect motions of more than one objects moving at the same time. In addition, applications of the TES are demonstrated by using LED illuminations as real‐time indicators to visualize the movement of a sliding object and the walking steps of a person. A self‐powered, single‐electrode‐based triboelectric sensor is reported to accurately detect the movement of an object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values.
      PubDate: 2014-10-06T23:57:42.538047-05:
      DOI: 10.1002/adfm.201402703
  • Hybrid CuTCNQ/AgTCNQ Metal‐Organic Charge Transfer Complexes via
           Galvanic Replacement vs Corrosion‐Recrystallization
    • Authors: Andrew Pearson; Rajesh Ramanathan, Anthony P. O'Mullane, Vipul Bansal
      Pages: n/a - n/a
      Abstract: This study reports a hybrid of two metal‐organic semiconductors that are based on organic charge transfer complexes of 7,7,8,8‐tetracyanoquinodimethane (TCNQ). It is shown that the spontaneous reaction between semiconducting microrods of CuTCNQ with Ag+ ions leads to the formation of a CuTCNQ/AgTCNQ hybrid, both in aqueous solution and acetonitrile, albeit with completely different reaction mechanisms. In an aqueous environment, the reaction proceeds by a complex galvanic replacement (GR) mechanism, wherein in addition to AgTCNQ nanowires, Ag0 nanoparticles and Cu(OH)2 crystals decorate the surface of CuTCNQ microrods. Conversely, in acetonitrile, a GR mechanism is found to be thermodynamically unfavorable and instead a corrosion‐recrystallization mechanism leads to the decoration of CuTCNQ microrods with AgTCNQ nanoplates, resulting in a pure CuTCNQ/AgTCNQ hybrid metal‐organic charge transfer complex. While hybrids of two different inorganic semiconductors are regularly reported, this report pioneers the formation of a hybrid involving two metal‐organic semiconductors that will expand the scope of TCNQ‐based charge transfer complexes for improved catalysis, sensing, electronics, and biological applications. A new metal organic semiconductor hybrid of CuTCNQ and AgTCNQ is reported. The synthesis of these hybrids in water and acetonitrile reveal two completely unexpected and different mechanisms in these solvents. A facile generalized approach to prepare hybrid materials comprising two metal‐TCNQs in a single system will expand the applicability of TCNQ‐based charge transfer complexes to new applications.
      PubDate: 2014-10-06T06:15:42.052483-05:
      DOI: 10.1002/adfm.201402320
  • Multi‐Shell Porous TiO2 Hollow Nanoparticles for Enhanced Light
           Harvesting in Dye‐sensitized Solar Cells
    • Authors: Sun Hye Hwang; Juyoung Yun, Jyongsik Jang
      Pages: n/a - n/a
      Abstract: An optimized configuration for nanomaterials in working electrodes is vital to the high performance of dye‐sensitized solar cells (DSSCs). Here, a fabrication method is introduced for multi‐shell TiO2 hollow nanoparticles (MS‐TiO2‐HNPs) via a sol–gel reaction, calcination, and an etching process. The prepared uniform MS‐HNPs have a high surface area (ca. 171 m2 g−1), multireflection, and facile electrolyte circulation and diffusion. During the MS‐HNP fabrication process, the amount of SiO2 precursor and H2O under reaction has a significant effect on aggregation and side reactions. The etching process to obtain pure TiO2 is influenced by anatase crystallinity. Additionally, single‐shell (SS)‐TiO2‐HNPs and double‐shell (DS)‐TiO2‐HNPs are synthesized as a control. The MS‐TiO2‐HNPs exhibit a high surface area and enhance light reflectance, compared with the SS‐ and DS‐TiO2‐HNPs of the same size. The power conversion efficiency of the optimized MS‐TiO2‐HNP‐based DSSCs is 9.4%, compared with the 8.0% efficiency demonstrated by SS‐TiO2‐HNP‐DSSCs (a 17.5% improvement). These results enable the utilization of multifunctional MS‐HNPs in energy material applications, such as lithium ion batteries, photocatalysts, water‐splitting, and supercapacitors. Multi‐shell porous TiO2 hollow nanoparticles (MS‐TiO2‐HNPs) are prepared by a sol–gel method and calcination and etching processes. Due to the porous multi‐shell structure, the MS‐TiO2‐HNPs exhibit strong light scattering and facile electrolyte diffusion and circulation. Additionally, the high surface area increases the adsorption of the dye molecules to the surface of the MS‐TiO2‐HNPs, resulting in an enhanced power conversion efficiency of 9.4%.
      PubDate: 2014-10-06T06:15:35.308165-05:
      DOI: 10.1002/adfm.201401915
  • Directed Electric Field Z‐Alignment Kinetics of Anisotropic
           Nanoparticles for Enhanced Ionic Conductivity
    • Authors: Saurabh Batra; Emre Unsal, Miko Cakmak
      Pages: n/a - n/a
      Abstract: In this study, the fast transient evolution of the electric field assisted thickness Z‐direction orientation and assembly of clay particles is studied using a instrumented real time system that simultaneously measures in‐plane and out of plane birefringence. The optical anisotropy master curves are developed, connecting the exposure time and electric field strength with orientation, using a superposition principle. Z‐oriented nanocomposite films manufactured through the R2R process show enhancement through thickness ionic conductivity, useful for membranes of batteries and fuel cells. Kinetics of electric field induced alignment of anisotropic particles through the thickness of polymer film is studied using birefringence. Kinetics of alignment is used to determine the processing conditions to create continuous oriented films using roll‐to‐roll manufacturing process. The directional percolation of these particles enhances thickness properties creating functional films for membranes and flexible electronics.
      PubDate: 2014-10-06T06:15:30.704751-05:
      DOI: 10.1002/adfm.201400760
  • Intracellular Microenvironment‐Responsive Dendrimer‐Like
           Mesoporous Nanohybrids for Traceable, Effective, and Safe Gene Delivery
    • Authors: Xin Du; Lin Xiong, Sheng Dai, Freddy Kleitz, Shi Zhang Qiao
      Pages: n/a - n/a
      Abstract: In order to create advanced functional nanocarriers for efficient gene therapy, novel intracellular microenvironment‐sensitive fluorescence label‐free nanostructured dendrimer‐like silica hybrid nanocarriers are developed for traceable, effective, and safe gene delivery. Dendrimer‐like mesoporous silica nanoparticles (DMSNs) with center‐radial large pores are covalently modified with short polyethyleneimine (PEI) for efficient gene loading and binding. Autofluorescent and biodegradable PEI (AC‐PEI) responsive to the intracellular microenvironment are then coated on the gene‐loaded nanoparticles for inhibiting gene leakage from the carriers. Moreover, AC‐PEI coating not only endows intracellular microenvironment‐responsive gene release property, but also allows monitoring the gene delivery process in the absence of external labelling, owing to the pH‐ and GSH‐responsive autofluorescence and biodegradability of AC‐PEI. The resultant nanocarriers show high gene loading capacity, low cytotoxicity, stimuli‐responsive gene release, label‐free, and simultaneous fluorescence tracking, and high gene silencing capability. Thus, these developed nanocarriers hold substantial and promising potential as effective and safe gene‐delivery carriers for future scientific investigation and practical implications in gene therapy. Novel intracellular microenvironment‐sensitive fluorescence label‐free nanostructured dendrimer‐like silica hybrid nanocarriers are successfully developed to achieve traceable, effective, and safe gene delivery. The pH‐ and GSH‐responsive autofluorescent and biodegradable properties of the coated polymer not only endow a responsive gene release property, but also allow real‐time monitoring of the gene delivery process.
      PubDate: 2014-10-06T06:06:43.817505-05:
      DOI: 10.1002/adfm.201402408
  • Bio‐Inspired, Water‐Soluble to Insoluble Self‐Conversion
           for Flexible, Biocompatible, Transparent, Catecholamine Polysaccharide
           Thin Films
    • Authors: Ji Hyun Ryu; Seongyeon Jo, Mi‐Young Koh, Haeshin Lee
      Pages: n/a - n/a
      Abstract: In nature, a variety of functional water‐insoluble organic materials are biologically synthesized in aqueous conditions without chemical additives and organic solvents. Insect cuticle, crustacean shells, and many others are representative examples. The insoluble materials are prepared by enzyme reactions and programmed self‐assembly in water from water‐soluble precursors. If the water‐basis could be adapted, environment‐friendly strategy developed in nature, many problems caused by the vast consumption of petroleum‐based olefin materials could be solved or significantly attenuated. Here, the spontaneous formation of water‐insoluble, biocompatible films from a water‐soluble polymer is demonstrated without using any chemical additives and organic solvents. It is found that a water‐soluble chitosan–catechol polymeric precursor is spontaneously self‐converted to flexible water‐insoluble thin film by simple dehydration. The preparation of mechanically robust, water‐insoluble, flexible, transparent chitosan–catechol film is a completely unexpected result because most water‐soluble polymers exist as powders when dehydrated. The film can be used as a bag similar to polyvinyl one and is multifunctional and biocompatible for drug delivery depots and tissue engineering applications. The water‐basis, environment‐friendly strategy evolutionarilly optimized in nature can solve problems shown in the widely implemented petroleum‐based olefin materials. Here, the spontaneous formation of water‐insoluble, biocompatible microfilms from a water‐soluble polymer is demonstrated without using any chemical additives similar to the biological process shown in the insect cuticle formation.
      PubDate: 2014-10-06T06:06:38.004306-05:
      DOI: 10.1002/adfm.201402250
  • Chain Length Dependence of the Photovoltaic Properties of Monodisperse
           Donor–Acceptor Oligomers as Model Compounds of Polydisperse Low Band
           Gap Polymers
    • Authors: Cheng Zhou; Yamin Liang, Feng Liu, Chen Sun, Xuelong Huang, Zengqi Xie, Fei Huang, Jean Roncali, Thomas P. Russell, Yong Cao
      Pages: n/a - n/a
      Abstract: Well‐defined conjugated oligomers (Sn) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings (S1) are synthesized by a bottom‐up approach. UV–Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO–LUMO gap (ΔE) to values slightly smaller than that of the parent polymer (P1). Plots of ΔE and of the band gap of films (E g) versus the reciprocal chain length show that ΔE and E g converge towards a limit corresponding to an effective conjugation length (ECL) of 7–8 S1 units. UV–Vis absorption and photoluminescence data of solutions and solid films show that chain extension enhances the propensity to inter‐chain aggregation. This conclusion is confirmed by GIXD analyses which reveal that the edge‐on orientation of short‐chain systems evolves toward a face‐on orientation as chain length increases while the π‐stacking distance decreases beyond 7 units. The results obtained on solution‐processed BHJ solar cells show a progressive improvement of power conversion efficiency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/polydispersity and chain aggregation. A series of donor–acceptor monodisperse oligomers (S1 –S8) and two analogous polydisperse polymers (P1, P2) are synthesized successfully. These materials serve as a model system to understand the relationship between conjugation length and the photophysical, morphological, and photovoltaic properties in donor–acceptor polymer solar cell materials, and provide a bridge between small molecules and the polymers.
      PubDate: 2014-10-06T05:56:21.120346-05:
      DOI: 10.1002/adfm.201401945
  • Understanding the Role of Underlayers and Overlayers in Thin Film Hematite
    • Authors: Ludmilla Steier; Isaac Herraiz‐Cardona, Sixto Gimenez, Francisco Fabregat‐Santiago, Juan Bisquert, S. David Tilley, Michael Grätzel
      Pages: n/a - n/a
      Abstract: Recent research on photoanodes for photoelectrochemical water splitting has introduced the concept of under‐ and overlayers for the activation of ultrathin hematite films. Their effects on the photocatalytic behavior were clearly shown; however, the mechanism is thus far not fully understood. Herein, the contribution of each layer is analyzed by means of electrochemical impedance spectroscopy, with the aim of obtaining a general understanding of surface and interface modifications and their influence on the hematite photoanode performance. This study shows that doping of the hematite from the underlayer and surface passivation from annealing treatments and an overlayer are key parameters to consider for the design of more efficient iron oxide electrodes. Understanding the contribution of these layers, a new design for ultrathin hematite films employing a combination of a gallium oxide overlayer with thin niobium oxide and silicon oxide underlayers is shown to achieve a photocurrent onset potential for the photoelectrochemical oxidation of water more negative than 750 mV versus the reversible hydrogen electrode (RHE) at pH 13.6, utilizing Co‐Pi as a water oxidation catalyst. It is demonstrated that multilayer hematite thin film photoanodes are a strategy to reduce the overpotential for this material, thereby facilitating more efficient tandem cells. Impedance spectroscopy reveals new details for efficiency‐enhancing modifications of hematite water splitting photo­anodes. Suitable underlayers such as Nb2O5 and SiOx dramatically increase the conductivity in hematite ultrathin films, thereby improving the plateau photocurrent, and the photocurrent onset potential is determined by the energetic position and density of surface states, which can be modified by annealing and surface treatments.
      PubDate: 2014-10-02T02:06:08.86857-05:0
      DOI: 10.1002/adfm.201402742
  • First Principles Calculations of Charge Transfer Excitations in
           Polymer–Fullerene Complexes: Influence of Excess Energy
    • Authors: Dorota Niedzialek; Ivan Duchemin, Thiago Branquinho de Queiroz, Silvio Osella, Akshay Rao, Richard Friend, Xavier Blase, Stephan Kümmel, David Beljonne
      Pages: n/a - n/a
      Abstract: The ability of quantum simulations to predict the electronic structure at donor/acceptor interfaces and correlate it with the quantum efficiency of organic solar cells remains a major challenge. The need to describe with increased accuracy electron‐electron and electron‐hole interactions, while better accounting for disorder and environmental screening in realistic interfaces, requires significant progress to improve both the accuracy and computational efficiency of available quantum simulation methods. In the present study, the results of different ab initio techniques are compared, namely time‐dependent density functional and many‐body perturbation theories, with experimental data on three different polymer/fullerene heterojunctions. It is shown that valuable information concerning the thermodynamic drive for electron‐hole dissociation or recombination into triplets can be obtained from such calculations performed on model interfaces. In particular, the ability of these approaches to reproduce the Veldman and co–workers classification of the three studied interfaces is discussed, showing the success and limits of state‐of‐the‐art ab initio techniques. A comparative first‐principle study is presented of polymer‐fullerene complexes that differ by the excess energy for charge separation. The measured quantum efficiencies of the bulk heterojunctions can be traced back to the presence of energy‐accessible charge‐transfer states with large electron‐hole radii and molecular triplets mediating competing recombination pathways.
      PubDate: 2014-10-02T02:06:06.210499-05:
      DOI: 10.1002/adfm.201402682
  • 3D TEM Tomography of Templated Bilayer Films of Block Copolymers
    • Authors: Kevin W. Gotrik; Thomas Lam, Adam F. Hannon, Wubin Bai, Yi Ding, Jonathan Winterstein, Alfredo Alexander‐Katz, J. Alexander Liddle, Caroline A. Ross
      Pages: n/a - n/a
      Abstract: Transmission electron microscope (TEM) tomography was used to visualize the morphology and 3D connectivity of a lithographically templated, self‐assembled bilayer film of cylinder‐forming 45.5 kg/mol polystyrene‐block‐polydimethylsiloxane. The structure, formed after a 5 min solvothermal anneal, was imaged with a resolution of ≈3 nm in 3D, enabling a comparison between measurement and self‐consistent mean‐field theory (SCFT) calculations. Images of etched and unetched samples showed that etching collapsed the PDMS microdomain structure and reduced the template dimensions. In addition to the general comparison between modeled and measured dimensions, the tomography revealed connections between the orthogonal layers of cylinders at their crossing points. Comparison with the SCFT model, even under solvothermal annealing conditions, shows that it is helpful in understanding the detailed nanoscale structure of features created by directed self‐assembly (DSA), which is essential in developing nanomanufacturing processes based on DSA. Understanding the 3D structure of self‐assembled block copolymer films is essential to their applications in nanolithography. The 3D microdomain structure of a block copolymer consisting of polydimethylsiloxane cylindrical domains in a polystyrene matrix, templated by posts, is determined by TEM tomography. The cylinders form a cross‐point array (left), which is compared with the predictions of self‐consistent field theory (right).
      PubDate: 2014-10-02T02:06:03.15494-05:0
      DOI: 10.1002/adfm.201402457
  • Photosystem I‐based Biophotovoltaics on Nanostructured Hematite
    • Authors: Kasim Ocakoglu; Tomasz Krupnik, Bart van den Bosch, Ersan Harputlu, Maria Pia Gullo, Julian David Janna Olmos, Saadet Yildirimcan, Ram K. Gupta, Fahrettin Yakuphanoglu, Andrea Barbieri, Joost N. H. Reek, Joanna Kargul
      Pages: n/a - n/a
      Abstract: The electronic coupling between a robust red algal photosystem I (PSI) associated with its light harvesting antenna (LHCI) and nanocrystalline n‐type semiconductors, TiO2 and hematite (α‐Fe2O3) is utilized for fabrication of the biohybrid dye‐sensitized solar cells (DSSC). PSI‐LHCI is immobilized as a structured multilayer over both semiconductors organized as highly ordered nanocrystalline arrays, as evidenced by FE‐SEM and XRD spectroscopy. Of all the biohybrid DSSCs examined, α‐Fe2O3/PSI‐LHCI biophotoanode operates at a highest quantum efficiency and generates the largest open circuit photo­current compared to the tandem system based on TiO2/PSI‐LHCI material. This is accomplished by immobilization of the PSI‐LHCI complex with its reducing side towards the hematite surface and nanostructuring of the PSI‐LHCI multilayer in which the subsequent layers of this complex are organized in the head‐to‐tail orientation. The biohybrid PSI‐LHCI‐DSSC is capable of sustained photoelectrochemical H2 production upon illumination with visible light above 590 nm. Although the solar conversion efficiency of the PSI‐LHCI/hematite DSSC is currently below a practical use, the system provides a blueprint for a genuinely green solar cell that can be used for molecular hydrogen production at a rate of 744 μmoles H2 mg Chl−1 h−1, placing it amongst the best performing biohybrid solar‐to‐fuel nanodevices. A fully integrated, stable and functional photosystem I‐based biohybrid dye‐sensitized solar cell is constructed with an improved solar‐to‐electric quantum efficiency over previously reported biohybrid devices. A highly robust oriented Cyanidioschyzon merolae PSI‐LHCI complex is used as a natural photosensitizer of the nanostructured hematite substrate for the sustained photodriven H2 production.
      PubDate: 2014-10-02T02:05:46.842898-05:
      DOI: 10.1002/adfm.201401399
  • Tailoring Electron‐Transfer Barriers for Zinc Oxide/C60 Fullerene
    • Authors: Philip Schulz; Leah L. Kelly, Paul Winget, Hong Li, Hyungchul Kim, Paul F. Ndione, Ajaya K. Sigdel, Joseph J. Berry, Samuel Graham, Jean‐Luc Brédas, Antoine Kahn, Oliver L. A. Monti
      Pages: n/a - n/a
      Abstract: The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C60. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies. Controlling the defect composition of the oxide surface allows the barriers to be changed for charge transfer at the ZnO/Fullerene interface. Direct and inverse electron spectroscopy is used to demonstrate the control over the transfer barrier by tracking electronic alignment and interface state formation. This is predicted by DFT and leads to observable alterations in charge injection in our devices.
      PubDate: 2014-10-01T11:41:06.29142-05:0
      DOI: 10.1002/adfm.201401794
  • Highly Stretchable Conductors Integrated with a Conductive Carbon
           Nanotube/Graphene Network and 3D Porous Poly(dimethylsiloxane)
    • Authors: Mengting Chen; Ling Zhang, Shasha Duan, Shilong Jing, Hao Jiang, Chunzhong Li
      Pages: n/a - n/a
      Abstract: Here, a novel and facile method is reported for manufacturing a new stretchable conductive material that integrates a hybrid three dimensional (3D) carbon nanotube (CNT)/reduced graphene oxide (rGO) network with a porous poly(dimethylsiloxane) (p‐PDMS) elastomer (pPCG). This reciprocal architecture not only alleviates the aggregation of carbon nanofillers but also significantly improves the conductivity of pPCG under large strains. Consequently, the pPCG exhibits high electrical conductivity with a low nanofiller loading (27 S m−1 with 2 wt% CNTs/graphene) and a notable retention capability after bending and stretching. The simulation of the mechanical properties of the p‐PDMS model demonstrates that an extremely large applied strain (εappl) can be accommodated through local rotations and bending of cell walls. Thus, after a slight decrease, the conductivity of pPCG can continue to remain constant even as the strain increases to 50%. In general, this architecture of pPCG with a combination of a porous polymer substrate and 3D carbon nanofiller network possesses considerable potential for numerous applications in next‐generation stretchable electronics. A highly stretchable conductor is manufactured by integrating porous poly(dimethylsiloxane) (p‐PDMS) with a CNT/graphene network (pPCG). Mechanical simulation of p‐PDMS demonstrates that large strains are accommodated through strut rotations and bending. After a slight decrease, the high conductivity (27 S m−1 with 2 wt% CNTs/graphene) remained constant, even as the strain was increased to 50%.
      PubDate: 2014-10-01T11:40:45.705075-05:
      DOI: 10.1002/adfm.201401886
  • Intranuclear Photosensitizer Delivery and Photosensitization for Enhanced
           Photodynamic Therapy with Ultralow Irradiance
    • Authors: Limin Pan; Jianan Liu, Jianlin Shi
      Pages: n/a - n/a
      Abstract: Photodynamic therapy (PDT) is a well‐established clinical treatment modality for various diseases. However, reactive oxygen species (ROS) generated by photosensitizers(PS) under proper irradiation exhibits the extremely short life span (
      PubDate: 2014-09-30T13:49:27.502667-05:
      DOI: 10.1002/adfm.201402255
  • Direct Growth of Nanographene on Silicon with Thin Oxide Layer for
           High‐Performance Nanographene‐Oxide‐Silicon Diodes
    • Authors: Qichong Zhang; Xiaojuan Wang, Dong Li, Zengxing Zhang
      Pages: n/a - n/a
      Abstract: Graphene‐silicon based configurations are attracting great attention for their potential application as electronics and optoelectronics. For their practical use, it is still limited by the configuration fabrication process. In this paper, a catalyst‐free method is reported to directly grow nanographene on silicon covered with a thin oxide layer to form nanographene‐oxide‐silicon configurations. Compared with previously reported nanographene‐silicon Schottky junctions, the nanographene‐oxide‐silicon structures exhibit a high performance on electronic and photovoltaic properties. The reverse leakage current of the nanographene‐oxide‐silicon is suppressed from over 10−5 A down to 10−8 A and the rectifier ratio is greatly enhanced from less than 5 up to 103. The photovoltage is enhanced over 50 times. The nanographene‐oxide‐silicon structures exhibit especially ultrasensitive to weak light at a photovoltage working mode, which exceeds up to 106 V/W at the light power of 0.025 μW. Due to the source material for nanographene is photoresist and the fabrication process is mainly based on the current‐used photolithography and silicon technique, the developed nanographene‐oxide‐silicon structures are very easy for device fabrication, integration, and miniaturization, and could be a promising way to produce metal‐free graphene‐silicon based electronics and optoelectronics for commercial use. A simple and low cost approach of directly producing high‐performance metal‐free nanographene‐oxide‐silicon diodes is developed. The nanographene is from photoresist without any transfer and the approach is based on the conventional photolithography and silicon technique. Due to the source material is photoresist, the fabrication approach is easy for device fabrication, integration and miniaturization, and thus for commercial use.
      PubDate: 2014-09-30T13:48:49.789173-05:
      DOI: 10.1002/adfm.201402099
  • Optimization of Solubility, Film Morphology and Photodetector Performance
           by Molecular Side‐Chain Engineering of Low‐Bandgap
           Thienothiadiazole‐Based Polymers
    • Authors: Ji Qi; Xiaokang Zhou, Dezhi Yang, Wenqiang Qiao, Dongge Ma, Zhi Yuan Wang
      Pages: n/a - n/a
      Abstract: A series of donor–acceptor (D‐A) type low‐bandgap polymers containing the terthiophene and thieno[3,4‐b]thiadiazole units in the main chain but different numbers of identical side chains are designed and synthesized in order to study the effect of side chain on the polymer properties and optimize the performance of polymer photodetectors. Variation in the side chain content can influence the polymer solubility, molecular packing, and film morphology, which in turn affects the photodetector performance, particularly with regard to the photoresponsivity and dark current. X‐ray diffraction patterns indicate that molecular ordering increases with more side chains. Atomic force microscopy shows that appropriate morphology of the active layer in the polymer photodetector is necessary for high photocurrent and low dark current. Using BCP as a hole blocking layer (10 nm), the photodetector based on P4 exhibits the optimized performance with specific detectivity of 1.4 × 1012 Jones at 800 nm, which is among the best reported values for polymer photodetectors and even comparable to that of a silicon photodetector. A series of thieno[3,4‐b]thiadiazole based low‐bandgap polymers with different amounts of side chains are designed for probing the effect of side chains on solubility, molecular packing, film morphology, and key performance of polymer photodetectors. Among them, the P4‐based photodetector demonstrates the best performance and shows fairly constant specific detectivity of about 1012 Jones in the spectral range of 330–950 nm.
      PubDate: 2014-09-30T13:48:39.452231-05:
      DOI: 10.1002/adfm.201401948
  • Joule Heating Characteristics of Emulsion‐Templated Graphene
    • Authors: Robert Menzel; Suelen Barg, Miriam Miranda, David B. Anthony, Salem M. Bawaked, Mohamed Mokhtar, Shaeel A. Al‐Thabaiti, Sulaiman N. Basahel, Eduardo Saiz, Milo S. P. Shaffer
      Pages: n/a - n/a
      Abstract: The Joule heating properties of an ultralight nanocarbon aerogel are investigated with a view to potential applications as energy‐efficient, local gas heater, and other systems. Thermally reduced graphene oxide (rGO) aerogels (10 mg cm−3) with defined shape are produced via emulsion‐templating. Relevant material properties, including thermal conductivity, electrical conductivity and porosity, are assessed. Repeatable Joule heating up to 200 °C at comparatively low voltages (≈1 V) and electrical power inputs (≈2.5 W cm−3) is demonstrated. The steady‐state core and surface temperatures are measured, analyzed and compared to analogous two‐dimensional nanocarbon film heaters. The assessment of temperature uniformity suggests that heat losses are dominated by conductive and convective heat dissipation at the temperature range studied. The radial temperature gradient of an uninsulated, Joule‐heated sample is analyzed to estimate the aerogel's thermal conductivity (around 0.4 W m−1 K−1). Fast initial Joule heating kinetics and cooling rates (up to 10 K s−1) are exploited for rapid and repeatable temperature cycling, important for potential applications as local gas heaters, in catalysis, and for regenerable of solid adsorbents. These principles may be relevant to wide range of nanocarbon networks and applications. A fundamental study of the direct resistive heating of graphene aerogels demonstrates efficient, uniform, fast, and repeatable Joule heating. The outlined principles pave a route towards new applications of three‐dimensional nanocarbon networks as viable light‐weight, high‐surface‐area local gas heaters and temperature‐controlled catalyst and adsorber supports.
      PubDate: 2014-09-30T13:48:22.466152-05:
      DOI: 10.1002/adfm.201401807
  • Wafer Scale Synthesis and High Resolution Structural Characterization of
           Atomically Thin MoS2 Layers
    • Authors: Aaron S. George; Zafer Mutlu, Robert Ionescu, Ryan J. Wu, Jong S. Jeong, Hamed H. Bay, Yu Chai, K. Andre Mkhoyan, Mihrimah Ozkan, Cengiz S. Ozkan
      Pages: n/a - n/a
      Abstract: Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photo­emission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers. Wafer scale synthesis of atomically thin MoS2 layers via thermolysis of spin coated films is presented. High resolution characterization of atomically thin layers is performed by HAADF‐STEM image analysis. This approach could be applied to a variety of substrates and provides a promising route towards wafer scale production of other TMD and doped materials for applications in electronics and optoelectronics.
      PubDate: 2014-09-30T13:44:12.124433-05:
      DOI: 10.1002/adfm.201402519
  • Green Emission in Ladder‐Type Quarterphenyl: Beyond the
    • Authors: Björn Kobin; Francesco Bianchi, Simon Halm, Joachim Leistner, Sylke Blumstengel, Fritz Henneberger, Stefan Hecht
      Pages: n/a - n/a
      Abstract: In polyfluorenes it is generally accepted that (photo)degradation leads to fluorenone type defects that accept the excitation energy and emit green‐to‐yellow light with rather low efficiency. Although initial spectroscopic studies suggest the same to hold true for ladder‐type poly(para‐phenylene)s (LPPPs), kinetic studies of the degradation process are not compatible with the established mechanism. In general, the observed green emission can be caused by the introduction of carbonyl groups; however, only if associated with an additional disruption of the backbone rigidity and hence planarity of the entire π‐system. This is clearly shown by comparison with synthesized model compounds, which are bearing the fluorenone motif yet possess very different optical properties as compared to the defects, which are actually formed. Degradation can be caused by solvent specific, yet substrate nonspecific aromatic formylation but mainly originates from reaction with in‐situ generated singlet oxygen, both in solution as well as in thin films. Time‐dependent photoluminescence measurements on thin films show that green emission is enhanced by energy transfer from intact molecules to defect centers. Photodegradation in polyfluorenes has traditionally been explained by fluorenone‐type defects. Thorough analysis of the photodegradation products of ladder‐type quarter­phenyl and comparison with separately synthesized, potential ketone products now shows that the observed green emission indeed originates from the introduction of carbonyl groups yet only if associated with an additional disruption of the backbone rigidity and hence planarity of the π‐system.
      PubDate: 2014-09-30T13:43:48.780968-05:
      DOI: 10.1002/adfm.201402638
  • Nano‐Bio‐Chemical Braille for Cells: The Regulation of Stem
           Cell Responses using Bi‐Functional Surfaces
    • Authors: Wojciech Chrzanowski; Jae Ho Lee, Alexey Kondyurin, Megan S. Lord, Jun‐Hyeog Jang, Hae‐Won Kim, Marcela M. M. Bilek
      Pages: n/a - n/a
      Abstract: Insufficient integration with local host tissues is a significant problem that adversely affects the performance of implanted biomedical devices. Poor tissue integration leaves patients susceptible to complications associated with adverse foreign body reactions and infections that typically mandate expensive and elevated‐risk revision surgery. The aging population and growing incidence of medical implants makes the development of bio‐functional implant surfaces a high priority research imperative. Here multifunctional surfaces are reported that are capable of regulating cell adhesion and triggering cell differentiation to facilitate osseointegration of implantable devices. The approach described is universal, cost‐ and time‐effective. It relies on a unique combination of two advances: i) a reactive interface provided by a plasma activated coating (PAC) that covalently immobilises bioactive molecules with significantly higher efficiency than conventional technologies, and ii) multifunctional molecules (bi‐functional fusion‐proteins) that regulate multiple cellular responses. Covalent linking of the molecules, their high density, and desired orientation are demonstrated. The effectiveness of these functional interfaces to regulate mesenchymal stem cell attachment and differentiation is confirmed suggesting the ability to regulate osseointegration. This method is a leap forward in the fabrication of truly biofunctional materials tailored for particular applications. A single step technology that activates the surfaces of biomedical implant materials is developed to enable the direct covalent immobilization of novel bi‐functional proteins via the formation of highly reactive radicals embedded in the surface. This multifunctional interface successfully regulates mesenchymal stem cell adhesion and differentiation at the surface, thus resulting in an osteoinductive surface that enhances implant integration within the body.
      PubDate: 2014-09-30T04:16:42.206589-05:
      DOI: 10.1002/adfm.201401696
  • Laser‐Activatible PLGA Microparticles for Image‐Guided Cancer
           Therapy In Vivo
    • Authors: Yang Sun; Yanjie Wang, Chengcheng Niu, Eric M. Strohm, Yuanyi Zheng, Haitao Ran, Rongzhong Huang, Di Zhou, Yuping Gong, Zhigang Wang, Dong Wang, Michael C. Kolios
      Pages: n/a - n/a
      Abstract: Poly(lactide‐co‐glycolic acid) (PLGA) particles are biocompatible and bio­degradable, and can be used as a carrier for various chemotherapeutic drugs, imaging agents and targeting moieties. Micrometer‐sized PLGA particles were synthesized with gold nanoparticles and DiI dye within the PLGA shell, and perfluorohexane liquid (PFH) in the core. Upon laser irradiation, the PLGA shell absorbs the laser energy, activating the liquid core (liquid conversion to gas). The rapidly expanding gas is expelled from the particle, resulting in a microbubble; this violent process can cause damage to cells and tissue. Studies using cell cultures show that PLGA particles phagocytosed by single cells are consistently vaporized by laser energies of 90 mJ cm−2, resulting in cell destruction. Rabbits with metastasized squamous carcinoma in the lymph nodes are then used to evaluate the anti‐cancer effects of these particles in the lymph nodes. After percutaneous injection of the particles and upon laser irradiation, through the process of optical droplet vaporization, ultrasound imaging shows a significant increase in contrast in comparison to the control. Histology and electron microscopy confirm damage with disrupted cells throughout the lymph nodes, which slows the tumor growth rate. This study shows that PLGA particles containing PFC liquids can be used as theranostic agents in vivo. PLGA particles containing gold nano­particles/DiI dye in the shell and perfluorohexane in the core are investigated as intravenous theranostic agents. Upon laser irradiation, the liquid core violently vaporizes into a microbubble, damaging nearby tissue. A tumor region can be selectively targeted in vivo, and the vaporization process verified through an increase in contrast during ultrasound imaging.
      PubDate: 2014-09-29T02:50:01.962985-05:
      DOI: 10.1002/adfm.201402631
  • Photoresponsive Soft‐Robotic Platform: Biomimetic Fabrication and
           Remote Actuation
    • Authors: Weitao Jiang; Dong Niu, Hongzhong Liu, Chaohui Wang, Tingting Zhao, Lei Yin, Yongsheng Shi, Bangdao Chen, Yucheng Ding, Bingheng Lu
      Pages: n/a - n/a
      Abstract: Biomimetic microsystems, which can be driven by various stimuli, are an emerging field in micro/nano‐technology and nano‐medicine. In this study, a soft and fast‐response robotic platform, constituted by PDMS/graphene‐nanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer, is presented. Due to the differences in coefficient of thermal expansion and Young's modulus of the two layers, the bilayer platform can be driven to bend to the PDMS/GNPs side by light irradiation. The robotic platform (1 mm in width and 7 mm in length) can be deflected about 1500 μm by near infrared irradiation (nIR)(808 nm in wavelength) within 3.4 s, and excellent reversibility and repeatability in actuation are also revealed by sweeping and multicycle light irradiation. The experiments also show that, the presented bilayer platform in various shapes, that is, fish‐like shapes, can float and swim to perspective location in fluid (i.e., water), whose moving directions and velocities can be remotely adjusted by light, indicating an excellent light‐actuation ability and well controllability. The results may be not only hopeful in developing light‐driven drug‐delivery platform, but also the bio‐robotic microgrippers applying in vivo and in vitro. Soft and fast‐response robotic platform constituted by PDMS/graphene‐nanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer are proposed. The robotic platform can be driven by near infrared irradiation (nIR) due to the photothermal effect of graphene to mimic the fish swimming, which is hopeful in developing light‐driven drug‐delivery platform, but also the bio‐robotic microgrippers applying in vivo and in vitro.
      PubDate: 2014-09-29T02:49:58.236213-05:
      DOI: 10.1002/adfm.201402070
  • Ortho‐ vs Bay‐Functionalization: a Comparative Study on
    • Authors: Glauco Battagliarin; Sreenivasa Reddy Puniredd, Sebastian Stappert, Wojciech Zajaczkowski, Suhao Wang, Chen Li, Wojciech Pisula, Klaus Müllen
      Pages: n/a - n/a
      Abstract: In this paper n‐type semiconductors synthesized via selective fourfold cyanation of the ortho‐ and bay‐positions (2,5,10,13‐ and 1,6,9,14‐positions respectively) of teyrrylenediimides are reported. A detailed study about the impact of the diverse functionalization topologies on the optoelectronic properties, self‐organization from solution, solid‐state packing, and charge carrier transport in field‐effect transistors is presented. The ortho‐substitution preserves the planarity of the core and favors high order in solution processed films. However, the strong intermolecular interactions lead to a microstructure with large aggregates and pronounced grain boundaries which lower the charge carrier transport in transistors. In contrast, the well‐soluble bay‐functionalized terrylenediimide forms only disordered films which surprisingly result in n‐type average mobilities of 0.17 cm2/Vs after drop‐casting with similar values in air. Processing by solvent vapor diffusion enhances the transport to 0.65 cm2/Vs by slight improvement of the order and surface arrangement of the molecules. This mobility is comparable to highest n‐type conductivities measured for solution processed PDI derivatives demonstrating the high potential of TDI‐based semiconductors. Ortho‐ vs Bay‐Functionalization: a Comparative Study on Tetracyano‐TerrylenediimidesOrtho‐ or bay‐tetracyanation? A comparative study on terrylenediimide reveals that the two functionalizations have similar impact on the optoelectronic properties, but remarkably different effects on self‐assembling from solution, with striking consequences on the n‐type behavior in field‐effect transistors. The pronounced electron mobilities here reported for the bay‐tetracyano derivative demonstrate the high potential of terrylenediimide as scaffold for n‐type semiconductors.
      PubDate: 2014-09-29T02:48:56.64124-05:0
      DOI: 10.1002/adfm.201401573
  • Insulator‐Conductor Type Transitions in Graphene‐Modified
           Silver Nanowire Networks: A Route to Inexpensive Transparent Conductors
    • Authors: Izabela Jurewicz; Azin Fahimi, Phillip E. Lyons, Ronan J. Smith, Maria Cann, Matthew L. Large, Mingwen Tian, Jonathan N. Coleman, Alan B. Dalton
      Pages: n/a - n/a
      Abstract: Silver nanowire coatings are an attractive alternative to indium tin oxide for producing transparent conductors. To fabricate coatings with low sheet resistance required for touchscreen displays, a multi‐layer network of silver nanowires must be produced that may not be cost effective. This problem is counteracted here by modifying the electrical properties of an ultra‐low‐density nanowire network through local deposition of conducting graphene platelets. Unlike other solution‐processed materials, such as graphene oxide, our pristine graphene is free of oxygen functional groups, resulting in it being electrically conducting without the need for further chemical treatment. Graphene adsorption at inter‐wire junctions as well as graphene connecting adjacent wires contributes to a marked enhancement in electrical properties. Using our approach, the amount of nanowires needed to produce viable transparent electrodes could be more than 50 times less than the equivalent pristine high density nanowire networks, thus having major commercial implications. Using a laser ablation process, it is shown that the resulting films can be patterned into individual electrode structures, which is a pre‐requisite to touchscreen sensor fabrication. A simple, scalable, and relatively inexpensive method is described for preparing highly conducting AgNW/graphene hybrid transparent electrodes that use low‐cost solution‐processed pristine graphene. A combination of spray deposition and Langmuir‐based techniques is used to produce ultrathin films with controlled nanowire and graphene densities. The results indicate that these graphene/nanowire hybrid films may serve as a cheap replacement for existing technologies in electronic devices.
      PubDate: 2014-09-26T02:45:43.572227-05:
      DOI: 10.1002/adfm.201402547
  • Memristor Kinetics and Diffusion Characteristics for Mixed
           Anionic‐Electronic SrTiO3‐δ Bits: The
           Memristor‐Based Cottrell Analysis Connecting Material to Device
    • Authors: Felix Messerschmitt; Markus Kubicek, Sebastian Schweiger, Jennifer L.M. Rupp
      Pages: n/a - n/a
      Abstract: Memristors based on mixed anionic‐electronic conducting oxides are promising devices for future data storage and information technology with applications such as non‐volatile memory or neuromorphic computing. Unlike transistors solely operating on electronic carriers, these memristors rely, in their switch characteristics, on defect kinetics of both oxygen vacancies and electronic carriers through a valence change mechanism. Here, Pt SrTiO3‐δ Pt structures are fabricated as a model material in terms of its mixed defects which show stable resistive switching. To date, experimental proof for memristance is characterized in hysteretic current–voltage profiles; however, the mixed anionic‐electronic defect kinetics that can describe the material characteristics in the dynamic resistive switching are still missing. It is shown that chronoamperometry and bias‐dependent resistive measurements are powerful methods to gain complimentary insights into material‐dependent diffusion characteristics of memristors. For example, capacitive, memristive and limiting currents towards the equilibrium state can successfully be separated. The memristor‐based Cottrell analysis is proposed to study diffusion kinetics for mixed conducting memristor materials. It is found that oxygen diffusion coefficients increase up to 3 × 10–15 m2s–1 for applied bias up to 3.8 V for SrTiO3‐δ memristors. These newly accessible diffusion characteristics allow for improving materials and implicate field strength requirements to optimize operation towards enhanced performance metrics for valence change memristors. The strategy for studying material‐dependent diffusion characteristics for mixed conducting memristors is extended by applying chronoamperometry and bias‐dependent resistive measurements. The memristor‐based Cottrell analysis and equation is proposed to derive oxygen diffusion coefficients of 3 × 10‐15 m2s‐1 for bias increase up to 3.8 V for SrTiO3‐δ memristors at room temperature.
      PubDate: 2014-09-25T06:34:05.601165-05:
      DOI: 10.1002/adfm.201402286
  • Ultrasensitive Plasmonic Response of Bimetallic Au/Pd Nanostructures to
    • Authors: Ruibin Jiang; Feng Qin, Qifeng Ruan, Jianfang Wang, Chongjun Jin
      Pages: n/a - n/a
      Abstract: Hydrogen detection is crucial for the safety of all hydrogen‐related applications. Compared to electrical hydrogen sensors, which usually suffer from possible electric sparks, optical hydrogen sensors offer advantages of remote and contact‐free readout and therefore the avoidance of spark generation. Herein, bimetallic Au/Pd nanostructure monolayers that exhibit ultrasensitive plasmonic response to hydrogen are reported. Bimetallic Au/Pd nanostructures with continuous and discontinuous Pd shells are prepared. The plasmonic response to hydrogen is monitored by measuring the extinction spectra of the ensemble Au/Pd nanostructures deposited on glass slides. Introduction of hydrogen induces red plasmon shifts, which become larger for the nanostructures with thicker Pd shells. For the nanostructures with continuous Pd shell, the plasmon shift can reach 56 nm at the hydrogen volume concentration below the explosion limit. The plasmon resonance wavelength displays an excellent linear dependence on the hydrogen volume concentration below 1%. The detection limit in the experiments reaches 0.2%. The nanostructures with discontinuous Pd shell show smaller plasmon shifts than those with continuous Pd shell. The extinction measurements on the ensemble nanostructures supported on transparent substrates and the unprecedentedly large plasmon shifts and sensitivity make the results very promising for the development of practical optical hydrogen sensors. The plasmonic response of bimetallic Au/Pd nanostructures to hydrogen is systematically investigated. Red plasmon shifts larger than 50 nm are observed when Au/Pd nanostructure monolayers are exposed to hydrogen at the volume concentration below the explosion limit. The facile measurements and ultrasensitive plasmonic response make the bimetallic nanostructures very promising for the development of practical optical hydrogen sensors.
      PubDate: 2014-09-24T06:15:11.925307-05:
      DOI: 10.1002/adfm.201402091
  • High‐Performance Hybrid Supercapacitor Enabled by a High‐Rate
           Si‐based Anode
    • Authors: Ran Yi; Shuru Chen, Jiangxuan Song, Mikhail L. Gordin, Ayyakkannu Manivannan, Donghai Wang
      Pages: n/a - n/a
      Abstract: A hybrid supercapacitor constructed of a Si‐based anode and a porous carbon cathode is demonstrated with both high power and energy densities. Boron‐doping is employed to improve the rate capability of the Si‐based anode (B‐Si/SiO2/C). At a high current density of 6.4 A/g, B‐Si/SiO2/C delivers a capacity of 685 mAh/g, 2.4 times that of the undoped Si/SiO2/C. Benefiting from the high rate performance along with low working voltage, high capacity, and good cycling stability of B‐Si/SiO2/C, the hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained, the highest values of any hybrid supercapacitor to date. Long cycling life (capacity retention of 70% after 6000 cycles) and low self‐discharge rate (voltage retention of 82% after 50 hours) are also achieved. This work opens an avenue for development of high‐performance hybrid supercapacitors using high‐performance Si‐based anodes. A hybrid supercapacitor is constructed of a high‐rate Si‐based anode and a porous carbon cathode. The hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained. Long cycling life and low self‐discharge rate are also achieved.
      PubDate: 2014-09-22T07:20:47.522239-05:
      DOI: 10.1002/adfm.201402398
  • General Formation of MS (M = Ni, Cu, Mn) Box‐in‐Box Hollow
           Structures with Enhanced Pseudocapacitive Properties
    • Authors: Xin‐Yao Yu; Le Yu, Laifa Shen, Xiaohui Song, Hongyu Chen, Xiong Wen (David) Lou
      Pages: n/a - n/a
      Abstract: Complex hollow structures of metal sulfides could be promising materials for energy storage devices such as supercapacitors and lithium‐ion batteries. However, it is still a great challenge to fabricate well‐defined metal sulfides hollow structures with multi‐shells, hierarchical architectures, and non‐spherical shape. In this work, a template‐engaged strategy is developed to synthesize hierarchical NiS box‐in‐box hollow structures with double‐shells. The NiS box‐in‐box hollow structures constructed by ultrathin nanosheets are evaluated as electrode materials for supercapacitors. As expected, the NiS box‐in‐box hollow structures exhibit excellent rate performance and impressive cycling stability due to their unique nano‐architecture. More importantly, the synthetic method can be easily extended to synthesize other transition metal sulfides box‐in‐box hollow structures. For example, we have also successfully synthesized similar CuS and MnS box‐in‐box hollow structures. The present work makes a significant contribution to the design and synthesis of transition metal sulfides hollow structures with non‐spherical shape and complex architecture, as well as their potential applications in electrochemical energy storage. Box in box: A template‐engaged method is successfully developed to synthesize hierarchical metal sulfide (NiS, CuS, MnS) box‐in‐box hollow structures with double‐shells. As an example, it is demonstrated that the NiS box‐in‐box hollow structure exhibits excellent pseudocapacitive performance with remarkable rate performance and cycling stability.
      PubDate: 2014-09-22T07:17:13.039836-05:
      DOI: 10.1002/adfm.201402560
  • Charge Carrier Localization and Transport in Organic Semiconductors:
           Insights from Atomistic Multiscale Simulations
    • Authors: Marko Mladenović; Nenad Vukmirović
      Pages: n/a - n/a
      Abstract: Organic electronic semiconducting materials exhibit complex atomic structures with a lack of periodicity that lead to charge carrier localization which, in turn, strongly affects the electronic transport properties of these materials. To understand charge carrier localization and electronic transport in organic semiconductors, simulations that take into account the details of the atomic structure of the material are of utmost importance. In this article, computational methods that can be used to simulate the electronic properties of organic semiconductors are reviewed and an overview of the results that have been obtained from such simulations is given. Using these methods the effects of static disorder, thermal disorder and interfaces between domains are investigated and the microscopic origin of these effects is identified. It is shown that in strongly disordered conjugated polymer materials the main origin of the localization of charge carrier wave functions is the disordered long‐range electrostatic potential. In ordered polymers, thermal disorder of main chains leads to wave function localization. In small molecule based organic semiconductors, grain boundaries introduce localized trap states at the points where electronic coupling is the strongest. It is also demonstrated that detailed atomistic simulations are necessary for quantitative and sometimes even qualitative description of charge mobility in organic materials. Organic semiconductor materials exhibit different types of disorder which lead to localization of charge carrier wave functions. Atomic multiscale simulations can be used to generate the models of atomic structure and to calculate the wave function localization lengths, electronic density of states and sometimes even the conductivity of the material.
      PubDate: 2014-09-22T03:24:42.613553-05:
      DOI: 10.1002/adfm.201402435
  • All Solution‐Processed Chalcogenide Solar Cells – from Single
           Functional Layers Towards a 13.8% Efficient CIGS Device
    • Authors: Yaroslav E. Romanyuk; Harald Hagendorfer, Patrick Stücheli, Peter Fuchs, Alexander R. Uhl, Carolin M. Sutter‐Fella, Melanie Werner, Stefan Haass, Josua Stückelberger, Cédric Broussillou, Pierre‐Philippe Grand, Veronica Bermudez, Ayodhya N. Tiwari
      Pages: n/a - n/a
      Abstract: Solution processing of inorganic thin films has become an important thrust in material research community because it offers low‐cost and high‐throughput deposition of various functional coatings and devices. Especially inorganic thin film solar cells – macroelectronic devices that rely on consecutive deposition of layers on large‐area rigid and flexible substrates – could benefit from solution approaches in order to realize their low‐cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin film technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre‐fabricated nanoparticles. By combining three promising approaches, an air‐stable Cu(In,Ga)Se2 thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates. A Cu(In,Ga)Se2 thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from aqueous solutions of metal salts using industrially scalable processes.
      PubDate: 2014-09-19T06:14:09.809095-05:
      DOI: 10.1002/adfm.201402288
  • Highly Efficient and Robust Blue Phosphorescent Pt(II) Compounds with a
           Phenyl‐1,2,3‐triazolyl and a
           Pyridyl‐1,2,4‐triazolyl Chelate Core
    • Authors: Xiang Wang; Shao‐Long Gong, Datong Song, Zheng‐Hong Lu, Suning Wang
      Pages: n/a - n/a
      Abstract: A new class of brightly phosphorescent Pt(II) compounds that contain an N∧C‐chelate phenyl‐1,2,3‐triazolyl ligand (ptrz) and an N∧C‐chelate pyridyl‐1,2,4‐triazolyl ligand (pytrz) in the central core is achieved. The impact of various substituent groups on phosphorescence of this class of molecules is examined. Crystal structural analyses revealed that this class of compounds has a great tendency to form stacked dimers—one of which is persistent even in the gas phase—leading to excimer emission. The introduction of bulky substituents, such as diphenyl amino (NPh2) or trityl (CPh3), is found to greatly diminish the excimer emission. Using this approach, several highly efficient blue and green phosphorescent Pt(II) compounds with λem at ≈450–460 nm and Φp ≈ 0.70 to 1.00 are obtained. These molecules are highly robust with exceptionally high thermal stability. Bright bluish‐green electrophosphorescent devices with external quantum efficiencies as high as 16.7% are fabricated. Bright blue and green phosphorescent Pt(II) complexes with an N∧C chelate 1,2,3‐triazolyl ligand and an N∧N chelate 1,2,4‐trizolyl ligand, near unity quantum efficiencies and high thermal stability are achieved. Steric blocking and the rigidity enhancement around the Pt(II) core by large substituent groups at the para‐position are found to be critical in the bright phosphorescence of this new class of compounds.
      PubDate: 2014-09-18T06:34:16.709229-05:
      DOI: 10.1002/adfm.201402366
  • Dendrimer‐Encapsulated Ruthenium Oxide Nanoparticles as Catalysts in
           Lithium‐Oxygen Batteries
    • Authors: Priyanka Bhattacharya; Eduard N. Nasybulin, Mark H. Engelhard, Libor Kovarik, Mark E. Bowden, Xiaohong S. Li, Daniel J. Gaspar, Wu Xu, Ji‐Guang Zhang
      Pages: n/a - n/a
      Abstract: Dendrimer‐encapsulated ruthenium oxide nanoparticles (DEN‐RuO2) have been used as catalysts in lithium‐oxygen (Li‐O2) batteries for the first time. The results obtained from ultraviolet‐visible spectroscopy, electron microscopy and X‐ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN‐RuO2 significantly improves the cycling stability of Li‐O2 batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO2 nanoparticles, making their entire surface area available for catalysis. The potential of using DEN‐RuO2 as a standalone cathode material for Li‐O2 batteries is also explored. Dendrimer‐encapsulated ruthenium nano­particles are readily oxidized to RuO2 when exposed to ambient conditions. These nanoparticles are used as catalysts in Li‐O2 batteries, which exhibited improved cycling thus suggesting that porous dendrimer‐encapsulated nanoparticles can be used to achieve superior performance in energy storage systems.
      PubDate: 2014-09-17T07:27:25.718797-05:
      DOI: 10.1002/adfm.201402701
  • Rationally Designed Dynamic Protein Hydrogels with Reversibly Tunable
           Mechanical Properties
    • Authors: Na Kong; Qing Peng, Hongbin Li
      Pages: n/a - n/a
      Abstract: Protein hydrogels have attracted considerable interest due to their potential applications in biomedical engineering. Creating protein hydrogels with dynamic mechanical properties is challenging. Here, the engineering of a novel, rationally designed protein‐hydrogel is reported that translates molecular level protein folding‐unfolding conformational changes into macroscopic reversibly tunable mechanical properties based on a redox controlled protein folding‐unfolding switch. This novel protein folding switch is constructed from a designed mutually exclusive protein. Via oxidation and reduction of an engineered disulfide bond, the protein folding switch can switch its conformation between folded and unfolded states, leading to a drastic change of protein's effective chain length and mechanical compliance. This redox‐responsive protein can be readily photochemically crosslinked into solid hydrogels, in which molecular level conformational changes (folding‐unfolding) can result in significant macroscopic changes in hydrogel's physical and mechanical properties due to the change of the effective chain length between two crosslinking points in the protein hydrogel network. It is found that when reduced, the hydrogel swells and is mechanically compliant; when oxidized, it swells to a less extent and becomes resilient and stiffer, exhibiting an up to fivefold increase in its Young's modulus. The changes of the mechanical and physical properties of this hydrogel are fully reversible and can be cycled using redox potential. This novel protein hydrogel with dynamic mechanical and physical properties could find numerous applications in material sciences and tissue engineering. Translating molecular events into macroscopic tunable mechanical properties: Using a redox potential‐controlled protein switch as a building block, protein‐based dynamic hydrogels are engineered. Upon redox potential‐controlled protein folding‐unfolding, these novel protein hydrogels exhibit dynamically tunable mechanical properties and can switch between a compliant state and a stiff yet resilient state.
      PubDate: 2014-09-17T07:27:09.252036-05:
      DOI: 10.1002/adfm.201402205
  • Pd‐Cu Bimetallic Tripods: A Mechanistic Understanding of the
           Synthesis and Their Enhanced Electrocatalytic Activity for Formic Acid
    • Authors: Lei Zhang; Sang‐Il Choi, Jing Tao, Hsin‐Chieh Peng, Shuifen Xie, Yimei Zhu, Zhaoxiong Xie, Younan Xia
      Pages: n/a - n/a
      Abstract: This article reports a facile synthesis of Pd‐Cu bimetallic tripods with a purity over 90%. Two requirements must be met in order to form tripods: i) formation of triangular, plate‐like seeds during the nucleation step and ii) preferential deposition of atoms onto the three corners of a seed during the growth step. In this synthesis, these requirements are fulfilled by adding CuCl2 and KBr into an aqueous synthesis. Specifically, it is demonstrated that the Cu atoms resulting from underpotential deposition could greatly reduce the energy barrier involved in the formation of triangular seeds with planar defects because of the much lower stacking fault energy (41 mJ·m−2 for Cu vs 220 mJ·m−2 for Pd). The Br− ions could strongly bind to the three {100} side faces of a triangular seed, forcing the Pd atoms to grow from the three corners of a seed to generate a tripod. When compared with commercial Pd black, the Pd‐Cu tripods exhibited substantially enhanced catalytic activity toward the electro‐oxidation of formic acid. This work offers a general strategy for the synthesis of nanocrystals with a tripod structure for catalytic applications. Pd‐Cu bimetallic tripods are prepared by adding CuCl2 and KBr into an aqueous synthesis that involves the reduction of a salt precursor by ascorbic acid. When compared with commercial Pd black, the Pd‐Cu tripods exhibit substantially enhanced (almost eight folds per unit mass of Pd) catalytic activity toward the electro‐oxidation of formic acid.
      PubDate: 2014-09-16T12:25:08.109714-05:
      DOI: 10.1002/adfm.201402350
  • Organic Electronics: Control of Ambipolar and Unipolar Transport in
           Organic Transistors by Selective Inkjet‐Printed Chemical Doping for
           High Performance Complementary Circuits (Adv. Funct. Mater. 40/2014)
    • Authors: Dongyoon Khim; Kang‐Jun Baeg, Mario Caironi, Chuan Liu, Yong Xu, Dong‐Yu Kim, Yong‐Young Noh
      Pages: 6245 - 6245
      Abstract: Selective tuning the operation mode of organic transistors from ambipolar to unipolar by using molecular doping is reported by Y. Xu, D.‐Y. Kim, Y.‐Y. Noh, and colleagues on page 6252. The ink‐jet printed dopants do not degrade device properties but rather distinctively alter the ambipolar operation to be either n‐channel or p‐channel with greater performance and stability. Complementary high‐performance inverters incorporating only one organic semiconductor and two different dopants are succeeded.
      PubDate: 2014-10-22T07:11:05.53332-05:0
      DOI: 10.1002/adfm.201470261
  • Piezoelectrics: Layer‐by‐Layer Controlled Perovskite
           Nanocomposite Thin Films for Piezoelectric Nanogenerators (Adv. Funct.
           Mater. 40/2014)
    • Authors: Younghoon Kim; Keun Young Lee, Sun Kak Hwang, Cheolmin Park, Sang‐Woo Kim, Jinhan Cho
      Pages: 6246 - 6246
      Abstract: Perovskite nanoparticle‐based nanocomposite thin films composed of oleic acid‐stabilized BaTiO3 nanoparticles and poly(acrylic acid) are prepared by S.‐W. Kim, J. Cho, and team on page 6262 using ligand exchange layer‐by‐layer assembly in organic media. The resultant nanocomposite films with high dielectric constant and low leakage current exhibit ferroelectric and piezoelectric properties that could be exactly controlled by the bilayer number, the type of inserted polymer, and the nanoparticle size.
      PubDate: 2014-10-22T07:10:58.283682-05:
      DOI: 10.1002/adfm.201470262
  • Contents: (Adv. Funct. Mater. 40/2014)
    • Pages: 6247 - 6251
      PubDate: 2014-10-22T07:10:58.124374-05:
      DOI: 10.1002/adfm.201470263
  • Control of Ambipolar and Unipolar Transport in Organic Transistors by
           Selective Inkjet‐Printed Chemical Doping for High Performance
           Complementary Circuits
    • Authors: Dongyoon Khim; Kang‐Jun Baeg, Mario Caironi, Chuan Liu, Yong Xu, Dong‐Yu Kim, Yong‐Young Noh
      Pages: 6252 - 6261
      Abstract: The selective tuning of the operational mode from ambipolar to unipolar transport in organic field‐effect transistors (OFETs) by printing molecular dopants is reported. The field‐effect mobility (μFET) and onset voltage (Von) of both for electrons and holes in initially ambipolar methanofullerene [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) OFETs are precisely modulated by incorporating a small amount of cesium fluoride (CsF) n‐type dopant or tetrafluoro‐tetracyanoquinodimethane (F4‐TCNQ) p‐type dopant for n‐channel or p‐channel OFETs either by blending or inkjet printing of the dopant on the pre‐deposited semiconductor. Excess carriers introduced by the chemical doping compensate traps by shifting the Fermi level (EF) toward respective transport energy levels and therefore increase the number of mobile charges electrostatically accumulated in channel at the same gate bias voltage. In particular, n‐doped OFETs with CsF show gate‐voltage independent Ohmic injection. Interestingly, n‐ or p‐doped OFETs show a lower sensitivity to gate‐bias stress and an improved ambient stability with respect to pristine devices. Finally, complementary inverters composed of n‐ and p‐type PCBM OFETs are demonstrated by selective doping of the pre‐deposited semiconductor via inkjet printing of the dopants. Local molecular doping via inkjet printing of dopants on a pre‐coated ambipolar semiconductors is demonstrated to unipolarize and optimize complementary transistors. The mobility and turn‐on voltages both for electrons and holes are precisely modulated by doping. Finally, high performance complementary ambipolar inverters are achieved by the selective inkjet printing of n‐ and p‐type dopant.
      PubDate: 2014-08-15T03:05:26.096071-05:
      DOI: 10.1002/adfm.201400850
  • Layer‐by‐Layer Controlled Perovskite Nanocomposite Thin Films
           for Piezoelectric Nanogenerators
    • Authors: Younghoon Kim; Keun Young Lee, Sun Kak Hwang, Cheolmin Park, Sang‐Woo Kim, Jinhan Cho
      Pages: 6262 - 6269
      Abstract: Perovskite nanoparticle‐based nanocomposite thin films strictly tailored using unconventional layer‐by‐layer (LbL) assembly in organic media for piezoelectric nanogenerators (NGs) are demonstrated. By employing sub‐20‐nm BaTiO3 nanoparticles stabilized by oleic acid ligands (i.e., OA‐BTONPs) and carboxylic acid (COOH)‐functionalized polymers, such as poly(acrylic acid) (PAA), the resulting OA‐BTONP/PAA nanocomposite multilayers are prepared by exploiting the high affinity between the COOH groups of PAA and the BTONPs. The ferroelectric and piezoelectric performance of the (PAA/OA‐BTONP)n thin films can be precisely controlled by altering the bilayer number, inserted polymer type, and OA‐BTONP size. It is found that the LbL assembly in nonpolar solvent media can effectively increase the quantity of adsorbed OA‐BTONPs, resulting in the dramatic enhancement of electric power output from the piezoelectric NGs. Furthermore, very low leakage currents are detected from the (PAA/OA‐BTONP)n thin films for obtaining highly reliable power‐generating performance of piezoelectric NGs. Perovskite nanoparticle‐based nanocomposites tailored using layer‐by‐layer (LbL) assembly in organic media are successfully synthesized. Ferroelectricity and piezoelectricity of multilayers composed of BaTiO3 nanoparticles and poly(acrylic acid) can be controlled by altering the bilayer number, inserted polymer type, and nanoparticle size. These LbL can increase the quantity of BaTiO3 nanoparticles, resulting in the enhancement of electric power output from the piezoelectric nanogenerators.
      PubDate: 2014-08-18T10:13:11.088765-05:
      DOI: 10.1002/adfm.201401599
  • Systematic Investigation of Side‐Chain Branching Position Effect on
           Electron Carrier Mobility in Conjugated Polymers
    • Authors: Jin‐Hu Dou; Yu‐Qing Zheng, Ting Lei, Shi‐Ding Zhang, Zhi Wang, Wen‐Bin Zhang, Jie‐Yu Wang, Jian Pei
      Pages: 6270 - 6278
      Abstract: Recently, polymer field‐effect transistors have gone through rapid development. Nevertheless, charge transport mechanism and structure‐property relationship are less understood. Here we use strong electron‐deficient benzodifurandione‐based poly(p‐phenylene vinylene) (BDPPV) as polymer backbone and develop six BDPPV‐based polymers (BDPPV‐C1 to C6) with various side‐chain branching positions to systematically study the side‐chain effect on device performance. All the polymers exhibited ambient‐stable n‐type transporting behaviors with the highest electron mobility of up to 1.40 cm2 V−1 s−1. The film morphologies and microstructures of all the six polymers were systematically investigated. Our results demonstrate that the interchain π–π stacking distance decreases as moving the branching position away from polymer backbones, and an unprecedentedly close π–π stacking distance down to 3.38 Å is obtained for BDPPV‐C4 to C6. Nonetheless, closer π–π stacking distance does not always correlate with higher electron mobility. Polymer crystallinity, thin film disorder, and polymer packing conformation, which all influenced by side‐chain branching position, are proved to show significant influence on device performance. Our study not only reveals that π–π stacking distance is not the decisive factor on carrier mobility in conjugated polymers but also demonstrates that side‐chain branching position engineering is a powerful strategy to modulate and balance these factors in conjugated polymers. Six BDPPV‐based polymers with various side‐chain branching positions are synthesized and characterized in details. All the polymers exhibit ambient‐stable n‐type transporting behavior with the highest electron mobility up to 1.40 cm2 V−1 s−1. By means of multiple characterization methods, film morphology, and microstructure of all the six polymers are systematically investigated.
      PubDate: 2014-08-19T12:26:43.585566-05:
      DOI: 10.1002/adfm.201401822
  • Lanthanides: Unraveling the Influence of Lanthanide Ions on Intra‐
           and Inter‐Molecular Electronic Processes in Fe10Ln10
           Nano‐Toruses (Adv. Funct. Mater. 40/2014)
    • Authors: Amer Baniodeh; Yu Liang, Christopher E. Anson, Nicola Magnani, Annie K. Powell, Andreas‐Neil Unterreiner, Simon Seyfferle, Michael Slota, Martin Dressel, Lapo Bogani, Karin Goß
      Pages: 6279 - 6279
      Abstract: On page 6280, A. K. Powell, A.‐N. Unterreiner, K. Goß, and co‐workers report an investigation of both intra‐ and intermolecular electron transfer processes in a family of nanotoroidal Fe(III)10Ln(III)10 cyclic coordination clusters. Photo‐induced intramolecular electron transport proceeds via exciton formation on the oxygen bridges. Intermolecular tranport is rationalized using a hopping model. In both cases, the Kramers parity of the lanthanide ion is important.
      PubDate: 2014-10-22T07:11:04.568133-05:
      DOI: 10.1002/adfm.201470264
  • Unraveling the Influence of Lanthanide Ions on Intra‐ and
    • Authors: Amer Baniodeh; Yu Liang, Christopher E. Anson, Nicola Magnani, Annie K. Powell, Andreas‐Neil Unterreiner, Simon Seyfferle, Michael Slota, Martin Dressel, Lapo Bogani, Karin Goß
      Pages: 6280 - 6290
      Abstract: We investigated the electronic properties of the molecular magnetic nanotoruses [FeIII 10LnIII 10(Me‐tea)10(Me‐teaH)10(NO3)10], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three‐step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo‐excitation. Using high‐resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface‐limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far‐IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility. Inter‐ and intra‐molecular electron‐transport processes are studied for a family of lanthanide‐based molecular toruses using ultrafast‐optical and electron‐transport techniques. A relationship between trap efficiency and gaps is found; charge‐hopping and surface‐limited transport are dominant. The comparison between intra‐ and inter‐molecular processes highlights the importance of excited electronic states, showing the influence of Kramers' parity on mobility.
      PubDate: 2014-08-20T11:25:31.591984-05:
      DOI: 10.1002/adfm.201400336
  • An Inkjet‐Printed Field‐Effect Transistor for Label‐Free
    • Authors: Mariana Medina‐Sánchez; Carme Martínez‐Domingo, Eloi Ramon, Arben Merkoçi
      Pages: 6291 - 6302
      Abstract: A flexible, biological field‐effect transistor (BioFET) for use in biosensing is reported. The BioFET is based on an organic thin‐film transistor (OTFT) fabricated mainly by inkjet printing and subsequently functionalized with antibodies for protein recognition. The BioFET is assessed for label‐free detection of a model protein, human immunoglobulin G (HIgG). It is characterized electrically to evaluate the contribution of each step in the functionalization of the OTFT and to detect the presence of the target protein. The fabrication, structure, materials optimization, electrical characteristics, and functionality of the starting OTFT and final BioFET are also discussed. Different materials are evaluated for the top insulator layer, with the aim of protecting the lower layers from the electrolyte and preserving the BioFET electrical performance. A flexible BioFET for label‐free biosensing is reported. It is based on an inkjet‐printed organic thin‐film transistor whose insulator is functionalized with specific antibodies for protein recognition. As proof‐of‐concept, the BioFET is evaluated for quantification of human immunoglobulin G (HIgG).
      PubDate: 2014-07-31T07:53:25.319361-05:
      DOI: 10.1002/adfm.201401180
  • Multifunctional Barium Titanate Coated Carbon Fibers
    • Authors: Christopher Bowland; Zhi Zhou, Henry A. Sodano
      Pages: 6303 - 6308
      Abstract: Multifunctional materials have received significant research interest due to the potential for performance enhancements over traditional materials through the integration of responsive properties. Composite materials are ideally suited for use as multifunctional materials due to their use of two or more phases and the ease at which their properties can be anisotropically tailored. Here, a methodology for the integration of ferroelectricity into a fiber reinforced polymer composite is presented by synthesizing a barium titanate nanowire film on the surface of carbon fibers using a novel two‐step hydrothermal process. A refined piezoelectric force microscopy method is used to quantify the piezoelectric properties of the core–shell fiber resulting in an average d33 of 31.6 ± 14.5 pm V−1 and an average d31 of −5.4 ± 3.2 pm V−1. The multifunctionality of this piezoelectric coated fiber is demonstrated through excitation of a cantilevered fiber with a 0.5 g sinusoidal base acceleration at the fiber's fundamental resonant frequency, producing a root‐mean‐square voltage of 16.4 mV. This result demonstrates the ferroelectric properties of the multifunctional structural fiber and its application for sensing and energy harvesting. Barium titanate is synthesized on carbon fiber through a two‐step hydrothermal reaction to create a multifunctional fiber. The mechanical strength of the carbon fiber is preserved while adding functionality from the ferroelectric properties of barium titanate. Ferroelectric property characterization and power harvesting tests are performed on these novel multifunctional fibers.
      PubDate: 2014-08-13T02:43:46.236022-05:
      DOI: 10.1002/adfm.201401417
  • Trap‐Assisted Recombination via Integer Charge Transfer States in
           Organic Bulk Heterojunction Photovoltaics
    • Authors: Qinye Bao; Oskar Sandberg, Daniel Dagnelund, Simon Sandén, Slawomir Braun, Harri Aarnio, Xianjie Liu, Weimin M. Chen, Ronald Österbacka, Mats Fahlman
      Pages: 6309 - 6316
      Abstract: Organic photovoltaics are under intense development and significant focus has been placed on tuning the donor ionization potential and acceptor electron affinity to optimize open circuit voltage. Here, it is shown that for a series of regioregular‐poly(3‐hexylthiophene):fullerene bulk heterojunction (BHJ) organic photovoltaic devices with pinned electrodes, integer charge transfer states present in the dark and created as a consequence of Fermi level equilibrium at BHJ have a profound effect on open circuit voltage. The integer charge transfer state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor–acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap‐assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed. The large variation in open circuit voltage for regioregular‐poly(3‐hexylthiophene):fullerene bulk heterojunction organic photovoltaic (BHJ) devices that yield a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor–acceptor interface is found to be a consequence of trap‐assisted recombination via integer charge transfer states. Based on the results, novel design rules for organic BHJ photovoltaics are proposed.
      PubDate: 2014-08-18T10:12:17.850687-05:
      DOI: 10.1002/adfm.201401513
  • Complementary Co‐assembling Peptides: From In Silico Studies to In
           Vivo Application
    • Authors: Andrea Raspa; Gloria A. A. Saracino, Raffaele Pugliese, Diego Silva, Daniela Cigognini, Angelo Vescovi, Fabrizio Gelain
      Pages: 6317 - 6328
      Abstract: Self‐assembling biomaterials offer an unprecedented chance of successfully facing most of the challenges of various biomedical fields, and, in particular, of tissue engineering. Nonetheless co‐assembling peptides (CAPs), taking advantage of the theory and empirical findings developed for self‐assembling peptides, could provide an even better control over cell cultures, drug delivery, and transplantation therapies. This study follows a “full” bottom‐up approach to develop new CAPs for neural tissue engineering applications. After molecular aggregation analysis via coarse‐grained simulations, LKLK12, LDLD12, and the functionalized KLPGWSG‐LDLD12 CAPs are synthesized and characterized assessing their co‐assembled secondary structures, the biomechanical properties of the obtained hydrogels, and the morphological features of the assembled nanofibers. The biological influence on viability and differentiation of human and murine neural stem cells are tested in vitro and neuroregenerative potentials in complete spinal cord transections are verified in vivo. Upon mixing of CAPs, the spontaneous formation of double layers of β‐sheets with a high degree of integration of the two CAP species is demonstrated. The formation of entangled nanofibrous structures give rise to shear‐thinning hydrogels. The in vitro results are comparable to a standard state‐of‐the‐art cell culture substrate and nervous regeneration in vivo is enhanced. New co‐assembling peptides for neural tissue engineering are developed with a “full” bottom‐up approach. LKLK12, LDLD12, and KLPGWSG‐LDLD12 are simulated in silico, synthesized and characterized to assess aggregate secondary structures, morphological features of the assembled nanofibers, and biomechanical properties of hydrogels. The biological influence on viability and differentiation of neural stem cells is tested and the neuroregenerative potential in complete spinal cord transections is verified.
      PubDate: 2014-08-19T12:22:44.272929-05:
      DOI: 10.1002/adfm.201400956
  • Plasmonic Nanocavity Organic Light‐Emitting Diode with Significantly
           Enhanced Light Extraction, Contrast, Viewing Angle, Brightness, and
    • Authors: Wei Ding; Yuxuan Wang, Hao Chen, Stephen Y. Chou
      Pages: 6329 - 6339
      Abstract: One central challenge in LEDs is to increase light extraction; but for display applications, other factors may have equal significance, such as ambient‐light absorption, contrast, viewing angle, image sharpness, brightness, and low‐glare. However, current LED structures enhance only some of the factors, while degrading the others. Here, a new organic LED (OLED) structure is proposed and demonstrated, with a novel plasmonic nanocavity, termed “plasmonic cavity with subwavelength hole‐array” (PlaCSH), and exhibits experimentally significant enhancements of all above factors with unprecedented performances. Compared to the conventional OLEDs (the same but without PlaCSH), PlaCSH‐OLEDs achieve experimentally: i) 1.57‐fold higher external‐quantum‐efficiency and light‐extraction‐efficiency (29%/32% without lens, 55%/60% with lens)—among the highest reported; ii) ambient‐light absorption not only 2.5‐fold higher but also broad‐band (400 nm) and nearly angle and polarization independent, leading to lower‐glare; iii) fivefold higher contrast (12 000 for 140 lux ambient‐light); iv) viewing angle tunable by the cavity length; v) 1.86‐fold higher normal‐view‐brightness; and vi) uniform color over all emission angles. The PlaCSH is an excellent optical antenna—excellent in both radiation and absorption of light. Furthermore, PlaCSH‐OLEDs, a simple structure to produce, are fabricated using nanoimprint over large‐area (≈1000 cm2), hence scalable to wallpaper size. A new organic LED structure is proposed and experimentally demonstrated using a novel plasmonic nanocavity, termed “plasmonic cavity with subwavelength hole‐array” (PlaCSH), to significantly enhance over conventional LEDs: i) 1.57‐fold higher external quantum efficiency and light extraction efficiency (55% and 60%); ii) 2.5‐fold higher ambient light absorption over 400 nm band; iii) a contrast of fivefold higher; and others.
      PubDate: 2014-08-19T12:25:26.457773-05:
      DOI: 10.1002/adfm.201400964
  • Printable, Transparent, and Flexible Touch Panels Working in Sunlight and
           Moist Environments
    • Authors: Tiina Vuorinen; Mari Zakrzewski, Satu Rajala, Donald Lupo, Jukka Vanhala, Karri Palovuori, Sampo Tuukkanen
      Pages: 6340 - 6347
      Abstract: The ongoing revolution of touch‐based user interfaces sets new requirements for touch panel technologies, including the need to operate in a wide range of environments. Such touch panels need to endure moisture and sunlight. Moreover, they often need to be curved or flexible. Thus, there is a need for new technologies suitable, for example, for home appliances used in the kitchen or the bathroom, automotive applications, and e‐paper. In this work, the development of transparent and flexible touch panels for moist environments is reported. A piezoelectric polymer, poly(vinylidene difluoride) (PVDF), is used as a functional substrate material. Transparent electrodes are fabricated on both sides of a PVDF film using a graphene‐based ink and spray coating. The excellent performance of the touch panels is demonstrated in moist and underwater conditions. Also, the transparent device shows very small pyroelectric response to radiative heating in comparison to a non‐transparent device. Solution processable electrode materials in combination with functional substrates allow the low‐cost and high‐throughput manufacturing of touch panels using printing technologies. Fabrication and functionality of transparent, flexible, and water‐proof touch panel is reported. Graphene‐based transparent electrodes are solution‐processed on a piezoelectric polymer, polyvinylidene difluoride (PVDF), which works as a functional substrate material. The use of solution‐processed electrodes allows the low‐cost and high throughput panel manufacturing. Also, the transparent touch panel shows very small pyroelectric response under exposure to light.
      PubDate: 2014-08-19T12:22:53.847623-05:
      DOI: 10.1002/adfm.201401140
  • Tunable Enhancement of Raman Scattering in Graphene‐Nanoparticle
    • Authors: Kannan Balasubramanian; Laura Zuccaro, Klaus Kern
      Pages: 6348 - 6358
      Abstract: The realization of graphene‐gold‐nanoparticle (G‐AuNP) hybrids is presented here through a versatile electrochemical approach, which allows the continuous tuning of the size and density of the particles obtainable on the graphene surface. Raman scattering from graphene, which is significantly enhanced in such hybrids, is systematically investigated as a function of the size and density of particles at the same location. In agreement with theory, it is shown that the Raman enhancement is tunable by varying predominantly the density of the nanoparticles. Furthermore, it is observed that the increase in Raman cross‐section and the strength of Raman enhancement varies as a function of the frequency of the vibrational mode, which may be correlated with the plasmonic fingerprint of the deposited AuNPs. In addition to this electromagnetic enhancement, support is found for a chemical contribution through the occurrence of charge transfer from the AuNPs onto graphene. Finally, G‐AuNP hybrids can be efficiently utilized as SERS substrates for the detection of specifically bound non‐resonant molecules, whose vibrational modes can be unambiguously identified. With the possibility to tune the degree of Raman enhancement, this is a platform to design and engineer SERS substrates to optimize the detection of trace levels of analyte molecules. A systematic investigation of surface‐enhanced Raman scattering (SERS) in graphene‐nanoparticle‐hybrids is obtained by a versatile electrochemical procedure. The evolution of Raman enhancement is followed by varying nanoparticle size and density at the same location. The magnitude of SERS enhancement is found to be dependent on the vibrational mode of graphene with both electromagnetic and chemical contributions.
      PubDate: 2014-08-19T06:20:38.125477-05:
      DOI: 10.1002/adfm.201401796
  • Creation of Superhydrophobic Electrospun Nonwovens Fabricated from
           Naturally Occurring Poly(Amino Acid) Derivatives
    • Authors: Hiroaki Yoshida; Doris Klee, Martin Möller, Mitsuru Akashi
      Pages: 6359 - 6364
      Abstract: Creation of superhydrophobic materials bio‐inspired by nature fascinates many scientists. One of the most intriguing challenges in this field is the fabrication of these materials using biopolymers from the viewpoint of green chemistry and environmental chemistry. Here, superhydrophobic and biodegradable nonwovens are constructed by electrospinning from a naturally occurring poly(amino acid), poly(γ‐glutamic acid) (γ‐PGA), modified with a hydrophobic α‐amino acid, l‐phenylalanine. The contact angle of a water droplet on the materials is 154°, and the droplet remains stuck to the material surface even if it is inverted, clearly indicating a petal‐type superhydrophobic property. Biodegradability and post‐functionalization of the nonwovens as well as cell adhesion on the superhydrophobic materials are also evaluated. As far as we know, this is the first report on biodegradable materials exhibiting a petal‐type superhydrophobicity. The material design and processing shown here can be applied to various bioresources and such functional materials will become a new class of functional materials satisfying some of the requirements in green science. Superhydrophobic, biodegradable nonwovens are fabricated by electrospinning from a naturally occurring poly(amino acid). The nonwovens exhibit a petal‐type superhydrophobicity and water droplet sticks to the surface even after it is turned over. The material design and processing is applicable to different biopolymers, and such functional materials can be useful for biomedical and environmental applications.
      PubDate: 2014-08-07T01:26:24.47764-05:0
      DOI: 10.1002/adfm.201401423
  • Pulsed Laser Deposition of Photoresponsive Two‐Dimensional GaSe
           Nanosheet Networks
    • Authors: Masoud Mahjouri‐Samani; Ryan Gresback, Mengkun Tian, Kai Wang, Alexander A. Puretzky, Christopher M. Rouleau, Gyula Eres, Ilia N. Ivanov, Kai Xiao, Michael A. McGuire, Gerd Duscher, David B. Geohegan
      Pages: 6365 - 6371
      Abstract: Synthesis of functional metal chalcogenide (GaSe) nanosheet networks by stoichiometric transfer of laser‐vaporized material from bulk GaSe targets is presented. Uniform coverage of interconnected, crystalline, and photoresponsive GaSe nanosheets in both in‐plane and out‐of‐plane orientations are achieved under different ablation conditions. The propagation of the laser‐vaporized material is characterized by in situ ICCD‐imaging. High (1 Torr) Ar background gas pressure is found to be crucial for the stoichiometric growth of GaSe nanosheet networks. Individual 1–3 layer GaSe triangular nanosheets of ≈200 nm domain size are formed within 30 laser pulses, coalescing to form nanosheet networks in as few as 100 laser pulses. The thickness of the deposited networks increases linearly with pulse number, adding layers in a two‐dimensional (2D) growth mode. GaSe nanosheet networks show p‐type semiconducting characteristics with mobilities reaching as high as 0.1 cm2V−1s−1. Spectrally‐resolved photoresponsivities and external quantum efficiencies range from 0.4 AW−1 and 100% at 700 nm, to 1.4 AW−1 and 600% at 240 nm, respectively. Pulsed laser deposition under these conditions appears to provide a versatile and rapid approach to stoichiometrically transfer and deposit functional networks of 2D nanosheets with digital thickness control and uniformity for a variety of applications. Novel synthesis techniques to rapidly explore the properties of new 2D layered materials, beyond graphene, are of significant current interest. Here, it is demonstrated that pulsed laser deposition (PLD) can be used to synthesize functional gallium selenide (GaSe) nanosheet networks by spatial confinement of the ablation plume to preserve the stoichiometric transfer of material while providing sufficient kinetic energy for surface diffusion.
      PubDate: 2014-08-11T14:58:30.491325-05:
      DOI: 10.1002/adfm.201401440
  • Hierarchical Composite Electrodes of Nickel Oxide Nanoflake 3D Graphene
           for High‐Performance Pseudocapacitors
    • Authors: Chundong Wang; Junling Xu, Muk‐Fung Yuen, Jie Zhang, Yangyang Li, Xianfeng Chen, Wenjun Zhang
      Pages: 6372 - 6380
      Abstract: NiO nanoflakes are created with a simple hydrothermal method on 3D (three‐dimensional) graphene scaffolds grown on Ni foams by microwave plasma enhanced chemical vapor deposition (MPCVD). Such as‐grown NiO‐3D graphene hierarchical composites are then applied as monolithic electrodes for a pseudo‐supercapacitor application without needing binders or metal‐based current collectors. Electrochemical measurements impart that the hierarchical NiO‐3D graphene composite delivers a high specific capacitance of ≈1829 F g−1 at a current density of 3 A g−1 (the theoretical capacitance of NiO is 2584 F g−1). Furthermore, a full‐cell is realized with an energy density of 138 Wh kg−1 at a power density of 5.25 kW kg−1, which is much superior to commercial ones as well as reported devices in asymmetric capacitors of NiO. More attractively, this asymmetric supercapacitor exhibits capacitance retention of 85% after 5000 cycles relative to the initial value of the 1st cycle. Hierarchical nickel oxide nanoflake 3D graphene electrodes are developed by growing NiO nanoflakes atop 3D architecture of graphene on Ni foam. The optimum structure enables the 3‐electrode pseudocapacitors and 2‐electrode full cells to deliver outstanding electrochemical performance. In a full cell configuration, the achieved power density is much higher than that of commercially available asymmetric capacitors.
      PubDate: 2014-08-14T14:17:01.21004-05:0
      DOI: 10.1002/adfm.201401216
  • Regulating Water Adhesion on Superhydrophobic TiO2 Nanotube Arrays
    • Authors: Ziying Hu; Xuming Zhang, Zhaoyue Liu, Kaifu Huo, Paul K Chu, Jin Zhai, Lei Jiang
      Pages: 6381 - 6388
      Abstract: Bioinspired surfaces with special wettability have attracted a significant attention in recent years because of their potential applications for no loss liquid transfer, anti‐icing, and self‐cleaning. Herein, the realization of two extreme superhydrophobic states on 1H, 1H, 2H, 2H–perfluorooctyltriethoxysilane‐modified TiO2 nanotube arrays (NTAs) is described by changing the structural characteristics of nanotubes while keeping the surface chemical composition constant. The water adhesive force is regulated in a wide range from ≈4.4 to ≈89.6 μN by the nanotubular diameter, length, density, and surface roughness. The cooperation effect between the negative pressures induced by the volume change of sealed air‐pockets and the van der Waals' attraction at solid–liquid interface contributes to the water adhesion. The superhydrophobic TiO2 NTAs with a high adhesive force is used as a “mechanical hand” to transfer water microdroplets without any loss, and the one with extremely low adhesive force is utilized as a self‐cleaning and anti‐icing surface. Two extreme superhydrophobic states with adhesive forces of ≈4.4 and ≈89.6 μN are realized on chemically modified TiO2 nanotubular arrays. The water droplet rolls off the low adhesive surface quickly, whereas it is pinned on the high adhesive surface at a tilted angle of 180°. The regulated water adhesion shows application for no‐loss liquid transfer, anti‐icing, and self‐cleaning.
      PubDate: 2014-08-19T06:20:28.326408-05:
      DOI: 10.1002/adfm.201401462
  • Highly Uniform Trilayer Molybdenum Disulfide for Wafer‐Scale Device
    • Authors: Alexey Tarasov; Philip M. Campbell, Meng‐Yen Tsai, Zohreh R. Hesabi, Janine Feirer, Samuel Graham, W. Jud Ready, Eric M. Vogel
      Pages: 6389 - 6400
      Abstract: Molybdenum disulfide (MoS2) is a layered semiconducting material with a tunable bandgap that is promising for the next generation nanoelectronics as a substitute for graphene or silicon. Despite recent progress, the synthesis of high‐quality and highly uniform MoS2 on a large scale is still a challenge. In this work, a temperature‐dependent synthesis study of large‐area MoS2 by direct sulfurization of evaporated Mo thin films on SiO2 is presented. A variety of physical characterization techniques is employed to investigate the structural quality of the material. The film quality is shown to be similar to geological MoS2, if synthesized at sufficiently high temperatures (1050 °C). In addition, a highly uniform growth of trilayer MoS2 with an unprecedented uniformity of ±0.07 nm over a large area (> 10 cm2) is achieved. These films are used to fabricate field‐effect transistors following a straightforward wafer‐scale UV lithography process. The intrinsic field‐effect mobility is estimated to be about 6.5±2.2 cm2 V–1 s–1 and compared to previous studies. These results represent a significant step towards application of MoS2 in nanoelectronics and sensing. A temperature‐dependent synthesis study of large‐area MoS2 by direct sulfurization of evaporated Mo thin films is presented. The resulting film quality is similar to geological MoS2. An unprecedented uniformity of ±0.07 nm over a large area (>10 cm2) is achieved with trilayer MoS2. The estimated intrinsic field‐effect mobility is approximately 6.5 ± 2.2 cm2 V–1 s–1.
      PubDate: 2014-08-19T12:22:56.268781-05:
      DOI: 10.1002/adfm.201401389
  • Conjugated Polymers: Systematic Investigation of Side‐Chain
           Branching Position Effect on Electron Carrier Mobility in Conjugated
           Polymers (Adv. Funct. Mater. 40/2014)
    • Authors: Jin‐Hu Dou; Yu‐Qing Zheng, Ting Lei, Shi‐Ding Zhang, Zhi Wang, Wen‐Bin Zhang, Jie‐Yu Wang, Jian Pei
      Pages: 6404 - 6404
      Abstract: Polymer field‐effect transistors have gone through rapid development. Nevertheless, charge transport mechanism and structure–property relationship are not well understood. On page 6270, J.‐Y. Wang, J. Pei, and co‐workers use strong electron‐deficient benzodifurandione‐based poly(p‐phenylene vinylene) (BDPPV) as the polymer backbone and develop six BDPPV‐based polymers with various side‐chain branching positions to systematically study the side‐chain effect on device performance.
      PubDate: 2014-10-22T07:11:01.041365-05:
      DOI: 10.1002/adfm.201470266
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