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    - CHEMISTRY (552 journals)
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CHEMISTRY (552 journals)                  1 2 3 4 5 6 | Last

2D Materials     Hybrid Journal   (Followers: 4)
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: 25)
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: 286)
ACS Photonics     Full-text available via subscription   (Followers: 5)
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: 4)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 5)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 8)
Advanced Functional Materials     Hybrid Journal   (Followers: 35)
Advances in Chemical Engineering and Science     Open Access   (Followers: 22)
Advances in Chemical Science     Open Access   (Followers: 9)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 14)
Advances in Drug Research     Full-text available via subscription   (Followers: 16)
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: 15)
Advances in Nanoparticles     Open Access   (Followers: 12)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 9)
Advances in Polymer Science     Hybrid Journal   (Followers: 39)
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   (Followers: 1)
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: 29)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 175)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 11)
American Journal of Chemistry     Open Access   (Followers: 18)
American Journal of Plant Physiology     Open Access   (Followers: 10)
American Mineralogist     Full-text available via subscription   (Followers: 3)
Analyst     Full-text available via subscription   (Followers: 35)
Angewandte Chemie     Hybrid Journal   (Followers: 17)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 230)
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: 19)
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: 220)
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)
Bioinspired Materials     Open Access  
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: 14)
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: 13)
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: 54)
Catalysis for Sustainable Energy     Open Access   (Followers: 2)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 5)
Catalysis Science and Technology     Free   (Followers: 4)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 4)
Catalysts     Open Access   (Followers: 7)
Cellulose     Hybrid Journal   (Followers: 5)

        1 2 3 4 5 6 | Last

Journal Cover Advanced Functional Materials
   [37 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]
  • Transparent and Stretchable Interactive Human Machine Interface Based on
           Patterned Graphene Heterostructures
    • Authors: Sumin Lim; Donghee Son, Jaemin Kim, Young Bum Lee, Jun‐Kyul Song, Suji Choi, Dong Jun Lee, Ji Hoon Kim, Minbaek Lee, Taeghwan Hyeon, Dae‐Hyeong Kim
      Pages: n/a - n/a
      Abstract: An interactive human‐machine interface (iHMI) enables humans to control hardware and collect feedback information. In particular, wearable iHMI systems have attracted tremendous attention owing to their potential for use in personal mobile electronics and the Internet of Things. Although significant progress has been made in the development of iHMI systems, those based on rigid electronics have constraints in terms of wearability, comfortability, signal‐to‐noise ratio (SNR), and aesthetics. Herein the fabrication of a transparent and stretchable iHMI system composed of wearable mechanical sensors and stimulators is reported. The ultrathin and lightweight design of the system allows superior wearability and high SNR. The use of conductive/piezoelectric graphene heterostructures, which consist of poly(l‐lactic acid), single‐walled carbon nanotubes, and silver nanowires, results in high transparency, excellent performance, and low power consumption as well as mechanical deformability. The control of a robot arm for various motions and the feedback stimulation upon successful executions of commands are demonstrated using the wearable iHMI system. A transparent and stretchable interactive human machine interface (iHMI) based on patterned graphene (GP) heterostructures is developed. The conductive/piezoelectric GP heterostructures enable the iHMI to have high transparency, excellent performance, low power consumption, and superb mechanical deformability. The control of a robot arm for various motions and feedback stimulation upon successful executions of commands are demonstrated using the wearable iHMI system.
      PubDate: 2014-11-14T06:46:26.105916-05:
      DOI: 10.1002/adfm.201402987
  • Mesostructured Intermetallic Compounds of Platinum and
           Non‐Transition Metals for Enhanced Electrocatalysis of Oxygen
           Reduction Reaction
    • Authors: Xing‐You Lang; Gao‐Feng Han, Bei‐Bei Xiao, Lin Gu, Zhen‐Zhong Yang, Zi Wen, Yong‐Fu Zhu, Ming Zhao, Jian‐Chen Li, Qing Jiang
      Pages: n/a - n/a
      Abstract: Alloying techniques show genuine potential to develop more effective catalysts than Pt for oxygen reduction reaction (ORR), which is the key challenge in many important electrochemical energy conversion and storage devices, such as fuel cells and metal‐air batteries. Tremendous efforts have been made to improve ORR activity by designing bimetallic nanocatalysts, which have been limited to only alloys of platinum and transition metals (TMs). The Pt‐TM alloys suffer from critical durability in acid‐media fuel cells. Here a new class of mesostructured Pt–Al catalysts is reported, consisting of atomic‐layer‐thick Pt skin and Pt3Al or Pt5Al intermetallic compound skeletons for the enhanced ORR performance. As a result of strong Pt–Al bonds that inhibit the evolution of Pt skin and produce ligand and compressive strain effects, the Pt3Al and Pt5Al mesoporous catalysts are exceptionally durable and ≈6.3‐ and ≈5.0‐fold more active than the state‐of‐the‐art Pt/C catalyst at 0.90 V, respectively. The high performance makes them promising candidates as cathode nanocatalysts in next‐generation fuel cells. A mesostructured ordered intermetallic of PtAl is developed by a facilely and cost‐effectively alloying/dealloying approach for the high‐performance ORR. The extremely strong covalent bonds between Pt and Al not only give rise to excellent kinetic stability, but also result in remarkable catalytic activity duo to the downshift of d‐band center.
      PubDate: 2014-11-14T06:46:18.180543-05:
      DOI: 10.1002/adfm.201401868
  • Response to Comment on Sponge‐Templated Preparation of High Surface
           Area Graphene with Ultrahigh Capacitive Deionization Performance
    • Authors: Zhi‐Yu Yang; Lin‐Jian Jin, Guo‐Qian Lu, Qing‐Qing Xiao, Yu‐Xia Zhang, Lin Jing, Xiao‐Xue Zhang, Yi‐Ming Yan, Ke‐Ning Sun
      Pages: n/a - n/a
      PubDate: 2014-11-14T06:41:24.363228-05:
      DOI: 10.1002/adfm.201403534
  • Comment on Sponge‐Templated Preparation of High Surface Area
           Graphene with Ultrahigh Capacitive Deionization Performance
    • Authors: Slawomir Porada; P. M. Biesheuvel, Volker Presser
      Pages: n/a - n/a
      PubDate: 2014-11-14T06:41:23.080532-05:
      DOI: 10.1002/adfm.201401101
  • Masthead: (Adv. Funct. Mater. 43/2014)
    • Pages: n/a - n/a
      PubDate: 2014-11-13T07:51:59.909835-05:
      DOI: 10.1002/adfm.201470283
  • Graphite Oxide and Aromatic Amines: Size Matters
    • Authors: Konstantinos Spyrou; Matteo Calvaresi, Evmorfia K. Diamanti, Theodoros Tsoufis, Dimitrios Gournis, Petra Rudolf, Francesco Zerbetto
      Pages: n/a - n/a
      Abstract: Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. Experimental and theoretical approaches are combined to demonstrate the successful intercalation of common organic polycyclic aromatic compounds between the layers of graphite oxide, and to examine in detail the mechanism by which each molecule interacts with the graphene oxide surface. It is proved that the type of interaction for aniline and naphthalene amine with the graphene oxide layers differs according to the size of the aromatic molecules.
      PubDate: 2014-11-12T14:11:30.972886-05:
      DOI: 10.1002/adfm.201402622
  • Controlled Growth from ZnS Nanoparticles to ZnS–CdS Nanoparticle
           Hybrids with Enhanced Photoactivity
    • Authors: Xiaojie Xu; Linfeng Hu, Nan Gao, Shaoxiong Liu, Swelm Wageh, Ahmed A. Al‐Ghamdi, Ahmed Alshahrie, Xiaosheng Fang
      Pages: n/a - n/a
      Abstract: Chalcogenide nanostructures and nanocomposites have been the focus of semiconductor nanomaterial research due to their remarkable optoelectronic and photocatalytic properties and potential application in photodegrading enviromental pollutions. However, currently available synthesizing methods tend to be costly and inefficient. In this paper, we propose a facile two‐step solution‐phase method to synthesize well‐defined monodisperse ZnS–CdS nanocomposites. The morphology and size of ZnS nanoparticles can be easily controlled by adjusting the amount of the source of sulfur. After surface modification with tiny CdS nanoparticles through natural electrostatic attraction, uniform ZnS–CdS nanocomposites are obtained, which has been further confirmed by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The photocatalytic activities of various ZnS samples and ZnS–CdS nanocomposites have been investigated by degrading Rhodamine B under UV‐light. Compared with pure ZnS nanoparticles and ZnS powders, the as‐obtained ZnS–CdS nanocomposites exhibit excellent photocatalytic performances due to the effective charge separation and increased specific surface area by the attachment of CdS. Moreover, resulting from the effective passivation of surface electronic states, the photoluminescence intensity of the ZnS–CdS nanocomposites is also significantly improved relative to plain ZnS. Chalcogenide nanostructure has attracted world‐wide attention due to the great potential of applications in photocatalysis and optoelectronics. Well‐defined heterostructures, which often exhibit superior properties, are of extreme importance. In this paper, a facile method to synthesize monodisperse ZnS nanoparticles (NPs) and ZnS–CdS nanocomposites (NCs) is proposed. The ZnS–CdS heterostructure not only shows obvious advantage in photoactivities, but also offers exciting opportunities for the development of new dual‐semiconductor nanostructures.
      PubDate: 2014-11-11T14:08:47.286709-05:
      DOI: 10.1002/adfm.201403065
  • Nanofragmentation of Ferroelectric Domains During Polarization Fatigue
    • Authors: Hanzheng Guo; Xiaoming Liu, Jürgen Rödel, Xiaoli Tan
      Pages: n/a - n/a
      Abstract: The microscopic mechanism for polarization fatigue in ferroelectric oxides has remained an open issue for several decades in the condensed matter physics community. Even though numerous models are proposed, a consensus has yet to be reached. Since polarization reversal is realized through ferroelectric domains, their behavior during electric cycling is critical to elucidating the microstructural origin for the deteriorating performance. In this study, electric field in situ transmission electron microscopy is employed for the first time to reveal the domain dynamics at the nanoscale through more than 103 cycles of bipolar fields. A novel mechanism of domain fragmentation is directly visualized in polycrystalline [(Bi1/2Na1/2)0.95Ba0.05]0.98La0.02TiO3. Fragmented domains break the long‐range polar order and, together with domain wall pinning, contribute to the reduction of switchable polarization. Complimentary investigations into crystal structure and properties of this material corroborate our microscopic findings. A novel mechanism of polarization fatigue is visualized in situ in polycrystalline [(Bi1/2Na1/2)0.95Ba0.05]0.98La0.02TiO3 by using transimission electron microscopy. Complementary to domain wall pinning, nanoscale domain fragmentation is found to take place during bipolar electric cycling. The broken long range polar order in the nanofragments is primarily responsible for the fatigue behavior measured from bulk specimens.
      PubDate: 2014-11-11T14:08:24.696935-05:
      DOI: 10.1002/adfm.201402740
  • Charge Separation Dynamics and Opto‐Electronic Properties of a
           Diaminoterephthalate‐C60 Dyad
    • Authors: Stefano Pittalis; Alain Delgado, Jörg Robin, Lena Freimuth, Jens Christoffers, Christoph Lienau, Carlo Andrea Rozzi
      Pages: n/a - n/a
      Abstract: A novel dyad composed of a diaminoterephthalate scaffold, covalently linked to a fullerene derivative, is explored as a nanosized charge separation unit powered by solar energy. Its opto‐electronic properties are studied and the charge separation rate is determined. Simulations of the coupled electronic and nuclear dynamics in the Ehrenfest approximation are carried out on a sub 100 fs time scale after photoexcitation in order to gain insights about the mechanisms driving the charge separation. In particular, the role of vibronic coupling and of the detailed morphology are highlighted. Photoinduced charge separation occurs on a 100 fs time scale in a diaminoterephthalate‐C60 dyad. Quantum simulations are performed to study the excited state dynamics of a new dyad. The chemical flexibility and optical properties of the chromophore moiety make this system a particularly useful model to study the early steps in the photovoltaic energy conversion. The simulations clarify the influence of electron‐nuclei coupling and molecular conformation on the charge separation efficiency of the molecule.
      PubDate: 2014-11-10T09:44:16.257492-05:
      DOI: 10.1002/adfm.201402316
  • High‐Mobility ZnO Thin Film Transistors Based on
           Solution‐processed Hafnium Oxide Gate Dielectrics
    • Authors: Mazran Esro; George Vourlias, Christopher Somerton, William I. Milne, George Adamopoulos
      Pages: n/a - n/a
      Abstract: The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO2). Despite their attractive properties, these high‐k dielectrics are usually manufactured using costly vacuum‐based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution‐processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high‐quality hafnium oxide (HfO2) gate dielectrics and their implementation in thin film transistors employing spray‐coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X‐ray diffraction, UV–Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field‐effect measurements. Analyses reveal polycrystalline HfO2 layers of monoclinic structure that exhibit wide band gap (≈5.7 eV), low roughness (≈0.8 nm), high dielectric constant (k ≈ 18.8), and high breakdown voltage (≈2.7 MV/cm). Thin film transistors based on HfO2/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (≈6 V), high on/off current modulation ratio (∼107) and electron mobility in excess of 40 cm2 V−1 s−1. Solution‐processed metal oxide thin film transistors (TFTs) employing sequential spray coated antimony‐doped tin oxide (SnO2:Sb) gate electrodes, hafnium oxide (HfO2) gate dielectrics and zinc oxide (ZnO) semiconducting channels are demonstrated. The transistors show excellent characteristics in terms of high transparency, hysteresis‐free operation, low operation voltage, high electron mobility and On/Off current modulation ratio.
      PubDate: 2014-11-10T09:22:22.546066-05:
      DOI: 10.1002/adfm.201402684
  • Silicon‐Based Current‐Controlled Reconfigurable
           Magnetoresistance Logic Combined with Non‐Volatile Memory
    • Authors: Zhaochu Luo; Xiaozhong Zhang, Chengyue Xiong, Jiaojiao Chen
      Pages: n/a - n/a
      Abstract: Silicon‐based complementary metal‐oxide‐semiconductor (CMOS) transistors have achieved great success. However, the traditional development pathway is approaching its fundamental limits. Magnetoelectronics logic, especially magnetic‐field‐based logic, shows promise for surpassing the development limits of CMOS logic and arouses profound attentions. Existing proposals of magnetic‐field‐based logic are based on exotic semiconductors and difficult for further technological implementation. Here, a kind of diode‐assisted geometry‐enhanced low‐magnetic‐field magnetoresistance (MR) mechanism is proposed. It couples p‐n junction's nonlinear transport characteristic and Lorentz force by geometry, and shows extremely large low‐magnetic‐field MR (>120% at 0.15 T). Further, it is applied to experimentally demonstrate current‐controlled reconfigurable magnetoresistance logic on the silicon platform at room temperature. This logic device could perform all four basic Boolean logic including AND, OR, NAND and NOR in one device. Combined with non‐volatile magnetic memory, this logic architecture with unique magnetoelectric properties has the advantages of current‐controlled reconfiguration, zero refresh consumption, instant‐on performance and would bridge the processor‐memory gap. Our findings would pave the way in silicon‐based magnetoelectronics and offer a route to make a new kind of microprocessor with potential of high performance. Magnetoelectronics logic shows promise for surpassing the development limits of CMOS logic and arouses profound attentions. Here, silicon‐based current‐controlled reconfigurable magnetoresistance logic is experimentally demonstrated. This logic device performs four basic Boolean logic (AND, OR, NAND, and NOR) in one device. It has the advantages of reconfiguration, ultralow consumption, instant‐on performance and would bridge the processor‐memory gap.
      PubDate: 2014-11-10T09:21:44.433721-05:
      DOI: 10.1002/adfm.201402955
  • Integration of 2D and 3D Thin Film Glassy Carbon Electrode Arrays for
           Electrochemical Dopamine Sensing in Flexible Neuroelectronic Implants
    • Authors: Jules J. VanDersarl; André Mercanzini, Philippe Renaud
      Pages: n/a - n/a
      Abstract: Here we present the development and characterization of a flexible implantable neural probe with glassy carbon electrode arrays. The use of carbon electrodes allows for these devices to be used as chemical sensors, in addition to their typical use as electrical sensors and stimulators. The devices are fabricated out of polyimide, platinum, titanium, and carbon with standard microfabrication techniques on carrier wafers. The devices are released from the substrate through either chemical or electrochemical dissolution of the underlying substrate material. The glassy carbon electrode arrays are produced through the pyrolysis of SU‐8 pillars at 900 °C as the first process step, as this temperature is incompatible with the other device materials. The process demonstrated here is generally applicable, allowing for the integration of various high temperature materials into flexible devices. Incorporating glassy carbon electrodes into flexible neural probes allows for implants to be used as chemical sensors as well as electrical sensors and stimulators. The devices are microfabricated on carrier wafers out of polyimide, platinum, titanium, and glassy carbon. The process demonstrated here is generally applicable for the integration of various high temperature materials into flexible devices.
      PubDate: 2014-11-06T06:13:25.222504-05:
      DOI: 10.1002/adfm.201402934
  • Controlling the Self‐Assembly of Periodic Defect Patterns in Smectic
           Liquid Crystal Films with Electric Fields
    • Authors: Iryna Gryn; Emmanuelle Lacaze, Roberto Bartolino, Bruno Zappone
      Pages: n/a - n/a
      Abstract: Large‐area periodic defect patterns are produced in smectic A liquid crystals confined between rigid plate electrodes that impose conflicting parallel and normal anchoring conditions, inducing the formation of topological defects. Highly oriented stripe patterns are created in samples thinner than 2 μm due to self‐assembly of linear defect domains with period smaller than 4 μm, whereas hexagonal lattices of focal conic domains appear for thicker samples. The pattern type (1d/2d) and period can be controlled at the nematic–smectic phase transition by applying an electric field, which confines the defect domains to a thin surface layer with thickness comparable to the nematic coherence length. The pattern morphology persists in the smectic phase even after varying the field or switching it off. Bistable, non‐equilibrium patterns are stabilized by topological constraints of the smectic phase that hinder the rearrangement of defects in response to field variations. Rapid formation of periodic defect patterns can be induced and controlled in smectic liquid crystal films by applying electric fields and varying the film thickness at the smectic‐nematic phase transition. The pattern type (1d/2d) and period persist in the smectic phase in a non‐equilibrium state, stabilized by large topological barriers, even after switching the field off.
      PubDate: 2014-11-06T06:13:21.301893-05:
      DOI: 10.1002/adfm.201402875
  • Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on
           Single Layer Graphene
    • Authors: Vasyl Skrypnychuk; Nicolas Boulanger, Victor Yu, Michael Hilke, Stefan C. B. Mannsfeld, Michael F. Toney, David R. Barbero
      Pages: n/a - n/a
      Abstract: The crystallization and electrical characterization of the semiconducting polymer poly(3‐hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X‐ray diffraction revealed that P3HT crystallizes with a mixture of face‐on and edge‐on lamellar orientations on graphene compared to mainly edge‐on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face‐on and edge‐on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with π–π stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film. The crystallinity and the electrical properties of thin films of the semiconducting polymer poly‐3‐hexylthiophene are investigated on a single layer of graphene. Enhanced vertical charge transport and a much higher charge carrier mobility are measured in thicker films due to the face‐on orientation induced by the graphene substrate and the formation of an interconnected path of crystallites.
      PubDate: 2014-11-06T06:13:17.562732-05:
      DOI: 10.1002/adfm.201403418
  • Kinetic Monte Carlo Study of the Sensitivity of OLED Efficiency and
           Lifetime to Materials Parameters
    • Authors: Reinder Coehoorn; Harm van Eersel, Peter Bobbert, René Janssen
      Pages: n/a - n/a
      Abstract: The performance of organic light‐emitting diodes (OLEDs) is determined by a complex interplay of the optoelectronic processes in the active layer stack. In order to enable simulation‐assisted layer stack development, a three‐dimensional kinetic Monte Carlo OLED simulation method which includes the charge transport and all excitonic processes is developed. In this paper, the results are presented of simulations including degradation processes in idealized but realizable phosphorescent OLEDs. Degradation is treated as a result of the conversion of emitter molecules to non‐emissive sites upon a triplet‐polaron quenching (TPQ) process. Under the assumptions made, TPQ provides the dominant contribution to the roll‐off. There is therefore a strong relationship between the roll‐off and the lifetime. This is quantified using a “uniform density model”, within which the charge carrier and exciton densities are assumed to be uniform across the emissive layer. The simulations give rise to design rules regarding the energy levels, and are used to study the sensitivity of the roll‐off and lifetime to various other materials parameters, including the mobility, the phosphorescent dye concentration, the triplet exciton emissive lifetime and binding energy, and the type of TPQ process. Kinetic Monte Carlo simulations are used to mechanistically analyze the influence of the organic semiconductor materials properties on the luminance decay due to degradation processes in phosphorescent organic light emitting diodes. A relationship is established between the lifetime and the efficiency roll‐off with increasing current density, assuming triplet‐polaron quenching processes as the root‐cause of the degradation, and design rules regarding the energy levels are developed.
      PubDate: 2014-11-04T02:54:04.945979-05:
      DOI: 10.1002/adfm.201402532
  • All‐Metallic Vertical Transistors Based on Stacked Dirac Materials
    • Authors: Yangyang Wang; Zeyuan Ni, Qihang Liu, Ruge Quhe, Jiaxin Zheng, Meng Ye, Dapeng Yu, Junjie Shi, Jinbo Yang, Ju Li, Jing Lu
      Pages: n/a - n/a
      Abstract: It is an ongoing pursuit to use metal as a channel material in a field effect transistor. All metallic transistor can be fabricated from pristine semimetallic Dirac materials (such as graphene, silicene, and germanene), but the on/off current ratio is very low. In a vertical heterostructure composed by two Dirac materials, the Dirac cones of the two materials survive the weak interlayer van der Waals interaction based on density functional theory method, and electron transport from the Dirac cone of one material to the one of the other material is therefore forbidden without assistance of phonon because of momentum mismatch. First‐principles quantum transport simulations of the all‐metallic vertical Dirac material heterostructure devices confirm the existence of a transport gap of over 0.4 eV, accompanied by a switching ratio of over 104. Such a striking behavior is robust against the relative rotation between the two Dirac materials and can be extended to twisted bilayer graphene. Therefore, all‐metallic junction can be a semiconductor and novel avenue is opened up for Dirac material vertical structures in high‐performance devices without opening their band gaps. Electron transport from one Dirac material to the other near E f is forbidden by momentum mismatch if the two Dirac cones of different layers are well separated. All‐metallic field effect transistor can be designed out of Dirac materials with a large transport gap and a high on/off current ratio of over 104 based on ab initio quantum transport simulations.
      PubDate: 2014-11-03T13:19:46.262995-05:
      DOI: 10.1002/adfm.201402904
  • Unraveling the Sinuous Grain Boundaries in Graphene
    • Authors: Zhuhua Zhang; Yang Yang, Fangbo Xu, Luqing Wang, Boris I. Yakobson
      Pages: n/a - n/a
      Abstract: Grain boundaries (GBs) in graphene are stable strings of pentagon‐heptagon dislocations. The GBs have been believed to favor an alignment of dislocations, but increasing number of experiments reveal diversely sinuous GB structures whose origins have long been elusive. Based on dislocation theory and first‐principles calculations, an extensive analysis of the graphene GBs is conducted and it is revealed that the sinuous GB structures, albeit being longer than the straight forms, can be energetically optimal once the global GB line cannot bisect the tilt angle. The unusually favorable sinuous GBs can actually decompose into a series of well‐defined bisector segments that effectively relieve the in‐plane stress of edge dislocations, and the established atomic structures closely resemble recent experimental images of typical GBs. In contrast to previously used models, the sinuous GBs show improved mechanical properties and are distinguished by a sizable electronic transport gap, which may open potential applications of polycrystalline graphene in functional devices. Grain boundaries are intrinsic to polycrystalline graphene and often exhibit diversely sinuous structures. Here, it is revealed that the sinuous grain boundaries are energetically preferred over the straight forms when the grain division is asymmetric, and their well‐defined configurations agree well with experimental observations. Importantly, such grain boundaries show improved strength as well as uniformly semiconducting electronic transport behavior.
      PubDate: 2014-10-31T11:31:16.244176-05:
      DOI: 10.1002/adfm.201403024
  • Using Polymer Electrolyte Gates to Set‐and‐Freeze Threshold
           Voltage and Local Potential in Nanowire‐based Devices and
    • Authors: Sofia Fahlvik Svensson; Adam M. Burke, Damon J. Carrad, Martin Leijnse, Heiner Linke, Adam P. Micolich
      Pages: n/a - n/a
      Abstract: The strongly temperature‐dependent ionic mobility in polymer electrolytes is used to “freeze in” specific ionic charge environments around a nanowire using a local wrap‐gate geometry. This makes it possible to set both the threshold voltage for a conventional doped substrate gate and the local disorder potential at temperatures below 220 K. These are characterized in detail by combining conductance and thermovoltage measurements with modeling. The results demonstrate that local polymer electrolyte gates are compatible with nanowire thermoelectrics, where they offer the advantage of a very low thermal conductivity, and hold great potential towards setting the optimal operating point for solid‐state cooling applications. A nanoscale patterned polymer electrolyte gate is used to “freeze in” ionic charge environments at low temperatures around an indium arsenide nanowire. The low thermal conductivity of the local wrap‐gate allows side‐by‐side investigations of the conductance and thermoelectric properties of the gated nanowire segment over a series of biases applied to the polymer electrolyte.
      PubDate: 2014-10-31T11:26:27.136249-05:
      DOI: 10.1002/adfm.201402921
  • Surface Directed Phase Separation of Semiconductor Ferroelectric Polymer
           Blends and their use in Non‐Volatile Memories
    • Authors: Albert van Breemen; Tomasz Zaba, Vsevolod Khikhlovskyi, Jasper Michels, Rene Janssen, Martijn Kemerink, Gerwin Gelinck
      Pages: n/a - n/a
      Abstract: The polymer phase separation of P(VDF‐TrFE):F8BT blends is studied in detail. Its morphology is key to the operation and performance of memory diodes. In this study, it is demonstrated that it is possible to direct the semiconducting domains of a phase‐separating mixture of P(VDF‐TrFE) and F8BT in a thin film into a highly ordered 2D lattice by means of surface directed phase separation. Numerical simulation of the surface‐controlled de‐mixing process provides insight in the ability of the substrate pattern to direct the phase separation, and hence the regularity of the domain pattern in the final dry blend layer. By optimizing the ratio of the blend components, the number of electrically active semiconductor domains is maximized. Pattern replication on a cm‐scale is achieved, and improved functional device performance is demonstrated in the form of a 10‐fold increase of the ON‐current and a sixfold increase in current modulation. This approach therefore provides a simple and scalable means to higher density integration, the ultimate target being a single semiconducting domain per memory cell. 3D morphology control in polymer resistive memories by surface directed phase separation of semiconductor ferroelectric blends is presented. Full 3D numerical simulation of the surface‐controlled de‐mixing process provides insight in the ability of the substrate pattern to direct the phase separation. Pattern replication on a cm‐scale is achieved leading to enhanced functional device performance.
      PubDate: 2014-10-29T12:44:41.382176-05:
      DOI: 10.1002/adfm.201401896
  • Comparison of Two D−A Type Polymers with Each Being Fluorinated
           on D and A Unit for High Performance Solar Cells
    • Authors: Jea Woong Jo; Seunghwan Bae, Feng Liu, Thomas P. Russell, Won Ho Jo
      Pages: n/a - n/a
      Abstract: For the purpose of investigating the effect of fluorination position on D−A type conjugated polymer on photophysical and photovoltaic properties, two types of fluorinated polymere are synthesized, HF with fluorination on electron‐donating unit and FH with fluorination on electron‐accepting unit. Compared to non‐fluorinated polymer, fluorinated polymers exhibit deeper HOMO energy levels without change of bandgap and stronger vibronic shoulder in UV−visible absorption, indicating that fluorination enhances intermolecular interaction. HF with fluorinated D unit exhibits well‐developed fibril network, low bimolecular recombination and high hole mobility, which lead a high PCE of 7.10% in conventional single‐junction solar cells, which is higher than the PCE (6.41%) of FH with fluorinated A unit. Therefore, this result demonstrates that fluorination on electron‐donating unit in D−A polymers could be a promising strategy for achieving high performance polymer solar cells. Two types of fluorinated D−A polymers with each being fluorinated on D and A unit are designed and synthesized. The D−A polymer with fluorinated D unit exhibits well‐developed fibril network, low bimolecular recombination and high hole mobility, leading to a high PCE of 7.10%, which is higher than the PCE (6.41%) of the polymer with fluorinated A unit.
      PubDate: 2014-10-27T16:23:01.125744-05:
      DOI: 10.1002/adfm.201402210
  • Graphene‐Directed Supramolecular Assembly of Multifunctional Polymer
           Hydrogel Membranes
    • Authors: Yufei Wang; Sheng Chen, Ling Qiu, Kun Wang, Huanting Wang, George P. Simon, Dan Li
      Pages: n/a - n/a
      Abstract: Polymer‐based nanoporous hydrogel membranes hold great potential for a range of applications including molecular filtration/separation, controlled drug release, and as sensors and actuators. However, to be of practical utility, polymer membranes generally need to be fabricated as ultrathin yet mechanically robust, have a large‐area yet be defect‐free and in some cases, their structure needs the capability to adapt to certain stimuli. These stringent and sometimes self‐conflicting requirements make it very challenging to manufacture such bulk nanostructures in a controllable, scalable and cost‐effective manner. Here, a versatile approach to the fabrication of multifunctional polymer‐based hydrogel membranes is demonstrated by a single step involving filtration of an aqueous dispersion containing chemically converted graphene (CCG) and a polymer. With CCG uniquely serving as a membrane‐ and pore‐forming directing agent and as a physical cross‐linker, a range of water soluble polymers can be readily processed into nanoporous hydrogel membranes through supramolecular interactions. With the interconnected CCG network as a robust and porous scaffold, the membrane nanostructure can easily be fine‐tuned to suit different applications simply by controlling the chemistry and concentration of the incorporated polymer. This work provides a simple and versatile platform for the design and fabrication of new adaptive supramolecular membranes for a variety of applications. A versatile approach to the fabrication of multifunctional polymer hydrogel membranes is demonstrated by exploiting the unique micro‐corrugated 2D configuration of chemically converted graphene, its self‐assembly behavior and rich supramolecular interactions. A range of water soluble polymers can be readily processed into such membranes with tunable nanostructures to suit a variety of potential applications.
      PubDate: 2014-10-27T05:39:18.300738-05:
      DOI: 10.1002/adfm.201402952
  • Highly Thermal Stable and Efficient Organic Photovoltaic Cells with
           Crosslinked Networks Appending Open‐Cage Fullerenes as Additives
    • Authors: Chih‐Ping Chen; Chien‐Yu Huang, Shih‐Ching Chuang
      Pages: n/a - n/a
      Abstract: Highly thermal stable organic bulk heterojunction (OBHJ) photovoltaic cells are demonstrated with crosslinkable open‐cage fullerenes (COF) as additives in the active layer. Partial incorporation of COF, ≈10–15 wt% with weight ratio of P3HT:PC61BM = 1:0.9, builds up three‐dimensional local borders upon heating treatment at 150 °C for 10 min. This process induces crosslinking chemical reaction through activating the styryl moiety in COF and reduces phase aggregation rates of fullerenes materials. Supported by statistics of devices degradation data analysis and optical microscopy study, the devices with COF show longer lifetime with keeping their efficiency (t = 144 h) under accelerated heating test at 150 °C, while PCE of normal devices without COF drop dramatically. These results demonstrate that the thermally crosslinkable COF is an excellent additive for highly thermal stable and durable OPVs applications. Highly thermal stable and durable organic bulk heterojunction photovoltaic cells are demonstrated with the incorporation of ≈10–15 wt% crosslinkable open‐cage fullerenes (COF) as additives in the active layer (weight ratio of P3HT:PC61BM = 1:0.9), through building up three‐dimensional local borders upon thermal treatment at 150 °C.
      PubDate: 2014-10-27T05:39:06.120973-05:
      DOI: 10.1002/adfm.201401735
  • Ultrasmall Sn Nanoparticles Embedded in Carbon as High‐Performance
           Anode for Sodium‐Ion Batteries
    • Authors: Yongchang Liu; Ning Zhang, Lifang Jiao, Zhanliang Tao, Jun Chen
      Pages: n/a - n/a
      Abstract: Designed as a high‐capacity, high‐rate, and long‐cycle life anode for sodium‐ion batteries, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8‐Sn@C) is prepared using an aerosol spray pyrolysis method. Instrumental analyses show that 8‐Sn@C nanocomposite with 46 wt% Sn and a BET surface area of 150.43 m2 g−1 delivers an initial reversible capacity of ≈493.6 mA h g−1 at the current density of 200 mA g−1, a high‐rate capacity of 349 mA h g−1 even at 4000 mA g−1, and a stable capacity of ≈415 mA h g−1 after 500 cycles at 1000 mA g−1. The remarkable electrochemical performance of 8‐Sn@C is owing to the synergetic effects between the well‐dispersed ultrasmall Sn nanoparticles and the conductive carbon network. This unique structure of very‐fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sn anode. Sn@C composite with ultrasmall Sn nano­particles (≈8 nm) homogeneously embedded in spherical carbon network is prepared by aerosol spray pyrolysis and further evaluated as anode material for rechargeable Na‐ion batteries. The nanocomposite exhibits excellent electrochemical performance with high reversible capacity, high‐rate capability, and long cycling stability.
      PubDate: 2014-10-27T05:39:02.530134-05:
      DOI: 10.1002/adfm.201402943
  • The Effect of Large Compositional Inhomogeneities on the Performance of
           Organic Solar Cells: A Numerical Study
    • Authors: Davide Bartesaghi; L. Jan Anton Koster
      Pages: n/a - n/a
      Abstract: The power conversion efficiency of solar cells based on a conjugated polymer (donor) and a fullerene derivative (acceptor) is very sensitive to the morphology of the active layer. One detrimental feature, which is often encountered in non‐optimal morphologies, is the occurrence of fullerene blobs in a finely mixed matrix containing both donor and acceptor material. Here, the effects of such fullerene blobs are studied in detail with a three‐dimensional drift‐diffusion model. It includes the effects of exciton diffusion and quenching; space‐charge; recombination, generation, drift and diffusion of charge carriers; and the injection/extraction of carriers at the contacts. The influence of blob size and shape, and matrix composition are quantified. The latter has the strongest effect on the overall efficiency, as most of the current is transported through the mixed phase. The total current flowing out of the solar cell can be split up in a part which comes from the interfacial region between the acceptor phase and the mixed phase, and a part that stems from the mixed phase itself. Depending on the bias voltage and the morphology, one or the other contribution is dominant. Finally, it is shown how both contributions can be computed with a simple one‐dimensional drift–diffusion simulator. A three‐dimensional model is presented to relate the efficiency of bulk heterojunction solar cells to the morphology of the active layer. With this, the effect of the occurrence of large acceptor domains dispersed in a mixed phase is quantified. The total current is split up in two contributions, both of which are calculated also with a one‐dimensional drift–diffusion model.
      PubDate: 2014-10-27T05:38:33.886352-05:
      DOI: 10.1002/adfm.201402260
  • 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
  • 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
  • Memristors: Nanoscale Resistive Switching in Amorphous Perovskite Oxide
           (a‐SrTiO3) Memristors (Adv. Funct. Mater. 43/2014)
    • Authors: Hussein Nili; Sumeet Walia, Sivacarendran Balendhran, Dmitri B. Strukov, Madhu Bhaskaran, Sharath Sriram
      Pages: 6733 - 6733
      Abstract: Controlled oxygen deficiencies are realized in amorphous SrTiO3 thin films. On page 6741 H. Nili, S. Sriram, and colleagues utilize these deficiencies to achieve CMOS‐compatible, high performance resistive switching in the room temperature processed thin films. The cover image depicts a cross‐bar arrangement with elements at different switching states. Image courtesy of Ella Marushchenko (Scientific Illustrations).
      PubDate: 2014-11-13T07:51:55.43033-05:0
      DOI: 10.1002/adfm.201470279
  • Biomimetics: A Versatile Approach towards Multifunctional Robust
           Microcapsules with Tunable, Restorable, and Solvent‐Proof
           Superhydrophobicity for Self‐Healing and Self‐Cleaning
           Coatings (Adv. Funct. Mater. 43/2014)
    • Authors: Gang Wu; Jinliang An, Xiu‐Zhi Tang, Yong Xiang, Jinglei Yang
      Pages: 6734 - 6734
      Abstract: Multifunctional superhydrophobic polymeric microcapsules with lotus‐leaf‐like hierarchical surface structure and moisture‐sensitive core are prepared by J. Yang and team on page 6751 by a facile and versatile strategy. The microcapsules exhibit superior shell tightness against solvents and heat, and possess widely tunable, repetitiously self‐restorable, and solvent‐proof superhydrophobicity. By incorporating these microcapsules in coating matrix, a biomimetic smart coating is developed, seamlessly combining self‐healing and self‐cleaning functionalities for anticorrosion and antifouling applications.
      PubDate: 2014-11-13T07:51:58.574785-05:
      DOI: 10.1002/adfm.201470280
  • Contents: (Adv. Funct. Mater. 43/2014)
    • Pages: 6735 - 6740
      PubDate: 2014-11-13T07:51:57.891552-05:
      DOI: 10.1002/adfm.201470281
  • Controlled Incorporation of Ni(OH)2 Nanoplates Into Flowerlike MoS2
           Nanosheets for Flexible All‐Solid‐State Supercapacitors
    • Authors: Chunxue Hao; Fusheng Wen, Jianyong Xiang, Limin Wang, Hang Hou, Zhibin Su, Wentao Hu, Zhongyuan Liu
      Pages: 6740 - 6740
      PubDate: 2014-11-13T07:51:52.414938-05:
      DOI: 10.1002/adfm.201403541
  • Nanoscale Resistive Switching in Amorphous Perovskite Oxide
           (a‐SrTiO3) Memristors
    • Authors: Hussein Nili; Sumeet Walia, Sivacarendran Balendhran, Dmitri B. Strukov, Madhu Bhaskaran, Sharath Sriram
      Pages: 6741 - 6750
      Abstract: Memristive devices are the precursors to high density nanoscale memories and the building blocks for neuromorphic computing. In this work, a unique room temperature synthesized perovskite oxide (amorphous SrTiO3: a‐STO) thin film platform with engineered oxygen deficiencies is shown to realize high performance and scalable metal‐oxide‐metal (MIM) memristive arrays demonstrating excellent uniformity of the key resistive switching parameters. a‐STO memristors exhibit nonvolatile bipolar resistive switching with significantly high (103–104) switching ratios, good endurance (>106I–V sweep cycles), and retention with less than 1% change in resistance over repeated 105 s long READ cycles. Nano‐contact studies utilizing in situ electrical nanoindentation technique reveal nanoionics driven switching processes that rely on isolatedly controllable nano‐switches uniformly distributed over the device area. Furthermore, in situ electrical nanoindentation studies on ultrathin a‐STO/metal stacks highlight the impact of mechanical stress on the modulation of non‐linear ionic transport mechanisms in perovskite oxides while confirming the ultimate scalability of these devices. These results highlight the promise of amorphous perovskite memristors for high performance CMOS/CMOL compatible memristive systems. High performance CMOS/CMOL compatible memristive arrays based on amorphous SrTiO3 thin films with engineered oxygen deficiencies are presented. Isolated nano‐switches are found to be responsible for the excellent switching performance of a‐STO memory cells. Nanoscale electromechanical investigations highlight the assistive role of mechanical stress in nanoionics based conduction and resistive switching in a‐STO devices and confirm their ultimate scalability.
      PubDate: 2014-08-26T01:09:51.57078-05:0
      DOI: 10.1002/adfm.201401278
  • A Versatile Approach towards Multifunctional Robust Microcapsules with
           Tunable, Restorable, and Solvent‐Proof Superhydrophobicity for
           Self‐Healing and Self‐Cleaning Coatings
    • Authors: Gang Wu; Jinliang An, Xiu‐Zhi Tang, Yong Xiang, Jinglei Yang
      Pages: 6751 - 6761
      Abstract: Numerous microencapsulation techniques have been developed to encase various chemicals, for which specific processing parameters are required to address the widely differing features of the encapsulated materials. Microencapsulation of reactive agents is a powerful technique that has been extensively applied to self‐healing materials. However, the poor solvent compatibility and insufficient thermal stability of microcapsules continue to pose challenges for long‐term storage, processing, and service in practical applications. Here, an easily modifiable and highly versatile method is reported for preparing various chemicals filled poly(urea‐formaldehyde) microcapsules that exhibit superior tightness against solvents and heat and that possess widely tunable, repetitiously self‐restorable, and solvent‐proof superhydrophobicity. In addition, the low‐cost fabrication of biomimetic multifunctional smart coatings is demonstrated for self‐healing anticorrosion and self‐cleaning antifouling applications by directly dispersing the superhydrophobic microcapsules into and onto a polymer matrix. The methodology presented in this study should inspire the development of multifunctional intelligent materials for applications in related fields. A variety of chemical‐filled multifunctional robust microcapsules exhibiting superior shell tightness against solvents and heat, and possessing widely tunable, multiple self‐restorable, and solvent‐proof superhydrophobicity are prepared by an easily modifiable and highly versatile method. The biomimetic multifunctional smart coatings for self‐healing anticorrosion and self‐cleaning antifouling applications are easily fabricated by directly dispersing the microcapsules into and onto a polymer resin.
      PubDate: 2014-08-22T09:41:11.449026-05:
      DOI: 10.1002/adfm.201401473
  • Ultra‐Thin Self‐Assembled Protein‐Polymer Membranes: A
           New Pore Forming Strategy
    • Authors: Patrick van Rijn; Murat Tutus, Christine Kathrein, Nathalie C. Mougin, Hyunji Park, Christopher Hein, Marco P. Schürings, Alexander Böker
      Pages: 6762 - 6770
      Abstract: Self‐assembled membranes offer a promising alternative for conventional membrane fabrication, especially in the field of ultrafiltration. Here, a new pore‐making strategy is introduced involving stimuli responsive protein‐polymer conjugates self‐assembled across a large surface area using drying‐mediated interfacial self‐assembly. The membrane is flexible and assembled on porous supports. The protein used is the cage protein ferritin and resides within the polymer matrix. Upon denaturation of ferritin, a pore is formed which intrinsically is determined by the size of the protein and how it resides in the matrix. Due to the self‐assembly at interfaces, the membrane constitutes of only one layer resulting in a membrane thickness of 7 nm on average in the dry state. The membrane is stable up to at least 50 mbar transmembrane pressure, operating at a flux of about 21 000–25 000 L m−2 h−1 bar−1 and displayed a preferred size selectivity of particles below 20 nm. This approach diversifies membrane technology generating a platform for “smart” self‐assembled membranes. Self‐assembled membranes offer a promising alternative for conventional membrane fabrication, especially in the field of ultrafiltration. Here a new pore‐making strategy is introduced involving stimuli responsive protein‐polymer conjugates self‐assembled across a large surface area using drying‐mediated interfacial self‐assembly. The membrane is flexible and assembled on porous supports. This approach diversifies membrane technology generating a platform for “smart” self‐assembled membranes.
      PubDate: 2014-09-01T09:35:06.33507-05:0
      DOI: 10.1002/adfm.201401825
  • In Situ Crosslinkable Gelatin Hydrogels for Vasculogenic Induction and
           Delivery of Mesenchymal Stem Cells
    • Authors: Sue Hyun Lee; Yunki Lee, Young Wook Chun, Spencer W. Crowder, Pampee P. Young, Ki Dong Park, Hak‐Joon Sung
      Pages: 6771 - 6781
      Abstract: Clinical trials utilizing mesenchymal stem cells (MSCs) for severe vascular diseases have highlighted the need to effectively engraft cells and promote pro‐angiogenic activity. A functional material accomplishing these two goals is an ideal solution as spatiotemporal and batch‐to‐batch variability in classical therapeutic delivery can be minimized, and tissue regeneration would begin rapidly at the implantation site. Gelatin may serve as a promising biomaterial due to its excellent biocompatibility, biodegradability, and non‐immuno/antigenicity. However, the dissolution of gelatin at body temperature and quick enzymatic degradation in vivo have limited its use thus far. To overcome these challenges, an injectable, in situ crosslinkable gelatin was developed by conjugating enzymatically crosslinkable hydroxyphenyl propionic acid (GHPA). When MSCs are cultured in 3D in vitro or injected in vivo in GHPA, spontaneous endothelial differentiation occurs, as evidenced by marked increases in endothlelial cell marker expressions (Flk1, Tie2, ANGPT1, vWF) in addition to forming an extensive perfusable vascular network after 2‐week subcutaneous implantation. Additionally, favorable host macrophage response is achieved with GHPA as shown by decreased iNOS and increased MRC1 expression. These results indicate GHPA as a promising soluble factor‐free cell delivery template which induces endothelial differentiation of MSCs with robust neovasculature formation and favorable host response. Injectable and in situ crosslinkable gelatin hydrogel is developed by conjugating hydroxyphenyl propionic acid to gelatin and used as a delivery platform for mesenchymal stem cells to reveal superior vasculo/angiogenic effects both in vitro and in vivo in a soluble factor‐free manner. Its superior bioactivity and ease of production, handling, and application makes it a promising biomaterial for treating vascular diseases.
      PubDate: 2014-08-26T12:55:35.336943-05:
      DOI: 10.1002/adfm.201401110
  • Nanotubes: An Experimental Insight into the Structural and Electronic
           Characteristics of Strontium‐Doped Titanium Dioxide Nanotube Arrays
           (Adv. Funct. Mater. 43/2014)
    • Authors: Hoda Amani Hamedani; Nageh K. Allam, Mostafa A. El‐Sayed, Mohammad A. Khaleel, Hamid Garmestani, Faisal M. Alamgir
      Pages: 6782 - 6782
      Abstract: A systematic study of the dopant incorporation mechanism and its distribution in the in situ doped TiO2 nanotube arrays is demonstrated by H. A. Hamedani and co‐workers on page 6783. The observed variations in the structural and electronic characteristics of the doped TiO2 nanotubes in correlation with heir enhanced visible light activity give an insight into the design of high efficiency photoelectrochemical material systems.
      PubDate: 2014-11-13T07:52:00.494383-05:
      DOI: 10.1002/adfm.201470282
  • An Experimental Insight into the Structural and Electronic Characteristics
           of Strontium‐Doped Titanium Dioxide Nanotube Arrays
    • Authors: Hoda Amani Hamedani; Nageh K. Allam, Mostafa A. El‐Sayed, Mohammad A. Khaleel, Hamid Garmestani, Faisal M. Alamgir
      Pages: 6783 - 6796
      Abstract: The possibility of in situ doping during electrochemical anodization of titania nanotube arrays is demonstrated and the mechanism and variations in structural and electronic characteristics of the nanotube arrays as after doping is systematically explored. In the presence of strontium as the dopant, bulk analysis shows strontium mainly incorporated into the lattice of TiO2. Surface analysis, however, reveals phase segregation of SrO in the TiO2 matrix at high Sr doping levels. The near edge X‐ray absorption fine structure (NEXAFS) spectroscopy analysis reveals that Sr2+ doping only alters the Ti and O ions interaction in the TiO2 lattice on the surface with no effect on their individual charge states. An in‐depth understanding of the dopant incorporation mechanism and distribution into TiO2 nanotube arrays is achieved using high resolution transmission electron microscopy (HRTEM) and the high angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) coupled with the electron energy loss spectroscopy (EELS) measurements on the surface and bulk of the nanotubes. Upon their use to photoelectrochemically split water, the Sr‐doped TiO2 nanotube film shows incident photon conversion efficiencies (IPCE) as high as 65%. The enhanced light activity in conjunction with the ordered one‐dimensional morphology makes the fabricated films promising candidates for water photoelectrolysis. Doping mechanism and the induced structural changes/defects in the bulk and surface of in situ synthesized strontium‐doped titania (Sr‐doped TiO2) nanotube arrays are systematically studied. Here, surface and bulk characterization of the doped nanotubes, which enables reliable identification of success or failure, uniformity, and the mechanism of divalent doping along the nanotube axisandin the radial direction, is reported.
      PubDate: 2014-08-28T13:28:40.395605-05:
      DOI: 10.1002/adfm.201401760
  • Tailoring the Plasmonic Modes of a Grating‐Nanocube Assembly to
           Achieve Broadband Absorption in the Visible Spectrum
    • Authors: Jeffrey Geldmeier; Tobias König, Mahmoud A. Mahmoud, Mostafa A. El‐Sayed, Vladimir V. Tsukruk
      Pages: 6797 - 6805
      Abstract: Engineered metal‐dielectric‐metal nanostructures with broadband absorbing properties in the visible spectral range are fabricated by combining the plasmonic resonances of different noble metal nanostructures. Silver nanocubes and gold nanogratings couple to each other using a dielectric polymer spacer with controllable thickness, resulting in a large multiplicative enhancement of absorption properties across a broad spectral range. Narrow, long nanogrooves in a gold film are first fabricated using electron beam lithography, after which a polymer spacer layer with a controllable thickness ranging from 4 to 12 nm is assembled by spin‐assisted layer‐by‐layer assembly. Finally, silver nanocubes with different surface coverages ranging from 12% to 22% are deposited using the Langmuir–Blodgett technique. The individual plasmon resonances of these different nanostructures are located at significantly different optical frequencies and are tuned in this study to allow a significant increase of light absorbance of the original gratings to an average value of 84% across the broad wavelength range of 450–850 nm. An efficient broadband absorber in the visible wavelength range is constructed from the individual plasmonic resonances of gold nanogratings and silver nanocubes separated from one another by a dielectric spacer. An average 84% absorption in the 450–850 nm wavelength range is ultimately achieved for this unique design.
      PubDate: 2014-08-26T12:53:54.018538-05:
      DOI: 10.1002/adfm.201401559
  • Anti‐Ferromagnet Controlled Tunneling Magnetoresistance
    • Authors: Yuyan Wang; Cheng Song, Guangyue Wang, Jinghui Miao, Fei Zeng, Feng Pan
      Pages: 6806 - 6810
      Abstract: The requirement for high‐density memory integration advances the development of newly structured spintronic devices, which have reduced stray fields and are insensitive to magnetic field perturbations. This could be visualized in magnetic tunnel junctions incorporating anti‐ferromagnetic instead of ferromagnetic electrodes. Here, room‐temperature anti‐ferromangnet (AFM)‐controlled tunneling anisotropic magnetoresistance in a novel perpendicular junction is reported, where the IrMn AFM stays immediately at both sides of AlOx tunnel barrier as the functional layers. Bi‐stable resistance states governed by the relative arrangement of uncompensated anti‐ferromagnetic IrMn moments are obtained here, rather than the traditional spin‐valve signal observed in ferromagnet‐based tunnel junctions. The experimental observation of room‐temperature tunneling magnetoresistance controlled directly by AFM is practically significant and may pave the way for new‐generation memories based on AFM spintronics. Anti‐ferromagnet controlled tunneling magnetoresistance is obtained at room‐temperature in a novel perpendicular IrMn/AlOx/IrMn junction, where the magnetoresistance is governed by the relative arrangement of the IrMn moments. In addition to the fundamental significance of the interactions between two anti‐ferromagnetic layers, it is promising to achieve high‐density anti‐ferromagnet spintronics that are far from ferromagnetic stray fields and magnetic field perturbations.
      PubDate: 2014-08-26T12:53:55.724571-05:
      DOI: 10.1002/adfm.201401659
  • Structure Tuning of Crown Ether Grafted Conjugated Polymers as the
           Electron Transport Layer in Bulk‐Heterojunction Polymer Solar Cells
           for High Performance
    • Authors: Yi‐Lun Li; Yu‐Shan Cheng, Po‐Nan Yeh, Sih‐Hao Liao, Show‐An Chen
      Pages: 6811 - 6817
      Abstract: A series of novel electron transport (ET) polymers composed of different conjugated main chains (fluorene, thiophene, and 2,7‐carbazole) and crown ether side chain (crown ether, aza‐crown ether and amine) is presented for bulk‐heterojunction polymer solar cells with poly(3‐hexylthiophene) (P3HT) or poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo [1,2‐b:4,5‐b′] dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]](PTB7) as the active polymer and aluminum metal as the cathode. Unexpectedly, it is found that the main chain of ET polymers has a greater effect on the interfacial dipole than the side chain, even when attaching a high polarity group. The electron‐rich bridge atom of the main chain may also contribute appreciably to the interfacial dipole. When used as the ET layer, all of these polymers can generate an optical interference effect for redistribution of the optical electric field as an optical spacer and, therefore, allow more light to be absorbed by the active layer, thus leading to an increase in short‐circuit current density. They can also block hole diffusion to the cathode and prevent electron–hole recombination during the ET process. Among the five ET polymers investigated, PCCn6 is the most effective one, providing a remarkable improvement in the power conversion efficiency (measured in air) of the device to 8.13% compared to 5.20% for PTB7:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). Alcohol‐soluble conjugated polymers are designed for use as the electron transport layer in polymer solar cells to improve the power conversion efficiency. The use of a suitable conjugated main chain increases the open‐circuit voltage via the interfacial dipole and enhances the short‐circuit current density of active the layer by rearranging the optical electric field within the device. Additionally, a deeper highest occupied molecular orbital level, compared to the light‐absorbing active polymer, serves to block holes and supress leakage current.
      PubDate: 2014-09-01T09:28:12.3232-05:00
      DOI: 10.1002/adfm.201401428
  • A Highly Sensitive Graphene‐Organic Hybrid Photodetector with a
           Piezoelectric Substrate
    • Authors: Wei‐Chun Tan; Wei‐Heng Shih, Yang Fang Chen
      Pages: 6818 - 6825
      Abstract: To create a sensitive photodetector, the transparent and conductive properties of graphene and the optical and photovoltaic properties of poly(3‐hexylthiophene) (P3HT) are combined as a hybrid composite. Based on the inherent nature of the band alignment between graphene and P3HT, the photogenerated holes are able to transfer to the graphene layer and improve the photoresponse to be much better than the traditional layer by layer organic system. Additionally, the graphene is deposited on a piezoelectric Pb(Zr0.2Ti0.8)O3 (PZT) substrate, and the photoresponse of such composite photodetectors is found to be ten times larger than on SiO2 base. It is demonstrated that the electric field of the polarization of piezoelectric substrate helps the spatial separation of photogenerated electrons and holes and promotes the hole doping of graphene to enhance the photoconduction. A detailed investigation of graphene layers, thickness of P3HT and time evolution shows that the composite of graphene and P3HT on PZT can be used as a sensitive photodetector and has potential as an effective solar cell. Moreover, with the replacement of P3HT by a thin layer of bulk heterojunction of polymer and fullerene, the photosensitivity can be further increased by more than one order of magnitude. The application of a piezoelectric substrate (PZT) to enhance (down polarized, D‐PZT) or decrease (up polarized, U‐PZT) the graphene‐organic semiconductor (P3HT) hybrid photodetector compared to that of a silica substrate is reported. The permanent polarization in PZT generates an electric field promoting or decreasing charge transfer behavior of the device.
      PubDate: 2014-09-08T10:31:00.094867-05:
      DOI: 10.1002/adfm.201401421
  • Hierarchical Carbon–Nitrogen Architectures with Both Mesopores and
           Macrochannels as Excellent Cathodes for Rechargeable Li–O2 Batteries
    • Authors: Zhang Zhang; Jie Bao, Chen He, Yanan Chen, Jinping Wei, Zhen Zhou
      Pages: 6826 - 6833
      Abstract: Lithium–oxygen batteries are attracting more and more interest; however, their poor rechargeability and low efficiency remain critical barriers to practical applications. Herein, hierarchical carbon–nitrogen architectures with both macrochannels and mesopores are prepared through an economical and environmentally benign sol–gel route, which show high electrocatalytic activity and stable cyclability over 160 cycles as cathodes for Li–O2 batteries. Such good performance owes to the coexistence of macrochannels and mesopores in C–N hierarchical architectures, which greatly facilitate the Li+ diffusion and electrolyte immersion, as well as provide an effective space for O2 diffusion and O2/Li2O2 conversion. Additionally, the mechanism of oxygen reduction reactions is discussed with the N‐rich carbon materials through first‐principles computations. The lithiated pyridinic N provides excellent O2 adsorption and activation sites, and thus catalyzes the electrode processes. Therefore, hierarchical carbon–nitrogen architectures with both macrochannels and mesopores are promising cathodes for Li–O2 batteries. Hierarchical carbon–nitrogen architectures are prepared for Li–O2 battery cathodes. The predominant cyclability originates from the coexistence of mesopores and macrochannels, which facilitates both diffusion of Li+ and O2 and accumulation of discharge products. Pyridinic N, which is dominant in this material, warrants the adsorption of O2 and activates it, thus catalyzing the electrochemical process according to first‐principles computations.
      PubDate: 2014-09-01T09:29:10.178651-05:
      DOI: 10.1002/adfm.201401581
  • Three‐Dimensional Inkjet‐Printed Interconnects using
           Functional Metallic Nanoparticle Inks
    • Authors: Jacob A. Sadie; Vivek Subramanian
      Pages: 6834 - 6842
      Abstract: Inkjet‐printed gold nanoparticle pillars are investigated as a high‐performance alternative to conventional flip‐chip interconnects for electronic packages, with significant advantages in terms of mechanical/chemical robustness and conductivity. The process parameters critical to pillar fabrication are described and highly uniform pillar arrays are demonstrated. More generally, this work underscores the impact of sintering on the electrical, mechanical, structural, and compositional properties of three‐dimensional nanoparticle‐based structures. Using heat treatments as low as 200 °C, electrical and mechanical performance that outcompetes conventional lead‐tin eutectic solder materials is achieved. With sintering conditions reaching 300 °C it is possible to achieve pillars with properties comparable to bulk gold. This work demonstrates the immense potential for both inkjet printing and metal nanoparticles to become a viable and cost‐saving alternative to both conventional electronic packaging processes and application‐specific integration schemes. Inkjet‐printed 3D nanoparticle pillars are investigated as a novel alternative to semiconductor packaging interconnects. The first detailed study of sintering in such large nanoparticle‐based structures reveals electrical, elastic, and shear properties that outperform conventional materials undergoing similar heat treatments. The results indicate much promise for nanoparticle‐based materials in advanced electronic packages and provide critical insights for further materials optimization.
      PubDate: 2014-09-11T12:55:34.500762-05:
      DOI: 10.1002/adfm.201401312
  • Layer‐by‐Layer Fabrication of Nanowire Sensitized Solar Cells:
           Geometry‐Independent Integration
    • Authors: Krishna P. Acharya; Zhiqiang Ji, Terry G. Holesinger, Jeffrey A. Crisp, Sergei A. Ivanov, Darrick J. Williams, Joanna L. Casson, Milan Sykora, Jennifer A. Hollingsworth
      Pages: 6843 - 6852
      Abstract: Thin film solar cells that are low in cost but still reasonably efficient comprise an important strategy for reaching price‐performance ratios competitive with fossil fuel electrical generation. Sensitized solar cells – most commonly dye but also semiconductor nanocrystal sensitized – are a thin film device option benefitting from lost cost material components and processing. Nanocrystal sensitized solar cells are predicted to outpace their dye‐based counterparts, but suffer from limited availability of approaches for integrating the nano‐sensitizers within a mesoporous oxide anode, which effectively limits the choice of sensitizer to those that are synthesized in situ or those that are easily incorporated into the oxide framework. The latter methods favor small, symmetric nanocrystals, while highly asymmetric semiconductors (e.g., nanowires, tetrapods, carbon nanotubes) have to date found limited utility in sensitized solar‐cell devices, despite their promise as efficient solar energy converters. Here, a new strategy for solar cell fabrication is demonstrated that is independent of sensitizer geometry. Nanocrystal‐sensitized solar cells are fabricated from either CdSe semiconductor quantum dots or nanowires with facile control over nanocrystal loading. Without substantial optimization and using low processing temperatures, efficiencies approaching 2% are demonstrated. Furthermore, the significance of a ‘geometry‐independent’ fabrication strategy is shown by revealing that nanowires afford important advantages compared to quantum dots as sensitizers. For equivalent nanocrystal masses and otherwise identical devices, nanowire devices yield higher power conversion efficiencies, resulting from both enhanced light harvesting efficiencies for all overlapping wavelengths and internal quantum efficiencies that are more than double those obtained for quantum dot devices. A new strategy for nanocrystal‐sensitized solar cell fabrication that is independent of the sensitizer geometry is demonstrated. Solar cells are fabricated from CdSe quantum dots or nanowires and show that nanowires afford consistently higher power‐conversion efficiencies for equivalent nanocrystal masses and otherwise identical devices. It is revealed that nanowires are characterized by both enhanced light harvesting and internal quantum efficiencies more than double their quantum dot counterparts.
      PubDate: 2014-08-28T12:37:12.778152-05:
      DOI: 10.1002/adfm.201401225
  • Patterning of Epitaxial Perovskites from Micro and Nano Molded Stencil
    • Authors: Maarten Nijland; Antony George, Sean Thomas, Evert P. Houwman, Jing Xia, Dave H. A. Blank, Guus Rijnders, Gertjan Koster, Johan E. ten Elshof
      Pages: 6853 - 6861
      Abstract: A process is developed that combines soft lithographic molding with pulsed laser deposition (PLD) to make heteroepitaxial patterns of functional perovskite oxide materials. Micro‐ and nanostructures of sacrificial ZnO are made by micro molding in capillaries (MiMiC) and nano transfer molding, respectively, and used to screen the single crystalline substrates during subsequent PLD. ZnO is used because of its compatibility with the high temperatures reached during PLD and because of the ease of its removal after use by benefiting from its amphoteric nature. Sub‐micrometer sized lines of La0.67Sr0.33MnO3 are made by the transfer molding approach, preserving the anisotropic features expected for a fully oriented thin film and taking account for the magnetostatic contribution from the line shapes. Different patterns of SrRuO3 are made with lateral dimensions of a few micrometers having individual features for which electrical isolation is illustrated. The bottom‐up soft lithographic methods can be compliantly utilized for making epitaxial structures of various shapes and sizes in the μm down to the nm range, and offer unique opportunities for fundamental studies as well as for realizing technological applications. Nano transfer molding and micro molding in capillaries are used to make stencil masks of ZnO on single crystalline SrTiO3 substrates. Isolated epitaxial structures of two functional perovskite oxides are formed after pulsed laser deposition and dissolution of ZnO. Bottom‐up fabricated patterns similar to those presented here were not shown before, illustrating the versatility of the soft lithographic approaches.
      PubDate: 2014-08-28T13:28:51.283772-05:
      DOI: 10.1002/adfm.201401170
  • Multimodal Magneto‐Plasmonic Nanoclusters for Biomedical
    • Authors: Chun‐Hsien Wu; Jason Cook, Stanislav Emelianov, Konstantin Sokolov
      Pages: 6862 - 6871
      Abstract: Multimodal nanostructures can help solve many problems in the biomedical field including sensitive molecular imaging, highly specific therapy, and early cancer detection. However, the synthesis of densely packed, multicomponent nanostructures with multimodal functionality represents a significant challenge. Here, a new type of hybrid magneto‐plasmonic nanoparticles is developed using an oil‐in‐water microemulsion method. The nanostructures are synthetized by self‐assembly of primary 6 nm iron oxide core‐gold shell particles resulting into densely packed spherical nanoclusters. The dense packing of primary particles does not change their superparamagnetic behavior; however, the close proximity of the constituent particles in the nanocluster leads to strong near‐infrared (NIR) plasmon resonances. The synthesis is optimized to eliminate nanocluster cytotoxicity. Immunotargeted nanoclusters are also developed using directional conjugation chemistry through the Fc antibody moiety, leaving the Fab antigen recognizing region available for targeting. Cancer cells labeled with immunotargeted nanoclusters produce a strong photoacoustic signal in the NIR that is optimum for tissue imaging. Furthermore, the labeled cells can be efficiently captured using an external magnetic field. The biocompatible magneto‐plasmonic nanoparticles can make a significant impact in development of point‐of‐care assays for detection of circulating tumor cells, as well as in cell therapy with magnetic cell guidance and imaging monitoring. A new generation of hybrid magneto‐plasmonic nanoparticles is developed by utilizing an oil‐in‐water microemulsion method. The nanoparticles combine a high density of magnetic and plasmonic functionalities together with biocompatibility and molecular targeting capability that provide a promising tool for sensitive and selective cancer detection and other biomedical applications.
      PubDate: 2014-09-01T09:29:36.172488-05:
      DOI: 10.1002/adfm.201401806
  • Functional Selenium Nanoparticles Enhanced Stem Cell Osteoblastic
           Differentiation through BMP Signaling Pathways
    • Authors: Chuping Zheng; Jinsheng Wang, Yanan Liu, Qianqian Yu, Ying Liu, Ning Deng, Jie Liu
      Pages: 6872 - 6883
      Abstract: Stem cells have generated a great deal of excitement in tissue engineering and regenerative medicine, and it is important to understand the interaction mechanisms between nanomaterials and mesenchymal stem cells (MSCs) for biomedical applications. In this study, ruthenium (II) functional selenium nanoparticles (Ru@Se) are used for stem cell research. Specifically, Ru@Se are compared with citric acid selenium nanoparticles (Cit@Se)to identify their effects on MSCs differentiation and associated molecular mechanism. These data suggest that the effective adsorbing abilities of Ru@Se and Cit@Se allow them to act as preconcentration materials for osteogenic chemical inducers, which accelerates MSCs differentiation into osteoblasts. Further results suggest that selenium nanoparticles enhance the differentiation of MSCs toward osteogenic lineage over adipocytes by promoting osteogenic transcription and attenuating adipogenic transcription. Ru@Se and Cit@Se exert these effects by activating Smad‐dependent BMP signaling pathway, which regulates the expression of relevant genes to induce osteogenic differentiation. Ru@Se, a good biocompatible nanoparticle, can be uptaken by human umbilical cord mesenchymal stem cells and can enhance the osteogenic differentiation of HUMSCs through the Smad‐dependent BMP signaling pathway. The activation of BMP pathway induces the Smad1/5 protein phosphorylation. p‐Smad1/5 combines with Smad 4 and translocates into the nucleus to promote the expression of the osteogenesis specific genes, such as BMP, OCN, OPN, thus driving HUCMSCs to differentiate into osteoblasts.
      PubDate: 2014-09-01T09:34:21.235163-05:
      DOI: 10.1002/adfm.201401263
  • Polar Cation Ordering: A Route to Introducing >10% Bond Strain Into
           Layered Oxide Films
    • Authors: Brittany B. Nelson‐Cheeseman; Hua Zhou, Prasanna V. Balachandran, Gilberto Fabbris, Jason Hoffman, Daniel Haskel, James M. Rondinelli, Anand Bhattacharya
      Pages: 6884 - 6891
      Abstract: The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. A new route is presented to strain the M–O bonds in epitaxial two‐dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formula unit via atomic layer‐by‐layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. This distortion is largest for the apical oxygen atoms (Oap), and alters the transition metal valence state via self‐doping without chemical substitution. The cations of a well‐known layered oxide, LaSrNiO4, are re‐arranged in a “polar” structure using molecular beam epitaxy. X‐ray probes reveal that the resulting electrostatic dipoles act on the Ni–O bonds, creating large distortions and changes to hybridization. This “electrostatic bond strain” approach has potential to tailor electronic properties in layered oxides by altering the local bonding without epitaxy or doping.
      PubDate: 2014-09-05T03:28:21.150505-05:
      DOI: 10.1002/adfm.201401077
  • Self‐Assembled Membranes: Ultra‐Thin Self‐Assembled
           Protein‐Polymer Membranes: A New Pore Forming Strategy (Adv. Funct.
           Mater. 43/2014)
    • Authors: Patrick van Rijn; Murat Tutus, Christine Kathrein, Nathalie C. Mougin, Hyunji Park, Christopher Hein, Marco P. Schürings, Alexander Böker
      Pages: 6896 - 6896
      Abstract: A new design concept is developed on page 6762 by A. Böker and co‐workers for preparing ultra‐thin membranes based on the self‐assembly of polymer‐decorated protein nanoparticles which is highly flexible and robust for testing in a macroscopic membrane setup. This approach opens the gate for the development of sophisticated membranes in which protein are used as selective and “smart” pores.
      PubDate: 2014-11-13T07:51:52.546841-05:
      DOI: 10.1002/adfm.201470284
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