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 2D MaterialsNumber of Followers: 14      Hybrid journal (It can contain Open Access articles) ISSN (Online) 2053-1583 Published by IOP  [71 journals]
• Near-zero hysteresis and near-ideal subthreshold swing in h-BN
encapsulated single-layer MoS 2 field-effect transistors
• Authors: Quoc An Vu; Sidi Fan, Sang Hyup Lee, Min-Kyu Joo, Woo Jong Yu Young Hee Lee
First page: 031001
Abstract: While two-dimensional (2D) van der Waals (vdW) layered materials are promising channel materials for wearable electronics and energy-efficient field-effect transistors (FETs), large hysteresis and large subthreshold swing induced by either dangling bonds at gate oxide dielectrics and/or trap molecules in bubbles at vdW interface are a serious drawback, hampering implementation of the 2D-material based FETs in real electronics. Here, we report a monolayer MoS 2 FET with near-zero hysteresis reaching 0.15% of the sweeping range of the gate bias, a record-value observed so far in 2D FETs. This was realized by squeezing the MoS 2 channel between top h-BN layer and bottom h-BN gate dielectrics and further removing the trap molecules in bubbles at the vdW interfaces via post-annealing. By segregating the bubbles out to the edge of the channel, we also obtain excellent switching characteristics with a minimum subthreshold swing of 63 mV/dec, an average subthreshold ...
Citation: 2D Materials
PubDate: 2018-03-27T23:00:00Z
DOI: 10.1088/2053-1583/aab672
Issue No: Vol. 5, No. 3 (2018)

• Evaluation of border traps and interface traps in HfO 2 /MoS 2 gate stacks
by capacitance–voltage analysis
• Authors: Peng Zhao; Ava Khosravi, Angelica Azcatl, Pavel Bolshakov, Gioele Mirabelli, Enrico Caruso, Christopher L Hinkle, Paul K Hurley, Robert M Wallace Chadwin D Young
First page: 031002
Abstract: Border traps and interface traps in HfO 2 /few-layer MoS 2 top-gate stacks are investigated by C – V characterization. Frequency dependent C – V data shows dispersion in both the depletion and accumulation regions for the MoS 2 devices. The border trap density is extracted with a distributed model, and interface traps are analyzed using the high-low frequency and multi-frequency methods. The physical origins of interface traps appear to be caused by impurities/defects in the MoS 2 layers, performing as band tail states, while the border traps are associated with the dielectric, likely a consequence of the low-temperature deposition. This work provides a method of using multiple C – V measurements and analysis techniques to analyze the behavior of high-k/TMD gate stacks and deconvolute border traps from interface traps.
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab728
Issue No: Vol. 5, No. 3 (2018)

• Black phosphorus: ambient degradation and strategies for protection
• Authors: Sruthi Kuriakose; Taimur Ahmed, Sivacarendran Balendhran, Vipul Bansal, Sharath Sriram, Madhu Bhaskaran Sumeet Walia
First page: 032001
Abstract: Elemental 2D black phosphorus (BP) is a highly anisotropic versatile material capable of exhibiting wide ranging electronic characteristics ranging from semi-metallic to semiconducting. Its thickness dependent tunable energy gap makes it an exciting prospect for deployment in a variety of applications. The main hurdle limiting diverse applications incorporating BP is its ambient instability. BP degrades rapidly under room conditions, affecting its structure and properties. In this report, we cover the recent progress that has occurred towards protecting BP from ambient degradation. We review the major developments in effectively countering the problem and compare their relative degrees of success. This is provided in the context of the mechanisms governing the atmospheric instability of this material. A targeted focus is kept on the various causes of degradation of BP in atmospheric conditions and the protection strategies that have been implemented so far.
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab810
Issue No: Vol. 5, No. 3 (2018)

• Direct growth of high crystallinity graphene from water-soluble polymer
powders
• Authors: Qiao Chen; Yujia Zhong, Meirong Huang, Guoke Zhao, Zhen Zhen Hongwei Zhu
First page: 035001
Abstract: The use of solid-state carbon sources is effective to produce graphene by safe and low-cost chemical vapor deposition (CVD) process. Water-soluble polymers are generally environmentally friendly and have great potential on large-scale green production of graphene. Here, we systematically study the growth of graphene from water-soluble polymers on copper foils. Two different conversion ways are adopted to investigate the growth mechanism of graphene from water-soluble polymers. We find that the metal-binding functional group hydroxyl strongly influences the vaporization of water-soluble polymers on Cu foils, which hinders the formation of graphene films by rapid thermal treatment. In direct CVD process using water-soluble polymer powders as precursors, oxygenated functional groups in polymers can enhance the crystallinity of as-grown graphene in contrast to solid hydrocarbons without containing oxygen (e.g. polyethylene). Large and continuous graphene films of high quality are sy...
Citation: 2D Materials
PubDate: 2018-03-27T23:00:00Z
DOI: 10.1088/2053-1583/aab729
Issue No: Vol. 5, No. 3 (2018)

• Optoelectronic response of a WS 2 tubular p - n junction
• Authors: Y J Zhang; M Onga, F Qin, W Shi, A Zak, R Tenne, J Smet Y Iwasa
First page: 035002
Abstract: Due to their favourable and rich electronic and optical properties, group-VI-B transition-metal dichalcogenides (TMDs) have attracted considerable interest. They have earned their position in the materials portfolio of the spintronics and valleytronics communities. The electrical performance of TMDs is enhanced by rolling up the two-dimensional (2D) sheets to form quasi-one-dimensional (1D) tubular structures. The fabrication of p-n junctions out of these tubular TMDs would boost their potential for optoelectronic devices as such junctions represent a fundamental building block. Here, we report the realization of a p-n junction out of a single, isolated WS 2 -nanotube (WS 2 -NT). Light-emitting diode operation and photovoltaic behaviour were observed based on such p-n junctions. The emitted light as well as the photovoltaic effect exhibit strong linear polarization characteristics due to the quasi-1D nature. The external quantum effi...
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab670
Issue No: Vol. 5, No. 3 (2018)

• Nanoscale doping heterogeneity in few-layer WSe 2 exfoliated onto noble
metals revealed by correlated SPM and TERS imaging
• Authors: Deep Jariwala; Andrey Krayev, Joeson Wong, A Edward Robinson, Michelle C Sherrott, Shuo Wang, Gang-Yu Liu, Mauricio Terrones Harry A Atwater
First page: 035003
Abstract: While extensive research effort has been devoted to the study of the 2D semiconductor–insulator interfaces in transition metal dichalcogenides (TMDCs), there is little knowledge about the electronic quality of the semiconductor–metal interface in the atomically thin limit. Here, we present the first correlated nanoscale mapping of the interface of atomically thin WSe 2 with noble metals using co-localized scanning probe microscopy and tip-enhanced optical spectroscopy (TEOS), such as tip-enhanced Raman spectroscopy (TERS). Nanoscale maps of the topography, surface potential, Raman spectra, and the photocurrent amplitude of the WSe 2 /metal interfaces reveal striking results. Specifically, correlations between surface potential, resonant Raman signatures and photocurrents that indicate the presence of inhomogeneities within interfacial electronic properties, which we attribute to variations in the local doping of the WSe 2 likely caused by intrinsic c...
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab7bc
Issue No: Vol. 5, No. 3 (2018)

• Impurity-assisted electric control of spin-valley qubits in monolayer MoS
2
• Authors: G Széchenyi; L Chirolli A Pályi
First page: 035004
Abstract: We theoretically study a single-electron spin-valley qubit in an electrostatically defined quantum dot in a transition metal dichalcogenide monolayer, focusing on the example of MoS 2 . Coupling of the qubit basis states for coherent control is challenging, as it requires a simultaneous flip of spin and valley. Here, we show that a tilted magnetic field together with a short-range impurity, such as a vacancy, a substitutional defect, or an adatom, can give rise to a coupling between the qubit basis states. This mechanism renders the in-plane g -factor nonzero, and allows to control the qubit with an in-plane ac electric field, akin to electrically driven spin resonance. We evaluate the dependence of the in-plane g -factor and the electrically induced qubit Rabi frequency on the type and position of the impurity. We reveal highly unconventional features of the coupling mechanism, arising from symmetry-forbidden intervalley scattering, in the case when the imp...
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab80e
Issue No: Vol. 5, No. 3 (2018)

• Electric field effect on the electronic structure of 2D Y 2 C electride
• Authors: Youngtek Oh; Junsu Lee, Jongho Park, Hyeokshin Kwon, Insu Jeon, Sung Wng Kim, Gunn Kim, Seongjun Park Sung Woo Hwang
First page: 035005
Abstract: Electrides are ionic compounds in which electrons confined in the interstitial spaces serve as anions and are attractive owing to their exotic physical and chemical properties in terms of their low work function and efficient charge-transfer characteristics. Depending on the topology of the anionic electrons, the surface electronic structures of electrides can be significantly altered. In particular, the electronic structures of two-dimensional (2D) electride surfaces are of interest because the localized anionic electrons at the interlayer space can be naturally exposed to cleaved surfaces. In this paper, we report the electronic structure of 2D Y 2 C electride surface using scanning tunneling microscopy (STM) and first-principles calculations, which reveals that anionic electrons at a cleaved surface are absorbed by the surface and subsequently resurged onto the surface due to an applied electric field. We highlight that the estranged anionic electrons caused by the e...
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab855
Issue No: Vol. 5, No. 3 (2018)

• Nucleation and growth mechanism of 2D SnS 2 by chemical vapor deposition:
initial 3D growth followed by 2D lateral growth
• Authors: Haodong Zhang; Thomas van Pelt, Ankit Nalin Mehta, Hugo Bender, Iuliana Radu, Matty Caymax, Wilfried Vandervorst Annelies Delabie
First page: 035006
Abstract: Tin disulfide (SnS 2 ) is a n-type semiconductor with a hexagonally layered crystal structure and has promising applications in nanoelectronics, optoelectronics and sensors. Such applications require the deposition of SnS 2 with controlled crystallinity and thickness control at monolayer level on large area substrate. Here, we investigate the nucleation and growth mechanism of two-dimensional (2D) SnS 2 by chemical vapor deposition (CVD) using SnCl 4 and H 2 S as precursors. We find that the growth mechanism of 2D SnS 2 is different from the classical layer-by-layer growth mode, by which monolayer-thin 2D transition metal dichalcogenides can be formed. In the initial nucleation stage, isolated 2D SnS 2 domains of several monolayers high are formed. Next, 2D SnS 2 crystals grow laterally while keeping a nearly constant height until layer closure is achieved, due to the higher reactivity of SnS 2
Citation: 2D Materials
PubDate: 2018-04-09T23:00:00Z
DOI: 10.1088/2053-1583/aab853
Issue No: Vol. 5, No. 3 (2018)

• First principles analysis of the CDW instability of single-layer 1 T -TiSe
2 and its evolution with charge carrier density
• Authors: Bogdan Guster; Enric Canadell, Miguel Pruneda Pablo Ordejón
First page: 025024
Abstract: We present a density functional theory study of the electronic structure of single-layer TiSe 2 , and focus on the charge density wave (CDW) instability present on this 2D material. We explain the ##IMG## [http://ej.iop.org/images/2053-1583/5/2/025024/tdmaab568ieqn001.gif] {$2\times 2$} periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2  ×  1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2  ×  2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduc...
Citation: 2D Materials
PubDate: 2018-03-23T00:00:00Z
DOI: 10.1088/2053-1583/aab568
Issue No: Vol. 5, No. 2 (2018)

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