NPJ 2D Materials and Applications

/NPJ 2D Materials and Applications

Identification of amino acids with sensitive nanoporous MoS<sub>2</sub>: towards machine learning-based prediction

2018-05-29T12:50:05+00:00May 29th, 2018|Categories: Publications|Tags: |

Identification of amino acids with sensitive nanoporous MoS2: towards machine learning-based predictionIdentification of amino acids with sensitive nanoporous MoS<sub>2</sub>: towards machine learning-based prediction, Published online: 24 May 2018; doi:10.1038/s41699-018-0060-8Molecular dynamics simulations combined with machine learning techniques enable the prediction of MoS2 nanopore sequencing capabilities. A team led by N. R. Aluru at the University of Illinois at Urbana-Champaign used logistic regression, nearest neighbor, and random forest classifiers to develop a machine learning-based platform capable of predicting the sensing capabilities of nanoporous, atomically thin MoS2. The material was shown to be able to identify individual amino acids in polypeptide chains with high accuracy and distinguishability. Twenty amino acids could be detected and categorized in different classes based on current-residence time training data, with an accuracy of up to 99.6%. These results show promise for the development of amino acid detection platforms with atomically thin materials assisted by machine learning.

Published in: "NPJ 2D Materials and Applications".

Tunable phase stability and contact resistance of monolayer transition metal dichalcogenides contacts with metal

2018-05-16T09:09:01+00:00May 16th, 2018|Categories: Publications|

Tunable phase stability and contact resistance of monolayer transition metal dichalcogenides contacts with metalTunable phase stability and contact resistance of monolayer transition metal dichalcogenides contacts with metal, Published online: 14 May 2018; doi:10.1038/s41699-018-0059-1Interfacial charge calculations enable the prediction of the contact resistance behaviour of MX2/metal structures. A team led by Bin Ouyang at the University of California Berkeley performed a systematic theoretical investigation of the interplay between interface interactions and phase stability in atomically thin MX2/metal systems, where M is a transition metal and X is a chalcogenide. A combination of interfacial charge calculations and contact resistance analysis allowed the identification of twenty-eight MX2/metal structures that can be further categorised in three groups according to their contact nature. Notably, the first type of contact possesses zero tunnel barrier between MX2 and the metal, whereas the second type enables substantial charge transfer accompanied to a 2H-to-1T’ structural phase transition in MX2. These results highlight viable design routes for contact resistance manipulation in MX2 transistors.

Published in: "NPJ 2D Materials and Applications".

Anisotropic band splitting in monolayer NbSe<sub>2</sub>: implications for superconductivity and charge density wave

2018-05-04T09:09:06+00:00May 4th, 2018|Categories: Publications|Tags: , |

Anisotropic band splitting in monolayer NbSe2: implications for superconductivity and charge density waveAnisotropic band splitting in monolayer NbSe<sub>2</sub>: implications for superconductivity and charge density wave, Published online: 03 May 2018; doi:10.1038/s41699-018-0057-3The interplay between symmetry breaking, superconductivity and charge density wave in monolayer NbSe2 is unveiled by spectroscopic techniques. A team led by Takafumi Sato at Tohoku University used molecular beam epitaxy to fabricate atomically thin NbSe2 films on bilayer graphene, and investigated their electronic properties by a combination of electrical transport measurements, scanning tunneling microscopy, and angle-resolved photoemission spectroscopy. A charge density wave transition with a strong periodic charge modulation was detected below 1.5 K, accompanied by the emergence of superconductivity. Owing to the inversion symmetry breaking occurring in monolayer NbSe2, a band splitting developed along the Γ-Κ direction of the Brillouin zone. Such band splitting was found to be related to the robustness of the observed superconductivity, as well as the formation of the charge density wave.

Published in: "NPJ 2D Materials and Applications".

Strain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloys

2018-05-01T09:09:58+00:00May 1st, 2018|Categories: Publications|Tags: |

Strain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloysStrain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloys, Published online: 30 April 2018; doi:10.1038/s41699-018-0056-4Composition modulation synthesis of ternary alloys of atomically thin transition metal dichalcogenides gives rise to intrinsic biaxial strain. A team led by Ali Adibi at Georgia Institute of Technology reported the onset of a substantial biaxial strain in monolayer MoS2xSe2(1-x) that is intrinsically linked to the two-step composition modulation synthesis used to grow the ternary alloy. As the S atoms replace the Se atoms of the starting MoSe2 host crystal, the resulting alloy forms a stretched lattice and develops a large biaxial tensile strain. Morphological and spectroscopic characterisations suggest that such strain results in the onset of fracture in the crystal, and further relaxes via formation of cracks within the crystal domains. Theoretical modelling indicates that pre-existing cracks give a substantial contribution in weakening the strength of the synthesized van der Waals alloy.

Published in: "NPJ 2D Materials and Applications".

Out-of-plane interface dipoles and anti-hysteresis in graphene-strontium titanate hybrid transistor

2018-04-10T09:09:07+00:00April 10th, 2018|Categories: Publications|Tags: |

Out-of-plane interface dipoles and anti-hysteresis in graphene-strontium titanate hybrid transistorOut-of-plane interface dipoles and anti-hysteresis in graphene-strontium titanate hybrid transistor, Published online: 09 April 2018; doi:10.1038/s41699-018-0055-5The dipole field at the surface of SrTiO3 strongly impacts the transfer characteristics of graphene/SrTiO3 field-effect transistors. A team led by Arindam Ghosh at the Indian Institute of Science (Bangalore) fabricated dual-gated field-effect transistors with graphene on a TiO2-terminated SrTiO3 (100) crystal, and observed a large, intrinsic out-of-plane electric polarization at the hetero-interface. The measured polarization, detected by means of gate-transfer characteristics and further supported by density functional theory calculations, was found to be as large as 12 μC cm−2. The nature of the anti-hysteretic transfer characteristics in both resistance and noise is indicative of formation of trap states at the SrTiO3 interface, due to band renormalization and electrostatic confinement. These results improve the physical understanding of the interfaces between atomically thin materials and polarizable substrates.

Published in: "NPJ 2D Materials and Applications".

Graphene wrinkle effects on molecular resonance states

2018-03-29T09:09:04+00:00March 29th, 2018|Categories: Publications|Tags: , |

Graphene wrinkle effects on molecular resonance statesGraphene wrinkle effects on molecular resonance states, Published online: 28 March 2018; doi:10.1038/s41699-018-0053-7The morphology of out-of-plane wrinkles in graphene determines the molecular growth and electronic structure of adsorbed pentacene molecules. A team led by Peter Nirmalraj at IBM Research (Zurich) performed a combined experimental and theoretical study on the interplay between the ubiquitous corrugations naturally present in graphene and the structure and electronic properties of pentacene molecular superstructures. The atomic scale wrinkle landscape was found to trigger substantial variations in molecular growth, along with pronounced electronic decoupling of pentacene adsorbed on wrinkles. This is in contrast to the behavior of pentacene on flat graphene, which featured broadened molecular energy levels owing to electronic interaction with the underlying substrate. These results may facilitate the understanding of interfacial effects between graphene and molecules and pave the way to improved design of nanoscale molecular electronic devices.

Published in: "NPJ 2D Materials and Applications".

Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk

2018-03-11T09:09:03+00:00March 11th, 2018|Categories: Publications|Tags: |

Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulkDielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk, Published online: 08 March 2018; doi:10.1038/s41699-018-0050-xThe out-of-plane dielectric constant of transition metal dichalcogenides and h-BN is thickness-dependent, unlike their in-plane counterpart. A team led by William Vandenberghe at the University of Texas at Dallas performed calculations of the optical and static relative permittivity of free-standing monolayer, bilayer, and bulk transition metal dichalcogenides, in the in-plane and out-of-plane directions. In h-BN, the in-plane contribution was found to be larger than its out-of-plane counterpart, and independent on the number of h-BN layers. Conversely, the out-of-plane h-BN dielectric constant showed an increase when going from monolayer to bulk. In transition metal dichalcogenides, the dielectric constant components displayed similar trends to those observed in h-BN with regards to their thickness evolution. The calculations also indicated that the electronic component dominates the overall dielectric response for most of the analyzed 2D materials.

Published in: "NPJ 2D Materials and Applications".

Electrical devices from top-down structured platinum diselenide films

2018-03-02T09:09:09+00:00March 2nd, 2018|Categories: Publications|Tags: |

Electrical devices from top-down structured platinum diselenide filmsElectrical devices from top-down structured platinum diselenide films, Published online: 28 February 2018; doi:10.1038/s41699-018-0051-9Transport measurements on channels of layered PtSe2 give insight into the realization of high-performance nanoelectronic PtSe2 devices. A team led by Niall McEvoy at Trinity College Dublin investigated the electrical contact properties of PtSe2 channels with controlled dimensions and thicknesses. Electron beam lithography was used to fabricate structures with different contact metals and different PtSe2 film thicknesses, and the corresponding contact resistivity and sheet resistance of the PtSe2 devices were extracted from transmission line method measurements. The charge-transport characteristics of the PtSe2 devices revealed that edge-contacted structures are able reduce the contact resistivity when compared to conventional devices with top contacts, thanks to enhancement of the carrier injection at the contacts. These results may pave the way to optimal design of PtSe2 nanoelectronic devices.

Published in: "NPJ 2D Materials and Applications".

Device physics of van der Waals heterojunction solar cells

2018-02-21T09:09:02+00:00February 21st, 2018|Categories: Publications|Tags: , , |

Device physics of van der Waals heterojunction solar cellsDevice physics of van der Waals heterojunction solar cells, Published online: 19 February 2018; doi:10.1038/s41699-018-0049-3The photophysics of van der Waals heterojunctions can be captured by a transport equation fully reproducing their photovoltaic response. A team led by Thomas Mueller at Vienna University of Technology presented an experimental study of a MoS2/WSe2 van der Waals heterostructure along with a device model capable of fully reproducing the current-voltage characteristics of type-II van der Waals heterojunctions under optical illumination. The model is able to capture some peculiar behaviors occurring in heterostructures of atomically thin transition metal dichalcogenides, including their high ideality factors and bias-dependent photocurrents. As a result, a modified transport equation should be used to describe their photovoltaic response, instead of the commonly used Shockley equation. These results pave the way to the optimization of future device architectures for photovoltaic applications.

Published in: "NPJ 2D Materials and Applications".

Large-grain MBE-grown GaSe on GaAs with a Mexican hat-like valence band dispersion

2018-01-28T09:09:06+00:00January 28th, 2018|Categories: Publications|Tags: |

Large-grain MBE-grown GaSe on GaAs with a Mexican hat-like valence band dispersionLarge-grain MBE-grown GaSe on GaAs with a Mexican hat-like valence band dispersion, Published online: 25 January 2018; doi:10.1038/s41699-017-0047-xMolecular beam epitaxy enables growth of high-quality, atomically thin GaSe on a GaAs substrate. A team led by Andras Kis at EPFL successfully demonstrated the synthesis of large-grain GaSe van der Waals epitaxial films using a two-step growth approach. The quality and spatial uniformity of the as-grown films were probed by various means of characterization, including scanning transmission electron microscopy, in-situ reflection high energy electron diffraction, and photoemission electron momentum microscopy. The results indicate a uniform distribution of Ga and Se in the GaSe film; at the atomically thin limit, the electronic band structure was found to exhibit inverted band dispersion at the Γ point, leading to a Mexican Hat-like valence band dispersion. These finding may pave the way to potential applications of GaSe in large-area electronics and spintronics.

Published in: "NPJ 2D Materials and Applications".

Substrate engineering of graphene reactivity: towards high-performance graphene-based catalysts

2018-01-19T09:09:29+00:00January 19th, 2018|Categories: Publications|Tags: |

Substrate engineering of graphene reactivity: towards high-performance graphene-based catalystsSubstrate engineering of graphene reactivity: towards high-performance graphene-based catalysts, Published online: 17 January 2018; doi:10.1038/s41699-017-0046-yEngineering the underlying substrate with defects promotes reactivity and catalytic activity of graphene. A team led by Chun Zhang at the Centre for Advanced 2D Materials of the National University of Singapore performed first-principles calculations revealing that, when defects are introduced in the lattice of a Ru(0001) substrate, the reactivity of the supported graphene is enhanced. As a consequence, O2 molecules can be readily adsorbed onto graphene at the location corresponding to the underlying defect. Such facilitated chemical adsorption can be explained in the light of impurity-induced charge transfer from the graphene/Ru(0001) interface to the O2 molecule orbitals. Furthermore, the charge transfer results in high catalytic activity in graphene towards CO oxidation. These results may promote the design of high-performance graphene catalysts supported on a defect-engineered substrate.

Published in: "NPJ 2D Materials and Applications".

Production of monolayer-rich gold-decorated 2H–WS<sub>2</sub> nanosheets by defect engineering

2018-01-10T09:09:21+00:00January 10th, 2018|Categories: Publications|Tags: |

Production of monolayer-rich gold-decorated 2H–WS2 nanosheets by defect engineeringProduction of monolayer-rich gold-decorated 2H–WS<sub>2</sub> nanosheets by defect engineering, Published online: 08 January 2018; doi:10.1038/s41699-017-0045-zDefect engineering of WS2 nanosheets via redox chemistry in liquid phase yields enhanced catalytic activity and monolayer enrichment. A team led by Claudia Backes at Ruprecht-Karls University demonstrated that liquid-phase exfoliated WS2 undergoes a spontaneous redox reaction with AuCl3, whereby thiol groups occurring at edges and defect sites reduce the AuCl3 to Au0. The reaction causes Au nanoparticles to nucleate at WS2 edges, and in turn such Au nanoparticle loading determines a substantial change in the nanosheet mass. As the Au decoration preferentially occurs at the edges of incompletely exfoliated WS2 flakes, the dispersions can be further enriched with monolayers by means of centrifugation. While the optical properties of Au-decorated WS2 sheets remain unaltered, their electrocatalytic activity is highly enhanced, showing promise for applications in hydrogen evolution reactions.

Published in: "NPJ 2D Materials and Applications".

Studies of two-dimensional h-BN and MoS<sub>2</sub> for potential diffusion barrier application in copper interconnect technology

2017-12-11T09:09:28+00:00December 11th, 2017|Categories: Publications|Tags: , |

Studies of two-dimensional h-BN and MoS2 for potential diffusion barrier application in copper interconnect technologyStudies of two-dimensional h-BN and MoS<sub>2</sub> for potential diffusion barrier application in copper interconnect technology, Published online: 08 December 2017; doi:10.1038/s41699-017-0044-0Atomically thin h-BN and MoS2 may provide a viable alternative to conventional barrier materials in Cu interconnects. A team led by Zhihong Chen at Purdue University utilized two-dimensional crystals to mitigate Cu diffusion into the dielectric, a known cause of chip failure. By means of time-dependent dielectric breakdown measurements to investigate the diffusion barrier properties of atomically thin h-BN and MoS2, they recorded a substantial improvement of the time-to-breakdown, owing to a reliability enhancement of the dielectric underneath Cu under normal operating conditions. A number of structural and electrical characterizations, including scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy confirmed that two-dimensional h-BN and MoS2 films effectively prevent Cu diffusion, highlighting their potential applicability as sub-nanometer barrier for interconnect technology.

Published in: "NPJ 2D Materials and Applications".

Two-dimensional negative capacitance transistor with polyvinylidene fluoride-based ferroelectric polymer gating

2017-11-23T09:09:10+00:00November 23rd, 2017|Categories: Publications|Tags: , |

Two-dimensional negative capacitance transistor with polyvinylidene fluoride-based ferroelectric polymer gatingTwo-dimensional negative capacitance transistor with polyvinylidene fluoride-based ferroelectric polymer gating, Published online: 02 November 2017; doi:10.1038/s41699-017-0040-4Replacing the conventional oxide with a ferroelectric polymer in 2D MoS2 field-effect transistors allows sub-60 mV/dec operation. A team led by Jianlu Wang at the Chinese Academy of Sciences fabricated a negative capacitance field-effect transistor based on a metal-ferroelectric-semiconductor structure, with a 2D semiconductor (MoS2 or MoSe2) as the channel. Notably, when the oxide commonly used in field-effect transistors was replaced by a ferroelectric poly(vinylidene difluoride-trifluoroethylene) polymer, the resulting device achieved a subthreshold slope of 24.2 mV/dec at a drain voltage of 0.1 V, at room temperature. Further reduction of the polymer thickness to 50 nm resulted in a 51.2 mV/dec subthreshold slope. These results show promise for overcoming the 60 mV/decade subthreshold slope limit which plagues conventional transistors.

Published in: "NPJ 2D Materials and Applications".

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe<sub>2</sub> and MoSe<sub>2</sub>

2017-11-23T09:09:09+00:00November 23rd, 2017|Categories: Publications|Tags: , |

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe<sub>2</sub> and MoSe<sub>2</sub> , Published online: 22 November 2017; doi:10.1038/s41699-017-0043-1The Raman spectra of ReSe2-xSx alloys allows investigation of the distribution of substitutional sulfur atoms within the lattice of ReSe2. A team led by Lewis S. Hart at the University of Bath performed a combination of Raman spectroscopy at visible excitation wavelengths and density functional perturbation theory on ternary ReSe2-xSx alloys obtained by chemical vapor transport. The combination of a traditional normal incidence configuration and an “edge-on” geometry allowed identification of in-plane and out-of-plane Raman features, optically active in the respective experiments owing to their specific selection rules. The frequencies of the observed local vibrational modes arising from sulfur and oxygen atoms were observed to change as a function of the stoichiometric composition of the alloy, thus providing a means of monitoring such impurities. A similar effect was predicted for MoSe2-xSx alloys.

Published in: "NPJ 2D Materials and Applications".

Contact morphology and revisited photocurrent dynamics in monolayer MoS<sub>2</sub>

2017-11-23T09:09:10+00:00November 23rd, 2017|Categories: Publications|Tags: , |

Contact morphology and revisited photocurrent dynamics in monolayer MoS2Contact morphology and revisited photocurrent dynamics in monolayer MoS<sub>2</sub> , Published online: 17 November 2017; doi:10.1038/s41699-017-0042-2The interplay between bolometric response and defect-related conductance effects in monolayer MoS2 is unveiled by spectroscopic techniques. A team led by Alexander Holleitner at the Technical University of Munich performed both continuous wave and ultrafast spectroscopy to identify the key contributions to the MoS2 ultrafast photoconductance dynamics. Scanning photocurrent experiments performed on a variety of samples in presence of a focused laser spot tracked the effects of contact annealing in metal/MoS2/metal devices, and showed that the former results in a permanent renormalization of the contact energy landscape. In turn, the built-in electric fields at the annealed contact promote a bolometric response in combination with defect-related conductance effects, which dominate the optoelectronic signal. These observations contribute to a better understanding of optoelectronic experiments on 2D materials that make use of a focused laser spot.

Published in: "NPJ 2D Materials and Applications".

Hypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohorns

2017-11-11T09:09:14+00:00November 11th, 2017|Categories: Publications|Tags: , |

Hypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohornsHypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohorns, Published online: 08 November 2017; doi:10.1038/s41699-017-0041-3

Published in: "NPJ 2D Materials and Applications".

Some say, that 2D Research is the best website in the world.