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Nanoindentation of circular multilayer graphene allotropes
摘要： Nanoindentaion has been proposed as an efficient technique to measure mechanical single-layer two-dimensional (2D) materials via combining the membrane theory with the indentation data. However, for multilayered structures of 2D materials, significant discrepancy exists between the Young’s modulus obtained from the existing membrane model and those from other methods. Here we develop a multilayer indentation model by taking the multilayer effect into account in the previous membrane model. We show that the present model can accurately predict the Young’s modulus of multilayered 2D carbon materials. For few layer graphene and twin graphene structures, the deviation of the Young’s moduli obtained by the present model are both within a reasonable range, while the error caused by the direct use of the previous single-layer membrane model increases with the number of layers. The present model provides an efficient tool to extract the mechanical properties of 2D materials from the nanoindentation data of their multilayered structures.
关键词： Young’s modulus,two-dimensional materials,nanoindentaion,molecular dynamics
更新于2025-09-04 15:30:14
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Bright Orange Electroluminescence from Lead-Free Two-Dimensional Perovskites
摘要： Lead halide perovskites are important materials for solar cells and light emitting diodes (LEDs), but the toxicity of lead is a matter of concern for these and other commercial applications. Here, we demonstrate a lead-free two-dimensional (2D) Ruddlesden-Popper-type (C18H35NH3)2SnBr4 perovskite with a strong emission from the self-trapped states, whose photoluminescence quantum yields in colloidal suspension and in film are 88% and 68%, respectively. The insulating character of the organic oleylamine cation prevents electronic band formation between the [SnBr6]4- octahedron layers, which results in the Stokes-shifted orange emission. Electroluminescence of these 2D lead-free perovskite materials was demonstrated in an inverted LED structure with a low turn-on voltage of 2.2 V and a luminance of 350 cd/m2.
关键词： orange emission,two-dimensional perovskites,self-trapped states,lead-free,electroluminescence
更新于2025-09-04 15:30:14
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Tunable Direct Semiconductor Gap and High Carrier Mobility of Mo <sub/>6</sub> Br <sub/>6</sub> S <sub/>3</sub> Monolayer
摘要： Two-dimensional materials with direct semiconductor gaps and high mobilities can play an important role in future electronic and optical applications. Here we propose that Mo6Br6S3 monolayer as a new two-dimensional material is stable and can be exfoliated from corresponding layered bulk. Our first-principles results show that the monolayer has a direct semiconductor gap beyond 1 eV (between PBE and HSE values) and a very high electron mobility (6880 cm2V?1s?1), and these can be tuned through in-plane strain by applying uniaxial stress. Furthermore, we show that the Mo6Br6S3/graphene heterostructure makes a p-type Schottky barrier and the amplitude of band bending (0.03 eV) is extremely low compared to other similar junctions because the Mo6Br6S3 monolayer has a close work function to graphene. With all these useful properties and functions, the Mo6Br6S3 monolayer can be very promising for nanoelectronic and optical applications.
关键词： Mo6Br6S3 monolayer,p-type Schottky barrier,optical applications,Two-dimensional materials,electron mobility,high mobilities,first-principles,direct semiconductor gaps,nanoelectronic
更新于2025-09-04 15:30:14
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Nitrogen-Doping Chemical Behavior of Graphene Materials with Assistance of Defluorination
摘要： Heteroatom-doping reactions are essential to achieve advanced graphene-based materials for energy and biological areas. Unfortunately, considerably less is known regarding the detailed reaction pathways up to now. Here, we focus on investigating the nitrogen (N) doping process of fluorinated graphene (FG) under the assistance of defluorination based on modified in situ fourier transform infrared spectroscopy. It was demonstrated FG possesses a higher and more effective reactivity with ammonia in comparison with other graphene derivatives, which enable N-doping to proceed efficiently with assistance of defluorination even at a lower temperature (16.8 at % of N at 300 °C, 19.9 at % of N at 400 °C). Combining with Density functional theory, it was proved that, at the initial reaction step of N-doping, ammonia molecule attacked and substituted the C-F of FG by the new C-NH2. Sequentially, amino group was cyclized to the three-membered ring of ethylenimine. More importantly, the dissociation and migration of C-F bonds facilitates the dissociating of C-C bonds and the recombining of C-N bonds, thus significantly promoting the N atom in ethylenimine ring to transform to the pyridinic-N or graphitic-N in graphene skeleton.
关键词： Fluorinated graphene,Reaction pathway,Defluorination,Nitrogen doping,Two-dimensional chemistry
更新于2025-09-04 15:30:14
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Variable-deceleration-ratio wide-acceptance-angle electrostatic lens for two-dimensional angular and energy analysis
摘要： Variable-deceleration-ratio wide-acceptance-angle electrostatic lens (VD-WAAEL) is proposed as a potential technique for two-dimensional angular and energy analysis. The basic features of the lens are studied using the charge simulation method and ray tracing calculation. The lens uses an ellipsoidal mesh electrode and allows a wide acceptance angle of ±50?. Two possible applications of the VD-WAAEL are discussed. One is a simple combination of the VD-WAAEL-projection-lens, in which an aperture is used for energy analysis. The other is a combination of the VD-WAAEL with a conventional electron spectrometer, which is responsible for obtaining higher energy resolution. The former is discussed in detail and the latter is described brie?y. While the ray tracing calculation is only for the case of an ideal mesh, a note on the disturbing effect of mesh holes is presented. The best possible energy resolution of the simple VD-WAAEL-projection-lens analyzer seems to be around 1/1000, given a ?ne mesh electrode to suppress the disturbing effect of mesh holes.
关键词： energy analysis,electrostatic lens,Variable-deceleration-ratio,two-dimensional angular,wide-acceptance-angle
更新于2025-09-04 15:30:14
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/epitaxial graphene van der Waals heterostructure
摘要： We report on direct observation of interface superconductivity in single-unit-cell SnSe2 films grown on graphitized SiC(0001) substrate. The tunneling spectrum in the superconducting state reveals a rather conventional character with a fully gapped order parameter. The occurrence of superconductivity is further confirmed by the observation of vortices under external magnetic field. Through interface engineering, we unravel the mechanism of superconductivity that originates from a two-dimensional electron gas formed at the interface of SnSe2 and graphene. Our finding opens up novel strategies to hunt for and understand interface superconductivity based on van der Waals heterostructures.
关键词： two-dimensional electron gas,interface superconductivity,van der Waals heterostructure,SnSe2,graphene
更新于2025-09-04 15:30:14
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monolayers on the hBN-layer thickness
摘要： The optical properties of two-dimensional transition-metal dichalcogenide monolayers, such as MoS2 or WSe2 are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due to the presence of hexagonal-boron nitride (hBN) surrounding layers have been investigated by solving the Bethe-Salpeter equation on top of GW wave functions in density functional theory calculations. We have calculated the dependence of both the quasiparticle gap and the binding energy of the neutral exciton ground-state Eb as a function of the hBN-layer thickness. This paper demonstrates that the effects of screening at this level of theory are more short ranged than is widely believed. The encapsulation of a WSe2 monolayer by three sheets of hBN (～1 nm) already yields a 20% decrease in Eb, whereas the maximal reduction is 27% for thick hBN. We have performed similar calculations in the case of a WSe2 monolayer deposited on stacked hBN layers. These results are compared to the recently proposed quantum electrostatic heterostructure approach.
关键词： GW wave functions,density functional theory,hexagonal-boron nitride,two-dimensional transition-metal dichalcogenide,Bethe-Salpeter equation,exciton
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Carrier Transport in a Two-Dimensional Topological Insulator Nanoribbon in the Presence of Vacancy Defects.
摘要： We model transport through two-dimensional topological insulator (TI) nanoribbons. To model the quantum transport, we employ the non-equilibrium Green’s function approach. With the presented approach, we study the effect of lattice imperfections on the carrier transport. We observe that the topologically protected edge states of TIs are robust against a high percentage (2%) of vacancy defects. We also investigate tunneling of the edge states in two decoupled TI nanoribbons.
关键词： nanoribbon,vacancy defects,non-equilibrium Green’s function,carrier transport,two-dimensional topological insulator
更新于2025-09-04 15:30:14
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The Origin of Two-Dimensional Vertical Ferroelectricity in WTe <sub/>2</sub> Bilayer and Multilayer
摘要： In a recent report, room-temperature vertical ferroelectricity was experimentally shown in WTe2 bilayer, while its mechanism of ferroelectric switching without vertical ion displacements remains unclarified. In this work we reveal its origin by first-principles calculations that the polarization stems from uncompensated interlayer vertical charge transfer depending on in-plane translation, which can be switched upon interlayer sliding. The calculated results are consistent with experimental data, and similar switching mechanism can be applied to multilayer counterpart. Despite its small ferroelectric switching barrier and polarization, the in-plane rigidity of WTe2 layer gives rise to a high Curie temperature. A Moire pattern of ferroelectric domain superlattice can be formed and tuned upon a small-angle twist of bilayer, which is unique compared with traditional ferroelectrics. Similar interlayer translational ferroelectricity may exist in a series of van der Waals bilayers or even bulk phases.
关键词： Two-dimensional,WTe2,First-principles calculations,Ferroelectricity,Interlayer sliding
更新于2025-09-04 15:30:14
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Two-Dimensional Materials and Their Role in Emerging Electronic and Photonic Devices
摘要： As the scaling of semiconducting devices in integrated circuits approaches dimensions less than 10 nm, the emphasis for future technologies has moved towards improved energy efficiency and the use of three dimensional (3D) integration schemes to achieve an increased density of devices per unit area. For many of these applications there is a need to explore new semiconducting materials which allow flexibility in electronic and optical properties, and can also be processed at reduced temperatures, which allows their integration above conventional silicon based integrated circuits. One class of materials that demonstrates considerable promise for these emerging applications is van der Waals bonded two dimensional (2D) semiconductors. The study of these 2D layered material systems is not new, with studies dating back to the 1920s and the identification of monolayers and bi-layers of MoS2 in the 1960s. What is particularly exciting about this general class of semiconductors is that they have a range of energy gaps which span from semi-metals through to wide bandgap semiconductors and as a consequence have potential applications in electronic devices, sensors, through to applications in flexible electronics, photovoltaics, and the light emitting diodes.
关键词： Two-Dimensional Materials,Semiconductors,Electronic Devices,Van der Waals,Photonic Devices
更新于2025-09-04 15:30:14