Modulation of MoTe2/MoS2 van der Waals heterojunction for multifunctional devices using N2O plasma with opposite doping effect

Nanoscale ◽  
2021 ◽  
Author(s):  
Yuan Xie ◽  
enxiu wu ◽  
shuangqing Fan ◽  
Guangyu Geng ◽  
Xiaodong Hu ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Doping Effect ◽  
Band Offsets ◽  
Wide Range ◽  
Multifunctional Devices

Van der Waals layered heterojunctions have a variety of band offsets, which open up possibilities for a wide range of novel and multifunctional devices. However, due to their poor pristine...

Efficient Prediction of Structural and Electronic Properties of Hybrid 2D Materials Using DFT and Machine Learning

2018 ◽  
Author(s):  
Sherif Tawfik ◽  
Olexandr Isayev ◽  
Catherine Stampfl ◽  
Joseph Shapter ◽  
David Winkler ◽  
...  
Keyword(s):  
Machine Learning ◽  
Band Gap ◽  
Density Functional ◽  
2D Materials ◽  
Van Der Waals ◽  
Building Blocks ◽  
Machine Learning Techniques ◽  
Interlayer Distance ◽  
Computational Screening ◽  
Wide Range

Materials constructed from different van der Waals two-dimensional (2D) heterostructures offer a wide range of benefits, but these systems have been little studied because of their experimental and computational complextiy, and because of the very large number of possible combinations of 2D building blocks. The simulation of the interface between two different 2D materials is computationally challenging due to the lattice mismatch problem, which sometimes necessitates the creation of very large simulation cells for performing density-functional theory (DFT) calculations. Here we use a combination of DFT, linear regression and machine learning techniques in order to rapidly determine the interlayer distance between two different 2D heterostructures that are stacked in a bilayer heterostructure, as well as the band gap of the bilayer. Our work provides an excellent proof of concept by quickly and accurately predicting a structural property (the interlayer distance) and an electronic property (the band gap) for a large number of hybrid 2D materials. This work paves the way for rapid computational screening of the vast parameter space of van der Waals heterostructures to identify new hybrid materials with useful and interesting properties.

TOWARDS A MOLECULAR THEORY FOR THE VAN DER WAALS–MAXWELL DESCRIPTION OF FLUID PHASE TRANSITIONS

2002 ◽  
Vol 01 (02) ◽  
pp. 381-406 ◽  
Author(s):  
ANDRIY KOVALENKO ◽  
FUMIO HIRATA
Keyword(s):  
Hydrogen Bonding ◽  
Phase Transitions ◽  
Phase Diagrams ◽  
Equations Of State ◽  
Van Der Waals ◽  
Fluid Phase ◽  
Carbon Aerogel ◽  
Molecular Fluids ◽  
Wide Range ◽  
Realistic Interaction

We briefly review developments of theories for phase transitions of molecular fluids and mixtures, from semi-phenomenological approaches providing equations of state with adjustable parameters to first-principles microscopic methods qualitatively correct for a variety of molecular models with realistic interaction potentials. We further present the generalization of the van der Waals–Maxwell description of fluid phase diagrams to account for chemical specificities of polar molecular fluids, such as hydrogen bonding. Our theory uses the reference interaction site model (RISM) integral equation approach complemented with the new closure we have proposed (KH approximation), successful over a wide range of density from gas to liquid. The RISM/KH theory is applied to the known three-site models of water, methanol, and hydrogen fluoride. It qualitatively reproduces their vapor-liquid phase diagrams and the structure in the gas as well as liquid phases, including hydrogen bonding. Furthermore, phase transitions of water and methanol sorbed in nanoporous carbon aerogel are described by means of the replica generalization of the RISM approach we have developed. The changes as compared to the bulk fluids are in agreement with simulations and experiment. The RISM/KH theory is promising for description of phase transitions in various associating fluids, in particular, electrolyte as well as non-electrolyte solutions and ionic liquids.

scholarly journals Manipulable Electronic and Optical Properties of Two-Dimensional MoSTe/MoGe2N4 van der Waals Heterostructures

Nanomaterials ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3338
Author(s):  
Jiali Wang ◽  
Xiuwen Zhao ◽  
Guichao Hu ◽  
Junfeng Ren ◽  
Xiaobo Yuan
Keyword(s):  
Optical Properties ◽  
Absorption Coefficient ◽  
High Performance ◽  
Density Functional ◽  
Van Der Waals ◽  
Two Dimensional ◽  
Van Der Waals Heterostructures ◽  
Electronic And Optical Properties ◽  
Wide Range ◽  
Direct Band

van der Waals heterostructures (vdWHs) can exhibit novel physical properties and a wide range of applications compared with monolayer two-dimensional (2D) materials. In this work, we investigate the electronic and optical properties of MoSTe/MoGe2N4 vdWH under two different configurations using the VASP software package based on density functional theory. The results show that Te4-MoSTe/MoGe2N4 vdWH is a semimetal, while S4-MoSTe/MoGe2N4 vdWH is a direct band gap semiconductor. Compared with the two monolayers, the absorption coefficient of MoSTe/MoGe2N4 vdWH increases significantly. In addition, the electronic structure and the absorption coefficient can be manipulated by applying biaxial strains and changing interlayer distances. These studies show that MoSTe/MoGe2N4 vdWH is an excellent candidate for high-performance optoelectronic devices.

scholarly journals Wafer scale synthesis of organic semiconductor nanosheets for van der Waals heterojunction devices

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Sirri Batuhan Kalkan ◽  
Emad Najafidehaghani ◽  
Ziyang Gan ◽  
Fabian Alexander Christian Apfelbeck ◽  
Uwe Hübner ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Physical Vapor Deposition ◽  
Field Effect Transistors ◽  
Van Der Waals ◽  
Transition Metal Dichalcogenides ◽  
Wafer Scale ◽  
Heterojunction Devices ◽  
Wide Range ◽  
Conformal Electronics ◽  
Metal Dichalcogenides

AbstractOrganic semiconductors (OSC) are widely used for consumer electronic products owing to their attractive properties such as flexibility and low production cost. Atomically thin transition metal dichalcogenides (TMDs) are another class of emerging materials with superior electronic and optical properties. Integrating them into van der Waals (vdW) heterostructures provides an opportunity to harness the advantages of both material systems. However, building such heterojunctions by conventional physical vapor deposition (PVD) of OSCs is challenging, since the growth is disrupted due to limited diffusion of the molecules on the TMD surface. Here we report wafer-scale (3-inch) fabrication of transferable OSC nanosheets with thickness down to 15 nm, which enable the realization of heterojunction devices. By controlled dissolution of a poly(acrylic acid) film, on which the OSC films were grown by PVD, they can be released and transferred onto arbitrary substrates. OSC crystal quality and optical anisotropy are preserved during the transfer process. By transferring OSC nanosheets (p-type) onto prefabricated electrodes and TMD monolayers (n-type), we fabricate and characterize various electronic devices including unipolar, ambipolar and antiambipolar field-effect transistors. Such vdW p-n heterojunction devices open up a wide range of possible applications ranging from ultrafast photodetectors to conformal electronics.

scholarly journals Coexistence of plastic and partially diffusive phases in a helium-methane compound

2020 ◽  
Vol 7 (10) ◽  
pp. 1540-1547
Author(s):  
Hao Gao ◽  
Cong Liu ◽  
Andreas Hermann ◽  
Richard J Needs ◽  
Chris J Pickard ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Diagram ◽  
First Principles ◽  
Van Der Waals ◽  
Van Der Waals Interactions ◽  
First Principles Calculations ◽  
Helium Atoms ◽  
Wide Range ◽  
Pure Methane ◽  
The Universe

Abstract Helium and methane are major components of giant icy planets and are abundant in the universe. However, helium is the most inert element in the periodic table and methane is one of the most hydrophobic molecules, thus whether they can react with each other is of fundamental importance. Here, our crystal structure searches and first-principles calculations predict that a He3CH4 compound is stable over a wide range of pressures from 55 to 155 GPa and a HeCH4 compound becomes stable around 105 GPa. As nice examples of pure van der Waals crystals, the insertion of helium atoms changes the original packing of pure methane molecules and also largely hinders the polymerization of methane at higher pressures. After analyzing the diffusive properties during the melting of He3CH4 at high pressure and high temperature, in addition to a plastic methane phase, we have discovered an unusual phase which exhibits coexistence of diffusive helium and plastic methane. In addition, the range of the diffusive behavior within the helium-methane phase diagram is found to be much narrower compared to that of previously predicted helium-water compounds. This may be due to the weaker van der Waals interactions between methane molecules compared to those in helium-water compounds, and that the helium-methane compound melts more easily.

Buoyancy-driven coalescence of slightly deformable drops

1997 ◽  
Vol 346 ◽  
pp. 117-148 ◽  
Author(s):  
MICHAEL A. ROTHER ◽  
ALEXANDER Z. ZINCHENKO ◽  
ROBERT H. DAVIS
Keyword(s):  
Thin Film ◽  
Van Der Waals ◽  
Small Deformation ◽  
Boundary Integral ◽  
Small Scale ◽  
Thin Film Equations ◽  
Present Solution ◽  
Wide Range ◽  
Van Der Waals Attraction ◽  
Medium Viscosity

The simultaneous effect of small deformation and short-range van der Waals attraction on the coalescence efficiency of two different-sized slowly sedimenting drops is considered. For spherical drops, it has been shown previously that the tangential mobility of drop surfaces makes collision possible even without van der Waals attraction; on the other hand, even a small amount of deformation precludes drops from coming into contact unless van der Waals attraction is accounted for. In the present work, the conditions are delineated when these two small-scale factors, acting in opposite directions, have a considerable combined effect on the coalescence efficiency. The problem is solved by matched asymptotic expansions valid for small capillary numbers (Ca). The outer solution, for two spherical drops moving in apparent contact without van der Waals attraction, determines the contact force as a function of time. This force is used as the driving force for the inner solution of the relevant integro-differential thin-film equations (coupling the flow in the small-gap region to that inside the drops) to determine whether coalescence occurs during the apparent contact motion. The initial gap profile for the inner solution is provided by matching with the outer trajectory for spherical drops approaching contact.The analysis shows that, for Ca[Lt ]1, the near-contact deformation is mainly axisymmetric, greatly simplifying the inner solution; nevertheless, determination of the critical horizontal offsets leading to coalescence and the parametric analysis are computationally very intensive. To facilitate these tasks, a substantially new, highly efficient, and absolutely stable numerical method for solving stiff thin-film equations is developed. Unlike for spherical drops, when the upstream intersection area is a circle, the existence of a second coalescence zone for deformable drops is found over much of the parameter space. Results are mapped out for a range of four dimensionless parameters (capillary number, size and drop-to-medium viscosity ratios, dimensionless Hamaker parameter). As a physical application, predicted coalescence efficiencies are shown for a system of ethyl salicylate drops in diethylene glycol.The present solution extends the range of drop sizes where the coalescence efficiencies are known theoretically and can be used in drop population dynamics. Comparison with full three-dimensional boundary-integral calculations for deformable drops without van der Waals attraction is also made to demonstrate that, when the drop-to-medium viscosity ratio is of the order of unity, the present asymptotic approach is valid in a wide range of small and moderately small capillary numbers.

scholarly journals Tunable Negative Poisson’s Ratio in Van der Waals Superlattice

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xiaowen Li ◽  
Xiaobin Qiang ◽  
Zhenhao Gong ◽  
Yubo Zhang ◽  
Penglai Gong ◽  
...  
Keyword(s):  
Poisson’S Ratio ◽  
Electronic Band Structure ◽  
Hexagonal Boron Nitride ◽  
Van Der Waals ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Electronic Band ◽  
Mechanical Metamaterials ◽  
Wide Range ◽  
Negative Poisson's Ratio

Negative Poisson’s ratio (NPR) materials are functional and mechanical metamaterials that shrink (expand) longitudinally after being compressed (stretched) laterally. By using first-principles calculations, we found that Poisson’s ratio can be tuned from near zero to negative by different stacking modes in van der Waals (vdW) graphene/hexagonal boron nitride (G/h-BN) superlattice. We attribute the NPR effect to the interaction of pz orbitals between the interfacial layers. Furthermore, a parameter calculated by analyzing the electronic band structure, namely, distance-dependent hopping integral, is used to describe the intensity of this interaction. We believe that this mechanism is not only applicable to G/h-BN superlattice but can also explain and predict the NPR effect in other vdW layered superlattices. Therefore, the NPR phenomenon, which was relatively rare in 3D and 2D materials, can be realized in the vdW superlattices by different stacking orders. The combinations of tunable NPRs with the excellent electrical/optical properties of 2D vdW superlattices will pave a novel avenue to a wide range of multifunctional applications.

scholarly journals Waveguide Schottky photodetector with tunable barrier based on Ti3C2T x /p-Si van der Waals heterojunction

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Changming Yang ◽  
Shiyu Qin ◽  
Yan Zuo ◽  
Yang Shi ◽  
Tong Bie ◽  
...  
Keyword(s):  
Work Function ◽  
Vacuum Annealing ◽  
Van Der Waals ◽  
Blue Shift ◽  
High Specific Surface Area ◽  
Flexible Working ◽  
Wide Range ◽  
Wavelength Tunability ◽  
Potential Applications ◽  
Simple Surface

Abstract MXene, a new advanced two-dimensional material, has attracted great attention in energy storage, transparent electrodes, and electromagnetic shielding due to its high conductivity, high specific surface area, and hydrophilic surface. Given the solution-processability and tunable work function, MXene also holds great potential for wide-range photodetection and integrated optics. Here, we demonstrate a waveguide integrated Schottky photodetector based on Ti3C2T x /Si van der Waals heterojunction. Specifically, the barrier of the Schottky photodetector can be adjusted by using simple surface treatment. The work function of the Ti3C2T x is reduced from 4.66 to 4.43 eV after vacuum annealing, and the barrier height of Ti3C2T x /p-Si Schottky junction is correspondingly increased from 0.64 to 0.72 eV, leading to 215 nm working wavelength blue-shift. The photodetector exhibits working wavelength tunability in short-wavelength infrared regions due to the engineered Schottky barrier. To our best knowledge, this is the first demonstration of utilizing MXene in waveguide-integrated photodetection, showing the potential applications for various scenarios thanks to the flexible working wavelength range induced by the tunable barrier.

scholarly journals The depletion attraction: an underappreciated force driving cellular organization

2006 ◽  
Vol 175 (5) ◽  
pp. 681-686 ◽  
Author(s):  
Davide Marenduzzo ◽  
Kieran Finan ◽  
Peter R. Cook
Keyword(s):  
Van Der Waals ◽  
Cellular Structures ◽  
Cellular Organization ◽  
Chromatin Loops ◽  
Wide Range ◽  
Ionic Bonds ◽  
In Cells

Cellular structures are shaped by hydrogen and ionic bonds, plus van der Waals and hydrophobic forces. In cells crowded with macromolecules, a little-known and distinct force—the “depletion attraction”—also acts. We review evidence that this force assists in the assembly of a wide range of cellular structures, ranging from the cytoskeleton to chromatin loops and whole chromosomes.

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