arXiv subjects

Yong-Wei Zhang

Publications and source records attributed to Yong-Wei Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Nonlocal Electrostatic Origin of Schottky-Barrier Variability in 2D Contacts

Electrical contacts often limit the performance of atomically thin semiconductor devices. The Schottky barrier height (SBH) is conventionally treated as a local interface property, yet reported values for the same metal/2D-semiconductor contact vary by hundreds of meV. Here we show that, in top contacts, the effective SBH exhibits a pronounced nonlocal electrostatic dependence on defects near the contact edge, beyond the conventional local interface framework. A nonlocal electrostatic model, supported by density-functional-theory-based transport calculations for Ti--MoS$_2$ and Au--MoS$_2$, captures the large, metal-dependent variations in SBH as a function of defect position relative to the contact edge. These results provide a unified explanation for the longstanding variability in experimentally extracted SBHs and establish nonlocal electrostatics, mediated by edge-proximal defects, as a key mechanism governing carrier injection in 2D contacts.

cond-mat.mtrl-sci↗

arXiv2025

Dual Role of Nb in Defect-Mediated Strength and Ductility of γ-TiAl Alloys

The origin of the superior high-temperature strength of γ-TiAl with high Nb addition remains highly controversial, largely due to the unclear role of Nb atoms. Using large-scale hybrid Monte Carlo and molecular dynamics simulations with a self-developed neural network potential,we show that Nb atoms predominantly occupy Ti sites and form short-range order with neighboring Al atoms, but a non-negligible fraction also occupies Al sites (NbAl) and promotes the formation of antisite defects (TiAl). Both the NbAl and TiAl antisites exceptionally reduce stacking fault energies and facilitate deformation twinning, thereby enhancing plasticity. Meanwhile, these substitutional and antisite defects also increase the Peierls stress of both screw and edge dislocations, which hinders dislocation motion to cause pronounced solid-solution strengthening. This work provides mechanistic insights into the dual role of Nb in enhancing both strength and ductility in γ-TiAl and further offers guidance for defect and composition engineering in advanced alloy systems.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous strain-dependent thermal conductivity in superelastic screw-dislocated graphites

The design of strain-stable, or even strain-enhanced thermal transport materials is critical for stable operation of high-performance electronic devices. However, most nanomaterials suffer from strain-induced degradation, with even minor tensile strains markedly reducing thermal conductivity. Here, we demonstrate that screw-dislocated graphites (SDGs), recently identified as topological semimetals, display an unusual increase in cross-plane thermal conductivity under both tensile and compressive strains, revealed by high-accuracy machine-learning-potential-driven non-equilibrium molecular dynamics. Notably, SDGs exhibit over 100% enhancement under tensile strains up to 80% along the dislocation axis, arising from strain-induced increase in dislocation interface tilt angle that elongates the effective heat transfer paths. Their thermal conductivity surpasses multilayer graphene by an order of magnitude. An analytical model is further derived linking thermal conductivity to dislocation number and strain, offering a predictive framework for designing strain-tunable screwdislocated structures. These findings highlight SDGs as a promising platform for high-performance electronic and wearable devices with tunable thermal properties.

cond-mat.mtrl-sci↗

arXiv2023

Sumanene monolayer of pure carbon: a two-dimensional Kagome-analogy lattice with desirable band gap, ultrahigh carrier mobility and strong exciton binding energy

Design and synthesis of novel two-dimensional (2D) materials that possess robust structural stability and unusual physical properties may open up enormous opportunities for device and engineering applications. Herein we propose a 2D sumanene lattice that be regarded as a derivative of the conventional Kagome lattice. Our tight-binding analysis demonstrates sumanene lattice contains two sets of Dirac cones and two sets of flat bands near the Fermi surface, distinctively different from the Kagome lattice. Using first-principles calculations, we theoretically suggest two possible routines for realization of stable 2D sumanene monolayers (named as a phase and b phase), and a-sumanene monolayer can be experimentally synthesized with chemical vapor deposition using C21H12 as a precursor. Small binding energies on Au(111) surface signify the possibility of their peel-off after grown on the noble metal substrate. Importantly, our GW plus Bethe-Salpeter equation calculations demonstrate both monolayers have moderate band gaps (1.94 eV for a) and ultrahigh carrier mobilities (3.4*104 cm2/Vs for a). In particular, a-sumanene monolayer possesses a strong exciton binding energy of 0.73 eV, suggesting potential applications in optics.

cond-mat.mtrl-sci↗

arXiv2023

Robust Sandwiched B/TM/B Structures by Metal Intercalating into Bilayer Borophene Leading to Excellent Hydrogen Evolution Reaction

Bilayer borophene, very recently synthesized on Ag and Cu, possesses extremely flat large surface and excellent conductivity. Besides, the van der Waals gap of bilayer borophene can be intercalated by metal atoms, thereby tailoring the properties of bilayer borophene. Herein, we propose that sandwiched B/TM/B (TM=Co, Ni, Cu, Pd) could be a new 2D formation by transiton metal atoms intercalated into bilayer borophene network, it is quiet robust with both energetic, structural and thermal stability, and exhibits heat resistance of at least 1300 K. Besides, it is novel platform for electrocatalytic hydrogen evolution reaction (HER). The interecalation metal atom serves as single-atomic catalyst, which acting the nonmetal boron layers. Beyond that, the transtion metal is protected by outside boron layers from being corroded by acidic/alkaline solution. B/Cux/B, B/Pdx/B and B/Alx/B with different metal coverage exhibit defect-independent extremely low HER free energy in the range of -0.162 ~ 0.179 eV, -0.134 ~ 0.183 eV and -0.082 ~ 0.086 eV which are comparable to noble metal Pt. Combining excellent conduction, high structural and thermal stability, low resistance to intercalated behaviour, effortless water splitting process, excellent defect-independent catalytic performance, cheapness and abundance of raw materials, free of corrodation, 2D sandwiched B/TM/B (TM=Co, Ni, Cu, Pd) is believed to promising for electrocatalytic HER applications.

cond-mat.mtrl-sci↗

arXiv2022

Sliding induced multiple polarization states in two-dimensional ferroelectrics

When the atomic layers in a non-centrosymmetric van der Waals structure slide against each other, the interfacial charge transfer results in a reversal of the structures spontaneous polarization. This phenomenon is known as sliding ferroelectricity and it is markedly different from conventional ferroelectric switching mechanisms relying on ion displacement. Here, we present layer dependence as a new dimension to control sliding ferroelectricity. By fabricating 3R MoS2 of various thicknesses into dual-gate field-effect transistors, we obtain anomalous intermediate polarization states in multilayer 3R MoS2. Using results from ab initio density functional theory calculations, we propose a generalized model to describe the ferroelectric switching process in multilayer 3R MoS2 and to explain the formation of these intermediate polarization states. This work reveals the critical roles that layer number and interlayer dipole coupling play in sliding ferroelectricity and presents a new strategy for the design of novel sliding ferroelectric devices.

cond-mat.mtrl-sci↗

arXiv2022

The effects of point defect type, location, and density on the Schottky barrier height of Au/MoS2 hetero-junction: A first-principles study

Using DFT calculations, we investigate the effects of the type, location, and density of point defects in monolayer MoS2 on electronic structures and Schottky barrier heights (SBH) of Au/MoS2 heterojunction. Three types of point defects in monolayer MoS2, that is, S monovacancy, S divacancy and MoS (Mo substitution at S site) antisite defects, are considered. The following findings are revealed: (1) The SBH for the monolayer MoS2 with defects is universally higher than that for its defect-free counterpart. (2) S divacancy and MoS antisite defects increase the SBH to a larger extent than S monovacancy. (3) A defect located in the inner sublayer of MoS2, which is adjacent to Au substrate, increases the SBH to a larger extent than that in the outer sublayer of MoS2. (4) An increase in defect density increases the SBH. These findings indicate a large variation of SBH with the defect type, location, and concentration. We also compare our results with previously experimentally measured SBH for Au/MoS2 contact and postulate possible reasons for the large differences among existing experimental measurements and between experimental measurements and theoretical predictions. The findings and insights revealed here may provide practice guidelines for modulation and optimization of SBH in Au/MoS2 and similar heterojunctions via defect engineering.

cond-mat.mtrl-sci↗

arXiv2022

Anharmonic quantum thermal transport across a van der Waals interface

We investigate the anharmonic phonon scattering across a weakly interacting interface by developing a quantum mechanics-based theory. We find that the contribution from anharmonic three-phonon scatterings to interfacial thermal conductance can be cast into Landauer formula with transmission function being temperature-dependent. Surprisingly, in the weak coupling limit, the transmission due to anharmonic phonon scattering is unbounded with increasing temperature, which is physically impossible for two-phonon processes. We further reveal that the anharmonic contribution in a real heterogeneous interface (e.g., between graphene and monolayer molybdenum disulfide) can dominate over the harmonic process even at room temperature, highlighting the important role of anharmonicity in weakly interacting heterogeneous systems.

cond-mat.mes-hall↗

arXiv2022

Effects of high order interatomic potential on elastic phonon scatterings

Interatomic potentials beyond quadratic order provide scattering sources for phonon transport in lattice. By using a weakly-interacting interface model, we investigated the relation between the order of interatomic potential and the multiple-phonon scattering process. We find that high order interatomic potential not only causes multiple-phonon scattering processes, but also has significant impacts on elastic phonon scattering processes. Using fourth order potential as an example, we show that it can significantly affects elastic phonon scatterings, through the formation of localized phonons. Such impact is closely related to the correlations of interfacial atoms and it becomes more significant with increasing temperature. Our work suggests that it is insufficient to consider only quadratic potential to investigate elastic phonon transport.

cond-mat.mtrl-sci↗

arXiv2021

Extraordinary strain hardening from dislocation loops in defect-free Al nanocubes

The interaction of crystalline defects leads to strain hardening in bulk metals. Metals with high stacking fault energy (SFE), such as aluminum, tend to have low strain hardening rates due to an inability to form stacking faults and deformation twins. Here, we use in situ SEM mechanical compressions to find that colloidally synthesized defect-free 114 nm Al nanocubes combine a high linear strain hardening rate of 4.1 GPa with a high strength of 1.1 GPa. These nanocubes have a 3 nm self-passivating oxide layer that has a large influence on mechanical behavior and the accumulation of dislocation structures. Post-compression TEM imaging reveals stable prismatic dislocation loops and the absence of stacking faults. MD simulations relate the formation of dislocation loops and strain hardening to the surface oxide. These results indicate that slight modifications to surface and interfacial properties can induce enormous changes to mechanical properties in high SFE metals.

cond-mat.mtrl-sci↗

arXiv2021

The role of flexural coupling in heat dissipation from a two-dimensional layered material to its hexagonal boron nitride substrate

Understanding the limits of phononic heat dissipation from a two-dimensional layered material (2DLM) to its hexagonal boron nitride (h-BN) substrate and how it varies with the structure of the 2DLM is important for the design and thermal management of h-BN-supported nanoelectronic devices. We formulate an elasticity-based theory to model the phonon-mediated heat dissipation between a 2DLM and its h-BN substrate. By treating the h-BN substrate as a semi-infinite stack of harmonically coupled thin plates, we obtain semi-analytical expressions for the thermal boundary conductance (TBC) and interfacial phonon transmission spectrum. We evaluate the temperature-dependent TBC of the $N$-layer 2DLM (graphene or MoS$_{2}$) on different common substrates (h-BN vs. a-SiO$_{2}$) at different values of $N$. The results suggest that h-BN is substantially more effective for heat dissipation from MoS$_{2}$ than a-SiO$_{2}$ especially at large $N$. To understand the limitations of the our stack model, we also compare its predictions in the $N=\infty$ limit to those of the more exact Atomistic Green's Function model for the graphite-BN and molybdenite-BN interfaces. Our stack model provides clear insights into the key role of the flexural modes in the TBC and how the anisotropic elastic properties of h-BN affect heat dissipation.

cond-mat.mes-hall↗

arXiv2021

Theoretical analysis of thermal boundary conductance of MoS2-SiO2 and WS2-SiO2 interface

Understanding the physical processes involved in interfacial heat transfer is critical for the interpretation of thermometric measurements and the optimization of heat dissipation in nanoelectronic devices that are based on transition metal dichalcogenide (TMD) semiconductors. We model the phononic and electronic contributions to the thermal boundary conductance (TBC) variability for the MoS$_{2}$-SiO$_{2}$ and WS$_{2}$-SiO$_{2}$ interface. A phenomenological theory to model diffuse phonon transport at disordered interfaces is introduced and yields $G$=13.5 and 12.4 MW/K/m$^{2}$ at 300 K for the MoS$_{2}$-SiO$_{2}$ and WS$_{2}$-SiO$_{2} $ interface, respectively. We compare its predictions to those of the coherent phonon model and find that the former fits the MoS$_{2}$-SiO$_{2}$ data from experiments and simulations significantly better. Our analysis suggests that heat dissipation at the TMD-SiO$_{2}$ interface is dominated by phonons scattered diffusely by the rough interface although the electronic TBC contribution can be significant even at low electron densities ($n\leq10^{12}$ cm$^{-2}$) and may explain some of the variation in the experimental TBC data from the literature. The physical insights from our study can be useful for the development of thermally aware designs in TMD-based nanoelectronics.

cond-mat.mes-hall↗

arXiv2020

Gate-tunable cross-plane heat dissipation in single-layer transition metal dichalcogenides

Efficient heat dissipation to the substrate is crucial for optimal device performance in nanoelectronics. We develop a theory of electronic thermal boundary conductance (TBC) mediated by remote phonon scattering for the single-layer transition metal dichalcogenide (TMD) semiconductors MoS$_{2}$ and WS$_{2}$, and model their electronic TBC with different dielectric substrates (SiO$_{2}$, HfO$_{2}$ and Al$_{2}$O$_{3}$). Our results indicate that the electronic TBC is strongly dependent on the electron density, suggesting that it can be modulated by the gate electrode in field-effect transistors, and this effect is most pronounced with Al$_{2}$O$_{3}$. Our work paves the way for the design of novel thermal devices with gate-tunable cross-plane heat-dissipative properties.

cond-mat.mes-hall↗

arXiv2020

A potential superhard carbon allotrope: T5-carbon

A novel stable carbon allotrope is predicted by using first-principles calculations. This allotrope is obtained by replacing one of the two atoms in the primitive cell of diamond with a carbon tetrahedron, thus it contains five atoms in one primitive cell, termed T5-carbon. The stabilities of T5-carbon are checked in structural, thermal, vibrational and energy calculations. The calculations on electronic, thermal, and mechanical properties reveal that T5-carbon is a semiconductor with an indirect band gap of 3.18 eV, and has a lattice thermal conductivity of 409 W/mK. More importantly, the Vickers hardness of T5-carbon is 76.5 GPa which is lower than that of diamond but larger than those of T-carbon and cubic boron nitride, confirming the superhard properties of T5-carbon, suggesting its wide applications in mechanical devices.

cond-mat.mtrl-sci↗

arXiv2019

Design of Phosphorene for Hydrogen Evolution Performance Comparable to Platinum

Phosphorene, a monolayer of bulk black phosphorus, is promising for light harvest owing to its high charge mobility and tunable direct band gap covering a broad spectral range of light. Here, via atomic-scale first-principles simulations, we report a ultrahigh activity of hydrogen evolution reaction (HER) of phosphorene originated from defective activation. Quantitative evaluation of the Gibbs free energy of the ad desorption of hydrogen (H) to from phosphorene (delta_GH) reveals that atomic vacancies and edges play a dominant role in activating the reaction. We find that the defective states, empty and well-localized around the defect core, are compensated by H species. This induces a proper hydrogen interaction complying with the thermoneutral condition of the free energy (delta_GH=0) comparable to platinum. Our findings of the highly activating defective states suggest the design of non-metal HER catalysts with structural engineering of earth-abundant phosphorus structures.

cond-mat.mtrl-sci↗

arXiv2019

Surface-charge-mediated Formation of H-TiO2@Ni(OH)2 Heterostructures for High-Performance Supercapcitors

Supercapacitors or ultracapacitors are promising for efficient energy storage applications, owing to their high power density, high charge-discharge rates, and long cycle life performance. To achieve this goal, a large specific surface area, an high electronic conductivity and a fast cation intercalation de-intercalation process are generally required in the design and preparation of materials for high-performance supercapacitors. Recently, core-shell heterostructures with multifunctionalities are regarded as one of promising materials for supercapacitors or ultracapacitors applications. In particular, one-dimensional (1D) core-shell heterostructures have sparked great scientific and technological interests due to their high versatility and applicability as the essential components in nanoscale electronics, catalysis, chemical sensing, and energy conversion storage devices. Various metal metal oxide, metal metal, metal oxide metal oxide and metal oxide conductive polymers so far have been investigated. Transition metal hydroxide oxide Co3O4, Co(OH)2, MnO2, Mn(OH)2, NiO, Ni(OH)2 and their compounds storing energy by surface faradaic (redox) reactions were generally integrated with conducting scaffold to build core-shell structure. Intensive studies show that an enlarged active surface area of transition metal hydroxide oxide enables a promoted surface redox reaction and enhanced electrochemical performance. Therefore, controllable synthesis of a hierarchically porous construction with high surface areas is critically important for energy storage.

cond-mat.mtrl-sci↗

arXiv2019

Evolution of Intrinsic Vacancies and Prolonged Lifetime of Vacancy Clusters in Black Phosphorene

Due to the relatively low formation energies and highly mobile characteristics of atomic vacancies in phosphorene, understanding their evolutions becomes crucial for its structural integrity, chemical activities and applications. Herein, by combining first-principles calculations and kinetic Monte Carlo simulation, we investigate the time evolution and formation of atomic vacancy clusters from isolated monovacancies (MVs), aiming to uncover the mechanisms of diffusion, annihilation, reaction of these atomic vacancies. We find that while isolated MVs possess a highly mobile character, they react and form MV pairs which possess much lower mobility and high stability under ambient condition. We also show that the disappearance of MVs at the edge is quite slow due to the relatively high energy barrier, and as a result, around 80% of MVs remains even after two years under ambient condition. Our findings on one hand provide useful information for the structural repairing of phosphorene through chemical functionalization of these vacancy clusters, and on the other hand, suggest that these rather stable vacancy clusters may be used as an activated catalyst.

cond-mat.mtrl-sci↗

arXiv2019

Three-terminal interface as a thermoelectric generator beyond Seebeck effect

We investigate thermoelectric transport through interfaces with inelastic scatterings by developing a quantum theory, which has been extensively validated by existing theories. We find that under temperature bias, while a two-terminal conductor-insulator interface behaves only as a thermal resistor, a three-terminal conductor-insulator-conductor interface can function as an electricity generator caused by phonon-mediated electron scatterings with heat-charge current separation. Unlike conventional thermoelectrics which is a property of a bulk caused by the Seebeck effect, this thermoelectric behavior is a property of an interface driven by electron-phonon scatterings.

cond-mat.mes-hall↗