arXiv subjects

Wengen Ouyang

Publications and source records attributed to Wengen Ouyang.

At least 19 recordsLinked to original sources

arXiv2026

Strain and Twist Engineering of Interfacial Thermal Transport in Homo- and Hetero-Interfaces of Graphene and Hexagonal Boron Nitride

A dramatic difference between the vertical thermal conductance response of homogeneous and heterogeneous graphene/h-BN interfaces to external mechanical perturbations, is predicted. Homogeneous graphene and h-BN interfaces exhibit strong conductance reduction for both in-plane strain and interfacial twist. Conversely, the vertical thermal conductance of the heterogeneous graphene/h-BN junction is insensitive to twist deformations but shows significant increase or decrease under compressive or tensile strains, respectively. Our atomistic simulations predictions are rationalized by Fermi's golden rule and density of phonon modes analyses, indicating that vertical phonons and local stacking configurations have a central role in the interlayer heat transport behavior. A simple phenomenological model, based on local interlayer distance and stacking, captures well the dependence of vertical heat conductance on strain and twist deformations.

cond-mat.mes-hall↗

arXiv2026

Persistent incommensurate amorphous/crystalline meta-interfaces enable engineering-grade superlubricity

Friction dissipates a substantial portion of global energy, motivating the pursuit of superlubricity, a state of near-zero friction, in real-world systems. Conventional approaches rely on crystalline lattice mismatch to suppress periodic energy barriers, but real interfaces invariably contain defects, edges and grain boundaries that restore high-friction states. Here we introduce a materials-agnostic strategy based on amorphous/crystalline heterointerfaces to achieve robust superlubricity under engineering-relevant conditions. Using diamond-like carbon (DLC) and crystalline MoS2 as a model system, we show through experiments and atomistic simulations that their interface remains incommensurate at all orientations and exhibits vanishing energy barriers during friction. In contrast, twisted MoS2 bilayers readily reorient into commensurate, high-friction states. We scale this effect by fabricating laser-patterned arrays of DLC/MoS2 meta-contacts reinforced with Ti3C2Tx MXene, forming hierarchical interfaces that sustain a friction coefficient of ~0.008 over 100000 cycles under combined extreme conditions: millimetre-scale contact size, 12.7 GPa contact pressure and RH 40% air. This unprecedented performance arises from four synergistic factors: intrinsic incommensurability at amorphous/crystalline interface, the rigidity of DLC support, MXene-based mechanical reinforcement and normalized load distribution by geometric patterning. These findings establish a general design paradigm that extends structural superlubricity from nanoscale model systems to practical technologies for sustainable engineering.

cond-mat.mtrl-sci↗

arXiv2026

A biomimetic feedback loop for sustaining self-lubrication and wear resistance

Intelligent materials that self-sense and self-regulate are an emerging frontier in sustainable technology. Here we introduce Cu(Au)/C nanocomposite films that act as bioinspired self-adjusting lubricants. In these films, frictional heating triggers melting and migration of soft metal nanoparticles (NPs) such as Cu or Au along nano-pores to the friction interface, where the metal catalyzes the in-situ formation of ordered carbon nano-structures. Real-time monitoring of friction coefficient, electrical resistance(R), and metal release confirms an autonomous cycle: high friction coefficient generates heat, melting the metal NPs; the migrating metal then lowers friction coefficent by creating low-friction nanostructures, which reduces heat and arrests further migration until friction rises again. This self-limiting feedback enables stable ultra-low friction (~0.04) and an exceptional wear life (>40 km) even in high vacuum. By utilizing friction-derived heat as an intrinsic activation signal, our system establishes a general paradigm for intelligent, self-regulating materials with applications extending beyond tribology.

cond-mat.mtrl-sci↗

arXiv2026

Modular hybrid machine learning and physics-based potentials for scalable modeling of van der Waals heterostructures

Accurately modeling the structural reconstruction and thermodynamic behavior of van der Waals (vdW) heterostructures remains a significant challenge due to the limitations of conventional force fields in capturing their complex mechanical, thermal, electronic, and tribological properties. To address these limitations, we develop a hybrid framework that combines single-layer machine-learned potential ($s$MLP) with physics-based anisotropic interlayer potential (ILP), effectively decoupling intralayer and interlayer interactions. This $s$MLP+ILP approach modularizes the modeling of vdW heterostructures like assembling LEGOs, reducing the required training configurations by at least an order of magnitude compared to the pure MLP approach, while retaining predictive accuracy and computational efficiency. We validate our framework by accurately reproducing the mechanical and thermal transport properties of graphite and bulk hexagonal boron nitride ($h$-BN), and by resolving intricate Moiré patterns in graphene/$h$-BN bilayer and graphene/graphene/$h$-BN trilayer heterostructures, achieving excellent agreement with experimental observations. Leveraging the developed $s$MLP+ILP approach, we reveal the stacking order-dependent formation of Moir{é} superlattice in trilayer graphene/$h$-BN/MoS$_2$ heterostructures, demonstrating its ability to accurately model large-scale vdW systems comprising hundreds of thousands of atoms with near $ab$ $initio$ precision. These findings demonstrate that the hybrid $s$MLP+ILP framework remarkably outperforms existing pure machine-learned or empirical potentials, offering a scalable and transferable solution for accurately and extensively modeling complex vdW materials across diverse applications, including sliding ferroelectricity, thermal management, resistive switching, and superlubric nanodevices.

physics.comp-ph↗

arXiv2025

PYSED: A tool for extracting kinetic-energy-weighted phonon dispersion and lifetime from molecular dynamics simulations

Machine learning potential-driven molecular dynamics (MD) simulations have significantly enhanced the predictive accuracy of thermal transport properties across diverse materials. However, extracting phonon-mode-resolved insights from these simulations remains a critical challenge. Here, we introduce PYSED, a Python-based package built on the spectral energy density (SED) method, designed to efficiently compute kinetic-energy-weighted phonon dispersion and extract phonon lifetime from large-scale MD simulation trajectories. By integrating high-accuracy machine-learned neuroevolution potential (NEP) models, we validate and showcase the effectiveness of the implemented SED method across systems of varying dimensionalities. Specifically, the NEP-driven MD-SED accurately reveals how phonon modes are affected by strain in carbon nanotubes, as well as by interlayer coupling strengths and the twist angles in two-dimensional molybdenum disulfide. For three-dimensional systems, the SED method effectively establishes the thermal transport regime diagram for metal-organic frameworks, distinguishing between particlelike and wavelike propagation regions. Moreover, using bulk silicon as an example, we show that phonon SED can efficiently capture quantum dynamics based on path-integral trajectories. The PYSED package bridges MD simulations with detailed phonon-mode insights, delivering a robust tool for investigating thermal transport properties with detailed mechanisms across various materials.

physics.comp-ph↗

arXiv2025

Accurate Modeling of Interfacial Thermal Transport in van der Waals Heterostructures via Hybrid Machine Learning and Registry-Dependent Potentials

Two-dimensional transition metal dichalcogenides (TMDs) exhibit remarkable thermal anisotropy due to their strong intralayer covalent bonding and weak interlayer van der Waals (vdW) interactions. However, accurately modeling their thermal transport properties remains a significant challenge, primarily due to the computational limitations of density functional theory (DFT) and the inaccuracies of classical force fields in non-equilibrium regimes. To address this, we use a recently developed hybrid computational framework that combines machine learning potential (MLP) for intralayer interactions with registry-dependent interlayer potential (ILP) for anisotropic vdW interlayer interaction, achieving near quantum mechanical accuracy. This approach demonstrates exceptional agreement with DFT calculations and experimental data for TMD systems, accurately predicting key properties such as lattice constants, bulk modulus, moiré reconstruction, phonon spectra, and thermal conductivities. The scalability of this method enables accurate simulations of TMD heterostructures with large-scale moiré superlattices, making it a transformative tool for the design of TMD-based thermal metamaterials and devices, bridging the gap between accuracy and computational efficiency.

physics.comp-ph↗

arXiv2025

Moiré-Driven Interfacial Thermal Transport in Twisted Transition Metal Dichalcogenides

Cross-plane thermal conductivity in homogeneous transition metal dichalcogenides (TMDs) exhibits a strong dependence on twist angle, originating from atomic reconstruction within moiré superlattices. This reconstruction redistributes interlayer stacking modes, reducing high-efficiency thermal transport regions and softening the transverse acoustic phonon modes as the twist angle increases. We propose a general theoretical expression to capture this behavior, validated against non-equilibrium molecular dynamics simulations across both homo- and heterogeneous twisted TMDs structures, as well as homogeneous twisted graphene and hexagonal boron nitride stacks. Our model demonstrates that the interfacial thermal conductance (ITC) scales with the twist angle ($θ$) as $\ln{\left(\text{ITC}\right)} \propto e^{-\sqrtθ}$. These findings advance the understanding of twist-engineered interfacial thermal transport, offering design principles for optimizing thermal management in devices based on van der Waals layered materials.

cond-mat.mtrl-sci↗

arXiv2025

Probing the ideal limit of interfacial thermal conductance in two-dimensional van der Waals heterostructures

Probing the ideal limit of interfacial thermal conductance (ITC) in two-dimensional (2D) heterointerfaces is of paramount importance for assessing heat dissipation in 2D-based nanoelectronics. Using graphene/hexagonal boron nitride (Gr/$h$-BN), a structurally isomorphous heterostructure with minimal mass contrast, as a prototype, we develop an accurate yet highly efficient machine-learned potential (MLP) model, which drives nonequilibrium molecular dynamics (NEMD) simulations on a realistically large system with over 300,000 atoms, enabling us to report the ideal limit range of ITC for 2D heterostructures at room temperature. We further unveil an intriguing stacking-sequence-dependent ITC hierarchy in the Gr/$h$-BN heterostructure, which can be connected to moiré patterns and is likely universal in van der Waals layered materials. The underlying atomic-level mechanisms can be succinctly summarized as energy-favorable stacking sequences facilitating out-of-plane phonon energy transmission. This work demonstrates that MLP-driven MD simulations can serve as a new paradigm for probing and understanding thermal transport mechanisms in 2D heterostructures and other layered materials.

physics.comp-ph↗

arXiv2024

Frictional Dissipation and Scaling Laws at van der Waals Interface: The Key Role of Elastic Pinning of Moiré at Edges and Corners

Van der Waals heterogeneous interfaces are promising candidates for the scaling up of structural superlubricity to meet practical applications. Several factors, however, have been identified that may eliminate superlubricity. Elasticity is one such intrinsic factor, where shear induced lattice reconstruction leads to local interfacial pinning, even at clean pristine contacts. Here, through detailed atomistic simulations, we reveal that incomplete moiré tile pinning at the corners and edges of finite sliders dominates friction from the nano- to the microscales. We further demonstrate that slider shape tailoring and twisting allow to control energy dissipation and its scaling with contact size, thus opening the way to achieve large-scale superlubricity.

cond-mat.mes-hall↗

arXiv2024

Ultra-Long Homochiral Graphene Nanoribbons Grown Within h-BN Stacks for High-Performance Electronics

Van der Waals encapsulation of two-dimensional materials within hexagonal boron nitride (h-BN) stacks has proven to be a promising way to create ultrahigh-performance electronic devices. However, contemporary approaches for achieving van der Waals encapsulation, which involve artificial layer stacking using mechanical transfer techniques, are difficult to control, prone to contamination, and unscalable. Here, we report on the transfer-free direct growth of high-quality graphene nanoribbons (GNRs) within h-BN stacks. The as-grown embedded GNRs exhibit highly desirable features being ultralong (up to 0.25 mm), ultranarrow ( < 5 nm), and homochiral with zigzag edges. Our atomistic simulations reveal that the mechanism underlying the embedded growth involves ultralow GNR friction when sliding between AA'-stacked h-BN layers. Using the grown structures, we demonstrate the transfer-free fabrication of embedded GNR field-effect devices that exhibit excellent performance at room temperature with mobilities of up to 4,600 $cm^{2} V^{-1} s^{-1}$ and on-off ratios of up to $10^{6}$. This paves the way to the bottom-up fabrication of high-performance electronic devices based on embedded layered materials.

cond-mat.mes-hall↗

arXiv2023

Shape-dependent friction scaling laws in twisted layered material interfaces

Static friction induced by moiré superstructure in twisted incommensurate finite layered material interfaces reveals unique double periodicity and lack of scaling with contact size. The underlying mechanism involves compensation of incomplete moiré tiles at the rim of rigid polygonal graphene flakes sliding atop fixed graphene or h-BN substrates. The scaling of friction (or lack thereof) with contact size is found to strongly depend on the shape of the slider and the relative orientation between its edges and the emerging superstructure, partially rationalizing scattered experimental data. With careful consideration of the flake edge orientation, twist angle, and sliding direction along the substrate, one should therefore be able to achieve large-scale superlubricity via shape tailoring.

physics.app-ph↗

arXiv2023

Anisotropic Interlayer Force Field for Group-VI Transition Metal Dichalcogenides

An anisotropic interlayer force field that describes the interlayer interactions in homogeneous and heterogeneous interfaces of group-VI transition metal dichalcogenides (MX2 where M = Mo, W and X = S, Se) is presented. The force field is benchmarked against density functional theory calculations for bilayer systems within the Heyd-Scuseria-Ernzerhof hybrid density functional approximation, augmented by a nonlocal many-body dispersion treatment of long-range correlation. The parametrization yields good agreement with reference calculations of binding energy curves and sliding potential energy surfaces. It is found to be transferable to TMD junctions outside the training set that contain the same atom types. Calculated bulk moduli agree with most previous dispersion corrected DFT predictions, which underestimate available experimental values. Calculated phonon spectra of the various junctions under consideration demonstrate the importance of appropriately treating the anisotropic nature of layered interfaces. Considering our previous parameterization for MoS2, the interlayer potential enables accurate and efficient large-scale simulations of the dynamical, tribological, and thermal transport properties of a large set of homogeneous and heterogeneous TMD interfaces.

cond-mat.mtrl-sci↗

arXiv2023

Anisotropic Interfacial Force Field for Interfaces of Water with Hexagonal Boron Nitride

This study introduces an anisotropic interfacial potential that provides an accurate description of the van der Waals (vdW) interactions between water and hexagonal boron nitride (h-BN) at their interface. Benchmarked against the strongly constrained and appropriately normed (SCAN) functional, the developed force field demonstrates remarkable consistency with reference data sets, including binding energy curves and sliding potential energy surfaces for various configurations involving a water molecule adsorbed atop the h-BN surface. These findings highlight the significant improvement achieved by the developed force field in empirically describing the anisotropic vdW interactions of the water/h-BN heterointerfaces. Utilizing this anisotropic force field, molecular dynamics simulations demonstrate that atomically-flat pristine h-BN exhibits inherent hydrophobicity. However, when atomic-step surface roughness is introduced, the wettability of h-BN undergoes a significant change, leading to a hydrophilic nature. The calculated water contact angle (WCA) for the roughened h-BN surface is approximately 64°, which closely aligns with experimental WCA values ranging from 52° to 67°. These findings indicate the high probability of the presence of atomic steps on the surfaces of experimental h-BN samples, emphasizing the need for further experimental verification. The development of the anisotropic interfacial force field for accurately describing interactions at the water/h-BN heterointerfaces is a significant advancement in accurately simulating the wettability of two-dimensional (2D) materials, offering a reliable tool for studying the dynamic and transport properties of water at these interfaces, with implications for materials science and nanotechnology.

physics.chem-ph↗

arXiv2023

Twist-Dependent Anisotropic Thermal Conductivity in Homogeneous MoS$_2$ Stacks

Thermal transport property of homogeneous twisted molybdenum disulfide (MoS$_2$) is investigated using non-equilibrium molecular dynamics simulations with the state-of-art force fields. The simulation results demonstrate that the cross-plane thermal conductivity strongly depends on the interfacial twist angle, while it has only a minor effect on the in-plane thermal conductivity, exhibiting a highly anisotropic nature. A frequency-decomposed phonon analysis showed that both the cross-plane and in-plane thermal conductivity of MoS$_2$ are dominated by the low-frequency phonons below 15 THz. As the interfacial twist angle increases, these low-frequency phonons significantly attenuate the phonon transport across the interface, leading to impeded cross-plane thermal transport. However, the in-plane phonon transport is almost unaffected, which allows for maintaining high in-plane thermal conductivity. Additionally, our study revealed the strong size dependence for both cross-plane and in-plane thermal conductivities due to the low-frequency phonons of MoS$_2$. The maximum in-plane to cross-plane thermal anisotropy ratio is estimated as 400 for twisted MoS$_2$ from our simulation, which is in the same order of magnitude as recent experimental results (~900). Our study highlights the potential of twist engineering as a tool for tailoring the thermal transport properties of layered materials.

physics.comp-ph↗

arXiv2022

Registry-Dependent Potential for interfaces of water with graphene

An anisotropic interlayer potential that can accurately describe the van der Waals interaction of the water-graphene interface is presented. The force field is benchmarked against the many-body dispersion-corrected density functional theory. The parameterization of ILP yields good agreement with the reference dataset of binding energy curves and sliding potential energy surfaces for various configurations of a water molecule deposited on monolayer graphene, indicating the developed force field enhancing significantly the accuracy in the empirical description of water-graphene interfacial interactions. The water contact angles of monolayer and multilayer graphene extracted from molecular dynamics simulations based on this force field are close to the experimental measurements and predict the hydrophilic nature of graphene. The theoretical approach proposed in this work can be easily extended to mimic the van der Waals interactions between water molecules and various two-dimensional layered materials for studying their wetting properties.

physics.chem-ph↗

arXiv2022

Origin of frictional scaling law in circular twist layered interfaces: simulations and theory

Structural superlubricity based on twisted layered materials has stimulated great research interests. Recent MD simulations show that the circular twisted bilayer graphene (tBLG) presenting a size scaling of friction with strong Moiré-level oscillations. To reveal the physical origin of observed abnormal scaling, we proposed a theoretical formula and derived the analytic expression of frictional size scaling law of tBLG. The predicted twist angle dependent scaling law agrees well with MD simulations and provides a rationalizing explanation for the scattered power scaling law measured in various experiments. Finally, we show clear evidence that the origin of the scaling law comes from the Moiré boundary, that is, the remaining part of the twisted layered interfaces after deleting the internal complete Moiré supercells. Our work provides new physical insights into the friction origin of layered materials and highlights the importance of accounting for Moiré boundary in the thermodynamic models of layered materials.

physics.app-ph↗

arXiv2022

Catalytic growth of ultralong graphene nanoribbons on insulating substrates

Graphene nanoribbons (GNRs) with widths of a few nanometres are promising candidates for future nano-electronic applications due to their structurally tunable bandgaps, ultrahigh carrier mobilities, and exceptional stability. However, the direct growth of micrometre-long GNRs on insulating substrates, which is essential for the fabrication of nano-electronic devices, remains an immense challenge. Here, we report the epitaxial growth of GNRs on an insulating hexagonal boron nitride (h-BN) substrate through nanoparticle-catalysed chemical vapor deposition (CVD). Ultra-narrow GNRs with lengths of up to 10 μm are synthesized. Remarkably, the as-grown GNRs are crystallographically aligned with the h-BN substrate, forming one-dimensional (1D) moiré superlattices. Scanning tunnelling microscopy reveals an average width of 2 nm and a typical bandgap of ~1 eV for similar GNRs grown on conducting graphite substrates. Fully atomistic computational simulations support the experimental results and reveal a competition between the formation of GNRs and carbon nanotubes (CNTs) during the nucleation stage, and van der Waals sliding of the GNRs on the h-BN substrate throughout the growth stage. Our study provides a scalable, single-step method for growing micrometre-long narrow GNRs on insulating substrates, thus opening a route to explore the performance of high-quality GNR devices and the fundamental physics of 1D moiré superlattices.

cond-mat.mes-hall↗

arXiv2021

Thermodynamic model of twisted bilayer graphene: Configuration entropy matters

Twisted bilayer materials have attracted tremendous attention due to their unique and novel properties. Here, we derive a thermodynamic model for twisted bilayer graphene (tBLG) within the framework of the classical statistical mechanics, based on which, the configuration entropy reflecting the number of micro-status in moire unit-cells, is directly derived from the Helmholtz free energy with a clear physical interpretation. More importantly, we show the configuration entropy of tBLG relative to the AB-stacked bilayer graphene is proportional to the logarithmic function of the ratio of moire period and the atomic lattice constant, which we found dominates the Helmholtz free energy of tBLG and can well explain experimental observations in superlubric contacts. Our work provides a theoretical foundation for studying moire effect of incommensurate contact interfaces and could facilitate twisting based applications such as superlubricity.

cond-mat.mes-hall↗