arXiv subjects

Quanshui Zheng

Publications and source records attributed to Quanshui Zheng.

At least 19 recordsLinked to original sources

arXiv2026

Edge-Dominated Twist Mechanics at van der Waals Interfaces

Despite the pivotal role of twist in modulating physical properties at van der Waals (vdW) interfaces, the mechanics governing torsional response remain poorly understood. Here, we probe twist mechanics at homo- and heterogeneous vdW interfaces, together with their sliding behaviors within a unified experimental framework. For both systems, the peak torque scales nearly linearly with contact area, in contrast to predictions from linear elastic and rigid models. Remarkably, while the sliding friction of the two interfaces diverges by over three orders of magnitude owing to different scaling laws, the corresponding torque follows the same linear scaling and differs by only about twenty-fold. Large-scale atomistic simulations reveal an edge-dominated yielding mechanism for torsional motion, wherein elastic reconstruction shifts the effective load-bearing region toward the edges, eliminating torque from the contact interior. This mechanism contrasts with the bulk-mediated stress transmission governing translational sliding, a distinction rooted in the different loading geometries inherent to the two motion modes, where torsional loading necessitates perimeter actuation, whereas sliding enables center-driven loading. This symmetry-imposed divergence demonstrates that translational and torsional properties cannot be predicted from one another at vdW interfaces, providing critical insights for the design of dynamically reconfigurable micro- and nanoelectromechanical devices.

cond-mat.mtrl-sci↗

arXiv2026

Observation of robust macroscale structural superlubricity

Structural superlubricity (SSL) promises nearly frictionless and wearless sliding, but has until now been considered a special and extreme interfacial phenomenon limited to micro- and nanoscale contacts. Here, we demonstrate robust macroscale SSL within a single sub-millimeter graphite contact. Previously reported near-zero friction coefficients, where friction is nearly independent of normal load, have only been observed at microscale contacts under low loads. Our system expands both contact size and load into the macroscopic regime, exhibiting friction coefficients that fluctuate around zero and reach values as low as $10^{-6}$ across a broad load range from 1 mN to 0.5 N. Negative friction coefficients are also observed. Similar behavior is observed at graphite/MoS$_2$ interfaces, indicating that macroscale SSL is a generalizable phenomenon across flat layered materials. These findings overturn long-standing scaling limitations and establish macroscale SSL as a paradigm-shifting platform for next-generation mechanical and electromechanical systems.

cond-mat.mtrl-sci↗

arXiv2025

On-Device Control of Electronic Friction

Friction causes mechanical energy dissipation and material degradation in machinery and devices. While phononic friction is well understood via anharmonic lattice dynamics, the physics of electronic friction remains unclear due to challenges in separating electronic degrees of freedom from phononic ones in experiments and analyzing the non-equilibrium interactions between ionic movement and electronic dynamics in theory. To tackle this problem, we construct a sliding device featuring 2D crystalline interfaces that possess ultra-smooth and minimally interacting surfaces, achieving the state of structural superlubricity with no wear and minimal friction. Using electrical and mechanical controls, we tuned the nature of interfacial electronic coupling and charge densities in materials in an on-device setting, which allows us to disentangle the electron and phonon contributions to friction. Our experimental data and theoretical analysis supported by first-principles calculations demonstrate that electronic friction can well surpass phononic contributions and dominate energy dissipation at structural superlubricity contacts. These findings offer fresh insights into the mechanism of electronic friction and promising opportunities for friction control in device applications.

cond-mat.mes-hall↗

arXiv2025

Observation of zero coefficient of friction above a critical pressure

Self-superlubricity is a highly anticipated phenomenon where certain solid pairs in contact, without lubricant, exhibit zero wear and virtually null static friction and coefficient of friction (CoF). We present the first experimental observation of self-superlubricity in a microscale single-crystalline graphite flake in contact with a nanoscale-rough Au substrate, achieved when the applied normal pressure exceeds a critical threshold. Theoretical analysis revealed that substrate roughness impedes full contact at low pressures, but increasing the pressure induces a transition to full contact, enabling self-superlubricity. We established a dimensionless criterion for this critical pressure, further validated by observing self-superlubricity between graphite and an atomically smooth sapphire substrate without requiring additional pressure. This breakthrough introduces a transformative principle for next-generation microsystems such as micro/nanoscale generators, motors, oscillators, sensors, etc., enabling reduced power consumption and extended operational lifetimes in applications such as 6G communication, humanoid robotics, and unmanned aerial vehicles.

cond-mat.mes-hall↗

arXiv2024

Comprehensive characterization of tumor therapeutic response with simultaneous mapping cell size, density, and transcytolemmal water exchange

Early assessment of tumor therapeutic response is an important topic in precision medicine to optimize personalized treatment regimens and reduce unnecessary toxicity, cost, and delay. Although diffusion MRI (dMRI) has shown potential to address this need, its predictive accuracy is limited, likely due to its unspecific sensitivity to overall pathological changes. In this work, we propose a new quantitative dMRI-based method dubbed EXCHANGE (MRI of water Exchange, Confined and Hindered diffusion under Arbitrary Gradient waveform Encodings) for simultaneous mapping of cell size, cell density, and transcytolemmal water exchange. Such rich microstructural information comprehensively evaluates tumor pathologies at the cellular level. Validations using numerical simulations and in vitro cell experiments confirmed that the EXCHANGE method can accurately estimate mean cell size, density, and water exchange rate constants. The results from in vivo animal experiments show the potential of EXCHANGE for monitoring tumor treatment response. Finally, the EXCHANGE method was implemented in breast cancer patients with neoadjuvant chemotherapy, demonstrating its feasibility in assessing tumor therapeutic response in clinics. In summary, a new, quantitative dMRI-based EXCHANGE method was proposed to comprehensively characterize tumor microstructural properties at the cellular level, suggesting a unique means to monitor tumor treatment response in clinical practice.

physics.med-ph↗

arXiv2024

Restriction-induced time-dependent transcytolemmal water exchange: Revisiting the Kärger exchange model

The Kärger model and its derivatives have been widely used to incorporate transcytolemmal water exchange rate, an essential characteristic of living cells, into analyses of diffusion MRI (dMRI) signals from tissues. The Kärger model consists of two homogeneous exchanging components coupled by an exchange rate constant and assumes measurements are made with sufficiently long diffusion time and slow water exchange. Despite successful applications, it remains unclear whether these assumptions are generally valid for practical dMRI sequences and biological tissues. In particular, barrier-induced restrictions to diffusion produce inhomogeneous magnetization distributions in relatively large-sized compartments such as cancer cells, violating the above assumptions. The effects of this inhomogeneity are usually overlooked. We performed computer simulations to quantify how restriction effects, which in images produce edge enhancements at compartment boundaries, influence different variants of the Kärger-model. The results show that the edge enhancement effect will produce larger, time-dependent estimates of exchange rates in e.g., tumors with relatively large cell sizes (>10 μm), resulting in overestimations of water exchange as previously reported. Moreover, stronger diffusion gradients, longer diffusion gradient durations, and larger cell sizes, all cause more pronounced edge enhancement effects. This helps us to better understand the feasibility of the Kärger model in estimating water exchange in different tissue types and provides useful guidance on signal acquisition methods that may mitigate the edge enhancement effect. This work also indicates the need to correct the overestimated transcytolemmal water exchange rates obtained assuming the Kärger-model.

physics.med-ph↗

arXiv2024

Phonon heat conduction across slippery interfaces in twisted graphite

Interlayer rotation in van der Waals (vdW) materials offers great potential for manipulating phonon dynamics and heat flow in advanced electronics with ever higher compactness and power density. However, despite extensive theoretical efforts in recent years, experimental measurements remain scarce especially due to the critical challenges of preparing single-crystalline twisted interfaces and probing interfacial thermal transport with sufficient resolution. Here, we exploited the intrinsic twisted interfaces in highly oriented pyrolytic graphite (HOPG). By developing novel experimental schemes based on microfabricated mesas, we managed to achieve simultaneous mechanical characterizations and thermal measurements. In particular, we pushed the HOPG mesas with a microprobe to identify and rotate single-crystalline intrinsic interfaces owing to their slippery nature as is well known in structural superlubricity. Remarkably, we observed over 30-fold suppression of thermal conductance for the slippery interfaces by using epitaxial graphite as a control. Nonetheless, the interfacial conductance remains around 600 $\mathrm{MWm^{-2}K^{-1}}$ which surpasses the highest values for artificially stacked vdW structures by more than five times. Further, atomic simulations revealed the predominant role of the transverse acoustic phonons. Together, our findings highlight a general physical picture that directly correlates interfacial thermal transport with sliding resistance, and lay the foundation for twist-enabled thermal management which are particularly beneficial to twistronics and slidetronics.

cond-mat.mes-hall↗

arXiv2022

Condensation Droplet Sieve

Large droplets emerging during dropwise condensation impair surface properties such as anti-fogging/frosting ability and heat transfer efficiency. How to spontaneously detach massive randomly distributed droplets with controlled sizes has remained a great challenge. Herein, we present a general solution called condensation droplet sieve, through fabricating microscale thin-walled lattice (TWL) structures coated with a superhydrophobic layer. Growing droplets were observed to jumped off this TWL surface with 100% probability once becoming slightly larger than the lattices. The maximum radius and residual volume of droplets were strictly confined to 16 μm and 3.2 nl/mm2 respectively, greatly surpassing the current state of the art. We reveal that this extremely efficient jumping is attributed to the large tolerance of coalescence mismatch and effective isolation of droplets between neighbouring lattices. Our work provides a new perspective for the design and fabrication of high-performance anti-dew materials.

cond-mat.mtrl-sci↗

arXiv2020

Superlubric Schottky Generator in Microscale with High Current Density and Ultralong Life

Miniaturized or even microscale generators that could effectively and persistently converse weak and random mechanical energy from environments into electricity promise huge applications in the internet of things, sensor networks, big data, personal health systems, artificial intelligence, etc. However, such generators haven't appeared yet because either the current density, or persistence, or both of all reported attempts were too low to real applications. Here, we demonstrate a superlubric Schottky generator (SLSG) in microscale such that the sliding contact between a microsized graphite flake and an n-type silicon is in a structural superlubric state, namely a ultralow friction and wearless state. This SLSG generates a stable electrical current at a high density (~119 Am-2) for at least 5,000 cycles. Since no current decay and wear were observed during the entire experiment, we believe that the real persistence of the SLSG should be enduring or substantively unlimited. In addition, the observed results exclude the mechanism of friction excitation in our Schottky generator, and provide the first experimental support of the conjectured mechanism of depletion layer establishment and destruction (DLED). Furthermore, we demonstrate a physical process of the DLED mechanism by the use of a quasi-static semiconductor finite element simulation. Our work may guide and accelerate future SLSGs into real applications.

physics.app-ph↗

arXiv2019

Superlubric Nanogenerators with Superb Performances

Nanogenerators promise self-powered sensors and devices for extensive applications in internet of things, sensor networks, big data, personal healthcare systems, artificial intelligence, et al. However, low electric current densities and short product lifespans have blocked nanogenerators' applications. Here we show that structural superlubricity, a state of nearly zero friction and wear between two contacted solid surfaces, provides a revolutionary solution to the above challenge. We investigate three types of superlubric nanogenerators (SLNGs), namely the capacitor-based, triboelectric, and electret-based SLNGs, and systematically analyze the influences of material and structural parameters to these SLNGs' performances. We demonstrate that SLNGs can achieve not only enduring lifespans, but also superb performances - three orders of magnitude in current densities and output powers higher than those of conventional nanogenerators. Furthermore, SLNGs can be driven by very weak external loads (down to ~1 $μ$N) in very low frequencies (down to ~1 $μ$Hz), and are thus capable to harvest electric energies from an extremely board spectrum of environments and biosystems. Among the three types of SLNGs, the capacitor-based is synthetically most competitive in the senses of performance, fabrication and maintaining. These results can guide designs and accelerate fabrications of SLNGs toward real applications.

physics.app-ph↗

arXiv2019

Drop Impact on Two-Tier Monostable Superrepellent Surfaces

Superrepellency is a favorable non-wetting situation featured by a dramatically reduced solid/liquid contact region with extremely low adhesion. However, drop impact often brings out a notable extension of the contact region associated with rather enhanced water affinity, such renders irreversible breakdowns of superhydrophobicity. Here, we report an alternative outcome, a repeated Cassie-Wenzel-Cassie (CWC) wetting state transition in the microscale occurs when a drop impacts a two-tier superhydrophobic surface, which exhibits a striking contrast to the conventional perspective. Influences of material parameters on the impact dynamics are quantified. We demonstrate that self-cleaning and dropwise condensation significantly benefit from this outcome - dirt particles or small droplets in deep textures can be taken away through the transition. The results reported in this study allows us to promote the strategy to design functional superrepellency materials.

physics.flu-dyn↗

arXiv2019

Rotational instability in superlubric joints

Surface and interfacial energies play important roles in a number of instability phenomena in liquids and soft matters, but are rare to play a similar role in solids. Here we report a new type of mechanical instabilities that are controlled by surface and interfacial energies and are valid for a large class of materials, in particular two-dimensional layered materials. When sliding a top flake cleaved from a square microscale graphite mesa by using a probe acted on the flake through a point contact, we observed that the flake moved unrotationally for a certain distance before it suddenly transferred to a rotating-moving state. The theoretical analysis that agrees well with the experimental observation reveals that this mechanical instability is an interesting effect of the structural superlubricity (a state of nearly zero friction). Our further analysis shows that this type of instability holds generally for various sliding joints on different scales, as long as the friction is ultralow. Thus, the uncovered mechanism provides useful knowledge for manipulating and controlling all these sliding joints, and can guide design of future structural superlubricity based devices.

cond-mat.mes-hall↗

arXiv2018

An Irreducible Function Basis of Isotropic Invariants of A Third Order Three-Dimensional Symmetric Tensor

In this paper, we present an eleven invariant isotropic irreducible function basis of a third order three-dimensional symmetric tensor. This irreducible function basis is a proper subset of the Olive-Auffray minimal isotropic integrity basis of that tensor. The octic invariant and a sextic invariant in the Olive-Auffray integrity basis are dropped out. This result is of significance to the further research of irreducible function bases of higher order tensors.

math-ph↗

arXiv2016

Observation of normal-force-independent superlubricity in mesoscopic graphite contacts

We investigate the dependence of friction forces on normal load in incommensurate micrometer size contacts between atomically smooth single-crystal graphite surfaces under ambient conditions. Our experimental results show that these contacts exhibit superlubricity (super-low friction), which is robust against the application of normal load. The measured friction coefficients are essentially zero and independent of the external normal load up to a pressure of 1.67 MPa. The observation of load-independent superlubricity in micro-scale contacts is a promising result for numerous practical applications.

cond-mat.mes-hall↗

arXiv2016

Liquid dispensing and writing by a nano-grooved pin

Liquid dispensing and writing in the extremely small size regime are important for applications in many current technologies, such as micro/nano fabrication, biological/chemical patterning and analysis, and drug discovery. Most of current dispensing/writing methods can be sorted into a category of liquid flowing through tiny tubes or nozzles that requires inputting an impulse energy, which leads to complex procedures, expensive equipment and narrow material applicability, especially for biomaterials. Here, we report a method that may lead to a new category: liquid flows over the tapered surface of a pin with longitudinal nano grooves on the surface to uninterruptedly perform droplet dispensing and direct writing. The dispensed droplet diameters were controllable from several microns down to 150 nm, and the written line heights were as low as 5 nm. The mechanism underlying automatic liquid storage on conical surface and spontaneous liquid transport through nano grooves is revealed and well modeled by a simple relationship. Furthermore, the nano-grooved pins are much simpler and cheaper in fabrication than nanoscale tubes and nozzles, and pins have much depressed clogging problems that are typically troublesome for tubes and nozzles. Our new strategy may constitute a basis for creating liquid dispensing/writing technologies that are simultaneously smaller, simpler, faster and applicable for more types of materials.

cond-mat.soft↗

arXiv2016

Monostable Superantiwettability

Superantiwettability, including superhydrophobicity, is an enhanced effect of surface ruggedness via the Cassie-Baxter wetting state, and has many applications such as antifouling, drop manipulation, and self-cleaning. However, superantiwettability is easily broken due to Cassie-Baxter to Wenzel wetting state transition caused by various environmental disturbances. Since all observed reverse transitions required energy inputs, it was believed that the Cassie-Baxter state couldn't be monostable. Here we show that there is a regime in the phase space of the receding contact angle and ruggedness parameters in which a Wenzel state can automatically transit into the Cassie-Baxter one without an external energy input, namely the Cassie-Baxter state in this regime is monostable. We further find a simple criterion that predicts very well experimentally observed Wenzel to Cassie-Baxter transitions for different liquids placed on various pillar-structured substrates. These results can be used as a guide for designing and engineering durable superantiwetting surfaces.

cond-mat.soft↗

arXiv2015

Accurate Measurement of the Cleavage Energy of Graphite

The basal plane cleavage energy (CE) of graphite is a key material parameter for understanding many of the unusual properties of graphite, graphene, and carbon nanotubes. The CE is equal to twice the surface energy and is closely related to the interlayer binding energy and exfoliation energy of graphite. Nonetheless, a wide range of values for these properties have been reported and no consensus has yet emerged as to their magnitude. Here, we report the first direct, accurate experimental measurement of the CE of graphite using a novel method based on the recently discovered self-retraction phenomenon in graphite. The measured value, 0.37 +/- 0.01 J/m2 for the incommensurate state of bicrystal graphite, is nearly invariant with respect to temperature (from 22°C to 198°C) and bicrystal twist angle, and insensitive to impurities (from the atmosphere). The cleavage energy for the ideal ABAB graphite stacking, 0.39 +/- 0.02 J/m2, is calculated based upon a combination of the measured CE and a theoretical calculation. These experimental measurements are ideal for use in evaluating the efficacy of competing theoretical approaches.

cond-mat.mtrl-sci↗

arXiv2014

Anomalous elastic buckling of hexagonal layered crystalline materials in the absence of structure slenderness

Hexagonal layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, and so on, have attracted enormous attentions, due to their unique combination of atomistic structures and superior thermal, mechanical, and physical properties. Making use of mechanical buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ finite element analysis (FEA), molecular dynamic (MD) simulations and continuum modeling to study the mechanical buckling of a column made of layered crystalline materials with the crystal layers parallel to the longitudinal axis. It is found that the mechanical buckling exhibits a gradual transition from a bending mode to a shear mode of instability with the reduction of slenderness ratio. As the slenderness ratio approaches to zero, the critical buckling strain εcr converges to a finite value that is much smaller than the material's mechanical strength, indicating that it is realizable under appropriate experimental conditions. Such a mechanical buckling mode is anomalous and counter-intuitive. The critical buckling strain εcr predicted by our continuum mechanics model agrees very well with the results from the FEA and MD simulations for a group of typical hexagonal layered crystalline materials. MD simulations on graphite indicate the continuum mechanics model is applicable down to a scale of 20 nm. This theoretical model also reveals that a high degree of elastic anisotropy is the origin for the anomalous mechanical buckling of a column made of layered crystalline materials in the absence of structural slenderness. This study provides avenues for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical buckling.

cond-mat.mtrl-sci↗