arXiv subjects

Zhibin Gao

Publications and source records attributed to Zhibin Gao.

63 records · Page 4Linked to original sources

arXiv2019

Anisotropic thermal expansion and thermomechanic properties of monolayer $β$-Te

Recently, $β$-Te (atomically 2D tellurium) with rectangular crystal structure has been synthesized successfully on highly oriented pyrolytic graphite substrates by using molecular beam epitaxy. It has been found possessing remarkable properties such as ultralow lattice thermal conductivity and high thermoelectric efficiency. Based on the first-principles calculations, we study the thermal expansion and thermomechanic properties of the experimental phase monolayer $β$-Te, using quasiharmonic approach. It is found $β$-Te shows large positive thermal expansion at elevated temperature, while the linear thermal expansion coefficient is negative along a direction at very low temperature. The linear thermal expansion coefficient along b direction is 4.9*10$^{-5}$ K$^{-1}$ at 500 K, which is considerably large in 2D materials. $β$-Te exhibits strong in-plane anisotropy, including thermal expansion, 2D elastic moduli and Poisson's ratios. However, the elastic moduli, Poisson's ratios and the in-plane anisotropy are weakened with increasing temperature, and the variations are dominated by the generalized mode Grüneisen parameters.

cond-mat.mtrl-sci↗

arXiv2019

Degenerately Doped Transition Metal Dichalcogenides as Ohmic Homojunction Contacts to Transition Metal Dichalcogenide Semiconductors

In search of an improved strategy to form low resistance contacts to MoS2 and related semiconducting transition metal dichalcogenides, we use ab initio density functional electronic structure calculations in order to determine the equilibrium geometry and electronic structure of MoO3/MoS2 and MoO2/MoS2 bilayers. Our results indicate that, besides a rigid band shift associated with charge transfer, the presence of molybdenum oxide modifies the electronic structure of MoS2 very little. We find that the charge transfer in the bilayer provides a sufficient degree of hole doping to MoS2, resulting in a highly transparent contact region.

cond-mat.mes-hall↗

arXiv2019

Strain Effects on the Mechanical Properties of Group-V Monolayers with Buckled Honeycomb Structures

Based on first-principles calculations, we study systematically the ideal tensile stress-strain relations of three monoatomic group-V monolayer two dimensional (2D) materials with buckled honeycomb lattices: blue phosphorene, arsenene, and antimonene. The ideal strengths and critical strains for these 2D materials are investigated under uniaxial and equibiaxial strains. It is found that the ideal strengths decrease significantly as the atomic number increases, while the critical strains change not so much. In particular, the ideal strength of antimonene along armchair direction is found to exceed Griffith strength limit. The distributions of charge density, buckling heights, bond lengths, and bond angles are also studied under different types of strains. It can be concluded that the critical strain is determined by the stretch and rotation of bonds simultaneously. Furthermore, the phonon dispersions, phonon instabilities, and failure mechanism of these materials under three types of strains are also calculated and explored.

physics.comp-ph↗

arXiv2018

Two-dimensional Mechanical Metamaterials with Unusual Poisson Ratio Behavior

We design two-dimensional (2D) mechanical metamaterials that may be deformed substantially at little or no energy cost. Examples of such deformable structures are assemblies of rigid isosceles triangles hinged in their corners on the macro-scale, or polymerized phenanthrene molecules forming porous graphene on the nano-scale. In these and in a large class of related structures, the Poisson ratio $ν$ diverges for particular strain values. $ν$ also changes its magnitude and sign, and displays a shape memory effect.

cond-mat.mes-hall↗

arXiv2018

A Computation Offloading Incentive Mechanism with Delay and Cost Constraints under 5G Satellite-ground IoV architecture

The 5G Internet of Vehicles has become a new paradigm alongside the growing popularity and variety of computation-intensive applications with high requirements for computational resources and analysis capabilities. Existing network architectures and resource management mechanisms may not sufficiently guarantee satisfactory Quality of Experience and network efficiency, mainly suffering from coverage limitation of Road Side Units, insufficient resources, and unsatisfactory computational capabilities of onboard equipment, frequently changing network topology, and ineffective resource management schemes. To meet the demands of such applications, in this article, we first propose a novel architecture by integrating the satellite network with 5G cloud-enabled Internet of Vehicles to efficiently support seamless coverage and global resource management. A incentive mechanism based joint optimization problem of opportunistic computation offloading under delay and cost constraints is established under the aforementioned framework, in which a vehicular user can either significantly reduce the application completion time by offloading workloads to several nearby vehicles through opportunistic vehicle-to-vehicle channels while effectively controlling the cost or protect its own profit by providing compensated computing service. As the optimization problem is non-convex and NP-hard, simulated annealing based on the Markov Chain Monte Carlo as well as the metropolis algorithm is applied to solve the optimization problem, which can efficaciously obtain both high-quality and cost-effective approximations of global optimal solutions. The effectiveness of the proposed mechanism is corroborated through simulation results.

cs.NI↗

arXiv2018

Unusually low thermal conductivity of atomically thin 2D tellurium

Tellurium is a high-performance thermoelectric material due to its superior electronic transport and low lattice thermal conductivity ($κ_L$). Here, we report the ultralow $κ_L$ in the monolayer tellurium, i.e., tellurene, which has been successfully synthesized in recent experiments. We find tellurene has a compellingly low room temperature $κ_L$ of 2.16 and 4.08 W m$^{-1}$ K$^{-1}$ along the armchair and zigzag directions, respectively, which is lower than any reported values for other 2D materials. We attribute this unusually low $κ_L$ to the soft acoustic modes, extremely low-energy optical modes and the strong scattering among optical-acoustic phonons, which place tellurene as a potential novel thermoelectric material. Finally, we disclose that $κ_L$ is proportional to the largest acoustic phonon frequency ($ω_{D}^{a}$) and the lowest optical phonon frequency at $Γ$ point ($ω_Γ^{o}$) in 2D materials, which reflect both harmonic and anharmonic thermal properties respectively.

cond-mat.mtrl-sci↗

arXiv2018

Novel Two-Dimensional Silicon Dioxide with in-plane Negative Poisson's Ratio

Silicon dioxide or silica, normally existing in various bulk crystalline and amorphous forms, is recently found to possess a two-dimensional structure. In this work, we use ab initio calculation and evolutionary algorithm to unveil three new 2D silica structures whose themal, dynamical and mechanical stabilities are compared with many typical bulk silica. In particular, we find that all these three 2D silica have large in-plane negative Poisson's ratios with the largest one being double of penta-graphene and three times of borophenes. The negative Poisson's ratio originates from the interplay of lattice symmetry and Si-O tetrahedron symmetry. Slab silica is also an insulating 2D material, with the highest electronic band gap (> 7 eV) among reported 2D structures. These exotic 2D silica with in-plane negative Poisson's ratios and widest band gaps are expected to have great potential applications in nanomechanics and nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2015

Heat conduction and energy diffusion in momentum-conserving 1D full lattice ding-a-ling model

The ding-a-ling model is a kind of half lattice and half hard-point-gas (HPG) model. The original ding-a-ling model proposed by Casati {\it et.al} does not conserve total momentum and has been found to exhibit normal heat conduction behavior. Recently, a modified ding-a-ling model which conserves total momentum has been studied and normal heat conduction has also been claimed. In this work, we propose a full lattice ding-a-ling model without hard point collisions where total momentum is also conserved. We investigate the heat conduction and energy diffusion of this full lattice ding-a-ling model with three different nonlinear inter-particle potential forms. For symmetrical potential lattices, the thermal conductivities diverges with lattice length and their energy diffusions are superdiffusive signaturing anomalous heat conduction. For asymmetrical potential lattices, although the thermal conductivity seems to converge as the length increases, the energy diffusion is definitely deviating from normal diffusion behavior indicating anomalous heat conduction as well. No normal heat conduction behavior can be found for the full lattice ding-a-ling model.

cond-mat.stat-mech↗

arXiv2015

Stretch diffusion and heat conduction in 1D nonlinear lattices

In the study of 1D nonlinear Hamiltonian lattices, the conserved quantities play an important role in determining the actual behavior of heat conduction. Besides the total energy, total momentum and total stretch could also be conserved quantities. In microcanonical Hamiltonian dynamics, the total energy is always conserved. It was recently argued by Das and Dhar that whenever stretch (momentum) is not conserved in a 1D model, the momentum (stretch) and energy fields exhibit normal diffusion. In this work, we will systematically investigate the stretch diffusions for typical 1D nonlinear lattices. No clear connection between the conserved quantities and heat conduction can be established. The actual situation is more complicated than what Das and Dhar claimed.

cond-mat.stat-mech↗