Gang Zhang

Gang Zhang
Institute of High Performance Computing · Engineering Mechanics

About

47
Publications
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6,053
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Publications

Publications (47)
Article
Full-text available
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...
Article
Full-text available
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 MoS2 and WS2, and model their electronic TBC with different diel...
Article
Full-text available
This review summarizes recent studies of thermal transport in nanoscaled semiconductors. Different from bulk materials, new physics and novel thermal properties arise in low dimensional nanostructures, such as the abnormal heat conduction, the size dependence of thermal conductivity, phonon boundary/edge scatterings. It is also demonstrated that ph...
Article
By using a combination of the first-principles density functional theory and nonequilibrium Green's function for electron and phonon transport, we investigate the thermoelectric properties of silicon-germanium superlattice nanowires (NWs). Our results show that introducing superlattice structures always increases thermoelectric figure of merit, ZT,...
Article
Full-text available
Thermal conductivity κ of both suspended and supported graphene has been studied by using molecular dynamics simulations. An obvious length dependence is observed in κ of suspended single-layer graphene (SLG), while κ of supported SLG is insensitive to the length. The simulation result of room temperature κ of supported SLG is in good agreement wit...
Article
Full-text available
Silicon dioxide and silicon (SiO$_{2}$/Si) interface plays a very important role in semiconductor industry. However, at nanoscale, its interfacial thermal properties haven't been well understood so far. In this paper, we systematically study the interfacial thermal resistance (Kapitza resistance) of a heterojunction composed of amorphous silicon di...
Article
Full-text available
Heat conduction is an important energy transport process in nature. Phonon is the major energy carrier for heat in semiconductors and dielectric materials. In analogy to Ohm’s law of electrical conduction, Fourier’s law is the fundamental law of heat conduction in solids. Although Fourier’s law has received great success in describing macroscopic h...
Article
Full-text available
By using nonequilibrium molecular dynamics simulations, we demonstrated that thermal conductivity of germanium nanowires can be reduced more than 25% at room temperature by atomistic coating. There is a critical coating thickness beyond which thermal conductivity of the coated nanowire is larger than that of the host nanowire. The diameter-dependen...
Article
By using first-principles electronic structure calculation and Boltzmann transport equation, we investigate the impact of gallium (Ga) doping on the thermoelectric property of [0001] zinc oxide nanowires (Zn1 − xGaxO NWs). Our results show that the thermoelectric performance of the Zn1 − xGaxO NWs is strongly dependent on the Ga contents. The maxim...
Article
Full-text available
By using molecular dynamics simulations, we study thermal conductivity of silicon nanowires (SiNWs) with different cross sectional geometries. It is found that thermal conductivity decreases monotonically with the increase of surface-to-volume ratio (SVR). More interestingly, a simple universal linear dependence of thermal conductivity on SVR is ob...
Article
We apply our understanding of the physics of failure in the post-breakdown regime of high-κ dielectric-based conventional logic transistors having a metal–insulator–semiconductor (MIS) structure to interpret the mechanism of resistive switching in resistive random-access memory (RRAM) technology metal–insulator–metal (MIM) stacks. Oxygen vacancies...
Article
By using molecular dynamics simulations, we have studied heat flux in graphene Y junctions with lengths of 16.7 nm. It is found that the heat flux runs preferentially from the branches to the stem, which demonstrates an obvious thermal rectification effect in these asymmetric graphene ribbons. More interesting, compared to single-layer graphene Y j...
Article
Full-text available
We study heat current autocorrelation function and thermal conductivity in core-shell nanowires by using molecular dynamics simulations. Interestingly, a remarkable oscillation effect in heat current autocorrelation function is observed in core-shell NWs, while the same effect is absent in pure silicon nanowires, nanotube structures and random dope...
Article
Full-text available
The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: By use of tailored models we demonstrate that phonons can be manipulated like electrons and...
Article
We study the thermal transport in completely unzipped carbon nanotubes, which are called graphene nanoribbons, partially unzipped carbon nanotubes, which can be seen as carbon-nanotube-graphene-nanoribbon junctions, and carbon nanotubes by using molecular dynamics simulations. It is found that the thermal conductivity of a graphene nanoribbon is mu...
Article
The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: by use of tailored models we demonstrate that phonons can be manipulated like electrons and...
Article
We propose to reduce the thermal conductivity of silicon nanowires (SiNWs) by introducing a small hole at the center, i.e., construct a silicon nanotube (SiNT) structure. Our numerical results demonstrate that a very small hole (only 1% reduction in cross section area) can induce a 35% reduction in room temperature thermal conductivity. Moreover, w...
Article
Full-text available
Thermal transport in nanoscale structures has attracted an increasing interest in the last two decades. On the one hand, the low dimensional nanostructured materials are platforms for testing novel phonon transport theories. On the other hand, nanomaterials are promising candidates for nanoscale on-chip coolers. This review is focused on the therma...
Article
In this paper, the effects of structural parameters on the optical characteristics of crystalline Si thin films with the surface decorated by Si nanocone (SiNC) arrays are investigated by simulation. It is found that the SiNC base diameter should be equal to the array periodicity for efficient solar energy harvesting, and the optimized light absorp...
Article
Equilibrium molecular dynamics (EMD) simulations through Green-Kubo formula (GKF) have been widely used in the study of thermal conductivity of various materials. However, there exist controversial simulation results which have huge discrepancies with experimental ones in literatures. In this paper, we demonstrate that the fluctuation in calculated...
Article
Full-text available
We investigate systematically the impacts of heat bath used in molecular dynamics simulations on heat conduction in nanostructures exemplified by Silicon Nanowires (SiNWs) and Silicon/Germanium nano junction. It is found that multiple layers of Nos\'e-Hoover heat bath are required to reduce the temperature jump at the boundary, while only a single...
Article
Full-text available
By using first-principles electronic structure calculation and Boltzmann transport equation, we investigate composition effects on the thermoelectric properties of silicon-germanium ( Si <sub>1-x</sub> Ge <sub>x</sub> ) nanowires (NWs). The power factor and figure of merit in n-type Si <sub>1-x</sub> Ge <sub>x</sub> wires are much larger than those...
Article
We study heat conduction and diffusion in silicon nanowires (SiNWs) systematically by using non-equilibrium molecular dynamics. It is found that the thermal conductivity (κ) of SiNWs diverges with the length as, κ ∝ Lβ, even when the length is up to 1.1 μm which is much longer than the phonon mean free path. The dependences of β on temperature and...
Preprint
We study heat conduction and diffusion in silicon nanowires (SiNWs) systematically by using non-equilibrium molecular dynamics. It is found that the thermal conductivity of SiNWs diverges with the length, even when the length is up to 1,100 nm which is much longer than the phonon mean free path. Moreover, an anomalous heat diffusion is observed whi...
Conference Paper
The solar energy harvesting of Si thin films with Si nanocone or nanopillar array decorated surfaces is systematically studied by simulation for the first time. It is found that the high and broad-width light absorption around 2.5 eV is the key to achieve high efficiencies for both structures. Nanostructure dimensions are optimized based on the enh...
Conference Paper
Heat due to lattice vibration (phonons) is traditionally regarded as harmful for information processing. In this paper, we will demonstrate via numerical simulation, theoretical analysis and experiments that, phonons, can be manipulated like electrons. They can be used to carry and process information. Basic phononic devices such as thermal diode,...
Article
In this letter, optimum periodic Si nanowire (SiNW) arrays are designed via simulation for solar cell application, in terms of the structural parameters, e.g., the array periodicity (P) and SiNW diameter (D). It is found that the more efficient light absorption compared to that of the Si thin film with the same thickness could be realized when P is...
Article
Full-text available
With finite element simulation, the time dependent thermoelectric performance of silicon nanowires (SiNWs) is studied systematically. Short response time has been observed in SiNW cooler which decreases with increasing of the number of SiNWs. Moreover, the impacts of inhomogeneous thermal conductivity distribution in one bundle on the cooling tempe...
Article
Full-text available
By using molecular dynamics simulation, we demonstrate that the thermal conductivity of silicon-germanium nanowires (Si1−xGex NWs) depends on the composition remarkably. The thermal conductivity reaches the minimum, which is about 18% of that of pure Si NW, when Ge content is 50%. More interesting, with only 5% Ge atoms (Si0.95Ge0.05 NW), SiNW’s th...
Article
Full-text available
By using first-principles tight-binding electronic structure calculation and Boltzmann transport equation, we investigate the size dependence of thermoelectric properties of silicon nanowires (SiNWs). With cross section area increasing, the electrical conductivity increases slowly, while the Seebeck coefficient reduces remarkably. This leads to a q...
Article
Full-text available
In this letter, Si thin film (800 nm thick) with nanopillar array decorated surface is studied via simulation for its solar energy absorption characteristics. It is found that the light absorption is significantly enhanced due to the adding of the Si nanopillar (SiNP) array to the Si thin film. The absorption characteristics of the SiNP structure w...
Article
Full-text available
In this paper, heat flux in graphene nano ribbons has been studied by using molecular dynamics simulations. It is found that the heat flux runs preferentially along the direction of decreasing width, which demonstrates significant thermal rectification effect in the asymmetric graphene ribbons. The dependence of rectification ratio on the vertex an...
Article
Full-text available
With molecular dynamics simulations, we demonstrate very obvious thermal rectification in large temperature range from 200 to 400 K in nanocone. We also observe that the rectification of nanocone does not depend on the length very sensitively, which is in stark contrast with the nanotube thermal rectifier in which the rectification decreases dramat...
Article
In this paper, systematic study on electrical contacts to silicon nanowires (SiNWs) is performed using a developed Schottky barrier simulator. At room temperature, the SiNW-metal contact is always characterized by Schottky behaviors, with the barrier height exhibiting a minimum at a diameter of about 4 nm. At ultralow temperature of 138 K, a Schott...
Article
With finite element simulation and analytic modeling, the thermoelectric performance of silicon nanowires (SiNWs) is studied. Large cooling temperature is observed which increases remarkably as thermal conductivity of SiNW decreases. Moreover, high cooling power density of 6.6×103 W/cm2 is achieved which is about 600 times larger than that of comme...
Article
Full-text available
In this letter, a nine-channel 100-GHz arrayed waveguide grating multiplexer/demultiplexer is monolithically integrated with a Mach-Zehnder interferometer thermo-optic variable optical attenuators (VOAs) arrayed on a silicon-on-insulator platform. The on-chip transmission loss is ~ 6 dB and the crosstalk is less than -25 dB for the transverse-elect...
Article
Full-text available
We investigate the surface lattice and electronic structure of [110] oriented hydrogen-passivated silicon nanowires (SiNWs) of different cross-sectional shapes by using the first-principles tight-binding method. Remarkable quantum confinement effects are observed on the surface lattice constant and the electron effective mass. Moreover, with the sa...
Article
The size dependence of the dielectric constants and optical absorption for silicon nanostructured films are investigated using density-functional theory. A critical thickness of 4.3 nm is observed for Si (100)-oriented thin films. Within this critical thickness, the dielectric function and optical absorption show remarkable size dependence, and a l...
Article
We propose a novel molecular junction with single walled carbon nanotube (SWNT) as electrodes bridged by an anthracene molecule. It is found that when the coupling between the molecule and the SWNT is noncovalent, the current-voltage (I-V) curve shows a striking nonlinear feature and a large negative differential resistance (NDR) at small bias. Whi...
Article
We use the first-principles tight binding method to investigate the electronic structure and band gap of [110] oriented hydrogen-passivated silicon nanowires (SiNWs) of different cross-sectional geometries. A quantitative universal band gap expression for [110] SiNWs is obtained, which shows a linear dependence of band gap on the surface area to vo...
Conference Paper
In this paper, we report the recent developments in the study of heat transport in nano materials. First of all, we show that phonon transports in nanotube super-diffusively which leads to a length dependence thermal conductivity, thus breaks down the Fourier law. Then we discuss how the introduction of isotope doping can reduce the thermal conduct...
Article
Full-text available
In this work, we provide a nanoscale scheme of the leakage current in SiO2 breakdown. In combination with first-principles calculation, the leakage current is explored with the Landauer–Büttiker transport formula. Large leakage current is generated from the band gap states. The effect of oxygen vacancy is remarkable in the conduction band while alm...
Article
The thermal conductivity of silicon nanowires (SiNWs) is investigated by molecular dynamics (MD) simulation. It is found that the thermal conductivity of SiNWs can be reduced exponentially by isotopic defects at room temperature. The thermal conductivity reaches the minimum, which is about 27% of that of pure 28Si NW, when doped with fifty percent...
Article
We demonstrate that at a finite temperature, an effective wall thickness of a single-walled carbon nanotube (SWNT) should be W = Ws + Wd, where Ws is the static thickness defined as the extension of the outmost electronic orbit and Wd the dynamic thickness due to thermal vibration of atoms. Both molecular simulations and a theoretical analysis show...
Article
Full-text available
We study the dependence of the thermal conductivity of single-walled nanotubes on chirality, isotope impurity, tube length, and temperature by nonequilibrium molecular-dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, howev...
Article
Full-text available
We study the vibrational energy diffusion in single-walled carbon nanotubes by using the molecular-dynamics method. It is found that energy transports ballistically at low temperature and superdiffusively at room temperature. The velocity of energy transport along the axis in carbon nanotube at room temperature is about 0.10 A/fs. It is also found...
Article
We study anomalous heat conduction and anomalous diffusion in low-dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is sigma(2)(t)=2Dt(alpha) (...

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