ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 12 Aug 2020 21:06:45 GMT2020-08-12T21:06:45Z50251- Topological effect on thermal conductivity in graphenehttps://scholarbank.nus.edu.sg/handle/10635/98418Title: Topological effect on thermal conductivity in graphene
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The topological effect on thermal conductivity is investigated through the comparison among graphene nanoribbons, carbon nanorings, and the Möbius-like graphene strips (MGS) by molecular dynamics simulation. It is found that the thermal conductivity of MGS is less than one half of that of graphene nanoribbons. The underlying mechanism whereby MGS acquire such low thermal conductivity may be attributable to the enhanced phonon-phonon scattering and localization property, which are induced by the nontrivial topology of Möbius strip. Moreover, by counting in the dimensions of MGS, a lower length/width ratio reduces its thermal conductivity, as the phonon-phonon scattering and localization within might be further elevated. © 2010 American Institute of Physics.
Wed, 15 Sep 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984182010-09-15T00:00:00Z
- Graphene-based torsional resonator from molecular-dynamics simulationhttps://scholarbank.nus.edu.sg/handle/10635/96741Title: Graphene-based torsional resonator from molecular-dynamics simulation
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: Molecular-dynamics simulations are performed to study graphene-based torsional mechanical resonators. The quality factor is calculated by Q F=ωτ/2π, where the frequency ω and lifetime τ are obtained from the correlation function of the normal mode coordinate. Our simulations reveal the radius dependence of the quality factor as Q F=2628/(22R- 1+0.004R2), which yields a maximum value at some proper radius R. This maximum point is due to the strong boundary effect in the torsional resonator, as disclosed by the temperature distribution in the resonator. Resulting from the same boundary effect, the quality factor shows a power law temperature dependence with power factors below 1.0. The theoretical results supply some valuable information for the manipulation of the quality factor in future experimental devices based on the torsional mechanical resonator. Copyright © EPLA, 2011.
Thu, 01 Dec 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967412011-12-01T00:00:00Z
- Molecular dynamics with quantum heat baths: Application to nanoribbons and nanotubeshttps://scholarbank.nus.edu.sg/handle/10635/97248Title: Molecular dynamics with quantum heat baths: Application to nanoribbons and nanotubes
Authors: Wang, J.-S.; Ni, X.; Jiang, J.-W.
Abstract: A generalized Langevin equation with quantum heat baths [quantum molecular dynamics (QMD)] for thermal transport is derived with the help of nonequilibrium Green's function (NEGF) formulation. The exact relationship of the quasiclassical approximation to NEGF is demonstrated using Feynman diagrams of the nonlinear self-energies. To leading order, the retarded self-energies agree but QMD and NEGF differ in lesser/greater self-energies. An implementation for general systems using Cholesky decomposition of the correlated noises is discussed. Some means of stabilizing the dynamics is given. Thermal conductance results for graphene strips and carbon nanotubes are presented. The "quantum correction" method is critically examined. © 2009 The American Physical Society.
Tue, 22 Dec 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972482009-12-22T00:00:00Z
- Molecular dynamics simulation for heat transport in thin diamond nanowireshttps://scholarbank.nus.edu.sg/handle/10635/97243Title: Molecular dynamics simulation for heat transport in thin diamond nanowires
Authors: Jiang, J.-W.; Wang, B.-S.; Wang, J.-S.
Abstract: The phonon thermal conductivity in diamond nanowires (DNWs) is studied by molecular dynamics simulation. It is found that the thermal conductivity in narrower DNW is lower and does not show obvious temperature dependence; a very small value (about 2.0 W/m/K) of thermal conductivity is observed in ultra-narrow DNW, which may be of potential applications in thermoelectric devices. These two phenomena are probably due to the dominant surface effect and phonon confinement effect in narrow DNW. Our simulation reveals a high anisotropy in the heat transport of DNW. Specifically, the thermal conductivity in DNW along [110] growth direction is about five times larger than that of [100] and [111] growth directions. The anisotropy is believed to root in the anisotropic group velocity for acoustic phonon modes in DNW along three different growth directions. © 2011 American Physical Society.
Thu, 30 Jun 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972432011-06-30T00:00:00Z
- High thermoelectric figure of merit in silicon-germanium superlattice structured nanowireshttps://scholarbank.nus.edu.sg/handle/10635/96798Title: High thermoelectric figure of merit in silicon-germanium superlattice structured nanowires
Authors: Shi, L.; Jiang, J.; Zhang, G.; Li, B.
Abstract: By using a combination of the first-principles density functional theory and nonequilibrium Greens 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, which depends on the periodic length of the superlattice NWs. For n-type superlattice NWs, the achievable maximum ZT is 4.7, which is 5-fold increase as compared to the equivalent pristine silicon NWs. For p-type wires, the achieved maximum ZT is 2.74, which is 4.6-fold increase as compared to the pristine silicon NWs. © 2012 American Institute of Physics.
Mon, 03 Dec 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967982012-12-03T00:00:00Z
- Thermal expansion in single-walled carbon nanotubes and graphene: Nonequilibrium Green's function approachhttps://scholarbank.nus.edu.sg/handle/10635/98357Title: Thermal expansion in single-walled carbon nanotubes and graphene: Nonequilibrium Green's function approach
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The nonequilibrium Green's function method is applied to investigate the coefficient of thermal expansion (CTE) in single-walled carbon nanotubes (SWCNT) and graphene. It is found that atoms expand about 1% from equilibrium positions even at T=0,K, resulting from the interplay between quantum zero-point motion and nonlinear interaction. The CTE in SWCNT of different sizes is studied and analyzed in terms of the competition between various vibration modes. As a result of this competition, the axial CTE is positive in the whole temperature range, while the radial CTE is negative at low temperatures. In graphene, the CTE is very sensitive to the substrate. Without substrate, CTE has large negative region at low temperatures and very small value at high-temperature limit, and the value of CTE at 300 K is -6× 10-6 , K -1 which is very close to a recent experimental result, -7× 10-6 , K-1. A very weak substrate interaction (about 0.06% of the in-plane interaction) can largely reduce the negative CTE region and greatly enhance the value of CTE. If the substrate interaction is strong enough, the CTE will be positive in whole temperature range and the saturate value at high temperatures reaches 2.0× 10-5 , K-1. © 2009 The American Physical Society.
Mon, 30 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983572009-11-30T00:00:00Z
- Bright and dark modes induced by graphene bubbleshttps://scholarbank.nus.edu.sg/handle/10635/95891Title: Bright and dark modes induced by graphene bubbles
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: Through a lattice dynamics analysis, it is revealed that the bubble plays a role of energy shield in the graphene, which helps to split the normal modes into two categories of distinct topological nature, namely the bright and dark modes. The topological invariants, Euler characteristic, of the bright and dark modes are 1 and 0, respectively. For bright modes, the energy is confined inside the bubble, so this type of modes is sensitive to the shape of the bubble; while the opposite phenomenon is observed for the dark modes. The different behavior of these two types of normal modes is examined and verified in the process of phonon thermal transport. The bright and dark modes are expected to be distinguished in experiment with existing scanning force microscope techniques, and they should play significant roles in many other physical processes. Copyright © EPLA, 2012.
Wed, 01 Feb 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958912012-02-01T00:00:00Z
- Conditions for the existence of phonon localized edge-modeshttps://scholarbank.nus.edu.sg/handle/10635/96058Title: Conditions for the existence of phonon localized edge-modes
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: The phonon localized edge-modes are systematically studied, and two conditions are proposed for the existence of the localized edge-modes: (I) coupling between different directions (x, y, or z) in the interaction and (II) different boundary conditions in three directions. The generality of these two conditions is illustrated by different lattice structures: one-dimensional (1D) chain, two-dimensional (2D) square lattice, 2D graphene, three-dimensional (3D) simple cubic lattice, 3D diamond structure, etc., and with different potentials: valence force field model, Brenner potential, etc. © 2010 The American Physical Society.
Tue, 25 May 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960582010-05-25T00:00:00Z
- A universal exponential factor in the dimensional crossover from graphene to graphitehttps://scholarbank.nus.edu.sg/handle/10635/95699Title: A universal exponential factor in the dimensional crossover from graphene to graphite
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: A universal exponential factor, γc =π /2, is disclosed for the dimensional crossover of few-layer graphene (FLG) from two-dimensional graphene to three-dimensional graphite. γc is found by analyzing available experimental data on different properties of FLG with varying thickness. A theoretical study on the phonon spectrum of the vertical acoustic mode in FLG is carried out to further check this exponential factor γc. Interestingly, the same exponential factor appears in the dimensional crossover of the phonon mode. It turns out that the exponential factor γc is related to the homogeneous Helmholtz-like molal equation in the mass transfer with a first order chemical reaction. The finding should provide valuable information for experimentalists and theorists in the future investigation on thickness dependent properties of FLG. © 2010 American Institute of Physics.
Wed, 15 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956992010-12-15T00:00:00Z
- Isotopic effects on the thermal conductivity of graphene nanoribbons: Localization mechanismhttps://scholarbank.nus.edu.sg/handle/10635/97010Title: Isotopic effects on the thermal conductivity of graphene nanoribbons: Localization mechanism
Authors: Jiang, J.-W.; Lan, J.; Wang, J.-S.; Li, B.
Abstract: Thermal conductivity of graphene nanoribbons (GNR) with length 106 Å and width 4.92 Å after isotopic doping is investigated by molecular dynamics with quantum correction. Two interesting phenomena are found, (1) isotopic doping reduces thermal conductivity effectively in low doping region, and the reduction slows down in high doping region, (2) thermal conductivity increases with increasing temperature in both pure and doped GNR, but the increasing behavior is much more slow in the doped GNR than that in pure ones. Further studies reveal that the physics of these two phenomena is related to the localized phonon modes, whose number increases quickly (slowly) with increasing isotopic doping in low (high) isotopic doping region. © 2010 American Institute of Physics.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970102010-01-01T00:00:00Z
- Minimum thermal conductance in graphene and boron nitride superlatticehttps://scholarbank.nus.edu.sg/handle/10635/97221Title: Minimum thermal conductance in graphene and boron nitride superlattice
Authors: Jiang, J.-W.; Wang, J.-S.; Wang, B.-S.
Abstract: The minimum thermal conductance versus supercell size (ds) is revealed in graphene and boron nitride superlattice with ds far below the phonon mean free path. The minimum value is reached at a constant ratio of ds/L ≈ 5, where L is the thickness of the superlattice; thus, the minimum point of ds depends on L. The phenomenon is attributed to the localization property and the number of confined modes in the superlattice. With the increase of ds, the localization of the confined mode is enhanced while the number of confined modes decreases, which directly results in the minimum thermal conductance. © 2011 American Institute of Physics.
Mon, 25 Jul 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972212011-07-25T00:00:00Z
- Topology-induced thermal rectification in carbon nanodevicehttps://scholarbank.nus.edu.sg/handle/10635/98425Title: Topology-induced thermal rectification in carbon nanodevice
Authors: Jiang, J.W.; Wang, J.S.; Li, B.
Abstract: The thermal rectification (TR) effect in a topological system, Möbius graphene strip, is studied by nonequilibrium molecular-dynamics simulation with Nóse-Hoover heat baths. Due to the nonlinear interaction in graphene and the topological asymmetry of the Möbius strip, the TR phenomenon emerges and the value of TR can be as large as 120%. This topology-induced TR is not very sensitive to the temperature and size of the system; while the position of heat bath is important, since it can induce additional asymmetry. © 2010 EPLA.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984252010-01-01T00:00:00Z
- Edge states induce boundary temperature jump in molecular dynamics simulation of heat conductionhttps://scholarbank.nus.edu.sg/handle/10635/96287Title: Edge states induce boundary temperature jump in molecular dynamics simulation of heat conduction
Authors: Jiang, J.-W.; Chen, J.; Wang, J.-S.; Li, B.
Abstract: We point out that the origin of the commonly occurred boundary temperature jump in the application of Nose-Hoover heat bath in molecular dynamics is related to the edge modes, which are exponentially localized at the edge of the system. If heat baths are applied to these edge regions, the injected thermal energy will be localized thus leading to a boundary temperature jump. The jump can be eliminated by shifting the location of heat baths away from edge regions. Following this suggestion, a very good temperature profile is obtained without increasing any simulation time and the accuracy of thermal conductivity calculated can be largely improved. © 2009 The American Physical Society.
Fri, 07 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962872009-08-07T00:00:00Z
- Why edge effects are important on the intrinsic loss mechanisms of graphene nanoresonatorshttps://scholarbank.nus.edu.sg/handle/10635/98586Title: Why edge effects are important on the intrinsic loss mechanisms of graphene nanoresonators
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: Molecular dynamics simulations are performed to investigate edge effects on the quality factor of graphene nanoresonators with different edge configurations and of various sizes. If the periodic boundary condition is applied, very high quality factors (3 × 10 5) are obtained for all kinds of graphene nanoresonators. However, if the free boundary condition is applied, quality factors will be greatly reduced by two effects resulting from free edges: the imaginary edge vibration effect and the artificial effect. Imaginary edge vibrations will flip between a pair of doubly degenerate warping states during the mechanical oscillation of nanoresonators. The flipping process breaks the coherence of the mechanical oscillation of the nanoresonator, which is the dominant mechanism for extremely low quality factors. There is an artificial effect if the mechanical oscillation of the graphene nanoresonator is actuated according to an artificial vibration (non-natural vibration of the system), which slightly reduces the quality factor. The artificial effect can be eliminated by actuating the mechanical oscillation according to a natural vibration of the nanoresonator. Our simulations provide an explanation for the recent experiment, where the measured quality factor is low and varies between identical samples with free edges. © 2012 American Institute of Physics.
Thu, 01 Mar 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985862012-03-01T00:00:00Z
- Thermal contraction in silicon nanowires at low temperatureshttps://scholarbank.nus.edu.sg/handle/10635/98352Title: Thermal contraction in silicon nanowires at low temperatures
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The thermal expansion effect of silicon nanowires (SiNW) in [100], [110] and [111] directions with different sizes is theoretically investigated. At low temperatures, all SiNW studied exhibit a thermal contraction effect due to the lowest energy of the bending vibration mode which has a negative effect on the coefficient of thermal expansion (CTE). The CTE in [110] direction is distinctly larger than the other two growth directions because of the anisotropy of the bending mode in SiNW. Our study reveals that CTE decreases with an increase of the structure ratio γ = length/diameter, and is negative in the whole temperature range with γ = 1.3. © 2010 The Royal Society of Chemistry.
Mon, 01 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983522010-11-01T00:00:00Z
- Manipulation of heat current by the interface between graphene and white graphenehttps://scholarbank.nus.edu.sg/handle/10635/97146Title: Manipulation of heat current by the interface between graphene and white graphene
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: We investigate the heat current flowing across the interface between graphene and hexagonal boron nitride (the so-called white graphene) using both molecular dynamics simulation and nonequilibrium Green's function approaches. These two distinct methods discover the same phenomena that the heat current is reduced linearly with increasing number of carbon atom at the interface, and the zigzag interface causes stronger reduction of heat current than the armchair interface. These phenomena are interpreted by both the lattice dynamics analysis and the transmission function explanation, which both reveal that the localized phonon modes at interfaces are responsible for the heat management. The room temperature interface thermal resistance is about 7×10- 10 m2 K/W in zigzag interface and 3.5×10- 10 m 2 K/W in armchair interface, which directly results in stronger heat reduction in the zigzag interface. Our theoretical results provide a specific route for experimentalists to control the heat transport in the graphene and hexagonal boron nitride compound through shaping the interface between these two materials. © 2011 Europhysics Letters Association.
Sat, 01 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971462011-10-01T00:00:00Z
- Young's modulus of graphene: A molecular dynamics studyhttps://scholarbank.nus.edu.sg/handle/10635/98614Title: Young's modulus of graphene: A molecular dynamics study
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The Young's modulus of graphene is investigated through the intrinsic thermal vibration in graphene which is "observed" by molecular dynamics and the results agree very well with the recent experiment. This method is further applied to show that the Young's modulus of graphene (1) increases with increasing size and saturates after a threshold value of the size; (2) increases from 0.95 to 1.1 TPa as temperature increases in the region [100, 500] K; (3) is insensitive to the isotopic disorder in the low disorder region (
Wed, 23 Sep 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/986142009-09-23T00:00:00Z
- Joule heating and thermoelectric properties in short single-walled carbon nanotubes: Electron-phonon interaction effecthttps://scholarbank.nus.edu.sg/handle/10635/97013Title: Joule heating and thermoelectric properties in short single-walled carbon nanotubes: Electron-phonon interaction effect
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: The electron-phonon interaction (EPI) effect in single-walled carbon nanotube is investigated by the nonequilibrium Green's function approach within the Born approximation. Special attention is paid to the EPI induced Joule heating phenomenon and the thermoelectric properties in both metallic armchair (10, 10) tube and semiconductor zigzag (10, 0) tube. For Joule heat in the metallic (10, 10) tube, the theoretical results for the breakdown bias voltage is quite comparable with the experimental value. It is found that the Joule heat can be greatly enhanced by increasing the chemical potential, while the role of the temperature is not so important for Joule heat. In the zigzag (10, 0) tube, the Joule heat is smaller than the armchair tube, resulting from nonzero bandgap in the electron band structure. For the electronic conductance G e and electron thermal conductance σ el, the EPI has important effect at higher temperature or higher chemical potential. Compared with ballistic transport, there is an opposite tendency for G e to decrease with increasing temperature after EPI is considered. This is due to the dominant effect of the electron phonon scattering mechanism in the electron transport in this situation. There is an interesting electron-drag phenomenon for the phonon thermal conductance in case of low temperature and high chemical potential, where phonons are dragged by electrons from low temperature region into high temperature region through EPI effect. © 2011 American Institute of Physics.
Thu, 15 Dec 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970132011-12-15T00:00:00Z
- Elastic and nonlinear stiffness of graphene: A simple approachhttps://scholarbank.nus.edu.sg/handle/10635/96388Title: Elastic and nonlinear stiffness of graphene: A simple approach
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The recent experiment C. G. Lee [Science 321, 385 (2008)] on the Young's modulus and third-order elastic stiffness of graphene are well explained in a very simple approach, where the graphene is described by a simplified system and the force constant for the nonlinear interaction is estimated from the Tersoff-Brenner potential. © 2010 The American Physical Society.
Fri, 12 Feb 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/963882010-02-12T00:00:00Z
- Self-repairing in single-walled carbon nanotubes by heat treatmenthttps://scholarbank.nus.edu.sg/handle/10635/97899Title: Self-repairing in single-walled carbon nanotubes by heat treatment
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: Structure transformation by heat treatment in single-walled carbon nanotubes (SWCNT) is investigated using molecular dynamics simulation. The critical temperature for the collapse of pure SWCNT is as high as 4655 K due to strong covalent carbon-carbon bonding. Above 2000 K, the cross section of SWCNT changes from circle to ellipse. The self-repairing capability is then investigated and two efficient processes are observed for the SWCNT to repair themselves. (1) In the first mechanism, vacancy defects aggregate to form a bigger hole, and a bottleneck junction is constructed nearby. (2) In the second mechanism, a local curvature is generated around the isolate vacancy to smooth the SWCNT. Benefit from the powerful self-repairing capability, defective SWCNT can seek a stable configuration at high temperatures; thus the critical temperature for collapse is insensitive to the vacancy defect density. © 2010 American Institute of Physics.
Wed, 01 Sep 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978992010-09-01T00:00:00Z
- Thermal conductance of graphene and dimeritehttps://scholarbank.nus.edu.sg/handle/10635/98346Title: Thermal conductance of graphene and dimerite
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: We investigate the phonon thermal conductance of graphene regarding the graphene sheet as the large-width limit of graphene strips in the ballistic limit. We find that the thermal conductance depends weakly on the direction angle θ of the thermal flux periodically with period π/3. It is further shown that the nature of this directional dependence is the directional dependence of group velocities of the phonon modes in the graphene, originating from the D6h symmetry in the honeycomb structure. By breaking the D6h symmetry in graphene, we see more obvious anisotropic effect in the thermal conductance as demonstrated by dimerite. © 2009 The American Physical Society.
Fri, 01 May 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983462009-05-01T00:00:00Z
- A nonequilibrium Green's function study of thermoelectric properties in single-walled carbon nanotubeshttps://scholarbank.nus.edu.sg/handle/10635/95655Title: A nonequilibrium Green's function study of thermoelectric properties in single-walled carbon nanotubes
Authors: Jiang, J.-W.; Wang, J.-S.; Li, B.
Abstract: The phonon and electron transport in single-walled carbon nanotubes (SWCNT) are investigated using the nonequilibrium Green's function approach. In zigzag SWCNT (n,0) with mod(n,3)≠0, the thermal conductance is mainly attributed to the phonon transport, while the electron only has few percentage contribution. The maximum value of the figure of merit (ZT) is about 0.2 in this type of SWCNT. The ZT is considerably larger in narrower SWCNT because of enhanced Seebeck coefficient. ZT is smaller in the armchair SWCNT, where Seebeck coefficient is small due to zero band gap. It is found that the cluster isotopic doping can reduce the phonon thermal conductance obviously and enhance the value of ZT. The uniaxial elongation and compress strain depresses phonons in whole frequency region, leading to the reduction in the phonon thermal conductance in whole temperature range. Interestingly, the elongation strain can affect the phonon transport more seriously than the compress strain, because the high frequency G mode is completely filtered out under elongation strain €>0.05. The strain also has important effect on the subband edges of the electron band structure by smoothing the steps in the electron transmission function. The ZT is decreased by strain as the reduction in the electronic conductance overcomes the reduction in the thermal conductance. © 2011 American Institute of Physics.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956552011-01-01T00:00:00Z
- First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defectshttps://scholarbank.nus.edu.sg/handle/10635/96641Title: First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defects
Authors: Jiang, J.-W.; Wang, B.-S.; Wang, J.-S.
Abstract: The thermal conductance in graphene nanoribbon with a vacancy or silicon point defect is investigated by nonequilibrium Green's function (NEGF) formalism combined with first-principles calculations of density-functional theory with local density approximation. The thermal conductance is very sensitive to the position of the vacancy defect, while insensitive to the position of silicon defect. A vacancy defect situated at the center of the nanoribbon generates a saddlelike surface, which greatly reduces the thermal conductance by strong scattering to all phonon modes; while an edge vacancy defect only results in a further reconstruction of the edge and slightly reduces the thermal conductance. © 2011 American Institute of Physics.
Mon, 14 Mar 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966412011-03-14T00:00:00Z
- How does folding modulate thermal conductivity of graphene?https://scholarbank.nus.edu.sg/handle/10635/96835Title: How does folding modulate thermal conductivity of graphene?
Authors: Yang, N.; Ni, X.; Jiang, J.-W.; Li, B.
Abstract: We study thermal transport in folded graphene nanoribbons using molecular dynamics simulations and the non-equilibrium Green's function method. It is found that the thermal conductivity of flat graphene nanoribbons can be modulated by folding and changing interlayer couplings. The analysis of transmission reveals that the reduction of thermal conductivity is due to scattering of low frequency phonons by the folds. Our results suggest that folding can be utilized in the modulation of thermal transport properties in graphene and other two dimensional materials. © 2012 American Institute of Physics.
Mon, 27 Feb 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968352012-02-27T00:00:00Z
- Theoretical study of thermal conductivity in single-walled boron nitride nanotubeshttps://scholarbank.nus.edu.sg/handle/10635/98340Title: Theoretical study of thermal conductivity in single-walled boron nitride nanotubes
Authors: Jiang, J.-W.; Wang, J.-S.
Abstract: We perform a theoretical investigation on the thermal conductivity of single-walled boron nitride nanotubes (SWBNT) using the kinetic theory. By fitting to the phonon spectrum of the boron nitride sheet, we develop an efficient and stable Tersoff-derived interatomic potential which is suitable for the study of heat transport in sp2 structures. We work out the selection rules for the three-phonon process with the help of the helical quantum numbers (κ,n) attributed to the symmetry group (line group) of the SWBNT. Our calculation shows that the thermal conductivity κph diverges with length as κphLβ with exponentially decaying β(T)e-T/Tc, which results from the competition between boundary scattering and three-phonon scattering for flexure modes. We find that the two flexure modes of the SWBNT make dominant contribution to the thermal conductivity, because their zero frequency locates at κ=±α, where α is the rotational angle of the screw symmetry in SWBNT. © 2011 American Physical Society.
Mon, 29 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983402011-08-29T00:00:00Z