Ballistic thermal resistance of graphene nano-junctions is investigated using non-equifibrium molecular dynamics simulation. The simulation system is consisted of two symmetrical trapezoidal or rectangular graphene na...Ballistic thermal resistance of graphene nano-junctions is investigated using non-equifibrium molecular dynamics simulation. The simulation system is consisted of two symmetrical trapezoidal or rectangular graphene nano- ribbons （GNRs） and a connecting nanoscale constriction in between. Prom the simulated temperature profile, a big temperature jump resulted from the constriction is found, which is proportionM to the heat current and corresponds to a local ballistic thermal resistance. Fixing the constriction width and the length of GNRs, this ballistic thermal resistance is independent of the width of the GNRs bottom layer, i.e., the convex angle. But interestingly, this thermal resistance has obvious size effect. It is inversely proportional to the constriction width and will disappear with the constriction being wider. Moreover, based on the phonon dynamics theory, a theoretical model of the ballistic thermal resistance in two-dimensional nano-systems is developed, which gives a good explanation on microcosmic level and agrees well with the simulation result quantitatively and qualitatively.展开更多
The transient heat conduction in both armchair and zigzag-edged graphene ribbons pulsed by local heating with a duration of 1 ps was studied using nonequilibrium molecular dynamics simulations. The results show that t...The transient heat conduction in both armchair and zigzag-edged graphene ribbons pulsed by local heating with a duration of 1 ps was studied using nonequilibrium molecular dynamics simulations. The results show that the heat pulse excites two waves which indicates non-Fourier heat conduction. One of the two waves is a sound wave(first sound), which has macroscopic momentum and propagates at the speed of sound. The other is a thermal wave(second sound), whose propagation speed is 1=ffiffi3pof the sound velocity. The sound wave excited by the heat pulse is a longitudinal wave, whose energy is only transported in the longitudinal direction. The thermal wave excited by the heat pulse is generated by transverse lattice vibrations, with the energy only having the transverse component. The observed anisotropy of the transient heat conduction suggests that the system is in a non-equilibrium state during propagation of the heat pulse. Further statistical analyses show that the displacement of the heat pulse energy is related to the time as hr2 i / t1:80, which implies that heat transport is ballistic-diffusive transport in graphene. The higher proportion of the ballistic transport will lead to stronger heat waves. At the crest of the thermal wave, energy is transported ballistically, while in the diffusive region and during attenuation of the thermal wave,the energy is transported diffusively.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos.51322603,51136001,51356001Science Fund for Creative Research Groups(No.51321002)+1 种基金the Program for New Century Excellent Talents in University,Tsinghua University Initiative Scientific Research Programthe Tsinghua National Laboratory for Information Science and Technology of China
文摘Ballistic thermal resistance of graphene nano-junctions is investigated using non-equifibrium molecular dynamics simulation. The simulation system is consisted of two symmetrical trapezoidal or rectangular graphene nano- ribbons （GNRs） and a connecting nanoscale constriction in between. Prom the simulated temperature profile, a big temperature jump resulted from the constriction is found, which is proportionM to the heat current and corresponds to a local ballistic thermal resistance. Fixing the constriction width and the length of GNRs, this ballistic thermal resistance is independent of the width of the GNRs bottom layer, i.e., the convex angle. But interestingly, this thermal resistance has obvious size effect. It is inversely proportional to the constriction width and will disappear with the constriction being wider. Moreover, based on the phonon dynamics theory, a theoretical model of the ballistic thermal resistance in two-dimensional nano-systems is developed, which gives a good explanation on microcosmic level and agrees well with the simulation result quantitatively and qualitatively.
基金supported by the National Natural Science Foundation of China (51322603, 51136001, 51356001)the Science Fund for Creative Research Groups (51321002)+2 种基金the Program for New Century Excellent Talents in UniversityTsinghua University Initiative Scientific Research Programthe Tsinghua National Laboratory for Information Science and Technology of China
文摘The transient heat conduction in both armchair and zigzag-edged graphene ribbons pulsed by local heating with a duration of 1 ps was studied using nonequilibrium molecular dynamics simulations. The results show that the heat pulse excites two waves which indicates non-Fourier heat conduction. One of the two waves is a sound wave(first sound), which has macroscopic momentum and propagates at the speed of sound. The other is a thermal wave(second sound), whose propagation speed is 1=ffiffi3pof the sound velocity. The sound wave excited by the heat pulse is a longitudinal wave, whose energy is only transported in the longitudinal direction. The thermal wave excited by the heat pulse is generated by transverse lattice vibrations, with the energy only having the transverse component. The observed anisotropy of the transient heat conduction suggests that the system is in a non-equilibrium state during propagation of the heat pulse. Further statistical analyses show that the displacement of the heat pulse energy is related to the time as hr2 i / t1:80, which implies that heat transport is ballistic-diffusive transport in graphene. The higher proportion of the ballistic transport will lead to stronger heat waves. At the crest of the thermal wave, energy is transported ballistically, while in the diffusive region and during attenuation of the thermal wave,the energy is transported diffusively.
