Molecular Dynamics Study On The Heat Transport Of Low-dimensional Carbon Nanomaterials

With 5G era approaching,heat dissipation will be the key factor which affecting the efficiency and lifetime of electronic equipment with high power density and high integration.It is expected that thermoelectric conversion technology will provide a comprehensive and coordinated solution for improving energy utilization and alleviating environmental pollution to meet the requirements of both energy-saving and emission-reduction in China.However,there exists the defect of insufficient thermoelectric conversion performance in the thermoelectric materials.Low dimensional carbon nanomaterials,including carbon nanotube,graphene and graphyne,have excellent physical and chemical properties,which can be applied to the fields of thermal management and thermoelectric conversion.Therefore,investigating the thermal transport properties of low dimensional carbon nanomaterials not only is useful to solve the heat dissipation problem of electronic devices,but also provides theoretical guidance for regulating and optimizing the performance of thermoelectric materials.In this dissertation,it was investigated deeply with the method of molecular dynamics simulation that the thermal transport properties for low dimensional carbon nanomaterials like single-walled carbon nanotube,graphene and graphyne.Moreover,it is mainly discussed how structural parameters,such as size,defect type and position affect the thermal conductivity.And the regulation mechanism of phonon thermal transport is revealed and analyzed.The main research results of the dissertation are as follows.（1）For single-walled carbon nanotubes,the effects of tube length and N-doping defect on their thermal transport properties were studied.The results show that the thermal conductivity of single-walled carbon nanotubes increases linearly with the increase of tube length,but the increase rate decreases gradually.It is found that the thermal conductivity of single-walled carbon nanotube is 1377W·m^-1k^-1through the simulation calculation.With the increase of N-doping defect concentration,the thermal conductivity first decreases sharply and then gradually stabilize.What’s more,it is shown that single-walled carbon nanotubes have high thermal conductivity,which is useful to solve the heat dissipation problem of electronic devices and have certain application potential.（2）For graphene nanoribbons,the effects of size,temperature,defect concentration and different types of defects on the thermal transport properties,were investigated,and the phonon thermal transport regulation mechanism was analyzed.It is found that the thermal conductivity of graphene nanoribbons is approximately linear with its length and width,and decreases with the increasing temperature.The regulation of temperature on phonon thermal transport is more obvious in graphene nanoribbons with doping defects.It is found that the effect of vacancy defects on the thermal conductivity is the most influential at 400K.However,the influence of doping defects gradually strengthens and exceeds that of vacancy defects as the temperature rises.Furthermore,the thermal conductivity of graphene obtained by reciprocal fitting method is as high as 4078W·m^-1k^-1,which indicates that graphene has great application potential in the field of electronic equipment cooling,and can be promising to solving the heat dissipation problem of high-power electronic equipment in the future.（3）In view of the good semiconductor properties of graphyne,the thermal transport properties of graphyne nanoribbons were studied comprehensively and deeply.And it is mainly discussed that how the influences of size,different defect types（including vacancy and N-doping defects）,defect location and arrangement effect on phonon thermal transport.The results show that the dependence of the thermal conductivity of graphene on size is much weaker than that of graphene nanoribbons.What’s more,the thermal conductivity of graphyne obtained by reciprocal fitting method is 24W·m^-1k^-1.Meanwhile,the phonon thermal transport properties of graphene nanoribbons can be regulated effectively by defect type,defect position（horizontal and vertical directions,benzene ring and acetylene chain）and arrangement.Among low dimensional carbon nanomaterials,graphyne conductivity is expected to become an excellent thermoelectric material for its low lattice thermal.