Effect And Control Of Thermal Transport Of Graphene Nanoribbons By Defect And Boundary

Low-dimensional nanostructures of graphene are more and more extensivelyresearched in both theory and experiment because of its excellent physical propertiesin electrical、thermal、 mechanical、 optical and magnetic field, and it is also widelyconsidered as a kind of ideal material that comprise novel nanoscale devices. In orderto precisely control the heat transport of graphene-based thermal devices and solve theheat dissipation problem of the highly integrated graphene electronic devices, it isparticularly important to research thermal transport properties of graphene-baseddevices in nanoscale. In this thesis, using Green’s function method, the thermaltransport properties of graphene nanoribbons with defects and boundary wasinvestigated.This thesis is divided into five chapters, the first chapter introduces thediscovery、preparation method and the unique physical properties of low-dimensionalmaterials of graphene. Finally, we summarize the contents of this thesis.In the chapter two, the Green’s function method is presented. Physical parametersof the thermal transport are investigated by using the Green’s function method, such as,transmission coefficient、local density of phonons and the thermal conductivity etc.In the chapter three, Using nonequilibrium Green’s function method, the thermaltransport properties of zigzag graphene nanoribbons (ZGNR) embedded in a finite(semi-infinite or infinite) long linear defect is investigated. The results show thatdefect type and defect length have significant influence on the thermal conductance ofZGNR. When the embedded linear defects have the same length, thermal conductanceof ZGNR embedding t5t7defect is lower than that of ZGNR embedding SW defect.As for the ZGNR embedded in a finite and same type defects, their thermalconductivity decreases with the length increase of the defect. By comparing theZGNRs embedded in a finite, semi-infinite and infinite long defects, we find that thethermal conductance of ZGNR embedding in an infinite long defect is higher than thatof ZGNR embedding in a semi-infinite defect, while the thermal conductance of thelatter is higher than that of ZGNR embedding in a finite long defect. These thermaltransport phenomena are explained by analyzing transmission coefficient and localdensity of states. These results indicate that linear defects can tune thermal transportproperties of ZGNR efficiently. In the chapter four，we study influence and control of thermal transportproperties of graphene nanoribbons by changing of force constant. Research shows,the stress can shift the phonon mode frequency. Under the condition that the stressP>1, some phonon of the high frequency transmission platform local on modulatedcarbon chains,and heat current only flow along the modulated carbon chains;thenumber of carbon chains have important role on thermal conductivity in the middle ofgraphene nanoribbon. Once the stree is determined, the thermal conductivity ofgraphene nanoribbon is only controlled by temperature and numbers of stree carbonchains.Finally, in the chapter five, we briefly summarize the work of this paper, andlook forward to the future of material area of graphene.