Regulation Of Thermal Transport Properties Of Graphene Like Carbon-based Two-dimensional Materials

Owing to the excellent physical properties,two-dimentional(2D)material has attracted growing research interest from scholars in many fields,such as electricity and light.Recently,the thermal properties of 2D material play a crucial role in thermal management within many applications.Hence,the transmission properties of phonons become one of the most important directions of studies of two-dimensional materials.By mastering the effects of different conditions on the thermal properties of materials,the application value and the heat transfer mechanism in 2D materials can be improved,which is of great significance for the development of 2D materials.In this thesis,we evaluate the calculation of the variational thermal conductivity(k)of graphene-like carbon-based 2D material with the parameters like random doped ratio,periodic length and the depth of the nanoindenter.We further analyze the phonon behaviors of 2D material to reveal the mechanism of affect by the different regulations.The main work includes:1.For the system of random doping by C3B and C3N,the thermal conductivity of monolayer C3BxN1-x alloy presents a U-shaped profile with the increasing of the doping ratio(x).The k arrives the minimum at x=0.5,which is equal to 81.78 W m-1 K-1.We analyze the inner information of phonon behaviors in monolayer C3BxN1-x alloy,and attribute the profile to the phonon-impurity scattering and localization.2.For the system of superlattice composed of C3B and C3N with a fixed x as 0.5,the k of C3B0.5N0.5-SL shows an initial decreasing and then rising trend.The minimum k is 146.85 W m-1 K-1,and the corresponding period length is 5.11 nm,which divide the superlattices into coherent region and incoherent region,and known as the coherent length.When the periodic length is smaller than coherent length,coherent phonon modes emerge because of the phonon interference,in which the superlattice can be regarded as a 'newly generated material',where the superlattice is located at the coherent region.When the periodic length is larger than coherent length,the decreasing number of the interfaces in superlattice lessens phonon-interface scattering and cause the increasing thermal conductivity.3.For the system of graphene-like carbon-based 2D material affected by the local strain caused by the nanoindenter,the thermal conductivity presents a decreasing trend with the increasing of the depth of the pressing,and when the depth become higher than the breaking point,the plank will be penetrated,and the k will rebound to a higher,but still lower than the k of plank without strain.The analysis of phonon behavior shows that the trend of thermal conductivity is resulted by the unevenness of the phonons in the plank and the strain-affected in the whole plank.The unevenness of phonons will bring out a large scattering of phonon,and the strain in plank will change the basic phonon information and result in a potential decreasing trend of k.According to the analysis of the mechanical properties of the 2D material,we reveal that the reason of the breaking is the excessive stress by the local strain and the wave-like transfer of the sheet.