Study On Thermoelectric Properties Of Novel Thin Film Materials

In recent years,with the development and preparation of low dimensional thin film materials,and because of its excellent physical properties,such as graphene has an extremely high electron mobility,transition metal dichalcogenides(TMD),boron and black phosphorus with natural band gap,which make it become the focus of people's research.With the increasing demand for new energy sources,environmental protection materials and thermoelectric devices.Therefore,it is very necessary to provide guidance for the application of these new low dimensional materials in daily life,industrial and electronic devices by theoretical calculations to explore improve their thermoelectric properties.The search for thermoelectrics with higher figures of merit(ZT)will never stop due to the demand of heat harvesting.Single layer transition metal dichalcogenides,namely,MX2(where M is a transition metal and X is a chalcogen),that have electronic band gaps are among the new materials that have been the focus of such research.Here,we investigate the thermoelectric transport properties of hybrid armchair-edged TMD nanoribbons,by using the non-equilibrium Green's function technique combined with the first principles and molecular dynamics methods.We find a ZT as high as 7.4 in hybrid MoS2/MoSe2 nanoribbons at 800 K,creating a new record for ZT.Moreover,the hybrid interfaces by substituting X atoms are more efficient than those by substituting M atoms to tune the ZT.The origin of such a high ZT of hybrid nanoribbons is the high density of the grain boundaries: the hybrid interfaces decrease thermal conductance drastically without a large penalty to electronic conductance.At the same time,in order to further explore the thermoelectric properties of new thin film materials.We studied the thermoelectric properties of stanene and its derivatives.The effects of spin orbit coupling(SOC)on their transport properties are analyzed.In this part,we investigate their electronic structure properties by using the first principles,and study their Seebeck coefficients,conductance,and power factor by using the semi empirical Boltzmann transport theory.According to our calculations,it is found that SnI has a significant SOC effect,which enables the band to open an indirect band with a gap of 341 meV and change the shape of the band.The SOC effect makes the outlines of the band at the(38)point change from a parabolic shape to a hump shape,increasing the effective mass of the electron state density and the Seebeck coefficient.However,the SOC effect has no significant effect on the thermoelectric properties of stanene.In the later chapter,we mainly study the influence of SOC effect on the thermoelectric transportproperties of stanene and its derivatives,which will provide some reference for the application of topology thermoelectric materials.