| The rapid development of 5G communications,Internet of Things,cloud computing and big data has made the integration of microelectronic devices higher and higher,and there is a trend of gradually exceeding Moore’s law prediction.In order to maintain the proper functioning of electronic devices.it is urgent to find alternatives to traditional heat dissipation materials.Meanwhile,in the context of the world’s energy shortage,human beings urgently need to develop new energy-saving technologies,and researchers have set their sights on thermoelectric materials with great commercial application potential.As a kind of graphene-like material with excellent physical performance,two-dimensional layered transition metal dichalcogenides have unique thermophysical properties that make them suitable for application in the field of heat dissipation for microelectronic devices and thermoelectric material.Therefore,it is of great significance to study the thermal transport properties of two-dimensional transition metal dichalcogenides.In this dissertation,combining with the first-principles method based on density functional theory and Boltzmann transport theory,several typical two-dimensional transition metal dichalcogenides are taken as the research objects.In-depth researches are conducted in the thermal transport properties of monolayer Mo S2,monolayer Sn S2,monolayer Sn Se2 and bilayer Sn S2/Sn Se2 heterojunctions,as well as the thermoelectric transport properties of Janus monolayers Sn SSe.At the same time,systematic analysis on the principle and regulation mechanism of phonon thermal transportation are accomplished in this dissertation so as to predict the thermoelectric properties of Janus monolayers Sn SSe.The research findings provide theoretical reference and guidance for the development,design,application and performance prediction of nanoelectronics devices and thermoelectric materials.The main research work of this dissertation is as follows:（1）For monolayer Mo S2,its phonon group velocity,phonon relaxation time and Grüneisen parameters are calculated for understanding of its thermal transport properties,and the lattice thermal conductivity is obtained as 101.5 W/（m·K）at 300 K.In order to analyze the influence of different phonon branches on thermal conductivity,the relationship between the lattice thermal conductivity with temperature,frequency and the mean free path of phonons are studied,finding that the influence of acoustic phonons on the lattice thermal conductivity is greater than that of the optical branch.As a conclusion,the heat dissipation capacity of monolayer Mo S2 is similar to that of traditional silicon-based materials.And if monolayer Mo S2could be effectively modulated in lower thermal conductivity,it will be commercially applied.（2）The study on thermal transport properties of monolayer Sn S2,monolayer Sn Se2 and bilayer Sn S2/Sn Se2 heterojunctions are made by calculating phonon spectrum,phonon group velocity and phonon relaxation time.Their lattice thermal conductivity at 300 K are calculated as 18.82,6.05 and 9.16 W/（m·K）respectively.By comparing the phonon dispersion curves of the three,the acoustic phonon branch coupled with the optical phonon branch of the heterojunction to a certain extent causes scattering between them,which inhibits the thermal transportation of phonons.Therefore,the construction of interlayer heterojunction is an effective method to modulate the thermal transport properties of two-dimensional transition metal dichalcogenides,which can provide theoretical guidance for the development,design and application of related thermoelectric devices.（3）The thermoelectric transport properties of Janus monolayers Sn SSe are researched,which shows the lattice thermal conductivity at 300K to be 23.6 W/（m·K）.Based on the GGA+HSE06 hybrid function,the band gap of the monolayer Sn SSe is calculated to be 1.59 e V.Simultaneously,the electronic transport coefficients including electrical conductivity,Seebeck coefficient and power factor are obtained.The thermoelectric properties of two-dimensional layered transition metal dichalcogenides can be modulated by applying strain to the material.The optimal ZT value of p-type doped monolayer Sn SSe at 700 K is 1.66,which reflects the application potential of monolayer Sn SSe in the field of thermoelectric power. |
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