The Thermoelectric Performance Of Low Dimensional Silicon Nanostructure

With the rapid development of science and technology,the world’s population is increasing and the world and industrialization is accelerating,energy shortage and environmental pollution problem are becoming increasingly serious,thermoelectric materials is an important means to solve these problems.Thermoelectric materials can directly convert temperature differences to electric voltage and vice versa,but they are limited in practical applications because of their low conversion efficiency and high cost.However,the discovery of graphene has triggered an upsurge of research on nano materials by scientists from all over the world.The thermoelectric properties of nano materials are better than those of bulk materials due to their larger crystal plane and quantum confinement effect.Silicon as the pillar of microelectronics industry,the study of thermoelectric properties of silicon-based nano thermoelectric materials not only provides theoretical guidance for obtaining higher performance thermoelectric materials,but also alleviates the energy crisis and environmental pollution.In this paper,we performed a comprehensive study on the thermoelectric property of dumbbell silicene nanoribbons(DB-SNRs)and Si24 nanowires via utilizing nonequilibrium Green’s function(NEGF)method as implemented in the density functional based tight-binding(DFTB)framework.These studys provided theoretical guidance for finding efficient silicon-based thermoelectric materials.The main research contents are as follows:1.The electronic,phonon transport properties and thermoelectric properties of armchair dumbbell silicene nanoribbons(A-DB-SNRs)and zigzag dumbbell silicene nanoribbons(Z-DB-SNRs)were investigated.Our results show that the DB-SNRs have good thermoelectric properties.At the same time,A unique step-like width dependence of phononic thermal conductance is also observed in Z-DB-SNRs.this phenomenon is explained by analyzing their phonon state density.In addition,we also explore the influence of temperature on thermoelectric property of DB-SNRs.The ZT value is increased with the increasing of temperature.At 600 k,the ZT values of A-DB-SNRs(NA=4)can reached 2.34.2.The thermoelectric properties of Si24 nanowires were also studied in order to combining photoelectric and thermoelectric techniques.By analyzing the thermoelectric properties of Si24 nanowires in different growth directions,it is found that Si24 nanowires in[010]crystal orientation have higher ZT value.Since then,we have mainly explored the influence of doping germanium atoms on it.The results show that the ZT value of Si24 nanowire gradually improved with the increase of doping concentration.Through the analysis of its power factor and phonon thermal conductivity,it is found that the decline of phonon thermal conductivity plays a leading role in ZT value of Si24 nanowires.The decrease of phonon thermal conductivity is due to doping which destroys the phonon transmission channel of[010]crystal of Si24 nanowires,causing phonon scattering and weakening phonon transmission.