Preparation And Properties Of Bi₂Se₃ Thermoelectric Thin Films Doped With Cu And Ag Metallic Elements

Recently,how to improve the thermoelectric properties and increase its thermoelectric conversion efficiency is a hotspot for the material scientists around the world.By the nanotechnology,quantum size effect,and size effect,the researcher is expected to synthesize a sort of new type thermoelectric thin film materials with higher thermal efficiency,cheap light,elasticity and plasticity.Aimed at the synthesis and thermoelectric performance of new thermoelectric materials,this thesis researched the Cu,Ag doping Bi₂Se₃ thermoelectric thin film materials.And the various characteristics of Cu and Ag doped thermoelectric samples were analyzed by using of various analytical testing equipments.The researching results have great significance to develop various novel Bi₂Se₃ thermoelectric materials and improve its thermoelectric optimal value and Seebeck coefficient,and to promote its application value.the main research work of the thesis is as follows:The two dimensional Bi₂Se₃ thermoelectric thin films were prepared by thermal evaporation method with high purity Bi₂Se₃ powder as raw material.And the microstructure,surface morphology,and its thermoelectric properties were analyzed by using of SEM,XRD,EDX testing and other testing equipments.Meanwhile,the thermoelectric conversion mechanism of the synthesized Bi₂Se₃ thermoelectric materials is analyzed and discussed.By thermal evaporation method,Cu and Ag metallic elements were doped into Bi₂Se₃semiconductor material.The different doping quality percentage composite Bi₂Se₃thermoelectric thin film samples were prepared.And the microstructure,surface morphology,and its thermoelectric properties of doped with Cu and Ag metallic elements were analyzed.Compare with the conventional carbon nanotube and organic polymer composite thermoelectric materials,the synthesized new type Bi₂Se₃ semiconductor thermoelectric materials reduce the manufacturing cost,improve the composite electronic transport properties.At the same time,through the doping with Cu and Ag metal elements,a large number of interfacial potential barriers are formed in the Bi₂Se₃ thermoelectric thin film material,increasing the scattering intensity to the low energy electron and phonon,and improve the optimal value of the synthesized thermoelectric materials.Because Bi₂Se₃ crystal structure is multilayer,the research of this thesis found this property can make the metal atoms embed its layered structure and disperse in grid system easily.And the embedded metal atoms can form a large number of phonon interfacial potential barrier in the Bi₂Se₃ thermoelectric thin film materials.It also can reduce the transmitting capacity of the low energy electron and phonon in grid system,to strengthen their scattering effect,reduce the thermal conductivity of thin film materials,improving the efficiency of thermoelectric efficiency.By comparing with different samples of Cu,Ag metallic elements doped into Bi₂Se₃materials,the results of the thesis found that the Ag/Bi₂Se₃ thermoelectric thin film material showed better thermoelectric properties.The testing result come from the metal and chemical activity of Ag element is better than Cu element.And the atomic radius of Ag element is bigger than the Cu atoms.As a small amount of Ag doped into the Bi₂Se₃ thermoelectric thin film material,it can significantly improve the conductivity of Ag/Bi₂Se₃ composite thin films.Meanwhile,the doped Ag atoms can form good connection with the layered Bi₂Se₃ crystal structure atoms.This effect can increase the transmission ability of the interlayer charge carrier in the composite system.And the part of Ag atoms can embedded in the lattice with interstitial atom and replacement ones,it can offers a sort of new carrier as donor?electrons and holes?,effectively improve the mean free path of lattice structure of electronic transmission and transmission efficiency.In the end,the carrier transmission performance in the composite system were increased.