전기화학적 방법을 이용한 1D 열전 나노 구조체 개발에 관한 연구

Abstract

Thermoelectric has been inquired as applied for cooler and power generators. The efficiency of thermoelectric materials is estimated by a Figure of merit (ZT), which express as ZT = (α2σ/κ)T (α : seebeck coefficient, σ : electrical conductivity and κ : thermal conductivity) and T is the absolute temperature. Thermoelectric materials have been investigated steadily since 1930s. There were various approaches to enhance the ZT value, but successful results was obtained recently as developments of nano science and engineering. Enhancing the electrical conductivity as inserting metal in thermoelectric material in bulk scale is investigated to enhance the ZT. Such research achieved the part of success as increasing the thermopower (=α2σ) but decreasing the ZT value because of increasing the heat conductivity according to Wiedmann-Franz law. However, Different properties of metal nanostructure are discovered as development of nano scale engineering. In nanoscale, different phenomena are observed because of their unique structure and large surface area. In case of metal nanowire, metal nanowire has not their bulk properties as much of increasing the scattering effects. Metal nanowire has the lower electrical conductivity as ordinary size effect but they have the more lower thermal conductivity compare with the bulk metal. However, metal nanowire has the good electrical conductivity compare with common thermoelectric material (Bi2Te3) and has the lower thermal conductivity compare with bulk metal. Synthesis of inserting metal nano structure into thermoelectric nano structure is investigated to enhance the thermoelectric efficiency. Decreasing the thermal conductivity at interface of nano segments is expected and also nanowire structure will be collaborated to enhance the surface scattering. Thermal conductivity could be decreased in enhanced scattering effect in this nanoscale structure. And inserting the metal nanostructure into thermoelectric material could be enhancing the electrical conductivity. This new concept of approach to enhance the thermoelectric has not been unprecedented before. In here, various electrochemical synthesis methods were investigated in advance as essential prerequisite backgrounds and experiments for synthesis of metal-bismuth telluride segmented nano structure by electrochemical methods. In here, this thesis is classified into three themes. In the first session “Electrodeposition of silver nickel thin film”, co-electrodeposition method was investigated whether this method is appropriate for the synthesis of silver-nickel electrodeposited thin film. After this method was estimated, co-electrodeposition method was applied to one dimensional structure. And also other synthesis method of silver-nickel one-dimensional nanowire was also investigated in the second session. In the second session “Electrodeposition of silver nickel segmented nanowire”, two electrochemical methods were performed and compared to optimize the synthesis of one dimensional silver-nickel nanostructure. In the third session “Galvanic displacement electrodeposition of silver nickel segmented nanowire”, synthesis of silver embedded bismuth telluride nanowire was investigated. That structure is could be synthesized by galvanic displacement reaction of nickel to bismuth telluride. Various studies of electrochemical methods from two-dimensional to one dimensional were investigated to approach the new concept of thermoelectric nano structure.