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A5: Nanoscale and low dimensional effects
Nanostructure has been introduced into thermoelectric (TE) field. And high performance TE devices with the nanostructure have been reported. Furthermore, Bismuth Telluride (Bi2Te3) has been studied long time and shown the highest efficiency around room temperature. Therefore, it should be expected that Bi2Te3 film within nanoparticles (NPs) is high potential TE composited material. To improve the efficiencies of TE materials, TE material with nanostructure have shown that those materials decrease thermal conductivities, due to scattering phonon [1]. In addition, fabricating NPs in uniform size and controlling distance between NPs are still difficult.
To overcome these problems, we have utilized Bio Nano Process (BNP) [2] in this study. BNP is using ferritin, which is one of the proteins, and that can fabricate the NPs in uniform size and distribute them. PEG-ferritin can control distribution of NPs [3]. Here we report that we have found the way with BNP method to control the NPs’ separated distances in the certain region, which is shorter than the phonon’s Mean Free Path (MFP) and longer than the electron’s MFP. In the materials which were controlled with NPs’ distances in Bi2Te3 thin films, thermal conductivities were decreased and Seebeck coefficients and electric conductivities were not changed. Consequently, ZT can be enhanced. In our research, we optimized protein concentration, ion strength, rotation speed of spin-coater and chemistry modified on ferritin etc. We achieved to control the distance of NP in around 40 nm. That distance is suitable to reduce the thermal conductivity in Bi2Te3 matrix.
Reference:
[1] J. F. Li, W. S. Liu, L. D. Zhao, and M. Zhou, NPGAsiaMater. 2 152-158 (2010).
[2]I.Yamashita, Thin Solid Film. 393, 12 (2001).
[3] R. Tsukamoto, M. Godonoga, R. Matsuyama, M. Igarashi, J. Heddle, S. Samukawa, I. Yamashita, Langmuir, 2013, 29 (41), pp 12737–12743.