Anomalous reduction of thermal conductivity in coherent nanocrystal architecture for silicon thermoelectric material

作者：Nakamura Yoshiaki^*; Isogawa Masayuki; Ueda Tomohiro; Yamasaka Shuto; Matsui Hideki; Kikkawa Jun; Ikeuchi Satoaki; Oyake Takafumi; Hori Takuma; Shiomi Junichiro; Sakai Akira

来源：Nano Energy, 2015, 12: 845-851.

DOI：10.1016/j.nanoen.2014.11.029

• Nano-structures
• Silicon
• Molecular beam epitaxy
• Thermal conductivity

Reduction of thermal conductivity kappa while preserving high electrical conductivity CS in materials continues to be a vital goal in thermoelectric study for the reuse of exhaust heat energy. In the use of an eco-friendly and ubiquitous element, Si as thermoelectric material, high kappa value in bulk Si is the essential bottleneck to achieve high dimensionless figure of merit. This is a motivation for many recent studies on reducing kappa in Si, by nanostructuring, e.g., using grains/wires with size smaller than the phonon mean free path. However; kappa reduction that can be achieved tends to be saturated presumably due to an amorphous limit. Here, we present a nanoarchitecture for defeating the kappa amorphous limit while preserving bulk-like sigma. This new nanoarchitecture is an assembly of Si nanocrystals with oriented crystals separated by a 1-monolayer amorphous layer with well-controlled nanoscale shaped interfaces. At these interfaces, novel phonon scattering occurs resulting in kappa reduction below the amorphous limit. Preservation of bulk-like CS results from the coherency of the carrier wavefunctions among the oriented nanocrystals separated by the ultrathin amorphous layer.

• 出版日期2015-3