(630a) Silicon Nanostructures As Efficient Thermoelectric Materials

 It has been recently reported that thermal conductivity greatly decreases in single crystalline silicon nanostructures without much affecting electrical properties. Although it is qualitatively demonstrated that surface roughness in nanowires and nanohole arrays in silicon membranes (holey silicon) play a significant role in reducing thermal conductivity, the underlying reasons remain unknown and warrant quantitative studies and analysis. In this report, silicon nanowires were controllably roughened and the surface roughness near the length scale of thermal phonon wavelength is shown to interfere with phonon transport below the Casimir limit. Furthermore, a platform to simultaneously measure thermal conductivity, electrical conductivity, and the Seebeck coefficient for holey silicon has been developed to extract ZT directly from a single device. Decoupling of electron and phonon transport associated with their mean free path has been studied at phonon glass electron crystal regime. Lastly, cross-plane thermal conductivity measurement of holey silicon unveiled the multi directional phonon-glass property of  holey silicon.