Reduced thermal conductivities of Si one-dimensional periodic structure and nanowire

Air-suspended Si nanowires and one-dimensional (1D) phononic crystals (PnC) nanostructures were fabricated and the thermal conductivity for each structure was measured. The nanostructures were fabricated by a top-down approach from a 145-nm-thick silicon-on-insulator wafer. The thermal conductivities of these nanostructures were measured by an all-optical system based on the time domain thermoreflectance method that we adapted to measure the properties of air-bridge structures. The reduction in thermal conductivity was clearly observed as the width of the nanowire is decreased due to more frequent surface scattering. The 1D PnC structure showed an unexpectedly low thermal conductivity, which is much lower than that of a nanowire with the average width of 1D PnC nanostructure. (C) 2014 The Japan Society of Applied Physics