Measurement of Thermal Conductivities of Bi2Te3 and Sb2Te3 Nano-Powders at Extreme Temperature and Strain

The Raman optothermal technique has been the most successful method for measurement of thermal conductivity of two dimensional (2D) materials, and was used to measure the thin films for the first time in this work. In this technique, a laser is focused at the center of a thin film and used to measure the peak position of a Raman-active mode. As the laser power is increased, the sample is heated which enables red-shift Raman mode due to thermal softening. Another comparison experiment is conducted by placing the samples on a heating platform and monitor the change of Raman-active mode peak position shift. Combining these two sections of experiments provide us the thermal modeling can then be used to extract the thermal conductivity from the measured shift rate. We have used a refined version of the optothermal Raman technique to study thermal conductivity of thin films of Bi2Te3 and Sb2Te3, at extreme temperatures and mechanical strains. It is the first thermal measurement on these two materials by Raman optothermal technique. This work also addresses several important issues in the measurement of thermal conductivity of thin films using Raman spectroscopy.

Raman Studies of Hydrogen Passivation in Silicon

ABSTRACTWe have studied the hydrogen passivation of boron acceptors in bulk crystalline silicon with Raman scattering. Upon hydro-genation, distinct changes in the optical phonon lineshape and the localized vibrational modes of boron are observed. The hy-drogen in the passivated region gives rise to a specific Raman-active mode, whose vibrational frequency depends strongly on temperature and uniaxial stress. Implications of these results on possible structural models are discussed.