Temperature coefficients of phonon frequencies and thermal conductivity in thin black phosphorus layers

We investigate the temperature dependence of three major Raman modes of black phosphorus (BP) prepared by mechanical exfoliation from room temperature to 325 °C. With increasing temperature, all the Raman peaks show redshift in peak position and broadening in linewidth, but they depend on the film thickness. The first-order temperature coefficients of Ag1, B2g, and Ag2 are measured to be −0.0199, −0.0304, and −0.0321 cm−1/K, respectively, in a ∼20-layer film. With decreasing thickness, the temperature coefficient decreases. The average thermal conductivity of a 70-nm thick BP film at room temperature is determined to be 15.8 W/mK when suspended, and 29.2 W/mK when supported on a SiO2/Si substrate. Thermal decomposition temperature is found to be around 350 °C in N2 environment.