Pump–probe scanning-tunneling-microscope light-emission spectroscopy of Sb2Te3

Abstract

We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pump-laser pulses using scanning-tunneling-microscope (STM) light emission synchronized with ps-probe-laser pulses delayed by times t after individual pump pulses. We determined the gap energy ΔE at the F point in the band diagram of Sb2Te3 from the STM light-emission spectra as a function of the delay time t. We found that ΔE increased monotonically with t from the original value of 1.62 eV for a delay time of 0 to 15.3 ps and it decreased toward that original value (1.62 eV) for t in the time span between 15.3 and 28 ps; we saw no change in ΔE for t≥28 ps. By comparing this t-dependence of ΔE with the dielectric functions of the crystalline and amorphous phases of Sb2Te3, we have concluded that the phase transition from the crystalline phase toward the amorphous phase is induced by the pump pulses. The phonon energy of the A2u mode is clearly seen in the STM light-emission spectra when ΔE is 1.62 eV, but not when ΔE is increased above 1.62 eV by pump-pulse irradiation. This feature appears to be consistent with the Raman signals, which are much stronger for the crystalline phase than for the amorphous phase.