Pump-Probe Scanning-Tunneling-Microscope Light-Emission Spectroscopy Of Sb2te3

We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pumplaser pulses using scanning-tunneling-microscope (STM) light emission synchronized with psprobe-laser pulses delayed by times t after individual pump pulses. We determined the gap energy Delta E 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 Delta E 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 Delta E for t >= 28 ps. By comparing this t-dependence of Delta E 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 A(2u) mode is clearly seen in the STM light-emission spectra when Delta E is 1.62 eV, but not when Delta E 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. Published by AIP Publishing.