Pump-Probe Time-Resolved Sum Frequency Spectroscopy of the H-Si(111)1X1 surface

We have performed time-resolved sum frequency (SF) spectroscopy of a H-Si(111)1×1 surface excited by pump visible pulses with the pulse width of ∼30 ps in ultra-high vacuum. Broad non-resonant SF signals as a function of the infrared wavenumber increased soon after the pump light irradiation, and decreased in ∼1 ns. A remarkable change in the intensity and the shape of the peak at 2085 cm^ attributed to the Si-H stretching vibration is observed as a function of the delay time. After the pump light irradiation, the symmetric peak in the SF spectra disappeared at ∼60 ps and recovered gradually with an asymmetric shape