Mid-infrared pump–probe spectroscopy of Si–H stretch modes in porous silicon

Using the Dutch free electron laser FELIX, we have investigated vibrational relaxation in free standing porous silicon (p-Si) films. Pump–probe measurements resonant with the SiH, SiH2 and O3SiH stretching modes yield temperature dependent measurements of the decay rates which demonstrate that all the modes decay via at least one internal defect mode with the excess vibrational energy distributed among the Si–Si bath phonons in a fourth order decay process.