EFFECTS OF POST-DESORPTION COLLISIONS ON THE ENERGY-DISTRIBUTION OF SICL MOLECULES PULSED-LASER DESORBED FROM CL-COVERED SI SURFACES - MONTE-CARLO SIMULATIONS COMPARED TO EXPERIMENTS

Si surfaces covered with up to a monolayer of chlorine by exposure to a low chlorine pressure have been irradiated with nanosecond excimer-laser pulses at a fluence just large enough to melt the surface. Angle-resolved time-of-flight (TOF) distributions and surface temperatures have been measured as a function of chlorine dose between laser pulses. The TOF distributions can be fitted well by Maxwell-Boltzmann (MB) distributions for all coverages and at all desorption angles. With increasing coverage, the intensity and kinetic energy distributions become increasingly peaked along the surface normal. Monte-Carlo simulations of the effect of post-desorption collisions, occurring when many molecules are desorbed within a very short time, reproduce the experimental results quite well. It is shown that just a few collisions per molecule are sufficient to convert any initial desorption distribution into a MB one.