PICOSECOND TIME-RESOLVED LASER DESORPTION

We have developed a pump-and-probe scheme for measuring the flux of desorbing particles with ultrafast time resolution. Neutral particles released during pulsed laser desorption are photoionized with the help of a delayed probe pulse and detected with a mass spectrometer. By changing the time delay of the probe pulse the temporal evolution of the flux of the various desorbing surface species can be measured. We have studied picosecond thermal desorption from GaAs(100) surfaces. Desorption of Ga is measured using a fixed frequency probe pulse for non-resonant two-photon ionization or a two-color tunable probe pulse for resonant two-photon ionization. A detailed study was made of the effect of ion sputtering and thermal annealing, which lead to interesting changes of the desorption flux and its time dependence. © 1990.