STM-INDUCED H ATOM DESORPTION FROM SI(100) - ISOTOPE EFFECTS AND SITESELECTIVITY

We investigate the scanning tunnelling microscopy-induced H and D atom desorption from Si(100)-(2 x 1):H(D). The desorption of both atoms sh ows the same energy threshold that corresponds well with the computed sigma --> sigma excitation energy of the Si-H group, The H desorption yield, however, is much higher than the D yield. We ascribe this to t he greater influence of quenching processes on the excited state of th e Si-D species. We use wavepacket dynamics to follow the motion of H a nd D atoms, and conclude that desorption occurs, for the most part, fr om the 'hot' ground state populated by the quenching process. Site-sel ective excitation-induced chemistry is found in the desorption of H fr om Si(100)-(3 x 1):H.