PHOTODESORPTION DYNAMICS OF CO FROM SI(111) - THE ROLE OF SURFACE-DEFECTS

Laser-induced desorption of CO from an ion beam etched and annealed Si (lll) surface is reported. State-resolved measurements of the desorbed CO reveal very high translational and vibrational energy contents, wi th the rotational excitation being quite low. The results suggest that the CO photodesorption is derived from CO bound to ion beam etch-indu ced active ''defect'' site(s) on the Si(111)7X7 surface that are only minimally influenced by either the ion beam etching conditions or the anneal. The very high translational energy in the CO implies desorptio n from active ''defect'' site(s) either in the very-near-surface regio n or on the surface. Comparison of the photoyields at 266 and 355 nm s uggests that the desorption mechanism cannot be described using existi ng models for thermal- or carrier-mediated processes.