Photodesorption dynamics of CO from Si (111): the role of surface defects

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Laser-induced desorption of CO from an ion beam etched and annealed Si (111) surface is reported. Stateresolved measurements of the desorbed CO reveal very high translational and vibrational energy contents, with the rotational excitation being quite low. The results suggest that the CO photodesorption is derived from CO bound to ion beam etch-induced active “defect” site(s) on the Si(111)7 × 7 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 desorption from active “defect” site(s) either in the very-near-surface region or on the surface. Comparison of the photoyields at 266 and 355 nm suggests that the desorption mechanism cannot be described using existing models for thermal- or carrier-mediated processes.