LASER-INDUCED BOND BREAKING AND STRUCTURAL-CHANGES ON SI(111)-7X7 SURFACES

We review the structural changes on the Si(111)-7 x 7 surface induced by irradiation of laser pulses with fluences below thresholds of melti ng and ablation. Atomic imaging of the irradiated surface by scanning tunnelling microscopy has shown that the bond breaking of adatoms of t his 7 x 7 structure, associated with Si-atom desorption, is induced by an electronic process. Bond breaking efficiency is strongly site-sens itive, resonantly wavelength-dependent, and highly non-linear with res pect to the excitation intensity. The electronic process responsible f or bond breaking is shown to originate from non-linear localization of excited species generated from surface electronic states. (C) 1998 El sevier Science B.V.