STM study of laser-induced desorption from Si(111) surfaces with adsorbates

Surface structure changes of hydrogen- or chlorine-adsorbed Si(111)-(7 x 7) caused by ultra-violet laserlight have been studied with a scanning tunneling microscope. Experiments were performed in ultra-high vacuum conditions with a small fluence of laser light in order to avoid gas-phase excitation and strong thermal effects. Polyhydrides art found to decompose slowly to monohydrides, and polychlorides are desorbed by electronic excitation with the light. On the other hand, monohydride and monochloride Si atoms on the surface are stable against irradiation. The results are discussed in terms of hot carriers excited by light in the substrate, and their relaxation to the vibration of the adsorbates at surfaces.