THE PHOTOINDUCED REACTION OF DISILANE WITH THE SI(100) AND SI(100)(2 X 1)-D SURFACES

Photo-induced surface reactions brought about by the ultraviolet photolysis of adsorbed disilane on the Si(100) and Si(100)-(2 X 1):D surfaces have been investigated under ultrahigh vacuum conditions using temperature programmed desorption. Even without UV irradiation, disilane adsorption on clean Si(100) at 120 K produces a chemisorbed SiHx (x = 1-3) layer and, for high exposures, a disilane multilayer. The chemisorption is limited to a monolayer, as determined by comparing the coverage dependence of the hydrogen, silane, and disilane thermal desorption yields. Silane desorption is used as an indicator of surface trihydride production. Post UV irradiation of the disilane-exposed Si(100) surface at 120 K does not affect the chemisorbed layer, but does lead to molecular disilane desorption. Simultaneous UV irradiation during disilane exposure at 120 K results in significantly enhanced reaction, beyond the first chemisorbed layer. For Si2H6 exposure during photo-irradiation, the desorption yields of hydrogen and silane are enhanced, and increase with increasing simultaneous exposure. A linear increase in the silane to hydrogen desorption ratio illustrates the increase in trihydride population with Si2H6 exposure during UV irradiation. Model mechanistic studies using the partially and fully deuterated Si(100)(2 X 1):D surface reveal that the photo-induced surface reaction is dominated by an insertion reaction by the photo-generated diradical species, silylene.