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 photo lysis of adsorbed disilane on the Si(100) and Si(100)-(2 X 1):D surfac es have been investigated under ultrahigh vacuum conditions using temp erature programmed desorption. Even without UV irradiation, disilane a dsorption on clean Si(100) at 120 K produces a chemisorbed SiHx (x = 1 -3) layer and, for high exposures, a disilane multilayer. The chemisor ption is limited to a monolayer, as determined by comparing the covera ge dependence of the hydrogen, silane, and disilane thermal desorption yields. Silane desorption is used as an indicator of surface trihydri de production. Post UV irradiation of the disilane-exposed Si(100) sur face at 120 K does not affect the chemisorbed layer, but does lead to molecular disilane desorption. Simultaneous UV irradiation during disi lane exposure at 120 K results in significantly enhanced reaction, bey ond the first chemisorbed layer. For Si2H6 exposure during photo-irrad iation, 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 tr ihydride population with Si2H6 exposure during UV irradiation. Model m echanistic studies using the partially and fully deuterated Si(100)(2 X 1):D surface reveal that the photo-induced surface reaction is domin ated by an insertion reaction by the photo-generated diradical species , silylene.