Thermal and low-energy ion-mediated surface chemistry of halocarbons on silicon(111) 7 x 7 silicon dioxide

Vibrational Electron Energy Loss spectroscopy (EELS) and Thermal Desorption Spectrometry (TDS) have been used to study thermally driven and ion-mediated surface reactions and adsorption properties induced by low-energy electron and ion irradiation on two popular model surfaces: Si(111) 7 x 7 and vitreous SiO2. Together with Low Energy Electron Diffraction (LEED), the present work seeks to investigate some of the more intriguing aspects of surface reactions mediated by low-energy fluorohydrocarbon ions and room-temperature chemisorption and thermal evolution of a family of chloroethylenes on these important substrate surfaces.; On Si(111) 7 x 7 and vitreous SiO2, thermal and ion-mediated reactions of two simple fluorinated urethanes, CF4 and CH 2F2 with F-to-C ratios of 4:1 and 2:1 respectively, along with one simple fluorinated ethylene, iso-C2H 2F2 with a F-to-C ratio of 1:1, have been studied. The observed adspecies, SiC and SiFx, produced on the 7 x 7 surface by ion irradiation in these sputtering gases are found to be similar. On a vitreous SiO 2 surface, ion irradiation in CF4 or CH2F 2 produces more SiFx than on Si(111) 7 x 7, which is consistent with the hypothesis that surface O facilitates the removal of surface C (and hydrocarbon fragments) leaving more fluorine to react with the silicon substrate. In contrast, the ion irradiation in iso-C2H 2F2, appears to produce less SiFx than that on the 7 x 7 surface, which indicates that surface O does not interact strongly with the C2-containing fragments. The presence or absence of a C=C bond in the sputtering gas and the relative F-to-C ratio of the sputtering gas could therefore produce important effects on the resulting surface products obtained by low-energy ion irradiation. Without ion-irradiation, iso-C2H2F2 predominantly chemisorbs via a [2+2] cycloaddition mechanism onto the 7 x 7 surface as a di-sigma bonded difluoroethane-1, 2-diyl adstructure, which undergoes H abstraction and defluorination producing hydrocarbon fragments and SiFx (x = 1--3) upon annealing to >700 K. These studies demonstrate the enormous potential of using low-energy ion irradiation for surface activation and functionalization. (Abstract shortened by UMI.)...