Decomposition of H2O ON Si(111)7 × 7 studied using laser-induced thermal desorption

The decomposition of water on Si(111)7 × 7 was studied using laser-induced thermal desorption (LITD), temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). Product yields versus H2O exposure were determined using TPD measurements. The only TPD reaction products were H2 and SiO which desorbed at approximately 800 and 950 K, respectively. The LITD yield from H2O on Si(111)7 × 7 also produced H2 and SiO desorption products. Moreover, H2O and SiOH were detected in the LITD yield after larger water exposures at temperatures above the H2O multilayer desorption at 160 K. The LITD desorption yield for H2O persisted until 550 K, whereas the SiOH LITD signals were observed up to 600 K. These H2O and SiOH LITD signals were associated with reaction intermediates on Si(111)7 × 7 because neither H2O nor SiOH was observed in the TPD yield above 160 K. Isothermal LITD experiments were performed to measure the disappearance of SiOH and H2O LITD signals from Si(111)7 × 7. The results for the isothermal decay were consistent with self-poisoning of the H2O decomposition caused by site-blocking by the reaction products. In addition, the effects of preadsorbed hydrogen on the H2O decomposition reaction were investigated. Hydrogen was observed to decrease the H2O decomposition reaction on Si(111)7 × 7 nearly linearly with hydrogen coverage.