Decomposition of H 2O on Si(111)7×7 studied using laser-induced thermal desorption

Abstract

Abstract 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 H 2 O exposure were determined using TPD measurements. The only TPD reaction products were H 2 and SiO which desorbed at approximately 800 and 950 K, respectively. The LITD yield from H 2 O on Si(111)7 × 7 also produced H 2 and SiO desorption products. Moreover, H 2 O and SiOH were detected in the LITD yield after larger water exposures at temperatures above the H 2 O multilayer desorption at 160 K. The LITD desorption yield for H 2 O persisted until 550 K, whereas the SiOH LITD signals were observed up to 600 K. These H 2 O and SiOH LITD signals were associated with reaction intermediates on Si(111)7 × 7 because neither H 2 O nor SiOH was observed in the TPD yield above 160 K. Isothermal LITD experiments were performed to measure the disappearance of SiOH and H 2 O LITD signals from Si(111)7 × 7. The results for the isothermal decay were consistent with self-poisoning of the H 2 O decomposition caused by site-blocking by the reaction products. In addition, the effects of preadsorbed hydrogen on the H 2 O decomposition reaction were investigated. Hydrogen was observed to decrease the H 2 O decomposition reaction on Si(111)7 × 7 nearly linearly with hydrogen coverage.