The adsorption and thermal decomposition of formic acid on Si(100) and Si(111) surfaces

摘要

The adsorption of formic acid (HCOOH) on the Si(100)c(4times;2), Si(100)(2times;1), Si(100)9deg; vicinal and Si(111)(7times;7) surfaces has been studied by means of high resolution electron energy loss spectroscopy. Formic acid is partially dissociated to form the unidentate formate species (HCOO) and H adatoms on these surfaces at both 90 and 300 K. The formate species is bonded to the Si surface with a covalent bond formed between one of its oxygen atoms and the dangling bond of the surface Si atom. A condensed multilayer of molecular formic acid is formed after the Si surface is saturated with the formate species at 90ndash;150 K. The thermal decomposition mechanism has been studied in detail. The decomposition temperatures of the formate species on Si(100) and Si(111) are sim;600 and 550 K, respectively. It appears that the surface steps do not play an important role in the Sindash;HCOOH interaction. As the formatehyphen;covered surface is exposed to atomic hydrogen, methylendiolate (H2COO) is formed on the Si surface.