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

Abstract

The adsorption of formic acid (HCOOH) on the Si(100)c(4×2), Si(100)(2×1), Si(100)9° vicinal and Si(111)(7×7) 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 90–150 K. The thermal decomposition mechanism has been studied in detail. The decomposition temperatures of the formate species on Si(100) and Si(111) are ∼600 and 550 K, respectively. It appears that the surface steps do not play an important role in the Si–HCOOH interaction. As the formate-covered surface is exposed to atomic hydrogen, methylendiolate (H2COO) is formed on the Si surface.