Desorption of fragment ions from condensed Si(OCH3)4 by localized inner-shell electron excitation at the silicon, oxygen, and carbonKedges

Abstract

Desorption of fragment ions from condensed Si(OCH3)4 (tetramethoxysilane) following localized inner-shell electron excitation at the silicon, oxygen, and carbon K edges has been investigated using monochromatized synchrotron radiation in the soft x-ray region. For Si K-edge excitation, the predominant species of the desorbed ions were Si(OCH3)n+ where n=2, 3, 4, which resembles the cracking pattern of gas-phase molecules excited by 70 eV electrons. In contrast, the CH3+ ions were the main species of the desorbed ions for the C and O K-edge excitations. The photon-energy dependencies of the CH3+ yield at the C K edge revealed that the CH3+ desorption happens only at the resonant excitation from C 1s to the σ* orbit localized at the C–O bond, which suggests that the core-to-valence resonant excitations are localized around the C–O bond until the C–O bond breaks. These results shed light on the possibility of low-temperature SiO2 deposition on a silicon surface by an x-ray-induced photochemical reaction through selective C–O bond scission using monochromatized synchrotron radiation.