Monochromatic soft-x-ray-induced reactions of CF2Cl2 adsorbed on Si(111)-7 × 7 studied by continuous-time photon-stimulated desorption spectroscopy near the F(1s) edge

Abstract

Continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was used to investigate the monochromatic soft x-ray photoreactions of CF2Cl2 adsorbed on Si(111)-7 × 7 near the F(1s) edge (681–704 eV). Sequential F+ PSD spectra were observed as a function of photon exposure at the CF2Cl2-covered surface (dose = 2.0 × 1014 molecules cm−2, ∼0.75 monolayer). The F+ PSD and total electron yield (TEY) spectra of solid CF2Cl2 near the F(1s) edge were also measured. Both F+ PSD and TEY spectra depict three features in the energy range of 687–695 eV, and are assigned to the excitations of F(1s) to (13a1 + 9b2)[(C–Cl)∗], (7b1 + 14a1)[(C–F)∗] antibonding and 5p Rydberg orbitals, respectively. Following the Auger decay process, two holes are created in the C–F bonding orbitals producing the 2h1e final state which results in the F+ desorption. This PSD mechanism, responsible for the F+ PSD of solid CF2Cl2, is used to explain the first F+ PSD spectrum in the sequential F+ PSD spectra. The variation of spectral shapes in the sequential F+ PSD spectra shows the consumption of adsorbed CF2Cl2 molecules and the production of surface SiF species as a function of photon exposure. The photolysis cross section of the adsorbed CF2Cl2 molecules by photons with varying energy (681–704 eV) is deduced from the sequential F+ PSD spectra and found to be ∼6.0 × 10−18 cm2.