Small silicon oxide clusters: chains and rings

Abstract

We study several silicon oxide cluster series with different Si:O stoichiometries using photoelectron spectroscopy (PES) of size-selected anions: (SiO) n − (n=3–5), (SiO2) n − (n =1–4), and Si(SiO2) n − (n = 2,3). The (SiO)n clusters are shown to be closed-shell molecules and the HOMOLUMO gaps are observed from the PES spectra to decrease for larger n. These clusters are shown to have ring sturctures. Si3O4 is known to have a D2d structure with two perpendicular Si2O2 rhombuses.The PES spectrum of Si4O 6 − is very similar to that of Si3O 4 − . It is concluded that Si4O6 has a similar structure with a chain of three Si2O2 rhombuses. The (SiO2)n clusters all exhibit high electron affinities and only one band is observed at 4.66 eV photon energy. These clusters are shown to have similar chain structures containing Si2O2 rhombuses, but the two terminal Si atoms are bonded to an extra 0 atom each. The possibility of using these clusters to provide structural models for oxygen-deficient defects in bulk silicon oxides is also discussed.