Photoluminescence of oxidized silicon nanoclusters deposited on the basal plane of graphite

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Abstract
Silicon (Si) nanoclusters, with an average size of 3–5 nm in diameter, have been deposited on the basal plane of highly oriented pyrolytic graphite in an ultrahigh vacuum chamber, and investigated by scanning tunneling microscopy. Clusters passivated in situ with hydrogen or oxygen showed no detectable visible photoluminescence (PL). Prolonged exposure of the clusters to ambient air, however, resulted in strong stable red to green-blue PL spectra. Further study of these clusters by x-ray photoelectron spectroscopy and Auger electron spectroscopy revealed the existence of only SiO2 for the prolonged air-exposed samples, and the existence of SiOx (x ranged from 0 to 2) for the in situ oxidized samples which did not exhibit any detectable visible PL. We believe that the observed visible PL originated from defects in SiO2.