Band-edge absorption spectroscopy of CdSe/a-SiOxCdSe/a-SiOx multilayer nanocomposites

CdSe/a-SiOxCdSe/a-SiOx multilayer nanocomposites containing CdSe nanocrystals between a-SiOxa-SiOx thin layers have been produced by sequential thermal vacuum deposition of CdSe and SiOxSiOx on quartz substrates. Strong confinement effect has been observed in absorption spectra. Average size of nanocrystals was estimated from the absorption spectra discriminating between confinement, oxidation and artificial effects. Areal density of nanocrystals in CdSe sublayers was estimated to be ∼1012cm-2. Oxidation of nanocrystals was observed as a decreasing of optical absorption in the region above the optical band-gap energy. The binding energies of Cd–O and Se–O bonds have been calculated as a function of the inter-atomic distances for the Cd17Se17Cd17Se17 cluster bounded to SiO4SiO4 fragment in the framework of self-consistent Hartree–Fock scheme by means of the semi-empirical PM3 method in approximation of NDDO (neglect of diatomic differential overlapping). The greater energy has been found for Cd–O bonds (∼123.5kcal/mol) that evidences the preferred oxidation of Cd facets of CdSe nanocrystals.