The atomic and electronic structure of a set of proposed thin (1.6 nm in
diameter) silicon/silica quantum nanodots and nanowires with narrow interface,
as well as parent metastable silicon structures (1.2 nm in diameter), was
studied in cluster and PBC approaches using B3LYP/6-31G* and PW PP LDA
approximations. The total density of states (TDOS) of the smallest
quasispherical silicon quantum dot (Si85) corresponds well to the TDOS of the
bulk silicon. The elongated silicon nanodots and 1D nanowires demonstrate the
metallic nature of the electronic structure. The surface oxidized layer opens
the bandgap in the TDOS of the Si/SiO2 species. The top of the valence band and
the bottom of conductivity band of the particles are formed by the silicon core
derived states. The energy width of the bandgap is determined by the length of
the Si/SiO2 clusters and demonstrates inverse dependence upon the size of the
nanostructures. The theoretical data describes the size confinement effect in
photoluminescence spectra of the silica embedded nanocrystalline silicon with
high accuracy.Comment: 22 pages, 5 figures, 1 tabl