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Journal of Nanomaterials
Volume 2010, Article ID 952172, 6 pages
http://dx.doi.org/10.1155/2010/952172
Research Article

Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

1Department of Physics, College of Science, University of Babylon, P.O. Box 4, Babylon, Iraq
2Directorate of Materials Science, Ministry of Science and Technology, P.O. Box 8012, Baghdad, Iraq

Received 5 August 2010; Revised 12 September 2010; Accepted 9 December 2010

Academic Editor: Bohua Sun

Copyright © 2010 Noor A. Nama et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter) that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001)-( ) surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.