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Title: Effects of alloy disorder and confinement on phonon modes and Raman scattering in Si{sub x}Ge{sub 1−x} nanocrystals: A microscopic modeling

Confinement and alloy disorder effects on the lattice dynamics and Raman scattering in Si{sub 1−x}Ge{sub x} nanocrystals (NCs) are investigated numerically employing two different empirical inter-atomic potentials. Relaxed NCs of different compositions (x) were built using the Molecular Dynamics method and applying rigid boundary conditions mimicking the effect of surrounding matrix. The resulting variation of bond lengths with x was checked against Vegard's law and the NC phonon modes were calculated using the same inter-atomic potential. The localization of the principal Raman-active (Si-Si, Si-Ge, and Ge-Ge) modes is investigated by analysing representative eigenvectors and their inverse participation ratio. The dependence of the position and intensity of these modes upon x and NC size is presented and compared to previous calculated results and available experimental data. In particular, it is argued that the composition dependence of the intensity of the Si-Ge and Ge-Ge modes does not follow the fraction of the corresponding nearest-neighbour bonds as it was suggested by some authors. Possible effects of alloy segregation are considered by comparing the calculated properties of random and clustered Si{sub x}Ge{sub 1−x} NCs. It is found that the Si-Si mode and Ge-Ge mode are enhanced and blue-shifted (by several cm{sup −1}for the Si-Simore » mode), while the intensity of the Si-Ge Raman mode is strongly suppressed by clustering.« less
Authors:
;  [1] ;  [2]
  1. Department of Physics and NIFTI, N. I. Lobachevskii University of Nizhnii Novgorod, Nizhnii Novgorod 603600 (Russian Federation)
  2. Centro de Física, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal)
Publication Date:
OSTI Identifier:
22273632
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 14; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; BOND LENGTHS; BOUNDARY CONDITIONS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; EIGENVECTORS; GERMANIUM SILICIDES; MOLECULAR DYNAMICS METHOD; NANOSTRUCTURES; PHONONS; POTENTIALS; RAMAN SPECTROSCOPY; VEGARD LAW