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Optical Phonons in CdS Nanocrystals: Effects of Size, Shape and Packing Density

Published online by Cambridge University Press:  10 February 2011

A.G. Rolo ,
M.I. Vasilevskiy ,
M.J.M. Gomes ,
O.V. Vikhrova ,
Yu.P. Rakovich  and
M.V. Artemyev
A.G. Rolo
Affiliation:
Departamento de Física, Universidade do Minho, 4700-320 Braga, Portugal
M.I. Vasilevskiy
Affiliation:
Departamento de Física, Universidade do Minho, 4700-320 Braga, Portugal, E-mail: mikhail@fisica.uminho.pt
M.J.M. Gomes
Affiliation:
Departamento de Física, Universidade do Minho, 4700-320 Braga, Portugal
O.V. Vikhrova
Affiliation:
Faculty of Physics, Nizhni Novgorod University, Russia
Yu.P. Rakovich
Affiliation:
Departamento de Física, Universidade do Minho, 4700-320 Braga, Portugal Department of Physics, Brest Polytechnic Institute, Brest, Belarus
M.V. Artemyev
Affiliation:
Physico-Chemical Research Institute, Belarussian State University, Minsk, Belarus
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Abstract

Optical vibrations confined in CdS nanocrystals (embedded in a glass film or forming a close-packed film with some organic-molecule links between them) have been studied experimentally, by means of FIR and Raman spectroscopies, and theoretically. The asymmetric Raman lineshape can be modelled considering resonant and non-resonant scattering on spherical modes with 1=0 (those with n>l are responsible for the low-frequency wing). A phonon-related dielectric response of the nanocrystal composites has been studied by measuring FIR reflectivity and transmission spectra. The theoretical consideration consists of the (i) calculation of the single-particle polarisability due to the confined 1=1 modes and (ii) including the dipole-dipole interaction between the particles. We show that, for the smallest particles, the FIR response has a bimodal structure, which disappears as the nanocrystal size increases. However, the experimentally observed bulk-CdS-like reflection band at 230–300 cm−1 is too broad and can not be explained by the model. Only making further assumptions, namely, of a fractal structure of the nanocrystal composites, enables us to fit well the experimental FIR spectra.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 571: Symposium W – Semiconductor Quantum Dots , 1999 , 217
Copyright
Copyright © Materials Research Society 2000

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References

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