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Nanotwinning and structural phase transition in CdS quantum dots

Pragati Kumar1*, Nupur Saxena2, Ramesh Chandra3, Vinay Gupta4, Avinash Agarwal1 and Dinakar Kanjilal2

Author Affiliations

1 Department of Physics, Bareilly College, Bareilly, Uttar Pradesh, 243005, India

2 Inter University Accelerator Centre, Aruna Asaf Ali Marg, P.O. Box 10502, New Delhi, 110067, India

3 Institute Instrumentation Centre, Indian Institute of Technology, Roorkee, 247667, India

4 Department of Physics & Astrophysics, Delhi University, Delhi, 110 007, India

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Nanoscale Research Letters 2012, 7:584  doi:10.1186/1556-276X-7-584

Published: 23 October 2012

Abstract

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I2LO/I1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm−1 respectively, two extra Raman modes at approximately 390 and 690 cm−1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.

Keywords:
CdS quantum dots; CdS thin films; Pulsed laser deposition; Phase transition; Raman scattering; Photoluminescence; 78.67.Hc; 64.70.Nd; 81.07.Ta