npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041
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Article

Research Paper

New Phys.: Sae Mulli 2019; 69: 16-24

Published online January 31, 2019 https://doi.org/10.3938/NPSM.69.16

Copyright © New Physics: Sae Mulli.

Study of the Shapes of CdSe/CdS Nanocrystals by Using Raman Spectroscopy and the Stokes Shift

Seong-Wook PARK, Hoon-Hyun CHO, Dong-Sun YOO, Il-Gon KIM*

Department of Physics, Changwon National University, Changwon 51140, Korea

Correspondence to:igkim@changwon.ac.kr

Received: September 16, 2018; Accepted: December 3, 2018

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In order to obtain data on the formation process of CdSe/CdS core/shell semiconductor nanocrystals, we subjected samples of nanocrystals to long-term heat treatment at a temperature of 80 $^\circ$C. After a certain time, the absorption and the emission spectra were measured using parts of the samples. As the heat treatment time was increased, the Stokes shift decreased until the growth of the CdSe nanocrystals stopped. The time when the Stokes shift increases after a certain time can be regarded as the time when the surfaces of nanocrystals change. A method for distinguishing whether CdSe/CdS has core-shell structure or is an alloy was studied by analyzing the Raman spectra and the X-ray diffraction (XRD) patterns of the samples at the time when the surfaces of the nanocrystals changed. When CdSe/CdS core-shell semiconductor nanocrystals are synthesized, a chance exists that interfaces will be observed in CdS$_x$Se$_{1-x}$ alloys. Thus, distinguishing whether the synthesized nanocrystals have a core-shell structure or are CdS$_x$Se$_{1-x}$ alloys is possible. If a new phonon is observed between phonon L01 and phonon L02 in the Raman spectra, the material is an alloy. A more precise core-shell structure can be identified by looking at the XRD pattern and the Stokes shift.

Keywords: Nanocrystals, Core/shell, Alloy, Stokes shift, Raman spectrum

Figures

Fig. 1. Raman spectra of CdSe/CdS nanocrystals.

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