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A size-dependent evolution of phonon confinement is revealed in Si nanoparticles (NPs) via Raman spectroscopy. By introducing a variable confinement factor, α, into a well-known phenomenological phonon confinement model (PCM) developed by Richter et al., acceptable fits are achieved to downshifted and asymmetrically broadened Raman spectra of Si NPs with different diameters, d, from 2.4 nm to 6.3 nm. A comparative study using Raman spectra of colloidal Si NPs, for the first time, shows an apparent positive linear correlation between α and the Si NP size. Based on the PCM, the amplitude of the atomic vibration (phonon) at the real physical boundary of NPs is proportional to e-α/2, which indicates that the amplitude of the first order optical phonon is relatively larger at the edges for smaller Si nanostructures despite of their stronger phonon confinement weighed by α/d2.
Bibliographical noteFunding Information:
This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). Responsibility for the views, information or advice expressed herein is not accepted by the Australian Government. Thanks to Electron Microscope Unit of UNSW for TEM imaging support. P. Zhang also thanks Yidan Huang for TEM imaging of 2.4-nm Si NPs. U. Kortshagen and R.J. Anthony were supported by the UMN MRSEC Program of the National Science Foundation under Award Numbers DMR-0819885 and DMR-1420013. [Correction added on 13 July 2015, after first online publication: the preceding sentence has been added to the Acknowledgement]
Copyright © 2015 John Wiley & Sons, Ltd.
- phonon confinement
- Raman spectroscopy
- Si nanoparticles
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