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Proceedings Paper

Ultra-low frequency Raman spectroscopy of SWNTs under high pressure
Author(s): Y. Shen; N. Quirke; D. Zerulla
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Paper Abstract

Radial deformation phenomena of carbon nanotubes (CNTs) are attracting increased attention because even minimal changes of the CNT's cross section can result in significant changes of their electronic and optical properties. It is therefore important to have the ability to sensitively probe and characterize this radial deformation. High pressure Raman spectroscopy offers a general and powerful method to study such effects in SWNTs. In this experimental work, we focus in particular on one theoretically predicted Raman vibrational mode, the so-called "Squash Mode" (SM), named after its vibrational mode pattern, which has an E2g symmetry representation and exists at shifts below the radial breathing mode (RBM) region. The Squash mode was predicted to be more sensitive to environmental changes than the RBM.

Here we report on a detailed, experimental detection of SMs of aligned SWNT arrays with peaks as close as 18 cm-1 to the laser excitation energy. Furthermore, we investigate how the SM of aligned CNT arrays reacts when exposed to a high pressure environment of up to 9 GPa. The results confirm the theoretical predictions regarding the angular and polarization dependent variations of the SM's intensity with respect to their excitation. Furthermore, clear Raman upshifts of SM under pressures of up to 9 GPa are presented. The relative changes of these upshifts, and hence the sensitivity, are much higher than that of RBMs because of larger radial displacement of some of the participating carbon atoms during the SM vibration.

These novel ultra-sensitive Raman SM shifts of SWNTs provide enhanced sensitivity and demonstrate new opportunities for nano-optical sensors applications.

Paper Details

Date Published: 26 September 2016
PDF: 8 pages
Proc. SPIE 9932, Carbon Nanotubes, Graphene, and Emerging 2D Materials for Electronic and Photonic Devices IX, 993209 (26 September 2016); doi: 10.1117/12.2236463
Show Author Affiliations
Y. Shen, Univ. College Dublin (Ireland)
N. Quirke, Imperial College London (United Kingdom)
D. Zerulla, Univ. College Dublin (Ireland)

Published in SPIE Proceedings Vol. 9932:
Carbon Nanotubes, Graphene, and Emerging 2D Materials for Electronic and Photonic Devices IX
Manijeh Razeghi; Maziar Ghazinejad; Can Bayram; Jae Su Yu, Editor(s)

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