Invoking forbidden modes in SnO_2 nanoparticles using tip enhanced Raman spectroscopy

TL;DR

This study uses tip enhanced Raman spectroscopy to detect forbidden and defect-related modes in SnO_2 nanoparticles, revealing surface disorder and defects crucial for catalysis and sensing applications.

Contribution

It demonstrates the effectiveness of TERS in identifying weak forbidden and defect-related Raman modes in SnO_2 nanoparticles, especially at the nanoscale.

Findings

TERS enhances symmetry allowed Raman modes by an order.

New defect-related peaks are observed with significant intensity.

Temperature studies correlate defect features with particle size.

Abstract

Raman forbidden modes and surface defect related Raman features in SnO_2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Due to the weak intensities of these peaks, it is difficult to identify these features by using conventional Raman spectroscopy. Tip enhanced Raman spectroscopy (TERS) studies conducted on SnO_2 nanoparticles (NPs) of size 4 and 25 nm have offered significant insights of prevalent defects and disorders. Along with one order enhancement in symmetry allowed Raman modes, new peaks related to disorder and surface defects of SnO_2 NPs were found with significant intensity. Temperature dependent Raman studies were also carried out for these NPs and correlated with the TERS spectra. For quasi-quantum dot sized 4 nm NPs, the TERS study was found to be the best technique to probe the finite size related Raman forbidden modes.