Invoking forbidden modes in SnO2 nanoparticles using tip enhanced Raman spectroscopy

Raman forbidden modes and surface defect-related Raman features in SnO2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Because of 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 SnO2 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 SnO2 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-nmNPs, the TERS study was found to be the best technique to probe the finite size-related Raman forbidden modes. Copyright (C) 2015 John Wiley & Sons, Ltd.