Re-Examining Tip-Enhanced Raman Signals at High Spatial Resolution Under Ambient Conditions Using Graphene Nanobubbles

High-spatial-resolution tip-enhanced Raman spectroscopy (TERS) measurements were carried out under ambient conditions on graphene nanobubbles with various associated structural features. The resulting signals were analyzed with consideration of the characteristic features inherent to high resolution TERS. Compared to flat graphene regions, nanobubbles and their associated nanoconvex pinning sites demonstrated enhanced TERS signals, attributed to the efficient coupling between the strong tip-enhanced electric field and out-of-plane deformations in graphene. Strong coupling with highly confined near-field light activates the D bands even in the absence of defects, with intensity depending on the degree of deformations. While the D band is observed across the nanobubbles, some local regions exhibit a weaker D band intensity compared to the surrounding areas. Given the finite number of hexagonal lattices within the area of highly confined near-field, this reduction in intensity is likely to result from defects that cause missing hexagonal lattices. These findings highlight the capability of near-field induced Raman signals in probing high resolution features of nanomaterials even under ambient conditions, providing deeper insights into their characteristics in situ.