Spatial Resolution in Nanoscale TERS Imaging: Current Status, Challenges, and Guidelines

Tip-enhanced Raman spectroscopy (TERS) was invented almost 25 years ago and was quickly recognized as one of the few nano-optical techniques that confine light at the nanoscale to explore light-matter interactions at the nanoscale. Even several years after its invention, the spatial resolution in TERS studies is not only somewhat controversial, especially for AFM-based TERS measurements of samples at room temperature, but also not reported in the literature in a consistent, generally accepted fashion. This Mini-Review discusses the current situation and how spatial resolution in TERS is reported in different ways that yield different values because no standard method is defined. More importantly, the spatial resolution in TERS is influenced by various experimental conditions and other factors in a comprehensive fashion, which have often been ignored. We consider all possible factors that affect spatial resolution in TERS and provide guidelines on how to determine and report spatial resolution.