Exploring the origin of tip-enhanced Raman scattering; preparation of efficient TERS probes with high yield

Tip-enhanced Raman scattering (TERS) spectroscopy is a promising technique for nanoscale chemical analysis. However, there are several challenges preventing widespread application of this technology, including reproducible fabrication of efficient TERS probes. These problems reflect a lack of clear understanding of the origins of, and the parameters influencing TERS. It is believed that the coating characteristics at the apex of the tip have a major effect on the near-field optical enhancement and thus the TERS activity of a metalized probe. Here we show that the aspect ratio of the tip can play a significant role in the efficiency of TERS probes. We argue that the electrostatic field arising from the lightning-rod effect has a substantial role in the observed TERS effect. This argument is supported by ‘edge-enhanced Raman scattering’ which is shown for a noble metal film. Furthermore, it is reported that an associated tip-surface-enhanced Raman scattering effect can be achieved by using a TERS-inactive metalized probe on a surface-enhanced Raman spectroscopy-inactive roughened surface. This observation can be explained by an interparticle enhancement of the electromagnetic field.