Tip-enhanced Raman spectroscopy – Recent developments and future prospects

Tip-enhanced Raman scattering (TERS) is becoming a general analytical tool. TERS has been observed for dye layers on glass as well as for adsorbates on silver, gold, or platinum substrates. TERS is found not only for very strong Raman scatterers, but also for species usually exhibiting normal Raman scattering. Among the latter are CN- and ClO4- ions, benzenethiol, mercaptopyridine, and the DNA bases (adenine, cytosine, guanine, and thymine), all adsorbed at smooth single-crystalline gold surfaces. TERS also provides excellent stimulation and a playground for theoretical studies on enhanced optical processes. The tip-substrate configuration can be considered as a unique photonic system with tunable optical resonances that provides huge near-field enhancements for species located in the tip-substrate cavity. A suitable theoretical description of such a photonic system is, even today, a great challenge, although the general features of such a system are well understood