Excitation-Tunable Tip-Enhanced Raman Spectroscopy

Abstract

Tip-enhanced\nRaman spectroscopy (TERS) is a powerful tool to investigate\nchemical composition, for obtaining molecular information and for\nrecording images with a spatial resolution on the nanometer scale.\nHowever, it typically has been limited to a fixed excitation wavelength.\nWe demonstrate excitation-dependent hyperspectral imaging by implementing\na wavelength-tunable laser to our TERS setup. Varying the excitation\nwavelength during the TERS experiments is a key to perform spatially\nresolved resonant Raman scattering with nanometer resolution, which\nenables mapping of transition centers and to study, for example, the\nquantum properties of electrons and phonons. To present the application\npotential and to verify the setup, we recorded excitation-dependent\nhyperspectral nanoimages of a densely packed film of carbon nanotubes\n(CNTs) on an Au surface and use the spectral position and intensity\nof the radial breathing modes for a unique assignment of the CNTs.\nWe succeeded in identifying and imaging at least nine different tube\nspecies. The nanoimages revealed the exact position and the distribution\nof certain CNTs inside the film. e-TERS will have manifold application\nin nanoimaging, for chemical analysis, and electronic studies on the\nnanometer scale, making it highly interesting in fields ranging from\nbiomedicine and chemistry to material science.