Excitation-Tunable Tip-Enhanced Raman Spectroscopy

Abstract

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

Present and Future of Surface-Enhanced Raman Scattering

“…Also note that most TERS systems are optimized to a particular wavelength as they operate with single-line laser excitation. Recently, an excitation-tunable TERS (eTERS) setup was reported by coupling a commercial TERS system with a tunable laser . The advantage of eTERS is twofold: first, the combined resonant enhancement and tip enhancement results in much higher EFs than those in conventional TERS; second, eTERS is able to map optical transition energies and specific resonant vibrations at nanometer spatial resolution.…”

“…The advantage of eTERS is twofold: first, the combined resonant enhancement and tip enhancement results in much higher EFs than those in conventional TERS; second, eTERS is able to map optical transition energies and specific resonant vibrations at nanometer spatial resolution. It can thus be used to measure, for example, an optically active component in large biomolecules or optical trap states in 2D materials . Although chemometric methods have been widely used in standard Raman and SERS studies, it would be advantageous if they could also be integrated into TERS software to improve signal quality and TERS imaging speed.…”

“…Recently, an excitation-tunable TERS (eTERS) setup was reported by coupling a commercial TERS system with a tunable laser. 879 The advantage of eTERS is twofold: first, the combined resonant enhancement and tip enhancement results in much higher EFs than those in conventional TERS; second, eTERS is able to map optical transition energies and specific resonant vibrations at nanometer spatial resolution. It can thus be used to measure, for example, an optically active component in large biomolecules or optical trap states in 2D materials.…”

Probing optical resonances of silicon nanostructures using tunable-excitation Raman spectroscopy

“…Tunable-excitation Raman spectroscopy is a far-field measurement technique, which is versatile, non-invasive and fast. Our setup used a tunable laser in the near infrared, but other tunable laser sources exist which permit to cover a broad part of the visible spectrum [39]. Combined with reflectance measurements, we have shown that Raman spectroscopy can identify faulty samples.…”

Selective excitation of one among the three peaks of tip‐enhanced Raman spectroscopy by a shaped ultrafast laser pulse

“…Combining the utility of scanning probe microscopy and Raman scattering, tip‐enhanced Raman spectroscopy (TERS) has become an ultrasensitive detection technique, and it is widely used in the fields of atomic structure, catalytic processes, and the redox behavior of single molecules . The selective Raman enhancement has been studied through the modifications and functionalization of TERS probes and controlling of surface plasmon polarizations and light polarizations .…”