High-resolution Raman imaging of bundles of single-walled carbon nanotubes by tip-enhanced Raman spectroscopy

Bundles of single-walled carbon nanotubes (SWCNTs) prepared by plasma torch method and further purified, are deposited over a glass coverslip to estimate the spatial resolution of tip-enhanced Raman spectroscopy measurements. For this purpose, near-field Raman maps and spectra of isolated bundles of carbon nanotubes are collected using optimized experimental conditions such as a tightly focused beam using a 1.4 numerical aperture oil immersion microscope objective and a gold coated atomic force microscope probe illuminated by a radially polarized 632.8 nm wavelength to selectively excite the localized surface plasmon confined at the extremity of the tip. The near-field nature of the collected Raman signals is evaluated through measuring the decay of the Raman signal with respect to the tip-sample separation. Key words: tip-enhanced Raman spectroscopy, localized surface plasmon resonance, near-field spectroscopy, radial polarization, atomic force microscopy, spatial resolution, enhancement factor, single-walled carbon nanotubes. Des fagots de nanofils de carbone simple-paroi, prepares par torche plasma puis purifies sont deposes sur des lamelles de microscope dans la perspective de mesurer la resolution spatiale de mesures Raman locales exaltees par effet de pointe. A cette fin, des cartographies ainsi que des spectres Raman sont collectes dans des conditions experimentales optimisees basees sur l'utilisation d'un objectif de microscope a forte ouverture numerique (O.N. 1.4) et d'une excitation avec une polarisation radiale a 632, 8 nm afin d'exciter selectivement le plasmon de surface localise et de confiner ce dernier a l'extremite de la pointe en or. Le champ proche Raman est evalue en analysant la decroissance du signal collecte en fonction de la distance entre la pointe et l'echantillon. Mots-cles: spectroscopie Raman exaltee par effet de pointe, plasmon de surface localise, microscopie en champ proche, polarisation radiale, microscopie a force atomique, resolution spatiale, facteur d'exaltation, nanofils de carbone a simple paroi.
Introduction The discovery of surface-enhanced Raman spectroscopy (SERS) in the early 1970's was a milestone in improving the inherent low efficiency of inelastic Raman scattering. (1, 2) The improved sensitivity [...]