Tip-enhanced Raman scattering microscopy is a powerful technique for analysing nanomaterials at high spatial resolution far beyond the diffraction limit of light. However, imaging of intrinsic properties of materials such as individual molecules or local structures has not yet been achieved even with a tip-enhanced Raman scattering microscope. Here we demonstrate colour-coded tip-enhanced Raman scattering imaging of strain distribution along the length of a carbon nanotube. The strain is induced by dragging the nanotube with an atomic force microscope tip. A silver-coated nanotip is employed to enhance and detect Raman scattering from specific locations of the nanotube directly under the tip apex, representing deformation of its molecular alignment because of the existence of local strain. Our technique remarkably provides an insight into localized variations of structural properties in nanomaterials, which could prove useful for a variety of applications of carbon nanotubes and other nanomaterials as functional devices and materials.

We report on the experimental identification of Raman modes that are enhanced through the chemical effect in surface enhanced Raman spectroscopy of 4-aminothiophenol (also known as p-mercaptoaniline) adsorbed on gold substrate. Introduction of a thin spacer layer between the metal and the sample can prevent any possible chemical bonding between metal atoms and sample molecules, hence such a sample shows only those Raman modes that are enhanced through the electromagnetic effect. Alternatively, a significant increase in the chemical effect could be observed in the presence of halide ions as compared to their absence. This result provides another way to experimentally identify those Raman modes that undergo chemical enhancement. In addition, apart from the electromagnetic-based resonance in SERS, chemical enhancement also shows a resonance with varying wavelength of the excitation light, which provides yet another way to experimentally identify chemically enhanced Raman modes in SERS. Some new chemically enhanced modes could be observed when the sample molecules were sandwiched between gold substrate and a gold nanotip. † Part of the "Martin Moskovits Festschrift".

No abstract

Tip-enhanced Raman spectroscopy (TERS) has emerged as a powerful tool for optical imaging at nanoscale spatial resolution, and for investigating the vibrational properties of molecules adsorbed on a substrate. Plasmonic enhancement of the electromagnetic fields near a metallic nanostructure plays a very important role in TERS, where resonant excitation of plasmons is crucial. When two metallic nanostructures are placed at a gap of nanometric distance, their plasmons can interact with one other and result in hybridized shifted plasmon modes. Here, we apply this idea to TERS and demonstrate a significant tunability of the plasmon resonance enabling large electric field enhancement at a desired excitation wavelength. This finding paves the way for efficient optimization of TERS in imaging and spectroscopy applications.

No abstract