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AFM-Raman-SNOM and Tip Enhanced Raman imaging studies of modern nanostructures

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We demonstrate instrumental realization and various applications of Atomic Force Microscopy integrated with Confocal Raman/Fluorescence/Rayleigh microscopy and Scanning Near Field Optical Microscopy (SNOM) produced by NT-MDT. Results on various samples are demonstrated: graphene, carbon nanotubes, semiconductor nanowires, quantum dots, nanodiamonds, plasmonic waveguides, photonic crystal optical fibers, various biological objects etc. For example, graphene on gold is investigated by different AFM and spectroscopy techniques providing comprehensive information about the sample. We study in details how the thickness (number of monolayers) in graphene affects its physical properties: surface potential (work function), local friction, elastic modulus, capacitance, conductivity, charge distribution, Raman and Rayleigh light scattering etc. Results for graphene flakes are qualitatively compared to those for carbon nanotubes of different diameters. We show how electrostatic charging of graphene flakes can be effectively measured and modified by AFM cantilever. Studies are performed both in ambient air conditions and in controlled atmosphere and humidity.

We also present results of Tip Enhanced Raman Spectroscopy (TERS) or “nano-Raman” mapping realized using integrated AFM -Raman system. Measurements are realized in two different excitation configurations: Inverted (for transparent samples) and Upright (reflected light configuration, for opaque samples, with side illumination option). In both geometries we demonstrate near field Raman enhancement effect due to resonant interaction of light with localized surface plasmon at the apex of a metal AFM probe. Various samples are studied by TERS technique: thin metal oxide layers, fullerenes, strained silicon, carbon nanotubes, graphene. Actual plasmonic and near field nature of the Raman enhancement is proven by a number of ways: dependence of the enhancement on the excitation wavelength and polarization, enhancement versus tip-sample distance curves, observation of selective enhancement of Raman signal from thin surface layers of the sample etc. Finally, the ultimate performance of TERS is demonstrated by measuring Raman 2D maps with subwavelength lateral resolution (down to 14 nm) – determined not by the wavelength of light, but by the localization area of the surface plasmon electromagnetic field. We discuss current progress in manufacturing reliable TERS probes.

This talk is part of the Physics of Living Matter - PLM series.

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