In this report, we demonstrate various applications of Atomic Force Microscope integrated with confocal Raman/fluorescence microscope. Physical characterization properties of AFM merge with chemical resolution of confocal Raman microscope and general capabilities of optical microscope to provide complete information about sample investigated.
Waveguiding properties of semiconductor nanofibers are studied. Light of different wavelengths is injected into an individual nanofiber either by a SNOM fiber tip or by a diffraction limited (~400 nm) spot of a high aperture objective. The point of light injection is chosen to be either nanofiber end, body or defect. A portion of light transmitted through nanofiber is collected from its end by a high aperture objective, and analyzed by a spectrometer. We study spectra of transmitted light with respect to the injected light wavelength. Graphene flakes (a few monolayers of graphite) are studied. AFM topography and phase pictures combined with Raman spectroscopy of the same sample area allow one to distinguish flakes of different thickness (down to single layer flake) and analyze flake’s structural uniformity. Advanced AFM techniques such as Kelvin probe microscopy and Electrostatic force microscopy applied to the same flake give further insight into its physical properties.
The ultimate goal of integrating AFM with optics is to bring resolution of optical methods (mainly, Raman and fluorescence) down to resolution of AFM (a few nm). There exists a number of ways how to use light interaction with the apex of AFM cantilever to produce an optical signal originated from a substantially subwavelength sample area (<100x100 nm2) located right below apex of AFM probe. By scanning the AFM probe along the sample, getting 2D maps of Raman or fluorescence signals with subwavelength resolution (down to a few dozens of nm) is possible. In this report, we demonstrate the results on Tip Enhanced Raman Scattering (TERS) experiments – where Raman signal from narrow sample area below the metallized AFM tip is resonantly enhanced due to interaction with plasmons localized at the tip apex. The resulting resolution of 2D Raman mapping is about 50 nm that goes far beyond the optical diffraction limit.
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