Nanoscale Raman Imaging

The spatial resolution of a standard confocal Raman microscope system is limited by the optical diffraction limit, resulting in an achievable spatial resolution in the order of <1 µm (depending on laser wavelength, objective and confocal coupling).  Moving to the diffraction limit and beyond requires a rigorous microscopic approach, which is why the HORIBA Scientific systems use true confocal optics to give the highest possible spatial resolution.

Our approach for high spatial resolution Raman imaging depends on the precise requirements for the measurement, but broadly falls into three main categories:

Standard micron-scale confocal Raman imaging

Enables localisation, identification and mapped imaging of particles and features on the micron scale, utilising mechanical sample stages and high magnification objectives.

Raman mapped image of 3 µm beams

Sub-micron confocal Raman imaging

The use of optimized microscope objectives, careful selection of the most appropriate laser wavelength, and specialized mapping acquisition enables Raman microscopy to push towards the true optical limit of resolution - the far field diffraction limit.

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Raman mapped image of 250 nm and 350 nm features on a semiconductor Sample provided by ATMEL ROUSSET Université Paul Cezanne, France

Nano-scale confocal Raman imaging

Moving beyond the traditional far field diffraction limit requires a near field approach – using techniques such as NSOM/SNOM and Raman-AFM tip enhanced Raman scattering (TERS).  Near field spectroscopy retains the nanometer spatial information which is lost in far field experiments, and thus allows Raman imaging with spatial resolution down to 50 nm and beyond.

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TERS mapping of 30nm high, 250nm wide SiOx features on a Si substrate Data courtesy of Professor Alexei Sokolov University of Tennessee, Knoxville, USA