The use of Raman microscopy has become an important tool for the analysis of materials on the micron scale. The unique confocal and spatial resolution of the HORIBA Scientific Raman microscopes has enabled optical far field resolution to be pushed to its limits with often sub-micron resolution achievable.

The next step to material analysis on a smaller scale has been the combination of Raman spectroscopic analysis with near field optics and an Atomic force microscope (AFM).   Such systems allow tip enhanced Raman scattering to be explored, making true NanoRaman achievable, with spatial resolution <100nm.

The TERS method is based on the combination of Raman, SERS and AFM.  Surface Enhanced Raman Scattering (SERS) has long been used to enhance weak Raman signals by means of surface plasmon resonance using nanoscale colloidal particles or rough metallic substrates, allowing detection of chemical species at parts per million (ppm) levels. The TERS effect is based on the same principle, but uses a metal-coated AFM tip as an antenna that enhances the Raman signal coming from the sample area which is in contact with the tip.  Since the AFM tip is on the nanometer scale, it is possible to obtain localised enhancement on the same scale.  By differentiating the tip enhanced Raman from the normal Raman (tip away from the sample) it is possible to obtain Raman information from areas <100nm in diameter.

Although not yet fully understood, the TERS effect has attracted a lot of interest, as it holds the promise of producing chemical images with nanometric resolution. The LabRAM NanoRaman platform combines state-of-the-art AFMs with HORIBA’s renowned Raman expertise to perform exploratory TERS experiments with confidence. 

TERS is being explored for many different application areas, and opens up new possibilities in micro-analysis and imaging which were previously limited by the micron optical diffraction limit of confocal Raman instruments.

Click here for typical Raman-AFM and TERS application examples.