SERS (surface-enhanced Raman scattering) and TERS (tip-enhanced Raman scattering) both involve the use of metallic particles or layers to boost the amount of Raman scattering from molecules very close to them. The enhancement can be over a billion times in some cases.
You can detect very low concentrations of material (SERS) and resolve very small features (TERS). These techniques are therefore exciting areas of Raman spectroscopy.
The enhancement mechanisms
Two effects cause the enhancement to the Raman scattering from molecules close to the metal:
- the metal can amplify the electric fields of the incoming laser light and the outgoing Raman scattered light
- the metal can alter the distribution of charges within adsorbed molecules, causing stronger scattering
SERS normally uses either a colloidal suspension of metal (e.g. silver) or a roughened metal surface. These enhance the Raman scattering from molecules adsorbed onto the metal surfaces. SERS enables new applications, such as the analysis of low concentrations and diagnostic information.
TERS uses a metallic-coated tip—typically on a scanning probe / atomic force microscope—to enhance the Raman signal from molecules within a few nanometres of the tip. You can determine the spectrum originating from molecules solely in the small volume close to the tip. This is done by comparing the spectrum from the surface with and without the tip present. This gives a much higher spatial resolution than normal Raman scattering (nanometre-scale, rather than about 0.2 µm).
Renishaw's combined Raman-SPM/AFM is available with TERS options.
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Brochure: Raman spectroscopy explained
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