Raman-Spektroskopie
Can a Raman microscope be used for depth profiling and analysis of features below the surface?
Yes. A confocal Raman microscope can be used to analyse features below the sample surface provided the sample matrix is transparent to the laser. Typical examples of such analyses include fluid/gas inclusions, contaminants in glass, and layered polymer structures.
On a basic system, manual focusing would be required to locate the required position within the sample, followed by spectral analysis. If the Raman microscope is equipped with motorised Z (focus) control, then it is possible to acquire depth (Z) profiles through the sample automatically. Such a profile comprises a full Raman spectrum at each and every depth within the profile, and is then interrogated to generate intensity profiles based on material composition and structure:
- Raman peak intensity yields a profile of material concentration and distribution
- Raman peak position yields a profile of molecular structure and phase, and material stress/strain
- Raman peak width yields a profile of crystallinity and phase
A system which has additional XY motorised sample control can be used to optically slice through the sample, for example, to create an XZ or YZ Raman spectral image.
- Raman depth profile of a layered polymer structure, showing the distribution of three chemically distinct layers from the surface (left hand side) down to 40 µm below the surface (right hand side)
- Raman cross section of a layered polymer structure, showing the capability of confocal Raman microscopy for analysis of µm thick layers. Total scan depth (Z) is 10 µm.
