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
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
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.
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