Raman spectroscopy can be used to analyze organic, inorganic, crystalline as well as amorphous materials. Due to its non-destructivity, it is one of the most exploited techniques in the field of heritage science. It is often used as a complementary technique to IR spectroscopy.
In Raman Spectroscopy, interaction of light with the molecular structure of a compound(s) generates a specific and unique signal.
Raman Spectroscopy uses lasers as probes: the instrument at SciCult-KHM (figure 1) is equipped with four laser units delivering light with five different wavelengths (488, 514, 633, 785 and 1064 nm), which enables the study of a wide range of materials.
The microscope coupled to the spectrophotometer at the SciCult laboratory is equipped with four objectives with magnifications between 5x and 100x. Samples or small objects (up to few cm high) can be placed directly into the microscope chamber (to avoid environmental light, see figure 2) for analysis (i.e. sampling is not always required). In general, it is possible to analyze solid samples, powders (also in very small amounts, down to a single grain), as well as liquids.
The instrument is additionally equipped with an extendible arm that enables the analysis of large objects outside the chamber, for example, illuminated manuscripts or books (figure 2), paintings, painted sculptures, etc.
The instrument allows point analysis, area mapping of flat samples (e.g. cross-sections) and 3D measurements, i.e. depth profiles of transparent materials (e.g. inclusions in minerals, glass, glazing, etc.).
When working with Raman Spectroscopy, one issue is the fluorescence; this can be reduced by a careful cleaning of the sample surface to remove organic residuals (e.g. dirt), or by choosing the correct laser for the material to be analyzed (e.g. glass, organics).
In some cases, for the analysis of organic materials, Surface-Enhanced Raman Scattering/Spectroscopy (SERS) can be used. This methodology involves the deposition of metallic nanoparticles that allows amplifying the Raman signal of specific molecules.
Objects and materials Raman Spectroscopy can analyse
Objects and materials that can be analyzed with Raman Spectroscopy include:
- stones (natural and artificial)
- natural or synthetic fibers and dyes
- Instrument: Renishaw inVia Raman Microscope
- Laser: 488nm, 514nm, 633nm, 785nm and 1064nm
- Microscope: Leica DM 2500 M equipped with Leica NPlan objectives 5x, 20x, 50x + Olympus LMPlanFLN 20x with 20mm working distance
- Attached devices: Bendable arm to conduct measurements outside the chamber.