Raman Spectroscopy allows for the determination of chemical structure and the identification of compounds using vibrational spectroscopy. Raman has higher lateral resolution than FTIR allowing for the chemical analysis of areas of <1µm.
Raman is the ideal technique for the qualitative or quantitative analysis of mixed organic/inorganic materials.
How Raman works – monochromatic light (typically from a laser) interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the sample.
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Instrumentation Available
Key Attributes
- Signal Detected: Raman scattering (photons)
- Chemical and molecular bonding information detected
- Detection Limits: >=1 wt%
- Depth Resolution: 1 – 5 µm in confocal mode
- Imaging/Mapping: Yes
- Lateral Resolution/Probe Size: >=1 µm
Strengths
- Can identify organic functional groups
- Spectral libraries allow for the identification of specific compounds
- No vacuum required
- Non-destructive
- Small analysis area (~1 µm)
Limitations
- Low sensitivity to the sample surface (typical sampling volumes are ~0.8 µm)
- Minimum analysis area: ~1 µm
- Information on inorganic samples limited
- Requires standards for quantitative analysis
- Sample fluorescence can limit usefulness
Applications
- Identification of the molecular structure of organic and inorganic compounds
- Stress measurements
- Characterization of carbon layers (graphitic vs. diamond)
- Orientation (random v. organized structure)
- Identification of organic molecules, polymers, biomolecules, and inorganic compounds both in the bulk and in individual particles
- Determine the presence different states of carbon — diamond, graphitic, amorphous, diamond-like, nanotubes, and their relative proportions
Additional Reading
