Raman Spectroscopy

RAMAN SPECTROSCOPY

Veronica Valentini -

DiaTHEMA Lab

Rome - Monterotondo

When a light beam passes through a surface inside a medium, part of the photons is subjected to elastic collisions with the matter (Rayleigh scattering) and part to inelastic collisions (Raman scattering), which can produce resonances of the interface components. This spectroscopy is a very straightforward tool to identify samples structures either crystalline or amorphous, as a film or adsorbed species, through their vibrational fingerprint In practice, a laser beam (for example as green light,  = 514.5 nm) is focused on the sample surface and the spectrum of scattered light is analyzed. Lines of a Ne lamp are used for frequency calibration. To avoid sample overheating a low power density is used.
By Raman spectroscopy it is possible to obtain information as:

Chemical composition
Crystalline phase and Phase transitions
Crystalline purity and structural disorder
Nanostructured systems’ dimensions
Stress and stress-induced effects
Defects and impurities
Temperature of samples

TECHNICAL SPECIFICATION

Raman measurements can be performed as single measurements and mono, bi and tridimensional maps even when the temperature varies from -196 °C to 600 °C in a controlled atmosphere using a dedicated Linkam accessory.
The laser light is focused using 100x, 50x, 10x and 5x objectives of an Olympus U5RE2 microscope. The spectra can be excited with the wavelength in the green (514.5 nm of maximum power 100 mW) or in the red (633 nm of maximum power 17 mW) in back-scattering geometry.
The Horiba Scientific LabRam HR Evolution spectrometer is equipped with an automatic XY stage, and an electron-multiplier CCD detector equipped with three different gratings 300, 600 and 1800 lines/mm).

AVAILABLE TECHNIQUES

Raman peaks are fitted by GRAMS software (Galactic) with mixed Gaussian-Lorentzian functions to obtain frequencies position, intensities and FWHM.

SAMPLES

Sample dimensions: from 2 x2 mm2 (min.) to 200 x 200 mm2 (max.)
Sample thickness: 30-40 mm (max.)
Samples are directly loaded and transferred to the measuring position

USE FOR

Silicon and Carbon-based materials
Semiconductors
Molecules and adsorbed species
Thin-films
Nanostructured and porous materials (e.g. Catalysts)
Organics (e.g. pharmaceuticals)
Polymers/Coatings
Archeological materials (e.g. tuffs in Etruscan tombs)

Raman Spectroscopy