Raman Scattering

When light of a wavelength applications/ed to materials, the light is scattered at the same wavelength as the incoming light (Rayleigh scattering). However, the wavelength of some of the scattered light changes according to the vibration of the molecules of the materials. These phenomenons are the Raman effect. The Scattering with a decrease in frequency (an increase in wavelength) of light in the Raman scattering is called the Stokes scattering. Conversely, the scattering with an increase in frequency (a decrease in wavelength) is called the Anti-Stokes scattering. In general, the strong Stokes scattering of light is used for spectroscope analysis.

Raman scattering

 

A molecule has a structure such as a system of weight (atoms) and spring (bond), each bond is vibrating constantly. While the Raman scattered light from the molecule passes through a spectrometer, it is found that the light of color determined by the binding is present in the scattered light.

Raman scattering by molecular vibrations

 

The Raman spectrum of a molecule contains a plurality of peaks. While Raman scattered light from molecules with a large of numeber of bonds passes through a spectrometer, a number of peaks of different colors can be obtained. The Raman spectrum is expressed according to differences in color.

The Raman spectrum of a molecule having a plurality of peaks

 

Raman spectra are unique fingerprints of materials. The Raman spectroscope measurement is to detect Raman spectra which depend on the materials. The binding of different molecules that make up the spectrum of Raman scattering material varies widely. In the spectrum of ribose and glucose, it can be seen that has a peak at a position different from the figure below. The positions of these peaks is unique to the material.

Raman spectra are unique fingerprints of materials.

 

Even pure carbon, for example, the Raman spectra will be different from each other, depanding on their crystalline forms. Althouch charcoal and graphite, diamond are made up of repeating units of carbon atoms, they have different crystallinities. The binding states with different crystallinities are different from each other, resulting in differences of crystal structure. The differences in the crystal structure will appear to be the difference of Raman spectrum. Thus, the difference of crystal structure cna be identified by the Raman spectra.

Raman spectra will be different from each other, depanding on their crystalline forms.

 

Since molecular vibrations lead to the change in the wavelength of the Raman scattering light, graphite and diamond can be distinguished even though they are both made up of repeating units of carbon atoms. Such characteristics play a significant role in the study of carbon nanotubes.
Furthermore, the stress applications/ed to a material can also lead to changes in its Raman spectrum. It can be used to detect minute defects of a semiconductor. In this field, the spatial resolution of about 1μm has a great advantage. Raman scattering peaks will shift in wavelength from the incident light, however, their intensities do not change. For fluorescent samples, the generation of fluorescence can be suppressed by a suitable wavelength selection of incident light, to perform Raman spectroscopy efficiently.
A Raman spectrum of the target substance can also be measured through a glass or other transparent material. The Raman spectrum of the transparent material can be eliminated. A confocal pinhole aperture can be used to obtain good spatial resolution in the depth direction. The Raman spectra of aqueous solution can also be detected and analyzed, because of the sufficient Raman scattering intensity of the substances contained in the aqueous solution.