Spectroscopy - What Is It?

The Use of Spectroscopy in Various Fields

The dispersion of an object's light into its various components is referred to as spectroscopy. This makes it possible for astronomers to deduce an object's temperature, mass, composition, and luminosity [1].

Raman Spectroscopy in Chemistry

Raman spectroscopy is a type of vibration-based spectroscopy that was developed in 1928 by C.V. Raman and K.S. Krishnan and is therefore named in honor of Sir C.V. Raman. It helps in chemistry because it gives molecules a fingerprint that can be recognized. This non-destructive approach to chemical analysis is one of its main uses [2]. Raman spectroscopy is used in different areas which are: Pharmaceuticals and cosmetics which is from molecular drug discovery, the design of innovative drug delivery systems and the quality control of finished products [3].

Raman Spectroscopy in Geology and Mineralogy

Raman spectroscopy is used in geology and mineralogy where it is used in the analysis of geological samples [4]. It also provides a non-destructive and efficient way of identifying specific materials with information on the molecular structure and chemicals environments of the materials. It evaluates the residual pressure and stress within the material and also shows the characteristics of a sample [4].

Raman Spectroscopy in Semiconductor Studies

Raman spectroscopy can be used in the study of semiconductors where it aids in companies to show the properties of semiconductor materials and their nature. The elements considered are such as silicon, germanium and composite materials semiconductor such as Gallium Arsenide [5].

Raman Spectroscopy in Carbon Materials Characterization

Raman spectroscopy today has been applied for the characterization of carbon materials such as distinguishing the spectrum of germanium and silicon [6]. For every band in the Raman spectrum, there is a corresponding vibrational frequency of a bond within a molecule [7].

Raman Spectroscopy in Life Sciences

This type of spectroscopy, apart from being used in solving chemical problems, it is also used in life sciences by providing a noninvasive, water insensitive probe and nondestructive solutions to these sciences. It helps to complement the existing methods such as testing the biocompatibility of dental implants, examining soil components and plant tissue alkaloids and the localization of single bacteria [8].

How Raman Spectroscopy Works

Raman spectroscopy works through a process which is as a result of molecular vibration which causes a difference in the polarizability of the molecule under investigation [9]. For this molecule to be infrared active, the vibration is supposed first to cause a change in the permanent dipole moment. An example of a simple Raman active molecule is a species such as CS2. There is a symmetrical stretch out and stretch in is then detected by the Raman spectroscopy. This molecule cannot be visible in infrared spectra since the molecule lacks a permanent dipole hence making the Raman spectra a complementary to show the vibrational modes of the molecule [10].

Raman Spectroscopy Detection Range

The Raman spectroscopy can detect a wide range of compounds from organic to inorganic materials [9]. The process bases on inelastic scattering of monochromatic radiation. In the process, there is an exchange of energy between the photon and the molecule and the scattered photon should have a higher or lower energy about the incident photon [11] [7]. This energy difference is made up by a change in the vibrational and rotational energy of the molecule, and it provides information on its energy levels. During the process also, there is an interaction between the laser light with the vibrating molecules, and this results in the shift, either upwards of downwards, of the laser photons. When a sample is illuminated with a laser beam, the illuminated spot is collected using a lens and sent through a device called a monochromator [7]. The elastic scattered radiation at the wavelength that corresponds to the laser line is filtered out by a band pass filter, a notch filter or an edge pass filter and the rest of the collected light passed onto a detector [5].

References:

R. Clark, Proceedings of the Eleventh International Conference on Raman Spectroscopy. Chichester [u.a.]: Wiley, 1988.

M. Amer, Raman spectroscopy, fullerenes and nanotechnology. Cambridge, UK: Royal Society of Chemistry, 2010.

M. Ghomi, Applications of Raman spectroscopy to biology.

S. Zhang and B. Zhu, Seventeenth International Conference on Raman Spectroscopy. Chichester: Wiley, 2000.

W. Jay, J. Cashion and B. Blenkinship, "Lancaster delftware: a Raman spectroscopy, electron microscopy and Mössbauer spectroscopy compositional study", Journal of Raman Spectroscopy, vol. 46, no. 12, pp. 1265-1282, 2015.

V. Volodin and D. Koshelev, "Quantitative analysis of hydrogen in amorphous silicon using Raman scattering spectroscopy", Journal of Raman Spectroscopy, vol. 44, no. 12, pp. 1760-1764, 2013.

E. Le Ru and P. Etchegoin, Principles of surface-enhanced Raman spectroscopy. Amsterdam: Elsevier, 2011.

P. Sindhu, Elements of molecular spectroscopy. Tunbridge Wells: New Academic Science, 2012.

D. Darnall and R. Wilkens, Methods for determining metal ion environments in proteins. Amsterdam: Elsevier, 1980.

R. Clark and R. Hester, Spectroscopy of biological systems. Chichester [etc.]: John Wiley & Sons, 1986.

A. Weber, Raman Spectroscopy of Gases and Liquids. Berlin, Heidelberg: Springer Berlin Heidelberg, 1979.