Basics and applications of Raman spectroscopy in materials science

The course focuses on Raman spectroscopy, its physical fundamentals, some experimental notes and some applications in the broad field of materials science.

Starting with some historical elements related to the period of the discovery of the effect by Indian physicist C.V. Raman, the course offers a quick overview of the many applications that Raman spectroscopy offers today: from the physics and chemistry of materials to biomedicine, from environmental monitoring to quality control in industrial processes, from forensic science to cultural heritage. These applications are made possible by the high informational value of the microscopic physical mechanisms responsible for the Raman signal, i.e. the vibrational dynamics in molecules and crystals.

The Raman effect will be illustrated both in a semi-classical approach and in the more comprehensive and satisfactory quantum-mechanical approach. In the field of condensed matter, and more specifically crystals, an in-depth analysis will be proposed to highlight how Raman spectroscopy allows us to obtain information about the crystalline phase, structural order and mean crystal size. Starting from the rigid selection rule that in an ideal crystal imposes Raman activity determined only by center-zone phonons, the role of defects and disorder in the activation of non-zero q phonons in Raman spectroscopy will be illustrated.

Using Porto's notation, we will show how it is possible to monitor different elements of the Raman scattering matrix in an oriented crystal as the scattering geometry varies and how group theory can be predictive of the Raman activity of a specific structure/material. Finally, a review of some typical instrumental elements of a Raman experiment will provide the basis for illustrating some modern variants of canonical Raman spectroscopy. The physical principles and main applications of Surface Enhanced Raman Scattering (SERS, Tip Enhanced Raman Scattering (TERS) and Spatially Offset Raman Scattering (SORS) will be illustrated and discussed.