Chapter 3: Raman-in-SEM studies of inorganic materials

SEM-EDS and micro-Raman spectroscopy have been combined for material characterization in several recent studies. Switching from one to the other is frequently considered as a problem that cannot be solved using specific solutions. Although both techniques have followed a parallel but very different evolution since their introduction in the early 1930s, the concept of Raman-in-SEM first began in the 1980s and the first commercial systems were marketed in the early 2000s. The two main systems and techniques that have been developed and marketed by three manufacturers are presented and described in this chapter. An evaluation of their advantages and limitations is proposed. A metrological study is then proposed for one of these systems, based on the ‘on-axis’ technique using a curved mirror placed under the SEM pole piece. This study allows a discussion of the performance and limitations of Raman spectroscopy when performed in a SEM. A comprehensive review of published work is provided, although papers are rare in the open literature. The technique is essentially used for controls, expert assessments and high technology applications. Advanced techniques that allow the use of Raman-in-SEM spectroscopy are discussed in detail using application examples taken from different fields in geosciences, materials chemistry or from expert assessments. The conclusions of this study show that Raman-in-SEM spectroscopy is to date the first step in the combination of two well-known and mature techniques enabling the synergy between them to be maximised. Raman-in-SEM spectroscopy is relatively easy to set up and effectively complements the capabilities and efficiency of analytical SEM for material characterization. What are the most likely development perspectives that may be considered for this analytical coupling? Today, commercial systems are limited to only point-level micro-Raman analysis at the micrometre scale. In the near future, developments in both hardware and software will probably allow analysts to acquire Raman maps, or to employ multi-technique analyses based on a combination of data from SEM, EDS Raman, etc. New hardware developments may enhance the spatial resolution of both SEM and Raman spectroscopy.