Within analytical sciences, energy dispersive X-ray spectroscopy (otherwise known as EDS) and CL in the scanning electron microscope (termed SEM) are vital microanalysis techniques.
During the process of EDS, the composition of a sample is revealed by the use of an X-ray fluorescence spectrum, which is based on characteristic X-rays arising from the atomic structure of an element.
In contrast, the technique of CL uses optical spectroscopy to reveal properties (both optical and electronic) resulting from the presence of trace elements or defects and the crystal structure.
A complete analysis will often require characterization using both of the aforementioned techniques. In many gems, minerals and cultural heritage items, for instance, the CL signal exposes the distribution of specific minor and trace elements, which are at concentrations far below the sensitivity level of EDS detection.
Gatan Microscopy Suite® is a combination of EDAX’s Octane Elite EDS system and Gatan’s Monarc® detector. It is used to capture cathodoluminescence (CL) and X-ray signals simultaneously.
Methods and Materials
It has historically been necessary to collect both CL and EDS maps sequentially as the CL detector tends to block the X-ray signal.
Moreover, samples have often had to be moved between analysis techniques due to dissimilar analytical working distances, resulting in extended data collection times, increased complexity of image registration and increased electron dose.
However, EDS, CL and SEM signals can be captured simultaneously within Gatan Microscopy Suite software as part of an efficient workflow using the Monarc CL detector and EDS detectors from EDAX.
A common analytical position can be used with a proprietary collection mirror, facilitating both exceptional collection efficiency and a line of sight to the EDS detector.
A kyanite (Al2SiO5) thin-section was used to provide an example dataset: the material was chosen due to its importance within the refractory industry and the ambiguity over the role that minor and trace elements play in determining the refractoriness.
Figure 1. (left) Secondary electron image of kyanite thin-section; (center) EDS map revealing a predominantly coarse-grained quartz-kyanite segregation with small amounts of staurolite; (right) distribution of chromium in the kyanite phase extracted from cathodoluminescence data revealing significant intra-grain segregation indicative of multiple generations of formation — a similar map for titanium was also deduced but is not shown here for clarity. Image Credit: Gatan Inc.
The researchers were able to collect results that could not be obtained using each technique in isolation, thanks to the deployment of capturing both EDS and CL signals. In this manner, three distinct mineral phases were revealed, along with the distribution of Cr and Ti trace impurities within kyanite.
It is clear that the techniques of CL and EDS complement one another, and a remarkable benefit is conferred on specimen analysis by this demonstration of simultaneous acquisition.
Gratitude is owed to Dr. Giulia Degli-Alessandrini of The Open University for providing the specimen used in this study.
This information has been sourced, reviewed and adapted from materials provided by Gatan Inc.
For more information on this source, please visit Gatan Inc.