JEOL recently sponsored a topical conference on cathodoluminescence that brought together experts and those new to the technique during the week of October 24-28, 2011. Held at the National Institute of Standards and Technology (NIST), Gaithersburg, MD, the event highlighted the use of CL in the SEM, TEM, and microprobe to investigate impurities and defects in a variety of materials. CL is undergoing a “revival of sorts with SEM and Microprobes,” says Peter McSwiggen, JEOL’s microprobe consultant. “CL has been around a long time in the geology world. It used to be done optically by flooding the sample with a broad e-beam. You could look at the color and see the zoning (sequence of crystal growth over time). Now you can look at the actual spectra and correlate the wavelengths of CL light with the elements that produce them. You can see variations like zoning in crystals in ppm – something that was always difficult to measure yet you see it very clearly.”
Sample preparation of polished cross sections for CL was the topic of JEOL scientist Dr. Natasha Erdman’s talk, which entailed use of the JEOL cross section polisher. Pristine cross sections are invaluable to analysis using CL, which employs an electron beam to induce a sample to emit light in the SEM that is subsequently collected by a dedicated detector (and/or spectrometer). Dr. Erdman, who has perfected the technique for creating highly polished cross sections of samples since joining JEOL in 2004 (when the CP was first introduced), is frequently consulted on a variety of soft, hard, and composite samples to help researchers employ the best methods to produce pristine cross sections. “CP is particularly effective in preparation of materials where strain effects can be studied via EBSD and CL,” she said.
The short course presented by the Microbeam Analysis Society and the Australian Microbeam Analysis Society pulled together experienced researchers and those new to the use of CL “to compare notes on where the field is now, and to generate ideas,” said McSwiggen. CL produces amazing images of crystal growth rings, similar to those found in tree growth rings. The ability to analyze one atom, one layer at a time reveals much about the chemical changes in the environment of a quartz crystal, for example.