Low voltage imaging, X-ray analysis and X-ray mapping has become very important for the investigation of nanomaterials and their surfaces. Consequently, there have been significant advances in the field of scanning electron microscopy, especially with instruments that have excellent low voltage capabilities. The improvements have not only been in electron column design but also in the development of stable emitters, different SE and BSE detectors and different microanalysis detectors (SDD’s, WDS’s and SXES).
Traditional microanalysis using energy dispersive X-ray spectroscopy (EDS) involves using higher accelerating voltages in the range of 15kV to 25kV in order to excite the well-known K-Lines. Operating the SEM at lower accelerating voltage allows for greater surface sensitivity, reduced beam damage, the ability to minimize charging effects, nanometer scale lateral X-ray spatial resolution and nanoscale X-ray depth sensitivity.
With the new generation of SDD’s, the sensitivity for X-rays in the low-energy part of the spectrum has substantially improved. SDD’s can now be purchased with varying windows/windowless systems, allowing greater sensitivity of the lower energy X-rays. Furthermore, SDD’s with large detector areas are being produced that allow greater X-ray collection efficiencies with higher count rate throughput aiding the possibility of operating at much lower accelerating voltages.
Low-voltage microanalysis has a distinct disadvantage in that fewer X-ray lines are available and the ones that do exist quite often overlap with lines from other elements. Extensive work is still required on fundamental parameters, algorithms, and mass absorption coefficients before any quantitative analysis can be performed. However, if a careful approach is taken, some excellent results can be obtained on a nanometer level, even if it is only a qualitative approach. For quantitative analysis, standards based analysis is the better way to go.
This presentation will cover low-voltage imaging and microanalysis with particular emphasis on low voltage X-ray mapping.