Microcalorimeter energy-dispersive spectrometry using a low voltage scanning electron microscope

We describe the current performance of the prototype microcalorimeter energy-dispersive spectrometer (&mgr;cal EDS) developed at NIST for X-ray microanalysis. We show that the low-energy &mgr;cal EDS, designed for operation in the energy range 0.2-2 keV, offers significant advantages for low-beam-energy microanalysis. We present several examples in which the prototype &mgr;cal EDS has been used to solve problems in low-voltage microanalysis, including the analysis of tungsten silicide (WSi2), titanium nitride (TiN) and barium titanate (BaTiO3) and the measurement of chemical shifts in Fe and C compounds.

Logarithmic 3-Band Color Encoding: Robust Method for Display and Comparison of Compositional Maps in Electron Probe X-ray Microanalysis.

: Electron-excited X-ray maps recorded with the scanning electron microscope (SEM)/electron probe X-ray microanalyzer (EPMA) are a major method of presenting compositional information. Digitally recorded maps are processed in a variety of ways to improve the visibility of features. Scaling of the recorded signal to match the 8-bit gray-scale intensity range of a typical computer display system is almost always necessary. Inherent limitations of gray-scale displays have led to other intensity-encoding methods for X-ray maps, including clipping, histogram normalization, and pseudocolor scales. While feature visibility is improved by applying these scales, comparisons among image sets are difficult. Quantitative comparisons must be based on standardized intensities corrected for background to produce intensity ratio (k-value) maps. We have developed a new logarithmic, multiband color-encoding method to view these k-value maps more effectively. Three color bands are defined, starting with a dark primary color and grading to a bright pastel: blue = trace (0.001 to 0.01); green = minor (0.01 to 0.1); and red = major (0.1 to 1.0). Within each band, the color is assigned according to a logarithmic scale that depends on intensity ratio or compositional measurements. Logarithmic multiband color encoding permits direct comparisons of maps, such as maps of different elements in the same field of view or maps of the same element in different areas, because the color scale is identical for all maps.

Standardless Quantitative Electron-Excited X-ray Microanalysis by Energy-Dispersive Spectrometry: What Is Its Proper Role?

: Electron beam X-ray microanalysis with semiconductor energy-dispersive spectrometry (EDS) performed with standards and calculated matrix corrections can yield quantitative results with a distribution such that 95% of analyses fall within +/-5% relative for major and minor constituents. Standardless methods substitute calculations for the standard intensities, based either on physical models of X-ray generation and propagation (first principles) or on mathematical fits to remotely measured standards (fitted standards). Error distributions have been measured for three different standardless analysis procedures with a suite of microanalysis standards including metal alloys, glasses, minerals, ceramics, and stoichiometric compounds. For the first-principles standardless procedure, the error distribution placed 95% of analyses within +/-50% relative, whereas for two commercial fitted standards procedures, the error distributions placed 95% of analyses within +/-25% relative. The implication of these error distributions for the accuracy of analytical results is considered, and recommendations for the use of standardless analysis are given.