No abstract

An X-ray Micro-Fluorescence (XRMF) spectrometer, with an analysis area of about 100 by 150 microns, has been used to collect 2-dimensional X-ray intensity maps over large-area (5 to 50 mm in X and Y) samples. These intensity maps were collected by scanning the sample on an XY stage, and converting X-ray Energy-Dispersive spectra to peak intensities for the elements of interest. The maps, when displayed using false-color or pseudogray scales, show the distribution of individual chemical elements over the analysis area. These maps can be collected at speeds from about 1 minute per frame (analysing 25 elements simultaneously). Greater precision of chemical intensities, or larger area maps, may require several hours, particularly if extensive data processing is performed at each point. XRMF has advantages over more conventional SEM-EDS X-ray mapping, including sample preparation and presentation, as well as improved signal-to-noise ratios.A technique is described which assists in analyzing the large amount of data which is collected in each map. Principal Component Analysis (PCA) is performed on all of the elemental maps simultaneously. This technique compresses the many elemental intensity maps into a few principal components, resulting in many fewer maps to evaluate. The intensity maps of these principal components display the most pertinent information. They can also be plotted as scatter plots which can help with the partitioning of the data into individual phases. This procedure can potentially be automated as a method for phase analysis. The selected pixels from the scatter plots can be averaged and converted into phase compositions, and the phase information re-displayed on the original elemental or principal component maps.This technique has been applied to a thin section of rock, and to a synthetic multiphase alloy sample.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

No abstract

This paper reports on our recent efforts leading to significant improvements of our large area Vortex-EM ® silicon drift detectors (SDD) [1] in low energy X-ray detection, energy resolution and peak-to-background ratio. These improvements, plus their already proven high throughput capabilities [2], make the Vortex-EM ® SDD an ideal choice for today's electron microanalysis applications including elemental chemistry, fast spectrum imaging and high throughput particle analysis.The new Vortex-EM ® SDDs have a circular active area of 50 mm 2 with an improved entrance window that enables detection of low energy x-rays down to Beryllium (Fig. 1a). In the detector package, an internal collimator is used to ensure best performance. Carbon peak distortions observed with earlier versions have been eliminated. The carbon peak resolution achieved is ~ 67 eV FWHM at 16 μs processor peaking time (Fig. 1b). At the same peaking time, the 55 Fe Mn K α FWHM is ~128 eV with a peak-to-background ratio of ~18000.Combined with the EDS2008 microanalysis system of IXRF Systems, Inc., the Vortex-EM ® SDD comes as the core of a unique EDS system -the e-Xpress TM which inherits all major state-of-theart features and functionality of the EDS2008 system in both hardware and software. One of the most important features of this system is its fast spectrum imaging capability, which adopts the latest event streaming technique that binds event information with position information in real time, allowing for acquisition of a complete spectrum pixel by pixel. The spectrum data of each pixel is saved with the maps and is conveniently retrievable from the map file. The hardware uses multiple buffers for seamless data transfer through high speed Ethernet communication, with an achievable data transfer rate of ~2.5 million events per second. The high output rate (> 300 kcps) at short peaking times of the Vortex-EM ® SDD makes it possible to acquire maps at very high speed. Figure 2 shows 128x128 maps of a metal particle sample, acquired in 120 seconds. Also shown is the whole spectrum from a selected pixel in the map. Since the maps shown were acquired at an output rate much less than the maximum achievable rate, it would be possible to acquire them with a shorter dwell time and less frames under optimum conditions and thus the total acquire time could be well less than a minute. All the data presented here were collected on a TESCAN Vega II scanning electron microscope.