Electron Probe Microanalysis Laboratory Department of Geological Sciences  |  University of Texas at El Paso (UTEP)     Electron Probe Microanalysis (EPMA) is a non-destructive method for determining the chemical composition of solid materials in micrometer scale size. The microprobe at UTEP has four wavelength dispersive detectors and a state-of-the-art Rontec solid state energy dispersive detector. The operating software of the SX50 has been recently upgraded to SX RAY N50 on Solaris 2, which operates nearly like an SX100 with SX100 version software compatibility. The probe has LIF, PET, TAP, and PC1 analyzing crystals and can quantitatively analyze elements from Carbon (Z=6) to uranium (Z=92) at routine levels as low as 100 ppm. It also has the ability to collect images as SE, BSE, and x-ray maps. Based on x-ray maps, the spatial distribution of elemental constituents can be visualized quantitatively and displayed in gray scale or false color. Variations in chemical composition within a material, such as a mineral grain or metal, can be readily determined.     Electron Probe Microanalysis (EPMA) is an elemental analysis technique which uses a focused beam of high energy electrons (5 - 30 KeV) to non-destructively ionize a solid specimen surface (including thin films and particles) for inducing emission of characteristic x-rays (0.1 - 15 KeV). It was developed by R. Castaing in Paris as his 1950 Ph.D. dissertation. Commercial electron microprobes became available in the 1960s, and have become standard analytical tools. The electron microprobe is designed specifically for detecting and measuring characteristic X-rays. The high-energy focused beam of electrons generates X-rays characteristic of the elements within a sample from volumes as small as a micrometer (10-6m) across. The resulting X-rays are diffracted by analyzing crystals (TAP, PET, LIF, ODPb, and PC) and counted using gas-flow and sealed proportional detectors. Chemical composition is determining by comparing the intensity of X-rays from standards (known composition) with those from unknown materials and correcting for the effects of absorption and fluorescence in the sample. The resulting data yield quantitative chemical information in a textural context. Quantitative matrix (inter-element) correction procedures based on first principle physical models provide great flexibility and accuracy in analyzing unknown samples of arbitrary composition.     These quantitative procedures have been demonstrated to produce error distributions characterized by a standard deviation of less than 3% relative when the samples are in the ideal form of a metallographically polished bulk solid. Standards utilized in these analyses are in the form of pure elements or simple compounds (e.g., MgO or GaP). This analytical approach provides great versatility in the analysis of multi-element unknowns of virtually any composition. Detection limits are of the order of 100 ppm with wavelength dispersive spectrometry and 1000 ppm with energy dispersive spectrometry. Typical applications include metallurgical studies, failure analysis, thin film, particulate analysis, mineral analysis, ceramic analysis, and many others. Capabilities of the Instrument     The electron microprobe offers several operational modes for chemical analysis. These are generally divided into qualitative and quantitative procedures. The qualitative analysis capabilities are briefly listed here : Qualitative Analysis Secondary electron imaging (SE) - provides topographic images (surfaces, cracks, voids) - magnification range from 63X to 10000X - on-line gray and false-color images - output in binary data file and TIFF image file Backscatter electron imaging (BSE) - provides average atomic number contrast images and topographic images - magnification range from 63X to 10000X - on-line gray and false-color images - output in binary data file and TIFF image file Qualitative x-ray imaging - provides x-ray mapping of sample surfaces for up to 4 elements (WDS) - on-line gray and false-color images - output in binary data file and TIFF image file Wavelength spectrometer scanning - simultaneous wavelength scan acquisition on 4 spectrometers - on-line database containing over 12,000 entries for peak identification - publication quality graphical output Quantitative Analysis Quantitative analysis generally involves the use of calibration standards and correction for deadtime, background, drift, matrix and interference effects in both the standards and the unknown sample. Quantitative element analysis - simultaneous analysis of 4 elements up to a maximum from C to U elements - large set of USNM, USGS, MAS and internal certified analytical standards - correction of deadtime, background, drift, matrix and interference effects for fully quantitative analysis - trace element procedure for low concentration elements - full automation for unknown and standard data acquisition - results in elemental and oxide weight percent, mole percent, formula atoms and mineral end-members - statistics on detection limits, sample homogeneity, and analytical sensitivity - draft and publication quality hard copy and ASCII file output Quantitative x-ray imaging  - software provides automatic acquisition of rectangular and irregular polygon areas for up to 10,000 analyses - large area mapping up to 25mm and larger - output in numerical ASCII file and publication quality contour plot, 3-D surface plot, gray or false color TIFF - image processing software EPMA photo of the month Contact information: Dr. Minghua Ren Geological Sciences Bldg. 106D Department of Geological Sciences The University of Texas @ El Paso El Paso, TX 79968 Ph. 915-747-5843 Fax. 915-747-5073 e-mail: ren@geo.utep.edu