Electron Probe Microanalysis Laboratory

Department of Earth and Planetary Science

University of California at Berkeley

UCB EPMA Home Page

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Introduction to Electron Probe MicroAnalysis

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). The spatial resolution of x-ray microanalysis of thick specimens is limited to a volume with dimensions of approximately 1 micrometer due to electron scattering effects. This volume may be even larger for low energy emission lines that can still be excited by lower energy electrons that have been highly scattered a significant distance from the impinging beam on the specimen surface.

Quantitative matrix (interelement) correction procedures based on first principle physical models provide great flexibility and accuracy in analyzing unknown samples of arbitrary composition. Spatial distribution of elemental constituents can be visualized quantitatively by digital composition maps and displayed in gray scale or false color.

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, with the significant exception of light elements (atomic numbers less than 8). 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.

Introduction to EPMA (747 Kb, Adobe Acrobat Format)

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Instrumentation and Facilities

The Department of Earth and Planetary Science purchased an electron microprobe analyzer with a generous grant from the National Science Foundation in 1994. The principle investigator of the proposal, "Purchase of a New Electron Microprobe", was Dr. Ian S. E. Carmichael and the proposal was co-investigated by Drs. Raymond Jeanloz, George Brimhall, Hans-Rudolf Wenk and Donald DePaolo.

The microprobe instrument is a Cameca SX-51 with 5 vertical high resolution wavelength dispersive spectrometers (WDS) and a atmospheric thin window (ATW) energy dispersive spectrometer (EDS). The instrument is under the direction of Dr. Ian. S. E. Carmichael.

The SX-51 includes a TV rate secondary electron (SE), backscattered electron (BSE), cathodo-luminescence (CL) and coaxial optical imaging capabilities. The instrument is completely computer controlled for automation of both the beam (high voltage, beam current, beam size, scan magnification, etc), spectrometer (analyzing crystal, Bragg position, PHA baseline/window/gain/bias/deadtime, count time, etc) and stage (x, y, z position).

In addition, new Windows PC based software has been developed (Win95/NT OS) to facilitate rapid and accurate acquisition, automation and quantitative analysis for all specimen types on the microprobe.

Summary of Specifications

Cameca SX-51 electron microprobe with 5 wavelength spectrometers
Oxford Si(Li) EDS detector, ATW thin window, 138 eV resolution
Secondary, backscattered, cathodo-luminescence and optical analog and digital imaging
Analytical range from Be to U
Analytical sensitivity from 100 % to 10 ppm
Analytical sensitivity typically from 100 % to 100 ppm
Analytical accuracy typically 1 - 5 % (major and minor elements)
Typical analysis time 10 sec (major elements) to 300 sec (traces)
Sample size range typically from 10 microns to 25 mm or larger
Analysis volume typically 1 - 10 cubic microns depending on x-ray energy
Reflected and Transmitted Light Optics in all configurations
Pentium PC based Windows multi-tasking acquisition and analysis interface
Numerical, graphical and false-color image hard copy and file output

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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

- 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 PC/Mac 256 color TIFF image file
- image processing software

Backscatter electron imaging

- provides average atomic number contrast images
- magnification range from 63X to 10000X
- on-line gray and false-color images
- output in binary data file and PC/Mac 256 color TIFF image file
- image processing software

Cathodo-luminescence imaging

- provides trace element and lattice dislocation imaging
- magnification range from 250X to 1000X (down to 63X using mosaic imaging)
- on-line gray and false-color images
- output in binary data file and PC/Mac 256 color TIFF image file
- image processing software

Qualitative x-ray imaging

- provides x-ray mapping of sample surfaces for up to 5 elements (WDS)
- provides x-ray mapping of sample surfaces for up to 16 elements (EDS)
- magnification range from 400X to 10000X (down to 63X using mosaic imaging)
- on-line gray and false-color images
- output in binary data file and PC/Mac 256 color TIFF image file
- image processing software

Wavelength spectrometer scanning

- simultaneous wavelength scan acquisition on 5 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. The following quantitative analysis capabilities are available :

Quantitative element analysis

- simultaneous analysis of 5 elements up to a maximum of 32 elements
- large set of NIST, USNM, USGS, MAS and internal certified analytical standards
- correction of deadtime, background, drift, matrix and interference effects for fully quantitative analysis
- on-line and off-line analysis software includes the CITZAF matrix correction library by John Armstrong (NIST)
- 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

Semi-quantitative wavelength shift scanning

- provides semi-quantitative analysis of oxidation states for some elements
- published procedures and results for Fe and S oxidation states

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Teaching

The Department of Earth and Planetary Science offers EPS 401, a course in the operation and theory of the electron microprobe. This pass/fail course is available each quarter and must be taken by all graduate students who require the microprobe for their thesis work.

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Recharge System

The SX-51 electron microprobe is available on a recharge basis for faculty and visiting researchers. The actual recharge rate varies from year to year but is typically $66 per hour with an additional 50% overhead charge for researchers whose funding source is outside the University of California system.

The number of hours recharged is automatically recorded by the automation, acquisition and quantitative analysis software. A typical session on the microprobe requires a minimum of two days of work (normally 10-18 charged hours), less for a very simple qualitative analysis of just a few points, more for complicated analytical situations or trace element work with extended counting times.

Please contact Tim Teague tteague@uclink2.berkeley.edu in the Petrographic Laboratory for sample preparation and the electron microprobe user schedule.

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Hot List

Microscopy:

EPMA Laboratories:

Instrument Vendors:

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Contact Information

John J. Donovan
Department of Geological Sciences
210 Cascade Hall
University of Oregon
Eugene, OR, 97403
(541) 346-4632 (voice)
(541) 346-4692 (FAX)

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Location

The UCB EPMA Laboratory is located in Room 447, McCone Hall on the Berkeley campus near North Gate.

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The Department of Earth and Planetary Science
Room 307, McCone Hall
The University of California
Berkeley, CA 94720-4767
Copyright 1998-2000, The Regents of the University of California

Last Updated 03/09/11