USGS-GD-Scientific Capabilities - MICROBEAM INSTRUMENTS ELECTRON MICROPROBE Equipment

MICROBEAM INSTRUMENTS

ELECTRON MICROPROBE

Equipment

 

In 1993 The Geologic Division purchased three state-of-the-art JEOL 8900 electron microprobes. These instruments are located at the Division's major centers in Reston, VA, Denver, CO, and Menlo Park, CA.

The JEOL 8900 represents the latest technology in fully automated, fully digital, quantitative electron microbeam analysis. The instruments are equipped with five wavelength x-ray spectrometers and twelve analyzing crystals enabling analysis of all elements heavier than lithium. The instruments are also equipped with fully integrated energy dispersive x-ray spectrometers for qualitative and quantitative x-ray analysis. The 8900 microprobes provide digital secondary and backscattered electron imaging and are equipped with automated optical auto-focusing. The microprobe laboratories in Reston, Denver, and Menlo Park each provide high resolution dye-sublimation printers, laser printers, and Polaroid film output capability and all three laboratories are fully integrated on the network for digital transfer of chemical and image data. The instruments are capable of fully automated, unattended analysis for twenty-four hour operation. Off-line image processing and data reduction software are available in each laboratory.

Accurate quantitative analysis is a fundamental component of most microanalytical studies in the Geologic Division. High quality quantitative microanalysis provides accurate chemical compositions from a volume less than two micrometers in diameter with a precision of +/- 1% relative concentration for major and minor elements and a precision equal to counting statistics for trace elements. The detection limit for most elements is between 100 and 500 ppm. Standards are critical in quantitative electron probe microanalysis. All three Division laboratories have hundreds of well-characterized standards providing the ability to produce the highest quality quantitative analyses of most materials including metals, ceramics, and all types of geological samples.

Elemental x-ray mapping and line scan profile analysis are extremely valuable analytical tools for determining the lateral distribution of elements within a sample. The 8900 microprobes have full digital, quantitative mapping and line scan capability. In addition, large area elemental mapping can provide information about chemical variations across a sample that is otherwise difficult to obtain. Traditional beam raster x-ray mapping with wavelength spectrometers is limited to relatively high magnification images (i.e., > 1000X). The 8900 microprobes employ stage raster mapping in addition to beam raster mapping. Stage raster mapping makes it possible to map areas as large as 10x10 cm by moving the stage under a stationary beam. Image resolution of approximately one micrometer can be obtained for most materials.

Visit the microbeam laboratory web sites in Reston and Denver.

 


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URL http://geology.cr.usgs.gov/capabilities/chema/microinst/emm/equip.html