The Brown University Electron Microprobe Facility is located in room 027 of the GeoChem building. The Cameca SX-100 electron microprobe is equipped with 5 wavelength dispersive spectrometers (WDS) and a Rontec energy dispersive spectrometer (EDS).

In 2014, through an internal research grant from Brown University, the microprobe was upgraded with a new computer, new software, an improved vacuum system, a new electron gun that could house a LaB6 filament, and a joystick.

Probe Lab

The Cameca SX-100 microprobe at Brown University (above).

The WDS spectrometers each contain two or four diffracting crystals and presently include LTAP, TAP (2), LPET (2), PET, LLIF (2), LIF, LPCO, PC1 and PC2. The last three crystals are used to measure the light elements (boron to sodium). The absolute detection limits for the instrument are approximately 50-200 ppm, depending on the element.

The EDS spectrometer is capable of detecting all elements above sodium (Na).

X-ray element maps can easily be acquired on the microprobe. Using 512x512 pixel maps, up to nine element maps (5 elements on WDS, 4 with EDS), plus a backscattered electron (BSE) image, can be obtained simultaneously. Maximum resolution on any one map is one micron per pixel. Utilizing the coordinate system, maps of entire thin sections can be generated. Individual element maps are stitched together using ImageJ software. Subsequently, red-green-blue (RGB) mosiac maps can be generated (see below).

Chaves MgChaves Ca
Chaves Al

Magnesium, calcium and aluminum element maps (above) of the basaltic meteorite, Chaves and a combined RGB mosaic map of those elements (below). Chaves, a howardite, is a breccia from the asteroid, Vesta. In the RGB map, red shows the different compositions in the mineral pigeonite (a type of low calcium pyroxene), blue shows plagioclase feldpsar, while green shows augite (a high calcium pyroxene).


Chaves MgCaAl

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