JEOL JXA-8230 Electron Microprobe
Our new (2012) JEOL JXA-8230 “SuperProbe” electron microprobe measures the elemental compositions of solid samples by detecting the X-rays emitted on excitation by a focused electron beam, down to a spatial resolution of about 1 micron. All elements heavier than beryllium can be detected, at concentrations as low as 100’s of ppm. Highly quantitative analyses are made using 5 wavelength dispersive X-ray spectrometers (WDS) with calibrations based on known standard materials; somewhat less quantitative data can be collected, often more rapidly, with a JEOL standardless energy dispersive spectrometer (EDS). Compositional images (maps) can readily be obtained with backscattered electrons (sensitive primarily to mean atomic number), or with WDS or EDS X-ray data. The instrument is adjacent to the Stanford Nanocharacterization Laboratory (SNL), at the west end of the first floor of the McCullough Building.
The microprobe is equipped with an “xCLENT III” advanced hyperspectral cathodoluminescence (CL) system, which provides full color images, as well as point-by-point optical spectra, of the visible light emissions induced by the scanning electron beam. Such images are often very useful for rapid mapping of mineral distributions in complex samples and for seeing patterns of zoning in distributions of trace elements. CL data can be readily combined with X-ray and electron signals at each point to provide great flexibility in mapping composition and phase distribution.
Samples for the electron microprobe must be solid and vacuum compatible. Small grains can readily be mounted and polished, and standard, uncovered, polished petrographic thin sections (e.g. 27x46 mm glass slides or 25 mm rounds) are easily accomodated. Other unmounted samples can be bonded to a mounting block with epoxy. Samples that are not electrically conductive must be coated with a thin layer of carbon using the carbon-coater in the lab. Thin films (< 1000 nm) can readily be analyzed by the microprobe, using special software to account for thickness and substrate effects.
Most users receive training for the electron microprobe in GES 275 “Electron Probe Microanalytical Techniques”, taught by the lab director Bob Jones. Other training can be done as needed, and analytical work can be done by the lab director, on a fee-for-service basis when time is available.