MIT Electron Microprobe Facility

The MIT Electron Microprobe Facility in the Department of Earth, Atmospheric and Planetary Sciences (EAPS) serves as the centerpiece of analytical instrumentation used in EAPS for research and teaching activities in geochemistry, petrology and mineral physics. The instruments in the facility form part of the Center for Geochemical Analysis (CGA), which comprises six instrument-oriented facilities. The microprobe facility serves a broad spectrum of research scientists at MIT (EAPS, Material Science and other engineering and science departments), Woods Hole Oceanographic Institution (WHOI), neighboring universities, academic institutions and the industry. Analytical services are available for the faculty and professionals. User training is also available.

The Electron Microprobe, also known as the Electron Probe X-ray Microanalyzer (EMPA), is a powerful and well established analytical tool that provides non-destructive, in-situ and complete quantitative chemical analysis of a flat solid surface with a spatial resolution of ~2 micron through X-ray emission spectrometry. It also provides high-resolution scanning electron and elemental X-ray images (concentration maps) showing spatial distribution of elements. A variety of earth, extraterrestrial and artificial materials including minerals, glasses, ceramics, metals and superconductors can be analyzed. Below is an illustration of the JXA-733. The basic components of the JXA-8200 and the JXA-733 are similar.

The JEOL JXA Superprobes are equipped with:

(*) Up to five wavelength dispersive spectrometers (WDS) working simultaneously and providing quantitative analysis of all elements with atomic number >4 (B to U) and minimum detection limits of ~10 ppm under favorable conditions. We have a large standard collection for analysis of most elements.
(*) The WDS can also be used to obtain X-ray maps showing elemental distributions.
(*) Energy dispersive spectrometer for quick qualitative analysis.
(*) Back-scattered electron detector for high resolution compositional imaging.
(*) Secondary electron detector for high resolution topographic imaging.
(*) An orthogonal translational stage that can hold up to nine 1-inch diameter sample mounts or a large sample (up to 80 mm x 80 mm) of irregular shape.
(*) Photomultiplier for cathodoluminescence imaging.
(*) Sample preparation facility includes diamond wafering blades, polishing grits and papers, lap-wheel units, automatic polishers, optical microscopes and carbon coaters.

The MIT Electron Microprobe Facility was established in 1972 and has been in continuous operation since that time. It has been upgraded several times. In its current configuration, the facility consists of two electron microprobes manufactured by JEOL, a JXA-8200 Superprobe and a JXA-733 Superprobe. The JXA-733 was purchased in 1984 with National Science Foundation, Earth Sciences: Instrumentation and Facilities (NSF-EAR I&F) and Keck Foundation funding. In 1992, a second JXA-733 was purchased with funds from NSF and MIT. In 1997, we obtained funding from the NSF-EAR I&F program to carry out a major upgrade for our JEOL instruments. The upgrade was purchased from Geller Microanalytical Lab, and included new automation for the wavelength dispersive spectrometers (WDS) and stage, new quantitative analysis and data reduction software, new digital imaging and stage mapping software, and new electronics and control software for the energy dispersive spectrometer (EDS). In 2005, we upgraded the automation hardware of both instruments by replacing the old Tracor-Northern PAC controllers with control hardware from Geller Microanalytical Lab.

In 2009, we obtained new funding from NSF-EAR I&F to replace one of the old and frequently malfunctioning JXA-733s with a state-of-the-art JXA-8200. This upgrade was completed in 2010 with National Science Foundation (NSF) and MIT funding. The JXA-8200 features a LaB6 electron gun that generates higher beam currents with smaller spot size compared to conventional W electron guns. New WDS spectrometer design and highly sensitive WDS analyzing crystals and detectors allow accurate trace element analysis. The new instrument also features the advance xClent II cathodoluminesence system that has wavelength discrimination capability allowing map acquisition at different light wavelengths and spectroscopy for phase characterization and identification of trace impurities.