Microanalysis

The electron microprobe is a CAMECA SX50 that is equipped with four wavelength-dispersive spectrometers and a high-resolution energy-dispersive solid state detector. We routinely analyze minerals, glasses, alloys, ceramics and other materials (e.g., concrete, biological materials, fossils, etc.).

The electron microprobe uses an energetic electron beam that is focussable to less than 1 micron diameter to excite a target material so that it emits characteristic X-radiation for each of the elements present. Under special conditions, spots as small as several hundred nanometers can be quantitatively analyzed. The energy-dispersive spectrometer is used for rapid (< 30 second) qualitative determination of the elemental make-up of the sample. Wavelength-dispersive spectrometers filter the complex X-ray spectrum to isolate the X-rays of a single element, and the measured intensity of X-radiation is used in comparison to known standards to provide a very precise analysis of the chemical composition of a sample for all elements from Fluorine to Uranium. A single analysis typically takes from 1 to 3 minutes, depending on the number of elements of interest. Automated routines allow the programming of the instrument to work for extended periods without an operator present (e.g, overnight).

Compositional Imaging

Surface areas of samples can be scanned either by moving the probe beam (smaller areas up to 200 micrometers square) or by moving the sample under a fixed beam (larger areas > 500 micrometers square) with each spectrometer set to detect X-ray intensity for a particular element. The result is an X-ray intensity map of the imaged area, or effectively an analog elemental concentration map (see images below). This capability is of extraordinary value in characterizing patterns of elemental zoning in natural and synthetic materials, for example in studies of syn-crystallization zoning or post-crystallization diffusional modification.

Examples:

Yttrium image-map for a monazite (Cerium-REE Phosphate mineral) from Virginia.

FOV is 120 microns.

Yttrium image-map for a monazite from Massachusetts.

FOV is approximately 200 microns.

Phosphorous (left) and Ytterbium (right) maps of a cross-section of doped, extruded glass optical fiber. FOV is approximately 100 microns.