Electron Probe Microanalysis
NREL uses electron probe microanalysis (EPMA) to probe the surface of a sample with high-energy electrons, thereby stimulating inner shell ionization in the atoms.
This results in the emission of characteristic X-rays that serve as signatures of the elements present. Either energy-dispersive spectroscopy (EDS) or wavelength-dispersive spectroscopy (WDS) are used to detect and identify the emitted X-rays.
The primary application of EPMA is compositional analysis of a sample, either for the sample as a whole or with respect to a local feature on the micron scale. With a sensitivity of ±0.2 at.%, it is the most convenient, accurate, and rapid method for compositional analysis, especially for microanalysis.
Employing either EDS or WDS, EPMA is used to produce elemental line scans or area scans that can be superimposed on topographic maps, thereby correlating topographical features with their chemical composition.
EDS is used for simultaneous display of most of the chemical spectrum (from boron to uranium) and for quick surveys of the area of interest before performing a more accurate quantitative analysis with WDS.
WDS features four spectrometers with ten diffracting crystals. The use of a single-channel analyzer allows much better peak resolution and helps to resolve peak overlap problems common in PV materials.
A computer system controls the electron beam, spectrometers, specimen stage, and data processing.