The Fredy & Nadine Herrmann Institute of Earth Sciences
Electron Probe Micro analyzer (EPMA) Laboratory
The Hebrew University, Jerusalem
In our lab, we have a JEOL Superprobe JXA-8230. The EPMA designed for chemical analysis of the characteristic X-Rays emitted from a sample when probed by an electron beam. An EPMA can quantify elemental concentration using electron dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) to detect and count characteristic X-Rays emitted from a sample. There are pros and cons to using the EDS and WDS detector (mainly time and the necessity of experience using the techniques) We will be happy to discuss these in person.
Imaging options in the EPMA:
- Back scattered electron imaging (BSEI) is sensitive to the mean electron density (atomic weight). Back scattered electrons ate a form of elastic scattering in which incoming incident electrons are bounced back off the sample to hit the detector.
- Secondary electron imaging (SEI) reveals the sample's topography due to the variation in SE production at different tilt angles. Secondary electrons ejected from the k-shell by inelastic scattering interactions with the electron beam. They originate within a few nanometers of the surface.
- Cathodoluminescence (CL) Promotion of valence band electron to conducting band can emit photon of electromagnetic radiation in the visible light region.
Chemical analysis in the EPMA:
- EDS Detector: Energy dispersive spectroscopy counts the number and energy of X-Rays emitted from a specimen. The energy spectrum of the X-Rays characterizes the atomic structure of the emitting element.
- WDS Detector: Wavelengthe dispersive spectroscopy counts the number of X-Rays of a specific wavelength diffracted by a crystal. In contrast to EDS, WDS detectors only count the X-Rays of a single wavelength at one time that characterize the atomic structure of the emitting element.