Omri Dvir - Instrument supervisor
Electron Probe Microanalyzer (EPMA) Lab at the Hebrew University of Jerusalem,
Fredy and Nadine Department of Earth Science
In our lab, we have a JEOL Superprobe JXA-8230. SEMs are built mainly for imaging
samples using SEI or BSEI detectors. An EPMA is 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.
(Electrons scattered by Coulombic interaction with the charge of the atomic nucleus
aka Rutherford scattering.)
-Secondary electron imaging (SEI) reveals the sample's topography due to the
variation in SE production at different tilt angles. Secondary electrons are ejected
from the k-shell by inelastic scattering interactions with the electron beam. They
originate within a few nanometers of the surface.
-Cathodoluminescence- 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.
For more information see the following website: http://epmalab.uoregon.edu/epmatext.htm
