Electron probe microanalysis (EPMA) is also known as electron microprobe analysis (EMPA). Among surface scientists, the technique is familiarly known as microprobe or even just “probe.” EPMA falls into the broad category of instruments for surface analysis that uses beams to investigate the surface of sample. In the case of EPMA, an electron beam is used as the probe, and the primary signal that is detected is in the form of X-rays. These X-rays are analyzed by energy dispersive spectrometers (EDS) and wavelength dispersive spectrometers (WDS). Both types of spectrometer provide information on the elemental composition of the sample surface underneath the “spot” of the electron beam. Generally speaking, an EDS detector has poorer energy resolution and is useful for relatively rapid qualitative examinations of the surface. A WDS detector provides more quantitative analysis of the elemental composition, and also has better performance with lighter elements. With appropriate electron optics, the beam size is typically about a micron in size, providing excellent spatial resolution of the surface.

EPMA provides elemental analysis of a small spot by rastering the electron beam across the surface and developing an elemental map. The map provides a detailed image of the surface’s composition. EPMA instruments are commonly outfitted with detectors for electrons that emerge or are scattered from the surface. This signal can be composed into an image of the surface, just as in a standard scanning electron microscope. Hence, there is a close kinship between an EPMA system and an electron microscope with attached EDS or WDS detectors. The primary difference is that the EPMA system is optimized for X-ray spectroscopy, while the microscope is optimized for imaging.

EPMA has important applications in many materials science fields, particularly in semiconductor materials, metallic alloys and ceramics. Given the high spatial resolution of the probe, the technique can be used to analyze small defects. With more sophisticated software analysis, EPMA can also be used to analyze thin films deposited on materials. Although EPMA is primarily an elemental analyzer, the technique is commonly used to identify minerals within rock specimens. The elemental composition of rock specimens can be tied to the identity of the mineral composing a particular grain in a rock sample. EPMA analysis is carried out under vacuum conditions that generally preclude the examination of life science samples due to the water content.

Including aftermarket and service, which are significant for these instruments, total EPMA market demand was about $55 million in 2009. The global economy’s general improvement, and the improvement in the semiconductor and electronics sector in particular, should provide good short-term growth. Relatively few vendors participate in the EPMA market. The leader is JEOL.

EPMA at a Glance:

Leading Suppliers

• JEOL

• Cameca (AMETEK)

• Shimadzu

Largest Markets

• Metals and Mining

• Academia

• Semiconductors and Electronics

Instrument Cost

• $400,000–$1,500,000