Electron Probe Microanalysis (EPMA)

Introduction to Electron Probe Microanalysis

Complex chemical variation within single phases (mainly glasses and minerals in geology) can be resolved and geological materials can be analyzed in situ thanks to the spatial scale of analysis and the capacity to provide precise pictures of the sample. With the electron optics of EPMA, features that are irresolvable under a light microscope can be easily imaged to study fine-scale context for an individual spot analysis or to obtain much higher resolution images than can be seen using visible-light optics. MaTestLab is one of the leading testing service providers in the USA and Canada. We have a large network of testing laboratories in the USA.

Principle and Methodology of EPMA

An electron microprobe is a tool used to analyze solid materials by bombarding them with an accelerated electron beam. This energy-driven interaction releases matter and energy from the sample, yielding derivative electrons and x-rays. Secondary and back-scattered electrons are beneficial for geological material analysis. X-rays are generated through inelastic collisions between electrons and atoms in the sample. When an inner-shell electron is ejected, a higher-shell electron falls into the vacancy, releasing energy as an X-ray. These quantized X-rays are characteristic of the element. EPMA analysis is considered non-destructive, meaning x-rays generated by electron interactions do not cause sample volume loss, allowing for multiple re-analysis of the same materials.

Instrumentation

There are four main components to EPMA. A source of electrons, usually a W-filament cathode known as a “gun.” Electron optics, which functions similarly to light optics, is a collection of electromagnetic lenses arranged in the instrument’s column for the purpose of condensing and focusing the electron beam coming from the source. A light microscope enables direct optical inspection of the sample. A vacuum-sealed sample chamber with a variable sample stage (X-Y-Z) keeps gas and vapor molecules from interfering with the electron beam as it travels to the sample. A range of detectors is used to gather electrons and x-rays released by the sample and placed around the chamber.

Applications of EPMA

Quantitative EPMA analysis is the most used technique for small-scale chemical examination of geological materials, particularly when igneous and metamorphic minerals require individual phase analysis or are small or valuable for other reasons. It can also determine the U-Th ages of minerals like monazite without measuring isotope ratios. EPMA is also used for the examination of artificial materials like optical wafers, thin films, microcircuits, semi-conductors, and superconducting ceramics.