What is an electron microprobe?
1.1. Introduction The electron microprobe is an instrument for spot chemical analysis of solid-state materials at the micron scale. In other words, a solid material such as a mineral, metal or glass can be analysed at a scale of a few microns or less. This allows the detection of small compositional variations within an individual crystal, for example, which could not be observed by some sort of bulk chemical analysis. 1.2. The Electron-Optical System Two fundamental components comprise the modern electron microprobe, the electron-optical system and the X-ray spectrometer. The electron-optical system or EOS consists of an electron gun and a series of magnetic lenses and apertures to focus a beam of electrons on to a sample. Typically, a hairpin tungsten wire is used in the electron gun to generate electrons by thermionic emission, although lanthanum hexaboride may also be used. The beam is directed through a vacuum chamber by the condenser lenses and then focussed on the sample. An ana
The electron microprobe, more formally called the Electron Probe Micro Analyzer (EPMA), is based upon the electron optical column of a conventional Scanning Electron Microscope (SEM), but incorporates a hardware addition specifically designed for the accurate, quantitative chemical analysis of solid materials. The application of this instrument can be most easily explained by breaking down the component parts of its acronym. The “Electron Probe” part Like the SEM, the EPMA uses a primary electron beam to stimulate signal emission. An important capability of the EPMA, however, is the ability to fix the beam into an immobile “spot” or probe of user-defined size and automatically monitored and regulated current. This permits the selection of single locations for irradiation at a constant electron flux over time. The “Micro” part With our instrument, the diameter of the fixed spot can be varied in the range of 0.2 to 20.0 m m. [Although larger spot sizes are available, they typically are n
Electron Probe Microanalysis (EPMA) is an elemental analysis technique which uses a focused beam of high energy electrons (5 – 30 KeV) to non-destructively analyze a solid specimen surface (including thin films and particles) for inducing emission of characteristic x-rays (0.1 – 15 KeV). The spatial resolution of x-ray microanalysis of thick specimens is limited to a volume with dimensions of approximately 1 micrometer due to electron scattering effects. This volume may be larger for low energy emission lines that can still be excited by lower energy electrons that have been highly scattered a significant distance from the impinging beam on the specimen surface. Quantitative matrix (interelement) correction procedures based on first principle physical models provide great flexibility and accuracy in analyzing unknown samples of arbitrary composition. Spatial distribution of elemental constituents can be visualized quantitatively by digital composition maps and displayed in gray scale o
