The principles and characteristics of electron probe microanalysis, explained by a testing‑probe manufacturer.
Release date:
2022-06-16
Test‑needle manufacturers contend that conventional chemical analysis methods can only determine the average composition of a sample, whereas electron microscopy enables micro‑area analysis correlated with local morphology, making it an extremely valuable technique for investigating material structure and elemental distribution. Today, we will discuss the principles and characteristics of electron probe microanalysis.
Test needle Manufacturers contend that conventional chemical analysis methods can only determine the average composition of a sample, whereas electron microscopy enables micro‑area analysis correlated with local morphology, making it an extremely valuable technique for investigating material structure and elemental distribution. Today, we will discuss the principles and characteristics of electron probe microanalysis.
Test needle Manufacturers regard the electron probe as primarily designed to analyze the composition of microregions. It is an analytical instrument developed on the principles of electron optics and X-ray spectroscopy. The column of the electron probe microscope is structurally similar to that of a scanning electron microscope; however, its detector incorporates an X-ray spectrometer, which is specifically used to measure the characteristic wavelengths or energies of X-rays, thereby enabling the analysis of the chemical composition of microscopic areas.
Test needle Manufacturers note that, in addition to dedicated electron probe instruments, a significant number of such instruments are mounted as accessories on the objective lenses of scanning electron microscopes or transmission electron microscopes, thereby enabling simultaneous three‑dimensional analysis of microstructural features, crystallographic information, and chemical composition at the microscale.
Test‑probe manufacturers contend that the electron probe’s column and sample chamber are fundamentally no different from those of a scanning electron microscope. Consequently, to enable an instrument to perform both morphological and compositional analyses, scanning electron microscopes and electron probes are often integrated. The signal‑detection system of an electron probe is an X‑ray spectrometer; the type that measures spectra at characteristic wavelengths is called a wavelength‑dispersive spectrometer (WDS) or simply a spectrometer, while the type that measures X‑ray characteristic energies is known as an energy‑dispersive spectrometer (EDS) or an energy spectrometer.
Test needle The manufacturer holds that, in an electron probe, X-rays are generated within a volume of one micrometer or even a nanometer beneath the sample surface. If this volume contains numerous elements, X-rays with characteristic wavelengths corresponding to each element can be excited. The wavelength (or frequency) of these characteristic X-rays does not vary with the energy of the incident electrons (i.e., the accelerating voltage); rather, it is determined by the elemental composition of the material—specifically, by the atomic number of the constituent elements.
The manufacturer of test probes notes that the characteristic X-ray wavelengths of different elements vary significantly. To ensure that the analyzable elements cover as many as possible across the periodic table, several spectrometer crystals with varying surface spacings must be employed. In the spectrometer, the X-ray signal originates from a tiny volume near the sample surface and can be regarded as a point source; consequently, the X-rays emitted by this point source are divergent, and only a very small fraction reaches the surface of the spectrometer crystal, resulting in an extremely weak signal.
Test needle The manufacturer states that a multichannel analyzer features a memory composed of numerous storage elements, referred to as channels. The number of clock pulses, which is proportional to the X-ray photon energy, is routed into different storage units according to its magnitude; each storage unit records the corresponding photon count for that pulse. Consequently, the channel address is proportional to the X-ray photon energy, and the channel count represents the number of X-ray photons.
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