Microchannel plates (MCPs) are actually solid-state detectors that contain parallel arrays of minute single-channel electron multipliers all integrated together in a parallel array. As depicted in Figure 1, channel densities measure around 1–10 million channels/cm2.
Figure 1. Microchannel plate made up of microscopic electron multiplier channels
These solid-state detectors can be used for detecting electrons, ions, soft and hard X-rays, and UV photons. At the time of operation, an input event hitting the focal plane will lead to a flood of electrons and cause an amplification factor of up to 100,000. An amplification factor of 100,000,000 (with less than 1 count/sec/cm2 additional noise) can occur upon the cascading of a second or third array.
Various Designs of Microchannel Plates
MCPs were originally developed for use in image intensifier tubes for night-vision applications. Currently, the most common MCPs are the round 18-mm formats, but these devices can be produced in different shapes and sizes ranging between 2 and 160 mm. MCPs can be easily fabricated and they can also be formed in large wafers.
Following fabrication, MCPs can be formed into intricate shapes through laser ablation, laser cutting, and diamond milling. These devices can be shaped to match the focal planes as well as to improve the detection efficiency. MCPs can even be fabricated with center holes that allow through-plate sample interrogation. This feature is appropriate for the focused ion beam, scanning electron microscope (SEM), and linear reflectron time of flight mass spectrometry. Narrow arrays are apt for magnetic sector mass spectrometers.
Figure 2. Schematics of TOF mass spectrometry and SEM/FIB analysis techniques
Designed in arc sections, MCPs can be used as a detector in an ion energy analyzer or electron energy analyzer. MCPs shaped in the form of an annular ring are suitable for use as a detector within a hemispherical energy analyzer system.
MCPs do not necessarily have to be flat. They may be either spherical (as depicted in Figure 3.) or cylindrical to match the focal plane of the instrument. Such devices can be used in vacuum ultraviolet spectrometers, where it is possible to match the curvature radius to the Roland Circle, as illustrated in Figure 3.
Figure 3. Curved microchannel plates
Micro Pore Optics
Advanced microchannel devices known as 'micro pore optics' have also been developed, comprised of millions of organized square channels
The surfaces in these square channels have minimal roughness and an almost perfect flatness. The total internal reflection at the grazing incidence angle within the micropore channels resulted in the collimation of X-ray and UV photons.
Microchannel plates can now be fabricated in sizes ranging between 2 and 160 mm. The fabrication of complicated shapes has been rendered possible by laser ablation, laser cutting, and diamond milling.
Microchannel plate geometries (such as center holes, annular rings, rectangular arc segments, and trapezoidal formats) have been developed. Large-area mosaic detectors can be created using trapezoidal segments. Now, microchannel plate geometries are limited only by the imagination of the instrument designer.
This information has been sourced, reviewed and adapted from materials provided by PHOTONIS Technologies S.A.S.
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