Development of dodecahedron type MCP detector for SEM toward full energy range and solid angle electron detection

A detector was developed for scanning electron microscopy (SEM) in which microchannel plates (MCPs) were mounted on the facets of a regular dodecahedron. This detector enables the detection of electrons emitted in multiple directions. By placing a bias grid in front of each MCP, both backscattered electrons (BSE) and secondary electrons (SE) can be discriminated and detected. Using this detector, images were obtained by detecting electrons emitted in the direction normal to the sample surface (Top0), in two different oblique upward directions (Up1 and Up2), and in an oblique downward direction (Down6), to evaluate the emission-angle dependence including components emitted toward the lower hemisphere. Three specimens were examined: (i) a Cu plate with fine curtain-like surface waviness, (ii) a Cu-Al eutectic microstructure and (iii) a three-dimensional stainless-steel sphere. For the Cu plate, surface corrugations were emphasized in the Up1/Up2 BSE images, whereas Top0 showed nearly uniform contrast. For the Cu-Al specimen, Top0 primarily provided compositional contrast, while the Up1/Up2 highlighted interfacial regions due to illumination-effect-like directional acceptance. For the stainless-steel sphere, obliquely downward BSE were clearly detected with Down6, indicating the usefulness of the downward channel for three-dimensional geometries. Since this regular dodecahedral detector operates without electric or magnetic fields that could distort electron trajectories, it enables analysis of the energy and emission-angle dependence of emitted electrons. This design uses identical MCP detectors at multiple viewing directions, which simplifies signal handling and facilitates multi-view analysis of direction- and energy-resolved signals.