Abstract:
The study of changes in beam properties of charged particles after passing through insulating microporous structures holds significant value for theoretical verification of beam transport control and innovation in experimental observation methodologies. Notably, the evolution of electrical characteristics displayed during the interaction between such microscopic particle flows and micro-scale structures can provide new insights into charge transport mechanisms in nanodevices. The low-energy electron beams at the 1.5 keV level penetrating a muscovite substrate with diamond-shaped micropore membranes were systematically investigated. The experiment focused on two critical parameters: the two-dimensional angular distribution characteristics of emitted particles and dynamic evolution patterns across the temporal dimension. To achieve high-precision synchronous detection, an innovative composite detection scheme was developed using an MCP (microchannel plate)-phosphor screen imaging system combined with a CCD (charge-coupled device) camera: The MCP enables cascaded amplification of incident electrons and their conversion into photon signals, generating spatial distribution images on the phosphor screen, while the CCD facilitates multi-temporal-node image acquisition and quantitative analysis. At this energy, it is found that the transmission rate changes with the micropore’s angle relative to the beam axis in a manner close to a Gaussian distribution. When the beam direction aligns with the micropore axis (i.e., at a tilt angle of 0°), the full width at half maximum (FWHM) of the angular distribution is within the micropore’s geometric opening angle, and transmission is observed within a tilt angle range of approximately 0.8° around 0°. The transmission intensity and FWHM remain stable within a specific tilt angle range where electrons can directly pass through geometrically, and rapidly decrease outside of this range. At 1.5 keV, the electron transmission rate initially increases slightly and then stabilizes, with no noticeable shift in the central position of the angular distribution. The width of the angular distribution is similar to the results observed for highly charged ions, but the shape of the exit angle distribution does not exhibit the imaging effects caused by mirror charges, as seen with high-charged ions. A Monte Carlo program, developed by the authors based on dielectric response and mirror charge forces, was used to simulate the angular distribution of emitted electrons and the results were compared with experimental data. It is found that the mirror charge force at this energy is relatively weak, insufficient to influence the electrons in the same way as highly charged ions, which typically form specific shapes due to the mirror charge effects.