A comprehensive analysis of electron emission from a-Si:H/Al₂O₃ at low energies

Abstract

Recently developed microchannel plates based on amorphous silicon offer potential advantages with respect to glass based ones. In this context, secondary electron emission at very low energies below 100 eV has been studied for relevant materials for these novel devices. The aim of this work was to quantify the low energy electron emission - secondary emission and elastic scattering - from amorphous silicon and alumina and the dependence of the emission energy distribution on the primary electron energy, which was previously unknown. Secondary emission and energy distribution were both modelled and measured using equipment particularly designed for this energy range. The effects of roughness, angle of incidence and surface composition were analysed. We show crossover energies as well as the angular dependence of electron emission from amorphous silicon and alumina, with a maximum experimental emission yield value of 2 and 2.8, respectively, at an incident angle of 75°. A parameterization for the energy dependence of the emission energy spectrum at low energies was derived. This extensive analysis is fundamental for a comprehensive understanding of the performance of amorphous silicon-based microchannel plate detectors. It provides a complete model for secondary electron emission for a detailed description of the detector operation. The present results thus set the basis for a simulation framework, which is an essential element to increase the performance of these detectors and enable further developments.

Fabrication and Characterization of High Aspect Ratio Amorphous Silicon Based Microchannel Plates

“…The measurement shows a maximum gain at a potential difference of 150 V between the photocathode and the AMCP. Measurements of the total secondary emission yield as a function of energy and angle showed a maximum closer to 200 eV [8].…”

“…Lastly, by tuning the etching parameters, channels with diameter of 1.6 µm and aspect ratios up to 25 are feasible. As a final step in the fabrication, a few devices are coated by atomic layer deposition (ALD) with either alumina (Al2O3) or magnesium oxide (MgO) to increase the secondary emission yield per collision and hence the final multiplication gain of the devices [8].…”

“…It is observed that the gain reaches a maximum value when applying a bias of 150 V between the photocathode and the top electrode of the AMCP. Measurements from the total emission yield as a function of energy show a maximum closer to 200 eV [8]. This could mean that most of the incoming electrons collide further down the channels rather than at the opening, hence their energy at the collision point is already higher than just the potential difference between the photocathode and the AMCP.…”