Ultra-thin corrugated metamaterial film as large-area transmission dynode

TL;DR

This paper presents the fabrication and characterization of ultra-thin corrugated metamaterial films acting as large-area transmission dynodes, with enhanced mechanical properties and high secondary electron yield for potential use in electron detection.

Contribution

The study introduces a novel ultra-thin corrugated membrane with engineered structure and conductivity, achieving high transmission secondary electron yield and improved mechanical robustness.

Findings

Achieved a maximum transmission secondary electron yield of 2.15 at 3.15 keV.

Fabricated two types of corrugated membranes: hexagonal honeycomb and octagonal.

Active transmission secondary electron emission surface is nearly 100%.

Abstract

Large-area transmission dynodes were fabricated by depositing an ultra-thin continuous film on a silicon wafer with a 3-dimensional pattern. After removing the silicon, a corrugated membrane with enhanced mechanical properties was formed. Mechanical materials, such as this corrugated membrane, are engineered to improve its strength and robustness, which allows it to span a larger surface in comparison to flat membranes while the film thickness remains constant. The ultra-thin film consists of three layers (Al$_2$O$_3$ /TiN/Al$_2$O$_3$) and is deposited by atomic layer deposition (ALD). The encapsulated TiN layer provides in-plane conductivity, which is needed to sustain secondary electron emission. Two types of corrugated membranes were fabricated: a hexagonal honeycomb and an octagonal pattern. The latter was designed to match the square pitch of a CMOS pixel chip. The transmission secondary electron yield was determined with a collector-based method using a scanning electron microscope. The highest transmission electron yield was measured on a membrane with an octagonal pattern. A yield of 2.15 was achieved for 3.15 keV incident electrons for an Al$_2$O$_3$ /TiN/Al$_2$O$_3$ tri-layer film with layer thicknesses of 10/5/15 nm. The variation in yield across the surface of the corrugated membrane was determined by constructing a yield map. The active surface for transmission secondary electron emission is near 100%, i.e. a primary electron generates transmission secondary electrons regardless of the point of impact on the corrugated membrane.