Measurement of the secondary electron emission from CVD diamond films using phosphor screen detectors

R Vaz,J.S Lapington,J.A Smith,P.W May,V Chatterjee,C.J Harwood,S Osbourne,N.A Fox,C.J Horsfield

doi:10.1088/1748-0221/10/03/p03004

Abstract

Diamond-based photomultipliers have the potential to provide a significant improvement over existing devices due to diamond's high secondary electron yield and narrow energy distribution of secondary electrons which improves energy resolution creating extremely fast response times. In this paper we describe an experimental apparatus designed to study secondary electron emission from diamond membranes only 400 nm thick, observed in reflection and transmission configurations. The setup consists of a system of calibrated P22 green phosphor screens acting as radiation converters which are used in combination with photomultiplier tubes to acquire secondary emission yield data from the diamond samples. The superior signal voltage sampling of the phosphor screen setup compared with traditional Faraday Cup detection allows the variation in the secondary electron yield across the sample to be visualised, allowing spatial distributions to be obtained. Preliminary reflection and transmission yield data are presented as a function of primary electron energy for selected CVD diamond films and membranes. Reflection data were also obtained from the same sample set using a Faraday Cup detector setup. In general, the curves for secondary electron yield versus primary energy for both measurement setups were comparable. On average a 15–20% lower signal was recorded on our setup compared to the Faraday Cup, which was attributed to the lower photoluminescent efficiency of the P22 phosphor screens when operated at sub-kilovolt bias voltages.

Highlights

Electron emission is a fundamental phenomenon associated with most interactions of energetic particles with solid surfaces, and its measurement in areas such as radiation biology [1], particle detectors [2], microscopy and surface analysis [3] is extremely important
This multiplication is usually achieved by dynode devices, such as the ones used in photomultiplier tubes (PMTs) or microchannel plates (MCPs), which use high voltages to accelerate the electrons onto surfaces with a high (> 1) secondary electron emission yield (SEY)
The results indicate that the new phosphor screens (PS)/PMT system produces a similar SEY profile, but the SEY values obtained for a given primary energy are on average 10-20% lower than those recorded in the Leicester Faraday Cup (FC) system

Summary

Introduction

Electron emission is a fundamental phenomenon associated with most interactions of energetic particles with solid surfaces, and its measurement in areas such as radiation biology [1], particle detectors [2], microscopy and surface analysis [3] is extremely important. The small number of emitted electrons must be multiplied in order to obtain a usable signal This multiplication is usually achieved by dynode devices, such as the ones used in photomultiplier tubes (PMTs) or microchannel plates (MCPs), which use high voltages to accelerate the electrons onto surfaces with a high (> 1) secondary electron emission yield (SEY). For these surfaces, the primary-electron impacts liberate a number of secondary electrons depending on the dynode material, which are accelerated deeper into the device to strike another dynode surface, which, in turn, emit yet more electrons. Using a dynode material with the highest possible SEY reduces the number of multiplication stages required, making the device simpler and cheaper

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Conclusion