Surface Characterization and Secondary Electron Emission Properties of Alumina Containing MgO Film on Ag-Mg-Al Alloy

Abstract

Ag-Mg alloy is used as a dynode material in electron multiplier tubes due to the high secondary electron yields (δ) of the surface of MgO film. However, MgO film is readily degraded under strong electron or ion bombardment, which results in a decrease in the lifetime of devices. In this study, alumina-containing MgO films of ~50–150 nm were developed on a Ag-2Mg-2Al alloy (silver alloy containing 2 wt % Mg and 2 wt % Al) after a thermal activation process performed at 500–600 °C under low oxygen pressures of 5.0–20.0 Pa. Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses reveal that the film consists of a thin layer of pure MgO and a relatively thicker layer of alumina-containing MgO located beneath the top MgO layer. The alumina-containing MgO film exhibits high δ value of 7.7 at a primary electron energy of 580 eV and a much better stability under energetic electron bombardment than pure MgO film on Ag-Mg alloy. Alumina has higher bond dissociation energy than MgO, and the presence of alumina in the film contributes to mitigating the dissociation of the MgO film under electron bombardment. The Ag-2Mg-2Al alloy with alumina-containing MgO film is a promising candidate as a dynode material for electron multiplier tubes.