The Effect of Absorbed Gases on Proton Induced Electron Emission from Titanium

The secondary electron coefficient γ for ions in the energy range 10-130 keV incident on titanium has been investigated. The effect of controlled pressures of oxygen, hydrogen and nitrogen has been studied using degassed surfaces. The effect of air at atmospheric pressure has also been observed. It has been observed that exposure of a degassed titanium surface to oxygen pressures as low as 2 × 10 -6 mmHg is sufficient to raise γ for 100 keV protons by 40%. The effect of nitrogen was also to increase γ, providing that the titanium was made to absorb it in sufficient quantity by heating. Hydrogen increased the emission by a small amount when the surface concentration was high enough. When titanium was oxidized in air at atmospheric pressure the secondary emission increased rapidly during the initial exposure, but after a few minutes the rate of increase of γ for 100 keV protons was very slow. Possible explanations are discussed in relation to a theory by Sternglass. It is concluded that the results cannot be explained in terms of one basic process changing, but that contributory factors are an increase in the rate of loss of energy with distance of the impinging ion where the gas is absorbed, and more favourable conditions for diffusion of low-energy electrons to the surface.