Der Vordurchschlagsstrom im Hochvakuum. II. Über die Natur der Emissionszentren

Pre-breakdown currents of low order of magnitude (10⁻¹⁵–10⁻¹¹ A) were measured with UHV-conditions in order to obtain information about the nature of the emitting sites. Heating the cathode to temperatures > 600°C or ionic bombardment in a glow discharge reduced strongly the current, but it was considerably increased by oxidation. Exposure to atmospheric air and following bake-out at 400°C had a similar effect as the artificial oxidation. Hence, starting the experiments the first emission may come from nonmetallic structures as oxide needles. It is therefore concluded that special precautions are necessary in order to avoid non-metallic emission sites of high emissivity even with UHV-conditions.