On the dose of bombarding residual gas ions for influencing pre-breakdown field emission in a vacuum

Field electron emission from extended Cu electrodes after cleaning by electric arcs has been compared with field emission from gas-covered monocrystalline W points when subjected to ion bombardment from the residual gas. With both emission systems, exposure to argon or to hydrogen in the pressure range 10 -5 -10 -2 Pa caused two subsequent stages: an emission growth explained as the removal of adsorbed gases (stage 1), and a noisy increase of the emission explained as sharpening due to surface migration of metal atoms (stage 2). With Cu there occurred a third stage: a decrease of the emission explained as reduction of the emitters by sputtering. The time constant tau 1 of the first stage was found to be proportional to the product p -1 i 0 -1 S FN 1 2/, p being the gas pressure, i 0 the initial electron-current, and S FN the apparent emitting surface determined from Fowler-Nordheim plots. The proportionality factor is given for the metals and gases used. The completely analogous behaviour of W points and Cu electrodes in stages 1 and 2 indicates an analogy between the emitting sites in both cases.