Physical processes in a super-tip gas field ion source

Intense ion beams of hydrogen and rare gases, can be extracted from W and Ir super-tips of a gas field ion source. In this study, the influence of temperature and electrical field on the emitted currents of Ar, Ne and He has been investigated. In particular, the system Ar/W has yielded most experimental details. Optimum operation temperatures are near to the condensation point of each gas species. Physical adsorption and desorption effects, modified by locally varying polarisation forces, give rise to three temperature regimes. The emitted current is controlled in complex competition between thermally activated diffusion and desorption processes. By assuming local dynamic equilibria with field-enhanced kinetic supply from the gas phase, a theoretical description of the emitter-temperature characteristics has been achieved. (orig.)