FLUENCE, FLUX, CURRENT AND CURRENT-DENSITY MEASUREMENT IN FARADAY CUPS FOR SURFACE-ANALYSIS

The manufacture and design of ideal Faraday cups for measuring currents and current densities in electron and ion beams is well understood and yet laboratories can still report values for surface science parameters involving sputtering that diverge by a factor of two. This is because the constraints of space and lack of properly designed specimen stages lead to difficulties in cup design. We have designed, here, Faraday cups for current and current density measurements that are simple, compact and may be inserted into a surface analysis system on a normal sample stub without the need for special electrical feed-throughs. The design parameters and operating conditions to achieve efficiencies demonstrated to be within 2% of the ideal behaviour are given in detail. The problems encountered in achieving this level of accuracy are discussed.