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

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