= Solution
The arrangement is \b[diode sputter deposition]: the Au target, \b[a], is attached to the upper cathode assembly \b[c]; positive Ar <ions> bombard it and sputter Au onto the wafer. The lower wafer-holder <electrode> \b[b is the anode] in the simple two-electrode arrangement shown.
Unlike evaporation, <sputtering> needs enough inert <gas> to sustain a discharge. Over a low-pressure operating interval, raising Ar pressure can increase <ionization> and <ion> current and hence the <sputtering> rate at comparable applied <voltage>. This is not a universal monotonic law: at higher pressure, scattering and thermalization of sputtered Au reduce the fraction reaching the wafer; at fixed regulated power, target <voltage> and current also adjust. \b[A pressure increase can initially increase the rate, but excessive pressure lowers transport efficiency.]
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