Influence of chlorine annealing on the low-temperature electrical conductivity of high-purity gold foil

Abstract

The effects of annealing high-purity polycrystalline gold foils (+99.999%) with thickness d approximately=25 mu m at 870+or-20 degrees C under reduced chlorine pressure p(Cl2) (in the range 11 >1 for surfaces etched in aqua regia. In both cases r is independent of temperature, Kondo-effect measurements reveal the presence of 3.0+or-0.1 at PPM Fe in the as-received Au foils. The decreasing rho infinity (4.2K) is attributed firstly to the physical removal of the Fe impurities, as previously found by Walker (1970), and secondly to the clustering, passivation and removal of other impurities, probably accompanied by reduced grain-boundary scattering. The results of the Cl2 annealing are compared with the well-known oxygen annealing method for noble metals, applied on some of the Au foils. It is inferred from this that the former method is much more effective (RRRinfinity being roughly ten times better). Important ageing effects in RRRinfinity at 300K, established in both methods, are reported for the first time and are tentatively correlated to changes in grain-boundary scattering with time.