At low HAuCl4 concentrations, the amount of ClOH -is assumed to be insufficient to maintain a steady-state in which a substantial net Au 0 oxidation is notable. This hypothesis also agrees with studies showing a preferred gold etching in acidic environments at high (initial) chlorine concentrations or demonstrating nucleation events at high dose rates, but low initial HAuCl4 concentrations. This is additionally demonstrated in the supporting information S6