Deposition of Au from aqueous HF onto Si(111) has been studied by Rutherford backscattering (RBS) and surface second harmonic generation (SHG), which at 532 nm is nearly resonant with the surface plasmon of Au nanoclusters. The RBS measurements indicate that Au deposition is rate-limited by diffusion, while the SHG measurements indicate that Au cluster growth is rate-limited by either a surface reaction involving a fluoride-containing species or electron transfer. This apparent contradiction can be reconciled by proposing that initial deposition in the form of AuCN is followed by a slow electroless reduction of Au(I) accompanied by Si oxidation. By addition of HCl and KF, the solution phase equilibria can be separately manipulated, motivating further SHG experiments which indicate that HF and not HF2- is the kinetically active fluoride-containing species. The apparent reaction order for Au cluster growth with respect to HF is approximately 1/2, and the reaction order for Au cluster growth with respect to Au(CN)2- is near zero in the concentration range 10-4 to 10-5 M. © 1999 the Electrochemical Society. All rights reserved.