Reductive deposition of Au3+(aq) on oxidized silicon surfaces

Abstract

X-ray photoelectron spectroscopy (XPS) is used to determine the oxidation state of gold deposited from an aqueous solution of AuCl4- on to various oxidized surfaces of silicon. Although the observed Au4f signal decreased with the thickness of the oxide layer, the oxidation state of Au was determined as 0 for all the samples analyzed. From the angular dependence of the Si2p and Au4f signals it was determined that Au is deposited on top of the oxidized surfaces of metallic silicon. It is postulated that from an aqueous solution of AuCl4-, gold would deposit in its zerovalent form on to any surface due to its large and positive electrochemical reduction potential (ε° (red) (Au3+/Au) = +1.50 V) and the substrate plays a role only in providing active deposition sites. To further support the proposal, it is shown that the same process takes place even in inert and hydrophobic polypropylene substrates. Similarly, it is also shown that more gold deposits if the surface of the polypropylene is made less hydrophobic (but probably more active) via the industrially used corona discharge treatment.