Control of Crystal Growth in Local Electroless Gold Deposition by Pyridinium Based Surfactants

Abstract

The formation and local deposition of well-shaped Au nanostructures on a nonconducting surface are described. Specifically, the local electroless deposition of Au in aqueous solutions in the presence of various n-alkylpyridinium surfactants is driven by electrochemically generating a flux of AuCl4 – at a gold tip close to a 3-mercaptopropyltrimethoxysilane modified Si oxidized wafer. Two reducing agents, NaBH4 and ascorbic acid, were used for the reduction of the gold ions. We studied the effect of the solution temperature, the potential applied to the gold tip and its distance from the surface, the reductant, and the nature of the alkylpyridinium on the structure of the gold deposit. The chloride salts of methylpyridinium, butylpyridinium, cetylpyridinium, 4-carbamoyl-1-cetylpyridinium, and 4-methyl-1-cetylpyridinium were added separately and showed remarkable effect on the shape of the structures that were formed. We find that short chain n-alkylpyridinium salts do not adsorb preferentially on the gold facets, whereas the longer chain n-alkylpyridinium ions cause the formation of well-faceted Au structures, such as cubes, hexagons, and even multipods. Moreover, comparison between local and bulk deposition revealed a significant difference in Au structures that were formed, presumably due to the different concentration profile of the AuCl4 –.

Photochemical Formation of Tunable Gold Nanostructures Using Versatile Water‐Soluble Thiolate Au(I) Precursor

“…At the same time, increasing AA concentration above 2.5 × 10 −3 m (e.g., 5 × 10 −3 m ; 4:1 AA‐to‐Au molar ratio) results in blueshift with the decrease in LSPR intensity. Thus, AA is also found to function as a shape selective agent by favoring star‐like structures through the kinetics of the growth . Optimal AA concentrations for the studied conditions of the photochemical synthesis of AuNSs using Au(I)‐thiolate precursor are found to be in the range of 1.25–2.5 × 10 −3 m (AA‐to‐Au molar ratios from 1:1 to 2:1).…”