Localized electroless deposition of gold nanoparticles using scanning electrochemical microscopy

The aim of this study is to locally deposit nanoparticles on an unbiased surface by electroless deposition (ED) using scanning electrochemical microscopy (SECM). We have developed an ED process that is based on the reduction of gold ions by hydroquinone (H2 Q) and catalyzed by a metallic surface, such as palladium. One of the advantages of this system is the ability to drive the ED at pH 1-7. The metal ions were electrogenerated in a solution consisting of H2 Q and KCl by anodic dissolution of a gold microelectrode. Au Cl4- reacted with H2 Q at the electrolyte/metallic interface to form benzoquinone and gold deposit. The ED has been studied initially in bulk solution containing KCl, H2 Q, and HAu Cl4, and then by SECM. We found that the pH had a significant effect on the nature of the deposited gold and could be correlated with the kinetics of gold ions reduction by H2 Q. Hence, either nanoparticles or much larger crystals could be formed, depending on the pH of the deposition solution. Time of deposition and H2 Q concentration also affected the shape and density of the deposition.