Morphological Control of Gold Electrodeposits Grown at the Gas-Liquid Interface

Abstract

We report the formation under potentiostatic and galvanostatic conditions of gold deposits having a high 2D character along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium (DODA) monolayer. When a constant potential is applied to the working electrode, both the growth mode and the morphology of the deposits are found to depend on the value of the applied potential. The existence of a negative overpotential for the air/water interface vs. bulk reduction of gold anions is due to the presence of a positively charged monolayer at the gas/liquid interface. A growth having a high 2D character is favored at low potential values [i.e., between −0.1 and 0.35 V vs. a saturated calomel electrode (SCE)], whereas a thickening of the gold deposit occurs at higher potential values (i.e., between 0.35 and 0.60 V vs. SCE). When a constant current is applied to the working electrode, a transition between 2D and 3D growth, thickening of the deposits is observed. It has been shown that this event occurs when the current density is sufficiently small to allow the 3D process to consume all the injected electrical charges. The application of a current ramp allows one to avoid such a transition in the growth mode. Moreover, adjusting the rate of the current ramp so that the current density remains during the whole growth close to the limiting value separating the two growth regimes induces the appearance of spontaneous oscillations between the regimes of 2D and 3D growth. Deposits with a well-defined, terraced structure are then obtained. © 2003 The Electrochemical Society. All rights reserved.