Spontaneous Oscillations During The Electrodeposition of Gold Thin Films
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Spontaneous Oscillations During The Electrodeposition of Gold Thin Films
Serge Ravaine, Raphaël Saliba, Christophe Mingotaud and Françoise Argoul Centre de Recherche Paul Pascal, C.N.R.S. Avenue A. Schweitzer, F-33600 Pessac, France
ABSTRACT
The galvanostatic electrodeposition of two-dimensional (2D) gold films along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium (DODA) monolayer is reported. When a constant current is applied to the working electrode, a transition between two-dimensional (2D) growth and threedimensional (3D) thickening of the deposits is observed. 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 with a rate such as 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.
INTRODUCTION
The ever increasing demand for advanced materials with superior electrical, optical or electrooptical properties has prompted numerous recent works devoted to the the construction of particulate films [1-9]. Monolayers of organic surfactants at the gas / liquid interface have been shown to provide convenient and chemically controllable templates for the chemical or electrochemical generation of a large variety of such films [10-14]. Fendler and co-workers have first reported that the presence of a monolayer with a surface charge opposite to that the precursor ion into the liquid subphase is essential for the formation of two-dimensional deposits along the gas / liquid interface [15-16]. Zeiri and co-workers have presented a systematic study of the electrodeposition of silver at the air / water and the water / dichloromethane interfaces under potentiostatic control [17]. We recently reported that gold deposits having a high twodimensional character can be formed along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium (DODA) monolayer [18-19]. Both the nature and the surface density of the surfactant molecules at the gas / liquid interface have a profound effect on the formation and the morphology of the metal deposits. We present here a study of the electrodeposition of gold under galvanostatic control. We show that a transition occurs during the formation of the gold deposits when a constant current is applied to the working electrode. This event is due to a continuous decrease of the current density during the growth. Controlling the rate of a current ramp applied to the working electrode in order to maintain the current density near this limit value induces the formation of deposits with a terraced structure. Such a morphology results from the appearance of spontaneous oscillations between the regimes of 2D and 3D growth.
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