Sputtered ir films evaluated for electrochemical performance - I. Experimental results

The present work deals with the microstructure and electrochemical characteristics of sputtered metallic iridium thin films. The thin films are characterized regarding their electrochemical performance in cyclic voltammetry. Distinct morphologies and microstructures of Ir thin films are generated by altering the process parameters of power, pressure, and target-to-substrate distance. Growth of films with high specific surface and high electroactivity can be fostered by process conditions that deliver a low surface mobility of the deposited atoms. The anodically delivered charge can be varied by factors of more than 30, merely determined by film morphology. Electrochemical characteristics of the thin films are strongly tied to crystallographic orientation. The development of preferred {111} orientation over adatom kinetic energy inversely correlates with the development of electrochemical activity. Enhanced shadowing effects during growth can be used to further increase the specific surface available for charge transfer. This is illustrated by changes in film thickness. Using a process supplying low-mobility Ir atoms to the surface, the thickest evaluated Ir film, at almost 3000 nm, delivers an anodic charge of 157 mC/cm(2) after 100-fold potential cycling. (C) 2008 The Electrochemical Society.