Influence of the Crystallographic Orientation of ITO on the Electrodeposition of Ag Nanoparticles

Nanometer-scale metal particles exhibit chemical and physical properties which differ significantly from macroscopic metal phases, including strong interaction with visible light due to their localized surface plasmon resonances. In particular, silver nanoparticles (Ag NPs) have had extensive attention due to the low-cost and abundance of elemental Ag. The strong and tuneable interaction of visible light with Ag NPs have found many applications.<br/>In many of these applications, it is essential to reliably and precisely control the size and density of Ag NPs on conducting transparent supports, such as indium tin oxide (ITO). Electrochemical deposition is an attractive growth method. However, electrochemical deposition of Ag on ITO naturally leads to scattered, low density irregular nanoparticle growth owing to the low surface energy and high nucleation barrier of ITO. While it is well known that surface properties of the substrate have a key role in nucleation dynamics, most studies involving ITO substrates do not pay complete attention to the physical properties of the surface, and often the only parameter specified is the sheet resistance.<br/>In this talk, we elucidate the influence of crystallographic orientation of the ITO surface on silver nanoparticle growth. We provide a careful and quantitative study of Ag nanoparticle nucleation and growth on two batches of ITO substrates. Even though all ITO substrates come from the same supplier and have the same nominal specifications, XRD scans clearly differentiate between two types of films based on the ratio between the (222) and (400) related peaks.<br/>We find that the preferential presence of lower index surfaces (e.g. (100)) leads to few orders of magnitude lower particle density compared to the preferential presence of higher index surfaces (e.g. (111)). Furthermore, the density on the lower index surface is strongly dependent on the nucleation pulse potential, while the higher index surface is barely affected. A geometrical analysis of multiple individual particles shows that ITO orientation also affects growth dynamics, where preferential presence of (100) surfaces leads to more isotropic nanoparticle growth.<br/>Controlling metal particle density and size is crucial in many applications. Beyond careful control of electrochemical parameters, here we show that neglecting the macroscopic surface characteristics of ITO (and any other polycrystalline substrate) can lead to major ambiguity in nucleation and growth dynamics. We show here that XRD characterisation prior to deposition is a simple additional measure to tailor metal nanoparticle electrochemical growth on ITO.