Silver Nanoparticles Self Assembled on HOPG: Unusual Behavior asProbed by Scanning Tunneling Microscopy

Extract

The controlled construction of nanostructures on solid surfaces for technological applications depends primarily on a deep understanding of the physical chemistry of the interface. Several methods have been devised to grow metallic nanostructures on solid surfaces, notably physical vapor deposition and electrodeposition. The electrochemical method led to the creation of a very promising technology called Electrochemical Step Edge Decoration (ESED) by the Penner group in Irvine, Ca. In this method, metallic nano and mesowires are built through electrochemical deposition on the step edges of the basal plane of Highly Oriented Pyrolytic Graphite (HOPG) [1]. The proposed growth mechanism is based on the Terrace-Ledge-Kink (TLK) model [2], in which the foreign adatoms nucleate the electrochemically induced growth of nanoparticles in the lower plane of step edges. White and collaborators [3], while studying the stability of gold nanoparticles electrodeposited on HOPG, noticed the preferential nucleation on the upper plane of step edges in stark opposition to the TLK model. They proposed that this preferential deposition is associated with a slippage of the atomic layer near the edge. This proposition indicates that the surface in the upper plane near the edge will present a decrease in the atomic distance in the plane, disrupting the registry with the underlying plane. To further assess this proposition we have devised another experimental approach where, instead of electrodepositing foreign adatoms for nucleation and growth, we deposited fully formed silver nanoparticles on HOPG through a Self Assembly mechanism and studied its spatial distribution. Through this approach, we intend to study the surface mobility of nanoparticles, as opposed to atomic species as studied in electrochemical deposition.