Formation of gold nanowires through self-assembly during scanning force microscopy

Abstract

Gold films with a nominal thickness of 5–40 monolayers were grown on dielectric substrates and imaged by scanning force microscopy (SFM). The films originally consisted of well-separated or densely packed clusters. During imaging in contact mode, the morphology of the films changed drastically. At low coverage, i.e. Θ<10 monolayers, the well-known stripes originating from mobile clusters, eventually accumulated into larger aggregates, were observed. In contrast, at larger coverage, highly ordered structures consisting of one-dimensional wires evolved during scanning. They often were parallel with equal separation, i.e. well-defined periodicity, over distances of several μm. Typically, the wires were 5–10 nm high and 50–100 nm wide. Investigations of Au films prepared at varying temperature on different dielectric substrates allow us to suggest a self-assembling mechanism for wire formation in which gold is periodically collected by the SFM tip and redeposited as soon as a critical amount is reached.