Nanoisland Manipulation Experiments at Oxidized, Contaminated and Nanorough Interfaces: Structural Superlubricity and Directional Locking

This chapter reports on atomic force microscopy based nano-manipulation experiments performed on noble metal nanoislands (gold and platinum), which were previously shown to exhibit structurally superlubric sliding under ambient conditions on highly oriented pyrolytic graphite (HOPG). Experiments performed on oxidized platinum nanoislands on HOPG demonstrate an increase in interfacial shear stress when compared with non-oxidized islands, but not a breakdown of structural superlubricity. In addition, an effect reminiscent of contact aging is observed on a sample system that comprises gold nanoislands on HOPG, which interestingly is suppressed in the presence of environmental contamination. Nanomanipulation of gold islands is also performed on molybdenum disulfide (MoS2). Here, the high degree of commensurability at the interface does not result in superlubricity, but rather in a specific “directional locking” effect. The effect was observed not only on freshly cleaved flat surfaces but also on bilayers grown on a nanorough silicon wafer, where atomic-scale resolution of the complex cross-section of the system could be achieved using HAADF-STEM.