Stability of Nanostructures on Surfaces

Self-assembly of ordered structures, a few nanometers wide, has been observed on many interfaces critical to new nanotechnologies. They are thought to arise because of a delicate balance between long-range strain field interactions and short-range chemical forces that stabilizes these structures. However, a detailed understanding of the driving forces does not exist. In this article, I will show how to identify and control these interactions that have the potential to surpass standard patterning technologies and thus, to lead the way to higher density magnetic storage, more selective catalytic materials, higher sensitivity chemical sensors, and perhaps, quantum computers. Wellordered networks of misfit dislocations that form in monolayer-high strained metal films can be used as templates to grow two-dimensional nano-arrays of largescale order and size uniformity in thermal equilibrium. Unique real-time measurements of the dynamics of selfassembled nano-arrays grown on silver and copper films on Ru(0001) and other metal surfaces using a variabletemperature scanning tunneling microscope (STM) will be presented. The results will guide the development of new dynamic models to describe the evolution of nanoscale structures on surfaces. In particular, vacancy islands formed during roomtemperature (RT) exposure to sulfur of a submonolayer Ag film on Ru(0001) order spontaneously to form a triangular lattice at an island area fraction just above 20%. A normal mode decomposition of the thermal vibrations of this vacancy island crystal, measured with timeresolved scanning tunneling microscopy, obtains Lamé coefficients in the range of 10 (N/m). I will show that these estimates are consistent with stabilizing forces derived from long-range elastic interactions between the islands.