Formation mechanism of Fe atomic structures on Cu(111) surfaces

Magnetic nanostructures are of current interest due to the rich emerging physics and potential applications. With the advance of modern growth and imaging techniques, it is now possible to fabricate structures down to the atomic level. Atomic manipulation through scanning tunneling microscopy (STM) provides an interesting way for creating structures in a designed fashion and investigating their physics. Alternatively, self-assembly growth is appealing especially for potential applications as the structures can be fabricated more economically and in relatively large-scale homogeneity. This paper presents a joint experimental and theoretical study of the self organization of Fe atomic structures on Cu(111) surfaces. A few percent monolayer of Fe atoms are deposited at around 5 K on a clean Cu(111) surface. Upon deposition, the Fe atoms are randomly distributed on the sample surface without apparent ordering. With annealing to 12 K, the Fe atoms form ordered structures on both flat and vicinal surfaces with chosen coverage. On the flat surfaces, quasi-ordered hexagonal superlattice with nearest neighbor distance of 1.2+0.1 nm is found. In combination with the kinetic Monte Carlo (KMC) simulations, two essential criterions are identified for the formation of the hexagonal superlattice: the ratio between the interaction energy and the diffusion barrier needs to be larger than 5% and the ratio between the position of the energy maximum and the position of the first energy minimum to be smaller than 20%.