Surface X-ray diffraction analysis of Fe nanostructured films grown on c(2 × 2)-N/Cu(100)

Abstract

We report the results of a Surface X-Ray Diffraction (SXRD) study of Fe nanostructured films deposited on c(2×2)-N/Cu(100) at room temperature (RT), with Fe coverage ΘFe=0.5ML and ΘFe=1ML. The c(2×2)-N/Cu(100) surface is an example of self-organised system, that can be used for growth of arrays of metal nano-islands and organic molecules assemblies. We chose two different values of N coverage, ΘN=0.3ML and ΘN=0.5ML, the second value corresponding to N saturation. We monitored the presence of surface diffraction peaks in hk scans and we performed Crystal Truncation Rods (CTR) analysis with ROD fitting programme. In the case of ΘN=0.5ML, i.e. at saturation coverage, the CTR could be fitted with one surface domain with p4gm(2×2) symmetry. In the surface cell adopted, N atoms occupy four-fold hollow sites, with Fe (intermixed with Cu) giving rise to a “clock” reconstruction previously observed on iron nitride films obtained by co-deposition and annealing. This result is an indirect confirmation of N surface segregation on top of the Fe films, occurring during the growth at RT. When subsaturation N coverage (ΘN=0.3ML) is used as a substrate for Fe deposition, the best results could be obtained with a model where two surface domains are present: the first one corresponds to a surface cell with Fe sitting in four-fold hollow sites on bare Cu areas, with possible interdiffusion in the second lattice. The second domain is assigned to growth of Fe on the N-covered square islands occurring once the bare Cu areas are fully covered. The SXRD analysis on N-covered surface domains shows that the mechanism of reconstruction and of N segregation on top layer is already active at RT for all N-coverage values.