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Growth of iron films on MgO(100) substrates at 560-600 K

The growth mechanism of heteroepitaxial thin iron films, deposited on MgO(100) substrates at 560-600 K, was investigated by means of tunnelling electron microscopy and spectroscopy. Scanning tunnelling microscopy (STM) analysis of the surface indicates the formation of long flat (about 10-20 nm) terraces for thicknesses greater than 3-4 nm. The fine structure of those samples contains sets of interpenetrating screw and helical dislocations. The onset of the formation of islands on these terraces and also their sizes were a result of stress relaxation in these films and this was supported by the Monte Carlo simulations. The resulting critical number of island layers needed to build up the gain in energy in a relaxed volume (compensating the misfit losses on its boundary) perfectly correlates with the observed STM pattern. At even larger thicknesses (greater than 9-10 nm) the surface becomes uniformly flat with a large number of mosaic voids. The differential conductivity spectra show the distinct surface peak of iron, positioned between the values for the iron crystal surface and the atomic limit. Manipulation of iron nanoparticles from the tip to the surface and back is demonstrated.