Self-assembly of iron nanoclusters on the ${\mathrm{Fe}}_3{\mathrm{O}}_4\left(111\right)$ superstructured surface

We report on the self-organized growth of a regular array of Fe nanoclusters on a nanopatterned magnetite surface. Under oxidizing preparation conditions, the (111) surface of magnetite exhibits a regular superstructure with three-fold symmetry and a $42\mathrm{\AA }$ periodicity. This superstructure represents an oxygen-terminated (111) surface, which is reconstructed to form a periodically strained surface. A Fe film of $0.5\mathrm{\AA }$ thickness was deposited on this surface at room temperature. Fe nanoclusters are formed on top of the surface superstructure creating a regular array with the periodicity of the superstructure. We demonstrate that at higher coverage Fe growth switches from two- to three-dimensional mode. In the areas of the surface where the strain pattern is not formed, random nucleation of Fe was observed.

Figure 1

$(1500\mathrm{\AA }\times 1300\mathrm{\AA })$ STM image of the surface superstructure. Three distinct areas are marked as I, II, and III. The periodicity of the superstructure is $42\mathrm{\AA }$.

Figure 2

$(600\mathrm{\AA }\times 600\mathrm{\AA })$ STM image of an ordered array of Fe islands formed on the superstructured magnetite surface (terrace $\left(\mathbf{A}\right)$. Fe islands (white blobs) of 1 monolayer thickness are nucleated in the areas III of superstructure (Fig. 1). Inset shows enhanced contrast image. The terrace $\left(\mathbf{B}\right)$ contains randomly nucleated Fe islands nucleated.

Figure 3

(a) $(250\mathrm{\AA }\times 220\mathrm{\AA })$ STM image of $0.2\mathrm{\AA }$ Fe film deposited on superstructured magnetite surace. Fe islands start to nucleate on the area III. (b) $(1000\mathrm{\AA }\times 1000\mathrm{\AA })$ differential contrast STM image of $1\mathrm{\AA }$ Fe film deposited at the same substrate as in (a). Calculated self-correlation in the inset shows a relatively high degree order of $42\mathrm{\AA }$ periodicity.