Water Ordering on the Magnetite Fe3O4 Surfaces.

The interaction of water with the most prominent surfaces of Fe3O4, (001) and (111), is directly compared using a combination of temperature-programmed desorption, temperature-programmed low energy electron diffraction (TP LEED), and scanning probe microscopies. Adsorption on the (√2 × √2)R45°-reconstructed surface of Fe3O4(001) is strongly influenced by the surface reconstruction, which remains intact at all coverages. Close to the completion of the first monolayer, however, the ad-layer adopts a longer-range (2 × 2) superstructure. This finding is discussed in the context of a similar (2 × 2) superstructure recently observed on the (111) facet, which exists over a significantly larger range of temperatures and coverages. In both cases, the long-range order is evidence that water-water interactions exert a significant influence on the structure already prior to the nucleation of the second layer. We conclude that the stability differences stem from the smaller unit cell on the (111) surface, and the ability of water to more easily form stable hexagonal ice-like structures on the hexagonal substrate.