Self-assembled alkali and alkaline earth metal nanopatterns onFe3O4(001)

We have studied the mechanism of nanopattern formation by self-assembly of impurities aggregated on the ${\mathrm{Fe}}_3{\mathrm{O}}_4\left(001\right)$ surface. Self-assembly was controlled by thermal diffusion from the bulk of natural and artificial single crystals. We show that the diffusion of potassium and calcium is of fundamental importance to the surface dynamics of magnetite. The self-assembly of $\mathrm{Ca}$ and $\mathrm{K}$ impurities, combined with the reduction in oxygen concentration, leads to the formation of nanotrenches that can be identified as a $\mathrm{p}\left(1\times 4\right)$ structure. According to our model, the formation of nanotrenches contributes in two ways to the reduction of the surface energy. Firstly, alkali and alkaline earth impurities cause a reduction of the strain energy due to their large ionic radii. Secondly, their segregation and the reduction of the $\mathrm{O}∕\mathrm{Fe}$ ratio at the surface cause a reduction of the surface polarity. The structure of ordered nanotrenches could be used as a template for the deposition of carbon nanotubes, fullerenes, and DNA molecules.