Self-organized chromium oxide monolayers on Fe(001)

The growth of ultrathin epitaxial oxide films on metal supports is attracting considerable scientific interest both on a fundamental level and for potential technological applications. Growth techniques such as reactive deposition (i.e., metal deposition in oxygen atmosphere) and/or post-oxidation are typically applied, leading to ordered phases and well defined oxide-metal interfaces on noble metal substrates. On the contrary, when a more reactive metal, such as Fe, is used as a substrate for the nano-oxide growth, these procedures fail to produce sharp metal/oxide interfaces. Indeed, during the metal deposition in oxygen atmosphere, extensive and uncontrolled oxidation of Fe occurs, preventing the stabilization of long-range ordered oxide monolayers. An alternative route to obtain a sharp interface between a single layer of transition metal oxide and a reactive substrate may be to exploit the oxygen adsorbed on the surface before metal deposition since, in this case, the amount of oxygen available is well defined. The well ordered and defect-free Fe(001)-p(1×1)O surface is an ideal template to implement this strategy. The surface is characterized by one oxygen atom per surface unit cell, which can be used as a reservoir for the stabilization of two-dimensional transition metal oxides. In this contribution, by means of a combination of high resolution Scanning Tunneling Microscopy images, Auger Electron Spectroscopy, and Density Functional Theory calculations, we show how the Fe(001)-p(1 × 1)O surface can be used as a template for the self assembly of two dimensional Cr oxides. Cr deposition on this surface leads to two different phases, depending on the amount of deposited Cr. At 0.75 monolayers coverage a c(4 × 2) overlayer with Cr3O4 formal stoichiometry is stabilized, while an overlayer with (???5 ×???5)R°27 symmetry and Cr4O5 stoichiometry is obtained at slightly higher coverages [1]. Furthermore, the magnetic properties of these oxide monolayers are investigated by means of X-ray magnetic circular dichroism. References: [1] A. Picone, G. Fratesi, M. Riva, G. Bussetti, A. Calloni, A. Brambilla, M. I. Trioni, L. Duò, F. Ciccacci, and M. Finazzi, Self-organized chromium oxide monolayers on Fe(001), Phys. Rev. B 87, 085403 (2013)