Self-organized chromium oxide monolayers on Fe(001)

Abstract

The oxygen-saturated Fe(001)-p(1 × 1)O surface has been used as a template to stabilize two-dimensional Cr oxides on Fe(001). Cr deposition at 400 • C leads to two different well-ordered phases, depending on the amount of Cr deposited. In the submonolayer regime a novel c(4 × 2) overlayer self-assembles on the Fe(001)-p(1 × 1)O surface, saturating for a coverage of about 0.75 monolayers. This phase becomes unstable for higher coverages, when a ( √ 5 × √ 5)R27 • superstructure emerges. The structural and electronic details of the two one-layer-thick oxides are studied by combining high-resolution scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, and density functional theory.

Self-organized nano-structuring of CoO islands on Fe(001)

“…The Co growth was performed at RT by means of MBE through an e-beam evaporator in UHV (base pressure in the 10 −9 Pa range), then the sample was heated at 470 K for about 5 minutes. As in other similar cases [32,[37][38][39][40], the oxygen segregates to the sample surface and this procedure results in a Co(001)-p(1 × 1)O surface, as testified by Low-Energy Electron Diffraction (LEED) and STM [36]. Cobalt oxide is then grown at 470 K by reactive deposition of metallic Co in a pure O 2 atmosphere, with partial pressure p O 2 = 1 · 10 −4 Pa, with thicknesses up to about 32 ML (1 ML of CoO is nominally equal to 0.213 nm).…”

Magnetism in thin Cr films grown on Fe(001)-p(1×1)O: a spin-resolved investigation of single and multi-layers

“…15 On Cr, we detected a more complex surface reorganization, leading to the formation of an highly ordered network of Cr vacancies which creates a √5 × √5 27° superstructure in an otherwise perfectly square CrO lattice 16 . During HT Cr deposition on Fe(001)-p(1×1)O, Cr inclusion in the Fe matrix is limited to the relaxed FeO layer.…”

Combined spectroscopic and ab initio investigation of monolayer-range Cr oxides on Fe(001): The effect of ordered vacancy superstructure

“…This procedure leads to the formation of the well-characterized Fe(001)-p(1×1)O surface in which each oxygen atom sits in a fourfold symmetrical Fe hollow site [22]. The Cr-( √ 5× √ 5)O superstructure was prepared by dosing about 0.8 ML of Cr on the Fe(001)-p(1×1)O surface kept at about 600 K [13]. The Cr deposition rate (about 0.5 ML/min) was monitored by a quartz microbalance.…”

“…The atomic coordinates were taken from our previous investigation on the energetic stability of surface reconstructions for monolayer-range Cr oxides grown on Fe(001) [13]. There we adopted a repeated slab model with 4 Fe(001) layers, where the bottom two are fixed at the bulk spacing.…”

“…• O superstructure [Cr-( √ 5× √ 5)O in the following], clearly observed with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) [13]; and (iii) a magnetization antiparallel to that of the substrate [14,15]. The Cr-( √ 5× √ 5)O superstructure consists in a regular network of cation (Cr) vacancies created in an otherwise stoichiometric CrO layer [Cr-p(1×1)O in the following], that is primarily due to electronic effects also responsible for the formation of cation vacancies in bulk oxides characterized by a rocksalt structure, as in the case of early 3d and 4d metal oxides [16].…”