arXiv subjects

A. Kiejna

Publications and source records attributed to A. Kiejna.

4 recordsLinked to original sources

arXiv2018

Moiré-free ultrathin iron oxide film: FeO(111) on Ag(111)

Ultrathin iron oxide films epitaxially grown on the (111)- and (0001)-oriented metal single crystal supports exhibit unique electronic, catalytic and magnetic properties not observed for the corresponding bulk oxides. These properties originate mainly from the presence of Moiré superstructures which, in turn, disqualify ultrathin films as model systems imitating bulk materials. We present a route for the preparation of a close-packed Moiré-free ultrathin iron oxide film, namely FeO(111) on Ag(111). Experimental scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) results confirm perfect structural order in the film. Density functional theory (DFT)-based calculations suggest full relaxation of the oxide layer that adopts the atomic lattice of the crystalline support and exhibits properties similar to those of a free-standing FeO. The results open new pathways for model-type studies of electronic, catalytic and magnetic properties of fully-relaxed iron oxide films and related systems.

cond-mat.mes-hall↗

arXiv2015

First principles study of the adsorption of MgO molecules on a clean Fe(001) surface

The adsorption of MgO molecules on a Fe(001) surface was studied using density functional theory (DFT) and projector augmented wave methods. The energetically most favored configurations for different adsorption sites considered were identified. The most preferable adsorption geometry is when the MgO molecules are parallel to the surface, with Mg in the interstitial site and O in on-top of the Fe atom. During the adsorption of subsequent MgO molecules in this geometry, a sharp, non-oxidized interface is formed between the MgO adlayer and Fe(001) surface. The adsorption of MgO perpendicular to the surface, with oxygen incorporated in the topmost Fe layer is less probable, but may lead to the formation of the FeO layer when stabilized with an excess of oxygen atoms. Structural, electronic and magnetic properties of both interface types were examined for the MgO coverage from 1/9 to 1 monolayer (ML). Electronic and magnetic properties are sensitive to the MgO coverage. For lower coverage of MgO, clear hybridization between the Fe 3d and O 2p states is shown. The average magnetic moment of the surface Fe atoms is reduced with coverage, achieving 2.78 $μ_{\rm B}$ for 1 ML of MgO.

cond-mat.mtrl-sci↗

arXiv2009

Cohesive and magnetic properties of grain boundaries in bcc Fe with Cr additions

Structural, cohesive, and magnetic properties of two symmetric $\Sigma3(111)$ and $\Sigma5(210)$ tilt grain boundaries (GBs) in pure bcc Fe and in dilute FeCr alloys are studied from first principles. Different concentration and position of Cr solute atoms are considered. We found that Cr atoms placed in the GB interstice enhance the cohesion by 0.5-1.2 J/m$^2$. Substitutional Cr in the layers adjacent to the boundary shows anisotropic effect on the GB cohesion: it is neutral when placed in the (111) oriented Fe grains, and enhances cohesion (by 0.5 J/m$^2$) when substituted in the boundary layer of the (210) grains. The strengthening effect of the Cr solute is dominated by the chemical component of the adhesive binding energy. Our calculations show that unlike the free iron surfaces, Cr impurities segregate to the boundaries of the Fe grains. The magnetic moments on GB atoms are substantially changed and their variation correlates with the corresponding relaxation pattern of the GB planes. The moments on Cr additions are 2-4 times enhanced in comparison with that in a Cr crystal and are antiparallel to the moments on the Fe atoms.

cond-mat.mtrl-sci↗

arXiv2003

Simple Model for Energy and Force Characteristics of Metallic Nanocontacts

The quantum size oscillations of the energetic properties and the elongation force of the gold slabs and wires, isolated and in a contact with electrodes, are calculated in a free-electron model. A simple relation between the Fermi energy and the square-potential-well depth is used and tested for low-dimensional systems. It is shown that considering the electron subsystem of a slab (or wire) in a contact as open one, the contact acts like a sort of electron pump which sucks or pumps out electrons from the sample. The effect of the contact potential difference on the elastic force oscillations is considered. The calculated amplitudes of force oscillations are in a qualitative agreement with those observed experimentally.

cond-mat.mes-hall↗