Electronic and atomic structure of surface oxides
Abstract
Copper metal-oxide interfaces are important technological systems and the structure of the oxide at the surface of metallic Cu is a topic that is being investigated with advanced experimental and theoretical techniques. In this project, such techniques will be used to study the so-called ‘29’ superstructure forms on the clean Cu(111) surface upon its exposure to oxygen and subsequent annealing. Its surface cell may be denoted as √13 R46°×√7 R21.8° and is 29 times bigger than the unit cell of clean Cu(111) surface [1].
This structural complexity requires a combined effort where the experimental investigations are supported by high level computational models to solve the structural features with the required degree of accuracy [2-4]. Based on experimental data, we have devised and tested different models of the ‘29’ superstructure in the previous project NAISS 2023/5-76, see report.
Another set of results was obtained for clean low-index surfaces of Cu, (111), (110), and (100) using VASP calulations with projector augmented wave (PAW) type pseudopotentials [5,6]. Their structural models were built assuming the slab geometry; surface core level shifts (SCLS) were computed, in the complete screening picture [7], by comparing the total energies of slabs with impurities [core holes or equivalent Z+1 (Zn) or Z+2 (Ga) species] in the bulk and in one of the three outermost surface layers.
In the continuation project, we will employ quantum mechanical modeling at the DFT level [5-9] to study the surfaces composed of copper and early-stage oxides. The goal is to aid the corresponding experimental studies that run in parallel at CoESCA beamline at BESSY II [2-4] using Auger Photoelectron Spectroscopy (APECS) to measure the 3d double hole energies with high accuracy. By adding the kinetic energies of the photoelectrons and the Auger electrons very accurate double hole energies can be determined. These spectra are then not broadened by the core hole life time, as is the case in normal Auger spectra.
The results of these studies are of relevance to materials for advanced batteries and may accelerate the development of the field. The methodologies developed for the oxidized copper surfaces will be useful in studies of oxidized surfaces of other alloys of high technological relevance (steels, superalloys).
References
[1] F. Wiame et al., Surface Science 601, 1193 (2007).
[2] T. Leitner, et al.,J. Electron Spectrosc. Relat. Phenom. 250, 147075 (2021).
[3] F.O.L. Johansson et al. J. Electron Spectrosc. Relat. Phenom. 256, 147174 (2022).
[4] A. Born et al., Scientific Reports 11, 16597 (2021).
[5] G. Kresse and J. Furthmüller, Phys. Rev. B 54, 11169-11186 (1996).
[6] G. Kresse and D. Joubert, Phys. Rev. B 59, 1758-1775 (1999).
[7] W. Olovsson et al., Journal of Electron Spectroscopy and Related Phenomena 178–179, 88–99 (2010).
[8] A. V. Ruban and I. A. Abrikosov, Rep. Prog. Phys. 71, 046501 (2008).
[9] P. Blaha, et al., J. Chem. Phys. 152, 074101 (2020).
