Abstract
The structure and functional properties of metal oxide films for device applications are largely affected by oxygen vacancies. While the macroscopic relationship between functionality and oxygen supply during growth is easy to access, the local influence of changing oxygen content on the incorporated metal atoms has been rarely investigated. As a model system, we use Mn as a local probe in hetero- and homoepitaxial ZnO thin films for electron paramagnetic resonance (EPR). Mn is expected to be incorporated as Mn2+ in the Zn-lattice site of ZnO films grown in a wide range of oxygen partial pressures. The zero field splitting (ZFS) parameter D depends on the crystallographic c/a ratio of ZnO : Mn lattice constants as it measures the trigonal distortion of oxygen tetrahedra at the Zn2+ site with respect to the Mn2+ site. The ZFS parameter D correlates linearly with displacement of Mn2+ ions along the c-axis in the MnO4 tetrahedra and the corresponding bond lengths between the Mn2+ ions and the axial oxygen ion.
Highlights
Oxide materials, in particular oxide thin lms, gain more and more attention from both basic and applied points of view, due to interesting phenomena such as strong electron correlations and transparent oxide electronics
Our work reveals a signi cant expansion of the ZnO lm structure along the c-axis combined with the a-axis compression with decreasing oxygen partial pressure that we ascribe to the enhanced formation of oxygen vacancies under oxygen de cient growth conditions
This increase of the c-axis lattice parameter translates into an increase of the bond distances between the metal ions and the axial oxygen ions along the c-axis in the metal ion–oxygen tetrahedra of the ZnO lms
Summary
In particular oxide thin lms, gain more and more attention from both basic and applied points of view, due to interesting phenomena such as strong electron correlations and transparent oxide electronics. The functional properties of metal oxide thin lms may be controlled by tuning the preparation conditions. In the interplay of structure, morphology and the functional properties such as conductivity or the ferroic properties, o en an oxygen de cient growth environment is chosen because of the requirements of a smooth surface and an interface.[1] In pulsed laser deposition (PLD), one of the most exible growth methods of oxide thin lms,[2] the oxygen partial pressure during growth controls the distribution of oxygen vacancies.[3] oxygen vacancies are a common phenomenon in functional oxides, due to the o en used oxygen de cient growth conditions. The effect of oxygen vacancies on structures and macroscopic functional properties is a highly interesting and current topic of interest, as the following examples show
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