Abstract
We demonstrate how ordered arrangements of oxygen vacancies can be engineered during the growth of superconducting La2CuO4 films by oxide molecular-beam epitaxy. These arrangements are seen using in situ reflection high-energy electron diffraction. Based on qualitative real-time observations, we propose a surface reconstruction mechanism emphasizing the active role of dopants and oxygen vacancies at the film surface. Due to the specific atomic arrangement induced by dopant positions, characteristic surface “stripes” are generated, and they determine the intrinsically heterogeneous structure characterized by distorted checkerboard patterns on the surface. Not only can the surface motif during growth be monitored via characteristic surface reconstructions, but it can also be customized by altering strain, doping, and oxygen activity.
Highlights
Crystal surfaces tend to form energetically favored atomic arrangements
Due to the specific atomic arrangement induced by dopant positions, characteristic surface “stripes” are generated, and they determine the intrinsically heterogeneous structure characterized by distorted checkerboard patterns on the surface
Some extent of stoichiometric uncertainty is inherent in oxide-molecular-beam epitaxy (MBE) synthesis, e.g., due to the precision limit in the initial calibration of the element fluxes, monitoring the in situ Reflection high-energy electron diffraction (RHEED) patterns permits a precise control of growth and allows the operator to avoid any undesired precipitation of secondary phases
Summary
Crystal surfaces tend to form energetically favored atomic arrangements. In the layer-by-layer synthesis of charged surfaces, electrostatic terms are major contributors to the energetics governing surface formation. Reflection high-energy electron diffraction (RHEED) using a collimated electron beam irradiating the sample surface [Fig. 1(a)] provides real-time information about the surface crystallinity[3,4,5] during the epitaxial growth of thin films. It allows for real-time growth monitoring, the study of surface reconstructions, and can be complemented by low-energy electron diffraction (LEED)[6] for more detailed analyses. Independent of interface functionalities, cationic intermixing is usually present at LCO-based heterointerfaces This intermixing is affected by growth kinetics,[34] the individual layer thicknesses,[35] and the sizes of the cations involved.[36]. The surface reconstructions caused by the coherent ordering of the surface atoms emerges due to the interrelation of dopant atoms and oxygen vacancies, which results in orthogonal “stripes.”
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