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Applied physics letters 118(8), 089901 (2021). doi:10.1063/5.0045052, Published by American Inst. of Physics, Melville, NY

The journal of chemical physics 152(11), 114705 (1-9) (2020). doi:10.1063/1.5142558, We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface x-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe$^{2+}$ sandwiched between two close-packed layers of tetrahedrally coordinated Fe$^{3+}$ and an overall stoichiometry of Fe$_3$O$_4$. As the structure is distinct from bulk iron oxide phases and the coupling with the silver substrate is weak, we propose that the phase should be classified as a metastable two-dimensional oxide. The chemical and physical properties are potentially interesting, thanks to the predicted charge ordering between atomic layers, and analogy with bulk ferrite spinels suggests the possibility of synthesis of a whole class of two-dimensional ternary oxides with varying electronic, optical, and chemical properties., Published by American Institute of Physics, Melville, NY

Iron oxide films were reactively grown on iron buffer films, which were deposited before on MgO(001) substrates to analyze the influence of the initial iron buffer layers on the magnetic properties of the magnetite films. X-ray photoelectron spectroscopy and low energy electron dif-fraction showed that magnetite films of high crystalline quality in the surface near region were formed by this two-step deposition procedure. The underlying iron film, however, was completely oxidized as proved by x-ray reflectometry and diffraction. The structural bulk quality of the iron oxide film is poor compared to magnetite films directly grown on MgO(001). Although the iron film was completely oxidized, we found drastically modified magnetic properties for these films using the magnetooptic Kerr effect. The magnetite films had strongly increased coercive fields, and their magnetic in-plane anisotropy is in-plane rotated by 45° compared to magnetite films formed directly by one step reactive growth on MgO(001).

Journal of applied physics 105, 124108 (2009). doi:10.1063/1.3152796, Films of hexagonal praseodymium sesquioxide (h-Pr$_2$O$_3$) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 °C. The films of the samples annealed at 300 °C or more were transformed to PrO2 with B-oriented Fmˉ3m structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO2 and PrO2−δ species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO$_2$, PrO$_2$−δ has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation, Published by American Institute of Physics, Melville, NY