Oriented single-crystalline thin films of NiO and Fe304, and Fe304/NiO superlattices have been grown on cleaved and polished substrates of MgO(001), using oxygen-plasma-assisted molecular-beam epitaxy. We report the growth mode and structural characterization of the grown films using in situ reflection high-energy electron diffraction (RHEED) and ex situ scanning electron microscopy and x-ray diffraction. The (001) surface of MgO provides an excellent template for the pseudomorphic growth of these thin films and superlattices, for it has a very small lattice mismatch (0.3-0.9%) to the cubic rocksalt structure of Ni0 and to the half unit-cell dimension of the spinel structure of Fe304. Superlattices consisting of alternating layers of NiO and Fe304 have been grown with a repeat wavelength down to 20 0 A (approximately one Fe304 unit cell plus two NiO unit cells) thick. These superlattices exhibit strong crystalline ordering and sharp interface formation. RHEED pattern evolution in situ during growth indicates formation of the rocksalt NiO crystalline symmetry and then the spinel Fe304 crystalline symmetry in a periodic sequence as each material is being deposited. Our data indicate single-phase crystal growth in registry with the substrate, with films of overall cubic symmetry. Strain in the grown films exhibits interesting effects that clearly do not follow a simple elastic model.
Surface magnetic structure of epitaxial magnetite thin films grown on MgO(001) J. Appl. Phys. 105, 07D545 (2009); 10.1063/1.3089493 Structural and magnetic properties of magnetite-containing epitaxial iron oxide films grown on MgO(001) substrates J. Appl. Phys. 103, 043902 (2008); 10.1063/1.2840118 Study of interdiffusion between thin Y-Ba-Cu-O films and MgO substrates by applying Rutherford backscattering spectrometry combined with scanning tunneling microscopy Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract)
Presently, the best epitaxial thin films of CrO2 are made by chemical-vapor deposition (CVD) in a two-zone furnace with oxygen flow from a CrO3 precursor. The growth mode has previously been described as CrO3 vaporizing in the first zone, and thermally decomposing at higher temperature in the second zone onto a substrate. In the more recent works, the focus has been on the properties of the obtained layers rather than on deposition mechanisms. In the present experimental work, we attack the epitaxial growth of CrO2 by two completely different methods, namely, molecular-beam epitaxy (MBE) and CVD. We focus on the CVD process itself, and show the importance of an intermediate compound, Cr8O21, for the growth of CrO2 films. We show that it is not necessary to start the CVD from CrO3; instead, one can prepare Cr8O21 ex situ, and use it directly for the growth of high-quality CrO2 epitaxial layers, avoiding any contamination caused by the decomposition of CrO3 to Cr8O21. We discuss in parallel our failed attempts to deposit CrO2 from either CrO3 or Cr and oxygen plasma by MBE and our experiments with the CVD process, and conclude that CrO3 does not decompose directly to CrO2 and oxygen, as was expected. We propose a hypothesis that the role of Cr8O21 in the CVD process is to exude unstable molecules of CrO4, and that the reaction on the substrate is the decomposition CrO4→CrO2+O2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.