ISBN 9783843947626

978-3-8439-4762-6, Reihe Anorganische Chemie

Daniel Stadler
Magnetic Field-assisted Chemical Vapor Deposition of Iron, Vanadium and Titanium Oxides

185 Seiten, Dissertation Universität Köln (2021), Softcover, A5

Zusammenfassung / Abstract

The aim of this thesis is to expand the experimental space needed to understand the effects associated with magnetic field application during MOCVD process, such as directed structure growth, stabilization of magnetic phases or reduced magnetocrystalline anisotropy. The decomposition of carbonyl and alkoxide precursors in magnetic fields up to 1000 mT led to increased photocatalytic performances or a reduction of magnetic anisotropy, respectively. The outcome of XRD and X-PEEM experiments clearly demonstrated that the characteristic phase transition from ferrimagnetic magnetite to antiferromagnetic hematite is suppressed by the applied magnetic field. In addition, XMCD showed that the relative ratio between ferromagnetically coupled Fe(III) and Fe(II) was enlarged, if an external magnetic field was applied throughout the process.

It was also shown that the application of magnetic fields during CVD allowed additional control to alter the chemical composition of CVD deposits. A set of early transition metal alkoxides were tested in field-assisted and zero field CVD processes. Magnetic field-assisted processes were found to boost chromium carbide formation that decomposed to the trivalent oxide under zero field conditions, while solely oxide formation was found for vanadium and titanium containing precursors. Increasing the precursor sublimation temperature of chromium(IV) alkoxide under zero-field conditions also led to carbide formation, indicating that the presence of magnetic fields during CVD causes partial pressure variations of the precursor in the reactor that was also verified by online mass spectrometry.

In summary, the application of magnetic fields offer additional control over structure growth and transformation in field-assisted CVD. External fields provide additional possibilities for in-situ control over fabrication of functional materials that need to be considered as additional parameter to influence materials formation.