On the Structural and Optical Properties of Ultrathin Iron Oxide
(English)Manuscript (preprint) (Other academic)
Nanostructured iron oxides and especially hematite are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low dimensional films is atomic layer deposition, ALD. Although a potent technique, ALD of ultrathin films is sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work the optical and structural properties of iron oxide films in the thickness range of 6 nm to 50 nm have been investigated. Below 10 nm nominal film thickness we find island formation and phase dependent particle crystallization that impose difficulties for ALD deposition of phase pure iron oxides on non-lattice matching substrates. For films between 10-20 nm, post-annealing steps were found to be needed to recrystallize iron polymorphs to hematite whereas for films thicker than 20 nm, phase pure hematite can be formed directly with ALD with very low influence of the substrate. Analysis of the indirect and direct band gaps of the thinnest films show a quantum confined blue shift of the absorption edge.
A. Thin films, B. Vapour deposition C. Raman spectroscopy, D. Crystal structure
IdentifiersURN: urn:nbn:se:uu:diva-232945OAI: oai:DiVA.org:uu-232945DiVA: diva2:750276