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Surface modification of iron oxides by ion bombardment – comparing depth profiling by HAXPES and Ar ion sputtering
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, Berlin 12489, Germany.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, Berlin 12489, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-7018-9617
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, Berlin 12489, Germany.ORCID iD: 0000-0002-9188-9604
2018 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 23-26Article in journal (Refereed) Published
Abstract [en]

Iron oxide in the form of maghemite  γ-Fe2O3  and hematite α-Fe2O3 has been studied with x-ray photoelectron spectroscopy. It is found that even low energy sputtering induces a reduction of the surface layer into FeO. Satellites in the Fe 2p  core level spectra are used to determine the oxidation state of iron. Depth profiling with changing photon energy shows that the unsputtered films are homogeneous and that the information obtained from sputtering thus, in this instance, represents sputter damages to the sample.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 224, p. 23-26
Keywords [en]
Hard X-ray Photoelectron Spectroscopy, Depth profiling, Iron oxide, HAXPES, synchrotron radiation
National Category
Materials Engineering Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-232947DOI: 10.1016/j.elspec.2017.09.008ISI: 000428825400005OAI: oai:DiVA.org:uu-232947DiVA, id: diva2:750278
Funder
EU, FP7, Seventh Framework Programme, 312284The Royal Swedish Academy of SciencesSwedish Research Council, 2014-6463Available from: 2014-09-28 Created: 2014-09-28 Last updated: 2018-06-05Bibliographically approved
In thesis
1. Synthesis and Characterisation of Ultra Thin Film Oxides for Energy Applications
Open this publication in new window or tab >>Synthesis and Characterisation of Ultra Thin Film Oxides for Energy Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes studies of materials which can be exploited for hydrogen production from water and sunlight. The materials investigated are maghemite (γ-Fe2O3), magnetite (Fe3O4) and especially hematite (α-Fe2O3), which is an iron oxide with most promising properties in this field. Hematite has been deposited using Atomic Layer Deposition (ALD) - a thin-film technique facilitating layer-by-layer growth with excellent thickness control and step coverage. The iron oxides were deposited using bis-cyclopentadienyl iron (Fe(Cp)2) or iron pentacarbonyl (Fe(CO)5) in combination with an O2 precursor. Since it is crucial to have good control of the deposition process, the influence of substrate, process temperature, precursor and carrier gas have been investigated systematically. By careful control of these deposition parameters, three polymorphs of iron oxide could be deposited: hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4).

The deposited materials were characterized using X-ray Diffraction, Raman and UV-VIS Spectroscopy, and Scanning Electron Microscopy. Hard X-ray Photoelectron Spectroscopy (HAXPES) was also used, since it is a non-destructive, chemically specific, surface sensitive technique – the surface sensitivity resulting from the short mean escape depth of the photoelectrons. The depth probed can be controlled by varying the excitation energy; higher photoelectron energies increasing the inelastic mean-free-path in the material.

HAXPES studies of atomic diffusion from F-doped SnO2 substrates showed increased doping levels of Sn, Si and F in the deposited films. Diffusion from the substrate was detected at annealing temperatures between 550 °C and 800 °C. Films annealed in air exhibited improved photocatalytic behavior; a photocurrent of 0.23 mA/cm2 was observed for those films, while the as-deposited hematite films showed no photo-activity whatsoever.

The optical properties of low-dimensional hematite were studied in a series of ultra-thin films (thicknesses in the 2-70 nm range). The absorption maxima were shifted to higher energies for films thinner than 20 nm, revealing a different electronic structure in thin films.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. p. 113
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1186
Keywords
Atomic Layer Deposition, Iron oxides, Hematite, Solar Water Splitting, Hard X-Ray Photoelectron Spectroscopy
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-232948 (URN)978-91-554-9048-5 (ISBN)
Public defence
2014-11-21, Polhemsalen, 10134, Ångström, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-10-30 Created: 2014-09-28 Last updated: 2015-01-23

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Fondell, MattisBoman, MatsLindblad, Andreas

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