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The influence of amorphous Al2O3 coating on the hydrogen uptake properties of materials
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
2008 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 464, no 1-2, L13-L16 p.Article in journal (Refereed) Published
Abstract [en]

An experimental exploration of the transport rate of hydrogen through amorphous Al2O3 layers is presented. Significant changes in the transport rate were observed when changing the thickness of the oxide from 1 to 3 nm. By coating the oxide with a catalytically active Pd layer, a fast dissociation of hydrogen is allowed, enabling a separation between the limitation imposed by dissociation and the transport through the oxide.

Place, publisher, year, edition, pages
2008. Vol. 464, no 1-2, L13-L16 p.
Keyword [en]
Thin films, Hydrogen absorbing materials
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:uu:diva-101143DOI: 10.1016/j.jallcom.2007.10.045ISI: 000259715300004OAI: oai:DiVA.org:uu-101143DiVA: diva2:211980
Available from: 2009-04-20 Created: 2009-04-20 Last updated: 2017-12-13
In thesis
1. Tailoring Properties of Materials at the Nanoscale
Open this publication in new window or tab >>Tailoring Properties of Materials at the Nanoscale
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The knowledge of growth and characterizing techniques is essential for the preparation of high quality thin films and multilayers. Here, structural properties have been investigated by X-ray reflectivity, X-ray diffraction, and transmission electron microscopy while the composition was determined by Rutherford backscattering spectrometry. For the magnetic studies, magneto-optical Kerr effect and X-ray magnetic circular dichroism have been used.

The structural properties of the metal/insulator multilayer system, Fe/MgO, have been investigated. The coherency of the layers was influenced by the difference of the atomic distance in the Fe and MgO layers, resulting in long range strain fields. As a consequence, the coherency between the layers is not maintained.

The atomic steps can not exist in amorphous materials, due to the absence of well defined atomic distances. Furthermore, the magnetic properties of amorphous materials allow a tuning of magnetic properties such as magnetic anisotropy and ordering temperature. The possibility to imprint arbitrary magnetic anisotropy in nanolaminated magnetic amorphous Co68Fe24Zr8 was demonstrated. The ratio of the orbital to spin moments for both Fe and Co was determined, for both thick and thin layers embedded in amorphous Al70Zr30 layers. When growing Co68Fe24Zr8 /Al2O3 the layers exhibit large changes in layer quality with thickness of the layers, ultimately affecting the magnetic properties of the stack.

The use of protective layers is of large importance when performing ex-situ measurements. Most of the materials used were capped by Al2O3, effectively hindering both the reaction with oxygen and water. The penetration of hydrogen through different thicknesses of alumina was investigated. The experiments confirmed high degree of passivation as well as the possibility to selectively diffuse hydrogen through these layers. The use of element specific diffusion barriers allows the tailoring of magnetic properties of magnetic thin films and multilayers.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2009. 69 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 665
Keyword
Multilayers, magnetic anysotropy, amorphous materials
National Category
Condensed Matter Physics
Research subject
Physics of Matter
Identifiers
urn:nbn:se:uu:diva-107425 (URN)978-91-554-7584-0 (ISBN)
Public defence
2009-09-24, Polhemssalen, Ångströmlaboratoriet, Ångströmlaboratoriet Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-09-02 Created: 2009-08-11 Last updated: 2010-12-16Bibliographically approved
2. Influence of Self-trapping, Clamping and Confinement on Hydrogen Absorption
Open this publication in new window or tab >>Influence of Self-trapping, Clamping and Confinement on Hydrogen Absorption
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dissociation of hydrogen molecules at surfaces is the first step in the absorption process. If the absorbing material is covered by an oxide, this layer will determine the effective uptake rate of an underlying absorbing material. This effect is illustrated when determining the rate of transport of hydrogen through amorphous aluminium oxide layers. The transport rate was determined to be strongly thickness dependent.

Hydrogen absorbed in a transition metal causes a volume expansion generated by a strain field around the absorbed hydrogen. This strain field causes a self-trapping of the hydrogen and a temperature dependent distribution in the atomic distances. The local strain field generated by the self-trapping process is found to be crucial for understanding both the hydrogen induced volume expansion as well as the diffusion of hydrogen. Ab-initio molecular dynamics simulations were used to reveal the temperature dependence of the unbinding of the hydrogen and the local strain field and its influence on the diffusion rate. The symmetry of the local strain field is also important for phase formation in metallic films and superlattices which are clamped to a substrate. As the thicknesses reduced from 50 to 10 nm thick vanadium films, substantial finite size effects become apparent in the phase diagrams. The volume change associated with the strain field cannot be accurately measured using x-ray diffraction because of its sensitivity to local arrangements of atoms. X-ray and neutron reflectivity were found to be more reliable probes of global effects of the sumof the local strainfields.

Finite size effects in extremely thin V layers were also explored in metallic superlattices composed of iron and vanadium. The co-existence region, composed of a hydrogen gas and a solid-like phase, was found to be suppressed by at least 100 K to below 300 K. The hydrogen-hydrogen interaction can also be influenced by the electronic states in the non hydrogen absorbing layers, as demonstrated when comparing hydrogen absorption in Fe/V and Cr/V superlattices.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 798
Keyword
hydrogen diffusion, thin films, superlattices, phase transitions, confinement, clamping, self-trapping, finite-size effect
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-140329 (URN)978-91-554-7983-1 (ISBN)
Public defence
2011-02-18, Häggsalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 728Available from: 2011-01-31 Created: 2011-01-04 Last updated: 2011-03-21Bibliographically approved

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Pálsson, Gunnar K.Hjörvarsson, Björgvin

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