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Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
Department of Materials Science and Engineering Royal Institute of Technology, Stockholm.
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan.
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2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, 125406-1-125406-7 p.Article in journal (Refereed) Published
Abstract [en]

We study the structural properties of ultrathin AgxPd1−x films on top of a Ru(0001) substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer (4-ML) Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.

Place, publisher, year, edition, pages
APS , 2008. Vol. 77, 125406-1-125406-7 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-44362DOI: 10.1103/PhysRevB.77.125406Local ID: 76396OAI: oai:DiVA.org:liu-44362DiVA: diva2:265224
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2012-06-20Bibliographically approved
In thesis
1. Theoretical Considerations of Local Environment Effects in Alloys
Open this publication in new window or tab >>Theoretical Considerations of Local Environment Effects in Alloys
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is devoted to a theoretical study of local environment effects in alloys. A fundamental property of a disordered system is that all chemically equivalent atoms are different due to their different chemical environments, in contrast to an ideal periodic solid where all the atoms that occupy equivalent positions in the crystal have exactly the same physical properties. The local environment effects have been largely ignored in earlier theories of disordered systems, that is the system has been treated as a whole and average properties have been derived. Moreover, inhomogeneous systems, such as surfaces and interfaces, induce local environment effects that are not necessarily present in the bulk.

The importance and presence of local environment effects are illustrated by calculating observable physical properties in various systems. In particular, by employing the complete screening picture the effects of local environments on the core-level binding energy shifts as well as Auger shifts in random alloys are in- vestigated. This so-called disorder broadening effect has recently been observed experimentally. It is shown that there are different contributions to the disorder broadening that vary with the local chemical environment. Furthermore, the influ- ence of inhomogeneous lattice distortions on the disorder broadening of the core- level photoemission spectra are considered for systems with large size-mismatch between the alloy components.

The effects of local chemical environments on physical properties in magnetic systems are illuminated. A noticeable variation in the electronic structure, local magnetic moments and exchange parameters at different sites is obtained. This reflects the sensitivity to different chemical environments and it is shown to be of qualitative importance in the vicinity of magnetic instability.

The local environment effects due to the presence of surfaces and interfaces are also considered. The effect is explicitly studied by considering the concentration profile of a thin Ag-Pd film deposited on a Ru substrate. Two computational approaches are utilized to calculate the relative composition in each layer of the thin film as a function of temperature in a theoretically consistent way. It is shown that, opposed to the situation in the bulk, where a complete solubility between Ag and Pd takes place, a non-uniform distribution of the alloy components across the film is observed.

In another study it is investigated whether the presence of TiN interfaces changes the dynamical and thermodynamic stability of B1 SiN. Phonon calcula- tions show that TiN interfaces have a stabilization effect on the lattice dynamics. On the other hand, calculations of the Si vacancy formation energy show that the structures are unstable with respect to composition variations.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 86 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1353
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-63443 (URN)978-91-7393-285-1 (ISBN)
Public defence
2010-12-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-12-27 Created: 2010-12-19 Last updated: 2010-12-27Bibliographically approved
2. Thermal properties of materials from first principles
Open this publication in new window or tab >>Thermal properties of materials from first principles
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the search of clean and efficient energy sources intermediate temperature solid oxide fuel cells are among the prime candidates. What sets the limit of their efficiency is the solid electrolyte. A promising material for the electrolyte is ceria. This thesis aims to improve the characteristics of these electrolytes and help provide thorough physical understanding of the processes involved. This is realised using first principles calculations.

The class of methods based on density functional theory generally ignores temperature effects. To accurately describe the intermediate temperature characteristics I have made adjustments to existing frameworks and developed a qualitatively new method. The new technique, the high temperature effective potential method, is a general theory. The validity is proven on a number of model systems.

Other subprojects include low-dimensional segregation effects, adjustments to defect concentration formalism and optimisations of ionic conductivity.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 62 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1453
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78755 (URN)978-91-7519-884-2 (ISBN)
Public defence
2012-06-15, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 14:00 (English)
Opponent
Supervisors
Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2012-06-20Bibliographically approved

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Marten, TobiasHellman, OlleAbrikosov, Igor

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