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Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
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2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 19, 195108- p.Article in journal (Refereed) Published
Abstract [en]

The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K, and Al L emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole matrix elements. The detailed investigation of the electronic structure and chemical bonding provides increased understanding of the physical properties of this type of nanolaminates. Three different types of bond regions are identified: The relatively weak Ti 3d-Al 3p bond 1 eV below the Fermi level and the Ti 3d-C 2p and Ti 3d-C 2s bonds which are stronger and deeper in energy are observed around 2.5 and 10 eV below the Fermi level, respectively. A strongly modified spectral shape of the 3s final states in comparison to pure Al is detected for the intercalated Al monolayers indirectly reflecting the Ti 3d-Al 3p hybridization. The differences between the electronic and crystal structures of Ti2AlC, Ti3AlC2, and TiC are discussed in relation to the number of Al layers per Ti layer in the two former systems and the corresponding change of the unusual materials properties.

Place, publisher, year, edition, pages
2006. Vol. 74, no 19, 195108- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96304DOI: 10.1103/PhysRevB.74.195108ISI: 000242409200045OAI: oai:DiVA.org:uu-96304DiVA: diva2:170835
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Synthesis and Characterization of Ternary Carbide Thin Films
Open this publication in new window or tab >>Synthesis and Characterization of Ternary Carbide Thin Films
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on synthesis, microstructure and properties of binary and ternary carbide thin films deposited by dc magnetron sputtering. These materials are interesting since they exhibit a wide range of useful properties, such as high hardness, resistance to wear and oxidation, and high electrical conductivity. Here, an early transition metal (M) and carbon (C) have been used as the basis, often with the addition of a second M-element or an A-group element (A). In these systems nanocomposites, metastable solid solutions, multilayers, or Mn+1AXn-phases have been deposited. The Mn+1AXn-phases are a group of nanolaminated compounds with a unique mixture of metallic and ceramic properties. In general X is carbon or nitrogen, although here only carbon has been used.

Epitaxial MAX-phase thin films of Ti2AlC, Ti3AlC2 and V2GeC have been deposited for the first time. They have been studied with emphasis on phase stability, phase composition and nucleation characteristics to gain deeper insights into their growth. The microstructure of the films was characterized by electron microscopy and X-ray diffraction. In addition, bond strength characteristics have been studied by soft X-ray spectroscopy and complementary calculations within DFT. Their mechanical and electrical properties have been studied, and the results are discussed on the basis of their electronic structure. Furthermore, by interleaving the Ti3SiC2 MAX-phase with TiC0.67 a multilayer structure has been formed, for which a new intrusion-type deformation behaviour has been described.

A new concept in the design of nanocomposite films has been developed, whereby a solid solution of a weak carbide-forming element in the carbide structure creates a driving force for surface segregation of C. This concept has been verified both theoretically and experimentally for the Ti-Al-C and Ti-Fe-C systems. It has been shown by pin-on-disc measurements that this surface segregation leads to graphitization and consequently a very low friction coefficient for these films. Finally, it has been demonstrated that low-friction films with tunable magnetic properties can be achieved in the Ti-Fe-C system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 353
Keyword
Chemistry, Thin film, dc magnetron sputtering, tribology, carbide, PVD, MAX-phase, DFT, solid solution, Kemi
Identifiers
urn:nbn:se:uu:diva-8265 (URN)978-91-554-6991-7 (ISBN)
Public defence
2007-11-09, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, 751 21, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2010-09-13Bibliographically approved

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Magnuson, MartinWilhelmsson, OlaJansson, UlfAhuja, RajeevEriksson, Olle

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