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Electronic structure and chemical bonding of nanocrystalline-TiC/amorphous-C nanocomposites
Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. (oorganisk kemi)
Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. (oorganisk kemi)
2009 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 80, no 23, 235108- p.Article in journal (Refereed) Published
Abstract [en]

The electronic structure of nanocrystalline (nc-) TiC/amorphous C nanocomposites has been investigated bysoft x-ray absorption and emission spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of thenanocomposites are compared to those of Ti metal and amorphous C. The corresponding intensities of theelectronic states for the valence and conduction bands in the nanocomposites are shown to strongly depend onthe TiC carbide grain size. An increased charge transfer between the Ti 3d-eg states and the C 2p states hasbeen identified as the grain size decreases, causing an increased ionicity of the TiC nanocrystallites. It issuggested that the charge transfer occurs at the interface between the nanocrystalline-TiC and the amorphous-Cmatrix and represents an interface bonding which may be essential for the understanding of the properties ofnc-TiC/amorphous C and similar nanocomposites.

Place, publisher, year, edition, pages
2009. Vol. 80, no 23, 235108- p.
Keyword [en]
Nanokomposit, RIXS, XES, XAS, TEY, TFY, XPS, XRD
National Category
Condensed Matter Physics Inorganic Chemistry
Research subject
Physics; Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-111387DOI: 10.1103/PhysRevB.80.235108ISI: 000273228800029OAI: oai:DiVA.org:uu-111387DiVA: diva2:280927
Available from: 2009-12-14 Created: 2009-12-13 Last updated: 2014-09-15Bibliographically approved
In thesis
1. Design of carbide-based nanocomposite coatings
Open this publication in new window or tab >>Design of carbide-based nanocomposite coatings
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis research on synthesis, microstructure and properties of carbide-based coatings is reported. These coatings are electrically conducting, and can be tailored for high hardness, low friction and wear, along with load-adaptive behaviour. Tailoring these properties is achieved by controlling the relative phase content of the material. Coatings have been synthesised by dc magnetron sputtering, and their structures have been characterised, mainly by X-ray photoelectron spectroscopy and X-ray diffraction.

It has been shown that nanocomposites comprising of a nanocrystalline transition metal carbide (nc-MeCx, Me = Ti, Nb or V) and an amorphous carbon (a-C) matrix can result in low contact resistance in electrical contacts. Such materials also exhibit low friction and high resistance to wear, making them especially suitable for application in sliding contacts. The lowest contact resistance is attained for small amounts of the amorphous carbon phase.

It has been shown that specific bonding structures are present in the interface between nc-TiCx and the a-C phases in the nanocomposite.  It was found in particular that Ti3d and C2p states are involved, and that considerable charge transfer occurs across the interface, thereby influencing the structure of the carbide.

Further design possibilities were demonstrated for TiCx-based nanocomposites by alloying them with weakly carbide-forming metals, i.e., Me = Ni, Cu or Pt.  Metastable supersaturated solid solution carbides, (T1-xMex)Cy, were identified to result from this alloying process. The destabilisation of the TiCx-phase leads to changes in the phase distribution in the deposited nanocomposites, thus providing further control over the amount of carbon phase formed. Additional design possibilities became available through the decomposition of the metastable (Ti1-xMex)Cy phase through an appropriate choice of annealing conditions, yielding either more carbon phase or a new metallic phase involving Me. This alloying concept was also studied theoretically for all 3d transition metals using DFT techniques.

It has also been demonstrated that Ar-ion etching (commonly used in the analysis of carbide based nanocomposites) can seriously influence the result of the analysis, especially for materials containing metastable phases. This implies that more sophisticated methods, or considerable care are needed in making these analyses, and that many of the earlier published results could well be in error.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 83 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 682
Keyword
chemistry, thin film, dc magnetron sputtering, carbide, nanocomposite, PVD, solid solution
National Category
Chemical Sciences Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-109427 (URN)978-91-554-7636-6 (ISBN)
Public defence
2009-11-27, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-11-06 Created: 2009-10-15 Last updated: 2014-01-21Bibliographically approved

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Lewin, ErikJansson, Ulf

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