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Me-Si-C (Me= Nb, Ti or Zr): Nanocomposite and Amorphous Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates thin films of the transition metal carbide systems Ti-Si-C, Nb-Si-C, and Zr-Si-C, deposited at a low substrate temperature (350 °C) with dc magnetron sputtering in an Ar discharge. Both the electrical and mechanical properties of these systems are highly affected by their structure. For Nb-Si-C, both the ternary Nb-Si-C and the binary Nb-C are studied. I show pure NbC films to consist of crystalline NbC grains embedded in a matrix of amorphous carbon. The best combination of hardness and electrical resistivity are for ~15 at.% a-C phase. The properties of nc-NbC/a-C are similar to films consisting of nc-TiC/a-C. I further show that in a model system of epitaxial TiCx (x ~0.7) up to 5 at.% Si can be incorporated. At higher Si content, Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy. Higher amounts of Si into the Nb-Si-C and Zr-Si-C systems make them become amorphous. These amorphous structures are unstable under electron irradiation were they crystallize. I show that the cause of crystallization is driven by atomic displacement events.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 31 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1561
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-85830Local ID: LIU-TEK-LIC-2012:46ISBN: 978-91-7519-730-2 (print)OAI: oai:DiVA.org:liu-85830DiVA: diva2:572989
Presentation
2012-12-19, Schrödinger, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Incorporation effects of Si in TiCx thin films
Open this publication in new window or tab >>Incorporation effects of Si in TiCx thin films
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2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

DC magnetron sputtered Ti-Si-C thin films with varying Si content between 0 to 13 at.% were deposited from elemental targets. The effects on microstructure were investigated using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Results show that the growth of pure TiCx onto Al2O3(0001) at a temperature of 350 °C is epitaxial and understoichiometric with x~0.7. For Si contents up to 5 at.%, the Si is incorporated into the TiCx with retained epitaxy. For Si contents above 5 at.%, the Si segregate out from the TiCx to the grain boundaries forming, causing a transition from of epitaxial to polycrystalline and nanocomposite growth.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85828 (URN)
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2016-08-31Bibliographically approved
2. Beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films during transmission electron microscopy
Open this publication in new window or tab >>Beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films during transmission electron microscopy
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2013 (English)In: MRS COMMUNICATIONS, Vol. 3, no 3, 151-155 p.Article in journal (Refereed) Published
Abstract [en]

We report that an electron beam focused for high-resolution imaging rapidly initiates observable crystallization of amorphous Me-Si-C films. For 200-keV electron irradiation of Nb-Si-C and Zr-Si-C films, crystallization is observed at doses of similar to 2.8 x 10(9) and similar to 4.7 x 10(9) e(-)/nm(2), respectively. The crystallization process is driven by atomic displacement events, rather than heating from the electron beam as in situ annealing (400-600 degrees C) retains the amorphous state. Our findings demand a critical analysis of alleged amorphous and nanocrystalline ceramics including reassessing previous reports on nanocrystalline Me-Si-C films for possible electron-beam-induced crystallization effects.

Place, publisher, year, edition, pages
Cambridge University Press, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85829 (URN)10.1557/mrc.2013.31 (DOI)000325095100007 ()
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2016-08-31
3. Structural, mechanical and electrical-contact properties of nanocrystalline-NbC/amorphous-C coatings deposited by magnetron sputtering
Open this publication in new window or tab >>Structural, mechanical and electrical-contact properties of nanocrystalline-NbC/amorphous-C coatings deposited by magnetron sputtering
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2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 2-3, 354-359 p.Article in journal (Refereed) Published
Abstract [en]

Niobium-carbide nanocomposite coatings with a carbon content varying from 43 to 64 at.% were deposited by dual DC magnetron sputtering. X-ray diffraction, x-ray photoelectron spectroscopy and electron microscopy showed that all coatings consisted of nanometer sized NbC grains embedded in a matrix of amorphous carbon. Mechanical properties and electrical resistivity showed a strong dependency on the amount of amorphous carbon (a-C) and NbC grain size in the coating. The highest hardness (23 GPa), elastic modulus (295 GPa) and the lowest resistivity (260 mu Omega cm) were measured for the coating with about 15% of a-C phase. Contact resistance measurements using a crossed cylinder set-up showed lowest contact resistance for the coating containing 33% a-C (140 mu Omega at a contact force of 100 N), which is comparable to a Ag reference (45 mu Omega at a contact force of 100 N). Comparison with TiC-based nanocomposites studied under similar conditions showed that the Nb-C system has less tendency to form a-C and that lowest contact resistance is obtained at comparable amounts of a-C phase in both material systems (33% for Nb-C compared to 35% for Ti-C). With these good electrical contact properties, the Nb- C nanocomposites can be considered as a potential material for electrical contact applications.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Nanocomposite, Niobium carbide, Electrical contact properties, Mechanical properties, Magnetron sputtering
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-71636 (URN)10.1016/j.surfcoat.2011.07.021 (DOI)000295386900023 ()
Note

Funding Agencies|Vinnova (Swedish Governmental Agency for Innovation Systems) through the VINN Excellence Centre FunMat||Swedish Research Council (VR)||

Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2017-12-08

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Tengstrand, Olof

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