Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Transition metal carbide nanocomposite and amorphous thin films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact resistance and high mechanical strength. Electrical contacts are one example of application that has been of special interest in this thesis. Since some industrially important substrates used in electrical contacts soften at higher temperature, all films were deposited with dc magnetron sputtering at a low substrate temperature (200-350 °C).

I show that the electrical resistivity and mechanical properties of composites consisting of nanocrystalline NbC grains (nc-NbC) in a matrix of amorphous C (a-C) depend strongly on the amount of amorphous C. The best combination of hardness (23 GPa) and electrical resistivity (260 μΩ*cm) are found in films with ~15 at.% a-C phase. This is a higher hardness and lower resistivity than measured for the more well studied Ti-C system if deposited under similar conditions. The better results can be explained by a thinner matrix of amorphous C phase in the case of NbC. The nc-NbC/a-C is therefore interesting as a material in electrical contacts.

Si can be added to further control the structure and thereby the properties of binary Me-C systems. There are however, different opinions in the literature of whether Si is incorporated on the Ti or C site in the cubic NaCl (B1) structure of TiC. In order to understand how Si is incorporated in a Me-Si-C material I use a model system of epitaxial TiCx (x ~0.7). In this model system a few atomic percent of Si can be incorporated in the cubic TiC structure. The experimental results together with theoretical stability calculations suggest that the Si is positioned at the C sites forming Ti(Si,C)x. The calculation further shows a strong tendency for Si segregation, which is seen at higher Si contents in the experiments, where Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy.

If Si is added to an Nb-C nanocomposite, it hinders the grain growth and thus a reduced size of the NbC grains is observed. The Si segregates to the amorphous matrix forming a-SiC. At the same time the resistivity increases and the hardness is reduced. With even higher amounts of Si (>25 at.%) into the Nb-Si-C material, grain growth is no longer possible and the material becomes amorphous. In order to separate between effects from the addition of Si and the choice of transition metal I compare the Nb-Si-C system to already published results for the Zr-Si-C system. I find that the hardness of the material depends on the amount of strong Si-C bonds rather than the type of transition metal. The reduced elastic modulus is, however, dependent on the choice of transition metal. I therefore suggest that it is possible to make Me-Si-C films with high wear resistance by an appropriate choice of transition metal and composition.

Electron microscopy was of importance for determining amorphous structures of Nb-Si-C and Zr-Si-C at high Si contents. However, the investigations were obstructed by electron beam induced crystallization. Further investigations show that the energy transferred from the beam electrons to C and Si atoms in the material is enough to cause atomic displacements. The displacements cause volume fluctuations and thereby enhance the mobility of all the atoms in the material. The result is formation of MeC grains, which are stable to further irradiation.

Finally, I have studied substitution of Ge for Si in a ternary system looking at Nb-Ge-C thin films. I show that the films consist of nc-NbC/a-C/a-Ge and that Ge in a similar way to Si decreases the size of the crystalline NbC grains. However, a transition to a completely amorphous material is not seen even at high Ge contents (~30 at.%). Another dissimilarity is that while Si bonds to C and forms a matrix of a-SiC, Ge tends to bond to Ge.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 50 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1576
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-104929DOI: 10.3384/diss.diva-104929ISBN: 978-91-7519-398-4 (print)OAI: oai:DiVA.org:liu-104929DiVA: diva2:700151
Public defence
2014-03-28, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2016-12-28Bibliographically approved
List of papers
1. 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
Show others...
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
2. Incorporation effects of Si in TiCx thin films
Open this publication in new window or tab >>Incorporation effects of Si in TiCx thin films
Show others...
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
3. Characterization of amorphous and nanocomposite Nb–Si–C thin films deposited by DC magnetron sputtering
Open this publication in new window or tab >>Characterization of amorphous and nanocomposite Nb–Si–C thin films deposited by DC magnetron sputtering
Show others...
2013 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 545, 272-278 p.Article in journal (Refereed) Published
Abstract [en]

Two series of Nb–Si–C thin films of different composition have been deposited using DC magnetron sputtering. In the first series the carbon content was kept at about 55 at.% while the Si/Nb ratio was varied and in the second series the C/Nb ratio was varied instead while the Si content was kept at about 45 at.%. The microstructure is strongly dependent on Si content and Nb–Si–C films containing more than 25 at.% Si exhibit an amorphous structure as determined by X-ray diffraction. Transmission electron microscopy, however, induces crystallisation during analysis, thus obstructing a more detailed analysis of the amorphous structure. X-ray photo-electron spectroscopy suggests that the amorphous films consist of a mixture of chemical bonds such as Nb–Si, Nb–C, and Si–C. The addition of Si results in a hardness decrease from 22 GPa for the binary Nb–C film to 18 – 19 GPa for the Si-containing films, while film resistivity increases from 211 μΩcm to 3215 μΩcm. Comparison with recently published results on DC magnetron sputtered Zr–Si–C films, deposited in the same system using the same Ar-plasma pressure, bias, and a slightly lower substrate temperature (300 °C instead of 350 °C), shows that hardness is primarily dependent on the amount of Si–C bonds rather than type of transition metal. The reduced elastic modulus on the other hand shows a dependency on the type of transition metal for the films. These trends for the mechanical properties suggest that high wear resistant (high H/E and H3/E2 ratio) Me–Si–C films can be achieved by appropriate choice of film composition and transition metal.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Magnetron sputtering, Carbide, Amorphous structure, Structure characterization, Mechanical properties, Electrical properties
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-100023 (URN)10.1016/j.tsf.2013.08.066 (DOI)000324820800045 ()
Note

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

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06
4. 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
Show others...
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
5. Model for electron-beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films
Open this publication in new window or tab >>Model for electron-beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films
Show others...
2014 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 29, no 23, 2854-2862 p.Article in journal (Refereed) Published
Abstract [en]

We use transmission electron microscopy (TEM) for in-situ studies of electronbeam-induced crystallization behavior in thin films of amorphous transition metal silicon carbides based on Zr (group 4 element) and Nb (group 5). Higher silicon content stabilized the amorphous structure while no effects of carbon were detected. Films with Nb start to crystallize at lower electron doses than Zr-containing ones. During the crystallization equiaxed MeC grains are formed in all samples with larger grains for Zr (~5nm) compared to Nb (~2nm). Eventually the sample stabilizes and the crystallization process stops. A model is presented where the metal carbide grains nucleate and grow while Si segregates into the remaining amorphous matrix. At a certain Si concentration in the matrix the graingrowth stops.

Place, publisher, year, edition, pages
Materials Research Society, 2014
Keyword
transmission electron microscopy (TEM); electron irradiation; radiation effects
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104926 (URN)10.1557/jmr.2014.345 (DOI)000346431100010 ()
Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2017-12-05Bibliographically approved
6. Structure and electrical properties of Nb-Ge-C nanocomposite coatings
Open this publication in new window or tab >>Structure and electrical properties of Nb-Ge-C nanocomposite coatings
Show others...
2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 4, 041509Article in journal (Refereed) Published
Abstract [en]

Nb-Ge-C nanocomposite thin films were deposited by dc magnetron sputtering using three elemental targets. The films consist of substoichiometric NbCx in a nanometer-thick matrix of amorphous C and Ge. Films with no Ge contain grains that are elongated in the growth direction with a (111) preferred crystallographic orientation. With the addition of ∼12 at. % Ge, the grains are more equiaxed and exhibit a more random orientation. At even higher Ge contents, the structure also becomes denser. The porous structure of the low Ge content films result in O uptake from the ambient. With higher C content in the films both the amount of amorphous C and C/Nb-ratio increases. The contact resistance was measured by four-point technique as a function of contact force between 0 and 10 N. The lowest contact resistance (1.7 mΩ) is obtained at 10 N. The resistivity varies between 470 and 1700 μΩ·cm depending on porosity and O content.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-109236 (URN)10.1116/1.4882856 (DOI)000338718400021 ()
Note

At the time for thesis presentation publication was in status: Manuscript

Available from: 2014-08-12 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved

Open Access in DiVA

Transition metal carbide nanocomposite and amorphous thin films(1794 kB)893 downloads
File information
File name FULLTEXT01.pdfFile size 1794 kBChecksum SHA-512
c30104ef6ff8ece1339ab9ea265e0379248ff06f6e6ab517126c455b093a35bf57e2807f1df4b92fc029cd6e842316fcd2e7008b734b496407ef322029a1ff93
Type fulltextMimetype application/pdf
omslag(3217 kB)27 downloads
File information
File name COVER01.pdfFile size 3217 kBChecksum SHA-512
6983635290c5e0b5936e6ec0bd118bddca4ad8b9d25c629dd32a71d32fe39f86d54327f2714d59e1529d1655e09c3e7629f1babaa1145332e1ec9e9d0be11167
Type coverMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Tengstrand, Olof
By organisation
Thin Film PhysicsThe Institute of Technology
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 893 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
isbn
urn-nbn

Altmetric score

doi
isbn
urn-nbn