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Tengstrand, Olof
Publications (10 of 18) Show all publications
Greczynski, G., Lu, J., Tengstrand, O., Petrov, I., Greene, J. E. & Hultman, L. (2016). Nitrogen-doped bcc-Cr films: Combining ceramic hardness with metallic toughness and conductivity. Scripta Materialia, 122, 40-44
Open this publication in new window or tab >>Nitrogen-doped bcc-Cr films: Combining ceramic hardness with metallic toughness and conductivity
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2016 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 122, p. 40-44Article in journal (Refereed) Published
Abstract [en]

We report the first results on nanostructured N-doped bcc-Cr films exhibiting the unique combination of ceramic hardness with metallic toughness and electrical conductivity at unexpectedly low N concentrations, ~ 5 at.%. The Cr:N films are deposited at 200 C in N2/Ar mixtures by high-power pulsed magnetron sputtering using tunable time-domain control of Cr+ and Cr2+ ion fluxes incident at the film growth surface. Subplanted N atoms impede annealing of metal-ion induced point defects and hinder bcc-Cr grain growth, resulting in a material with a nearly isotropic nanostructure and atomically smooth surface, rather than typical Cr:N solid solutions consisting of faceted microcolumns. © 2016 Elsevier Ltd.

Place, publisher, year, edition, pages
Elsevier Ltd, 2016
Keywords
CrN, HIPIMS, Ion mass spectrometry, Magnetron sputtering, Resistivity, Thin films, Toughness, Transition-metal nitrides
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-129248 (URN)10.1016/j.scriptamat.2016.05.011 (DOI)2-s2.0-84971328580 (Scopus ID)
Note

Funding Agencies|#2011.0143, Swedish Research Council; 2013-4018, Swedish Research Council; 2014-5790, Swedish Research Council

Available from: 2016-06-14 Created: 2016-06-14 Last updated: 2017-11-28
Tengstrand, O., Nedfors, N., Alling, B., Jansson, U., Flink, A., Eklund, P. & Hultman, L. (2014). Incorporation effects of Si in TiCx thin films. Surface & Coatings Technology, 258, 392-397
Open this publication in new window or tab >>Incorporation effects of Si in TiCx thin films
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 258, p. 392-397Article in journal (Refereed) Published
Abstract [en]

Ti-Si-C thin films with varying Si content between 0 to 10 at.% were deposited by DC magnetron sputtering from elemental targets. The effects on microstructure and lattice parameters were investigated using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, and first-principles calculations. The results show that the growth of pure TiCx onto Al2O3(0001) substrates at a temperature of 350 degrees C yields (111) epitaxial and understoichiometric films with x similar to 0.7. For Si contents up to 4 at.%, the TiCx epitaxy is retained locally. Si starts to segregate out from the TiCx to column boundaries at concentrations between 1 and 4 at.%, and causes a transition from epitaxial to polycrystalline growth above 4 at.%. Eventually, the top part of the films form a nanocomposite of crystalline TiC grains surrounded by amorphous SiC and C for Si contents studied up to 10 at.%. The results show that Si takes the place of carbon when incorporated in the TiC lattice.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
First-principles calculations; Thin films; Ti-C; Silicon; Physical vapor deposition (PVD)
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113582 (URN)10.1016/j.surfcoat.2014.08.064 (DOI)000346895000049 ()
Note

Funding Agencies|Swedish Agency for Innovation Systems (VINNOVA); Swedish Research Council (VR) [621-2011-4417]; Knut and Alice Wallenberg Foundation

Available from: 2015-01-23 Created: 2015-01-23 Last updated: 2017-12-05
Tengstrand, O., Nedfors, N., Andersson, M., Lu, J., Jansson, U., Flink, A., . . . Hultman, L. (2014). Model for electron-beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films. Journal of Materials Research, 29(23), 2854-2862
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
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2014 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 29, no 23, p. 2854-2862Article 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
Keywords
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
Nedfors, N., Tengstrand, O., Eklund, P., Hultman, L. & Jansson, U. (2014). Nb-B-C thin films for electrical contact applications deposited by magnetron sputtering. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 32(4), 041503
Open this publication in new window or tab >>Nb-B-C thin films for electrical contact applications deposited by magnetron sputtering
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2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 4, p. 041503-Article in journal (Refereed) Published
Abstract [en]

The high wear resistance, high chemical inertness, and high electrical conductivity of magnetron-sputtered transition metal diborides make them a candidate material for sliding electrical contacts. However, their high hardness makes it difficult to penetrate surface oxides, resulting in a high electrical contact resistance. In this study, the authors have investigated how the contact resistance can be improved by the formation of softer Nb-B-C films. The Nb-B-C films were deposited by magnetron sputtering and shown to exhibit a nanocomposite microstructure consisting of nanocrystalline NbB2-x grains with a solid solution of C separated by an amorphous BCx phase. The formation of the BCx phase reduces the hardness from 41 GPa for the NbB2-x film to 19 GPa at 36 at. % C. As a consequence the contact resistance is drastically reduced and the lowest contact resistance of 35 m Omega (contact force 5N) is achieved for a film containing 30 at. % C. However, crack formation and subsequent delamination and fragmentation is observed for the C-containing Nb-B-C films in tribology tests resulting in high friction values for these films.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-109235 (URN)10.1116/1.4875135 (DOI)000338718400015 ()
Available from: 2014-08-12 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved
Nedfors, N., Tengstrand, O., Flink, A., Andersson, A. M., Eklund, P., Hultman, L. & Jansson, U. (2014). Reactive sputtering of NbCx-based nanocomposite coatings: An up-scaling study. Surface & Coatings Technology, 253, 100-108
Open this publication in new window or tab >>Reactive sputtering of NbCx-based nanocomposite coatings: An up-scaling study
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 253, p. 100-108Article in journal (Refereed) Published
Abstract [en]

Nanocomposite Nb-C coatings, with a C/Nb ratio of 0.93-1.59, have been deposited by reactive sputtering in a commercial sputtering system where the C is supplied from an acetylene gas at deposition rates of up to 200 nm/min. The coatings are compared to non-reactively sputtered Nb-C coatings deposited from Nb and C targets in lab-scale equipment at deposition rates two orders of magnitude lower. X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy are used to conclude that all coatings consist of nanoctystalline Nbc(x) grains (nc-NbCx) embedded in a matrix of amorphous C (a-C). The coating performance was evaluated in terms of their mechanical, tribological, and electrical properties. The chemical stability of the coatings was evaluated by exposure to a flowing mixture of corrosive gases. It is found that the coatings have comparable microstructure and performance to the coatings deposited by non-reactive sputtering. The high deposition rate and presence of different C-radicals on the coating surface during film growth for the reactively sputtered coatings are believed to result in a smaller NbCx grain size compared to the non-reactively sputtered coatings (reactive process: 10-3 nm, non-reactive process: similar to 75-3 nm). This difference results in a thinner a-C matrix of about 0.2 nm, which is not varying with C content for the reactively sputtered coatings. The thinner a-C matrix is reflected in coating properties, with a higher conductivity and slightly higher hardness. The coating richest in C content (C/Nb ratio 1.59) shows the lowest friction (0.23), wear rate (0.17 x 10(-6) mm(3)/mN), and contact resistance before (11 m Omega at 10 N) and after (30 m Omega at 10 N) the chemical stability test. These results imply that nc-NbCx/a-C coatings of this composition are a good candidate for electrical contact applications, and that up-scaling of the process is achievable.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Thin film; Carbide; Electrical contacts; Contact resistance; Friction
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-109358 (URN)10.1016/j.surfcoat.2014.05.021 (DOI)000339150200014 ()
Available from: 2014-08-15 Created: 2014-08-15 Last updated: 2017-12-05Bibliographically approved
Eriksson, A., Tengstrand, O., Lu, J., Jensen, J., Eklund, P., Rosén, J., . . . Hultman, L. (2014). Si incorporation in Ti1-xSixN films grown on TiN(001) and (001)-faceted TiN(111) columns. Surface & Coatings Technology, 257, 121-128
Open this publication in new window or tab >>Si incorporation in Ti1-xSixN films grown on TiN(001) and (001)-faceted TiN(111) columns
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 257, p. 121-128Article in journal (Refereed) Published
Abstract [en]

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiNy tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiNy solid solubility in TiN and probe the effects of surface segregation during the growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1-5 nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550 degrees C and the TiN buffer layers at 900 degrees C On TiN(001), the films are NaCl-structure single-phase metastable Ti1-xSixN(001) with N/(Ti + Si) = 1 and 0 less than= x less than= 0.19. These alloys remain single-crystalline to critical thicknesses h(c) ranging from 100 +/- 30 nm with x = 0.13 to 40 +/- 10 nm with x = 0.19. At thicknesses h greater than h(c), the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiNy. For Ti1-xSixN layers with global average composition values less than x greater than = 0.16, the local x value in the middle of Ti1-xSixN columns increases from 0.08 for columns with radius r similar or equal to 2 nm to x = 0.14 with r similar or equal to 4 nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiNy decreases monotonically with increasing Si fraction less than x greater than, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiNy.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Sputtering; Titanium silicon nitride; Superhardness; Nanocomposite; Solid solution
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112640 (URN)10.1016/j.surfcoat.2014.05.043 (DOI)000344423100016 ()
Note

Funding Agencies|VINN Excellence Center on Functional Nanoscale Materials (FunMat); Swedish Foundation for Strategic Research through the Synergy Grant FUNCASE; Wallenberg Scholar Grant; Doubly-Corrected Linkoping FEI Titan3 60-300 electron microscope

Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2017-12-05
Tengstrand, O., Nedfors, N., Fast, L., Flink, A., Jansson, U., Eklund, P. & Hultman, L. (2014). Structure and electrical properties of Nb-Ge-C nanocomposite coatings. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 32(4), Article ID 041509.
Open this publication in new window or tab >>Structure and electrical properties of Nb-Ge-C nanocomposite coatings
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2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 4, article id 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
Nedfors, N., Tengstrand, O., Lu, J., Eklund, P., Persson, P. O., Hultman, L. & Jansson, U. (2014). Superhard NbB2 −x thin films deposited by dc magnetron sputtering. Surface & Coatings Technology, 257, 295-300
Open this publication in new window or tab >>Superhard NbB2 −x thin films deposited by dc magnetron sputtering
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 257, p. 295-300Article in journal (Refereed) Published
Abstract [en]

We have deposited weakly textured substoichiometric NbB2-x thin films by magnetron sputtering from an NbB2 target. The films exhibit superhardness (42 +/- 4 GPa), previously only observed in overstoichiometric TiB2 thin films, and explained by a self-organized nanostructuring, where thin TiB2 columnar grains hinder nucleation and slip of dislocations and a B-rich tissue phase between the grains prevent grain-boundary sliding. The wide homogeneity range for the NbB2 phase allows a similar ultra-thin B-rich tissue phase to form between thin (5-10 nm) columnar NbB2-x grains also for films with a B/Nb atomic ratio of 1.8, as revealed here by analytical aberration-corrected scanning transmission electron microscopy. Furthermore, a coefficient of friction of 0.16 is measured for an NbB2-x film sliding against stainless steel with a wear rate of 5 x 10(-7) mm(3)/Nm. X-ray photoelectron spectroscopy results suggest that the low friction is due to the formation of a lubricating boric acid film.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Boride; Magnetron sputtering; Structure characterization; Mechanical properties; Friction; Tribological properties
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112641 (URN)10.1016/j.surfcoat.2014.07.087 (DOI)000344423100029 ()
Note

Funding Agencies|Vinnova (Swedish Governmental Agency for Innovation Systems) through the VINN Excellence Centre FunMat; Swedish Foundation of Strategic Research through the Synergy Grant FUNCASE; Knut and Alice Wallenberg Foundation

Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2017-12-05Bibliographically approved
Tengstrand, O. (2014). Transition metal carbide nanocomposite and amorphous thin films. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Transition metal carbide nanocomposite and amorphous thin films
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. p. 50
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1576
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104929 (URN)10.3384/diss.diva-104929 (DOI)978-91-7519-398-4 (ISBN)
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: 2019-11-19Bibliographically approved
Tengstrand, O., Nedfors, N., Andersson, M., Lu, J., Jansson, U., Flink, A., . . . Hultman, L. (2013). Beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films during transmission electron microscopy. MRS COMMUNICATIONS, 3(3), 151-155
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, p. 151-155Article 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
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