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Jansson, Ulf
Alternative names
Publications (10 of 177) Show all publications
Kádas, K., Iusan, D., Hellsvik, J., Cedervall, J., Berastegui, P., Sahlberg, M., . . . Eriksson, O. (2017). AlM2B2 (M =Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials. Journal of Physics: Condensed Matter, 29(15), Article ID 155402.
Open this publication in new window or tab >>AlM2B2 (M =Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 15, 155402Article in journal (Refereed) Published
Abstract [en]

Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono-and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keyword
nanolaminated ternary borides, phase stability, elastic constants, hardness, scanning electron microscopy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-320624 (URN)10.1088/1361-648X/aa602a (DOI)000397921600002 ()28192279 (PubMedID)
Funder
Swedish Research Council
Available from: 2017-08-15 Created: 2017-08-15 Last updated: 2017-08-15Bibliographically approved
Johansson, F., Ahlberg, P., Jansson, U., Zhang, S.-L., Lindblad, A. & Nyberg, T. (2017). Minimizing sputter-induced damage during deposition of WS2 onto graphene. Applied Physics Letters, 110(9), Article ID 091601.
Open this publication in new window or tab >>Minimizing sputter-induced damage during deposition of WS2 onto graphene
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2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 9, 091601Article in journal (Refereed) Published
Abstract [en]

We demonstrate the sputter-deposition of WS2 onto a single-layer graphene film leaving the latter disorder-free. The sputtering process normally causes defects to the graphene lattice and adversely affects its properties. Sputtering of WS2 yields significant amounts of energetic particles, specifically negative S ions, and reflected neutral Ar, and it is therefore used as a model system in this work. The disorder-free sputtering is achieved by increasing the sputteringpressure of Ar thereby shifting the kinetic energy distribution towards lower energies for the impinging particle flux at the substrate. Raman spectroscopy is used to assess the amount of damage to the graphene film. Monte Carlo simulations of the sputteringprocess show that W is completely thermalized already at relatively low sputtering pressure, whereas Ar and S need a comparably higher pressure to thermalize so as to keep the graphene film intact. Apart from becoming completely amorphous at 2.3 mTorr, the graphene filmremains essentially disorder-free when the pressure is increased to 60 mTorr. The approach used here is generally applicable and readily extendable to sputter-deposition of other material combinations onto sensitive substrates. Moreover, it can be used without changing the geometry of an existing sputtering setup.

National Category
Other Physics Topics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-316602 (URN)10.1063/1.4977709 (DOI)000397871600010 ()
Available from: 2017-03-04 Created: 2017-03-04 Last updated: 2017-04-27Bibliographically approved
Nygren, K., Samuelsson, M., Arwin, H. & Jansson, U. (2017). Optical methods to quantify amorphous carbon in carbide-based nanocomposite coatings. Thin Solid Films, 638, 291-297.
Open this publication in new window or tab >>Optical methods to quantify amorphous carbon in carbide-based nanocomposite coatings
2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 638, 291-297 p.Article in journal (Other academic) Published
Abstract [en]

We report how the total carbon content and the amorphous carbon (a-C) phase fraction in transition metal carbide/a-C nanocomposite coatings can be obtained using optical methods, which are much more practical for industrial use than conventional X-ray photoelectron spectroscopy. A large set of carbon-containing nanocomposite coatings deposited using different magnetron sputtering techniques were analyzed by X-ray photoelectron spectroscopy, reflectance spectrophotometry, and spectroscopic ellipsometry. The chemical composition and the a-C phase fraction were determined by X-ray photoelectron spectroscopy for each coating and results are presented for the Ti-C, Cr-C, and Nb-C systems. The composition and the a-C phase fraction are correlated to optical reflectance in the visible range, by parametrization in L*a*b* color space, and by ellipsometry primary data. Results show that it is possible to rapidly estimate the composition and the a-C fraction using these optical methods. We propose that optical methods have promising use in the industry as a cost-efficient technique for characterization of carbide-based coatings.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302062 (URN)10.1016/j.tsf.2017.07.053 (DOI)000411775900038 ()
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2017-12-20Bibliographically approved
Nygren, K., Andersson, A. M., Eklund, P. & Jansson, U. (2017). Passive films on nanocomposite carbide coatings for electrical contact applications. Journal of Materials Science, 52(13), 8231-8246.
Open this publication in new window or tab >>Passive films on nanocomposite carbide coatings for electrical contact applications
2017 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 13, 8231-8246 p.Article in journal (Refereed) Published
Abstract [en]

Nanocomposite transition metal carbide/amorphous carbon coatings (Me-C/a-C) deposited by magnetron sputtering have excellent electrical contact properties. The contact resistance can be as low as that of noble metal coatings, although it is known to vary by several orders of magnitude depending on the deposition conditions. We have investigated a nanocrystalline niobium carbide/amorphous carbon (NbC (x) /a-C:H) model system aiming to clarify factors affecting the contact resistance for this group of contact materials. For the first time, the surface chemistry is systematically studied, by angle-resolved X-ray photoelectron spectroscopy, and in extension how it can explain the contact resistance. The coatings presented a mean oxide thickness of about 1 nm, which could be grown to 8 nm by annealing. Remarkably, the contact resistances covered four orders of magnitude and were found to be exponentially dependent on the mean oxide thickness. Moreover, there is an optimum in the amount of a-C:H phase where the contact resistance drops very significantly and it is thus important to not only consider the mean oxide thickness. To explain the results, a model relying on surface chemistry and contact mechanics is presented. The lowest contact resistance of a nanocomposite matched that of a gold coating at 1 N load (vs. gold), and such performance has previously not been demonstrated for similar nanocomposite materials, highlighting their useful properties for electrical contact applications.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302061 (URN)10.1007/s10853-017-1039-0 (DOI)000399422000050 ()
Funder
Swedish Foundation for Strategic Research VINNOVASwedish Research Council, VR 2011-3492
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2017-05-23Bibliographically approved
Malinovskis, P., Palisaitis, J., Persson, P. O., Jansson, U. & Lewin, E. (2017). Synthesis and characterisation of Mo-B-C thin films deposited by non-reactive DC magnetron sputtering. Surface & Coatings Technology, 309, 506-515.
Open this publication in new window or tab >>Synthesis and characterisation of Mo-B-C thin films deposited by non-reactive DC magnetron sputtering
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 309, 506-515 p.Article in journal (Refereed) Published
Abstract [en]

Thin films in the Mo-B-C system with varying carbon content (up to 37 at.%) were deposited using non-reactive DC magnetron sputtering. The phase composition and microstructure were determined and the potential use of the films in sliding electrical contact applications was evaluated. Films with lower than 23 at.% carbon content consisted of nanocrystalline MoB2 - x grains surrounded by an amorphous tissue phase (a-B for binary, and a-BCx for ternary films). With increasing carbon content grain sizes was found to decrease (from 16 to 5 nm), and above 23 at.% carbon the films deposited at room temperature were X-ray amorphous. Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy reveal that these films contain Mo-rich and Mo-poor regions, and thus are two-phase amorphous nanocomposites. Low-carbon content samples exhibited a friction coefficient against the steel counter surface of 1.1; this was reduced to 0.8 for high carbon-content films. Analysis of the tribofilm revealed formation of molybdenum oxide and amorphous carbon, however without significant lubricating effect at room temperature. Hardness and elastic modulus decrease with carbon content from similar to 29 to similar to 22 GPa and similar to 526 to similar to 326 GPa. These values give an WE ratio of 0.06 to 0.07, indicating brittle material. Resistivity was found to increase with carbon content from similar to 175 mu Omega cm for binary Mo-B to similar to 395 mu Omega cm for Mo-B-C thin film with 37 at.% of C. Therefore all the above results suggest that the Mo-B-C films are not suitable for sliding electrical contacts.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keyword
Mo-B-C, Magnetron sputtering, Films, Hard coatings, Molybdenum diboride, Nanocomposite
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-319135 (URN)10.1016/j.surfcoat.2016.12.003 (DOI)000396184400059 ()
Funder
Swedish Research Council, 621-2012-4359 622-2008-405Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research , RMA11-0029
Available from: 2017-03-31 Created: 2017-03-31 Last updated: 2018-01-18Bibliographically approved
Nygren, K., Folkenant, M., Jansson, U. & Nyholm, L. (2017). The influence of nanoeffects on the oxidation of magnetron sputtered Cr-C/Ag thin films containing silver nanoparticles. Chemelectrochem, 4(2), 418-429.
Open this publication in new window or tab >>The influence of nanoeffects on the oxidation of magnetron sputtered Cr-C/Ag thin films containing silver nanoparticles
2017 (English)In: Chemelectrochem, ISSN 2196-0216, Vol. 4, no 2, 418-429 p.Article in journal (Refereed) Published
Abstract [en]

Well-controlled functionalization of carbide-based nanocomposite films with noble-metal surface nanoparticles of different sizes may lead to new materials with novel multifunctional properties. In this work, magnetron sputtering was used to deposit nanocomposite films comprising amorphous chromium carbide (a-CrCx), amorphous carbon (a-C), and a minority of silver in the form of embedded nanoclusters. Up to 510(10) surface nanoparticles per cm(2) with different size distributions were also found to be formed, owing to the diffusion of silver from the bulk of the film. The influences of these conductive nanoparticles on the electrochemical behavior of the films were investigated in dilute sulfuric acid. Although silver is a noble metal, the oxidation potential of the nanoparticles was about 0.4V more negative than the Ag+/Ag standard potential, meaning that the nanoparticles were oxidized in the Cr passive potential region. While this effect can mainly be explained by a low concentration of Ag+ in the electrolyte, the sizes of the nanoparticles and interactions with the matrix were also found to be important. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the surface chemistries. As Ag can be replaced by other noble metals, the concept is of general interest for further studies.

Keyword
Nanoelectrochemistry, Noble metals, Carbides, Nanoparticles, Thin films
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-302060 (URN)10.1002/celc.201600615 (DOI)000394905900026 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2017-04-25Bibliographically approved
Mao, F., Nyberg, T., Thersleff, T., Andersson, A. & Jansson, U. (2016). Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure. Materials & Design, 91, 132-142.
Open this publication in new window or tab >>Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure
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2016 (English)In: Materials & Design, ISSN 0261-3069, Vol. 91, 132-142 p.Article in journal (Refereed) Published
Abstract [en]

The main objective of this study is to demonstrate the strength of the combinatorial approach to rapidly and effectively identify suitable process parameters for the synthesis of AgFeO2 filmswith layered delafossite structure. (00l)- textured delafossite AgFeO2 thin films have been successfully deposited for the first time without post-annealing by magnetron sputtering from elemental silver and iron targets in a reactive Ar-O-2 atmosphere. Gradient filmswith a wide composition range were deposited on singlewafers and subsequent screenings of phase- and chemical compositions were employed to optimize process parameters. The optimum deposition temperature for single-phase AgFeO2 growth was 450 degrees C using a Ag target powered at 15 W with a pulsing frequency of 150 kHz and a Fe target powered at constant 120 W at a total pressure of 4 mTorr and a O-2 partial pressure of 0.8 mTorr. Selected films were studied with scanning electron microcopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The optical band gap for the indirect transition in the AgFeO2 film was determined to 1.7 +/- 0.1 eV, and the band gap for the direct transition was 2.5 +/- 0.1 eV. The film showed insulating electrical properties.

Keyword
Combinatorial sputtering, Delafossite, Thin film, AgFeO2
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-274897 (URN)10.1016/j.matdes.2015.11.092 (DOI)000367235400016 ()
External cooperation:
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageKnut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2016-02-02 Created: 2016-01-26 Last updated: 2017-11-30Bibliographically approved
Mao, F., Taher, M., Kryshtal, O., Kruk, A., Czyrska-Filemonowicz, A., Ottosson, M., . . . Jansson, U. (2016). Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties. ACS Applied Materials and Interfaces, 8(44), 30635-30643.
Open this publication in new window or tab >>Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties
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2016 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 44, 30635-30643 p.Article in journal (Refereed) Published
Abstract [en]

A combinatorial approach is applied to rapidly deposit and screen Ag-Al thin films-to evaluate the mechanical, tribological, and electrical properties as a function of chemical composition. Ag-Al thin films with large continuous composition gradients (6-60 atom % Al) were deposited by a custom-designed combinatorial magnetron sputtering system. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and four-point electrical resistance screening were employed to characterize the chemical composition, structure, and physical properties of the films in a time-efficient way. For low Al contents (<13 atom %), a highly (111)-textured fcc phase was formed. At higher Al contents, a (002)-textured hcp solid solution phase was formed followed by a fcc phase in the most At-rich regions. No indication of a mu phase was observed. The Ag-Al films with fcc-Ag matrix is prone to adhesive material transfer leading to a high friction coefficient (>1) and adhesive wear, similar to the behavior of pure Ag. In contrast, the hexagonal solid solution phase (from ca. 15 atom %Al) exhibited dramatically reduced friction coefficients (about 15% of that of the fcc phase) and dramatically reduced adhesive wear when tested against the pure Ag counter surface. The increase in contact resistance of the Ag Al films is limited to only 50% higher than a pure Ag reference sample at the low friction and low wear region (19-27 atom %). This suggests that a hcp Ag Al alloy can have a potential use in sliding electrical contact applications and in the future will replace pure Ag in specific electromechanical applications.

Keyword
Ag-Al alloy, combinatorial approach, low friction, adhesive wear, hexagonal phase, electrical contact
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-310756 (URN)10.1021/acsami.6b10659 (DOI)000387737200089 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 38432-1Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved
Ahlberg, P., Johansson, F., Zhang, Z., Jansson, U., Zhang, S.-L., Lindblad, A. & Nyberg, T. (2016). Defect formation in graphene during low-energy ion bombardment [Letter to the editor]. APL Materials, 4(4), Article ID 046104.
Open this publication in new window or tab >>Defect formation in graphene during low-energy ion bombardment
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2016 (English)In: APL Materials, ISSN 2166-532X, Vol. 4, no 4, 046104Article in journal, Letter (Refereed) Published
Abstract [en]

This letter reports on a systematic investigation of sputter induced damage in graphene caused by low energy Ar+ ion bombardment. The integral numbers of ions per area (dose) as well as their energies are varied in the range of a few eV's up to 200 eV. The defects in the graphene are correlated to the dose/energy and different mechanisms for the defect formation are presented. The energetic bombardment associated with the conventional sputter deposition process is typically in the investigated energy range. However, during sputter deposition on graphene, the energetic particle bombardment potentially disrupts the crystallinity and consequently deteriorates its properties. One purpose with the present study is therefore to demonstrate the limits and possibilities with sputter deposition of thin films on graphene and to identify energy levels necessary to obtain defect free graphene during the sputter deposition process. Another purpose is to disclose the fundamental mechanisms responsible for defect formation in graphene for the studied energy range.

National Category
Materials Chemistry Nano Technology
Identifiers
urn:nbn:se:uu:diva-284702 (URN)10.1063/1.4945587 (DOI)000375846100007 ()
Funder
Knut and Alice Wallenberg Foundation, 2011.0082Swedish Research Council, 2014-5591 2014-6463
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2017-01-25Bibliographically approved
Sahlberg, M., Karlsson, D., Zlotea, C. & Jansson, U. (2016). Superior hydrogen storage in high entropy alloys. Scientific Reports, 6, Article ID 36770.
Open this publication in new window or tab >>Superior hydrogen storage in high entropy alloys
2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, 36770Article in journal (Refereed) Published
Abstract [en]

Metal hydrides (MHx) provide a promising solution for the requirement to store large amounts of hydrogen in a future hydrogen-based energy system. This requires the design of alloys which allow for a very high H/M ratio. Transition metal hydrides typically have a maximum H/M ratio of 2 and higher ratios can only be obtained in alloys based on rare-earth elements. In this study we demonstrate, for the first time to the best of our knowledge, that a high entropy alloy of TiVZrNbHf can absorb much higher amounts of hydrogen than its constituents and reach an H/M ratio of 2.5. We propose that the large hydrogen-storage capacity is due to the lattice strain in the alloy that makes it favourable to absorb hydrogen in both tetrahedral and octahedral interstitial sites. This observation suggests that high entropy alloys have future potential for use as hydrogen storage materials.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-310755 (URN)10.1038/srep36770 (DOI)000388087800001 ()27829659 (PubMedID)
Funder
Swedish Foundation for Strategic Research
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved
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