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  • 201.
    Chubarov, M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Engelbrecht, J.A. A.
    Nelson Mandela Metropolitan University, South Africa .
    O'Connel, J.
    Nelson Mandela Metropolitan University, South Africa .
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Boron nitride: A new photonic material2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, p. 29-34Article in journal (Refereed)
    Abstract [en]

    Rhombohedral boron nitride (r-BN) layers were grown on sapphire substrate in a hot-wall chemical vapor deposition reactor. Characterization of these layers is reported in details. X-ray diffraction (XRD) is used as a routine characterization tool to investigate the crystalline quality of the films and the identification of the phases is revealed using detailed pole figure measurements. Transmission electron microscopy reveals stacking of more than 40 atomic layers. Results from Fourier Transform InfraRed (FTIR) spectroscopy measurements are compared with XRD data showing that FTIR is not phase sensitive when various phases of sp(2)-BN are investigated. XRD measurements show a significant improvement of the crystalline quality when adding silicon to the gas mixture during the growth; this is further confirmed by cathodoluminescence which shows a decrease of the defects related luminescence intensity.

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  • 202.
    Chubarov, M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Engelbrecht, J.A. A.
    Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
    O'Connel, J.
    Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Characterization of Boron Nitride Thin Films2013Conference paper (Refereed)
    Abstract [en]

    Rhombohedral Boron Nitride layers were grown on sapphire substrate in a hot-wall CVD reactor. The characterization of those layers is reported and the results are discussed in correlation with the various growth parameters used.

  • 203. Order onlineBuy this publication >>
    Chubarov, Mikhail
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Chemical Vapour Deposition of sp2 Hybridised Boron Nitride2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this work was to develop a chemical vapour deposition process and understand the growth of sp2 hybridised Boron Nitride (sp2-BN). Thus, the growth on different substrates together with the variation of growth parameters was investigated in details and is presented in the papers included in this thesis. Deposited films of sp2-BN were characterised with the purpose to determine optimal deposition process parameters for the growth of high crystal quality thin films with further investigations of chemical composition, morphology and other properties important for the implementation of this material towards electronic, optoelectronic devices and devices based on graphene/BN heterostructures.

    For the growth of sp2-BN triethyl boron and ammonia were employed as B and N precursors, respectively. Pure H2 as carrier gas is found to be necessary for the growth of crystalline sp2-BN. Addition of small amount of silane to the gas mixture improves the crystalline quality of the growing sp2-BN film.

    It was observed that for the growth of crystalline sp2-BN on c-axis oriented α-Al2O3 a thin and strained AlN buffer layer is needed to support epitaxial growth of sp2-BN, while it was possible to deposit rhombohedral BN (r-BN) on various polytypes of SiC without the need for a buffer layer. The growth temperature suitable for the growth of  crystalline sp2-BN is 1500 °C. Nevertheless, the growth of crystalline sp2-BN was also observed on α-Al2O3 with an AlN buffer layer at a lower temperature of 1200 °C. Growth at this low temperature was found to be hardly controllable due to the low amount of Si that is necessary at this temperature and its accumulation in the reaction cell. When SiC was used as a substrate at the growth temperature of 1200 °C, no crystalline sp2-BN was formed, according to X-ray diffraction.

    Crystalline structure investigations of the deposited films showed formation of twinned r-BN on both substrates used. Additionally, it was found that the growth on α-Al2O3 with an AlN buffer layer starts with the formation of hexagonal BN (h-BN) for a thickness of around 4 nm. The formation of h-BN was observed at growth temperatures of 1200 °C and 1500 °C on α-Al2O3 with AlN buffer layer while there were no traces of h-BN found in the films deposited on SiC substrates in the temperature range between 1200 °C and 1700 °C. As an explanation for such growth behaviour, reproduction of the substrate crystal stacking is suggested.  Nucleation and growth mechanism are investigated and presented in the papers included in this thesis.

    List of papers
    1. Epitaxial CVD growthof sp2-hybridized boron nitrideusing aluminum nitride as buffer layer
    Open this publication in new window or tab >>Epitaxial CVD growthof sp2-hybridized boron nitrideusing aluminum nitride as buffer layer
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    2011 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, no 10-11, p. 397-399Article in journal (Refereed) Published
    Abstract [en]

    Epitaxial growth of sp2-hybridized boron nitride (BN) using chemical vapour deposition, with ammonia and triethyl boron as precursors, is enabled on sapphire by introducing an aluminium nitride (AlN) buffer layer. This buffer layer is formed by initial nitridation of the substrate. Epitaxial growth is verified by X-ray diffraction measurements in Bragg–Brentano configuration, pole figure measurements and transmission electron microscopy. The in-plane stretching vibration of sp2-hybridized BN is observed at 1366 cm–1 from Raman spectroscopy. Time-of-flight elastic recoil detection analysis confirms almost perfect stoichiometric BN with low concentration of carbon, oxygen and hydrogen contaminations.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2011
    Keywords
    chemical vapor deposition;BN;epitaxy;X-ray diffraction
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-73160 (URN)10.1002/pssr.201105410 (DOI)000297747600014 ()
    Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-08
    2. Growth of High Quality Epitaxial Rhombohedral Boron Nitride
    Open this publication in new window or tab >>Growth of High Quality Epitaxial Rhombohedral Boron Nitride
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    2012 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 6, p. 3215-3220Article in journal (Refereed) Published
    Abstract [en]

    Epitaxial growth of sp(2)-hybridized boron nitride (sp(2) BN) films on sapphire substrates is demonstrated in a hot wall chemical vapor deposition reactor at the temperature of 1500 degrees C, using triethyl boron and ammonia as precursors. The influence of the main important process parameters, temperature, N/B ratio, B/H-2 ratio, and carrier gas composition on the quality of the grown layers is investigated in detail. X-ray diffraction shows that epitaxial rhombohedral BN (r-BN) film can be deposited only in a narrow process parameter window; outside this window either turbostratic-BN or amorphous BN is favored if BN is formed. In addition, a thin strained AlN buffer layer is needed to support epitaxial growth of r-BN film on sapphire since only turbostratic BN is formed on sapphire substrate. The quality of the grown film is also affected by the B/H-2 ratio as seen from a change of the spacing between the basal planes as revealed by X-ray diffraction. Time-of-flight elastic recoil detection analysis shows an enhancement of the C and O impurities incorporation at lower growth temperatures. The gas phase chemistry for the deposition is discussed as well as the impact of the growth rate on the quality of the BN film.

    Place, publisher, year, edition, pages
    American Chemical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-79095 (URN)10.1021/cg300364y (DOI)000304838000062 ()
    Note

    Funding Agencies|Swedish Research Council|VR 621-2009-5264VR 622-2008-1247|

    Available from: 2012-06-29 Created: 2012-06-29 Last updated: 2017-12-07
    3. On the effect of silicon in CVD of sp2 hybridized boron nitride thin films
    Open this publication in new window or tab >>On the effect of silicon in CVD of sp2 hybridized boron nitride thin films
    2013 (English)In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 3, p. 455-458Article in journal (Refereed) Published
    Abstract [en]

    The influence of silicon on the growth of epitaxial rhombohedral boron nitride (r-BN) films deposited on sapphire (0001) by chemical vapor deposition is investigated. X-ray diffraction measurements and secondary ion mass spectrometry show that silicon favors the formation of r-BN and is incorporated into the film.

    Place, publisher, year, edition, pages
    Royal Society of Chemistry, 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-87243 (URN)10.1039/c2ce26423d (DOI)000312197600006 ()
    Note

    Funding Agencies|Swedish Research Council|VR 621-2009-5264VR 622-2008-1247|

    Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
    4. Chemical vapour deposition of epitaxial rhombohedral BN thin films on SiC substrates
    Open this publication in new window or tab >>Chemical vapour deposition of epitaxial rhombohedral BN thin films on SiC substrates
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    2014 (English)In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 24, p. 5430-5436Article in journal (Refereed) Published
    Abstract [en]

    Epitaxial growth of rhombohedral boron nitride (r-BN) on different polytypes of silicon carbide (SiC) is demonstrated using thermally activated hot-wall chemical vapour deposition and triethyl boron and ammonia as precursors. With respect to the crystalline quality of the r-BN films, we investigate the influence of the deposition temperature, the precursor ratio (N/B) and the addition of a minute amount of silicon to the gas mixture. From X-ray diffraction and transmission electron microscopy, we find that the optimal growth temperature for epitaxial r-BN on the Si-face of the SiC substrates is 1500 degrees C at a N/B ratio of 642 and silicon needs to be present not only in the gas mixture during deposition but also on the substrate surface. Such conditions result in the growth of films with a c-axis identical to that of the bulk material and a thickness of 200 nm, which is promising for the development of BN films for electronic applications.

    Place, publisher, year, edition, pages
    Royal Society of Chemistry, 2014
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-108816 (URN)10.1039/c4ce00381k (DOI)000336839900032 ()
    Available from: 2014-07-07 Created: 2014-07-06 Last updated: 2017-12-05
    5. Polytype pure sp2-BN thin films as dictated by the substrate crystal structure
    Open this publication in new window or tab >>Polytype pure sp2-BN thin films as dictated by the substrate crystal structure
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    2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 5, p. 1640-1645Article in journal (Refereed) Published
    Abstract [en]

    Boron nitride (BN) is a promising semiconductor material, but its current exploration is hampered by difficulties in growth of single crystalline phase-pure thin films. We compare the growth of sp2-BN by chemical vapor deposition on (0001) 6H-SiC and on (0001) α-Al2O3 substrates with an AlN buffer layer. Polytype-pure rhombohedral BN (r-BN) with a thickness of 200 nm is observed on SiC whereas hexagonal BN (h-BN) nucleates and grows on the AlN buffer layer. For the latter case after a thickness of 4 nm, the h-BN growth is followed by r-BN growth to a total thickness of 200 nm. We find that the polytype of the sp2-BN films is determined by the ordering of Si-C or Al-N atomic pairs in the underlying crystalline structure (SiC or AlN). In the latter case the change from h-BN to r-BN is triggered by stress relaxation. This is important for the development of BN semiconductor device technology.

    Place, publisher, year, edition, pages
    Washington: American Chemical Society (ACS), 2015
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-112577 (URN)10.1021/cm5043815 (DOI)000350919000025 ()
    Note

    This work was supported by the Swedish Research Council (VR, Grant 621-2013-5585), Carl Tryggers Foundation (No. 12:175), and the CeNano program at Linkoping University. H.H. acknowledges support from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU No. 2009-00971). Z.C. acknowledges the support of the Bolyai Janos research scholarship of the Hungarian Academy of Sciences. The Knut and Alice Wallenberg (KAW) Foundation is acknowledged for the Electron Microscope Laboratory in Linkoping. Sven G. Andersson is gratefully acknowledged for his technical support of the growth activities.

    Available from: 2014-12-04 Created: 2014-12-04 Last updated: 2017-12-05Bibliographically approved
    6. Nucleation and initial growth of sp2-BNon α-Al2O3 and SiC by chemical vapour deposition
    Open this publication in new window or tab >>Nucleation and initial growth of sp2-BNon α-Al2O3 and SiC by chemical vapour deposition
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    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Knowledge on thin films evolution from the early stages of growth is important for the control of quality and properties of the film. Here we present study of the early growth stages and evolution of the crystalline structure of sp2 hybridised Boron Nitride (BN) thin films deposited by chemical vapour deposition from triethyl boron and ammonia. Nucleation of hexagonal BN (h-BN) is observed already at 1200 °C on α-Al2O3 substrate with an AlN buffer layer (AlN/α-Al2O3) while no formation of h-BN is detected when the growth is done on 6H-SiC in a growth temperature range between 1200 °C and 1700 °C. We demonstrate that h-BN grows on AlN/α-Al2O3 exhibiting a layer-by-layer growth mode up to ca. 4 nm followed by a transition to r-BN growth when grown at 1500 °C. The following r-BN growth is suggested to proceed with mixed layer-by-layer and island growth mode; after a thin continuous layer of r-BN, islands formation is favoured leading to a twinned r-BN structure of the film. We find that h-BN does not grow on 6H-SiC substrates instead r-BN nucleates and grows directly as a twinned crystal. The twinning is found to be suppressed by a surface preparation of the SiC substrate with SiH4 prior to BN growth. These results open up for a more controlled epitaxial growth of sp2-BN for future electronic applications.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-112578 (URN)
    Available from: 2014-12-04 Created: 2014-12-04 Last updated: 2015-03-11Bibliographically approved
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    Chemical Vapour Deposition of sp2 Hybridised Boron Nitride
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  • 204.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Challenge in determining the crystal structure of epitaxial 0001 oriented sp(2)-BN films2018In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 36, no 3, article id 030801Article, review/survey (Refereed)
    Abstract [en]

    Boron nitride (BN) as a thin film is promising for many future electronic applications. On 0001 alpha-Al2O3 and 0001 4H/6H-SiC substrates, chemical vapor deposition yields epitaxial sp(2)-hybridized BN (sp(2)-BN) films oriented around the c-axis. Here, the authors seek to point out that sp(2)-BN can form two different polytypes; hexagonal BN (h-BN) and rhombohedral BN (r-BN), only differing in the stacking of the basal planes but with the identical distance between the basal planes and in-plane lattice parameters. This makes structural identification challenging in c- axis oriented films. The authors suggest the use of a combination of high-resolution electron microscopy with careful sample preparation and thin film x-ray diffraction techniques like pole figure measurements and glancing incidence (in-plane) diffraction to fully distinguish h-BN from r-BN. (C) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.

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  • 205.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zsolt
    Hungarian Academic Science, Hungary .
    Andersson, Sven G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nucleation and initial growth of sp2-BNon α-Al2O3 and SiC by chemical vapour deposition2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Knowledge on thin films evolution from the early stages of growth is important for the control of quality and properties of the film. Here we present study of the early growth stages and evolution of the crystalline structure of sp2 hybridised Boron Nitride (BN) thin films deposited by chemical vapour deposition from triethyl boron and ammonia. Nucleation of hexagonal BN (h-BN) is observed already at 1200 °C on α-Al2O3 substrate with an AlN buffer layer (AlN/α-Al2O3) while no formation of h-BN is detected when the growth is done on 6H-SiC in a growth temperature range between 1200 °C and 1700 °C. We demonstrate that h-BN grows on AlN/α-Al2O3 exhibiting a layer-by-layer growth mode up to ca. 4 nm followed by a transition to r-BN growth when grown at 1500 °C. The following r-BN growth is suggested to proceed with mixed layer-by-layer and island growth mode; after a thin continuous layer of r-BN, islands formation is favoured leading to a twinned r-BN structure of the film. We find that h-BN does not grow on 6H-SiC substrates instead r-BN nucleates and grows directly as a twinned crystal. The twinning is found to be suppressed by a surface preparation of the SiC substrate with SiH4 prior to BN growth. These results open up for a more controlled epitaxial growth of sp2-BN for future electronic applications.

  • 206.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zsolt
    Hungarian Academic Science, Hungary .
    Garbrecht, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Polytype pure sp2-BN thin films as dictated by the substrate crystal structure2015In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 5, p. 1640-1645Article in journal (Refereed)
    Abstract [en]

    Boron nitride (BN) is a promising semiconductor material, but its current exploration is hampered by difficulties in growth of single crystalline phase-pure thin films. We compare the growth of sp2-BN by chemical vapor deposition on (0001) 6H-SiC and on (0001) α-Al2O3 substrates with an AlN buffer layer. Polytype-pure rhombohedral BN (r-BN) with a thickness of 200 nm is observed on SiC whereas hexagonal BN (h-BN) nucleates and grows on the AlN buffer layer. For the latter case after a thickness of 4 nm, the h-BN growth is followed by r-BN growth to a total thickness of 200 nm. We find that the polytype of the sp2-BN films is determined by the ordering of Si-C or Al-N atomic pairs in the underlying crystalline structure (SiC or AlN). In the latter case the change from h-BN to r-BN is triggered by stress relaxation. This is important for the development of BN semiconductor device technology.

  • 207.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    On the effect of silicon in CVD of sp2 hybridized boron nitride thin films2013In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 3, p. 455-458Article in journal (Refereed)
    Abstract [en]

    The influence of silicon on the growth of epitaxial rhombohedral boron nitride (r-BN) films deposited on sapphire (0001) by chemical vapor deposition is investigated. X-ray diffraction measurements and secondary ion mass spectrometry show that silicon favors the formation of r-BN and is incorporated into the film.

  • 208.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Czigany, Zsolt
    Hungarian Academic Science, Hungary.
    Initial stages of growth and the influence of temperature during chemical vapor deposition of sp(2)-BN films2015In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 33, no 6, p. 061520-Article in journal (Refereed)
    Abstract [en]

    Knowledge of the structural evolution of thin films, starting by the initial stages of growth, is important to control the quality and properties of the film. The authors present a study on the initial stages of growth and the temperature influence on the structural evolution of sp(2) hybridized boron nitride (BN) thin films during chemical vapor deposition (CVD) with triethyl boron and ammonia as precursors. Nucleation of hexagonal BN (h-BN) occurs at 1200 degrees C on alpha-Al2O3 with an AlN buffer layer (AlN/alpha-Al2O3). At 1500 degrees C, h-BN grows with a layer-by-layer growth mode on AlN/alpha-Al2O3 up to similar to 4 nm after which the film structure changes to rhombohedral BN (r-BN). Then, r-BN growth proceeds with a mixed layer-by-layer and island growth mode. h-BN does not grow on 6H-SiC substrates; instead, r-BN nucleates and grows directly with a mixed layer-by-layer and island growth mode. These differences may be caused by differences in substrate surface temperature due to different thermal conductivities of the substrate materials. These results add to the understanding of the growth process of sp(2)-BN employing CVD. (C) 2015 American Vacuum Society.

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  • 209.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of High Quality Epitaxial Rhombohedral Boron Nitride2012In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 6, p. 3215-3220Article in journal (Refereed)
    Abstract [en]

    Epitaxial growth of sp(2)-hybridized boron nitride (sp(2) BN) films on sapphire substrates is demonstrated in a hot wall chemical vapor deposition reactor at the temperature of 1500 degrees C, using triethyl boron and ammonia as precursors. The influence of the main important process parameters, temperature, N/B ratio, B/H-2 ratio, and carrier gas composition on the quality of the grown layers is investigated in detail. X-ray diffraction shows that epitaxial rhombohedral BN (r-BN) film can be deposited only in a narrow process parameter window; outside this window either turbostratic-BN or amorphous BN is favored if BN is formed. In addition, a thin strained AlN buffer layer is needed to support epitaxial growth of r-BN film on sapphire since only turbostratic BN is formed on sapphire substrate. The quality of the grown film is also affected by the B/H-2 ratio as seen from a change of the spacing between the basal planes as revealed by X-ray diffraction. Time-of-flight elastic recoil detection analysis shows an enhancement of the C and O impurities incorporation at lower growth temperatures. The gas phase chemistry for the deposition is discussed as well as the impact of the growth rate on the quality of the BN film.

  • 210.
    Chubarova, E.
    et al.
    Royal Institute Technology KTH.
    Nilsson, D.
    Royal Institute Technology KTH.
    Lindblom, M.
    Royal Institute Technology KTH.
    Reinspach, J.
    Royal Institute Technology KTH.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Vogt, U.
    Royal Institute Technology KTH.
    Hertz, H. M.
    Royal Institute Technology KTH.
    Holmberg, A.
    Royal Institute Technology KTH, Department Appl Phys, SE-10691 Stockholm, Sweden.
    Platinum zone plates for hard X-ray applications2011In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 88, no 10, p. 3123-3126Article in journal (Refereed)
    Abstract [en]

    We describe the fabrication and evaluation of platinum zone plates for 5-12 kV X-ray imaging and focusing. These nano-scale circular periodic structures are fabricated by filling an e-beam generated mold with Pt in an electroplating process. The plating recipe is described. The resulting zone plates, having outer zone widths of 100 and 50 nm, show good uniformity and high aspect ratio. Their diffraction efficiencies are 50-70% of the theoretical, as measured at the European Synchrotron Radiation Facility. Platinum shows promise to become an attractive alternative to present hard X-ray zone plate materials due to its nano-structuring properties and the potential for zone-plate operation at higher temperatures.

  • 211.
    Chun, JS
    et al.
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Carlsson, JRA
    Desjardins, P
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Bergstrom, DB
    Petrov, I
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Greene, JE
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Lavoie, C
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Cabral, C
    Univ Illinois, Dept Mat Sci, Urbana, IL 61801 USA Univ Illinois, Frederick Seitz Mat Res Lab, Urbana, IL 61801 USA IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA Linkoping Univ, Dept Phys, Div Thin Film, S-58183 Linkoping, Sweden.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Synchrotron x-ray diffraction and transmission electron microscopy studies of interfacial reaction paths and kinetics during annealing of fully-002-textured Al/TiN bilayers2001In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 19, no 1, p. 182-191Article in journal (Refereed)
    Abstract [en]

    Dense fully-002-textured polycrystalline TiN layers, 110 nm thick with a N/TI ratio of 1.02+/-0.03, were grown on SiO2 by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition at T-s = 450 degreesC in pure N-2 utilizing high N-2(+)/Ti Aux ratios and low energy (E-N2(+) = 20 eV) ion irradiation of the growing film. Al overlayers, 160 nm thick and possessing a strong 002 texture inherited from the underlying TiN, were then deposited at T-s = 100 degreesC without breaking vacuum. Synchrotron x-ray diffraction was used to follow interfacial reaction paths and kinetics during postdeposition annealing as a function of time (t(a) = 200 - 1200 s) and temperature (T-a = 500 - 580 degreesC). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of cross-sectional and plan-view specimens by energy dispersive x-ray analysis. The initial bilayer reaction step during annealing involves the formation of a continuous AIN interfacial layer which, due to local epitaxy with the TIN underlayer, grows with the metastable zinc-blende structure up to a thickness x similar or equal to3-5 nm, and with the wurtzite structure thereafter. Ti atoms released during AIN formation diffuse into the Al layer leading to supersaturation followed by the nucleation of dispersed regions of tetragonal Al3Ti with inherited 002 preferred orientation. The aluminide domains grow rapidly until they reach the free surface, thereafter growth is two dimensional as Al3Ti grains spread radially. The overall activation energy for Al3Ti formation and growth is 1.8+/-0.1 eV. In situ synchrotron x-ray diffraction analyses during thermal ramping show that the onset temperature for interfacial reactions was increased by more than 100 degreesC for fully dense completely 002-textured bilayers compared to Ill-textured bilayers deposited by conventional reactive sputter deposition. (C) 2001 American Vacuum Society.

  • 212.
    Correa Filho, Luimar
    et al.
    Uppsala Univ, Sweden.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lopez, Alejandro
    Uppsala Univ, Sweden.
    Cogrel, Mathilde
    Uppsala Univ, Sweden.
    Leifer, Klaus
    Uppsala Univ, Sweden.
    Engqvist, Hakan
    Uppsala Univ, Sweden.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Cecilia
    Uppsala Univ, Sweden.
    The Effect of Coating Density on Functional Properties of SiNx Coated Implants2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, MATERIALS, Vol. 12, no 20, article id 3370Article in journal (Refereed)
    Abstract [en]

    Ceramic coatings may be applied onto metallic components of joint replacements for improved wear and corrosion resistance as well as enhanced biocompatibility, especially for metal-sensitive patients. Silicon nitride (SiNx) coatings have recently been developed for this purpose. To achieve a high coating density, necessary to secure a long-term performance, is however challenging, especially for sputter deposited SiNx coatings, since these coatings are insulating. This study investigates the time-dependent performance of sputter-deposited SiNx based coatings for joint applications. SiNx coatings with a thickness in the range of 4.3-6.0 mu m were deposited by reactive high power impulse magnetron sputtering onto flat discs as well as hip heads made of CoCrMo. SiNx compositional analysis by X-ray photoelectron spectroscopy showed N/Si ratios between 0.8 and 1.0. Immersion of the flat disks in fetal bovine serum solution over time as well as short-term wear tests against ultra-high molecular weight polyethylene (UHMWPE) discs showed that a high coating density is required to inhibit tribocorrosion. Coatings that performed best in terms of chemical stability were deposited using a higher target power and process heating.

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  • 213.
    Croci, Gabriele
    et al.
    Univ Milano Bicocca, Italy; CNR, Italy; INFN, Italy.
    Muraro, Andrea
    CNR, Italy.
    Cippo, Enrico Perelli
    CNR, Italy.
    Tardocchi, Marco
    CNR, Italy.
    Grosso, Giovanni
    Univ Milano Bicocca, Italy.
    Albani, Georgia
    Univ Milano Bicocca, Italy.
    Angella, Giuliano
    CNR, Italy.
    Defendi, Ilario
    Tech Univ Munich, Germany.
    Hall-Wilton, Richard
    ESS, Sweden; Mid Sweden Univ, Sweden.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. ESS, Sweden.
    Raspino, Davide
    Rutherford Appleton Lab, England.
    Rhodes, Nigel
    Rutherford Appleton Lab, England.
    Robinson, Linda
    ESS, Sweden.
    Schmidt, Susan
    ESS, Sweden.
    Schooneveld, Erik
    Rutherford Appleton Lab, England.
    Zeitelhack, Karl
    Tech Univ Munich, Germany.
    Gorini, Giuseppe
    CNR, Italy; ESS, Sweden.
    A high-efficiency thermal neutron detector based on thin 3D (B4C)-B-10 converters for high-rate applications2018In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 123, no 5, article id 52001Article in journal (Refereed)
    Abstract [en]

    new position-sensitive thermal neutron detector based on boron-coated converters has been developed as an alternative to todays standard He-3-based technology for application to thermal neutron scattering. The key element of the development is a novel 3D (B4C)-B-10 converter which has been ad hoc designed and realized with the aim of combining a high neutron conversion probability via the B-10(n, alpha)(7) Li reaction together with an efficient collection of the produced charged particles. The developed 3D converter is composed of thin aluminium grids made by a micro-waterjet technique and coated on both sides with a thin layer of( 10)B(4)C. When coupled to a GEM detector this converter allows reaching neutron detection efficiencies close to 50% at neutron wavelengths equal to 4 angstrom. In addition, the new detector features a spatial resolution of about 5 min and can sustain counting rates well in excess of 1 MHz/cm(2). The newly developed neutron detector will enable time-resolved measurements of different kind of samples in neutron scattering experiments at high flux spallation sources and can find a use in applications where large areas and custom geometries of thermal neutron detectors are foreseen. Copyright (C) EPLA, 2018

  • 214.
    Cubarovs, Mihails
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jens, Jensen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Epitaxial CVD growthof sp2-hybridized boron nitrideusing aluminum nitride as buffer layer2011In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, no 10-11, p. 397-399Article in journal (Refereed)
    Abstract [en]

    Epitaxial growth of sp2-hybridized boron nitride (BN) using chemical vapour deposition, with ammonia and triethyl boron as precursors, is enabled on sapphire by introducing an aluminium nitride (AlN) buffer layer. This buffer layer is formed by initial nitridation of the substrate. Epitaxial growth is verified by X-ray diffraction measurements in Bragg–Brentano configuration, pole figure measurements and transmission electron microscopy. The in-plane stretching vibration of sp2-hybridized BN is observed at 1366 cm–1 from Raman spectroscopy. Time-of-flight elastic recoil detection analysis confirms almost perfect stoichiometric BN with low concentration of carbon, oxygen and hydrogen contaminations.

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  • 215. Czigany, Zs.
    et al.
    Brunell, I.F.
    Neidhardt, Jörg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Suenaga, K.
    JST, c/o Meijo University, 468-8502 Nagoya, Japan.
    Growth of fullerene-like carbon nitride thin solid films consisting of cross-linked nano-onions2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, no 16, p. 2639-2641Article in journal (Refereed)
    Abstract [en]

    Fullerene-like CNx (x˜0.12) thin solid films were deposited by reactive magnetron sputtering of graphite in a nitrogen and argon discharge on cleaved NaCl and Si(001) substrates at 450°C. As-deposited films consist of 5 nm diam CNx nano-onions with shell sizes corresponding to Goldberg polyhedra determined by high-resolution transmission electron microscopy. Electron energy loss spectroscopy revealed that N incorporation is higher in the core of the onions than at the perimeter. N incorporation promotes pentagon formation and provides reactive sites for interlinks between shells of the onions. A model is proposed for the formation of CNx nano-onions by continuous surface nucleation and growth of hemispherical shells. © 2001 American Institute of Physics.

  • 216. Czigany, Zs.
    et al.
    Neidhardt, Jörg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Brunell, I.F.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Imaging of fullerene-like structures in CNx thin films by electron microscopy, Sample preparation artefacts due to ion-beam milling2003In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 94, no 3-4, p. 163-173Article in journal (Refereed)
    Abstract [en]

    The microstructure of CNx thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CNx surfaces. The thickness of the damaged surface layer at 5° grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CNx films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CNx was observed at 200kV. © 2002 Elsevier Science B.V. All rights reserved.

  • 217.
    Czigany, Zsolt
    et al.
    Hungarian Academy of Science.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Interpretation of electron diffraction patterns from amorphous and fullerene-like carbon allotropes2010In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 110, no 7, p. 815-819Article in journal (Refereed)
    Abstract [en]

    The short range order in amorphous and fullerene-like carbon compounds has been characterized by selected area electron diffraction (SAED) patterns and compared with simulations of model nanoclusters. Broad rings in SAED pattern from fullerene-like CNx at similar to 1.2, similar to 2, and similar to 3.5 angstrom indicate short-range order similar to that in graphite, but peak shifts indicate sheet curvature in agreement with high-resolution transmission electron microscopy images. Fullerene-like CPx exhibits rings at similar to 1.6 and 2.6 angstrom, which can be explained if it consists of fragments with short-range order and high curvature similar to that of C-20.

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  • 218. Order onlineBuy this publication >>
    Dahlqvist, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Materials Design from First Principles: stability and magnetism of nanolaminates2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, first-principles calculations within density functional theory are presented, with a principal goal to investigate the phase stability of so called Mn+1AXn (MAX) phases. MAX phases are a group of nanolaminated materials comprised of a transition metal (M), a group 12-16 element (A), and carbon or nitrogen (X). They combine ceramic and metallic characteristics, and phase stability studies are motivated by a search for new phases with novel properties, such as magnetism, and for the results to be used as guidance in attempted materials synthesis in the lab.

    To investigate phase stability of a hypothetical material, a theoretical approach has been developed, where the essential part is to identify the set of most competing phases relative to the material of interest. This approach advance beyond more traditional evaluation of stability, where the energy of formation of the material is generally calculated relative to its single elements, or to a set of ad hoc chosen competing phases. For phase stability predictions to be reliable, validation of previous experimental work is a requirement prior to investigations of new, still hypothetical, materials. It is found that the predictions from the developed theoretical approach are consistent with experimental observations for a large set of MAX phases. The predictive power is thereafter demonstrated for the new phases Nb2GeC and Mn2GaC, which subsequently have been synthesized as thin films. It should be noted that Mn is used for the first time as sole M-element in a MAX phase. Hence, the theory is successfully used to find new candidates, and to guide experimentalists in their work on novel promising materials. Phase stability is also evaluated for MAX phase alloys. Incorporation of oxygen in different M2AlC phases are studied, and the results show that oxygen prefer different sites depending on M-element, through the number of available non-bonding M d-electrons. The theory also predicts that oxygen substituting for carbon in Ti2AlC stabilizes the material, which explains the  experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx).

    Magnetism is a recently attained property of MAX phase materials, and a direct result of this Thesis work. We have demonstrated the importance of choice of magnetic spin configuration and electron correlations approximations for theoretical evaluation of the magnetic ground state of Cr2AC (A = Al, Ga, Ge). Furthermore, alloying Cr2AlC with Mn to obtain the first magnetic MAX phase have been theoretically predicted and experimentally verified. Using Mn2GaC as model system, Heisenberg Monte Carlo simulations have been used to explore also noncollinear magnetism, suggesting a large set of possible spin configurations (spin waves and spin spirals) to be further investigated in future theoretical and experimental work.

    List of papers
    1. Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation
    Open this publication in new window or tab >>Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation
    2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 2, p. 024111-1-024111-8Article in journal (Refereed) Published
    Abstract [en]

    The phase stability of Ti2AlC upon oxygen incorporation has been studied by means of first-principles calculations. Recent experimental observations of this so-called MAX phase (M = early transition metal, A = A-group element, and X = C or N) show that the characteristic nanolaminated structure is retained upon oxygen incorporation, with strong indications of O substituting for C. Therefore, a solid solution of C and O on the carbon sublattice has been simulated by the so-called special quasirandom structure method. Through a developed systematic approach, the enthalpy of formation of Ti2Al(C1−x,Ox) has been compared to all experimentally known competing phases, and has been found favorable for all C to O ratios at the composition of the MAX phase. A negative isostructural formation enthalpy has also been predicted for Ti2Al(C1−x,Ox). Altogether, the results indicate that a large amount of oxygen, at least up to x=0.75, might be present in the Ti2AlC MAX-phase structure without decomposition of the material into its competing phases. Furthermore, an effect of an increased oxygen content is a corresponding increase in the bulk modulus and a change in electronic properties. These results are of importance for further understanding and identification of possible composition range of the MAX-phase oxycarbide, and hence for the prospect of tuning the material properties by a varying incorporation of oxygen.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-53771 (URN)10.1103/PhysRevB.81.024111 (DOI)
    Available from: 2010-02-09 Created: 2010-02-03 Last updated: 2017-12-12Bibliographically approved
    2. Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations
    Open this publication in new window or tab >>Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We have studied oxygen incorporation and defect formation in M2AlC (M = Ti, V, Cr) MAX phases using first principles calculations. Evaluating phase stability and electronic structure for different oxygen and/or vacancy configurations, we show that oxygen prefer different lattice sites depending on M-element, which can be correlated to the number of available non-bonding M d-electrons. The results show that oxygen substitutes for carbon in Ti2AlC, while forming an interstitial oxygen in the Al-layer for Cr2AlC. We also predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx). Due to similar valence electron configuration of Ti2AlC and the hypothetical M2AlC (M =Zr, Hf), we also investigate if oxygen can be used to stabilize the latter MAX phases.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-104758 (URN)
    Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
    3. Stability trends of MAX phases from first principles
    Open this publication in new window or tab >>Stability trends of MAX phases from first principles
    2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, p. 220102-Article in journal (Refereed) Published
    Abstract [en]

    We have developed a systematic method to investigate the phase stability of M(n+1)AX(n) phases, here applied for M=Sc, Ti, V, Cr, or Mn, A=Al, and X=C or N. Through a linear optimization procedure including all known competing phases, we identify the set of most competitive phases for n=1-3 in each system. Our calculations completely reproduce experimental occurrences of stable MAX phases. We also identify and suggest an explanation for the trend in stability as the transition metal is changed across the 3d series for both carbon- and nitrogen-based systems. Based on our results, the method can be used to predict stability of potentially existing undiscovered phases.

    Place, publisher, year, edition, pages
    American Physical Society, 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-58288 (URN)10.1103/PhysRevB.81.220102 (DOI)000279147000001 ()
    Note
    Original Publication: Martin Dahlqvist, Björn Alling and Johanna Rosén, Stability trends of MAX phases from first principles, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 22, 220102. http://dx.doi.org/10.1103/PhysRevB.81.220102 Copyright: American Physical Society http://www.aps.org/ Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12
    4. Discovery of the Ternary Nanolaminated Compound Nb2GeC by a Systematic Theoretical-Experimental Approach
    Open this publication in new window or tab >>Discovery of the Ternary Nanolaminated Compound Nb2GeC by a Systematic Theoretical-Experimental Approach
    Show others...
    2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 3, p. 035502-Article in journal (Refereed) Published
    Abstract [en]

    Since the advent of theoretical materials science some 60 years ago, there has been a drive to predict and design new materials in silicio. Mathematical optimization procedures to determine phase stability can be generally applicable to complex ternary or higher-order materials systems where the phase diagrams of the binary constituents are sufficiently known. Here, we employ a simplex-optimization procedure to predict new compounds in the ternary Nb-Ge-C system. Our theoretical results show that the hypothetical Nb2GeC is stable, and excludes all reasonably conceivable competing hypothetical phases. We verify the existence of the Nb2GeC phase by thin film synthesis using magnetron sputtering. This hexagonal nanolaminated phase has a and c lattice parameters of similar to 3.24 angstrom and 12.82 angstrom.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-79981 (URN)10.1103/PhysRevLett.109.035502 (DOI)000306466900014 ()
    Note

    Funding Agencies|European Research Council under the European Community|258509|Swedish Research Council (V.R.)||Swedish Foundation for Strategic Research||Swedish Agency for Innovation Systems (VINNOVA) Excellence Center FunMat||

    Available from: 2012-08-17 Created: 2012-08-17 Last updated: 2017-12-07
    5. Correlation between magnetic state and bulk modulus of Cr2AlC
    Open this publication in new window or tab >>Correlation between magnetic state and bulk modulus of Cr2AlC
    2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 21Article in journal (Refereed) Published
    Abstract [en]

    The effect of magnetism on the bulk modulus (B0) of M2AlC (M  = Ti, V, and Cr) has been studied using first principles calculations. We find that it is possible to identify an energetically favorable magnetic Cr2AlC phase without using any adjustable parameter, such as the Hubbard U. Furthermore, we show that an in-plane spin polarized configuration has substantially lower B0 as compared to the non-magnetic model. The existences of local magnetic moments on Cr atoms considerably improve agreement between theory and experiment regarding trends in B0 for M2AlC phases.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-96430 (URN)10.1063/1.4808239 (DOI)000320674500104 ()
    Note

    Funding Agencies|European Research Council under the European Community|258509|Swedish Research Council (VR)|621-2012-4425621-2011-4417|

    Available from: 2013-08-20 Created: 2013-08-19 Last updated: 2017-12-06
    6. Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation
    Open this publication in new window or tab >>Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We have studied the interplay between spin configuration and electron correlations approximations as well as their influence on calculated lattice parameters, magnetic moments, and bulk modulus of the nanolaminated MAX phase materials Cr2AlC, Cr2GaC, and Cr2GeC. By considering non-, ferro- and, and five different antiferromagnetic configurations, we show the importance of including a broad range of magnetic states in search for the ground state. Our calculations show that when electron correlation is treated on the level of the generalized gradient approximation or with an additional Hubbard U interaction term up to a value of 1 eV, the magnetic ground state of Cr2AC (A=Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments and calculated lattice parameters and bulk modulus close to experimentally reported values.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-104759 (URN)
    Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
    7. Magnetic nanoscale laminates with tunable exchange coupling from first principles
    Open this publication in new window or tab >>Magnetic nanoscale laminates with tunable exchange coupling from first principles
    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 22, article id 220403Article in journal (Refereed) Published
    Abstract [en]

    The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling.

    Place, publisher, year, edition, pages
    American Physical Society, 2011
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-73313 (URN)10.1103/PhysRevB.84.220403 (DOI)000297763300001 ()
    Available from: 2012-01-03 Created: 2012-01-02 Last updated: 2020-02-14Bibliographically approved
    8. A Nanolaminated Magnetic Phase: Mn2GaC
    Open this publication in new window or tab >>A Nanolaminated Magnetic Phase: Mn2GaC
    Show others...
    2014 (English)In: Materials Research Letters, ISSN 2166-3831, Vol. 2, no 2, p. 89-93Article in journal (Refereed) Published
    Abstract [en]

    Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2014
    Keywords
    MAX phases, sputtering, transmission electron microscopy (TEM), ab initio calculation
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-77774 (URN)10.1080/21663831.2013.865105 (DOI)
    Note

    On the day of the defence date the status of this article was previous Manuscript. The original title of the Manuscript was Magnetic nanoscale laminates from first principles and thin film synthesis.

    Available from: 2012-05-29 Created: 2012-05-29 Last updated: 2018-03-15Bibliographically approved
    9. Complex magnetism in nanolaminated Mn2GaC
    Open this publication in new window or tab >>Complex magnetism in nanolaminated Mn2GaC
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    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-104760 (URN)
    Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
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    Materials Design from First Principles: stability and magnetism of nanolaminates
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  • 219.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 2, p. 024111-1-024111-8Article in journal (Refereed)
    Abstract [en]

    The phase stability of Ti2AlC upon oxygen incorporation has been studied by means of first-principles calculations. Recent experimental observations of this so-called MAX phase (M = early transition metal, A = A-group element, and X = C or N) show that the characteristic nanolaminated structure is retained upon oxygen incorporation, with strong indications of O substituting for C. Therefore, a solid solution of C and O on the carbon sublattice has been simulated by the so-called special quasirandom structure method. Through a developed systematic approach, the enthalpy of formation of Ti2Al(C1−x,Ox) has been compared to all experimentally known competing phases, and has been found favorable for all C to O ratios at the composition of the MAX phase. A negative isostructural formation enthalpy has also been predicted for Ti2Al(C1−x,Ox). Altogether, the results indicate that a large amount of oxygen, at least up to x=0.75, might be present in the Ti2AlC MAX-phase structure without decomposition of the material into its competing phases. Furthermore, an effect of an increased oxygen content is a corresponding increase in the bulk modulus and a change in electronic properties. These results are of importance for further understanding and identification of possible composition range of the MAX-phase oxycarbide, and hence for the prospect of tuning the material properties by a varying incorporation of oxygen.

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  • 220.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnetic nanoscale laminates with tunable exchange coupling from first principles2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 22, article id 220403Article in journal (Refereed)
    Abstract [en]

    The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling.

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  • 221.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Ingason, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnus, F.
    2Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Thore, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Petruhins, Andrejs
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Mockute, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Meshkian, Rahele
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sahlberg, M.
    3Department of Chemistry, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hjörvarsson, B.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Abrikosov, A.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Complex magnetism in nanolaminated Mn2GaC2014Manuscript (preprint) (Other academic)
    Abstract [en]

    We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.

  • 222.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    A critical evaluation of GGA plus U modeling for atomic, electronic and magnetic structure of Cr2AlC, Cr2GaC and Cr2GeC2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 9, p. 095601-Article in journal (Refereed)
    Abstract [en]

    In this work we critically evaluate methods for treating electron correlation effects in multicomponent carbides using a GGA + U framework, addressing doubts from previous works on the usability of density functional theory in the design of magnetic MAX phases. We have studied the influence of the Hubbard U-parameter, applied to Cr 3d orbitals, on the calculated lattice parameters, magnetic moments, magnetic order, bulk modulus and electronic density of states of Cr2AlC, Cr2GaC and Cr2GeC. By considering non-, ferro-, and five different antiferromagnetic spin configurations, we show the importance of including a broad range of magnetic orders in the search for MAX phases with finite magnetic moments in the ground state. We show that when electron correlation is treated on the level of the generalized gradient approximation (U = 0 eV), the magnetic ground state of Cr(2)AC (A = Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments, and calculated lattice parameters and bulk modulus close to experimentally reported values. By comparing GGA and GGA + U results with experimental data we find that using a U-value larger than 1 eV results in structural parameters deviating strongly from experimentally observed values. Comparisons are also done with hybrid functional calculations (HSE06) resulting in an exchange splitting larger than what is obtained for a U-value of 2 eV. Our results suggest caution and that investigations need to involve several different magnetic orders before lack of magnetism in calculations are blamed on the exchange-correlation approximations in this class of magnetic MAX phases.

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  • 223.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Correlation between magnetic state and bulk modulus of Cr2AlC2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 21Article in journal (Refereed)
    Abstract [en]

    The effect of magnetism on the bulk modulus (B0) of M2AlC (M  = Ti, V, and Cr) has been studied using first principles calculations. We find that it is possible to identify an energetically favorable magnetic Cr2AlC phase without using any adjustable parameter, such as the Hubbard U. Furthermore, we show that an in-plane spin polarized configuration has substantially lower B0 as compared to the non-magnetic model. The existences of local magnetic moments on Cr atoms considerably improve agreement between theory and experiment regarding trends in B0 for M2AlC phases.

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    fulltext
  • 224.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation2014Manuscript (preprint) (Other academic)
    Abstract [en]

    We have studied the interplay between spin configuration and electron correlations approximations as well as their influence on calculated lattice parameters, magnetic moments, and bulk modulus of the nanolaminated MAX phase materials Cr2AlC, Cr2GaC, and Cr2GeC. By considering non-, ferro- and, and five different antiferromagnetic configurations, we show the importance of including a broad range of magnetic states in search for the ground state. Our calculations show that when electron correlation is treated on the level of the generalized gradient approximation or with an additional Hubbard U interaction term up to a value of 1 eV, the magnetic ground state of Cr2AC (A=Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments and calculated lattice parameters and bulk modulus close to experimentally reported values.

  • 225.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stability trends of MAX phases from first principles2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, p. 220102-Article in journal (Refereed)
    Abstract [en]

    We have developed a systematic method to investigate the phase stability of M(n+1)AX(n) phases, here applied for M=Sc, Ti, V, Cr, or Mn, A=Al, and X=C or N. Through a linear optimization procedure including all known competing phases, we identify the set of most competitive phases for n=1-3 in each system. Our calculations completely reproduce experimental occurrences of stable MAX phases. We also identify and suggest an explanation for the trend in stability as the transition metal is changed across the 3d series for both carbon- and nitrogen-based systems. Based on our results, the method can be used to predict stability of potentially existing undiscovered phases.

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  • 226.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ingason, Arni Sigurdur
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnus, F.
    Uppsala University, Sweden.
    Thore, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petruhins, Andrejs
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Arnalds, U. B.
    University of Iceland, Iceland.
    Sahlberg, M.
    Uppsala University, Sweden.
    Hjorvarsson, B.
    Uppsala University, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia; Tomsk State University, Russia.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 1, p. 014410-Article in journal (Refereed)
    Abstract [en]

    Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.

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  • 227.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jansson, Ulf
    Uppsala University, Sweden.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Influence of boron vacancies on phase stability, bonding and structure of MB2 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) with AlB2 type structure2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 43, p. 435702-Article in journal (Refereed)
    Abstract [en]

    Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M = Ti, Zr, Hf). For group V (M = V, Nb, Ta) and group VI (M = Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level.

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  • 228.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Meshkian, Rahele
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Tao, Quanzheng
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Prediction and synthesis of a family of atomic laminate phases with Kagome-like and in-plane chemical ordering2017In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 7, article id e1700642Article in journal (Refereed)
    Abstract [en]

    The enigma of MAX phases and their hybrids prevails. We probe transition metal (M) alloying in MAX phases for metal size, electronegativity, and electron configuration, and discover ordering in these MAX hybrids, namely, (V2/3Zr1/3)(2)AlC and (Mo2/3Y1/3)(2)AlC. Predictive theory and verifying materials synthesis, including a judicious choice of alloying M from groups III to VI and periods 4 and 5, indicate a potentially large family of thermodynamically stable phases, with Kagome-like and in-plane chemical ordering, and with incorporation of elements previously not known for MAX phases, including the common Y. We propose the structure to be monoclinic C2/c. As an extension of the work, we suggest a matching set of novel MXenes, from selective etching of the A-element. The demonstrated structural design on simultaneous two-dimensional (2D) and 3D atomic levels expands the property tuning potential of functional materials.

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  • 229.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Meshkian, Rahele
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Dataset on the structure and thermodynamic and dynamic stability of Mo2ScAlC2 from experiments and first-principles calculations.2017In: Data In Brief, ISSN 2352-3409, Vol. 10, p. 576-582Article in journal (Refereed)
    Abstract [en]

    The data presented in this paper are related to the research article entitled "Theoretical stability and materials synthesis of a chemically ordered MAX phase, Mo2ScAlC2, and its two-dimensional derivate Mo2ScC" (Meshkian et al. 2017) [1]. This paper describes theoretical phase stability calculations of the MAX phase alloy MoxSc3-xAlC2 (x=0, 1, 2, 3), including chemical disorder and out-of-plane order of Mo and Sc along with related phonon dispersion and Bader charges, and Rietveld refinement of Mo2ScAlC2. The data is made publicly available to enable critical or extended analyzes.

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  • 230.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petruhins, Andrejs
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Origin of Chemically Ordered Atomic Laminates (i-MAX): Expanding the Elemental Space by a Theoretical/Experimental Approach2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 8, p. 7761-7770Article in journal (Refereed)
    Abstract [en]

    With increased chemical diversity and structural complexity comes the opportunities for innovative materials possessing advantageous properties. Herein, we combine predictive first-principles calculations with experimental synthesis, to explore the origin of formation of the atomically laminated i-MAX phases. By probing (Mo2/3M1/32)(2)AC (where M-2 = Sc, Y and A = Al, Ga, In, Si, Ge, In), we predict seven stable i-MAX phases, five of which should have a retained stability at high temperatures. (Mo2/3Sc1/3)(2)GaC and (Mo2/3Y1/3)(2)GaC were experimentally verified, displaying the characteristic in-plane chemical order of Mo and Sc/Y and Kagome-like ordering of the A-element. We suggest that the formation of i-MAX phases requires a significantly different size of the two metals, and a preferable smaller size of the A-element. Furthermore, the population of antibonding orbitals should be minimized, which for the metals herein (Mo and Sc/Y) means that A elements from Group 13 (Al, Ga, In) are favored over Group 14 (Si, Ge, Sn). Using these guidelines, we foresee a widening of elemental space for the family of i-MAX phases and expect more phases to be synthesized, which will realize useful properties. Furthermore, based on i-MAX phases as parent materials for 2D MXenes, we also expect that the range of MXene compositions will be expanded.

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  • 231.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Order and disorder in quaternary atomic laminates from first-principles calculations2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 47, p. 31810-31821Article in journal (Refereed)
    Abstract [en]

    We report on the phase stability of chemically ordered and disordered quaternary MAX phases - TiMAlC, TiM2AlC2, MTi2AlC2, and Ti2M2AlC3 where M = Zr, Hf (group IV), M = V, Nb, Ta (group V), and M = Cr, Mo, W (group VI). At 0 K, layered chemically ordered structures are predicted to be stable for M from groups V and VI. By taking into account the configurational entropy, an order-disorder temperature T-disorder can be estimated. TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) are found with Tdisorder 4 1773 K and are hence predicted to be ordered at the typical bulk synthesis temperature of 1773 K. Other ordered phases, even though metastable at elevated temperatures, may be synthesized by non-equilibrium methods such as thin film growth. Furthermore, phases predicted not to be stable in any form at 0 K can be stabilized at higher temperatures in a disordered form, being the case for group IV, for MTi2AlC2 (M = V, Cr, Mo), and for Ti2M2AlC3 (M = V, Ta). The stability of the layered ordered structures with M from group VI can primarily be explained by Ti breaking the energetically unfavorable stacking of M and C where M is surrounded by C in a face-centered cubic configuration, and by M having a larger electro-negativity than Al resulting in a fewer electrons available for populating antibonding Al-Al orbitals. The results show that these chemically ordered quaternary MAX phases allow for new elemental combinations in MAX phases, which can be used to add new properties to this family of atomic laminates and in turn prospects for tuning these properties.

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  • 232.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations2014Manuscript (preprint) (Other academic)
    Abstract [en]

    We have studied oxygen incorporation and defect formation in M2AlC (M = Ti, V, Cr) MAX phases using first principles calculations. Evaluating phase stability and electronic structure for different oxygen and/or vacancy configurations, we show that oxygen prefer different lattice sites depending on M-element, which can be correlated to the number of available non-bonding M d-electrons. The results show that oxygen substitutes for carbon in Ti2AlC, while forming an interstitial oxygen in the Al-layer for Cr2AlC. We also predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx). Due to similar valence electron configuration of Ti2AlC and the hypothetical M2AlC (M =Zr, Hf), we also investigate if oxygen can be used to stabilize the latter MAX phases.

  • 233.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Predictive theoretical screening of phase stability for chemical order and disorder in quaternary 312 and 413 MAX phases2020In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 12, no 2, p. 785-794Article in journal (Refereed)
    Abstract [en]

    In this work we systematically explore a class of atomically laminated materials, M(n+1)AX(n) (MAX) phases upon alloying between two transition metals, M and M , from groups III to VI (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The materials investigated focus on so called o-MAX phases with out-of-plane chemical ordering of M and M , and their disordered counterparts, for A = Al and X = C. Through use of predictive phase stability calculations, we confirm all experimentally known phases to date, and also suggest a range of stable ordered and disordered hypothetical elemental combinations. Ordered o-MAX is favoured when (i) M next to the Al-layer does not form a corresponding binary rock-salt MC structure, (ii) the size difference between M and M is small, and (iii) the difference in electronegativity between M and Al is large. Preference for chemical disorder is favoured when the size and electronegativity of M and M is similar, in combination with a minor difference in electronegativity of M and Al. We also propose guidelines to use in the search for novel o-MAX; to combine M from group 6 (Cr, Mo, W) with M from groups 3 to 5 (Sc only for 312, Ti, Zr, Hf, V, Nb, Ta). Correspondingly, we suggest formation of disordered MAX phases by combing M and M within groups 3 to 5 (Sc, Ti, Zr, Hf, V, Nb, Ta). The addition of novel elemental combinations in MAX phases, and in turn in their potential two-dimensional MXene derivatives, allow for property tuning of functional materials.

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  • 234.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thore, Andreas
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Electronic structure, bonding characteristics, and mechanical properties in (W2/3Sc1/3)(2)AIC and (W2/3Y1/3)(2)AIC i-MAX phases from first-principles calculations2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 30, article id 305502Article in journal (Refereed)
    Abstract [en]

    With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ((M2/3M1/32)-M-1)(2)AC comes addition of non-traditional MAX phase elements. In the present study, we use density functional theory calculations to investigate the electronic structure, bonding nature, and mechanical properties of the novel (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC i-MAX phases. From analysis of the electronic structure and projected crystal orbital Hamilton populations, we show that the metallic i-MAX phases have significant hybridization between W and C, as well as Sc(Y) and C states, indicative of strong covalent bonding. Substitution of Sc for Y (M-2) leads to reduced bonding strength for W-C and Al-Al interactions while M-2-C and M-2-Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Youngs moduli along the series of M-1 = Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.

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  • 235.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thore, Andreas
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Electronic structure, bonding characteristics, and mechanical properties in (W2/3Sc1/3)(2)AIC and (W2/3Y1/3)(2)AIC i-MAX phases from first-principles calculations2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 30, article id 305502Article in journal (Refereed)
    Abstract [en]

    With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ((M2/3M1/32)-M-1)(2)AC comes addition of non-traditional MAX phase elements. In the present study, we use density functional theory calculations to investigate the electronic structure, bonding nature, and mechanical properties of the novel (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC i-MAX phases. From analysis of the electronic structure and projected crystal orbital Hamilton populations, we show that the metallic i-MAX phases have significant hybridization between W and C, as well as Sc(Y) and C states, indicative of strong covalent bonding. Substitution of Sc for Y (M-2) leads to reduced bonding strength for W-C and Al-Al interactions while M-2-C and M-2-Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Youngs moduli along the series of M-1 = Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.

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  • 236.
    Dalibon, Eugenia. L.
    et al.
    UTN, Argentina.
    Czerwiec, Thierry
    Univ Lorraine, France.
    Trava-Airoldi, Vladimir J.
    INPE, Brazil.
    Ghafoor, Naureen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rogström, Lina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Bruhl, Sonia P.
    UTN, Argentina.
    Characterization of DLC coatings over nitrided stainless steel with and without nitriding pre-treatment using annealing cycles2019In: JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMRandT, ISSN 2238-7854, Vol. 8, no 2, p. 1653-1662Article in journal (Refereed)
    Abstract [en]

    Amorphous hydrogenated diamond-like carbon (DLC) coatings were deposited using plasma assisted chemical vapour deposition (PACVD) on precipitation hardening (PH) stainless steel.Plasma nitriding has been used as pre-treatment to enhance adhesion and mechanical properties. Chemical and mechanical properties of DLC coatings are dependent on the hydrogen content and so on the relation between sp(3)/sp(2) bondings. The bondings and the structure of the DLC film change with temperature. In this work, a study of the thermal degradation and the evolution of the mechanical properties of DLC coatings over PH stainless steel have been carried out, including the effect of an additional nitrided layer. Nitrided and non-nitrided steel samples were subjected to the same coated in the same conditions, and they were submitted to the same thermal cycles, heating from room temperature to 600 degrees C in several steps. After each cycle, Raman spectra and surface topography measurements were performed and analyzed. Nanohardness measurements and tribological tests, using a pin-on-disc machine, were carried out to analyze variations in the friction coefficient and the wear resistance. The duplex sample, with nitriding as pre-treatment showed a better thermal stability. For duplex sample, the coating properties, such as adhesion, and friction coefficient were sustained after annealing at higher temperatures; whereas it was not the case for only coated sample. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.

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  • 237.
    Dalibon, Eugenia L.
    et al.
    University of Tecnol Nacl UTN FRCU, Argentina.
    Ghafoor, Naureen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rogström, Lina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Trava-Airoldi, Vladimir J.
    INPE, Brazil.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Bruhl, Sonia P.
    University of Tecnol Nacl UTN FRCU, Argentina.
    Carbon Based Coatings Deposited on Nitrided Stainless Steel: Study of Thermal Degradation2017In: PROCEEDINGS OF THE 3RD PAN AMERICAN MATERIALS CONGRESS, SPRINGER INTERNATIONAL PUBLISHING AG , 2017, p. 57-66Conference paper (Refereed)
    Abstract [en]

    Amorphous hydrogenated carbon (DLC) coatings have a high hardness depending on the relative amount of sp(3)/sp(2) bondings. They also exhibit an extremely low friction coefficient and are chemically inert. However, these coatings have some disadvantages which limit their applications. For instance, adhesion is poor when they are deposited on metallic substrates and they are also unstable at high temperatures, degrading into graphite and loosing hardness. In this work, DLC coatings were deposited on precipitation hardening stainless steel (PH Corrax) which was plasma nitrided before the coating deposition. The samples were submitted to annealing treatments for an hour at different temperatures from 200 to 600 degrees C, together with a control group, which was only coated but not nitrided. After each annealing cycle, Raman Spectroscopy, nanoindentation and microscopy were used to check film properties. It was demonstrated that the nitriding pre treatment improved not only adhesion but also the thermal stability of the DLC, slowing degradation and preventing delamination.

  • 238.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Barradas, N P
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorenz, K
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Alves, E
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Schubert, M
    University Nebraska, Department Elect Engn, Lincoln, NE 68588 USA .
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Munnik, F
    Forschungszentrum Dresden Rossendorf, D-01314 Dresden, Germany .
    Hsiao, Ching-Lien
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Tu, L W
    Natl Sun Yat Sen University, Department Phys, Kaohsiung 80424, Taiwan Natl Sun Yat Sen University, Centre Nanosci and Nanotechnol, Kaohsiung 80424, Taiwan .
    Schaff, W J
    Cornell University, Department Elect and Comp Engn, Ithaca, NY 14853 USA .
    Role of impurities and dislocations for the unintentional n-type conductivity in InN2009In: PHYSICA B-CONDENSED MATTER, ISSN 0921-4526, Vol. 404, no 22, p. 4476-4481Article in journal (Refereed)
    Abstract [en]

    We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

  • 239.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Beckers, Manfred
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Carlin, J.-F
    Grandjean, N.
    Strain and compositional analyzes of Al-rich Al1-xInxN alloys grown by MOVPE: impact on the applicability of Vegard's rule2008In: Physica Status Solidi (C) Current Topics in Solid State Physics, 2008, p. 1859-1862Conference paper (Refereed)
    Abstract [en]

    We have studied composition and strain in Al1–xInxN films with 0.128 x 0.22 grown on GaN-buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub-layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • 240.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Beckers, Manfred
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Carlin, J-. F.
    Feltin, E.
    Gonschorek, M.
    Grandjean, N.
    Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 10, p. 103513-Article in journal (Refereed)
    Abstract [en]

    The lattice parameters and strain evolution in Al1-x In x N films with 0.07≤x≤0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard's rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1-x Inx N films with low degree of strain or partially relaxed, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. © 2008 American Institute of Physics.

  • 241.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Strain evolution in high temperature AlN buffer layers for HVPE-GaN growth2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, p. 59-64Article in journal (Refereed)
    Abstract [en]

    High temperature AlN buffer layers are deposited on a-plane sapphire by reactive magnetron sputtering. The effect of the buffer thickness on the AlN structural properties and surface morphology are studied in correlation with the subsequent hydride vapour phase epitaxy of GaN. A minimum degree of mosaicity and screw dislocation density is determined for a 50 nm thick AlN buffer. With increasing the AlN thickness, a strain relaxation occurs as a result of misfit dislocation generation and higher degree of mosaicity. A blue shift of the E-1(TO) frequency evaluated by means of infrared reflection spectroscopy is linearly correlated with an increase in biaxial compressive stress in the films through the IR stress factor k(E1)(b) = 2.57 +/- 0.26 cm(-1) GPa(-1).

  • 242.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hofmann, T.
    University of Nebraska-Lincoln, USA.
    Schubert, M.
    University of Nebraska-Lincoln, USA.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Per O. A.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Schaff, W. J.
    Cornell University, Ithaca, NY, USA.
    Hsiao, C.-L.
    National Taiwan University, Taipei, Taiwan.
    Chen, L.-C.
    National Taiwan University, Taipei, Taiwan.
    Nanishi, Y
    Ritsumeikan University, Shiga, Japan.
    Unravelling the free electron behavior in InN2008In: Optoelectronic and Microelectronic Materials and Devices, 2008, IEEE , 2008, p. 90-97Conference paper (Refereed)
    Abstract [en]

    Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.

  • 243.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Hofmann, T
    University of Nebraska.
    Schubert, M
    University of Nebraska.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Alves, E
    Sacavem, Portugal.
    Lu, H
    Cornell University.
    Schaff, W J
    Cornell University.
    Free electron behavior in InN: On the role of dislocations and surface electron accumulation2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 2, p. 022109-Article in journal (Refereed)
    Abstract [en]

    The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.

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  • 244.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Deformation potentials of the E-1(TO) mode in AlN2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, p. 2302-2304Article in journal (Refereed)
    Abstract [en]

    The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

  • 245.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Schubert, M.
    Fak. für Phys./Geowiss., Iniversität Leipzig, 04103 Leipzig, Germany.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Kasic, A.
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Generalized infrared ellipsometry study of thin epitaxial AlN layers with complex strain behavior2003Conference paper (Refereed)
    Abstract [en]

    The effect of film thickness on the strain and structural properties of thin epitaxial AlN films has been investigated, and a sub-layer model of the degree of strain and related defects for all films is suggested. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sub-layer model has been successfully applied to the analysis of the ellipsometry data trough model calculations of the infrared dielectric function. © 2003 Elsevier B.V. All rights reserved.

  • 246.
    Darakchieva, Vanya
    et al.