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  • 1.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutionsManuscript (preprint) (Other academic)
    Abstract [en]

    First-principles calculations are employed to investigate the stability and properties of cubic rock-salt like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a favorable coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to a have cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.

  • 2.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions2013In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 31, no 3Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are employed to investigate the stability and properties of cubic rock-salt-like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a suitable fourfold coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to have a cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.

  • 3.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Activation energy of fcc-corundum phase transformation in (Al1-xCrx)2O3 Thin Films2011Conference paper (Other academic)
    Abstract [en]

    Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited using dual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. The (Al1-xCrx)2O3 films are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, in-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1000 °C and annealing time of 8 h. The fcc structure remains intact up to 700 °C. A gradual phase transformation from fcc to corundum at 1000 °C is observed, where annealing for 1-3 h yields a partial transformation and annealing for > 4 h results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3.

  • 4.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Cr-Al-O Ternary Oxide Thin Films Deposited by Magnetron Sputtering2009Conference paper (Other academic)
  • 5.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Deposition and Phase Transformations of Ternary Al-Cr-O Thin Films2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the ternary Al-Cr-O system. (Al1-xCrx)2O3 solid solution thin films with 0.6<x<0.7 were deposited on Si(001) substrates at temperatures of 400-500 °C by reactive radio frequency magnetron sputtering from metallic targets of Al and Cr in a flow controlled Ar / O2 gas mixture. As-deposited and annealed (Al1-xCrx)2O3 thin films were analyzed by x-ray diffraction, elastic recoil detection analysis, scanning electron microscopy, transmission electron microscopy, and nanoindentation. (Al1-xCrx)2O3 showed to have face centered cubic structure with lattice parameter of 4.04 Å, which is in contrast to the typical corundum structure reported for these films. The as-deposited films exhibited hardness of ~ 26 GPa and elastic modulus of 220-235 GPa. Phase transformation from cubic to corundum (Al0.32Cr0.68)2O3 starts at 925 °C. Annealing at 1000 °C resulted in complete phase transformation, while no precipitates of alumina and chromia were observed. Studies on kinetics of phase transformation showed a two-step thermally activated process; phase transformation and grain growth with the apparent activation energies 213±162 and 945±27 kJ/mol, respectively.

    List of papers
    1. Face-Centered Cubic (Al1-xCrx)2O3
    Open this publication in new window or tab >>Face-Centered Cubic (Al1-xCrx)2O3
    Show others...
    2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 8, p. 2426-2429Article in journal (Refereed) Published
    Abstract [en]

    We report the discovery of a face-centered cubic (Al1−xCrx)2O3 solid solution [0.60bxb0.70] in films grownonto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. Theproposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å asdetermined by X-ray diffraction. The films have a b100N preferred crystallographic orientation and exhibithardness values up to 26 GPa and an elastic modulus of 220–235 GPa.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-65698 (URN)10.1016/j.tsf.2010.11.052 (DOI)000287631500008 ()
    Funder
    Swedish Research Council
    Note
    Original Publication: Ali Khatibi, Justinas Palisaitis, Carina Höglund, Anders Eriksson, Per O. Å. Persson, Jens Jensen, Jens Birch, Per Eklund and Lars Hultman, Face-Centered Cubic (Al1-xCrx)2O3 , 2011, Thin Solid Films, (519), 2426-2429. http://dx.doi.org/10.1016/j.tsf.2010.11.052 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2011-02-21 Created: 2011-02-17 Last updated: 2017-12-11Bibliographically approved
    2. Kinetics of Phase Transformation in fcc-(Al0.32Cr0.68)2O3 Thin Films
    Open this publication in new window or tab >>Kinetics of Phase Transformation in fcc-(Al0.32Cr0.68)2O3 Thin Films
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Thermal stability of fcc-(Al0.32Cr0.68)2O3 thin film is investigated by ex-situ annealing of films in the temperature range of 500-1100 °C and annealing times of 2-10 h. X-ray diffraction indicates that the phase transformation from fcc to corundum crystal structure starts at 925 °C and completes at 1000 °C. This is further confirmed by high resolution transmission electron microscopy and selected area electron diffraction. The kinetics of phase transformation is analyzed by Johnson-Avrami-Mehl model. The phase transformation from fcc to corundum in (Al0.32Cr0.68)2O3 thin films is a two-stage thermally activated process. The first stage is phase transformation and has the apparent activation energy of 213±162 kJ/mol (0.44±0.34 eV/atom). This is followed by a second stage with a larger apparent activation energy of 945±27 kJ/mol (1.96±0.06 eV/atom). This is likely associated with the grain growth of a-phase upon completion of the phase transformation.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-65699 (URN)
    Available from: 2011-02-17 Created: 2011-02-17 Last updated: 2011-12-05Bibliographically approved
  • 6.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Face-Centered Cubic (Al1-xCrx)2O3 Thin Films: Deposition and Characterization Studies2011Conference paper (Other academic)
    Abstract [en]

    Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited usingdual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperatureof 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined byx-ray diffraction and high resolution transmission electron microscopy techniques. The (Al1-xCrx)2O3 films aresuggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites.Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa.In the present work, in-situ annealing studies were performed on as-deposited samples for a series of temperaturesup to 1100°C and annealing time of 8 h. The results show that fcc structure remains intact up to 950°C. A gradualphase transformation from fcc to corundum at 1000°C is observed, where annealing for 1-3 h yields a partialtransformation and annealing for > 4 h results in complete transformation to alpha-(Al1-xCrx)2O3. There is noindication of any phase separation into alpha-Cr2O3 and alpha-Al2O3.

  • 7.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Face-Centered Cubic (Al1-xCrx)2O3 Thin Films: Deposition, Characterization, and Heat Treatment Studies2011Conference paper (Other academic)
    Abstract [en]

    Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited using dual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. The (Al1-xCrx)2O3 films are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, ex-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1100 °C and annealing time of 2,4,6,8, and 10 hours. The fcc structure remains intact up to 950 °C. A gradual phase transformation from fcc to corundum at 925 °C is observed, where annealing for 2 h yields a partial transformation and annealing for >6 h results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3.

  • 8.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Face-Centered Cubic (Al,Cr)2O3 Thin Films2010Conference paper (Other academic)
  • 9.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Face-Centered Cubic and corundum (Al1-xCrx)2O3 Thin Films:  Deposition, Characterization, and Heat Treatment Studies2012Conference paper (Other academic)
  • 10.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Growth and Heat Treatment Studies of Al-Cr-O and Al-Cr-O-N Thin Films2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Aluminum oxide based thin films are applied on cutting tool inserts as a top layer to protect the underlying nitride or carbide functional layer from the harsh working environment in terms of abrasive and chemical wear under thermal and pressure load. This Thesis explores the synthesis and characterization of the next generations of multifunctional wear-resistant thin film coatings in the form of Al-Cr-O and Al-Cr-O-N compounds. The experiments include the deposition of oxide films by reactive magnetron sputtering and cathodic arc evaporation as well as investigation of structural and mechanical properties in as-deposited and annealed states. Ternary (Al1-xCrx)2+yO3-y films were deposited on Si(001) and WC-Co substrates kept at 400-575 °C from elemental Al and Cr or alloyed Al/Cr cathodes in Ar/O2, O2/N2, and pure O2 atmospheres. Also, quaternary (Al1-xCrx)2+z(O1-yNy)3-z films were deposited at substrate temperature of ~400 °C on WC-Co substrates in O2/N2 atmosphere. X-ray diffraction and analytical electron microscopy combined with ab initio calculations showed the existence of a new face centered cubic (Al,Cr)2O3 phase with 33% vacancies on the metallic Al/Cr sites. Increasing the temperature during annealing of these metastable cubic films resulted in phase transformation to corundum solid solution in the temperature range of 900-1100 °C. The apparent activation energy of this phase transformation process was calculated as 380-480 kJ/mol by using the Johnson-Mehl-Avrami model. The mechanical properties of the cubic and corundum oxide films were measured in terms of nanoindentation hardness and metal cutting performance. The cubic and corundum films showed hardness values of 26-28 GPa and 28-30 GPa, respectively. The oxynitride solid solution films showed to be predominantly cubic Al-Cr-N and cubic-(Al,Cr)2O3 and secondary corundum-(Al,Cr)2O3 with a hardness of ~30 GPa, slightly higher than Al-rich ternary oxides. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.

    List of papers
    1. Face-Centered Cubic (Al1-xCrx)2O3
    Open this publication in new window or tab >>Face-Centered Cubic (Al1-xCrx)2O3
    Show others...
    2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 8, p. 2426-2429Article in journal (Refereed) Published
    Abstract [en]

    We report the discovery of a face-centered cubic (Al1−xCrx)2O3 solid solution [0.60bxb0.70] in films grownonto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. Theproposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å asdetermined by X-ray diffraction. The films have a b100N preferred crystallographic orientation and exhibithardness values up to 26 GPa and an elastic modulus of 220–235 GPa.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-65698 (URN)10.1016/j.tsf.2010.11.052 (DOI)000287631500008 ()
    Funder
    Swedish Research Council
    Note
    Original Publication: Ali Khatibi, Justinas Palisaitis, Carina Höglund, Anders Eriksson, Per O. Å. Persson, Jens Jensen, Jens Birch, Per Eklund and Lars Hultman, Face-Centered Cubic (Al1-xCrx)2O3 , 2011, Thin Solid Films, (519), 2426-2429. http://dx.doi.org/10.1016/j.tsf.2010.11.052 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2011-02-21 Created: 2011-02-17 Last updated: 2017-12-11Bibliographically approved
    2. Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
    Open this publication in new window or tab >>Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
    2012 (English)Conference paper, Oral presentation only (Other academic)
    Abstract [en]

    Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited using dual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, ex-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1000 °C and annealing time of 0-8 h. The fcc structure remains intact up to 700 °C. The onset of phase transformation from fcc to corundum is observed in the sample annealed at 900 °C for 2 h, where annealing for 2 h at 1000 °C results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3 prior and after the annealing, confirmed by the in-plane and out-of-plane line scans performed in EDX TEM and long-time small step size q/2q XRD patterns. The kinetics of phase transformation studied by the Jahnson-Avrami-Mehl model shows the apparent activation energy of the phase transformation process in the range of 380-480 kJ/mol. Ongoing work is focused on theoretical studies of the stability and composition of the structure of the as-deposited fcc-(Al1-xCrx)2O3 solid solution films, which are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites.

    National Category
    Manufacturing, Surface and Joining Technology Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-84381 (URN)
    Conference
    39th International Conference on Metallurgical Coatings and Thin Films (ICMCTF), 23-27 April 2012, San Diego, USA
    Available from: 2012-10-05 Created: 2012-10-05 Last updated: 2013-01-21
    3. Structural and mechanical properties of Cr-Al-O-N thin films grown by cathodic arc deposition
    Open this publication in new window or tab >>Structural and mechanical properties of Cr-Al-O-N thin films grown by cathodic arc deposition
    Show others...
    2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 19, p. 6494-6507Article in journal (Refereed) Published
    Abstract [en]

    Coatings of (CrxAl1-x)(delta)(O1-yNy)(xi) with 0.33 less than= x less than= 0.96, 0 less than= y less than= 1 and 0.63 less than= delta/xi less than= 1.30 were deposited using cathodic arc evaporation in N-2/O-2 reactive gas mixtures on 50 V negatively biased WC-10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N-2 less than 63% of the total gas, ternary (Cr,Al)(2)O-3 films containing less than1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N-2 fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr-Al-N and cubic-(Cr,Al)(2)O-3 solid solutions and secondary hexagonal alpha-(Cr,Al)(2)O-3 solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24-28 GPa, whereas the oxynitride films have a hardness of similar to 30 GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Physical vapor deposition; Solid solution; Face-centered cubic crystals; Alumina (alpha-Al2O3); Oxynitride
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-87218 (URN)10.1016/j.actamat.2012.08.010 (DOI)000311188400006 ()
    Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
    4. Structural and Mechanical Properties of (AlxCr1-x)2+yO3-y Coatings Grown by Reactive Cathodic Arc Evaporation in As-deposited and Annealed States
    Open this publication in new window or tab >>Structural and Mechanical Properties of (AlxCr1-x)2+yO3-y Coatings Grown by Reactive Cathodic Arc Evaporation in As-deposited and Annealed States
    Show others...
    2013 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 13, p. 4811-4822Article in journal (Refereed) Published
    Abstract [en]

    Coatings of (AlxCr1-x)2+yO3-y with 0.51≤x≤0.84 and 0.1≤y≤0.5 were deposited on hard cemented carbides substrates in an industrial cathodic arc evaporation system from powder-metallurgy prepared Cr/Al targets in pure O2 and O2+N2 atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and -120 V, respectively. The composition of the coatings measured by energy dispersive x-ray spectroscopy and elastic recoil detection analysis was the same as that of the targets. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed depending on the Cr/Al ratio of the coatings and O2 flow per activetarget during deposition. The corundum phase was promoted by high Cr content and high O2 flow per target, while the cubic phase was mostly observed for high Al content and low O2 flow per active target. In situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum completed in the temperature range of 900-1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio < 0.4 was 26-28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28-30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al-Cr-O have improved resistance to crater wear at the cost of flank wear compared to TiAlN coatings.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Physical vapor deposition (PVD); Ternary alloys; Alumina (α-Al2O3); Solid solution; Al-Cr-O alloys
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-87666 (URN)10.1016/j.actamat.2013.05.002 (DOI)000321601400011 ()
    Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2017-12-06Bibliographically approved
    5. Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions
    Open this publication in new window or tab >>Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    First-principles calculations are employed to investigate the stability and properties of cubic rock-salt like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a favorable coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to a have cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-87667 (URN)
    Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2016-08-31Bibliographically approved
  • 11.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Heat Treatment Studies of Cubic Al-Cr-O Thin Films2011Conference paper (Other academic)
  • 12.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Kinetics of Phase Transformation in fcc-(Al0.32Cr0.68)2O3 Thin FilmsManuscript (preprint) (Other academic)
    Abstract [en]

    Thermal stability of fcc-(Al0.32Cr0.68)2O3 thin film is investigated by ex-situ annealing of films in the temperature range of 500-1100 °C and annealing times of 2-10 h. X-ray diffraction indicates that the phase transformation from fcc to corundum crystal structure starts at 925 °C and completes at 1000 °C. This is further confirmed by high resolution transmission electron microscopy and selected area electron diffraction. The kinetics of phase transformation is analyzed by Johnson-Avrami-Mehl model. The phase transformation from fcc to corundum in (Al0.32Cr0.68)2O3 thin films is a two-stage thermally activated process. The first stage is phase transformation and has the apparent activation energy of 213±162 kJ/mol (0.44±0.34 eV/atom). This is followed by a second stage with a larger apparent activation energy of 945±27 kJ/mol (1.96±0.06 eV/atom). This is likely associated with the grain growth of a-phase upon completion of the phase transformation.

  • 13.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films2012Conference paper (Other academic)
    Abstract [en]

    Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited using dual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, ex-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1000 °C and annealing time of 0-8 h. The fcc structure remains intact up to 700 °C. The onset of phase transformation from fcc to corundum is observed in the sample annealed at 900 °C for 2 h, where annealing for 2 h at 1000 °C results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3 prior and after the annealing, confirmed by the in-plane and out-of-plane line scans performed in EDX TEM and long-time small step size q/2q XRD patterns. The kinetics of phase transformation studied by the Jahnson-Avrami-Mehl model shows the apparent activation energy of the phase transformation process in the range of 380-480 kJ/mol. Ongoing work is focused on theoretical studies of the stability and composition of the structure of the as-deposited fcc-(Al1-xCrx)2O3 solid solution films, which are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites.

  • 14.
    Khatibi, Ali
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Genvad, Axel
    Sandvik Coromant AB, Materials and Processes R&D, Stockholm, Sweden.
    Göthelid, Emmanuelle
    Sandvik Coromant AB, Materials and Processes R&D, Stockholm, Sweden.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Structural and Mechanical Properties of (AlxCr1-x)2+yO3-y Coatings Grown by Reactive Cathodic Arc Evaporation in As-deposited and Annealed States2013In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 13, p. 4811-4822Article in journal (Refereed)
    Abstract [en]

    Coatings of (AlxCr1-x)2+yO3-y with 0.51≤x≤0.84 and 0.1≤y≤0.5 were deposited on hard cemented carbides substrates in an industrial cathodic arc evaporation system from powder-metallurgy prepared Cr/Al targets in pure O2 and O2+N2 atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and -120 V, respectively. The composition of the coatings measured by energy dispersive x-ray spectroscopy and elastic recoil detection analysis was the same as that of the targets. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed depending on the Cr/Al ratio of the coatings and O2 flow per activetarget during deposition. The corundum phase was promoted by high Cr content and high O2 flow per target, while the cubic phase was mostly observed for high Al content and low O2 flow per active target. In situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum completed in the temperature range of 900-1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio < 0.4 was 26-28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28-30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al-Cr-O have improved resistance to crater wear at the cost of flank wear compared to TiAlN coatings.

  • 15.
    Khatibi, Ali
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lu, Jun
    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.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Phase transformations in face centered cubic (Al0.32Cr0.68)(2)O-3 thin films2012In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 14, p. 3216-3222Article in journal (Refereed)
    Abstract [en]

    Face centered cubic (Al0.32Cr0.68)(2)O-3 thin films have been annealed in the temperature range of 500-1000 degrees C during 2-8 h. The fcc structure of the film remains intact when annealed at temperatures up to 700 degrees C for 8 h. X-ray diffraction and transmission electron microscopy show the onset of phase transformation to corundum phase alloys in the sample annealed at 900 degrees C for 2 h, where annealing at 1000 degrees C for 2 h results in complete phase transformation to alpha-(Al0.32Cr0.68)(2)O-3. In-plane and out-of-plane line scans performed in EDX TEM and theta/2 theta XRD patterns did not show any phase separation into alpha-Cr2O3 and Al2O3 prior and after the annealing. The apparent activation energy of this process is 380-480 kJ/mol as determined by the Johnson-Mehl-Avrami model.

  • 16.
    Khatibi, Ali
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Eriksson, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per O. Å.
    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.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Face-Centered Cubic (Al1-xCrx)2O32011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 8, p. 2426-2429Article in journal (Refereed)
    Abstract [en]

    We report the discovery of a face-centered cubic (Al1−xCrx)2O3 solid solution [0.60bxb0.70] in films grownonto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. Theproposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å asdetermined by X-ray diffraction. The films have a b100N preferred crystallographic orientation and exhibithardness values up to 26 GPa and an elastic modulus of 220–235 GPa.

  • 17.
    Khatibi, Ali
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sjolen, J.
    SECO Tools AB, Sweden .
    Greczynski, Grzegorz
    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.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Structural and mechanical properties of Cr-Al-O-N thin films grown by cathodic arc deposition2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 19, p. 6494-6507Article in journal (Refereed)
    Abstract [en]

    Coatings of (CrxAl1-x)(delta)(O1-yNy)(xi) with 0.33 less than= x less than= 0.96, 0 less than= y less than= 1 and 0.63 less than= delta/xi less than= 1.30 were deposited using cathodic arc evaporation in N-2/O-2 reactive gas mixtures on 50 V negatively biased WC-10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N-2 less than 63% of the total gas, ternary (Cr,Al)(2)O-3 films containing less than1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N-2 fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr-Al-N and cubic-(Cr,Al)(2)O-3 solid solutions and secondary hexagonal alpha-(Cr,Al)(2)O-3 solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24-28 GPa, whereas the oxynitride films have a hardness of similar to 30 GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.

  • 18.
    Kolahdouz, M.
    et al.
    KTH.
    Maresca, L.
    KTH.
    Ghandi, R.
    KTH.
    Khatibi, Ali
    KTH.
    Radamson, H.
    KTH.
    Kinetic model of SiGe selective epitaxial growth using RPCVD technique2010In: ECS Transactions, ISSN 1938-6737, Vol. 33, no 6, p. 581-593Article in journal (Refereed)
    Abstract [en]

    Recently, selective epitaxial growth (SEG) of B-doped SiGe layershas been used in recessed source/drain (S/D) of pMOSFETs. Theuniaxial induced strain enhances the carrier mobility in the channel.In this work, a detailed model for SEG of SiGe has been developed topredict the growth rate and Ge content of layers indichlorosilane(DCS)-based epitaxy using a reduced-pressure CVDreactor. The model considers each gas precursor contributions fromthe gas-phase and the surface.The gas flow and temperature distribution were simulated in the CVDreactor and the results were exerted as input parameters for Maxwellenergy distribution. The diffusion of molecules from the gasboundaries was calculated by Fick’s law and Langmuir isothermtheory (in non-equilibrium case) was applied to analyze the surface.The pattern dependency of the selective growth was also modeledthrough an interaction theory between different subdivisions of thechips. Overall, a good agreement between the kinetic model and theexperimental data were obtained.

  • 19.
    Kolahdouz, Mohammadreza
    et al.
    KTH.
    Hållstedt, Julius
    KTH.
    Khatibi, Ali
    KTH.
    Östling, Mikael
    KTH.
    Wise, Rick
    Texas Instruments.
    Riley, Deborah J.
    Texas Instruments.
    Radamson, Henry
    KTH.
    Comprehensive Evaluation and Study of Pattern Dependency Behavior in Selective Epitaxial Growth of B-Doped SiGe Layers2009In: IEEE transactions on nanotechnology, ISSN 1536-125X, E-ISSN 1941-0085, Vol. 8, no 3, p. 291-297Article in journal (Refereed)
    Abstract [en]

    The influence of chip layout and architecture on thepattern dependency of selective epitaxy of B-doped SiGe layers hasbeen studied. The variations of Ge-, B-content, and growth ratehave been investigated locally within a wafer and globally fromwafer to wafer. The results are described by the gas depletion theory.Methods to control the variation of layer profile are suggested.

  • 20.
    Sjölén, Jacob
    et al.
    Seco Tools, Fagersta.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Oxynitride Coatings - Opportunities and Challenges from an Industrial Perspective2011Conference paper (Other academic)
    Abstract [en]

    The development of wear resistant coatings produced by different PVD techniques has mainly been focused onmetal-nitride and metal-carbide coatings, such as (Ti,Al)N, (Cr,Al)N, Ti(C,N) and (Ti,Si)N etc. However, duringthe recent years there has been a tremendous progress in the attempts to produce crystalline metal-oxide coatings,such as (Cr,Al)2O3, especially by using cathodic arc evaporation. Challenges, such as target poisoning andinsulating anodes have been overcome, opening up for a completely new group of materials. By the combinationof nitride and oxide coating processes, a new dimension in the material space has been opened, giving us metaloxy-nitrides. This presentation concerns coatings such as (Ti,Al)(O,N) and (Cr,Al)(O,N) deposited onto WC-Cosubstratesusing cathodic arc evaporation. Results for coating structure, analyzed by SEM, XRD, TEM, etc., andmechanical properties, analyzed by nanoindentation and metal cutting tests will be presented as a function of theO/N ratio. A unique advantage of the highly ionized plasmas combined with the relatively low depositiontemperatures in the cathodic arc processes is that the energy of the impinging species cause collision cascades inthe lattice that makes it possible to quench solid solutions and metastable compounds. These coatings have shownimproved metal cutting performance with enhanced tool life in both turning and milling applications.

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