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  • 1.
    Alami, Jones
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating 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.
    Andersson, Jon M.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Lattemann, Martina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Böhlmark, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating 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.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Phase tailoring of Ta thin films by highly ionized pulsed magnetron sputtering2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 7-8, p. 3434-3438Article in journal (Refereed)
    Abstract [en]

    Ta thin films were grown on Si substrates at different inclination angles with respect to the sputter source using high power impulse magnetron sputtering (HIPIMS), an ionized physical vapor deposition technique. The ionization allowed for better control of the energy and directionality of the sputtered species, and consequently for improved properties of the deposited films. Depositions were made on Si substrates with the native oxide intact. The structure of the as deposited films was investigated using X-ray diffraction, while a four-point probe setup was used to measure the resistivity. A substrate bias process-window for growth of bcc-Ta was observed. However, the process-window position changed with changing inclination angles of the substrate. The formation of this low-resistivity bcc-phase could be understood in light of the high ion flux from the HIPIMS discharge.

  • 2.
    Andersson, Jon M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Czigány, Zs.
    Research Institute for Technical Physics and Materials Science, Budapest, Hungary.
    Jin, P.
    National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560, Japan.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Microstructure of α-alumina thin films deposited at low temperatures on chromia template layers2004In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 22, no 1, p. 117-121Article in journal (Refereed)
    Abstract [en]

    Radio frequency sputtering has been used to deposit -alumina (-Al2O3) thin films at substrate temperatures of 280–560 °C. The films are shown to be single phased and hard. Nanoindentation gives values of 306±31 and 27±3 GPa for elastic modulus and hardness, respectively, for a substrate temperature of 280 °C. Growth of the phase was achieved by in situ predeposition of a chromia template layer. Chromia crystallizes in the same hexagonal structure as -alumina, with a lattice mismatch of 4.1% in the a- and 4.6% in the c-parameter, and is shown to nucleate readily on the amorphous substrates (silicon with a natural oxide layer). This results in local epitaxy of -alumina on the chromia layer, as is shown by transmission electron microscopy. The alumina grains are columnar with grain widths increasing from 22±7 to 41±9 nm, as the temperature increases from 280 to 560 °C. This is consistent with a surface diffusion dominated growth mode and suggests that -alumina deposition at low temperatures is possible once initial grain nucleation has occurred. Results are also presented demonstrating chromia/-alumina growth on a technological substrate (Haynes230 Ni-based super alloy, Haynes International, Inc.).

  • 3.
    Andersson, Jon M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Münger, E. Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Ab initio calculations on the effects of additives on alumina phase stability2005In: Physical review. B, Condensed matter and materials physics, ISSN 1098-0121, Vol. 71, no 014101, p. 014101-Article in journal (Refereed)
    Abstract [en]

    The effects of substitutional additives on the properties and phase stability of - and -alumina (Al2O3), are investigated by density functional theory total energy calculations. The dopants explored are 5 at. % of Cr, Mo, Co, and As substituting for Al, respectively, N and S substituting for O, in the and lattices. Overall, the results show that it is possible to shift, and even reverse, the relative stability between - and -alumina by substitutional additives. The alumina bulk moduli are, in general, only slightly affected by the dopants but density of states profiles reveal additional peaks in the alumina band gaps. We also show that phase separations into pure oxides are energetically favored over doped alumina formation, and we present results on a number of previously unstudied binary oxides.

  • 4.
    Andersson, Jon M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Münger, E. Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Molecular content of the deposition flux during reactive Ar/O2 magnetron sputtering of Al2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 05, p. Art. No. 054101 JAN 30 2006-Article in journal (Refereed)
    Abstract [en]

    The deposition flux obtained during reactive radio frequency magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by mass spectrometry. The results show significant amounts of molecular AlO+ (up to 10% of the Al+ flux) in the ionic flux incident onto the substrate. In the presence of ~10–4 Pa H2O additional OH+ and AlOH+ were detected, amounting to up to about 100% and 30% of the Al+ flux, respectively. Since the ions represent a small fraction of the total deposition flux, an estimation of the neutral content was also made. These calculations show that, due to the higher ionization probability of Al, the amount of neutral AlO in the deposition flux is of the order of, or even higher than, the amount of Al. These findings might be of great aid when explaining the alumina thin film growth process.

  • 5.
    Andersson, Jon M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 3, p. Art. No. 033305 AUG 1 2006-Article in journal (Refereed)
    Abstract [en]

    The ion flux obtained during reactive magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by energy-resolved mass spectrometry, as a function of the total and O2 partial pressures. The positive ions of film-forming species exhibited bimodal energy distributions, both for direct current and radio frequency discharges, with the higher energy ions most likely originating from sputtered neutrals. For the negative oxygen ions a high-energy peak was observed, corresponding to ions formed at the target surface and accelerated towards the substrate over the sheath potential. As the total pressure was increased the high-energy peaks diminished due to gas-phase scattering. Based on these results, the role of energetic bombardment for the phase constituent of alumina thin films are discussed.

  • 6.
    Andersson, Jon Martin
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Controlling the Formation and Stability of Alumina Phases2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this work, physical phenomena related to the growth and phase formation of alumina, Al2O3, are investigated by experiments and computer calculations. Alumina finds applications in a wide variety of areas, due to many beneficial properties and several existing crystalline phases. For example, the α and κ phases are widely used as wear-resistant coatings due to their hardness and thermal stability, while, e.g., the metastable γ and θ phases find applications as catalysts or catalyst supports, since their surface energies are low and, hence, they have large surface areas available for catalytic reactions.

    The metastable phases are involved in transition sequences, which all irreversibly end in the transformation to the stable α phase at about 1050 °C. As a consequence, the metastable aluminas, which can be grown at low temperatures, cannot be used in high temperature applications, since they are destroyed by the transformation into α. In contrast, α-alumina, which is the only thermodynamically stable phase, typically require high growth temperatures (~1000 °C), prohibiting the use of temperature sensitive substrates. Thus, there is a need for increasing the thermal stability of metastable alumina and decreasing the growth temperature of the α phase.

    In the experimental part of this work, hard and single-phased α-alumina thin films were grown by magnetron sputtering at temperatures down to 280 °C. This dramaticdecrease in growth temperature was achieved by two main factors. Firstly, the nucleation stage of growth was controlled by pre-depositing a chromia “template” layer, which is demonstrated to promote nucleation of α-alumina. Secondly, it is shown that energetic bombardment was needed to sustain growth of the α phase. Energy-resolved mass spectrometry measurements demonstrate that the likely source of energetic bombardment, in the present case, was oxygen ions/atoms originating from the target surface. Overall, these results demonstrate that low-temperature α-alumina growth is possible by controlling both the nucleation step of growth as well as the energetic bombardment of the growing film. In addition, the mass spectrometry studies showed that a large fraction of the deposition flux consisted of AlO molecules, which were sputtered from the target. Since the film is formed by chemical bonding between the depositing species, this observation is important for the fundamental understanding of alumina thin film growth.

    In the computational part of the work, the effect of additives on the phase stability of α- and θ-alumina was investigated by density functional theory calculations. A systematic study was performed of a large number of substitutional dopants in the alumina lattices. Most tested dopants tended to reverse the stability between α- and θ-alumina; so that, e.g., Modoping made the θ phase energetically favored. Thus, it is possible to stabilize the metastable phases by additives. An important reason for this is the physical size of the dopant ions with respect to the space available within the alumina lattices. For example, large ions induced θ stabilization, while ions only slightly larger than Al, e.g., Co and Cu, gave a slight increase in the relative stability of the α phase. We also studied the stability of some of these compounds with respect to pure alumina and other phases, containing the dopants, with the result that phase separations are energetically favored and will most likely occur at elevated temperatures.

    List of papers
    1. Microstructure of α-alumina thin films deposited at low temperatures on chromia template layers
    Open this publication in new window or tab >>Microstructure of α-alumina thin films deposited at low temperatures on chromia template layers
    2004 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 22, no 1, p. 117-121Article in journal (Refereed) Published
    Abstract [en]

    Radio frequency sputtering has been used to deposit -alumina (-Al2O3) thin films at substrate temperatures of 280–560 °C. The films are shown to be single phased and hard. Nanoindentation gives values of 306±31 and 27±3 GPa for elastic modulus and hardness, respectively, for a substrate temperature of 280 °C. Growth of the phase was achieved by in situ predeposition of a chromia template layer. Chromia crystallizes in the same hexagonal structure as -alumina, with a lattice mismatch of 4.1% in the a- and 4.6% in the c-parameter, and is shown to nucleate readily on the amorphous substrates (silicon with a natural oxide layer). This results in local epitaxy of -alumina on the chromia layer, as is shown by transmission electron microscopy. The alumina grains are columnar with grain widths increasing from 22±7 to 41±9 nm, as the temperature increases from 280 to 560 °C. This is consistent with a surface diffusion dominated growth mode and suggests that -alumina deposition at low temperatures is possible once initial grain nucleation has occurred. Results are also presented demonstrating chromia/-alumina growth on a technological substrate (Haynes230 Ni-based super alloy, Haynes International, Inc.).

    Keywords
    alumina, chromium compounds, sputtered coatings, indentation, elastic moduli, hardness, sputter deposition, transmission electron microscopy, epitaxial layers, grain size, surface diffusion, nucleation, wear resistant coatings, thermal barrier coatings
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13578 (URN)10.1116/1.1636157 (DOI)
    Available from: 2008-11-13 Created: 2008-09-29 Last updated: 2017-12-13
    2. Phase control of Al2O3 thin films grown at low temperatures
    Open this publication in new window or tab >>Phase control of Al2O3 thin films grown at low temperatures
    Show others...
    2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 513, no 1-2, p. 57-59Article in journal (Refereed) Published
    Abstract [en]

    Low-temperature growth (500 °C) of α-Al2O3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr2O3 nucleation layers and the effects of the total and O2 partial pressures were investigated. At 0.33 Pa total pressure and ≥ 16 mPa O2 partial pressure α-Al2O3 films formed, while at lower O2 pressure or higher total pressure (0.67 Pa), only γ phase was detected in the films (which were all stoichiometric). Based on these results we suggest that α phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al2O3 films can be controlled by controlling the energy of the depositing species. The effect of residual H2O (10− 4 Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al2O3 growth processes.

    Place, publisher, year, edition, pages
    Elsevier, 2006
    Keywords
    Aluminum oxide, Chromium oxide, Sputtering, Ion bombardment, X-ray diffraction
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-14318 (URN)10.1016/j.tsf.2006.01.016 (DOI)
    Note
    Original publication: Andersson, J.M., Wallin, E., Helmersson, U., Kreissig, U. and Münger, E.P., Phase control of Al2O3 thin films grown at low temperatures, 2006, Thin Solid Films, (513), 1-2, 57-59. http://dx.doi.org/10.1016/j.tsf.2006.01.016. Copyright: Elsevier B.V., http://www.elsevier.com/ Available from: 2007-03-02 Created: 2007-03-02 Last updated: 2017-12-13Bibliographically approved
    3. Molecular content of the deposition flux during reactive Ar/O2 magnetron sputtering of Al
    Open this publication in new window or tab >>Molecular content of the deposition flux during reactive Ar/O2 magnetron sputtering of Al
    2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 05, p. Art. No. 054101 JAN 30 2006-Article in journal (Refereed) Published
    Abstract [en]

    The deposition flux obtained during reactive radio frequency magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by mass spectrometry. The results show significant amounts of molecular AlO+ (up to 10% of the Al+ flux) in the ionic flux incident onto the substrate. In the presence of ~10–4 Pa H2O additional OH+ and AlOH+ were detected, amounting to up to about 100% and 30% of the Al+ flux, respectively. Since the ions represent a small fraction of the total deposition flux, an estimation of the neutral content was also made. These calculations show that, due to the higher ionization probability of Al, the amount of neutral AlO in the deposition flux is of the order of, or even higher than, the amount of Al. These findings might be of great aid when explaining the alumina thin film growth process.

    Place, publisher, year, edition, pages
    Institutionen för fysik, kemi och biologi, 2006
    Keywords
    alumina, dielectric thin films, sputter deposition, mass spectra
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-10452 (URN)10.1063/1.2170404 (DOI)
    Note
    Original publication: Andersson, J.M., Wallin, E., Münger, E.P. & Helmersson, U., Molecular content of the deposition flux during reactive Ar/O2 magnetron sputtering of Al, 2006, Applied Physics Letters, (88), 054101. http://dx.doi.org/10.1063/1.2170404. Copyright: American Institute of Physics, http://apl.aip.org/apl/top.jspAvailable from: 2007-12-17 Created: 2007-12-17 Last updated: 2017-12-14
    4. Effects of additives in α- and θ-alumina: an ab initio study
    Open this publication in new window or tab >>Effects of additives in α- and θ-alumina: an ab initio study
    2004 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, Vol. 16, no 49, p. 8971-8980Article in journal (Refereed) Published
    Abstract [en]

    It is of high fundamental and practical importance to be able to control the formation and stability of the different crystalline phases of alumina (Al2O3). In this study, we have used density functional theory methods to investigate the changes induced in the thermodynamically stable α phase and the metastable θ phase as one eighth of the Al atoms are substituted for different additives (Sc, W, Mo, Cr, Cu, Si, and B). The calculations predict that the additives strongly affect the relative stability between the two phases. Most tested additives are shown to shift the relative stability towards, and in some cases completely stabilize, the θ phase, while Cu doping is predicted to increase the relative stability of the α phase. The reasons for these effects are discussed, as are possible implications on the growth and use of doped aluminas in practical applications. In addition, the effects of the additives on bulk moduli and densities of states have been investigated.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13581 (URN)10.1088/0953-8984/16/49/012 (DOI)
    Available from: 2005-12-13 Created: 2005-12-13 Last updated: 2013-10-30
    5. Ab initio calculations on the effects of additives on alumina phase stability
    Open this publication in new window or tab >>Ab initio calculations on the effects of additives on alumina phase stability
    Show others...
    2005 (English)In: Physical review. B, Condensed matter and materials physics, ISSN 1098-0121, Vol. 71, no 014101, p. 014101-Article in journal (Refereed) Published
    Abstract [en]

    The effects of substitutional additives on the properties and phase stability of - and -alumina (Al2O3), are investigated by density functional theory total energy calculations. The dopants explored are 5 at. % of Cr, Mo, Co, and As substituting for Al, respectively, N and S substituting for O, in the and lattices. Overall, the results show that it is possible to shift, and even reverse, the relative stability between - and -alumina by substitutional additives. The alumina bulk moduli are, in general, only slightly affected by the dopants but density of states profiles reveal additional peaks in the alumina band gaps. We also show that phase separations into pure oxides are energetically favored over doped alumina formation, and we present results on a number of previously unstudied binary oxides.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13582 (URN)10.1103/PhysRevB.71.014101 (DOI)
    Available from: 2005-12-13 Created: 2005-12-13 Last updated: 2013-10-30
    6. Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures
    Open this publication in new window or tab >>Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures
    2006 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 3, p. Art. No. 033305 AUG 1 2006-Article in journal (Refereed) Published
    Abstract [en]

    The ion flux obtained during reactive magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by energy-resolved mass spectrometry, as a function of the total and O2 partial pressures. The positive ions of film-forming species exhibited bimodal energy distributions, both for direct current and radio frequency discharges, with the higher energy ions most likely originating from sputtered neutrals. For the negative oxygen ions a high-energy peak was observed, corresponding to ions formed at the target surface and accelerated towards the substrate over the sheath potential. As the total pressure was increased the high-energy peaks diminished due to gas-phase scattering. Based on these results, the role of energetic bombardment for the phase constituent of alumina thin films are discussed.

    Place, publisher, year, edition, pages
    College Park, MD, United States: American Institute of Physics (AIP), 2006
    Keywords
    aluminium, sputter deposition, diffusion, mass spectra, high-frequency discharges, plasma materials processing
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-10472 (URN)10.1063/1.2219163 (DOI)000239764100014 ()
    Note

    Original publication: Jon M. Andersson, E. Wallin, E. P. Münger & U. Helmersson, Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures, 2006, Journal of Applied Physics, (100), 033305. http://dx.doi.org/10.1063/1.2219163. Copyright: American Institute of Physics, http://jap.aip.org/jap/top.jsp

    Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2017-12-14
  • 7.
    Andersson, Jon Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Kreissig, U.
    Institute for Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, PF 510119, D-01314 Dresden, Germany.
    Münger, E. Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Phase control of Al2O3 thin films grown at low temperatures2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 513, no 1-2, p. 57-59Article in journal (Refereed)
    Abstract [en]

    Low-temperature growth (500 °C) of α-Al2O3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr2O3 nucleation layers and the effects of the total and O2 partial pressures were investigated. At 0.33 Pa total pressure and ≥ 16 mPa O2 partial pressure α-Al2O3 films formed, while at lower O2 pressure or higher total pressure (0.67 Pa), only γ phase was detected in the films (which were all stoichiometric). Based on these results we suggest that α phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al2O3 films can be controlled by controlling the energy of the depositing species. The effect of residual H2O (10− 4 Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al2O3 growth processes.

  • 8.
    Trinh, David Huy
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. 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.
    Andersson, Jon M.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Collin, M.
    Sandvik Tooling, Stockholm, Sweden.
    Reineck, I.
    Sandvik Tooling, Stockholm, Sweden.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating 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.
    Radio frequency dual magnetron sputtering deposition and characterization of nanocomposite Al2O3-ZrO2 thin films2006In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 24, no 2, p. 309-316Article in journal (Refereed)
    Abstract [en]

    Radio frequency magnetron sputtering from oxide targets has been used to synthesize crystalline alumina–zirconia nanocomposites at a relatively low temperature of 450  °C. Films of different compositions have been deposited ranging from pure zirconia to pure alumina, the compositions being measured with Rutherford backscattering and elastic recoil detection analysis. X-ray diffraction studies show the presence of the monoclinic zirconia phase in pure zirconia films. Addition of alumina into the film results in the growth of the cubic zirconia phase and amorphous alumina. No crystalline alumina was detected in either the composite or the pure alumina film. The microstructure of the films as studied by high resolution electron microscopy and scanning transmission electron microscopy shows a columnar growth mode in both the pure zirconia and nanocomposite films, but reveals differences in the intracolumnar structure. For the nanocomposite small equiaxed grains, ~5  nm in size, are found at the base of the columns at the interface with the substrate. An amorphous tissue of alumina was present between the small crystallites in the case of the nanocomposite.

  • 9.
    Wallin, Erik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Andersson, Jon M.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Effects of additives in α- and θ-alumina: an ab initio study2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, Vol. 16, no 49, p. 8971-8980Article in journal (Refereed)
    Abstract [en]

    It is of high fundamental and practical importance to be able to control the formation and stability of the different crystalline phases of alumina (Al2O3). In this study, we have used density functional theory methods to investigate the changes induced in the thermodynamically stable α phase and the metastable θ phase as one eighth of the Al atoms are substituted for different additives (Sc, W, Mo, Cr, Cu, Si, and B). The calculations predict that the additives strongly affect the relative stability between the two phases. Most tested additives are shown to shift the relative stability towards, and in some cases completely stabilize, the θ phase, while Cu doping is predicted to increase the relative stability of the α phase. The reasons for these effects are discussed, as are possible implications on the growth and use of doped aluminas in practical applications. In addition, the effects of the additives on bulk moduli and densities of states have been investigated.

  • 10.
    Wallin, Erik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Andersson, Jon Martin
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Lattemann, Martina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 12, p. 3877-3883Article in journal (Refereed)
    Abstract [en]

    The effects of residual water on the phase formation, composition, and microstructure evolution of magnetron sputter deposited crystalline alumina thin films have been investigated. To mimic different vacuum conditions, depositions have been carried out with varying partial pressures of H2O. Films have been grown both with and without chromia nucleation layers. It is shown that films deposited onto chromia nucleation layers at relatively low temperatures (500 °C) consists of crystalline alpha-alumina if deposited at a low enough total pressure under ultra high vacuum (UHV) conditions. However, as water was introduced a gradual increase of the gamma phase content in the film with increasing film thickness was observed. At the same time, the microstructure changed drastically from a dense columnar structure to a structure with small, equiaxed grains. Based on mass spectrometry measurements and previous ab initio calculations, we suggest that either bombardment of energetic negative (or later neutralized) species being accelerated over the target sheath voltage, adsorbed hydrogen on growth surfaces, or a combination of these effects, is responsible for the change in structure. For films containing the metastable gamma phase under UHV conditions, no influence of residual water on the phase content was observed. The amounts of hydrogen incorporated into the films, as determined by elastic recoil detection analysis, were shown to be low. Overall, the results demonstrate that residual water present during film growth drastically affects film properties, also in cases where the hydrogen incorporation is found to be low.

  • 11.
    Wallin, Erik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Andersson, Jon Martin
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Münger, E. Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 12, p. 125409-1-125409-9Article in journal (Refereed)
    Abstract [en]

    The interactions of Al, O, and O2 with different α- Al2O3 (0001) surfaces have been studied using ab initio density functional theory methods. All three surface terminations obtainable by cleaving the bulk structure [single Al-layer (AlO), double Al-layer (AlAl), and O terminations] have been considered, as well as a completely hydrogenated O-terminated surface. Adsorbed Al shows strong ioniclike interaction with the AlO - and O-terminated surfaces, and several metastable adsorption sites are identified on the O-terminated surface. On the completely hydrogenated surface, however, Al adsorption in the bulk position is found to be unstable or very weak for the studied configurations of surface H atoms. Atomic O is found to interact strongly with the AlAl -terminated surface, where also O2 dissociative adsorption without any appreciable barrier is observed. In contrast, O adsorption on the AlO -terminated surface is metastable relative to molecular O2. On the O-terminated surface, we find the creation of O surface vacancies to be plausible, especially upon exposure to atomic O at elevated temperatures. The results are mainly discussed in the context of alumina thin film growth and provide insight into phenomena related to, e.g., preferred adsorption sites and effects of hydrogen on the growth.

  • 12.
    Wallin, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Andersson, Jon
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Münger, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Chirita, Valeriu
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Ab initio studies of adsorption and diffusion processes on alpha-Al2O3 (0001) surfaces2007In: AVS 54th International Symposium,2007, 2007Conference paper (Other academic)
  • 13.
    Wallin, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Andersson, Jon
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Münger, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Chirita, Valeriu
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Ab initio studies of adsorption and diffusion processes on alpha-Al2O3 (0001) surfaces2007In: International Symposium on Reactive Sputter Deposition,2007, 2007Conference paper (Other academic)
    Abstract [en]

    As one of the technologically most important ceramic materials, alumina (Al2O3) thin film growth has been studied extensively in the past. However, the mechanisms behind the formation of different phases and microstructures are still poorly understood, especially for physically vapor deposited films. An increased atomic scale understanding of alumina surface processes would thus be an important step towards a more complete understanding and control of the deposition process. In the present work, density functional theory based methods were used to study the adsorption of Al, O, AlO, and O2 on different terminations of alpha-alumina (0001) surfaces. The results show the existence of several metastable adsorption sites on the O-terminated surface and provide a possible explanation for the well-known difficulties in growing -Ñ-alumina at lower temperatures. Moreover, we demonstrate that Al adsorption in bulk positions is unstable, or considerably weaker, for completely hydrogenated surfaces, indicating that hydrogen stemming from residues in vacuum systems, might hinder the growth of crystalline alpha-alumina. Furthermore, nudged elastic band investigations of dynamic energy barriers for different surface diffusion processes show that Al diffusion, on the Al-terminated (0001) surface, requires only ~0.7 eV. This value is considerably lower than what is generally expected for the low temperature synthesis of alpha-alumina phase. These results add significantly to understanding the effects of several important factors on alumina growth, and their implication, on optimizing deposition processes for the synthesis of alumina films with desired properties, will be discussed.

1 - 13 of 13
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