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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.
    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.

  • 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.
    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.

  • 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, 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.

  • 5.
    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.

  • 6.
    Helmersson, Ulf
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Lattemann, Martina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Hysteresis-free reactive deposi-tion of alpha-Al2O3 using high HIPIMS2007In: HIPIMS ABS-Days Conference,2007, 2007Conference paper (Other academic)
  • 7.
    Helmersson, Ulf
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Lattemann, Martina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Reactive High Power Impulse Magnetron Sputter Deposition of Alumina2007In: AVS 54th International Symposium,2007, 2007Conference paper (Other academic)
  • 8.
    Lattemann, Martina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Microstructure evolution in high power impulse magnetron sputtering deposited titanium nitride2007In: AVS 54th International Symposium,2007, 2007Conference paper (Other academic)
  • 9.
    Lundin, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Brenning, Nils
    Royal Institute of Technology.
    Jädernäs, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Larsson, Petter
    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.
    Lattemann, Martina
    Tech University of Darmstadt.
    Raadu, Michael A
    Royal Institute Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Transition between the discharge regimes of high power impulse magnetron sputtering and conventional direct current magnetron sputtering2009In: PLASMA SOURCES SCIENCE and TECHNOLOGY, ISSN 0963-0252, Vol. 18, no 4, p. 045008-Article in journal (Refereed)
    Abstract [en]

    Current and voltage have been measured in a pulsed high power impulse magnetron sputtering (HiPIMS) system for discharge pulses longer than 100 mu s. Two different current regimes could clearly be distinguished during the pulses: (1) a high-current transient followed by (2) a plateau at lower currents. These results provide a link between the HiPIMS and the direct current magnetron sputtering (DCMS) discharge regimes. At high applied negative voltages the high-current transient had the characteristics of HiPIMS pulses, while at lower voltages the plateau values agreed with currents in DCMS using the same applied voltage. The current behavior was found to be strongly correlated with the chamber gas pressure, where increasing gas pressure resulted in increasing peak current and plateau current. Based on these experiments it is suggested here that the high-current transients cause a depletion of the working gas in the area in front of the target, and thereby a transition to a DCMS-like high-voltage, lower current regime.

  • 10.
    Lundin, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Petter
    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.
    Lattemann, Martina
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Brenning, Nils
    Royal Institute of Technology, Stockholm.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Cross-field ion transport during high power impulse magnetron sputtering2008In: Plasma Sources Science and Technology, ISSN 0963-0252, Vol. 17, no 035021Article in journal (Refereed)
    Abstract [en]

    In this study, the effect on thin film growth due to an anomalous electron transport, found in high power impulse magnetron sputtering (HiPIMS), has been investigated for the case of a planar circular magnetron. An important consequence of this type of transport is that it affects the way ions are being transported in the plasma. It was found that a significant fraction of ions are transported radially outwards in the vicinity of the cathode, across the magnetic field lines, leading to increased deposition rates directly at the side of the cathode (perpendicular to the target surface). Furthermore, this mass transport parallel to the target surface leads to that the fraction of sputtered material reaching a substrate placed directly in front of the target is substantially lower in HiPIMS compared with conventional direct current magnetron sputtering (dcMS). This would help to explain the lower deposition rates generally observed for HiPIMS compared with dcMS. Moreover, time-averaged mass spectrometry measurements of the energy distribution of the cross-field transported ions were carried out. The measured distributions show a direction-dependent high-energy tail, in agreement with predictions of the anomalous transport mechanism.

  • 11.
    Selinder, T.I.
    et al.
    Sandvik Tooling, SE-126 80 Stockholm, Sweden.
    Coronel, E.
    Sandvik Tooling, SE-126 80 Stockholm, Sweden.
    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.
    α-alumina coatings on WC/Co substrates by physical vapor deposition2009In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 27, no 2, p. 507-512Article in journal (Refereed)
    Abstract [en]

    Physical vapor deposition coatings for cutting tools may be deposited by, e.g. reactive magnetron sputtering. Alumina growth in Ar/O2 gas mixtures gives rise to problems due to insulating layers on targets, and hysteresis effects with respect to oxygen gas flow. In this paper is described a technology for the deposition of crystalline alumina: reactive high power impulse magnetron sputtering. Pure Al was used as target material, and the cemented carbide (WC/Co) substrates were kept at 500-650 ºC. Hysteresis effects with respect to oxygen gas flow were alleviated, which enabled stable growth at a high deposition rate. The high power impulses were helpful in obtaining a crystalline oxide coating. X-ray diffraction and crosssection transmission electron microscopy showed that α-alumina films were formed. Technological testing of these PVD alumina coatings, with state-of-the-art AlTiN as benchmark, showed significantly improved crater wear resistance in steel turning.

  • 12.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Alumina Thin Film Growth: Experiments and Modeling2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.

    In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.

    In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.

    List of papers
    1. 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
    2. Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
    Open this publication in new window or tab >>Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
    Show others...
    2006 (English)In: 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) Published
    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.

    Place, publisher, year, edition, pages
    College Park, MD, United States: American Physical Society, 2006
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-10427 (URN)10.1103/PhysRevB.74.125409 (DOI)000240872500080 ()
    Note

    Original publication: E. Wallin, J.M. Andersson, E.P. Münger, V. Chirita & U. Helmersson, Ab initio studies of Al, O, and O2 adsorption on α- Al2 O3 (0001) surfaces, 2006, Physical Review B, (74), 125409. http://dx.doi.org/10.1103/PhysRevB.74.125409. Copyright: The America Physical Society, http://prb.aps.org/

    Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2018-07-03Bibliographically approved
    3. Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
    Open this publication in new window or tab >>Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
    2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 12, p. 3877-3883Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    ScienceDirect, 2008
    Keywords
    Aluminum oxide, Phase formation, Sputtering, Water
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-11476 (URN)10.1016/j.tsf.2007.07.135 (DOI)
    Note
    Original publication: E. Wallin, J.M. Andersson, M. Lattemann, and U. Helmersson, Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films, 2008, Thin Solid Films, (516), 12, 3877-3883. http://dx.doi.org/10.1016/j.tsf.2007.07.135. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2017-12-13Bibliographically approved
  • 13.
    Wallin, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Alumina Thin Films: From Computer Calculations to Cutting Tools2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis deals with experimental and theoretical studies related to alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. However, controlling thin film growth of this material, in particular at low substrate temperatures, is not straightforward. The aim of this work is to increase the understanding of the basic mechanisms governing alumina growth and to investigate novel ways of synthesizing alumina coatings. The thesis can be divided into two main parts, where the first part deals with fundamental studies of mechanisms affecting alumina growth and the second part with more application-oriented studies of high power impulse magnetron sputter (HiPIMS) deposition of the material.

    In the first part, it was shown that the thermodynamically stable α phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of merely 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α-alumina (in addition to the effect of the chromia nucleation layer). Moreover, the effects of residual water on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1*10-5 Torr was introduced, the columnar α-alumina growth was disrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the γ-alumina content was found to increase with increasing film thickness.

    To gain a better understanding of the atomistic processes occurring on the surface, density functional theory based computational studies of adsorption and diffusion of Al, O, AlO, and O2 on different α-alumina (0001) surfaces were also performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites and also show how adsorbed hydrogen might inhibit further growth of α-alumina crystallites. In addition, it was shown that the Al surface diffusion activation energies are unexpectedly low, suggesting that limited surface diffusivity is not the main obstacle for low-temperature α-alumina growth. Instead, it is suggested to be more important to find ways of reducing the amount of impurities, especially hydrogen, in the process and to facilitate α-alumina nucleation when designing new processes for low-temperature deposition of α-alumina.

    In the second part of the thesis, reactive HiPIMS deposition of alumina was studied. In HiPIMS, a high-density plasma is created by applying very high power to the sputtering magnetron at a low duty cycle. It was found, both from experiments and modeling, that the use of HiPIMS drastically influences the characteristics of the reactive sputtering process, causing reduced target poisoning and thereby reduced or eliminated hysteresis effects and relatively high deposition rates of stoichiometric alumina films. This is not only of importance for alumina growth, but for reactive sputter deposition in general, where hysteresis effects and loss of deposition rate pose a substantial problem. Moreover, it was found that the energetic and ionized deposition flux in the HiPIMS discharge can be used to lower the deposition temperature of α-alumina. Coatings predominantly consisting of the α phase were grown at temperatures as low as 650 °C directly onto cemented carbide substrates without the use of nucleation layers. Such coatings were also deposited onto cutting inserts and were tested in a steel turning application. The coatings were found to increase the crater wear resistance compared to a benchmark TiAlN coating, and the process consequently shows great potential for further development towards industrial applications.

    List of papers
    1. 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
    2. Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
    Open this publication in new window or tab >>Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
    Show others...
    2006 (English)In: 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) Published
    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.

    Place, publisher, year, edition, pages
    College Park, MD, United States: American Physical Society, 2006
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-10427 (URN)10.1103/PhysRevB.74.125409 (DOI)000240872500080 ()
    Note

    Original publication: E. Wallin, J.M. Andersson, E.P. Münger, V. Chirita & U. Helmersson, Ab initio studies of Al, O, and O2 adsorption on α- Al2 O3 (0001) surfaces, 2006, Physical Review B, (74), 125409. http://dx.doi.org/10.1103/PhysRevB.74.125409. Copyright: The America Physical Society, http://prb.aps.org/

    Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2018-07-03Bibliographically approved
    3. Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
    Open this publication in new window or tab >>Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
    2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 12, p. 3877-3883Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    ScienceDirect, 2008
    Keywords
    Aluminum oxide, Phase formation, Sputtering, Water
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-11476 (URN)10.1016/j.tsf.2007.07.135 (DOI)
    Note
    Original publication: E. Wallin, J.M. Andersson, M. Lattemann, and U. Helmersson, Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films, 2008, Thin Solid Films, (516), 12, 3877-3883. http://dx.doi.org/10.1016/j.tsf.2007.07.135. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2017-12-13Bibliographically approved
    4. Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration
    Open this publication in new window or tab >>Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration
    2009 (English)In: JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN 0022-3727, Vol. 42, no 12, p. 125302-Article in journal (Refereed) Published
    Abstract [en]

    Investigations of activation energy barriers for Al surface hopping on alpha-Al2O3 (0 0 0 1) surfaces have been carried out by means of first-principles density functional theory calculations and the nudged elastic band method. Results show that surface diffusion on the (most stable) Al-terminated surface is relatively fast with an energy barrier of 0.75 eV, whereas Al hopping on the O-terminated surface is slower, with barriers for jumps from the two metastable positions existing on this surface to the stable site of 0.31 and 0.99 eV. Based on this study and on the literature, the governing mechanisms during low-temperature alpha-alumina thin film growth are summarized and discussed. Our results support suggestions made in some previous experimental studies, pointing out that limited surface diffusivity is not the main obstacle for alpha-alumina growth at low-to-moderate temperatures, and that other effects should primarily be considered when designing novel processes for low-temperature alpha-alumina deposition.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-19393 (URN)10.1088/0022-3727/42/12/125302 (DOI)
    Note
    Original Publication: Erik Wallin, Peter Münger, Valeriu Chirita and Ulf Helmersson, Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration, 2009, JOURNAL OF PHYSICS D-APPLIED PHYSICS, (42), 12, 125302. http://dx.doi.org/10.1088/0022-3727/42/12/125302 Copyright: Iop Publishing Ltd http://www.iop.org/ Available from: 2009-06-29 Created: 2009-06-22 Last updated: 2013-10-30Bibliographically approved
    5. Hysteresis-free reactive high power impulse magnetron sputtering
    Open this publication in new window or tab >>Hysteresis-free reactive high power impulse magnetron sputtering
    2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 18, p. 6398-6401Article in journal (Refereed) Published
    Abstract [en]

    High power impulse magnetron sputtering (HIPIMS) of an Al target in Ar/O2 mixtures has been studied. The use of HIPIMS is shown to drastically influence the process characteristics compared to conventional sputtering. Under suitable conditions, oxide formation on the target as the reactive gas flow is increased is suppressed, and the hysteresis effect commonly observed as the gas flow is varied during conventional sputtering can be reduced, or even completely eliminated, using HIPIMS. Consequently, stoichiometric alumina can be deposited under stable process conditions at high rates. Possible explanations for this behavior as well as a model qualitatively describing the process are presented.

    Keywords
    Reactive Sputtering, High Power Impulse Magnetron Sputtering, Alumina, Process modeling
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-15028 (URN)10.1016/j.tsf.2007.08.123 (DOI)
    Note
    Original publication: E. Wallin and U. Helmersson, Hysteresis-free reactive high power impulse magnetron sputtering, 2008, Thin Solid Films, (516), 18, 6398-6401.http://dx.doi.org/10.1016/j.tsf.2007.08.123. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2008-10-10 Created: 2008-10-10 Last updated: 2017-12-11Bibliographically approved
    6. Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering
    Open this publication in new window or tab >>Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering
    2008 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 82, no 3, p. 36002-Article in journal (Refereed) Published
    Abstract [en]

    α-alumina coatings have been deposited directly onto cemented-carbide and Mo substrates at a temperature as low as 650 °C using reactive high-power impulse magnetron sputtering (HiPIMS) of Al in an Ar/O2 gas mixture. The coatings consisted of plate-like crystallites, as revealed by scanning electron microscopy. α phase growth was retained over the studied range of substrate bias voltages (from floating potential up to -100 V), with films exhibiting a slightly denser microstructure at higher bias voltages. X-ray diffraction indicated that the α-alumina grains had a preferred orientation of (0001)-planes perpendicular to the substrate surface. X-ray analysis of films deposited at 575 °C indicated the presence of γ-alumina, whereas films grown at 500 °C or lower were X-ray amorphous.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-15354 (URN)10.1209/0295-5075/82/36002 (DOI)
    Note
    Original Publication: Erik Wallin, T. I. Selinder, M. Elfwing and Ulf Helmersson, Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering, 2008, Europhysics letters, (82), 36002. http://dx.doi.org/10.1209/0295-5075/82/36002 Copyright: EDP Sciences. http://publications.edpsciences.org/ Available from: 2009-02-22 Created: 2008-11-05 Last updated: 2017-12-14Bibliographically approved
    7. α-alumina coatings on WC/Co substrates by physical vapor deposition
    Open this publication in new window or tab >>α-alumina coatings on WC/Co substrates by physical vapor deposition
    2009 (English)In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 27, no 2, p. 507-512Article in journal (Refereed) Published
    Abstract [en]

    Physical vapor deposition coatings for cutting tools may be deposited by, e.g. reactive magnetron sputtering. Alumina growth in Ar/O2 gas mixtures gives rise to problems due to insulating layers on targets, and hysteresis effects with respect to oxygen gas flow. In this paper is described a technology for the deposition of crystalline alumina: reactive high power impulse magnetron sputtering. Pure Al was used as target material, and the cemented carbide (WC/Co) substrates were kept at 500-650 ºC. Hysteresis effects with respect to oxygen gas flow were alleviated, which enabled stable growth at a high deposition rate. The high power impulses were helpful in obtaining a crystalline oxide coating. X-ray diffraction and crosssection transmission electron microscopy showed that α-alumina films were formed. Technological testing of these PVD alumina coatings, with state-of-the-art AlTiN as benchmark, showed significantly improved crater wear resistance in steel turning.

    Keywords
    HiPIMS, HPPMS, ionized-PVD, alumina, corundum
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-15359 (URN)10.1016/j.ijrmhm.2008.10.007 (DOI)
    Note
    On the day of defence date the status of article VII was: Accepted. Original Publication: T.I. Selinder, E. Coronel, Erik Wallin and Ulf Helmersson, α-alumina coatings on WC/Co substrates by physical vapor deposition, 2009, International journal of refractory metals & hard materials, (27), 2, 507-512. http://dx.doi.org/10.1016/j.ijrmhm.2008.10.007 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2009-02-23 Created: 2008-11-05 Last updated: 2017-12-14Bibliographically approved
  • 14.
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Deposition of crystalline alumina by reactive high power impulse magnetron sputtering2007In: Symposium on Ionized Physical Vapor Deposition,2007, 2007Conference paper (Other academic)
  • 15.
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Deposition of Crystalline Alumina Coatings using Reactive High Power Impulse Magnetron Sputtering - Process and Film Properties2008In: The 11:th International Conference on Plasma Surface Engineering,2008, 2008Conference paper (Other academic)
  • 16.
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Deposition of Metal Oxide Coatings using Reactive High Power Impulse Magnetron Sputtering2008In: AVS 55th International Symposium,2008, 2008Conference paper (Other academic)
    Abstract [en]

      

  • 17.
    Wallin, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Low-temperature Hysteresis-free Reactive Deposition of Alpha-alumina2008In: 51st SVC Annual Technical Conference,2008, 2008Conference paper (Other academic)
    Abstract [en]

       

  • 18.
    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.

  • 19.
    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.

  • 20.
    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.

  • 21.
    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)
  • 22.
    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.

  • 23.
    Wallin, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Hysteresis-free reactive high power impulse magnetron sputtering2007In: The Symposium on Reactive Sputter Deposition,2007, 2007Conference paper (Other academic)
  • 24.
    Wallin, Erik
    et al.
    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.
    Hysteresis-free reactive high power impulse magnetron sputtering2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 18, p. 6398-6401Article in journal (Refereed)
    Abstract [en]

    High power impulse magnetron sputtering (HIPIMS) of an Al target in Ar/O2 mixtures has been studied. The use of HIPIMS is shown to drastically influence the process characteristics compared to conventional sputtering. Under suitable conditions, oxide formation on the target as the reactive gas flow is increased is suppressed, and the hysteresis effect commonly observed as the gas flow is varied during conventional sputtering can be reduced, or even completely eliminated, using HIPIMS. Consequently, stoichiometric alumina can be deposited under stable process conditions at high rates. Possible explanations for this behavior as well as a model qualitatively describing the process are presented.

  • 25.
    Wallin, Erik
    et al.
    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.
    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.
    Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration2009In: JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN 0022-3727, Vol. 42, no 12, p. 125302-Article in journal (Refereed)
    Abstract [en]

    Investigations of activation energy barriers for Al surface hopping on alpha-Al2O3 (0 0 0 1) surfaces have been carried out by means of first-principles density functional theory calculations and the nudged elastic band method. Results show that surface diffusion on the (most stable) Al-terminated surface is relatively fast with an energy barrier of 0.75 eV, whereas Al hopping on the O-terminated surface is slower, with barriers for jumps from the two metastable positions existing on this surface to the stable site of 0.31 and 0.99 eV. Based on this study and on the literature, the governing mechanisms during low-temperature alpha-alumina thin film growth are summarized and discussed. Our results support suggestions made in some previous experimental studies, pointing out that limited surface diffusivity is not the main obstacle for alpha-alumina growth at low-to-moderate temperatures, and that other effects should primarily be considered when designing novel processes for low-temperature alpha-alumina deposition.

  • 26.
    Wallin, Erik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Selinder, T. I.
    Sandvik Tooling AB.
    Elfwing, M.
    Sandvik Tooling AB.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering2008In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 82, no 3, p. 36002-Article in journal (Refereed)
    Abstract [en]

    α-alumina coatings have been deposited directly onto cemented-carbide and Mo substrates at a temperature as low as 650 °C using reactive high-power impulse magnetron sputtering (HiPIMS) of Al in an Ar/O2 gas mixture. The coatings consisted of plate-like crystallites, as revealed by scanning electron microscopy. α phase growth was retained over the studied range of substrate bias voltages (from floating potential up to -100 V), with films exhibiting a slightly denser microstructure at higher bias voltages. X-ray diffraction indicated that the α-alumina grains had a preferred orientation of (0001)-planes perpendicular to the substrate surface. X-ray analysis of films deposited at 575 °C indicated the presence of γ-alumina, whereas films grown at 500 °C or lower were X-ray amorphous.

  • 27.
    Wallin, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Svedin, S
    IFM Linköpings universitet.
    Lattemann, Martina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Deposition of crystalline alumina by reactive high power impulse magnetron sputtering2007In: International Vacuum Congress,2007, 2007Conference paper (Other academic)
1 - 27 of 27
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