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  • 1.
    Aiempanakit, M
    et al.
    Plasma & Coatings Physics Division, IFM-Material Physics, Linköpings universitet.
    Aijaz, A
    Plasma & Coatings Physics Division, IFM-Material Physics, Linköpings universitet.
    Lundin, D
    Plasma & Coatings Physics Division, IFM-Material Physics, Linköpings universitet.
    Helmersson, U
    Plasma & Coatings Physics Division, IFM-Material Physics, Linköpings universitet.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides2012Conference paper (Refereed)
  • 2.
    Aiempanakit, Montri
    et al.
    Linkoping University.
    Aijaz, Asim
    Linkoping University.
    Helmersson, Ulf
    Linkoping University.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hysteresis effect in reactive high power impulse magnetron sputtering of metal oxides2011Conference paper (Refereed)
    Abstract [en]

    In order to get high deposition rate and good film properties, the stabilization of the transition zone between the metallic and compound modes is beneficial. We have shown earlier that at least in some cases, HiPIMS can reduce hysteresis effect in reactive sputtering. In our previous work, mechanisms for the suppression/elimination of the hysteresis effect have been suggested. Reactive HiPIMS can suppress/eliminate the hysteresis effect in the range of optimum frequency [1] lead to the process stability during the deposition with high deposition rate. The mechanisms behind this optimum frequency may relate with high erosion rate during the pulse [2,3] and gas rarefaction effect in front of the target [4]. 

     

    In this contribution, reactive sputtering process using high power impulse magnetron sputtering (HiPIMS) has been studied with focus on the gas rarefaction. Through variations in the sputtering conditions such as pulse frequencies, peak powers, and target area, their effect on the shape of current waveforms have been analyzed. The current waveforms in compound mode are strongly affected. Our experiments show that the shape and amplitude of peak current cannot be explained by the change of the secondary electron yield due to target oxidation only. Reduced rarefaction in compound mode contributes to the observed very high peak current values.

  • 3. Aiempanakit, Montri
    et al.
    Aijaz, Asim
    Lundin, Daniel
    Helmersson, Ulf
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 13, p. 133302-Article in journal (Refereed)
    Abstract [en]

    The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.

  • 4.
    Aiempanakit, Montri
    et al.
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Helmersson, Ulf
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Aijaz, Asim
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Larsson, Petter
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Magnusson, Roger
    Laboratory of Applied Optics, Linköping University.
    Jensen, Jens
    Thin Film Physics Division, IFM, Materials Physics, Linköping University.
    Kubart, Tomáš
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 20, p. 4828-4831Article in journal (Refereed)
    Abstract [en]

    The effect of peak power in a high power impulse magnetron sputtering (HiPIMS) reactive deposition of TiO(2) films has been studied with respect to the deposition rate and coating properties. With increasing peak power not only the ionization of the sputtered material increases but also their energy. In order to correlate the variation in the ion energy distributions with the film properties, the phase composition, density and optical properties of the films grown with different HiPIMS-parameters have been investigated and compared to a film grown using direct current magnetron sputtering (DCMS). All experiments were performed for constant average power and pulse on time (100W and 35 mu s, respectively), different peak powers were achieved by varying the frequency of pulsing. Ion energy distributions for Ti and O and its dependence on the process conditions have been studied. It was found that films with the highest density and highest refractive index were grown under moderate HiPIMS conditions (moderate peak powers) resulting in only a small loss in mass-deposition rate compared to DCMS. It was further found that TiO2 films with anatase and rutile phases can be grown at room temperature without substrate heating and without post-deposition annealing.

  • 5.
    Aiempanakit, Montri
    et al.
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsson, Petter
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Sarakinos, Kostas
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Jensen, Jens
    Thin Film Physics Division , IFM, Material Physics, Linköping University.
    Helmersson, Ulf
    Plasma & Coatings Physics Division, IFM, Material Physics, Linköping University.
    Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 22, p. 7779-7784Article in journal (Refereed)
    Abstract [en]

    In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O(2) atmosphere as a function of the pulsing frequency and the pumping speed are investigated. Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for elimination/suppression of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS. Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al(2)O(3) at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.

  • 6.
    Aijaz, Asim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Carreri, Felipe de Campos
    Fraunhofer Institute for Surface Engineering and Thin Films, IST, Braunschweig, Germany.
    Sabelfeld, Alex
    Fraunhofer Institute for Surface Engineering and Thin Films, IST, Braunschweig, Germany.
    Gerdes, Holger
    Fraunhofer Institute for Surface Engineering and Thin Films, IST, Braunschweig, Germany.
    Bandorf, Ralf
    Fraunhofer Institute for Surface Engineering and Thin Films, IST, Braunschweig, Germany.
    Kubart, Tomáš
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Bräuer, Günter
    Fraunhofer Institute for Surface Engineering and Thin Films, IST, Braunschweig, Germany.
    Industrial Scale Deposition of Diamond-like Carbon Thin Films using Ne-based HiPIMS Discharge2015Conference paper (Other academic)
    Abstract [en]

    High power impulse magnetron sputtering (HiPIMS) has been successful in providing highly ionized deposition fluxes for most common metals (Cu, Al, Ti). However, it is challenged when non-metals such as carbon is considered. Highly ionized carbon fluxes (up to 100%) are essential for the synthesis of diamond-like carbon and tetrahedral amorphous carbon thin films. Earlier reports have shown that the C+/C0 ratio in HiPIMS does not exceed 5% and film densities and sp3/sp2 bond fractions are substantially lower than those achieved using ionized physical vapour deposition based methods such as filtered cathodic vacuum arc and pulsed laser deposition. In our previous work, we demonstrated that Ne-based HiPIMS discharge entails energetic electrons as compared to Ar-based HiPIMS discharge facilitating the generation of highly ionized C fluxes as well as diamond-like carbon thin films with mass densities in the order of 2.8 g/cm3

    In this work, we perform industrial scale deposition of diamond-like carbon thin films using Ne- as well as Ar-based HiPIMS discharge. In order to investigate the effect of electron temperature enhancement and its correlation to generation of C1+ ion fluxes in Ne-based HiPIMS discharge, we perform time-averaged and time-resolved measurements of electron temperature as well as ion density at the substrate position using a flat probe. We also investigate the effect of plasma properties on the ionization of sputtered C as well as buffer gas species by measuring the optical emission from the discharge. In order to correlate the plasma and film properties, we synthesize C thin films under energetic deposition conditions and investigate structural (mass density, sp3/sp2 bond fraction, H content) and mechanical (hardness, elastic modulus, adhesion strength) properties of the resulting diamond-like carbon thin films.

  • 7.
    Aijaz, Asim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ji, Yu-Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kubart, Tomás
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Low-temperature synthesis of thermochromic vanadium dioxide thin films using reactive magnetron sputtering2015In: Abstracts, 2015Conference paper (Refereed)
  • 8.
    Aijaz, Asim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ji, Yu-Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Montero, Jose
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kubart, Tomáš
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Deposition of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering2014Conference paper (Other academic)
    Abstract [en]

    Vanadium dioxide exhibits a reversible phase transition from semiconducting state (monoclinic structure) to a metallic state (tetragonal structure) at ~68 oC. This so-called metal-insulator transition (MIT) entails thermochromic behavior manifested by large changes in optical properties, such as high infrared transmittance modulation in thin films, thereby making VO2-based films a suitable candidate for optical switching applications such as self-tunable infrared filters. Thermochromic VO2 thin films have been widely investigated for optical applications, but high growth temperatures (> 400 oC) required for synthesizing crystalline VO2 thin films, high MIT temperature (68 oC) as well as low visible transmittance (typically ~50%) limit their applicability for example for energy efficient smart windows.

     

    Synthesis of metal-oxide thin films using highly ionized vapor fluxes has been shown to facilitate low-temperature film growth as well as control over phase formation and resulting film properties. In the present work, we synthesize VO2 thin films by use of highly ionized vapor fluxes that are generated by high power impulse magnetron sputtering (HiPIMS). In order to establish a correlation between the plasma and film properties, we investigate the discharge characteristics by analyzing the discharge current-voltage characteristics under varied process parameters such as peak-power, pulse-width and gas phase composition and grow VO2 thin films under suitable process conditions. We investigate the effect of growth temperature (room temperature to 500 oC), energy of the deposition flux (controlled by substrate bias potential) and type of substrate (Si, glass, ITO-coated glass) on crystallinity, phase formation and on optical properties (visible transmittance and infrared modulation) of the resulting thin films. For reference, the discharge characteristics and properties of films deposited by pulsed direct current magnetron sputtering are also studied.         

  • 9.
    Aijaz, Asim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ji, Yu-Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Montero, Jose
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering2016In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 149, p. 137-144Article in journal (Refereed)
    Abstract [en]

    Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature tau(s). At present, temperatures in excess of 450 degrees C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high tau(s) by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows tau(s) to be reduced from 500 to 300 degrees C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of tau(s) thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at tau(s) approximate to 200 degrees C in HiPIMS-produced films.

  • 10.
    Aijaz, Asim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ion induced stress relaxation in dense sputter-deposited DLC thin films2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 5, article id 051902Article in journal (Refereed)
    Abstract [en]

    Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was similar to 2.7 g/cm(3), and the compressive stresses did not exceed similar to 2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films. Published by AIP Publishing.

  • 11.
    Aijaz, Asim
    et al.
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden.;Uppsala Univ, Dept Engn Sci, Angstrom Lab, POB 534, SE-75121 Uppsala, Sweden..
    Louring, Sascha
    Aarhus Univ, Interdisciplinary Nanosci Ctr iNANO, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.;Danish Technol Inst, Tribol Ctr, Teknol Pk,Kongsvang Alle 29, DK-8000 Aarhus C, Denmark..
    Lundin, Daniel
    Univ Paris Saclay, Univ Paris Sud, LPGP, CNRS,UMR 8578, F-91405 Orsay, France..
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Jensen, Jens
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Sarakinos, Kostas
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Helmersson, Ulf
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Synthesis of hydrogenated diamondlike carbon thin films using neon-acetylene based high power impulse magnetron sputtering discharges2016In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 6, article id 061504Article in journal (Refereed)
    Abstract [en]

    Hydrogenated diamondlike carbon (DLC:H) thin films exhibit many interesting properties that can be tailored by controlling the composition and energy of the vapor fluxes used for their synthesis. This control can be facilitated by high electron density and/or high electron temperature plasmas that allow one to effectively tune the gas and surface chemistry during film growth, as well as the degree of ionization of the film forming species. The authors have recently demonstrated by adding Ne in an Ar-C high power impulse magnetron sputtering (HiPIMS) discharge that electron temperatures can be effectively increased to substantially ionize C species [Aijaz et al., Diamond Relat. Mater. 23, 1 (2012)]. The authors also developed an Ar-C2H2 HiPIMS process in which the high electron densities provided by the HiPIMS operation mode enhance gas phase dissociation reactions enabling control of the plasma and growth chemistry [Aijaz et al., Diamond Relat. Mater. 44, 117 (2014)]. Seeking to further enhance electron temperature and thereby promote electron impact induced interactions, control plasma chemical reaction pathways, and tune the resulting film properties, in this work, the authors synthesize DLC: H thin films by admixing Ne in a HiPIMS based Ar/C2H2 discharge. The authors investigate the plasma properties and discharge characteristics by measuring electron energy distributions as well as by studying discharge current characteristics showing an electron temperature enhancement in C2H2 based discharges and the role of ionic contribution to the film growth. These discharge conditions allow for the growth of thick (>1 mu m) DLC: H thin films exhibiting low compressive stresses (similar to 0.5 GPa), high hardness (similar to 25 GPa), low H content (similar to 11%), and density in the order of 2.2 g/cm(3). The authors also show that film densification and change of mechanical properties are related to H removal by ion bombardment rather than subplantation.

  • 12.
    Austgen, M
    et al.
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Koehl, D
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Zalden, P
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Pflug, A
    Fraunhofer IST, Braunschweig, Tyskland.
    Siemers, M
    Fraunhofer IST, Braunschweig, Tyskland.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wuttig, M
    Institute of Physics (IA), and, JARA-FIT, RWTH Aachen University, Tyskland.
    Sputter yield amplification by tungsten doping of Al(2)O(3) employing reactive serial co-sputtering: process characteristics and resulting film properties2011In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 44, no 34, p. 345501-Article in journal (Refereed)
    Abstract [en]

    The deposition rate of reactively sputtered Al(2)O(3) coatings is demonstrated to increase by 80% upon tungsten doping of the used aluminium target. This effect is based on the recoil of the sputtering species at implanted dopants below the target surface and is termed sputter yield amplification. For the investigation of this effect, a novel type of magnetron sputter deposition system is employed that facilitates serial co-sputtering. In this technique doping of the elementary target is enabled by a dynamic sputtering process from an auxiliary cathode. In our case, the rotating aluminium target is dynamically coated with tungsten from this auxiliary cathode. Since the primary target rotates, the auxiliary cathode is placed in series with the primary erosion zone. The deposition rate of Al(2)O(3) can be considerably increased in this process already for very low concentrations of approximately 1% of tungsten in the resulting film. A characterization of the dynamics of reactive sputtering as a function of target rotation speed is performed.

  • 13.
    Berg, Sören
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sputtering yield amplification in reactive sputtering2010Conference paper (Refereed)
  • 14. Borges, J.
    et al.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kumar, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rodrigues, M. S.
    Duarte, N.
    Martins, B.
    Dias, J. P.
    Cavaleiro, A.
    Vaz, F.
    Microstructural evolution of Au/TiO2 nanocomposite films: The influence of Au concentration and thermal annealing2015In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 580, p. 77-88Article in journal (Refereed)
    Abstract [en]

    Nanocomposite thin films consisting of a dielectric matrix, such as titanium oxide (TiO2), with embedded gold (Au) nanoparticles were prepared and will be analysed and discussed in detail in the present work. The evolution of morphological and structural features was studied for a wide range of Au concentrations and for annealing treatments in air, for temperatures ranging from 200 to 800 degrees C. Major findings revealed that for low Au atomic concentrations (at.%), there are only traces of clustering, and just for relatively high annealing temperatures, T >= 500 degrees C. Furthermore, the number of Au nanoparticles is extremely low, even for the highest annealing temperature, T = 800 degrees C. It is noteworthy that the TiO2 matrix also crystallizes in the anatase phase for annealing temperatures above 300 degrees C. For intermediate Au contents (5 at.% <= C-Au <= 15 at.%), the formation of gold nanoclusters was much more evident, beginning at lower annealing temperatures (T >= 200 degrees C) with sizes ranging from 2 to 25 nm as the temperature increased. A change in the matrix crystallization from anatase to rutile was also observed in this intermediate range of compositions. For the highest Au concentrations (>20 at.%), the films tended to form relatively larger clusters, with sizes above 20 nm (for T >= 400 degrees C). It is demonstrated that the structural and morphological characteristics of the films are strongly affected by the annealing temperature, as well as by the particular amounts, size and distribution of the Au nanoparticles dispersed in the TiO2 matrix.

  • 15.
    Borges, J.
    et al.
    Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, CR-16635 Prague 6, Czech Republic..
    Rodrigues, M. S.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal.;Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, P-3030199 Coimbra, Portugal..
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kumar, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Evaristo, M.
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, P-3030788 Coimbra, Portugal..
    Cavaleiro, A.
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, P-3030788 Coimbra, Portugal..
    Apreutesei, M.
    INSA Lyon, MATEIS Lab, F-69621 Villeurbanne, France..
    Pereira, R. M. S.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal.;Univ Minho, Ctr Matemat, Braga, Portugal..
    Vasilevskiy, M. I.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Polcar, T.
    Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, CR-16635 Prague 6, Czech Republic.;Univ Southampton, Natl Ctr Adv Tribol Southampton nCATS, Southampton SO17 1BJ, Hants, England..
    Vaz, F.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Thin films composed of gold nanoparticles dispersed in a dielectric matrix: The influence of the host matrix on the optical and mechanical responses2015In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 596, p. 8-17Article in journal (Refereed)
    Abstract [en]

    Gold nanoparticles were dispersed in two different dielectric matrices, TiO2 and Al2O3, using magnetron sputtering and a post-deposition annealing treatment. The main goal of the present work was to study how the two different host dielectric matrices, and the resulting microstructure evolution (including both the nanoparticles and the host matrix itself) promoted by thermal annealing, influenced the physical properties of the films. In particular, the structure and morphology of the nanocomposites were correlated with the optical response of the thin films, namely their localized surface plasmon resonance (LSPR) characteristics. Furthermore, and in order to scan the future application of the two thin film system in different types of sensors (namely biological ones), their functional behaviour (hardness and Young's modulus change) was also evaluated. Despite the similar Au concentrations in both matrices (similar to 11 at.%), very different microstructural features were observed, which were found to depend strongly on the annealing temperature. The main structural differences included: (i) the early crystallization of the TiO2 host matrix, while the Al2O3 one remained amorphous up to 800 degrees C; (ii) different grain size evolution behaviours with the annealing temperature, namely an almost linear increase for the Au:TiO2 system (from 3 to 11 nm), and the approximately constant values observed in the Au:Al2O3 system (4-5 nm). The results from the nanoparticle size distributions were also found to be quite sensitive to the surrounding matrix, suggesting different mechanisms for the nanoparticle growth (particle migration and coalescence dominating in TiO2 and Ostwald ripening in Al2O3). These different clustering behaviours induced different transmittance-LSPR responses and a good mechanical stability, which opens the possibility for future use of these nanocomposite thin film systems in some envisaged applications (e.g. LSPR-biosensors).

  • 16.
    Borges, J.
    et al.
    Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, CR-16635 Prague 6, Czech Republic..
    Rodrigues, M. S.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal.;Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, P-3030199 Coimbra, Portugal..
    Lopes, C.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Costa, D.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Couto, F. M.
    Norte Fluminense State Univ, Phys Sci Lab, BR-28013602 Campos, RJ, Brazil..
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Martins, B.
    Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, P-3030199 Coimbra, Portugal..
    Duarte, N.
    Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, P-3030199 Coimbra, Portugal..
    Dias, J. P.
    Inst Pedro Nunes, Lab Ensaios Desgaste & Mat, P-3030199 Coimbra, Portugal..
    Cavaleiro, A.
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, P-3030788 Coimbra, Portugal..
    Polcar, T.
    Czech Tech Univ, Fac Elect Engn, Dept Control Engn, Tech 2, CR-16635 Prague 6, Czech Republic.;Univ Southampton, Natl Ctr Adv Tribol Southampton, Southampton SO17 1BJ, Hants, England..
    Macedo, F.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Vaz, F.
    Univ Minho, Ctr Fis, P-4710057 Braga, Portugal..
    Thin films composed of Ag nanoclusters dispersed in TiO2: Influence of composition and thermal annealing on the microstructure and physical responses2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 358, p. 595-604Article in journal (Refereed)
    Abstract [en]

    Noble metal powders containing gold and silver have been used for many centuries, providing different colours in the windows of the medieval cathedrals and in ancient Roman glasses. Nowadays, the interest in nanocomposite materials containing noble nanoparticles embedded in dielectric matrices is related with their potential use for a wide range of advanced technological applications. They have been proposed for environmental and biological sensing, tailoring colour of functional coatings, or for surface enhanced Raman spectroscopy. Most of these applications rely on the so-called localised surface plasmon resonance absorption, which is governed by the type of the noble metal nanoparticles, their distribution, size and shape and as well as of the dielectric characteristics of the host matrix. The aim of this work is to study the influence of the composition and thermal annealing on the morphological and structural changes of thin films composed of Ag metal clusters embedded in a dielectric TiO2 matrix. Since changes in size, shape and distribution of the clusters are fundamental parameters for tailoring the properties of plasmonic materials, a set of films with different Ag concentrations was prepared. The optical properties and the thermal behaviour of the films were correlated with the structural and morphological changes promoted by annealing. The films were deposited by DC magnetron sputtering and in order to promote the clustering of the Ag nanoparticles the as-deposited samples were subjected to an in-air annealing protocol. It was demonstrated that the clustering of metallic Ag affects the optical response spectrum and the thermal behaviour of the films.

  • 17.
    Ericson, Tove
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Reactive sputtering of precursors for Cu2ZnSnS4 thin film solar cells2012In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 24, p. 7093-7099Article in journal (Refereed)
    Abstract [en]

    The quaternary semiconductor Cu2ZnSnS4 (CZTS) is a possible In-free replacement for Cu(In,Ga)Se-2. Here we present reactive sputtering with the possibility to obtain homogeneous CZTS-precursors with tunable composition and a stoichiometric quantity of sulfur. The precursors can be rapidly annealed to create large grained films to be used in solar cells. The reactive sputtering process is flexible, and morphology, stress and metal and sulfur contents were varied by changing the H2S/Ar-flow ratio, pressure and substrate temperature. A process curve for the reactive sputtering from CuSn and Zn targets is presented. The Zn-target is shown to switch to compound mode earlier and faster compared to the CuSn-target. The precursors containing a stoichiometric amount of sulfur exhibit columnar grains, have a crystal structure best matching ZnS and give a broad peak, best matching CZTS, in Raman scattering. In comparing process gas flows it is shown that the sulfur content is strongly dependent on the H2S partial pressure but the total pressures compared in this study have little effect on the precursor properties. Increasing the substrate temperature changes the film composition due to the high vapor pressures of Zn, SnS and S. High substrate temperatures also give slightly denser and increasingly oriented films. The precursors are under compressive stress, which is reduced with higher deposition temperatures. (C) 2012 Elsevier B.V. All rights reserved.

  • 18.
    Ericson, Tove
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, p. 22-26Article in journal (Refereed)
    Abstract [en]

    Reactively sputtered Cu–Zn–Sn–S precursor films are prepared and recrystallized by rapid thermal processing to generate Cu2ZnSnS4 solar cell absorber layers. We study how the film properties are affected by substrate heating and composition. The stress, density and texture in the films were measured. Compressive stress was observed for the precursors but did not correlate to the deposition temperature, and had no influence on the properties of the annealed films or solar cells. However, the substrate temperature during precursor deposition had a large effect on the behavior during annealing and on the solar cell performance. The films deposited at room temperature had, after annealing, smaller grains and cracks, and gave shunted devices. Cracking is suggested to be due to a slightly higher sulfur content, lower density or to minor differences in material quality. The grain size in the annealed films seems to increase with higher copper content and higher precursor deposition temperature. The best device in the current series gave an efficiency of 4.5%.

  • 19.
    Ferreira, Fabio
    et al.
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, Rua Luis Reis Santos, P-3030788 Coimbra, Portugal..
    Aijaz, Asim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cavaleiro, Albano
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, Rua Luis Reis Santos, P-3030788 Coimbra, Portugal.;Inst Pedro Nunes, LED&Mat IPN, Lab Ensaios Desgaste & Mat, Rua Pedro Nunes, P-3030199 Coimbra, Portugal..
    Oliveira, Joao
    Univ Coimbra, Dept Mech Engn, SEG CEMUC, Rua Luis Reis Santos, P-3030788 Coimbra, Portugal..
    Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering2018In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 336, p. 92-98Article in journal (Refereed)
    Abstract [en]

    Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500 degrees C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp(3) content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp(3)/sp(2) ratio in the films increases with increasing substrate biasing. However, the sp(3) bonds convert back to sp(2) upon annealing. Never the less, a significantly higher amount of sp(3) bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.

  • 20.
    Figueiredo, Nuno M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sanchez-Garcia, J. A.
    Escobar Galindo, R.
    Climent-Font, A.
    Cavaleiro, A.
    Optical properties and refractive index sensitivity of reactive sputtered oxide coatings with embedded Au clusters2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 6, p. 063512-Article in journal (Refereed)
    Abstract [en]

    In the present study, nanocomposite coatings of Au clusters embedded in two different oxides, TiO2 and Al2O3, were synthesized using pulsed DC magnetron sputtering. The depositions were carried out in three steps, by depositing the oxide, the Au clusters, and again the oxide. The deposition time of the Au clusters was varied in order to achieve different cluster sizes, morphologies, and nanocomposite topographies. The structure, microstructure, morphology, and the optical properties of the coatings were studied. With the increase in Au content, red-shifted surface plasmon resonance (SPR) peaks with higher intensity and increased widths were observed due to changes in the metal clusters sizes and morphology and due to interparticle effects. In order to relate the peculiar SPR extinction bands with the different clusters shapes and distributions, a simulation of the optical properties of the nanocomposites was performed making use of the Renormalized Maxwell-Garnett approach. A theoretical study concerning the refractive index sensitivity was made in order to predict the optimal coatings parameters for sensing experiments. The increased surface area and the strong SPR extinction bands make these coatings suitable for gas sensing and also catalysis, albeit many other application fields can be envisaged.

  • 21.
    Figueiredo, Nuno
    et al.
    University of Coimbra .
    Oliveira, Joao
    University of Coimbra .
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cavaleiro, Albano
    University of Coimbra .
    Nanocomposite coatings consisting of noble metal nanoclusters embedded into a dielectric matrix by reactive HIPIMS2011In: 2nd International Conference on Fundamentals and Applications of HIPIMS, June 2011, Braunschweig, 2011Conference paper (Refereed)
  • 22.
    Gao, Xindong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Smith, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lu, J.
    Hultman, L.
    Kellock, A.
    Zhen, Zhang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lavoie, C.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness2011In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 12, p. H268-H270Article in journal (Refereed)
  • 23.
    Gao, Xindong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Smith, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lu, Jun
    Dept of Physics, Chemistry and Biology (IFM), Linköping University.
    Hultman, Lars
    Dept of Physics, Chemistry and Biology (IFM), Linköping University.
    Kellock, Andrew J
    IBM Almaden Research Center, San Jose, CA, USA.
    Zhang, Zhen
    IBM T J Watson Research Center, Yorktown Heights, NY, USA.
    Lavoie, Christian
    IBM T J Watson Research Center, Yorktown Heights, NY, USA.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness2011In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 7, p. H268-H270Article in journal (Refereed)
    Abstract [en]

    This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.

  • 24. Hallman, R.
    et al.
    Andersson, J.
    Särhammar, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Studies of TiN films deposited by HIPIMS at different substrate temperatures and substrate bias2010Conference paper (Refereed)
  • 25. Hubicka, Z.
    et al.
    Kment, S.
    Olejnicek, J.
    Cada, M.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Brunclikova, M.
    Ksirova, P.
    Adamek, P.
    Remes, Z.
    Deposition of hematite Fe2O3 thin film by DC pulsed magnetron and DC pulsed hollow cathode sputtering system2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 549, p. 184-191Article in journal (Refereed)
    Abstract [en]

    Semiconducting hematite Fe2O3 thin films were fabricated by means of reactive sputtering in a high power DC pulsed magnetron (HIPIMS) and in a DC pulsed hollow cathode plasma jet sputtering system. Fused silica slides (quartz) were used as substrates. Both plasma processes were monitored with the help of a quartz crystal monitor (QCM) that was also fitted with magnetic field electron suppression filter and biased collecting electrode. This set up measured the deposition rate and the ratio of ionized to neutral fluxes of depositing particles on the substrate during the coating process. The deposition methods were compared in terms of the properties of produced films such as crystalline structure, optical absorption and surface topography. The as-deposited hematite Fe2O3 thin films (without annealing) and after their thermal treatment (with annealing) were examined.

  • 26.
    Hubicka, Zdenek
    et al.
    Institute of Physics, ASCR v.v.i., Prague, Czech Republic.
    Cada, Martin
    Institute of Physics, ASCR v.v.i., Prague, Czech Republic.
    Kmet, Stepan
    Institute of Physics, ASCR v.v.i., Prague, Czech Republic.
    Olejnicek, Jiri
    Institute of Physics, ASCR v.v.i., Prague, Czech Republic.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Adamek, Jiri
    Institute of Physics, ASCR v.v.i., Prague, Czech Republic.
    Reactive sputtering of Fe2O3 thin films by high power pulsed plasma systems2012Conference paper (Refereed)
    Abstract [en]

    Semiconductor oxide thin films of Fe2O3 were deposited by reactive sputtering in a high power pulse magnetron and in a pulsed hollow cathode plasma jet sputtering system.  Properties of deposited Fe2O3 were investigated for photocatalytic water splitting applications. Fe2O3 provide a potential to capture a relatively significant portion of the available solar light due to lower band-gap energies. The first system used in this study was the high power pulsed magnetron sputtering system (HIPIMS) employing metallic target of pure iron with outer diameter 50 mm and working in a gas mixture of Ar and O2.  Influence of different magnitudes of the applied pulsed power and pulsing frequency on the formation of crystalline structure, physical properties and photocatalytical properties was investigated.  The maximum pulsed current density used in our reactive HIPIMS magnetron system was ≈ 5 A/cm2. Oxide Fe2O3 thin films were deposited also by a low pressure DC pulsed hollow cathode system. The metallic hollow cathode with internal diameter 5 mm and length 30 mm was sputtered in argon plasma flow and reactive gas oxygen was supplied directly to the reactor. The hollow cathode discharge was supplied from the DC pulsed power supplier working in high power pulsed mode. The maximum attained pulsed current density in our hollow cathode discharge  was approximately  ≈ 3 A/cm2.  The main advantage of this system was the high deposition rate which was nearly independent on the amount of used oxygen in the plasma. A plasma diagnostics was carried out in all the investigated systems. The most important was measurement with various forms of quartz crystal microbalance QCM with several types systems of grids. These systems were used to determine ionization fraction of sputtered and reactively sputtered particle fluxes to the substrate under different deposition conditions of these oxide thin films. The higher ionization fraction of sputtered particles was found for higher current densities in the pulse. In the HIPIMS magnetron, the maximum of ionization fraction of reactively sputtered particles was found around ≈ 60-70% for 5% duty cycle of pulsing frequency. The maximum ionization fraction of sputtered particles in the reactive pulsed hollow cathode system was usually lower than in the investigated reactive HIPIMS magnetron system.

  • 27.
    Jablonka, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gustavsson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Abedin, Ahmad
    KTH Royal Institute of Technology.
    Hellström, Per-Erik
    KTH Royal Institute of Technology.
    Östling, Mikael
    KTH Royal Institute of Technology.
    Jordan-Sweet, Jean L.
    IBM, TJ Watson Research Center.
    Lavoie, Christian
    IBM, TJ Watson Research Center.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scalability Study of Nickel Germanides2016Conference paper (Refereed)
  • 28.
    Jablonka, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gustavsson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Descoins, Marion
    Mangelinck, Dominique
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Improving the morphological stability of nickel germanide by tantalum and tungsten additions2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 10Article in journal (Refereed)
    Abstract [en]

    To enhance the morphological stability of NiGe, a material of interest as a source drain-contact in Ge-based field effect transistors, Ta or W, is added as either an interlayer or a capping layer. The efficacy of this Ta or W addition is evaluated with pure NiGe as a reference. While interlayers increase the NiGe formation temperature, capping layers do not retard the NiGe formation. Regardless of the initial position of Ta or W, the morphological stability of NiGe against agglomeration can be improved by up to 100 °C. The improved thermal stability can be ascribed to an inhibited surface diffusion, owing to Ta or W being located on top of NiGe after annealing, as confirmed by means of transmission electron microscopy, Rutherford backscattering spectrometry, and atom probe tomography. The latter also shows a 0.3 €‰at. % solubility of Ta in NiGe at 450 °C, while no such incorporation of W is detectable.

  • 29.
    Jablonka, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Abedin, Ahmad
    KTH Royal Inst Technol, Sch Informat & Commun Technol, SE-16440 Kista, Sweden..
    Hellstrom, Per-Erik
    KTH Royal Inst Technol, Sch Informat & Commun Technol, SE-16440 Kista, Sweden..
    Ostling, Mikael
    KTH Royal Inst Technol, Sch Informat & Commun Technol, SE-16440 Kista, Sweden..
    Jordan-Sweet, Jean
    IBM Corp, TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA..
    Lavoie, Christian
    IBM Corp, TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA..
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Formation of nickel germanides from Ni layers with thickness below 10 nm2017In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 35, no 2, article id 020602Article in journal (Refereed)
    Abstract [en]

    The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleationcontrolled for Ni thicknesses < 5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.

  • 30.
    Jablonka, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Riekehr, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Highly conductive ultrathin Co films by high-power impulse magnetron sputtering2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 4, article id 043103Article in journal (Refereed)
    Abstract [en]

    Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.

  • 31.
    Jensen, J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Sanz, R.
    Martin, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surpi, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Vázquez, M.
    Hernandez-Velez, M.
    Implantation of anatase thin film with 100 keV 56Fe ions: Damage formation and magnetic behaviour2009In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 267, no 16, p. 2725-2730Article in journal (Refereed)
    Abstract [en]

    We have investigated the damage morphology and magnetic properties of titanium dioxide thin films following implantation with Fe ions. The titanium dioxide films, having a polycrystalline anatase structure, were implanted with 100 keV 56Fe+ ions to a total fluence of 1.3 × 1016 ions/cm2. The ion bombardment leads to an amorphized surface with no indication of the presence of secondary phases or Fe clusters. The ion-beam induced damage manifested itself by a marked change in surface morphology and film thickness. A room temperature ferromagnetic behaviour was observed by SQUID in the implanted sample. It is believed that the ion-beam induced damage and defects in the polycrystalline anatase film were partly responsible for the observed magnetic response.

  • 32.
    Jensen, Jens
    et al.
    Linkoping University.
    Aiempanakit, Montri
    Linkoping University.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ion irradiation-induced modification of TiO2 thin films2011In: E-MRS 2011 Spring Meeting, 2011Conference paper (Refereed)
  • 33.
    Jensen, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Martin, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surpi, A
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Topalian, Z
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Yousef, H
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Sanz, R
    Damage formation in TiO2 by heavy ions: consequences for micro- and nano-struring2008In: 7th International Symposium on Swift Heavy Ions in Matter (SHIM2008), Lyon, France, 2008Conference paper (Refereed)
  • 34.
    Jensen, Jens
    et al.
    Linkoping University.
    Martin, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surpi, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    ERD analysis and modification of TiO2 thin films with heavy ions2010In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 268, no 11-12, p. 1893-1898Article in journal (Refereed)
  • 35.
    Jensen, Jens
    et al.
    Linkoping University.
    Surpi, Alessandro
    CIVEN, Italy.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hultman, Lars
    Linkoping University.
    Implantation and surface modification of TiO2 by a Focused Ion Beam2011In: E-MRS 2011 Spring Meeting, 2011Conference paper (Refereed)
  • 36.
    Kappertz, Oliver
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics. Fasta tillståndets elektronik.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics. Fasta tillståndets elektronik.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics. Fasta tillståndets elektronik.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics. Fasta tillståndets elektronik.
    Advanced Process Modelling of the Rotating Magnetron2006Conference paper (Refereed)
  • 37.
    Keller, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chalvet, Francis
    Solibro Res AB, Vallvagen 5, S-75151 Uppsala, Sweden.
    Joel, Jonathan
    Solibro Res AB, Vallvagen 5, S-75151 Uppsala, Sweden.
    Aijaz, Asim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Riekehr, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Stolt, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Solibro Res AB, Vallvagen 5, S-75151 Uppsala, Sweden.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells2018In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 1, p. 13-23Article in journal (Refereed)
    Abstract [en]

    This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.

  • 38.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Modelling of reactive magnetron sputtering: Towards comprehensive model2012Conference paper (Refereed)
    Abstract [en]

    Modelling of reactive sputtering is a very useful tool to reduce the need for trial-and-error based process optimization as well as to support process development. It also provides a test platform for our understanding of the process. Although the classical "Berg's model" describes the basic behaviour of reactive sputtering remarkably well, there is still a number of open questions regarding the underlying physical processes.

    In this contribution, we first summarize the latest development in the modelling, such as extensions of the basic model taking into account the ion current distribution, various mechanisms of the reactive gas incorporation or process dynamics. Then we briefly describe some of the intriguing experimental results from reactive High Power Impulse Magnetron Sputtering (HiPIMS).

    In order to develop a comprehensive model applicable to reactive HiPIMS, more accurate description of the individual effects taking place in sputtering is essential. A first step in the development of such a model is outlined with focus on the surface processes.

  • 39.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Process modelling for reactive magnetron sputtering2011In: Potential and Applications of Thin Ceramic and Metal Coatings 2011. 2nd PATCMC, 6th - 8th June, 2011 Plzeň, Czech Republic / [ed] Pavel Baroch, Milan Kubasek, Plzen: University of West Bohemia , 2011, p. 25-28Conference paper (Refereed)
    Abstract [en]

    Reactive magnetron sputtering is a widely used technique for deposition of various compound thin films such as oxides and nitrides. This contribution deals with process modelling for reactive sputtering. A brief discussion of the hysteresis effect and classical Berg’s model is presented, followed by examples of application. Finally, some current topics in reactive sputtering are presented.

  • 40.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Reactive magnetron sputtering: from fundamentals to high deposition rate processes2013In: Proceedings of the Twelfth th International Symposium on Sputtering & Plasma Processes ISSP 2013 / [ed] Yasuhito Gotoh, 2013, p. 5-9Conference paper (Refereed)
    Abstract [en]

    Reactive magnetron sputtering is widely used for synthesis of various compound thin films. The technique is very versatile and scalable. Especially in industry, high productivity is essential and there is a need for processes with high deposition rates. Achieving high deposition rate and true compound stoichiometry of the deposited film is, however, challenging in reactive sputtering. As a consequence of complex interaction between the reactive gas and the sputtered metal, the relation between deposition rate or composition of the coating and flow of reactive gas is very non-linear and usually exhibits hysteresis behaviour.

    This contribution deals with modelling based development of reactive sputtering processes. First, the basic model of reactive sputtering is briefly reviewed. A steady state model is derived, discussing the most important assumptions and illustrating the physical processes taking place in reactive sputtering. The model is then used to discuss some strategies for high deposition rate processes, such as using high pumping speed or substoichiometric targets. Another strategy for increased deposition rate employs sputtering yield amplification. Here, the sputtering target is doped by a heavy element in order to reduce the depth of collision cascades thus increasing the sputtering yield of target. This technique is suitable for reactive sputtering of oxides as demonstrated for reactive deposition of Al2O3 with W doping. In this case, the deposition rate may be increased by about 100% as confirmed experimentally.

    Although reactive sputtering is well understood, recent research on reactive High Power Impulse Magnetron Sputtering (HiPIMS) brought some intriguing experimental results. In order to develop a comprehensive model applicable to reactive HiPIMS, more accurate description of the individual effects taking place in sputtering is essential. As a first step towards such a model, discharge current behaviour in reactive HiPIMS is analysed. It is shown that in HiPIMS, the discharge behaviour is strongly influenced by ionized particles sputtered from the target.

  • 41.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aiempanakit, M.
    Andersson, J.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Helmersson, U.
    Studies of hysteresis effect in reactive HiPIMS deposition of oxides2010Conference paper (Refereed)
  • 42.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aiempanakit, M
    Plasma & Coatings Physics Division, IFM, materials Physics, Linköping University, Linköping.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Helmersson, U
    Plasma & Coatings Physics Division, IFM, materials Physics, Linköping University, Linköping.
    Studies of hysteresis effect in reactive HiPIMS deposition of oxides2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no Suppl. 2, p. S303-S306Article in journal (Refereed)
    Abstract [en]

    High power impulse magnetron sputtering (HiPIMS) has proven to be capable of substantial improvement of the quality of deposited coatings. Lately, there have been a number of reports indicating that the hysteresis effect may be reduced in HiPIMS mode resulting in an increase of the deposition rate of stoichiometric compound as compared to a direct current magnetron sputtering process in oxide mode. In this contribution, we have studied the hysteresis behaviour of Ti metal targets sputtered in Ar + O(2) mixtures. For fixed pulse on time and a constant average power, there is an optimum frequency minimizing the hysteresis. The effect of gas dynamics was analyzed by measurements of the gas refill time and rarefaction. Results indicate that the gas rarefaction may be responsible for the observed hysteresis behaviour. The results are in agreement with a previous study of Al oxide reactive process.

  • 43.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aijaz, Asim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Evolution of sputtering target surface composition in reactive high power impulse magnetron sputtering2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 17, article id 171903Article in journal (Refereed)
    Abstract [en]

    The interaction between pulsed plasmas and surfaces undergoing chemical changes complicates physics of reactive High Power Impulse Magnetron Sputtering (HiPIMS). In this study, we determine the dynamics of formation and removal of a compound on a titanium surface from the evolution of discharge characteristics in an argon atmosphere with nitrogen and oxygen. We show that the time response of a reactive process is dominated by surface processes. The thickness of the compound layer is several nm and its removal by sputtering requires ion fluence in the order of 1016 cm−2, much larger than the ion fluence in a single HiPIMS pulse. Formation of the nitride or oxide layer is significantly slower in HiPIMS than in dc sputtering under identical conditions. Further, we explain very high discharge currents in HiPIMS by the formation of a truly stoichiometric compound during the discharge off-time. The compound has a very high secondary electron emission coefficient and leads to a large increase in the discharge current upon target poisoning.

  • 44.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Modelling of target effects in reactive HIPIMS2011In: 2nd Internation Conference on Fundamentals and Applications of HIPIMS, June 2011, Braunschweig, 2011Conference paper (Refereed)
    Abstract [en]

    In reactive HIgh Power Impulse Magnetron Sputtering (HIPIMS) of oxides, target effects such as reduced surface oxidation during pulse off time, increased implantation of reactive gas due to the higher discharge voltage as compared to normal DC sputtering, and enhanced target cleaning during on time  are considered to be responsible for the differences compared to reactive DC sputtering. These effects are assumed to cause changes in the target oxide coverage and hence lead to the hysteresis shifts observed in experimental studies. In this contribution, the target processes are simulated using the binary collision approximation code TRIDYN. Using an Al target sputtered in Ar+O2 mixture as a model system, a range of pulse configurations is simulated for different oxygen partial pressures. The results indicate that the target effects alone are not sufficient to explain the observed shift of hysteresis and its frequency dependence.

  • 45.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Arapan, Sergiu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Molecular dynamics simulations of low energy Ar sputtering of TiO2 surfaces2010Conference paper (Refereed)
  • 46.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cada, Martin
    ASCR, Institute of Physics.
    Hubicka, Zdenek
    ASCR, Institute of Physics.
    Measurement of Ionized Metal Flux Fraction in HiPIMS by Retarding Field QCM Analyzer2014In: 41st International Conference on Metallurgical Coatings and Thin Films, San Diego, CA, April 28 - May 2, 2014, 2014Conference paper (Refereed)
    Abstract [en]

    In this contribution, we describe measurements of the ionized metal flux fraction, the ratio between ionized and neutral metal species, arriving to the substrate in High Power Impulse Magnetron Sputtering (HiPIMS).  The ionized metal flux fraction is determined from the deposition rate of ions and neutrals. In order to determine the respective rates, a combination of a retarding field and by a quartz crystal microbalance (QCM) was used. Two different sensors were tested. A standard QCM equipped with a set of grids and an alternative grid-less sensor which was developed in order to increase the sensitivity. The grid-less sensor uses magnetic field to repel electrons and the bias voltage is applied directly to the QCM top electrode.

    We report results for two materials, Ni and Ti. Ti was characterized both in nonreactive (Ar) and reactive (Ar+O2) atmosphere. Measurements with the QCM analyzer showed an ionized fraction of up to 50% for Ni. Somewhat higher values, exceeding 60%, were measured for Ti. In this case, shorter on times lead to higher ionized fraction at the same deposition rate and average discharge power. In reactive sputtering of Ti, substantially higher ionized fraction was observed in the oxide mode as compared to the metal mode. Already at lower values of the peak power, there was a significant fraction of Ti ions in the oxide mode.

  • 47.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cada, Martin
    Institute of Physics v.v.i., Academy of Science of the Czech Republic.
    Lundin, Daniel
    Université Paris-Sud.
    Hubicka, Zdenek
    Institute of Physics v.v.i., Academy of Science of the Czech Republic.
    Investigation of ionized metal flux fraction in HiPIMS discharge with Ti and Ni target2013Conference paper (Refereed)
    Abstract [en]

    In deposition of thin film, energetic bombardment during the film growth has a strong impact on the film growth with respect to the film density, adhesion, or internal stresses. Since the energy of impinging ions can be readily controlled by a substrate bias, various means of increasing the ionization degree in sputtering have been investigated. In High Power Impulse Magnetron Sputtering (HiPIMS), high degree of ionization of the sputtered material may be achieved thanks to the high peak powers and thus high plasma densities.

    In this contribution, the ionized metal flux fraction, the ratio between ionized and neutral metal species, arriving to the substrate in HiPIMS was analyzed.  A combination of retarding field analyzer and quartz crystal microbalance (QCM) was used. The QCM sensor can measure the deposition rate from ions and neutrals separately by changing the applied bias voltage allowing for fast determination of the total ionized fraction of material flux to the substrate.

    Two target materials, Ni and Ti were studied, in the case of Ti in both nonreactive (Ar) and reactive (Ar+O2) atmosphere. Measurements with the QCM analyzer showed an ionized fraction of up to 50% for Ni. Somewhat higher values, exceeding 60%, were measured for Ti. In this case, shorter on times lead to higher ionized fraction at the same deposition rate and average discharge power.

    In reactive sputtering of Ti, substantially higher ionized fraction was observed in the oxide mode as compared to the metal mode. Already at lower values of the peak power, there was a significant fraction of Ti ions in the oxide mode. The results are very important for thin film synthesis because show process conditions for ion assisted depositions.

  • 48.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cada, Martin
    Lundin, Daniel
    Hubicka, Zdenek
    Investigation of ionized metal flux fraction in HiPIMS discharges with Ti and Ni targets2014In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 238, p. 152-157Article in journal (Refereed)
    Abstract [en]

    Ionized metal flux fractions in high power impulse magnetron sputtering (HiPIMS) were analyzed by a combination of a retarding field analyzer and a quartz crystal microbalance (QCM). Two target materials, Ni and Ti, were studied in an Ar atmosphere. In the case of Ti, the reactive (Ar + O-2) mode was also investigated. Ionized metal flux fractions of up to 50% for Ni were observed at a pulse power density of 1 kW cm(-2). The pulse on-time had negligible influence on the ionized fraction. Somewhat higher values, exceeding 60%, were measured for Ti at 2 kW cm(-2). In this case, shorter on-times led to higher ionized fractions at the same deposition rate and average discharge power density. In reactive sputtering of Ti, substantially higher ionized fraction was observed in the oxide mode as compared to the metal mode. Already at lower values of the pulse power, there was a significant fraction of Ti ions in the flux.

  • 49.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Depla, D
    Martin, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    On the high rate reactive sputtering of substoichiometric titanium oxide targets2007Conference paper (Refereed)
  • 50.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Depla, Diederik
    Ghent University.
    Dynamics of the sputtering target surface evolution in reactive HiPIMS2014In: Invited talk, 14th International Conference on Plasma Surface Engineering, September 15 - 19, 2014, Garmisch-Partenkirchen, Germany, 2014Conference paper (Refereed)
    Abstract [en]

    Reactive High Power Impulse Magnetron Sputtering is a promising deposition technique with many interesting properties. Because of the high plasma densities and dynamic nature of the process, many basic aspects of the ongoing physical processes are still unclear. In this contribution, we study the evolution of the  target surface composition in reactive HiPIMS. Using Ti and Al targets in Ar+O2 and Ar+N2 mixtures, the formation and removal of the corresponding compound at the surface is determined from the time evolution of discharge current waveforms. For comparison, pulsed DC process is also analysed.

    Our results show that the ion dose, required to remove the compound from a poisoned sputtering target, is at least 10 times higher in HiPIMS as compared to pulse DC sputtering. Although the compound removal is comparable for both O and N, target poisoning is much slower in the Ar+N2 atmosphere. The slow cleaning in HiPIMS cannot be explained by sputtering only, as evaluated with simulations using the code TRIDYN. In addition to surface effect, significant fraction of the sputtered reactive gas is “recycled” in the HiPIMS discharge and returns back to the target surface. Because the ultimate goal is to provide a reliable description of the sputtering dynamics, the sputtered flux is analysed by mass spectroscopy.

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