| 1. |
- Elo, Robin, 1988-, et al.
(författare)
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Tailoring residual stresses in CrNx films on alumina and silicon deposited by high-power impulse magnetron sputtering
- 2020
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 397
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Tidskriftsartikel (refereegranskat)abstract
- Chromium nitride films, deposited using reactive magnetron sputtering, were optimised for wear resistance. The performance was measured by scratch resistance and optimised by tailoring the residual stresses. The depositions were carried out with either direct current magnetron sputtering (DCMS) or high-power impulse magnetron sputtering (HiPIMS), and with varying substrate bias and nitrogen gas flow. With DCMS, all films remained under tensile stresses and exhibited poor performance in scratch testing. Although the tensile stresses could be reduced by increasing the nitrogen flow, compressive stresses could only be induced when employing HiPIMS. Substrate bias had a strong effect in HiPIMS in contrast to the DCMS. The effect of the substrate bias in HiPIMS can be explained by the high ionisation of the flux of film forming species. In all cases, increased nitrogen flow favoured formation of CrN over Cr2N. All films showed signs of limited adhesion, which was improved using a titanium interlayer. Cracking across the scratch could be completely avoided for films with lower tensile or compressive stresses, the latter also exhibiting the highest critical load. The results show that it is possible to increase the scratch resistance by tailoring the residual stresses, for which HiPIMS proved a very useful tool.
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| 2. |
- Nyberg, Harald, et al.
(författare)
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Extreme friction reductions during inital running-in of W-S-C-Ti low-friction coatings
- 2013
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 302:1-2 SI, s. 987-997
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Tidskriftsartikel (refereegranskat)abstract
- The disulphides of tungsten and molybdenum are known for their low friction properties when used as solid lubricants. Due to their low hardness, their load bearing capacity when used as thin films is poor. When carbon is added to a WS2 coating, both of these shortcomings are improved, and a structure consisting of nanocrystals of WS2, and possibly tungsten carbide, in a matrix of amorphous carbon is formed. In this study, an attempt is made for further increasing the hardness of such coatings, by addition of Ti, a strong carbide former. A number of W–S–C(–Ti) coatings were deposited using magnetron co-sputtering, and characterised with regard to chemical composition, structure and tribological properties. It was seen that addition of Ti significantly increased the hardness of the coatings, while maintaining their excellent low friction properties in dry atmosphere. However, the coatings with Ti showed extremely high initial friction, a feature not seen for the coatings without Ti. The mechanisms behind this running-in behaviour were investigated by studying surfaces at early stages of wear. It was observed that tribofilms formed during sliding for the coatings containing Ti consisted mainly of TiO2, with platelets of WS2 appearing in the contact only after prolonged sliding. For the pure W–S–C coatings, WS2 was observed in the sliding interface almost instantly at the onset of sliding.
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| 3. |
- Kubart, Tomas, 1977-, et al.
(författare)
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Reactive high power impulse magnetron sputtering
- 2019
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Ingår i: High Power Impulse Magnetron Sputtering: Fundamentals, Technologies, Challenges and Applications. - : Elsevier. - 9780128124543 - 9780128124550 ; , s. 223-263
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Reactive magnetron sputtering is essential in many industrial processes where it is applied to deposit compound films or coatings. Reactive sputtering is attractive because a range of compounds can be prepared from a low-cost metal target by addition of an appropriate reactive gas to the noble working gas. To understand the reactive HiPIMS process, we here start with an overview of reactive sputtering and an introduction to process hysteresis in dcMS, which is followed by an overview of fundamental surface and plasma processes focusing on the behavior specific for reactive sputtering. In the second half of the chapter, HiPIMS-specific aspects of reactive sputtering are reviewed. This includes hysteresis in reactive HiPIMS operation, which is the subject of much debate, as some report reduction or elimination of the hysteresis effect, while others claim that a feedback control is essential. To provide a deeper insight into the process physics, a combination of experimental and computational model results are presented and discussed throughout the text.
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| 4. |
- Ren, Yi, et al.
(författare)
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Reactively sputtered films in the CuxS–ZnS–SnSy system : From metastability to equilibrium
- 2015
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 582, s. 208-214
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Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSnS4 is a promising photovoltaic absorber containing earth abundant elements. Using a two stage process, low temperature reactive co-sputtering followed by heat treatment, we have previously achieved a 7.9% efficient solar cell. Because the sputtered precursors contain non-equilibrium phases with unusual crystal structures, it is crucial to understand their nature and their conversion into Cu2ZnSnS4 (and secondary phases) during heat treatment. In this study, we report phase analysis of reactively sputtered binary and ternary sulfides in the CuxS–ZnS–SnSy system before and after annealing. In the as deposited films, Raman spectroscopy with 532 and 325 nm excitation wavelengths reveals expected phases for the binaries (CuS, ZnS and SnS2) and the ternary (Cu2SnS3), and unique metastable phases for the Cu–Zn–S and Zn–Sn–S precursors. Upon annealing, the non-equilibrium phases disappear, accompanied by additional chemical changes. Excess S content in the films is removed, and in the Sn–S and Zn–Sn–S films, further S loss from decomposition of SnSx (x > 1) and CuS respectively generates SnS and CuxS (x > 1). Due to the presence of SnS vapor, Cu2ZnSnS4 is generated from the Cu–Zn–S precursor. Additionally, the range of sulfur partial pressure in the annealing process is estimated according to the temperature–pressure phase diagram. This gives us useful insight allowing better control of annealing conditions.
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| 5. |
- Aijaz, Asim, et al.
(författare)
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Deposition of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Aijaz, Asim, et al.
(författare)
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Industrial Scale Deposition of Diamond-like Carbon Thin Films using Ne-based HiPIMS Discharge
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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/cm3In 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.
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| 7. |
- Aijaz, Asim, et al.
(författare)
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Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 149, s. 137-144
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Borges, J., et al.
(författare)
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Microstructural evolution of Au/TiO2 nanocomposite films : The influence of Au concentration and thermal annealing
- 2015
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 580, s. 77-88
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Borges, J., et al.
(författare)
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Thin films composed of Ag nanoclusters dispersed in TiO2 : Influence of composition and thermal annealing on the microstructure and physical responses
- 2015
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 358, s. 595-604
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Ericson, Tove, 1983-, et al.
(författare)
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Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells
- 2013
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 535, s. 22-26
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Tidskriftsartikel (refereegranskat)abstract
- 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%.
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