Reactive High Power Impulse Magnetron Research Articles

Microstructure and high-temperature tribological properties of Ti/Si co-doped diamond-like carbon films fabricated by twin-targets reactive HiPIMS

In order to enhance high-temperature tribological properties of the diamond-like carbon (DLC) films, Ti/Si co-doped DLC films were synthesized by twin-targets reactive high power impulse magnetron sputtering and effects of doped elements on mechanical performances were investigated. The results showed that a mid-doped DLC film with a Ti content of 13.8 at.% and a Si content of 12.6 at.% obtained the best high temperature tribological performance and its wear resistance was significantly less affected. The friction coefficient of the Ti/Si co-doped DLC film at 450 °C dropped to as low as 0.08. In addition, compared with the mono Ti-doped DLC film, its wear rate at 450 °C decreased from 5.24 × 10−4 to 1.40 × 10−5 mm3·N−1·m−1. Raman spectra revealed that Si could hinder the sp3-C to sp2-C transition at elevated temperatures, which impeded adhesive wear in the high temperature tribological process.

HiPIMS-grown AlN buffer for threading dislocation reduction in DC-magnetron sputtered GaN epifilm on sapphire substrate

Gallium nitride (GaN) epitaxial films on sapphire (Al2O3) substrates have been grown using reactive magnetron sputter epitaxy with a liquid Ga target. Threading dislocations density (TDD) of sputtered GaN films was reduced by using an inserted high-quality aluminum nitride (AlN) buffer layer grown by reactive high power impulse magnetron sputtering (R-HiPIMS) in a gas mixture of Ar and N2. After optimizing the Ar/N2 pressure ratio and deposition power, a high-quality AlN film exhibiting a narrow full-width at half-maximum (FWHM) value of the double-crystal x-ray rocking curve (DCXRC) of the AlN(0002) peak of 0.086° was obtained by R-HiPIMS. The mechanism giving rise the observed quality improvement is attributed to the enhancement of kinetic energy of the adatoms in the deposition process when operated in a transition mode. With the inserted HiPIMS-AlN as a buffer layer for direct current magnetron sputtering (DCMS) GaN growth, the FWHM values of GaN(0002) and (10 1‾ 1) XRC decrease from 0.321° to 0.087° and from 0.596° to 0.562°, compared to the direct growth of GaN on sapphire, respectively. An order of magnitude reduction from 2.7 × 109 cm−2 to 2.0 × 108 cm−2 of screw-type TDD calculated from the FWHM of the XRC data using the inserted HiPIMS-AlN buffer layer demonstrates the improvement of crystal quality of GaN. The result of TDD reduction using the HiPIMS-AlN buffer was also verified by weak beam dark-field (WBDF) cross-sectional transmission electron microscopy (TEM).

Band-gap engineering of zirconia by nitrogen doping in reactive HiPIMS: a step forward in developing innovative technologies for photocatalysts synthesis.

In the global context of climate change and carbon neutrality, this work proposes a strategy to improve the light absorption of photocatalytic water-splitting materials into the visible spectrum by anion doping. In this framework, reactive high power impulse magnetron sputtering (HiPIMS) of a pure Zr target in Ar/N2/O2 gas mixture was used for the deposition of crystalline zirconium oxynitride (ZrO2-xNx) thin films with variable nitrogen doping concentration and energy band-gap. The nitrogen content into these films was controlled by the discharge pulsing frequency, which controls the target surface poisoning and peak discharge current. The role of the nitrogen doping on the optical, structural, and photocatalytic properties of ZrO2-xNx films was investigated. UV-Vis-NIR spectroscopy was employed to investigate the optical properties and to assess the energy band-gap. Surface chemical analysis was performed using X-ray photoelectron spectroscopy, while structural analysis was carried out by X-ray diffraction. The increase in the pulse repetition frequency determined a build-up in the nitrogen content of the deposited ZrO2-xNx thin films from ∼10 to ∼25at.%. This leads to a narrowing of the optical band-gap energy from 3.43 to 2.20eV and endorses efficient absorption of visible light. Owing to its narrow bandgap, ZrO2-xNx thin films obtained by reactive HiPIMS can be used as visible light-driven photocatalyst. For the selected processing conditions (pulsing configuration and gas composition), it was found that reactive HiPIMS can suppress the hysteresis effect for a wide range of frequencies, leading to a stable deposition process with a smooth transition from compound to metal-sputtering mode.

Photocatalytic activity of TiO2 deposited by reactive HiPIMS with long target-to-substrate distance

Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of TiO2 thin films was carried out to investigate the influence of ion parameters and the deposition temperature on the film crystallinity and photocatalytic performance. In order to limit unintentional substrate heating, a deposition setup with long target-to-substrate distance was used. Different HiPIMS pulse configurations, deposition temperatures and substrate bias were evaluated. TiO2 films prepared by pulsed dc magnetron sputtering were used as reference. Films deposited at room temperature were all found to be X-ray amorphous, and a minimum temperature of 200 °C was needed for film crystallization irrespective of the mode of operation. This is attributed to the relatively long target-to-substrate distance of 180 mm used in this work. The growth of a specific polymorph was shown to be dependent on the operation mode, where a high oxygen partial pressure was ideal for anatase formation. The photodegradation rates were, as expected, found to be highest for crystalline samples, where single- and mixed-phase films yielded similar rates. Furthermore, the photodegradation rates of HiPIMS films deposited without substrate heating could be enhanced up to 3 times as compared to the corresponding pulsed dc reference film. The ion assistance in HiPIMS is also beneficial at moderate temperatures, here 200 °C, where an improved crystallinity as compared to pdcMS, was observed.

Deposition and characterisation of c-axis oriented AlScN thin films via microwave plasma-assisted reactive HiPIMS

In this work, we demonstrate that highly oriented c-axis aluminium scandium nitride (AlScN) piezoelectric thin films can be deposited via microwave plasma-assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS), without the necessity of substrate heating. A combination of in situ plasma diagnostics, i.e. time-of-flight mass spectrometry (ToF-MS), modified quartz crystal microbalance (m-QCM), and magnetic field measurements allowed to optimise the deposition conditions, in turn maximising the nitrogen supply and ionic flux at the substrate region, while maintaining stable discharge conditions. The AlScN thin films synthesised in this study were deposited as chemically gradient coatings with varying levels of scandium doping, and were characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Obtaining highly textured films was made possible with the addition of microwave plasma to the optimised HiPIMS discharge, where the wurtzite AlScN films (with up to 20 at. % Sc) exhibited a stronger texture in the (0002) orientation compared to films prepared without microwave plasma. Additionally, the use of a microwave plasma led to a significant decrease in oxygen content in the films and increase in nitrogen content, ensuring stoichiometric compositions. Based on the results mentioned above, it is expected that the AlScN thin films fabricated via MAR-HiPIMS would exhibit a strong piezoelectric response.

Pulse length dependence of a reactive high power impulse magnetron (HiPIMS) discharge

The pulse length dependence of a reactive high power impulse magnetron sputtering (HiPIMS) discharge with a tungsten cathode in an argon+oxygen gas mixture gas was investigated. The HiPIMS discharge is operated with a variable pulse length of 20–500 µs. Discharge current measurements, optical emission spectroscopy of neutral Ar, O, and W lines, and energy-resolved ion mass spectrometry are employed. A pronounced dependence of the discharge current on pulse length is noted while the initial discharge voltage is maintained constant. Energy-resolved mass spectrometry shows that the oxygen-to-tungsten (O+/W+) and the tungsten oxide-to-tungsten (WO+/W+) ion ratio decreases with pulse length due to target cleaning. Simulation results employing the SDTrimSP program show the formation of a non-stoichiometric sub-surface compound layer of oxygen which depends on the impinging ion composition and thus on the pulse length.

The stress release of morphological change on thermochromic properties of nitrogen-incorporated VO2 thin films

VO2 thin films are fabricated by the reactive high power impulse magnetron sputtering technique. Their thermochromic properties are found to be greatly affected by the addition of nitrogen during the deposition process. These include an effect of localized surface plasmon resonance due to isolated island structures. Furthermore, low transition temperatures below 45 °C are observed due to oxygen-deficient conditions. Also, the transition temperature decreases with an increase in the thickness of the TiO2 buffer layer. The reduction in transition temperature could be as low as 39 °C with a solar modulating ability of 4% at a thicker buffer of 300 nm under a high gas ratio of 21.7% for nitrogen. The crystalline phase is identified by x-ray diffraction, showing that the intensity of monoclinic crystallites at a diffraction angle of 2θ = 27.8° for (011) phase decreases with an increase in the amount of nitrogen, whereas a relaxing shift is detected near the diffraction angle of 2θ = 37.0° for (2¯11) phase. Similar behavior is seen in the peak shift of the (004) phase for TiO2. The d-spacing of the crystallization phase with island structure is identified by high-resolution transmission electron microscopy. The evolution of stress release, which is strongly dependent on surface morphology, is consistent with x-ray pole figure representation. The visible transmittance and solar modulation ability as functions of the amount of nitrogen and the buffer thickness of TiO2 are discussed.

Microwave plasma-assisted reactive HiPIMS of InN films: Plasma environment and material characterisation

This work focuses on the low temperature fabrication process of InN thin films via microwave plasma-assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS). The influence of microwave plasma on the HiPIMS discharge process at various nitrogen flows and microwave powers was monitored and characterised through in situ diagnostics, including following HiPIMS I(V,t) curves, optical emission spectroscopy (OES), as well as performing time-resolved Langmuir probe and time-of-flight mass spectroscopy (ToF-MS) measurements. This was followed by the deposition of InN films via standard reactive HiPIMS (reference sample) and MAR-HiPIMS and their characterisation via X-ray diffraction (XRD), reflectometry (XRR), as well as scanning and transmission electron microscopy (SEM, TEM). It was found that the microwave plasma facilitates the dissociation/activation of nitrogen species and supplies seed electrons to the magnetron discharge plasma. Furthermore, the energy of the incoming ions was determined via ToF-MS, and it was possible to identify their plasma origin and temporal behaviour. The produced R-HiPIMS sample was highly metallic, with no nitride phase detected. The MAR-HiPMS film, however, was stoichiometric and exhibited (0002) direction texturing, with an optical bandgap of approx. 1.5 eV, electron concentration of 2.72 × 1020 cm−3 and electron mobility of 7.16 cm2V−1 s−1 (in the range for polycrystalline InN).

Copper tungsten oxide (CuxWOy) thin films for optical and photoelectrochemical applications deposited by reactive high power impulse magnetron co-sputtering

Copper tungsten oxide films are deposited with the help of reactive high power impulse magnetron sputtering (HiPIMS) in an argon/oxygen gas mixture. Two magnetrons, one equipped with a tungsten target and the other with a copper target, are employed. The HiPIMS discharge is operated with a repetition frequency of f=100 Hz. Pulse widths of 100 and 20 μs separated by 25 μs are chosen for the tungsten and copper target, respectively. Films deposited on two different glass substrates [soda lime glass and fluorine doped tin oxide (FTO) coated glass] are characterized by energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, Raman spectroscopy, and ellipsometry. Photoelectrochemical activity was investigated by linear voltammetry. The composition and crystal structure of as-deposited and annealed films are found to depend on the deposition conditions. Annealed films deposited on FTO glass are composed of WO3 and CuWO4 or Cu2WO4 crystal phases. Films deposited on soda lime glass are subject to sodium diffusion into the films during annealing and the formation of Na2W2O7 and Na2W4O13 phases.

Al L2,3 near edge structure captures the dopant activation and segregation in Al-doped ZnO films

Aluminum-doped zinc oxide (AZO) films have been synthesized using reactive high power impulse magnetron sputtering (HiPIMS) in a wide range of Al contents, 0.6–14.7 at.%. The film structure and microstructure investigated by X-ray diffraction and transmission electron microscopy evolves from nanocrystalline columnar film towards ultrafine nanocrystalline films of wurtzite ZnO structure upon increasing the Al content. Electrical properties measured by 4-point probe and Hall effect setups revealed that effective doping maybe achieved up to 3 at.% Al by using HiPIMS. Most importantly, optical transmittance and electronic structure measurements at the Al L2,3 of electron energy loss near edge structure (ELNES) contain signatures of dopant activation, and dopant segregation that may serve to investigate on the origin of electrical properties degradation and to optimize the electrical properties of AZO films.

Tailoring of rhenium oxidation state in ReOx thin films during reactive HiPIMS deposition process and following annealing

Bulk rhenium trioxide (ReO3) has an unusually high electrical conductivity and, being nanosized, has promising catalytic properties. However, the production of pure ReO3 thin films is challenging due to the difficulty to stabilize rhenium in a 6+ oxidation state. Here we present a novel approach for the deposition of ReOx (x ≈ 1.6–2.9) thin films using reactive high power impulse magnetron sputtering (r-HiPIMS) from a metallic rhenium target in a mixed Ar/O2 atmosphere. The thin films were deposited in the gas-sustained self-sputtering regime, observed during r-HiPIMS process according to current waveforms. The influence of the substrate temperature, the oxygen-to-argon flow ratio and post-annealing at 250 °C in the air for 3 h on the properties of the films were studied. The as-deposited films have an X-ray amorphous structure (a-ReOx) when deposited at room temperature while a nano-crystalline β-ReO2 phase when deposited at elevated temperatures (150 or 250 °C). The amorphous a-ReOx can be converted into the crystalline ReO3 with a lattice parameter of 3.75 Å upon annealing in the air. The surface morphology of the films is dense without detectable voids when elevated substrate temperatures are used. Various Re oxidation states are observed on the surface of the films in different ratios depending on the deposition parameters. All samples exhibit electrical resistivity on the order of 10−3 Ωcm and optical properties typical for thin metallic films.

Mechanical and Tribological Properties of Ta-N and Ta-Al-N Coatings Deposited by Reactive High Power Impulse Magnetron Sputtering.

In this article, the depositions and functional characterizations of Ta-N and Ta-Al-N coatings for protection purposes, grown by reactive high-power impulse magnetron sputtering onto silicon substrates, are described. Nitride films were grown while changing the substrate polarization voltage (i.e., the applied bias voltage) during the process. Moreover, the effects of adding Al to form a ternary system and the resulting variation of the coatings’ mechanical and tribological properties have been widely investigated by nanoindentation, scratch, and wear tests. Micro-Raman characterization has been applied to the wear tracks to explore the comprehensive tribo-environment and wear mechanism. Interestingly, Ta-Al-N films, despite significantly improved mechanical properties, show a premature failure with respect to Ta-N coatings. The wear mechanisms of Ta-N and Ta-Al-N systems were revealed to be very different. Indeed, Ta-Al-N films suffer higher oxidation phenomena during wear, with the formation of an oxidized surface tribofilm and a reduced wear resistance, while Ta-N coatings undergo plastic deformation at the wear surface, with a slightly adhesive effect.

Tribocorrosion behaviors of superhard yet tough Ti-C-N ceramic coatings

Ceramic materials are widely used as protective coatings for marine engineering components in seawater environments due to their high wear and corrosion resistance. However, the applications and lifetimes of these materials have been always limited by the high brittleness of ceramic coatings. Hence, in this work, we report superhard yet tough Ti-C-N coatings with mixed TiC and TiN phases deposited by reactive high power impulse magnetron sputtering. Ti-C-N coatings exhibit a simultaneous superhardness of 40.2 GPa and favorable toughness due to fully dense microstructure and smooth surface morphology. These superhard yet tough Ti-C-N coatings show excellent seawater-lubricating behaviors with an extremely low friction coefficient of 0.03 and mild wear track in 3.5 wt% NaCl aqueous solution. The enhanced tribocorrosion performance is attributed to the increased resistance to crack initiation and propagation, restraining the synergistic actions of wear and pitting corrosion.

Structural morphology and electrical transitions of V[formula omitted]O[formula omitted] thin films grown on SiO[formula omitted]/Si by high power impulse magnetron sputtering

The study presents the synthesis of V2O3 films on thermally oxidized Si(001) substrates by reactive high power impulse magnetron sputtering. The effect of film thickness and oxygen variation were explored at fixed discharge parameters. X-ray diffraction (XRD), grazing incidence-XRD and pole scans reveal the films to be textured. The results show that for a critical thickness up to ∼ 5 nm, highly strained V2O3 films are obtained, and with increased thickness the film exhibit increased surface roughness and the formation of a granular structure arising from strain relaxation in the films. With increasing thickness the films exhibit a variation in the lattice parameters affecting their electrical characteristic i.e. metal-insulator transition (MIT). Subject to variation in O2 flow setting we observe the MIT magnitude and transition temperatures to be strongly dependent on the film stoichiometry and lattice parameters which can be fine tuned by mapping the O2 flow settings. The most dominant transition out of the studied structures was observed for those having film thickness of ∼ 36 nm with an O2 flow setting ranging from 0.8 to 0.95 sccm and displaying a low c/a lattice ratio. The MIT observed for these structures displayed a change in resistance of up to ∼ 4 decades with a total change in resistance of ∼ 7 decades.

Multicomponent TixNbCrAl nitride films deposited by dc and high-power impulse magnetron sputtering

Multicomponent TixNbCrAl nitride films were deposited on Si(100) substrates by reactive direct current magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) in the absence of substrate heating and bias. Three single Ti, Nb, and Cr50Al50 targets were either driven by three dc or three HiPIMS power supplies. The Ti content in the films was varied by tuning the power applied to the Ti target. The composition was determined by ion beam analysis. The nitrogen content is nearly stoichiometric (48–50 at.%) in the HiPIMS series, while the dcMS are understoichiometric (39–45 at.%). The crystal structure, stress and density of the studied film were investigated by X-ray techniques and the microstructure was examined by scanning electron microscopy. All the Ti-containing films for both series exhibit an fcc NaCl-type phase structure. In particular, the dcMS series shows a (111) preferred orientation, resulting in a faceted surface morphology compared to a dense and smooth microstructure of the HiPIMS films. The compressive stress of the HiPIMS series (> 2.0 GPa) is significantly larger than the values of the dcMS series (<0.5 GPa). Nanoindentation measurements show a maximum hardness of 29.9 GPa and Young's modulus of 304 GPa were obtained in the HiPIMS series. The results may promote HiPIMS techniques for the synthesis of complex multicomponent films for the application aspect to protective and hard coatings.

Controlling preferential growth of chromium – Nitrogen R-HiPIMS and R-DCMS films by substrate magnetic biasing

The effect of magnetic biasing on the structure of Cr-N coatings deposited on silicon substrates by reactive magnetron sputtering has been investigated. The magnetic biasing setup consisted of a permanent magnet placed close to the substrate holder to modify the plasma species dynamics and deposition flux. Three magnetic field configurations for reactive direct current magnetron sputtering (R-DCMS) and reactive High Power Impulse Magnetron Sputtering (R-HiPIMS) were compared. Deposition parameters such as deposition time, gun power, substrate distance, temperature, gas pressure, and gas composition were constant through the six R-DCMS/HiPIMS-magnetic-field combinations. Processes were monitored through optical emission spectroscopy (OES) and closely compared to the voltage and current curves at the target/substrate. An excitation mechanism was proposed accounting for the enhanced ionization detected by OES and the implications in the film’s growth. The films’ stoichiometry, structure, thickness, morphology, and crystal texture were characterized and associated with the process parameters. The R-DCMS processes led to Cr-N solid solution films, while the enhanced reactivity of R-HiPIMS plasma species increased the N content and formed CrN. Overall, the R-DCMS deposited samples were thicker than the R-HiPIMS deposited samples, but the different magnetic field biasing setups allowed for specific control of films’ thickness, texture, and microstructure.

Effects of the Ethyne Flow Ratio on Structures and Mechanical Properties of Reactive High Power Impulse Magnetron Sputtering Deposited Chromium-Carbon Films

Chromium-carbon films were deposited by utilizing reactive high-power impulse magnetron sputtering with different mixture ratios of ethyne and argon with a constant deposition total pressure while the deposition temperature, pulse frequency, duty cycle and average power of the chromium cathode remain the same. The microstructure and chemical bonding of the obtained films within different composition were compared. The results show that with the increasing ethyne ratio, the carbon content in films increases linearly with two slopes. Moreover, the microstructure of the deposited film changes from a dense glassy structure into a columnar structure, even a clusters structure. The sp2-C bonding in films decreases but the Cr–C bonding increases with decreasing the ethyne ratio. This reveals the main phase of films changes from a hydrogenated amorphous carbon phase into a glassy amorphous chromium carbide phase. Such changes of the microstructure and phase cause a large difference on the film hardness and elasticity.

Tailoring properties of indium tin oxide thin films for their work in both electrochemical and optical label-free sensing systems

This work is devoted to the identification properties of indium tin oxide (ITO) thin films responsible for their possible application in combined optical and electrochemical label-free sensing systems offering enhanced functionalities. Since any post-processing would make it difficult to identify direct relation between deposition parameters and properties of the ITO films, especially when deposition on temperature-sensitive substrates is considered, the films were deposited using reactive high power impulse magnetron sputtering (HiPIMS) at low temperature and with no post-deposition annealing. We focused mainly on the impact of reactive gases, such as oxygen or nitrogen introduced to the process chamber, on control over plasma parameters and subsequently properties of the films. The properties of the films were investigated using X-ray diffractometry, spectroscopic ellipsometry, four-point probe, and cyclic voltammetry. For presenting optical sensing capabilities, the tailored ITO films in addition to silicon and glass wafers were also deposited on the core of optical fibers to induce the lossy-mode resonance (LMR) phenomenon. The existence of specific deposition conditions resulting in ITO film properties offering both high-quality electrochemical and LMR responses has been experimentally proven. It has been found that the crystalline structure of ITO plays a key role in the determination of both the sensing capabilities. Finally, label-free sensing of antibody-antibody interactions in both optical and electrochemical domains for the sensor with tailored ITO film has been shown.

Production Strategies of TiNx Coatings via Reactive High Power Impulse Magnetron Sputtering for Selective H2 Separation.

This scientific work aims to optimize the preparation of titanium nitride coatings for selective H2 separation using the Reactive High Power Impulse Magnetron Sputtering technology (RHiPIMS). Currently, nitride-based thin films are considered promising membranes for hydrogen. The first series of TiNx/Si test samples were developed while changing the reactive gas percentage (N2%) during the process. Obtained coatings were extensively characterized in terms of morphology, composition, and microstructure. A 500 nm thick, dense TiNx coating was then deposited on a porous alumina substrate and widely investigated. Moreover, the as-prepared TiNx films were heat-treated in an atmosphere containing hydrogen in order to prove their chemical and structural stability; which revealed to be promising. This study highlighted how the RHiPIMS method permits fine control of the grown layer’s stoichiometry and microstructure. Moreover, it pointed out the need for a protective layer to prevent surface oxidation of the nitride membrane by air and the necessity to deepen the study of TiNx/alumina interface in order to improve film/substrate adhesion.

On the description of metal ion return in reactive high power impulse magnetron sputtering

Abstract Back-attraction of ionized metal is an important process in reactive high power impulse magnetron sputtering (R-HiPIMS). Here, we discuss the implementation of the metal return in balance type models for reactive magnetron sputtering. We show that the existing description of surface processes needs to be modified to satisfy mass conservation. A new steady-state time-averaged model is presented and used to evaluate the effect of the metal return in R-HiPIMS. The results show that the metal return leads to an increased oxide fraction in the deposited coating in R-HiPIMS. This effect can explain the high rate deposition of stoichiometric compounds deposited in the metal mode of operation that has been observed experimentally.