Ultra-short pulse HiPIMS: a strategy to suppress arcing during reactive deposition of SiO2 thin films with enhanced mechanical and optical properties

In this contribution, based on the detailed understanding of the processes’ characteristics during reactive high-power impulse magnetron sputtering (HiPIMS), we demonstrated the deposition of silicon oxide (SiO2) thin films with improved optical and mechanical performances. A strategy for stabilizing the arc-free HiPIMS of Si target in the presence of oxygen was investigated. Arcing was suppressed by suitable pulse configurations, ensuring good process stability without using any feedback control system. It was found that arcing can be significantly alleviated when ultra-short HiPIMS pulses are applied on the target. The optical and mechanical properties of SiO2 coatings deposited at various pulsing configurations were analyzed. The coatings prepared by ultra-short pulse HiPIMS exhibited better optical and mechanical performance compared to the coatings prepared by long pulse HiPIMS. The optimized SiO2 coatings on quartz substrates exhibited an average transmittance of 98.5% in the 190–1100-nm wavelength range, hardness of 9.27 GPa, hardness/Young’s modulus ratio of 0.138, and critical adhesion load of 14.8 N. The optical and mechanical properties are correlated with the film morphology, which is inherently related to energetic conditions and process stability during film growth.D. Cristea acknowledges the structural funds’ project PRO-DD (POS-CCE, O.2.2.1., ID123, SMIS 2637,ctr. no 11/2009) for providing the CSM Instruments infrastructure used for this wo

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 ∼25 at.%. This leads to a narrowing of the optical band-gap energy from 3.43 to 2.20 eV 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

Tantalum oxynitride thin films: Assessment of the photocatalytic efficiency and antimicrobial capacity

Tantalum oxynitride thin films have been deposited by reactive magnetron sputtering, using a fixed proportion reactive gas mixture (85% N2 + 15% O2). To produce the films, the partial pressure of the mixture in the working atmosphere was varied. The characteristics of the produced films were analyzed from three main perspectives and correspondent correlations: the study of the bonding states in the films, the efficiency of photo-degradation, and the antibacterial/antibiofilm capacity of the coatings against Salmonella. X-ray Photoelectron Spectroscopy results suggest that nitride and oxynitride features agree with a constant behavior relative to the tantalum chemistry. The coatings deposited with a higher reactive gas mixture partial pressure exhibit a significantly better antibiofilm capacity. Favorable antibacterial resistance was correlated with the presence of dominant oxynitride contributions. The photocatalytic ability of the deposited films was assessed by measuring the level of degradation of an aqueous solution containing methyl orange, with or without the addition of H2O2, under UV or VIS irradiation. Degradation efficiencies as high as 82% have been obtained, suggesting that tantalum oxynitride films, obtained in certain configurations, are promising materials for the photodegradation of organic pollutants (dyes).This research was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011. Daniel Cristea, Camelia Gabor, Ioana Ghiuta, and Catalin Croitoru acknowledge the structural funds project PRO-DD (POSCCE, O.2.2.1., ID 123, SMIS 2637, ctr. no 11/2009) for providing some of the infrastructure used in this work.info:eu-repo/semantics/publishedVersio

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

International audienceReactive High Power Impulse Magnetron Sputtering (HiPIMS) of a pure Zn target in Ar/N$_2$/O$_2$ gas mixture was used to synthesize ZnO$_x$N$_y$ thin films with nitrogen content and optical band-gap energy values ranging over 0–6.2 at.% and 3.34–1.67 eV, respectively. The fine control of the nitrogen content in the deposited ZnO$_x$N$_y$ thin films composition was possible through the stabilization of the reactive HiPIMS discharge in the transition region, between the metallic and compound target sputtering modes. Various analytical techniques such as AFM, XPS, XRD, UV–Vis and Raman spectroscopy have been employed to characterize the properties of the deposited thin films. The photocatalytic activity, light excitation efficiency and life time of photo-generated charge carriers in the ZnO$_x$N$_y$ films were investigated by photo-electrochemical and photo-current measurements during visible light on/off irradiation cycles. The as-deposited films showed poor visible-light photocatalytic activity and photo-current response. Post-deposition annealing of the films in nitrogen atmosphere resulted in a slight enhancement of crystalline order. However, the thermal treatment improved considerably the film photocatalytic activity and stability for water splitting under visible light irradiation. The optimum photo-current response and photocata-lytic activity have been obtained for the annealed ZnO$_x$N$_y$ films with a nitrogen content of 3.4 at.% (photon-to-current efficiency up to 33% at λ = 370 nm and 0.5 V biasing potential vs. Ag/AgCl). Increasing the nitrogen content above this value, in spite of lowering the energy band-gap, worsened the visible light photocatalytic activity of the films due to deterioration of the crystalline order

Effect of Pulsing Configuration and Magnetic Balance Degree on Mechanical Properties of CrN Coatings Deposited by Bipolar-HiPIMS onto Floating Substrate

Despite its great potential for thin films deposition and technological applications, the HiPIMS technology has its own limitations including the control of ion energy and flux towards the substrate when coping with the deposition of electrical insulating films and/or the deposition onto insulating/electrically grounded substrates. The bipolar-HiPIMS has been recently developed as a strategy to accelerate the plasma ions towards a growing film maintained at ground potential. In this work, the benefits of bipolar-HiPIMS deposition onto floating or nonconductive substrates are explored. The effect of bipolar-HIPIMS pulsing configuration, magnetic balance-unbalance degree, and substrate’s condition on plasma characteristics, microstructure evolution, and mechanical properties of CrN coatings was investigated. During the deposition with a balanced magnetron configuration, a significant ion bombardment effect was detected when short negative pulses and relative long positive pulses were used. XRD analysis and AFM observations revealed significant microstructural changes by increasing the positive pulse duration, which results in an increase in hardness from 7.3 to 16.2 GPa, during deposition on grounded substrates, and from 4.9 to 9.4 GPa during the deposition on floating substrates. The discrepancies between the hardness values of the films deposited on floating substrates and those of the films deposited on grounded substrates become smaller/larger when a type I/type II unbalanced magnetron configuration is used. Their hardness ratio was found to be 0.887, in the first case, and 0.393, in the second one. Advanced application-tailored coatings can be deposited onto floating substrates by using the bipolar-HiPIMS technology if short negative pulses, relative long positive pulses together with type I unbalanced magnetron are concomitantly used

Room Temperature Deposition of Nanocrystalline SiC Thin Films by DCMS/HiPIMS Co-Sputtering Technique

Due to an attractive combination of chemical and physical properties, silicon carbide (SiC) thin films are excellent candidates for coatings to be used in harsh environment applications or as protective coatings in heat exchanger applications. This work reports the deposition of near-stoichiometric and nanocrystalline SiC thin films, at room temperature, on silicon (100) substrates using a DCMS/HiPIMS co-sputtering technique (DCMS—direct current magnetron sputtering; HiPIMS—high-power impulse magnetron sputtering). Their structural and mechanical properties were analyzed as a function of the process gas pressure. The correlation between the films’ microstructure and their mechanical properties was thoroughly investigated. The microstructure and morphology of these films were examined by appropriate microscopic and spectroscopic methods: atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy, while their mechanical and tribological properties were evaluated by instrumented indentation and micro-scratch techniques. The lowest value of the working gas pressure resulted in SiC films of high crystallinity, as well as in an improvement in their mechanical performances. Both hardness (H) and Young’s modulus (E) values were observed to be significantly influenced by the sputtering gas pressure. Decreasing the gas pressure from 2.0 to 0.5 Pa led to an increase in H and E values from 8.2 to 20.7 GPa and from 106.3 to 240.0 GPa, respectively. Both the H/E ratio and critical adhesion load values follow the same trend and increase from 0.077 to 0.086 and from 1.55 to 3.85 N, respectively

Tantalum-titanium oxynitride thin films deposited by DC reactive magnetronic co-sputtering: mechanical, optical, and electrical characterization

The possibility to tune the elemental composition and structure of binary Me oxynitride-type compounds (Me1Me2ON) could lead to attractive properties for several applications. For this work, tantalum-titanium oxynitride (TaTiON) thin films were deposited by DC reactive magnetron co-sputtering, with a –50 V bias voltage applied to the substrate holder and a constant substrate temperature of 100 ◦C. To increase or to decrease in a controlled manner, the Ti and Ta content in the co-sputtered films, the Ti and Ta target currents were varied between 0.00 and 1.00 A, in 0.25 A steps, while keeping the sum of the currents applied to the two targets at 1.00 A. The reactive gases flow, consisting of a nitrogen and oxygen gas mixture with a constant N2/O2 ratio (85%/15%), was also kept constant. The single-metal oxynitrides (TaON and TiON) showed a low degree of crystallinity, while all the other co-sputtered films revealed themselves to be essentially amorphous. These two films also exhibited higher adhesion to the metallic substrate. The TaON film showed the highest hardness value (14.8 GPa) and the TiON film a much lower one (8.8 GPa), while the co-sputtered coatings exhibited intermediary values. One of the most interesting findings was the significant increase in the O content when the Ti concentration surpassed the Ta one. This significantly influenced the optical characteristic of the films, but also their electrical properties. The sheet resistivity of the co-sputtered films is strongly dependent on the O/(Ta + Ti) atomic ratio.This research was funded by a grant of the Romanian Ministry of Education and Research, CNCS–UEFISCDI, project number PN-III-P1-1.1-TE-2019-1209, within PNCDI III.Romanian Ministry of Research, NUCLEU Program LAPLAS VI (contract No. 16N/2019) and ELI-RO_2020_12

On the chemistry, photocatalytical, and corrosion behavior of co-sputtered tantalum and titanium oxynitride thin films

Direct current magnetron co-sputtered titanium and tantalum based oxynitride coatings (TaTiON) were analyzed in terms of their chemistry, surface morphology, surface energy, photocatalytic activity, and corrosion resistance. The variable parameter for the deposition was the applied current on each target, changing between 0.75A and 0.25A for the Ta target, and from 0.25A to 0.75 A for the Ti target, to obtain a total current of 1A. Reference single-sputtered samples (TaON and TiON) were deposited under identical conditions. It was observed that a higher degree of oxidation occurred in the samples deposited with higher current on the Ti target, while nitriding and oxynitriding processes occurred only on the surfaces of the films containing Ta. In terms of surface roughness, the co-sputtered coatings exhibited significantly smaller values, compared to the single-sputtered coatings. The highest photodegradation efficiency was registered for the co-sputtered sample which contains the highest N concentration. The corrosion rate, obtained from electrochemical tests, varies in a rather large domain, as function of the chemical species in the coatings.Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1- 1.1-TE-2019-1209, within PNCDI III. Valentin Craciun acknowledges the Romanian Ministry of Education and Research under the Romanian National Nuclear Program LAPLAS VI (contract no. 16 N/2019, ELI-RO_2020_12)

Chlorine doping impact on the photocatalytic and antibacterial activity of sprayed In2S3 films

In this study, the surface chemistry and morphology and the photocatalytic and antibacterial potential of pure and chlorine (Cl)-doped indium sulfide (In2S3) thin films, produced by spray pyrolysis, were analyzed. The root-mean-square roughness seemed not to be affected significantly by the chlorine concentration in three of the doped films (around 12 nm). The roughness seemed not to affect the characteristics of the films analyzed in this study. The samples presented a photocatalytic efficiency higher than 80%, but no correlation with the chlorine concentration was found. The antibacterial potential of the films was assessed against the multidrug-resistant bacteria Pseudomonas aeruginosa, responsible for serious infections, which are extremely difficult to treat in hospitals. The obtained results evidence an increase in antibacterial activity with the increase in chlorine concentration. These results encourage further studies to support the potential of this material to be used in biomedical applications.Part of this work was supported by the Portuguese Foundation for Science and Technology in the framework of the Strategic Funding UIDB/04650/2020. D.C. and I.G. acknowledge the structural fund project PRO-DD (POS-CCE, O.2.2.1., ID123, SMIS 2637, contract number 11/2009) for providing some of the infrastructure used in this work. Part of this work was supported by a grant of the Romanian Ministry of Education and Research, CNCS-UEFISCDI, project number PN-III-P1-1.1-TE-2019-1209, within PNCDI III. V.C. acknowledges the Romanian Ministry of Research, NUCLEU Program LAPLAS VI (contract number 16N/2019) and ELI-RO_2020_12