Titanium oxide (TiO₂) and iron oxide (α-Fe₂O₃) hematite films have potential applications as photoanodes in electrochemical water splitting. In the present work TiO₂ and α-Fe₂O₃ thin films were prepared by two methods, e.g., sol-gel and High Power Impulse Magnetron Sputtering (HiPIMS) and judged on the basis of physical properties such as crystalline structure and surface topography and functional properties such as simulated photoelectrochemical (PEC) water splitting conditions. It was revealed that the HiPIMS method already provides crystalline structures of anatase TiO₂ and hematite Fe₂O₃ during the deposition, whereas to finalize the sol-gel route the as-deposited films must always be annealed to obtain the crystalline phase. Regarding the PEC activity, both TiO₂ films show similar photocurrent density, but only when illuminated by UV light. A different situation was observed for hematite films where plasmatic films showed a tenfold enhancement of the stable photocurrent density over the sol-gel hematite films for both UV and visible irradiation. The superior properties of plasmatic films could be explained by ability to address some of the hematite drawbacks by the deposition of very thin films (25 nm) consisting of small densely packed particles and by doping with Sn.

We explored the effect of magnetic field strength $\left|\mathbf{B}\right|$ and geometry (degree of balancing) on the deposition rate and ionized flux fraction $F_{\mathrm{flux}}$ in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium. The HiPIMS discharge was run in two different operating modes. The first one we refer to as “fixed voltage mode” where the cathode voltage was kept fixed at 625 V while the pulse repetition frequency was varied to achieve the desired time average power (300 W). The second mode we refer to as “fixed peak current mode” and was carried out by adjusting the cathode voltage to maintain a fixed peak discharge current and by varying the frequency to achieve the same average power. Our results show that the dcMS deposition rate was weakly sensitive to variations in the magnetic field while the deposition rate during HiPIMS operated in fixed voltage mode changed from 30% to 90% of the dcMS deposition rate as $\left|\mathbf{B}\right|$ decreased. In contrast, when operating the HiPIMS discharge in fixed peak current mode, the deposition rate increased only slightly with decreasing $\left|\mathbf{B}\right|$ . In fixed voltage mode, for weaker $\left|\mathbf{B}\right|$ , the higher was the deposition rate, the lower was the $F_{\mathrm{flux}}$ . In the fixed peak current mode, both deposition rate and $F_{\mathrm{flux}}$ increased with decreasing $\left|\mathbf{B}\right|$ . Deposition rate uniformity measurements illustrated that the dcMS deposition uniformity was rather insensitive to changes in $\left|\mathbf{B}\right|$ while both HiPIMS operating modes were highly sensitive. The HiPIMS deposition rate uniformity could be 10% lower or up to 10% higher than the dcMS deposition rate uniformity depending on $\left|\mathbf{B}\right|$ and in particular the magnetic field topology. We related the measured quantities, the deposition rate and ionized flux fraction, to the ionization probability ${\alpha }_{\mathrm{t}}$ and the back attraction probability of the sputtered species ${\beta }_{\mathrm{t}}$ . We showed that the fraction of the ions of the sputtered material that escape back attraction increased by 30% when $\left|\mathbf{B}\right|$ was reduced during operation in fixed peak current mode while the ionization probability of the sputtered species increased with increasing $\left|\mathbf{B}\right|$ , due to increased discharge current, when operating in fixed voltage mode.

Reactive high power impulse magnetron sputtering (HiPIMS) of a cobalt cathode in pure argon gas and with different oxygen admixtures was investigated by time-resolved optical emission spectroscopy (OES) and time-integrated energy-resolved mass spectrometry. The HiPIMS discharge was operated with a bipolar pulsed power supply capable of providing a large negative voltage with a typical pulse width of 100 μs followed by a long positive pulse with a pulse width of about 350 μs. The HiPIMS plasma in pure argon is dominated by Co⁺ ions. With the addition of oxygen, O⁺ ions become the second most prominent positive ion species. OES reveals the presence of Ar I, Co I, O I, and Ar II emission lines. The transition from an Ar⁺ to a Co⁺ ion sputtering discharge is inferred from time-resolved OES. The enhanced intensity of excited Ar^+* ions is explained by simultaneous excitation and ionisation induced by energetic secondary electrons from the cathode. The intensity of violet Ar I lines is drastically reduced during HiPIMS. Intensity of near-infrared Ar I lines resumes during the positive pulse indicating an additional heating mechanism.

High power impulse magnetron sputtering (HiPIMS) of a cobalt cathode in argon gas was investigated by time-resolved electrical (Langmuir) probe diagnostics and by time-integrated energy-resolved mass spectrometry. The HiPIMS discharge was operated with a bipolar pulsed power supply, providing a large negative voltage with a typical pulse width of 100 μs followed by a long positive pulse with a pulse width of about 310 μs. The time-resolved Langmuir probe results yield a small negative plasma potential in the negative pulse regime and a large positive floating potential and plasma potential in the positive pulse regime. The electron density is significantly reduced during the positive pulse regime. The probe results are supported by ion energy measurements.

Catalytic total oxidation is an effective procedure to minimize emissions of volatile organic compounds (VOC) emissions in industrial gases. Catalysts in the form of meshes are remarkable as they minimize the internal diffusion of reactants during the reaction as well as the need of expensive active components. In this paper, various conditions of radio frequency magnetron sputtering of cobalt on stainless-steel meshes was applied during catalyst preparation. Properties of the supported Co₃O₄ catalysts were characterized by SEM, XRD, temperature programmed reduction (H₂-TPR), FTIR, XPS, and Raman spectroscopy. Catalytic activity was examined in deep oxidation of ethanol chosen as a model VOC. Performance of the catalysts depended on the amount of Co₃O₄ deposited on the supporting meshes. According to specific activities (the amounts of ethanol converted per unit weight of Co₃O₄), smaller Co₃O₄ particle size led to increased catalytic activity. The catalyst prepared by sputtering in an Ar+O₂ atmosphere without calcination showed the highest catalytic activity, which decreased after calcination due to enlargement of Co₃O₄ particles. However, specific activity of this catalyst was more than 20 times higher than that of pelletized commercial Co₃O₄ catalyst used for comparison.