Hematite, α-Fe₂O₃, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity of hematite is a substantial limitation reducing its efficiency in real experimental conditions. Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to 4 orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. Here, we present a strategy for controlling the crystal orientation of very thin hematite films by adjusting energy of ion flux during advanced pulsed reactive magnetron sputtering technique. The texture and effect of the deposition mode on the film properties were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott–Schottky analysis. The precise control of the synthetic conditions allowed to fabricate hematite photoanodes exhibiting fully textured structures along (110) and (104) crystal planes with huge differences in photocurrents of 0.65 and 0.02 mA cm^–2 (both at 1.55 V versus RHE), respectively. The photocurrent registered for fully textured (110) film is among record values reported for thin planar films. Moreover, the developed fine-tuning of crystal orientation having a huge impact on the photoefficiency would induce further improvement of thin hematite films mainly if cation doping will be combined with the controllable texture.

The ionization of sputtered Ti, Al, and C has been investigated in non-reactive high-power impulse magnetron sputtering discharges using Ar as a process gas. Two complementary techniques, time-resolved Langmuir probe diagnostics and a recently developed gridless ion meter, have for the first time been used to estimate absolute values of the ionized fractions of the sputtered material. To cover a range of commonly used discharge conditions we have carried out measurements for different process gas pressures, discharge current densities, and pulse lengths. It is found that by increasing the current density from 0.5 to 2.0 A cm−2 there is a general increase of independently of target material and position in time with maximum plasma densities of about 1 × 1018–5 × 1018 m−3 above the target race track. Also the ionized flux fraction, measured by ion meter, is increased when increasing the current density and reaches a maximum value of 78% in the Al discharge. By using the recorded and values to calculate the ionization probability of the sputtered material, and benchmark these results using the ion meter, we also show that Langmuir probe diagnostics is a useful tool to estimate trends and changes in the degree of ionization for different process conditions.

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.

Time-resolved comparative study of dual magnetron sputtering (dual-MS) and dual high power impulse magnetron sputtering (dual-HiPIMS) systems arranged with closed magnetic field is presented. The dual-MS system was operated with a repetition frequency 4.65 kHz (duty cycle $\approx 50\mathrm{\%}$ ). The frequency during dual-HiPIMS is lower as well as its duty cycle ($f=100\text{Hz}$ , duty 1%). Different metallic targets (Ti, Cu) and different cathode voltages were applied to get required stoichiometry of Ti–Cu thin films. The plasma parameters of the interspace between magnetrons in the substrate position were investigated by time-resolved optical emission spectroscopy, Langmuir probe technique, and measurement of ion fluxes to the substrate. It is shown that plasma density as well as ion flux is higher about two orders of magnitude in dual-HiPIMS system. This fact is partially caused by low diffusion of ionized sputtered particles $\left({\text{Ti}}^{+},{\text{Cu}}^{+}\right)$ which creates a preionized medium.