The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.

In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O 2 atmosphere as a function of the pulsing frequency and the pumping speed are investigated.Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for suppression/elimination of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS.Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al 2 O 3 at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.

The effect of peak power in a high power impulse magnetron sputtering (HiPIMS) reactive deposition of TiO 2 films has been studied with respect to the deposition rate and coating properties. With increasing peak power not only the ionization of the sputtered material increases but also their energy. In order to correlate the variation in the ion energy distributions with the film properties, the phase composition, density and optical properties of the films grown with different HiPIMS-parmeters have been investigated and compared to a film grown using direct current magnetron sputtering (DCMS). All experiments were performed for constant average power and pulse on time (100W and 35 μs, respectively), different peak powers were achieved by varying the frequency of pulsing. Ion energy distributions for Ti and O and its dependence on the process conditions have been studied. It was found that films with the highest density and highest refractive index were grown under moderate HiPIMS conditions (moderate peak powers) resulting in only a small loss in massdeposition rate compared to DCMS. It was further found that TiO 2 films with anatase and rutile phases can be grown at room temperature without substrate heating and without postdeposition annealing.

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TiO2 nanotubes (TNTs) were prepared by the electrochemical anodization method using titanium thin films deposited on indium tin oxide (ITO) substrates by the DC magnetron sputtering technique. The effect of voltage (20-40 V) and amount of ammonium fluoride (NH4F) (0.4-1.4 wt%) were investigated. The fabricated TNTs were characterized by field emission scanning electron microscopy (FE-SEM), X-Ray Diffraction (XRD), X-ray Photoemission spectroscopy (XPS), and Fourier-Transformed Infrared Spectrophotometry (FT-IR) techniques. XRD pattern data exhibited anatase phase when TNTs were annealed at 400 o C for 3 h. The XPS results revealed complement of Ti, O, F, Sn, In and C. The FT-IR spectrum exhibited the characteristic bands of the TiO2 which indicate the Ti-O stretching mode. The average diameter and length of TNTs depend on ammonium fluoride, water and voltage and the optimal conditions were found to be 0.8 wt% ammonium fluoride, and voltage at 30 V. The obtained TNTs have an averaged diameter of 38 nm and length of 763 nm. For dye-sensitized solar cells (DSSCs) application, ruthenium complex (N719) was used as a sensitizer in this work. The energy conversion efficiency (η) of TNTs was also evaluated.

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In this study, curcumin modified TiO2 nanotubes (Cur-TNT) were prepared by a modified impregnationelectrochemical anodization method with 0.01, 0.025, 0.05 mM of curcumin concentrations. The physical properties of the Cur-TNT were studied by several techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fouriertransformed infrared spectroscopy (FT-IR), and UV-Vis diffused reflectance spectroscopy (DRS). The XRD patterns data revealed anatase phase for both the TNT sample and the Cur-TNT samples. The high magnification images from SEM technique showed that the TNT sample and the Cur-TNT samples possess nanotube-like structures with an average diameter of 85 nm. The FT-IR spectra exhibited the characteristic bands of the TiO2 and hydroxyl groups on the TNT surface. Instead of hydroxyl groups, the characteristic bands of curcumin were observed on the surface of the Cur-TNT samples. The EDS results complementarily confirmed the existence of Ti, O, C as the main elements of the Cur-TNT samples. Interestingly, the DRS spectra of the Cur-TNT samples extended into the visible region. The photocatalytic properties of the Cur-TNT samples were evaluated from the degradation of methylene blue under visible light irradiation. It was found that the Cur-TNT samples exhibited higher photocatalytic performance than the TNT sample. A possible photocatalytic mechanism has also been proposed.

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