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Abstract Bipolar Pulse High Power Impulse Magnetron Sputtering (BP-HiPIMS) was investigated and used in this work to control the ion bombardment process of growing thin films and to improve their structure and properties. Energy-resolving mass spectroscopy was used to investigate the effect of reverse target voltage on the ion energies and fluxes during BP-HiPIMS of a high-purity copper target, in argon gas. It was found that the reverse target voltage provides a wide range of ion energies and fluxes incident to the growing film, which, in turn, produce a wide variety of effects during the deposition process, improving the adhesion strength and influencing both surface and bulk properties. Fast ICCD imaging was used to investigate both HiPIMS and BP-HiPIMS plasma dynamics. The temporal and spatial distributions of plasma potential measurements were performed in order to explain the mechanisms for accelerating the ions. The topological, structural and mechanical properties of the deposited coatings were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), nanoindentation and scratch tests. The obtained results indicate an energy-enhanced deposition process during BP-HiPIMS, the deposited films being characterized by smooth surfaces, dense microstructure, small inert gas inclusions, high elastic strain to failure, scratch resistance and good adhesion to the substrate. These improvements in the films' structure and properties may be attributed to the intense and energetic ion bombardment taking place during the deposition process. During BP-HiPIMS operation, there is no net increase in the deposition rate as compared to the monopolar regime due to the re-sputtering process. Highlights • Copper thin films were deposited on Si substrates by bipolar pulse HiPIMS technique. • The ICCD images reveal a plasma deconfinement process during bipolar HiPIMS. • The reverse target voltage provides a wide range of ion energies and fluxes. • The energy-enhanced deposition process occurs for reverse voltage above 100 V. • The films exhibit smooth surfaces, dense microstructure and good adhesion. [ABSTRACT FROM AUTHOR]

[Display omitted] • WO 3 modification of air-formed TiO 2 significantly enhances its photoactivity. • Laser treatment improves surface homogeneity and enhances its oxygen deficiency. • Laser-treated composite (L-WO 3 /TiO 2) exhibits lower flat band potential. • L-WO 3 /TiO 2 ensures faster kinetics and more cathodic onset potential of O 2 evolution. • At L-WO 3 /TiO 2 , UV-assisted methanol anodic oxidation is strongly enhanced. The effectiveness of the electrochemical WO 3 -modification as a method for improving the photoactivity of native air-formed TiO 2 layers was assessed. The way in which a mild laser treatment influences the photoelectrochemical performances of the thus obtained WO 3 /TiO 2 systems was also investigated. At laser-treated electrodes (L-WO 3 /TiO 2), the melting-solidification process induced by the treatment led to a smaller size of the deposited WO 3 particles and to their better dispersion on the surface. The treatment also enhanced the surface oxygen deficiency and ensured better relative absorptivity of the oxygenated species on the surface. These features, together with the intrinsic narrower bandgap of the WO 3 -TiO 2 composites, the higher donor density and the lower flat band potential of L-WO 3 /TiO 2 enabled faster kinetic of the oxygen photoanodic evolution. Importantly, the same process exhibited a cathodic shift of its onset potential. The laser treatment also strongly enhanced the photoelectrocatalytic performances for UV-assisted methanol anodic oxidation. [ABSTRACT FROM AUTHOR]