Adriano F. Feil

In this study, TiO _x thin films were deposited by DC reactive magnetron sputtering (DC-RMS), using different Ar/O₂ ratios in the absence of substrate bias and substrate heating. We observe a gradual change in the crystal structure and stoichiometry of the films with increasing Ar/O₂ ratio, enabling to obtain TiO _x films either with a pure anatase phase, a mixture between anatase and rutile, or a pure rutile phase. Our experimental results demonstrate that, by fine tuning the Ar/O₂ ratio during DC-RMS deposition process, a TiO _x thin film with tunable crystal structure and properties (surface morphology, atomic density, index of refraction, and film hardness) can be obtained in a simple way.

Highly ordered TiO ₂ NT arrays were easily decorated with CdSe via RF magnetron sputtering.

Metal oxide nanotubes (NTs) semiconductors prepared by anodization are promising materials due to their expected unique optical and electric properties. However, most of the work reported to date did not find photoelectrochemical devices with higher efficiency than those assembled with nanoparticles. Moreover, this behavior is due to the difficulty of having non-defective crystalline structures and the disruption of the tubular shape during thermal treatment while trying to reduce oxygen vacancies. This work describes in detail the local atomic configuration, surface area and morphology properties of Ta₂O₅ NTs prepared by anodization as a function of the temperature and the crystallization time by using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The crystallization process of adhered and freestanding Ta₂O₅ NTs is discussed. Adhered NTs crystallized at 550 °C due to the oxidation of the Ta metal during annealing in the air atmosphere and not the NT array itself. Freestanding Ta₂O₅ NTs crystallized after annealing at 800 °C. Rietveld refinements were performed to investigate the effects of the temperature and the annealing time on the grain size and microstrain and obtain information about Ta–O interatomic distances. The local structure of amorphous and crystalline Ta₂O₅ NTs was investigated with EXAFS. Low coordination numbers were found in the as-anodized samples as well as the samples annealed for 30 min at 800 °C. The coordination number increased when annealing was performed above 800 °C or when the annealing time was longer than 30 min. Moreover, the decrease of defects was followed by an increase in the crystal size and collapse of the tubular shape due to the increase in internal stress generated by the increase in the crystallinity of the tubes and the orthorhombic Ta₂O₅ crystal size.

A simple one-step method based on the sputtering deposition of Ni nanoparticles (NP) has been developed for the production of magnetic biocatalysts, avoiding the complications and drawbacks of methods based on chemical functionalisation or coating of magnetic NP. This new technique provided high levels of recovery, reusability and catalytic activity for the lipase–Ni biocatalyst.

Micro- and nanostructures of Ti-γCu (γ = 0, 30, 50, 70, and 100 wt %) intermetallic alloys were produced through a single anodization step. It was found that the original alloy composition influences the final oxide morphology obtained after anodization which presented formation of a microstructure with nanotubes, nanoparticles or nanopillars on the surface. Pure Ti and Cu oxide metals and their alloys presented hydrophilic or superhydrophilic properties immediately after anodization. When the anodized pure metal and/or Ti-γCu surfaces were functionalized with trimethoxypropylsilane (TPMSi), by dipping and coating with a thin perfluorinated layer, the treated substrates became in all cases superhydrophobic (water contact angles in the range of 152–166°), showing excellent self-cleaning properties with hysteresis below 3°. These results can be explained by a combination of nanomicro morphologies with low surface energy compounds in the topmost monolayers. The decrease in hysteresis was associated with a higher M–OH bond concentration on the anodized surfaces, which allowed for more complete TMPSi coating coverage. This study also indicates that easy and effective fabrication of superhydrophobic surfaces in pure metals and alloys is possible without involving traditional multistep processes.