Abstract Structuring by femtosecond laser process is a promising technique for improving the performance of porous transport layers (PTL) in proton exchange membrane (PEM) electrolysis. As an increase in surface area and a raise of crevices always promotes corrosion, a method must be found to prevent a shortening of the component lifespan. In this paper a method of implanting additional elements from coatings into titanium, while simultaneously nitriding the surface by processing under nitrogen atmosphere is presented. Ruthenium and Iridium were chosen as materials because they are commonly used as catalyst and corrosion-inhibitor in PEM-cells. Especially ruthenium showed promising ability in decreasing corrosion rates while increasing surface conductivity at the same time. Specifically, in samples processed under nitrogen, the addition of ruthenium was able to decrease the impact of laser processing on corrosion rates by up to 46%.

In this study, we present a thermochromic solar absorber coating that reaches a high thermal emittance change by using a thin, optically switching VOx film located on an infrared transparent interlayer (spacer) of Si or Ge with an optical thickness of λ/4 (for λ = 7 μm). Using this so-called “lambda/4-concept,” temperature-dependent reflection measurements in the spectral range between 2500 and 50 000 nm from an absorber with a 450 nm Si spacer and a VOx film oxidized from a 30-nm-thick V display an overall increase in emittance from ε(25 °C) = 12.2% to ε(150 °C) = 55.1%, resulting in a change of Δε = 42.9%. In addition, using an absorber with a 400 nm Ge spacer in combination with a VOx film oxidized from 17.5-nm-thick V, an increase in emittance from ε(25 °C) = 8.2% to ε(150 °C) = 49.2% with a change of Δε = 41.0% was achieved. In addition, the optical properties of Ge and Si thin films over a wide spectral range of 250–38 000 nm were determined using spectroscopic ellipsometry. Using this optical data and a simple optical model of the VOx film, reflectance simulations could be performed by using the ellipsometry analysis software WVASE©. It was shown by x-ray diffraction measurements that the optically switching VOx films oxidized from V in a belt furnace consist of the VO2 and the V2O5 phases. Using scanning electron microscopy images, the surface morphology of optically switching VOx films was compared with over-oxidized VOx films. A correlation between the surface morphology and the crystalline phases was revealed and applied to search for the optimal furnace parameters. This method could significantly reduce the time cost to achieve optically switching VOx coatings using an oxidation process.

As a special class of materials, transition metal oxides exhibit in their crystalline phase a variety of interesting properties, such as metal–insulator transition, ferroelectricity, magnetism, superconductivity, and so forth. However, for industrially widely applied methods such as room temperature magnetron sputtering, during initial fabrication steps of these materials, they are mostly amorphous, and control of stoichiometry during fabrication is challenging. It is, therefore, of pivotal importance to control the stoichiometry of transition metal oxides during growth in the amorphous state. One particularly important example for the necessity of stoichiometry control is vanadium dioxide (VO2), where small deviations in stoichiometry during fabrication result in unfavorable changes in the electronic and structural properties, for example, the metal–insulator transition temperature and optical permittivity. In this work, the stoichiometry of amorphous vanadium oxides is adjusted to VO2 using in situ spectroscopic ellipsometry (in situ SE) and verified by x-ray photoelectron spectroscopy. After an annealing process, a monoclinic VO2 crystalline structure is observed through x-ray diffraction at 30 °C. At an elevated temperature of 150 °C, which is higher than the typical metal–insulator transition temperature in VO2 of around 67 °C, a rutile crystalline structure is observed, which verifies the correctness of the stoichiometry of VO2. A Mott metal–insulator transition is revealed by the change in the imaginary part of optical permittivity through SE as well.

In common, one of the most characteristic properties of pulsed laser deposition is the stoichiometry transfer between target and substrate, which has been used heavily for many complex systems. In this paper we show that it is yet possible to obtain drastic deviations from stoichiometry transfer in a binary system by just varying the fluence during laser deposition. In the W–Cu system, the W concentration of films grown from a composite W60Cu40 target (60 wt% W) was indeed continuously changed over an unprecedented large range of 0–70 wt% W. Close to the deposition threshold, pure Cu films are formed due to the much higher vapor pressure of Cu. At higher laser fluences, more and more W-rich W–Cu alloy samples are obtained, since ion implantation and intermixing processes occur. These alloys can reach W contents even higher than that of the target because of enhanced resputtering and reflection of the lighter Cu atoms at the film surface. Stoichiometric films with 60 wt% of W are only obtained at laser fluences around 2.7 J/cm2, when the strong Cu evaporation from the target and reflection and resputtering effects of Cu at the film surface are in balance.