arXiv subjects

E. Strods

Publications and source records attributed to E. Strods.

3 recordsLinked to original sources

arXiv2026

Growth-controlled photochromism in yttrium oxyhydride thin films deposited by HiPIMS and pulsed-DC magnetron sputtering

The present study investigates photochromic oxygen-containing yttrium hydride (YHO) thin films deposited by reactive high power impulse magnetron sputtering (HiPIMS) and compares their photochromic, optical, and structural properties with those of films synthesized by reactive pulsed direct current magnetron sputtering (pulsed-DCMS). Optical emission spectroscopy reveals that, unlike pulsed-DCMS where Ar$^{+}$ ions dominate, HiPIMS discharges are characterised by strong Y$^{+}$ emission, evidencing high yttrium ionisation and substantial self-sputter recycling. The critical working pressure (P$_c$) required to obtain transparent and photochromic films is higher for HiPIMS (Pc $\approx$ 1.0 Pa) than for pulsed-DCMS (Pc $\approx$ 0.5 Pa). Although films deposited near Pc exhibit similar solar transmittance (~72 %) and lattice parameters (5.38--5.39 \r{A}), the pulsed-DCMS film shows a substantially higher relative photochromic contrast (34 %) and a lower optical band gap (2.70 eV) compared with the HiPIMS film (9 % contrast and 2.94 eV). This difference is partly attributed to a lower oxygen-to-hydrogen atomic ratio in the pulsed-DCMS film. Structurally, HiPIMS films are largely polycrystalline with random out-of-plane crystallographic orientation, whereas pulsed-DCMS films exhibit a pronounced <100> out-of-plane preferred orientation. These results demonstrate that, beyond composition, thin-film growth conditions and microstructure play a crucial role in governing the photochromic performance of YHO.

cond-mat.mtrl-sci↗

arXiv2022

Tailoring of rhenium oxidation state in ReOx thin films during reactive HiPIMS deposition process and following annealing

Bulk rhenium trioxide (ReO3) has an unusually high electrical conductivity and, being nanosized, has promising catalytic properties. However, the production of pure ReO3 thin films is challenging due to the difficulty to stabilize rhenium in a 6+ oxidation state. Here we present a novel approach for the deposition of ReOx (x = 1.6-2.9) thin films using reactive high power impulse magnetron sputtering (r-HiPIMS) from a metallic rhenium target in a mixed Ar/O2 atmosphere. The thin films were deposited in the gas-sustained self-sputtering regime, observed during r-HiPIMS process according to current waveforms. The influence of the substrate temperature, the oxygen-to-argon flow ratio and post-annealing at 250 {\deg}C in the air for 3 h on the properties of the films were studied. The as-deposited films have an X-ray amorphous structure (a-ReOx) when deposited at room temperature while a nano-crystalline \b{eta}-ReO2 phase when deposited at elevated temperatures (150 or 250 {\deg}C). The amorphous a-ReOx can be converted into the crystalline ReO3 with a lattice parameter of 3.75 {\AA} upon annealing in the air. The surface morphology of the films is dense without detectable voids when elevated substrate temperatures are used. Various Re oxidation states are observed on the surface of the films in different ratios depending on the deposition parameters. All samples exhibit electrical resistivity on the order of 10-3 Ohmxcm and optical properties typical for thin metallic films.

cond-mat.mtrl-sci↗

arXiv2022

Optical properties of oxygen-containing yttrium hydride thin films during and after the deposition

The synthesis of the photochromic YHO films is based on the oxidation of deposited yttrium hydride in ambient conditions. The actual state of the films during the deposition process, which is influenced by the deposition pressure and the oxidation caused by the residual gases, is not completely known. We report on the YHxOy thin films deposited by reactive pulsed-DC magnetron sputtering. Since the visible light transmittance is closely related to the phase and chemical composition of the films, in-situ transmittance measurements during and after deposition are performed. Ex-situ spectroscopic ellipsometry is used to determine the optical constants of YHxOy throughout the film thickness. In order to obtain metallic YH2-x films, the densest possible structure with a high deposition rate is required, otherwise the films could already be partially transparent during the deposition. The transmittance is higher if deposition pressure is increased. This is because of the oxidation promoted by more porous growth of the microstructure that is observed at the surface and cross-section images of the films. The films exhibit a refractive index gradient perpendicular to the substrate surface, which is related to the porosity and variation of the chemical composition.

cond-mat.mtrl-sci↗