arXiv subjects

Jiří Rezek

Publications and source records attributed to Jiří Rezek.

6 recordsLinked to original sources

arXiv2026

Low-resistivity nitrogen-doped p-type Cu2O thin films enabled by millisecond flash lamp annealing

Flash lamp annealing (FLA) provides millisecond-scale thermal processing, but its effects on p-type Cu2O and nitrogen-related defects remain poorly understood. Reactively sputtered Cu2O:N films with different nitrogen content were deposited using reactive high-power impulse magnetron sputtering and exposed to a single 1.9 ms FLA pulse at 4.9 - 11.7 J cm-2. Their compositional,morphological, structural, vibrational, electrical, and optical responses were evaluated. WDS showed no statistically significant change in total elemental composition, and XRD confirmed retention of cubic Cu2O. Nitrogen-containing films exhibited surface coarsening, shifts of the Cu2O reflections, and non-monotonic changes in the Raman band assigned to molecular N2. Nitrogen incorporation substantially reduced the as-deposited resistivity. The very low value of 0.045 Ωcm was obtained after FLA at 4.9 J cm-2, whereas higher energy densities markedly increased resistivity. Hall measurements showed increasing mobility but decreasing hole concentration. At high energy densities, the optical band gap of nitrogen-rich films widened. The results define a narrow low-energy processing window with a positive effect on electrical properties, whereas high-energy FLA modifies the structure and optical absorption edge but degrades electrical conductivity.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced hydrogen response of copper-doped TiO$_2$ synthesised by helium-assisted magnetron sputtering

Cu-doped TiO$_2$ thin films for hydrogen sensing were synthesised by reactive DC magnetron sputtering in Ar/O$_2$/He mixtures, with the He fraction used as a control parameter for film growth. By combining normal-angle deposition (NAD) and glancing-angle deposition (GLAD) with post-deposition annealing, the effects of He on microstructure formation and sensor performance were examined. X-ray diffraction and electron microscopy revealed that He promotes nanostructuring, lattice expansion in as-deposited NAD films, increased porosity after annealing, and a stronger anatase character in the final oxide layers. These structural changes, which enhance the reactive surface area, lead to improved hydrogen sensing at 300\,$^\circ$C in 1~vol.\,\% H$_2$. The response of NAD films increased from 1.4 to 6.0 simply by replacing part of the argon with helium, whereas GLAD films showed only a modest increase. The observed nanostructuring is discussed in terms of a simulation-supported growth scenario involving energetic backscattered He, a reduced hammering effect, and cooling-related suppression of adatom mobility, which together favour the formation of a more open sensing layer. Helium-assisted sputtering represents a useful physical route for tailoring oxide thin films for gas-sensing applications.

cond-mat.mtrl-sci↗

arXiv2026

Boron-assisted stabilization of low-resistivity mixed-valence Cu-O thin films prepared by reactive magnetron sputtering

This study systematically investigated the influence of boron incorporation in Cu-O thin films and the effect of oxygen partial pressure ($p_{\rm ox}$) on the phase evolution, chemical bonding, and electrical characteristics of the prepared films. A phase transition from Cu$_2$O to Cu$_2$O/Cu$_4$O$_3$ to CuO was observed as oxygen partial pressure increased. Boron incorporation significantly broadened the stability window of the Cu$_2$O and Cu$_4$O$_3$ phases and delayed the transition to CuO at higher oxygen partial pressure. In the highly B-doped Cu-O films, Cu$_4$O$_3$ was stabilized even under oxygen-rich conditions along with the CuO phase, suggesting that boron significantly altered the oxidation pathway. The formation of B-O and possible B-O-Cu configurations altered the local oxygen chemistry and promoted mixed-valence copper oxide phases. Electrical measurements revealed that highly B-doped Cu-O films exhibited a delayed transition from a high-resistivity low-$p_{\rm ox}$ regime to a low-resistivity mixed-valence regime, ultimately reaching approximately 0.06 $Ω$ cm, among the lowest reported resistivities for a CuO-like material. These findings demonstrate that boron doping is an effective approach for tailoring the phase stability, defect chemistry, and electrical characteristics of Cu-O thin films for optoelectronic and photovoltaic applications.

cond-mat.mtrl-sci↗

arXiv2026

Corrosion-resistant and conductive Ti-Nb-O coatings tailored for ultra-low Pt-loaded BPPs and PTLs in PEM electrolyzers

We develop highly corrosion-resistant and conductive Ti-Nb-O coatings for metallic components -- bipolar plates (BPPs) and porous transport layers (PTLs) -- in PEM water electrolyzers. Using reactive high-power impulse magnetron sputtering (HiPIMS), we deposit compact 200 nm bilayer coatings onto SS316L substrates, systematically tailoring their composition. By precisely controlling oxygen partial pressure and Nb/Ti ratio, we adjust stoichiometry and structure, directly affecting electrical resistivity and corrosion resistance. We examine interfacial contact resistance (ICR) and electrochemical parameters before and after accelerated corrosion testing. Optimized coatings exhibit resistivity on the order of 10^-4 Ohmcm and extremely low corrosion current densities (J_corr = 0.01-0.08 uA/cm^2), well below the U.S. DOE 2026 target. Most importantly, these coatings enable the ICR target after accelerated corrosion testing with a Pt overlayer as thin as 5 nm, reducing Pt loading by up to two orders of magnitude compared to conventional approaches.

cond-mat.mtrl-sci↗

arXiv2025

Ultra-low-resistivity nitrogen-doped p-type Cu2O thin films fabricated by reactive HiPIMS

We have successfully fabricated the nitrogen-doped cuprous oxide thin films on the amorphous standard soda-lime glass by reactive high-power impulse magnetron sputtering. The energy of film-forming particles was controlled by the value of pulse-averaged target power density, which has a significant impact on the elemental composition, structure and optoelectrical properties of the films. We have shown that the high-energy regime is more suitable for preserving Cu2O structure and leads to continuous substitution of oxygen by nitrogen compared with the low-energy regime. Moreover, in the high-energy regime, it is possible, to some extent, to independently control the electrical resistivity and optical properties. The electrical resistivity decreases down to 5 x10-2 ohm.cm at the optical band gap 2.0-2.3 eV. Special attention is paid to the formation of nitrogen molecules and their ability to form shallow acceptor states. Experimental results supported by our DFT calculations indicate that N2 replacing Cu in the Cu2O lattice is one possible (but not the only possible) acceptor. We have also found that the formation of nitrogen molecules is preferred in a high-energy regime.

cond-mat.mtrl-sci↗

arXiv2024

Extraordinary oxidation behavior of W-Zr thin-film metallic glasses: A route for tailoring functional properties of W-Zr-O films

The oxidation behavior of W-Zr thin-film metallic glasses (TFMGs) with 32, 48 and 61 at.% Zr, prepared by dc magnetron co-sputtering, was comprehensively studied after annealing in synthetic air. The study focuses on the effect of the annealing temperature (up to 600°C) on the oxidation process, oxygen saturation, structure evolution, and their subsequent impact on electrical, optical and mechanical properties. The findings reveal that controlled oxidation transforms W-Zr TFMGs into amorphous ceramic W-Zr-O films with substoichiometric compositions. This is a consequence of an oxidation process that does not proceed through the formation of a stoichiometric oxide layer on the surface of W-Zr TFMGs, acting as a diffusion barrier against fast oxidation, but leads to a gradual incorporation of oxygen across the film volume due to thermodynamics factors. Higher Zr content accelerates the oxygen incorporation and its depth uniformity in the films. As a result, the mechanical properties are significantly enhanced achieving hardness values of up to 17.5 GPa at approximately 50% oxygen saturation. Simultaneously, the electrical and optical properties are finely tuned with the resistivity and the extinction coefficient (measured at 550 nm) ranging from 1.7 to 95.7x10-4 Ohm.cm and 0.28 to 1.06, respectively.

cond-mat.mtrl-sci↗