Open Access

Cerium oxide-tin oxide (CeOx/SnOx) thin films with varying Sn content were deposited using RF magnetron sputtering and investigated for hydrogen sensing applications. Structural, compositional, and morphological properties were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). Gas sensing measurements showed effective hydrogen detection at room temperature, with the sensitivity strongly influenced by Sn content and oxygen vacancy concentration. Higher Sn concentration enhanced the sensing response, which was correlated with microstructural features obtained from AFM and EDX, as well as with the presence of Ce3+ and Ce4+ oxidation states identified by XPS. This study highlights the potential of CeOx/SnOx thin films for possible back-end-of-line integration and provides proof-of-principle for room-temperature hydrogen sensing.

The pressure to reduce greenhouse gas emissions is growing, which demands new and innovative technologies to produce mobile as well as stationary energy. The methanation offers a pathway to reduce greenhouse gas emissions by directly converting to . This also plays a crucial role in “power‐to‐gas” (P2G) technologies by providing an approach to store excess renewable energy in the form of methane in an existing natural gas infrastructure. However, methanation is a complex process due to its exothermic nature, interaction of the gas species with the catalyst, and possible catalyst degradation. Therefore, a deeper understanding is required for the methanation reaction, its different reaction pathways, and side reactions. In this work, we aim to understand the direct production of synthetic natural gas from and in a Sabatier process with the help of experiments over a Ni/ catalyst. A detailed surface reaction mechanism is developed to extend the study numerically by validating the simulation results with the experimental data. A one‐dimensional model, LOGEcat, based on a single‐channel catalyst model, is used for kinetic modeling. Experiments as well as simulations have been performed at various conditions, such as temperature variation and dilution to the inlet composition. We have successfully captured the experimental trends using the kinetic model developed for the conditions considered for the analysis.

Cerium oxide thin films were prepared by electron beam evaporation (EBE) under three deposition conditions: standard process, substrate heating at 200 °C, and ion beam assisted deposition (IBAD). The high optical transparency of the PVD-prepared coatings enables integration with transparent microelectronic devices, an aspect seldom explored in ceria-based gas sensors. Raman and optical analyses revealed various levels of oxygen vacancy-related defects in all films. Gas sensing measurements of the Pd/CeOx structures were correlated with their structural and electronic characteristics, including changes in Ce4+/Ce3+ ratios and band alignment during exposure to reducing gases, providing insight into the redox-driven sensing mechanism. All structures exhibit high ethanol sensitivity, while the highest response achieved for the films deposited with substrate heating and IBAD is consistent with their larger defect density and modified morphology. These findings demonstrate that tailoring EBE conditions provides an effective route to optimize CeOx thin films for improved gas sensing performance.

This study explores the role of atomic layer deposition (ALD) as an enabling technique for the defect engineering of catalytically active ultrathin deposits. In particular, we demonstrate the feasibility of tuning the O/Ce ratio in thermal ALD-based cerium oxide layers grown on silicon-based or alumina substrates by using the organometallic precursor tris(N, N’-diisopropyl-2-dimethylamido-guanidinato)cerium(III) ([Ce(dpdmg)3]) with H2O, O2, or O3 as coreactants. As revealed by in situ X-ray photoelectron spectroscopy (XPS), the Ce3+ concentration, i.e., the concentration of oxygen vacancies, depends strongly on three factors: the type of oxygen source, the chosen substrate, and the film thickness. The fixation of Ce3+ states during the early stages of growth is primarily determined by interface formation and the appearance of silicate and aluminate species, along with changes in morphology and surface-to-volume ratio. For thicker deposits (>5 nm), the intrinsic oxygen vacancies are coreactant-dependent. Furthermore, the chosen oxygen source also influences the morphology of ultrathin deposits, enabling potential surface functionalization with ceria nanoislands of varying composition and size. We point to a likely connection between this chemical and morphological tuning and changes in the ALD reaction pathway. The evolution of different nitrogen and carbon species depends on the oxygen source and the number of ALD cycles, indicating a shift in the ALD reaction mechanism from ligand exchange using H2O to ligand combustion for O3. The comprehensive investigation of these growth parameters is crucial for tailoring film properties via precise defect engineering.

Copper sulfide (CuS) is a multifunctional semiconductor with broad potential in catalysis, energy storage, and spintronics. In this work, Cr-doped CuS nanoparticles (Cu1-xCrxS, 0 ≤ x ≤ 0.4) were synthesized and investigated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and synchrotron-based X-ray absorption fine-structure spectroscopy (XAFS). SEM/EDX analyses reveal the nanostructured morphology of the samples and the homogeneous distribution of Cr within the Cu1-xCrxS matrix. XRD suggests the retention of the hexagonal covellite CuS phase across the entire doping series, while increasing Cr content, particularly beyond x ≈ 0.2, induces asymmetric peak broadening, selective intensity variations, and suppression of specific reflections, indicating increased lattice strain and solubility-limit-related structural perturbations. EPR reveals the presence of Cr3+ ions and magnetic defect states, accompanied by non-monotonic variations in linewidth and signal asymmetry at higher doping levels. XANES and EXAFS analyses support the substitution of Cu by Cr3+ within the covellite lattice, with the Cu–S first coordination shell remaining largely preserved, whereas higher-shell disorder progressively increases with Cr incorporation. Combined XRD, EPR, and XAFS results identify a composition range of x ≈ 0.05–0.1 associated with minimal structural perturbation, a transition regime at x = 0.1–0.2, and increasing local disorder at x ≥ 0.2. These findings correlate local Cr coordination with defect formation, lattice distortion, and local electronic-structure evolution. The results provide a spectroscopic and structural framework for understanding Cr-induced modifications in CuS-based materials.