Synthesis, Structural and Sensor Properties of Nanosized Mixed Oxides Based on In2O3 Particles

The paper considers the relationship between the structure and properties of nanostructured conductometric sensors based on binary mixtures of semiconductor oxides designed to detect reducing gases in the environment. The sensor effect in such systems is determined by the chemisorption of molecules on the surface of catalytically active particles and the transfer of chemisorbed products to electron-rich nanoparticles, where these products react with the analyzed gas. In this regard, the role is evaluated of the method of synthesizing the composites, the catalytic activity of metal oxides (CeO₂, SnO₂, ZnO), and the type of conductivity of metal oxides (Co₃O₄, ZrO₂) in the sensor process. The effect of oxygen vacancies present in the composites on the performance characteristics is also considered. Particular attention is paid to the influence of the synthesis procedure for preparing sensitive layers based on CeO₂-In₂O₃ on the structure of the resulting composites, as well as their conductive and sensor properties.

Cation-doping strategies for tuning of zirconia acid-base properties

The role of Y-, Ca- and Ce-doping of cubic zirconia (c-ZrO₂) (111) surface on its acidity, basicity and the interplay between surface acid-base pairs is investigated by computational methods. The most stable surface structures for this investigation were initially determined based on previous studies of Y-doped c-ZrO₂ (111) and by a detailed exploration of the most stable configuration for Ca-doped c-ZrO₂ (111) and Ce-doped c-ZrO₂ (111). Next, surface mapping by basic probe molecules (NH₃ and pyridine) revealed a general reduction of the acidity of the surface sites, although a few exceptions were observed for zirconium ions at next nearest neighbour (NNN) positions to the oxygen vacancy and at the nearest neighbour (NN) position to the dopants. Adsorption of CO₂ over basic sites revealed a cooperative interplay between acid-base groups. In this case, the overall effect observed was the decrease of the calculated adsorption energies when compared with the pristine surface. Moreover, spontaneous formation of η ³-CO₂ systems from initial η ²-CO₂ configurations indicates a decrease in the required energy for forming oxygen vacancies in the doped ZrO₂ systems at NNN positions or further away from the existing vacancy site.

A full monolayer of superoxide: oxygen activation on the unmodified Ca3Ru2O7(001) surface

Activating the O2 molecule is at the heart of a variety of technological applications, most prominently in energy conversion schemes including solid oxide fuel cells, electrolysis, and catalysis. Perovskite oxides, both traditionally-used and novel formulations, are the prime candidates in established and emerging energy devices. This work shows that the as-cleaved and unmodified CaO-terminated (001) surface of Ca3Ru2O7, a Ruddlesden-Popper perovskite, supports a full monolayer of superoxide ions, O2-, when exposed to molecular O2. The electrons for activating the molecule are transferred from the subsurface RuO2 layer. Theoretical calculations using both, density functional theory (DFT) and more accurate methods (RPA), predict the adsorption of O2- with Eads = 0.72 eV and provide a thorough analysis of the charge transfer. Non-contact atomic force microscopy (nc-AFM) and scanning tunnelling microscopy (STM) are used to resolve single molecules and confirm the predicted adsorption structures. Local contact potential difference (LCPD) and X-ray photoelectron spectroscopy (XPS) measurements on the full monolayer of O2- confirm the negative charge state of the molecules. The present study reports the rare case of an oxide surface without dopants, defects, or low-coordinated sites readily activating molecular O2.

Molecular and dissociative O2 adsorption on the Cu2O(111) surface

Dissociative O₂ is preferred on the reconstructed Cu₂O(111) surface thermodynamically at high coverage.

Thermal energy harvesting near-infrared radiation and accessing low temperatures with plasmonic sensors

Near-infrared (NIR) thermal energy harvesting has been demonstrated for gold nanorods (AuNRs), allowing concentration dependent, ppm-level, gas detection of H2, CO, and NO2 at 500 °C without using a white light source. Part-per-million detection capabilities of the gold nanorods are demonstrated with a factor of 11 reduction in collection times in the NIR as compared to measurements made in the visible light region. Decreased collection times are enabled by an increase in S : N ratio, which allowed a demonstration of selectivity through the use of both full spectral and a reduced spectral-based principal component analysis. Furthermore, low temperature thermal imaging spectra have been obtained at sample temperatures ranging from 275-500 °C, showing the possibility of energy harvested gas sensing at lower temperatures. These findings are promising in the area of miniaturizing plasmonic gas sensing technology and integration in areas such as gas turbines.

Oxidative methane activation over yttrium stabilised zirconia

The methane C-H bond is extremely stable, requiring significant energy input in reforming processes. We present a novel mechanism for energetically favourable methane C-H bond breaking over yttrium stabilised zirconia in the presence of oxygen, based on results of Density Functional Theory (DFT) and HSE06 hybrid functional calculations. We argue that this mechanism will be relevant to C-H activation over many metal oxide catalyst materials.

Revealing the properties of the cubic ZrO2 (111) surface by periodic DFT calculations: reducibility and stabilization through doping with aliovalent Y2O3

The reducibility of the clean cubic ZrO₂ (111) surface, as well as its stabilization through doping, have been investigated by hybrid DFT calculations within a periodic approach and localized basis sets.

Retardation mechanism of ultrathin Al2O3 interlayer on Y2O3 passivated gallium nitride surface

A systematic investigation was carried out by incorporating an ultrathin aluminum oxide (Al2O3) as an interlayer between yttrium oxide (Y2O3) passivation layer and GaN substrate. The sandwiched samples were then subjected to postdeposition annealing in oxygen ambient from 400 to 800 °C. The Al2O3 interlayer was discovered to play a significant role in slowing down inward diffusion of oxygen through the Y2O3 passivation layer as well as in impeding outward diffusion of Ga(3+) and N(3-) from the decomposed GaN surface. These beneficial effects have suppressed subsequent formation of interfacial layer. A mechanism in association with the function of Al2O3 as an interlayer was suggested and discussed. The mechanism was explicitly described on the basis of the obtained results from X-ray diffraction, X-ray photoelectron spectroscopy, energy-filtered transmission electron microscopy (TEM), high resolution TEM, and electron energy loss spectroscopy line scan. A correlation between the proposed mechanism and metal-oxide-semiconductor characteristics of Y2O3/Al2O3/GaN structure has been proposed.