•A simple gas sensor with nanostructured SnO2 sensitive layer was studied in-situ by NAP-XPS at conditions, which are close to working conditions of the gas sensor.•The chemisorbed oxygen on the tin ...oxide surface was not detected while exposing to oxygen atmosphere, however, the shift of XPS peaks caused by the band bending indirectly confirmed it.•Exposure of the surface to mixture of O2/EtOH resulted in disappearance of the band bending effect in the XPS spectra.•Different carbonaceous groups including ethoxy and acetate groups were observed on the sensor surface by NAP-XPS that supported the existing theory about the chemical interaction of ethanol with the chemisorbed oxygen.
In this article, we present the results of an investigation into chemical processes which take place at the surface of SnO2-based chemiresistor in various atmospheres (1 mbar of argon, 1 mbar of oxygen, 0.1 mbar of ethanol, 1 mbar of oxygen + 0.1 mbar of ethanol mixture) at common working temperatures (450 and 573 K). The key method for nanoscale analysis was the Near Ambient Pressure X-ray Photoelectron Spectroscopy. In parallel the resistance and DC-responses of SnO2 layer were in-situ monitored providing information about macroscale processes during gas sensing. The change in the sensor resistance after exposure to the ethanol-containing atmospheres together with the disappearance of the band bending effect and observation of different carbonaceous groups including ethoxy groups and acetaldehyde molecules on the sensor surface in the XPS spectra supported the theory of chemical interaction of ethanol with the chemisorbed oxygen. The NAP-XPS spectra also showed that the nanostructured tin oxide is partially reduced even after being exposed to pure oxygen at 573 K. Exposing this surface to the mixture of O2/EtOH did not significantly increase the surface reduction probably due to slow kinetics of the ethanol reduction process and fast kinetics of the oxygen re-oxidation process. However, it was demonstrated that the surface of sensor is slowly getting contaminated by carbon.
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Adjustable morphology and degree of reduction represent desirable properties of model oxide substrates for heterogeneous catalysis. We investigate these properties in CeO2 (ceria) thin films on ...Cu(111) using scanning tunneling microscopy and photoelectron spectroscopy. We identify growth mechanisms of ceria on Cu(111): formation of incomplete oxide interfacial layer and formation of three-dimensional ceria pyramids by stacking of monolayer-high islands. Using these mechanisms, we control the coverage, the number of open monolayers, and the step density of ceria thin films on Cu(111). Annealing in vacuum allows us to control besides the morphology also the degree of ceria surface reduction. We find a correlation between surface reduction and morphological stability in annealed ceria layers. Oriented and stoichiometric thin films of ceria on Cu(111) can be prepared at temperatures as low as 150 and 250 °C. Both the morphology and the surface reduction of these films readily change with increasing temperature, which must be accounted for in considering temperature-programmed experiments with ceria on Cu(111).
Interaction of water with fully oxidized and partially reduced CeO₂(111) thin film model catalyst grown on a Cu(111) surface was investigated by photoelectron spectroscopy (PES), scanning tunneling ...microscopy (STM) and temperature programmed desorption (TPD). On the stoichiometric surface water adsorbs molecularly at low temperatures (≤120K) while on the reduced surface the adsorption is partially dissociative with formation of OH groups. STM indicates no morphology variation and a very sensitive Ce 4d–4f resonant photoelectron spectroscopy (RPES) no noticeable change of the oxidation state of ceria upon water adsorption and subsequent complete desorption. Formation of co-adsorbed phase of residual water with OH during molecular water desorption, on the other hand, leads to a substantial resonance of the Ce³⁺ photoemission state around 170K. We propose that this behaviour indicating ceria reduction is in this case an electronic effect of the Ce 4f charge accumulation and Ce 5d charge depletion.
Ceramics with nominal chemical composition CaCu3Ti4O12 (CCTO), CaCu3Ti3.96Al0.04O11.96F0.04 (CCTOAF), and Ca0.98Mg0.08Cu2.94Ti3.96Al0.04O11.96F0.04 (CCTOMAF) were prepared by the solid-state ...reactions technique. Using SEM, EDX, XPS, EPR, NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε′ at 1 kHz is 5.6 × 104, 7.1 × 104, and 4.3 × 104, respectively. Additives of Al, Mg, F and milled particles (ZrO2, Al2O3, and SiO2) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples.
Nickel ferrite solid solutions remain one of the main materials for a whole range of applications, including microwave equipment and components, the requirements for parameters and homogeneity of ...materials are constantly increasing. In this work, Ni
1-x
Zn
x
Fe
2
O
4
nanoparticles with an average diameter of 12.5 nm were successfully synthesized by the microwave-assisted urea method. The temperature of a single-phase product formation was 400 °C, which is lower compared to more common precipitation from aqueous solution methods or solid-state route. Ni
1-x
Zn
x
Fe
2
O
4
materials demonstrate high saturation magnetization and low coercive force. The magnetization changes with increasing Zn concentration and reaches the maximum at x = 0.5. Also, the increase in zinc content leads to an increase in the lattice parameters. The average size of ferrite nanoparticles synthesized by the microwave-assisted urea method is smaller compared to ferrites synthesized earlier by the co-precipitation method. Also, lower treatment temperatures provide higher stoichiometry, and homogeneity of materials while magnetization difference is negligible. These research results provide a general and effective route to synthesize other nanostructures for a variety of microwave components.
Ceramic CaCu3Ti4O12 (ССТО), Ca0.98Cu3Ti4O11.96F0.04 (CΔCTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted ...grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO2-zSiO2-wСaF2 (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In CΔCTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum ε′1kHz = 6.9 × 104 demonstrates CΔCTOF and the minimum tan δ = 0.045 is characteristic of CCTOF.
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The work is devoted to obtaining of transparent nanocomposite materials as low loss, highly thermally conductive materials for potential laser applications. We report Ho3+:Y2O3–MgO nanocomposite ...ceramics with excellent mechanical and optical properties by combining glycine-nitrate process and spark plasma sintering. Morphology, structural-phase state, infrared transmittance and luminescence depending on the holmium concentration (0–12 at.%) were studied for the first time. It was found that optical transmittance reaches 75%@6000 nm for 3 at.% Ho3+:Y2O3–MgO ceramics. The absorption cross-section at 1931 nm and the emission cross-section at 2118 nm were determined to be σabs = 0.51 × 10−20 cm2 and σem = 0.29 × 10−20 cm2, respectively. Based on the testing results of luminescent characteristics it was demonstrated that Ho3+:Y2O3–MgO nanocomposite is a promising material for high-power eye-safe lasers operating in the 2 μm wavelength range.
YAG:Sm3+ (5 аt.%) optical ceramics were obtained by the solid-state reactive sintering in the 1700–1800°C temperature range. The effect of the sintering temperature on the microstructure, phase ...composition and optical properties of YAG:Sm3+ ceramics has been studied. It has been shown that the optimal sintering temperature in order to produce YAG:Sm3+ transparent ceramics is 1725°С. The sintered ceramics are characterized by high optical transmittance (>82% at 808 nm), low residual porosity and the average grain size of 21 μm. It has been shown that the sintering temperature has a little effect on the average grain size of synthesized ceramics. Microstructure of YAG:Sm3+ ceramics consolidated at 1800°C is characterized by the presence of large grains up to 90 μm surrounded by the main fraction with an average grain size of 19 μm, which could be evidence of starting bimodal grain size distribution.
•YAG:Sm3+ ceramics have been produced by the reactive sintering.•Optimal sintering temperature of YAG:Sm3+ transparent ceramics is 1725°С.•Large grains up to 90 μm appear in ceramics sintered at 1800°С.•The absorption coefficient α1064 is 2.25 cm−1 for YAG:Sm3+ ceramics.
The interaction of Pt with CeO2 layers was investigated by using photoelectron spectroscopy. The 30 nm thick Pt doped CeO2 layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) ...substrate, multiwall carbon nanotubes (CNTs) supported by a carbon diffusion layer of a polymer membrane fuel cell and on CNTs grown on the silicon wafer by the CVD technique. The synchrotron radiation X-ray photoelectron spectra showed the formation of cerium oxide with completely ionized Pt2+, 4+ species, and with the Pt2+/Pt4+ ratio strongly dependent on the substrate. The TEM and XRD study showed the Pt2+/Pt4+ ratio is dependent on the film structure.
For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon ...flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field emission scanning electron microscopy (FESEM), and current density–voltage (J–V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP‐XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J‐V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J‐V sweeps.
Solar cell deactivation: For similar exposures, the soaking of light proves more detrimental to the perovskite film than water vapor. Absorbed photons create Frenkel defects in the perovskite crystal. The number of created Frenkel defects depends strongly on the used illumination. The higher the photon flux, the higher the creation of Frenkel defects, and thus the stronger the degradation of power conversion efficiency and the stronger the hysteresis in the J–V characteristics.
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