CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO₂ sensing based on semiconducting CuO-Cu_xFe_3−xO₄ (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO₂ target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO₂=1.9) at 250 °C and 700 Hz for a CO₂ concentration of 5000 ppm.     

Reflection absorption infrared spectroscopy during atomic layer deposition of HfO2 films from tetrakis(ethylmethylamido)hafnium and water

Tetrakis(ethylmethylamido)hafnium and water are commonly used precursors for atomic layer deposition of HfO₂. Using reflection absorption infrared spectroscopy with a buried-metal-layer substrate, we probe surface species present during typical deposition conditions. We observe evidence for thermal decomposition of alkylamido ligands at 320 °C. Additionally, we find that complete saturation of the SiO₂ substrate occurs in the first cycle at ≈100 °C whereas incomplete coverage is apparent even after many cycles at higher temperatures. The use of this technique as an in situ diagnostic useful for process optimization is demonstrated.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

A combined experimental and theoretical analysis of Fe-implanted TiO2 modified by metal plasma ion implantation

Photocatalyst titanium dioxide (TiO₂) thin films were prepared using sol-gel process. To improve the photosensitivity of TiO₂ at visible light, transition metal of Fe was implanted into TiO₂ matrix at 20 keV using the metal plasma ion implantation process. The primary phase of the Fe-implanted TiO₂ films is anatase, but X-ray diffraction revealed a slight shift of diffraction peaks toward higher angles due to the substitutional doping of iron. The additional band gap energy levels were created due to the formation of the impurity levels (Fe-O) verified by X-ray photoelectron spectroscopy, which resulted in a shift of the absorption edge toward a longer wavelength in the absorption spectra. The optical band gap energy of TiO₂ films was reduced from 3.22 to 2.87 eV with an increase of Fe ion dosages from 0 to 1 × 10¹⁶ ions/cm². The band gap was determined by the Tauc plots. The photocatalysis efficiency of Fe-implanted TiO₂ was assessed using the degradation of methylene blue under ultraviolet and visible light irradiation. The calculated density of states for substitutional Fe-implanted TiO₂ was investigated using the first-principle calculations based on the density functional theory. A combined experimental and theoretical Fe-implanted TiO₂ film was formed, consistent with the experimentally observed photocatalysis efficiency of Fe-implanted TiO₂ in the visible region.     

Structural properties of the titanium dioxide thin films grown by atomic layer deposition at various numbers of reaction cycles

A dependence of structural properties of TiO₂ films grown on both Si- and Ti-substrates by atomic layer deposition (ALD) at the temperature range of 250-300 °C from titanium ethoxide and water on the number of reaction cycles N was investigated using Fourier-transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). TiO₂ films grown on both Si- and Ti-substrates revealed amorphous structure at low values of N < 400. However, an increase of N up to values 400-3600 resulted in the growth of polycrystalline TiO₂ with structure of anatase on both types of substrates and according to XRD-measurements the sizes of crystallites rose with the increase of N. The maximum anatase crystallite size for TiO₂ grown on Ti-substrate was found to be on ∼35% lower in comparing with that for TiO₂ grown on Si-substrate. A use of titanium methoxide as a Ti precursor with the ligand size smaller than in case of titanium ethoxide allowed to observe an influence of the ligand size on both the growth per cycle and structural properties of TiO₂. The average growth per cycle of TiO₂ deposited from titanium methoxide and water (0.052 ± 0.01 nm/cycle) was essentially higher than that for TiO₂ grown from titanium ethoxide and water (0.043 ± 0.01 nm/cycle). Ligands of smaller sizes were found to promote the higher crystallinity of TiO₂ in comparison with the case of using the titanium precursor with ligands of bigger sizes.     

Characterization on titanium surfaces and its effect on photocatalytic bactericidal activity

Many studies have been published on the use of TiO₂ as a photocatalyst, which decomposes various organic compounds under UV illumination by generating various radicals. The purpose of the present study was to evaluate the photocatalytic bactericidal effects of variously treated titanium surfaces on Escherichia coli K-12. The specimens were fabricated from grade 4 commercially pure titanium, 12 mm in diameter and 1 mm in thickness. Five different surfaces were prepared (MA: machined surface; AO: anodized at 300 V; NO: NaOH-treated; NW: NaOH- and water-treated; and HT: heat-treated). Surface analysis was performed using scanning electron microscopy, optical interferometer, and thin-film X-ray diffractometry. Photocatalytic activity of each group was confirmed by degradation of methylene blue (MB). The antibacterial activity was assessed by calculating the survival ratio in a drop of a culture of E. coli placed on the surface under UV illumination. Significant photocatalytic activity and bactericidal effects were observed on the titanium surfaces of AO and NW, regardless of the surface roughness (P < 0.01). The group with anatase was the most susceptible to the photocatalytic effect, while the surface without anatase showed the least susceptibility. Based on this in vitro study, the crystallography of the oxide layer on its titanium surfaces is an important factor affecting the photocatalytic bactericidal activity.     

咔咯锰(Ⅴ)氧配合物与苯乙烯的氧原子转移反应机理

采用密度泛函理论B3LYP方法研究了咔咯锰(Ⅴ)氧配合物(MnVO corrole)与苯乙烯氧原子转移(oxygen atom transfer,OAT)反应途径和吸电子取代基的影响.计算结果发现氧原子进攻苯乙烯中双键的β碳原子形成过渡态,结合内禀反应坐标法(intrinsic reaction coordinate ...     

Gas Forming Processes within Lignite Mining Dumps

Abstract

Gas analyses of the soil atmosphere of lignite mining dumps yielded increased contents of carbon dioxide. To get information about the potential sources and the carbon dioxide releasing capacity of the dumps, samples of dump material were investigated for their contents and isotopic compositions of organic and inorganic carbon as well as the carbon dioxide in the soil atmosphere. The contents of organic and inorganic carbon were found to vary depending on type of dump material. The isotopic composition of the organic carbon ranges between ?24.5 and ?26.5‰, which is typical for humous materials. The carbonates are found to be of marine origin (δ¹³C: +0.5 to ?1.1‰). By means of the isotope investigations it could be shown that the carbon dioxide in the lignite mining dump arises from these two different sources. Mixing ratios can be calculated using the isotope balance equation. Both reaction paths are associated with oxygen consumption and do not result in an increased gas pressure within the dump.     

Synthese und Qualitätskontrolle 15N-markierter Stickoxide mit hoher 15N-Häufigkeit für umweltrelevante Tracer-Untersuchungen

Für die Untersuchung ausgewählter Probleme des Verhaltens und der Wirkung der Stickoxide NO _x (NO + NO₂) in Ökosystemen, z.B. die Aufnahme und Freisetzung von NOx durch das System “Boden-Pflanze”, bietet sich der Einsatz ¹⁵N-markierter Stickoxide an. Die dazu benötigten ¹⁵N-markierten Gasgemische hoher Reinheit werden aus eigens dafür synthetisiertem [¹⁵N]Stickstoffmonoxid oder [¹⁵N]Stickstoffdioxid mit hoher ¹⁵N-Häufigkeit hergestellt. Beide Synthesen gehen jeweils von der kostengünstig kommerziell erhältlichen [¹⁵N]Salpetersäure aus.

Im Falle des [¹⁵N]Stickstoffdioxids erfolgt die Herstellung über die Präparation von Bleinitrat und dessen thermische Zersetzung. Die Ausbeute liegt bei 70–75% bezogen auf eingesetzte [¹⁵N]Salpetersäure.

Die Herstellung von [¹⁵N]Stickstoffmonoxid erfolgt durch Reduktion von [¹⁵N]Salpetersäure mit Eisen-II-sulfat in stark saurer Lösung. Die Ausbeute beträgt 60–70%, bezogen auf eingesetzte Salpetersäure.

The application of ¹⁵N is very useful for the investigation of the behavior and the effect of the nitrogen oxides NO _x (nitric oxide + nitrogen dioxide) in ecosystems, e.g. the uptake and release of NO _x by the soil-plant system. The ¹⁵N labelled gas mixture needed for that purpose has to be prepared from synthesized highly enriched [¹⁵N]nitric oxide and [¹⁵N]nitrogen dioxide. These two syntheses both use the commercially available and reasonable [¹⁵N]nitric acid.

In the case of [¹⁵N]nitrogen dioxide the synthesis is carried out via [¹⁵N]lead nitrate and its decomposition with increasing temperature. The yield is 70–75% related to the [¹⁵N]nitric acid input. The preparation of [¹⁵N]nitric oxide is done by reduction of [¹⁵N]nitric acid by means of FeSO₄ in strong acid solution. The yield amounts to 60–70%.