Solid-state spreading of oxides: Morphology and conductivity of In2O3-based films

Spontaneous solid-state spreading of In₂O₃ over the surface of ceramic and single crystal substrates of Al₂O₃, ZrO₂(0.08Y₂O₃), Y₃Al₅O₁₂ and YAlO₃ at 1380 and 1500 °C has been investigated. The films structure, element and phase composition were studied by means of XRD and SEM/EDS. The phase compositions of all films correspond to that of powder In₂O₃. The most films are dense with monolithic “film/substrate” interface. AC-conductivity in the range 25–250 °C is reported. Depending on the substrate material, the films demonstrate a whole set of conductivity types (semi-conductive, metallic) and wide range of magnitudes (more than 3 orders).Thermodynamic and kinetic aspects of oxide spreading and subsequent crystallization on the surface of primary border film are discussed. It is shown, in particular, that the solid-state spreading is facilitated in systems with high chemical affinity (mutual solubility, formation of intermediate interface compounds). In the case of eutectic-type systems, heteroepitaxy of diffusant at substrate surface results in formation of dense films.     

Ultrafast nonresonant response of TiO2 nanostructured films

We present a detailed study of the nonresonant third-order ultrafast response of TiO(2) nanostructured films, combining a classical heterodyned optical Kerr effect experiment, with two polarization selective Kerr techniques, based on transient lensing and phase modulation effects. The complementarity of these techniques is highlighted and demonstrated with calculations. Different aspects of the experimental results are addressed in detail and, finally, the possibilities of performing experiments on liquid dynamics in the pores of TiO(2) films, are discussed in the light of the present results.     

New benchmark for water photooxidation by nanostructured alpha-Fe2O3 films

Thin films of silicon-doped Fe2O3 were deposited by APCVD (atmospheric pressure chemical vapor deposition) from Fe(CO)5 and TEOS (tetraethoxysilane) on SnO2-coated glass at 415 degrees C. HRSEM reveals a highly developed dendritic nanostructure of 500 nm thickness having a feature size of only 10-20 nm at the surface. Real surface area determination by dye adsorption yields a roughness factor of 21. XRD shows the films to be pure hematite with strong preferential orientation of the [110] axis vertical to the substrate, induced by silicon doping. Under illumination in 1 M NaOH, water is oxidized at the Fe2O3 electrode with higher efficiency (IPCE = 42% at 370 nm and 2.2 mA/cm2 in AM 1.5 G sunlight of 1000 W/m2 at 1.23 VRHE) than at the best reported single crystalline Fe2O3 electrodes. This unprecedented efficiency is in part attributed to the dendritic nanostructure which minimizes the distance photogenerated holes have to diffuse to reach the Fe2O3/electrolyte interface while still allowing efficient light absorption. Part of the gain in efficiency is obtained by depositing a thin insulating SiO2 interfacial layer between the SnO2 substrate and the Fe2O3 film and a catalytic cobalt monolayer on the Fe2O3 surface. A mechanistic model for water photooxidation is presented, involving stepwise accumulation of four holes by two vicinal iron or cobalt surface sites.     

Sensor properties of the nanostructured In2O3-CeO2 system in detection of reducing gases

The sensor properties of nanostructured In₂O₃-CeO₂ composite films with different compositions in hydrogen and carbon monoxide detection in air in the temperature range 280–500°C were studied. The temperature curves of the sensor effect S have a shape typical for metal oxide sensors with maxima S _max at definite temperatures Tmax. The maxima characterize the sensor properties of the films and increased considerably when small amounts of CeO₂ were added to In₂O₃. The highest sensitivity was found in composite films with 3–10 wt % CeO₂. When the composite was further enriched with ceric oxide, the sensitivity decreased; at 40 wt % CeO₂ it was considerably lower than that of pure In₂O₃. The introduction of CeO₂ in In₂O₃ also caused a shift of Tmax toward lower temperatures. The mechanism of the sensitivity of the In₂O₃-CeO₂ composite was considered; it includes the promotion of sensor reactions by small CeO₂ nanoclusters lying on the surface of In₂O₃ crystals and an electron transfer from In₂O₃ to CeO₂.     

O(3P)+O2H→OH+O2反应机理的密度泛函理论研究

用密度泛函理论方法研究了O(3P)与O2H反应生成羟基和氧分子的反应机理. 在PW91/6-31+G水平上用梯度解析技术全自由度优化上述反应物、产物和反应路径上的中间体及过渡态几何构型, 并通过频率振动分析加以确认, 计算IRC反应路径及中间体异构化过程, 确定了此反应的可能反应通道. 结果表明: 该反应是多通道多步骤的强放热反应. 首先形成顺式或反式O3H富能中间体, 此过程无能垒; 然后跨过一个能垒分解成产物OH和O2. 通道IM1→TS1比IM2→TS2克服的能垒要大, 反应放热372.822 kJ*mol-1. IM1TS3IM2 可相互转化.     

Short-period superlattice structure of Sn-doped In(2)O(3)(ZnO)(4) and In(2)O(3)(ZnO)(5) nanowires

Two longitudinal superlattice structures of In(2)O(3)(ZnO)(4) and In(2)O(3)(ZnO)(5) nanowires were exclusively produced by a thermal evaporation method. The diameter is periodically modulated in the range of 50-90 nm. The nanowires consist of one In-O layer and five (or six) layered Zn-O slabs stacked alternately perpendicular to the long axis, with a modulation period of 1.65 (or 1.9) nm. These superlattice nanowires were doped with 6-8% Sn. The X-ray diffraction pattern reveals the structural defects of wurtzite ZnO crystals due to the In/Sn incorporation. The high-resolution X-ray photoelectron spectrum suggests that In and Sn withdraw the electrons from Zn and enhance the number of dangling-bond O 2p states, resulting in the reduction of the band gap. Photoluminescence and cathodoluminescence exhibit the peak shift of near band edge emission to the lower energy and the enhancement of green emission as the In/Sn content increases.     

缔合水分子对H_2O_2+NH_3→H_2O+ONH_3反应机理的影响

对反应H2O2+NH3→NH3O+H2O中H2O2上的O转移至NH3上所涉及的2种可能途径(即H2O2中H的迁移是否优先于O转移)及缔合水分子对反应的影响进行了量子化学计算.结果表明,两步式机理比一步式机理有利,而反应物缔合的水分子数及其排列方式对反应能垒的影响甚大.当缔合水分子数n=5时,反应活化能值达到最低,经溶剂化效应校正后反应活化能与实验值相当.溶剂化效应的大小与反应机理和反应物缔合的水分子数有关.     

Mixed alkali effect and optical properties of Ni2+ doped 20ZnO+xLi2O+(30-x)Na2O+50B2O3 glasses

Optical and physical properties of Ni2+ doped 20ZnO+xLi2O+(30-x)Na2O+50B2O3 (5≤x≤25) glasses are carried out at room temperature. Powder XRD pattern of all the glass samples confirms the amorphous nature. Several physical parameters are evaluated for all the glasses with respect to the composition. The optical absorption spectra confirm the site symmetry of the Ni2+ doped glasses are near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. It is interesting to observe that the optical band gap and Urbach energies exhibit the mixed alkali effect. The FT-IR spectral investigations of Ni2+ doped glasses exhibit characteristic vibrations of BO3 and BO4 units.     

CH2+O2反应的反应机理

CH2与 O2的反应是不饱和碳氢化合物燃烧过程中的一个十分重要的反应 .CH2（基态,三重态）与 O2反应的实验研究工作已有不少报导 [1－ 5],其主要产物有两 组 :H2O＋ CO和 CO2＋ H2,这些产物表明反应在反应体系的单重态位能面上发生 .至今还未见到关于 CH2＋ O2反应机理的完整的理论研究报导 .本文用 CASSCF方法详细研究了 CH2＋ O2反应的机理,给出从反应物至两组不同最终产物的完整的反应途经的描写 .1计算方法 　　计算使用量子化学高斯 98 W软件 .用从头算 CASSCF(8,8)/6-31G(d,p)方法在 CH2＋ O2单重态位能面上以优化…     

Ab Initio Study on the Mechanism of the Atmospheric Reaction OH+O3→HO2+O2

The atmospheric reaction (1) OH + O₃→HO₂ + O₂ was investigated theoretically by using MP2, QCISD, QCISD(T), and CCSD(T) methods with various basis sets. At the highest level of theory, namely, QCISD, the reaction is direct, with only one transition state between reactants and products. However, at the MP2 level, the reaction proceeds through a two‐step mechanism and shows two transition states, TS1 and TS2 , separated by an intermediate, Int . The different methodologies employed in this paper consistently predict the barrier height of reaction (1) to be within the range 2.16–5.11 kcal mol^?1, somewhat higher than the experimental value of 2.0 kcal mol^?1.     

Photoinduced hydrophilic and photocatalytic response of hydrothermally grown TiO2 nanostructured thin films

It is demonstrated that nanostructured titanium (IV) oxide (TiO₂) films can be deposited on glass substrates at 95 °C using hydrothermal growth, their properties being greatly affected by the substrate materials. Anatase TiO₂ films grown on ITO for deposition period of 50 h were observed to exhibit a very efficient, reversible light-induced transition to super-hydrophilicity, reaching a nearly zero contact angle. Enhanced photocatalytic activity (65%) was found for the rutile TiO₂ samples grown on microscope glass, possibly due to their higher roughness with respect to anatase grown on ITO. The effect of the substrate material used is discussed in terms of the TiO₂ phase and morphology control, for the best photoinduced hydrophilic and photocatalytic performance of the samples.     

Aerosol assisted chemical vapor deposition of In2O3 films from Me3In and donor functionalized alcohols

The reaction of Me3In and ROH (R = CH2CH2NMe2, CH(CH3)CH2NMe2, C(CH3)2CH2OMe, CH2CH2OMe) in toluene under aerosol assisted chemical vapor deposition (AACVD) conditions leads to the production of indium oxide thin films on glass. The indium oxide films were deposited at 550 degrees C and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction, wavelength dispersive analysis of X-rays (WDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. This CVD technique offers a rapid, convenient route to In2O3, which presumably involves the in situ formation of dimethylindium alkoxides, of the type [Me2InOR]2. In order to identify compounds present in the aerosol mist, the solution-phase reaction between Me3In and ROH (R = CH2CH2NMe2, C(CH3)2CH2OMe, CH(CH3)CH2NMe2, CH(CH2NMe2)2) at room temperature in toluene was carried out. Dimeric indium alkoxides, of the type [Me2In(OR)]2, were isolated, and their structures were determined by X-ray crystallography.     

An Ab Initio Study on the Mechanism of the Atmospheric Reaction NH2+O3→H2NO+O2

The atmospheric reaction NH₂+O₃→H₂NO+O₂ has been investigated theoretically by using MP2, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. At the MP2 level of theory, the hypersurface of the potential energy (HPES) shows a two step reaction mechanism. Therefore, the mechanism proceeds along two transition states (TS1 and TS2), separated by an intermediate designated as Int. However, when the single‐reference higher correlated QCISD and the multiconfigurational CASSCF methodologies have been employed, the minimum structure Int and TS2 are not found on the HPES, which thus confirms a direct reaction mechanism. Single‐reference high correlated and multiconfigurational methods consistently predict the barrier height of the reaction to be within the range of 3.9 to 6.6 kcal mol^?1, which is somewhat higher than the experimental value. ¹ The calculated reaction enthalpy is ?67.7 kcal mol^?1.     

Electrical conductivity of g-Bi2O3-V2O5 solid solution

The total conductivity (σ_T) in bcc γ-Bi₂O₃ doped with V₂O₅ system has been measured in the composition range between 1 and 7 mol% V₂O₅ at different temperatures. Phase transitions for different addition amounts depending on the temperature were investigated by quenching the samples. According to the XRD and DTA/TG results, this bcc type solid solution was stable up to about 720°C and the solubility limit was found at ˜7 mol% V₂O₅ in γ-phase. This system showed predominantly an oxide ionic conduction. As the V₂O₅ addition increased, the ionic conduction increased up to 5 mol% V₂O₅ at which the highest conductivity was found to be 8.318·10^-2 Ω^-1 cm^-1 at 700°C and then decreased. It has been proposed that γ-Bi₂O₃ phase contains a large number of oxide anion vacancies and incorporated vanadium cations at tetrahedral sites which affect the oxygen sublattice of the crystal structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of heterodimer nanocrystals: UO2/In2O3 and FePt/In2O3

This Article reports a mechanistic study on the formation of colloidal UO(2)/In(2)O(3) and FePt/In(2)O(3) heterodimer nanocrystals. These dimer nanocrystals were synthesized via the growth of In(2)O(3) as the epitaxial material onto the seed nanocrystals of UO(2) or FePt. The resulting dimer nanocrystals were characterized using X-ray powder diffraction (XRD), energy dispersion spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy, and high-resolution TEM (HRTEM). The results from XRD and HRTEM clearly show that lattice strains exist in both of these dimer nanocrystals. Interestingly, the lattice of In(2)O(3) expands in UO(2)/In(2)O(3) dimers, whereas FePt/In(2)O(3) dimers exhibit compressed In(2)O(3) lattices. Using HRTEM and nanocrystal structure simulations, we have identified the crystallographic orientation of the attachment of the two segments in these two types of dimers. An unconventional Miller index was introduced to describe the crystallographic orientation of these heterodimer nanocrystals. On the basis of the results herein as well as those from other researchers, we propose an empirical law for the determination of the crystallographic attachment orientation in heterodimers: instead of growth on the facet of the seed nanocrystals where lattice mismatch is minimized, the growth of an epitaxial material often chooses the crystal facets where the first atomic monolayer of this material has the strongest affinity for the seed nanocrystals.     

Cataluminescence sensor for gaseous acetic acid using a thin film of In2O3

We report on a cataluminescence sensor for the determination of gaseous acetic acid. It is based on a 60-nm thick sol–gel film of In₂O₃ on a ceramic support. SEM, XPS and surface profiling were applied for its characterization. It is found that aluminum ions of the ceramic substrate penetrate into the film and produce a synergetic catalytic effect. The sensor displays high sensitivity and specificity for acetic acid, a low detection limit, a wide linear range and a fast response. No (or only very low) interference was observed by formic acid, ammonia, acrolein, benzene, formaldehyde, ethanol, and acetaldehyde. The sensor was successfully applied to the determination of acetic acid in spiked air samples. We also discuss a conceivable mechanism (based on the reaction products) for the cataluminescence resulting from the oxidation reaction on the surface of the sensor film.

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

In2O3-based multicomponent metal oxide films and their prospects for thermoelectric applications

Thermoelectric properties of In₂O₃–SnO₂-based multi-component metal oxide films formed by spray pyrolysis method are studied. It is shown that the introduction of additional components such as gallium and zinc can control the parameters of the deposited layers. At that, the doping with gallium is more effective for optimization of the efficiency of the thermoelectric conversion. The explanation of the observed changes in the electro-physical and thermoelectric properties of the films at the composition change is given. It is found that the main changes in the properties of multicomponent metal oxide films take place at concentrations of dopants which correspond to their limit solubility in the dominant oxide.