Treatment In Oxygen Atmosphere Research Articles

Optimising PtFe nanoparticle structure to enhance catalytic activity and stability for propane oxidation

Although the development of highly active and stable platinum catalysts for the complete oxidation of hydrocarbons is crucial, there are still significant challenges that need to be addressed. Herein, the surface structure of PtFe nanoparticles (NPs) on PtFe/CeO2-x (x = CO, H, O) catalysts was precisely tuned via thermal treatment in CO, H2 and O2 atmospheres. The structure of the PtFe NPs on the PtFe/CeO2-O catalyst consisted of dispersed FeOx nanoclusters anchored on the PtFe NPs core. As a result, the PtFe/CeO2-O exhibited superior activity and water resistance for propane oxidation among all catalysts, which stems from the cooperation among robust metallic Pt sites, abundant active oxygen species, and FeOx nanoclusters as additional sites for oxygen supply. However, the reaction path of propane oxidation was similar among the PtFe/CeO2-x catalysts. This study offers encouraging insights for the deliberate development of robust and high-performing bimetallic catalysts to eradicate volatile organic compound pollutants. SynopsisThe CeO2‑supported core-shell-like PtFe-FeOx NPs catalyst synthesised via calcination treatment in oxygen atmosphere exhibits the excellent activity, good durability and water resistance for propane oxidation at low temperature.

Redox controllable switch of crystalline phase and physical property in SrVOx epitaxial films

Transition-metal oxides have attracted much attention due to its abundant crystalline phases and intriguing physical properties. However, some of these compounds are difficult to be fabricated directly in film form due to the ease of valence variation of transition-metal elements. In this work, we reveal the reversible structural transition between SrVO3 and Sr2V2O7 films via thermal treatment in oxygen atmosphere or in vacuum. Based on this, Sr2V2O7 epitaxial films are successfully synthesized and studied. Property characterizations show that the semitransparent and metallic SrVO3 could reversibly switch into transparent and insulating Sr2V2O7, implying potential applications in controllable electronic and optical devices.

XAFS Investigation of Nanoparticle Formation in 64Zn+ Ion Implanted and Thermo Oxidized Si

The single crystal CZ n-Si(100) substrates with electron concentration no = 5 × 1016 cm−3 were implanted by 64Zn+ ions with dose of 5 × 1016 cm−2 and energy of 50 keV. During implantation the ion beam current density was less than 0.5 μA/cm2 to avoid the substrate magnetically heating. After implantation, the plates were subjected to isochronous for one hour heat treatment in oxygen atmosphere at temperatures from 400 up to 1000oC with a step of 100oC. Zn K-edge EXAFS spectra were measured in fluorescent mode. Si(111) channel-cut monochromator was used for energy scanning; energy resolution ΔE/E = 2 × 10–4. According to Zn K-edge EXAFS data, all Zn implanted in Si at 900oC is fully oxidized: an absolute maximum of EXAFS Fourier transform at R ~ 1.6 A corresponds to Zn–O distance. Based on XANES data, we suggest an interaction between implanted Zn atoms and Si support.

Impact of Hf and Al Co-Incorporation into the Atomic-Layer-Deposited ZnO Active Channel for the Thin-Film Transistor Applications

ZnO-based oxide semiconductors have attracted much attention as active layer for thin film transistors (TFTs) due to their special features such as low-temperature process compatibility, high transparency, and wide bandgap (~3.37 eV). However, the instability and difficulty in controlling the electrical conductivity of ZnO still remain as critical issues. To solve these problems, various metal atoms have been introduced in ZnO, such as In, Ga, Sn, Al, and Hf. Among them, Hf and Al can be acted as stability enhancer by suppressing oxygen vacancies formation and as conductivity modulator by adjusting doping concentration, respectively. To effectively exploit their advantages, the composition control is one of the important parameters to be carefully adjusted. Furthermore, the active channel layer should have homogenous and smooth surface for forming good interface between Hf-Al-Zn-O (HAZO) active and Al2O3 gate insulator layers. From these viewpoints, atomic layer deposition (ALD) can be an optimum method to deposit the HAZO thin films because of such benefits as excellent conformality and good controllability for composition and film thickness. Thus, in this work, we fabricated top-gate transparent oxide TFTs using newly presented HAZO active channels deposited by ALD method and investigated the effects of Hf and Al concentration on the device performance including basic characteristics such as carrier mobility, subthreshold swing (SS), and turn-on voltage (Von), and reliability characteristics. The ALD temperature of HAZO was fixed at 100 oC. Tetrakis(ethylmethylamino)hafnium (TEMAHf), trimethylaluminium (TMA), diethylzinc (DEZ), and H2O were used as Hf, Al, Zn, and O2 sources, respectively. In this work, the composition control of Hf and Al was selected as main strategy to modulate device property. The atomic composition of 20-nm-thick HAZO thin films was controlled by adding TEMAHf and TMA cycles among a total 100 cycles. Total ALD cycles were designed so that the HfO2 and Al2O3 were located in the intervals of ZnO. For the HAZO thin film with 2-at%-Hf and 2-at%-Al, the position of two TEMAHf cycles were placed on 40th and 80th cycles, and two TMA cycles were placed on 20th and 60th cycles of total 100 cycles, separately. The incorporated amounts of Hf and Al were modulated into 2, 4, 6, 8, and 10 at% and 2 and 4 at%, respectively. The data figure shows the comparisons in transfer characteristics for the fabricated top-gate TFTs using HAZO active layers with various amounts of incorporated Hf when the incorporated Al amount was fixed at 2 at%. The fabricated devices show distinct differences in device characteristics depending on the incorporated Hf and Al compositions. When the Hf amounts were varied from 2 to 10 at%, the Von’s shifted to positive direction from negative side toward 0 V and SS values were improved from 1.12 to 0.37 V/dec. In contrast, the carrier mobility was slightly decreased from 2.97 to 1.24 cm2/Vs. The post-annealing effects were also investigated. The fabricated TFTs were thermally treated at the temperature range from 150 to 250 oC for 1 h in oxygen atmosphere. The Von shifted toward positive direction and SS were improved as the increase in annealing temperature, although the on-current and carrier mobility showed decreasing trend. In conclusion, we successfully confirmed that the new composition of oxide semiconductor, HAZO, can be utilized as an active layer for the oxide TFT, and that the electronic natures of the HAZO channel layers can be well controlled by adjusting the ALD conditions. The top-gate TFT using the HAZO channel with 10-at%-Hf and 2-at%-Al showed the best device characteristics such as low SS value of 370 mV/dec, low-voltage operation at around 0 V, and comparable carrier mobility of 1.24 cm2/Vs. It was also found that thermal treatment in oxygen atmosphere markedly influenced on the transfer characteristics including the location of Von. Here, we believe that the device performance can be far improved by simultaneously optimizing the Hf and Al incorporating amounts and the post annealing process condition. Optimum ALD conditions for preparing the HAZO channel layers will also be important for better device performance for the HAZO TFTs. Furthermore, we have plans to investigate the device reliability, which is one of the most important factor in evaluating device characteristics, such as positive bias temperature stress stability (PBTS), and negative bias illumination stability (NBIS). As results, highly-stable TFTs will be implemented with practical value of carrier mobility by employing HAZO channel with appropriate incorporating amounts of Hf and Al at optimum ALD conditions. Figure 1

Structure and dielectric relaxations of CaCu3Ti4O12 ceramics by heat treatments in different atmospheres

CaCu3Ti4O12 (CCTO) ceramics have drawn much attention for their potential application in energy storage components and overvoltage protection devices. In order to improve the electrical properties and understand the colossal dielectric behavior, several CCTO ceramic samples were prepared and heat treated in different atmospheres. The results showed that the breakdown field and nonlinear coefficient were effectively intensified, and the dielectric loss was reduced after heat treatments in the oxidizing atmosphere including air and oxygen. However, CCTO phases will decompose into TiO2, CuO and CaTiO3 phases when heat treated in the neutral atmosphere such as nitrogen, losing its colossal dielectric behaviors and excellent electrical properties. It was found that the oxygen atmosphere played the most beneficial effect in improving the characteristics of CCTO ceramics in this research. The maximum stored energy density of CCTO can be promoted from 7.7 to 26.5 kJ/m3, and the barrier height between grain boundaries were increased from 0.46 to 0.62 eV which may be closely related with its high breakdown filed. Three dielectric relaxations were observed in CCTO ceramics. After heat treatment in oxygen atmosphere, the activation energies of the two relaxation peaks (peak 1 and peak 2) in high frequencies kept nearly constant, at 0.11 and 0.51 eV respectively, while the activation energy of relaxation peak 3 at low frequency were enhanced from 0.75 to 0.85 eV, which may be related to the oxygen vacancy defects. Moreover, the contribution of dc conductivity to dielectric loss can be effectively restrained. An equivalent circuit model was proposed according to impedance analysis to expound the correlation between electrical properties and dielectric relaxations.

Ferromagnetism of Na0.5Bi0.5TiO3 (1 0 0) surface with O2 adsorption

Na0.5Bi0.5TiO3 (NBT) nanocrystalline powders prepared by sol-gel method with annealing at 900°C in air 1h present room-temperature ferromagnetism (FM). The subsequent annealing in vacuum at 900°C for 30min weakens the room-temperature FM, while subsequent treatments in oxygen atmosphere at room-temperature enhances the room-temperature FM, indicating that the room-temperature FM may be induced by the adsorbed oxygen on the NBT nanoparticle surface. The adsorption of O2 molecule on the NBT (1 0 0) surface is studied by using density functional theory within local density approximation plus on-site effect method. The physisorption of configuration R5 is the most stable, whereas the chemisorption of O2 is unfavorable at all adsorption sites. The physisorbed O2 molecule on the NBT (1 0 0) surface with a magnetic moment (MM) closes to that for an isolated O2 molecule. The magnetism of configuration R5 is mainly from the O p orbitals. The stable ferromagnetic coupling mechanism is the direct exchange interaction between the nearest-neighbor O2 molecules adsorbed on the surface. The adsorption of O2 molecule on ferroelectric materials may be a promising approach to achieve multiferroic materials.

In-situ monitoring by Raman spectroscopy of the thermal doping of graphene and MoS2 in O2-controlled atmosphere.

The effects of temperature and atmosphere (air and O2) on the doping of monolayers of graphene (Gr) on SiO2 and Si substrates, and on the doping of MoS2 multilayer flakes transferred on the same substrates have been investigated. The investigations were carried out by in situ micro-Raman spectroscopy during thermal treatments up to 430 °C, and by atomic force microscopy (AFM). The spectral positions of the G and 2D Raman bands of Gr undergo only minor changes during treatment, while their amplitude and full width at half maximum (FWHM) vary as a function of the temperature and the used atmosphere. The thermal treatments in oxygen atmosphere show, in addition to a thermal effect, an effect attributable to a p-type doping through oxygen. The thermal broadening of the line shape, found during thermal treatments by in situ Raman measurements, can be related to thermal phonon effects. The absence of a band shift results from the balance between a red shift due to thermal effects and a blue shift induced by doping. This shows the potential of in situ measurements to follow the doping kinetics. The treatment of MoS2 in O2 has evidenced a progressive erosion of the flakes without relevant spectral changes in their central zone during in situ measurements. The formation of MoO3 on the edges of the flakes is observed indicative of the oxygen-activated transformation.

Size Dependence of Oxygen-Annealing Effects on Superconductivity of Fe1+yTe1−xSx

For the Fe-based superconductor Fe{1+y}Te{1-x}S{x}, superconductivity is induced by annealing treatment in oxygen atmosphere, whereas as-grown samples do not show superconductivity. We have investigated the sample-size dependence of O2-annealing effects in Fe1.01Te0.91S0.09. The annealing conditions are fixed to be 1 atm, 200 C, and 2 hours. We have carried out magnetic susceptibility and specific heat measurements in order to evaluate the superconducting volume fraction. We have found that Fe{1+y}Te{1-x}S{x} has an optimal size for the induction of bulk superconductivity by O2 annealing. Our results indicate that O2 annealing is probably effective near the surface of samples over a length of a few tens of micro meters.

Thermal stability of perovskite phase in heavily Mn-doped SrTiO3 nanoparticles in oxidizing and reducing atmospheres

Complex investigations of the thermal stability as well as Mn-dopant distribution depending on chemical composition and processing condition have been performed in heavily doped SrTi1-xMnxO3 nanoparticles with x=0.2 and 0.4. Prepared nanopowders reveal stable enough cubic perovskite structure even after treatment in oxidizing atmosphere up to 1000°C. At the same time treatment in reducing atmosphere leads to decrease of the Mn solubility limit. Mn distribution evidences a weak tendency of Mn ions to migrate to surface. This migration increases in air and decreases at treatment in oxygen atmosphere.

Synthesis and optical study of heat-treated ZnO nanopowder for optoelectronic applications

UV emitting ZnO nanopowder was chemically synthesized and subsequently subjected to heat treatment in oxygen atmosphere for potential optoelectronic properties. Characterization including Raman spectroscopy, photoluminescence, SEM, FT-IR and XRD were performed to see the effect of high temperature heat treatment and subsequently oxygen defects on the physical properties of ZnO powder. Chemically prepared product was highly pure polycrystalline w-ZnO with random crystallites orientation. Study showed a magnificent absorption of oxygen by the product as manifested by the decreased intensity of deep-level green emission and E1 (LO) phonon mode. The phonon modes appeared at 276 and 970 cm−1 and which have been assigned to ZnO by the previous researchers under relaxed Raman selection rule were no longer found with heat treatment. UV emission was enhanced and the ratio of UV to green emission (I UV /I green) was correlated with the crystal structure and oxygen vacancies before and after heat treatment. FT-IR study established strong Zn-O bending and stretching bands at 356 and 498 cm−1. SEM analysis demonstrated fine crystallites distribution in ZnO nanopowder with almost spherical morphologies. Reasonably, a more spherical and ordered morphologies with large grains were found with heat treatment. The investigated findings manifested improved structural and optical properties for various optoelectronic and biomedical applications of technological importance.

Growth and high-temperature characterization of langasite-family Ca3NbGa3−xAlxSi2O14 single crystals

Langasite-family single crystals Ca3NbGa3−xAlxSi2O14 (CNGAS) (x = 0.1–0.8) were grown by a Czochralski technique along the x-axis. With increasing amount of Al substituent, the lattice constants decreased and the electric resistivity in a high temperature range was improved. The CNGAS (x = 0.8) specimen had an electric resistivity of 1010 Ω cm at 350 °C. From the dependence of the resistivity on temperature, an activation energy of about 1.19 eV was obtained. Thermal treatment in oxygen atmosphere was also considered effective for the improvement in electric resistivity. However, the dielectric features associated with loss tangent jump at about 400 °C were not improved by the Al substituent and thermal treatment. Spectroscopic ellipsometry was applied to determine the pseudodielectric function ε = ε1 + iε2 spectrum of the Ca3NbGa3Si2O14 crystal from 2 to 6 eV at 27 to 450 °C. No crystal structure change was observed from room temperature to 450 °C. The mechanism of the loss tangent change above 400 °C needs further investigation.

Oxygen‐Vacancy‐Related High Temperature Dielectric Relaxation in (Pb1−xBax)ZrO3 Ceramics

(Pb1−xBax)ZrO3 (x = 0, 0.025, 0.05, 0.075, 0.1) ceramics were synthesized by a traditional solid‐state reaction method, and the pure phase was obtained of all sintered samples. For all compositions, substitution of Pb2+ by Ba2+ reduced the phase transition temperature of antiferroelectric to ferroelectric and Curie temperature. Polarization–electric field hysteresis loops were conducted and typical ferroelectric hysteresis loops were observed in higher temperature range. Impedance and dielectric measurements were studied on the high temperature relaxation. Relaxation behavior could be suppressed after annealing treatment in oxygen atmosphere. Value of activation energy calculated from impedance was lower than that calculated from conduction measurements. It was concluded that short‐range hopping of oxygen vacancy contributes to the dielectric relaxation and long‐distance movement of doubly ionized oxygen vacancies contributes to the conduction.

Preparation and properties of solution-processed zinc tin oxide films from a new organic precursor

Transparent, smooth and dense zinc tin oxide (ZTO) thin films have been successfully produced by using a new precursor solution, zinc acetate and tin(II) 2-ethylhexanoate mixed with 2-ethanolamine in methoxyethanol. The ZTO films have been prepared by spin-coating, followed by thermal treatment in oxygen atmosphere. The morphology, composition, crystallinity and band gap energy (Eg) of the ZTO thin films have been characterized by Atomic Force Microscopy (AFM), Atomic Emission Spectrometry (AES), X-ray Diffraction (XRD) and UV-vis spectrophotometry. The conductivity of ZTO is about 9.8 × 10−9 S/cm, as estimated from the current-voltage (I-V) curve. The effect of the thermal treatment process on the morphology of ZTO thin films is also discussed.

Microstructure characterization and propane oxidation over supported Ru nanoparticles synthesized by the microwave-polyol method

Ruthenium nanoparticles deposited on γ-Al2O3 were prepared in one step by a microwave-polyol method and tested in the complete oxidation of propane. The oxidation reaction was carried out under oxygen rich-conditions over the as prepared colloidal 4.9wt.% Ru/γ-Al2O3 catalyst and heated in H2 at 500°C for 15h. The as prepared catalyst contained Ru nanoparticles with mean size of 1.6nm and narrow size distribution, while hydrogen treated metal particles with mean size of 6nm. Before examining catalytic properties, the Ru nanoparticles were subjected to heat treatment in oxygen atmosphere to study their microstructure evolution. HRTEM, SAED, XRD, BET, XPS, as well as hydrogen chemisorption and O2 uptake techniques were applied to characterize the supported Ru nanoparticles. It was established that catalyst with the 1.6nm Ru nanoparticles exhibited slightly higher specific activity than the catalyst with the 6nm Ru nanoparticles. The superior catalytic performance of the Ru nanoparticles could be correlated with a high metallic dispersion and low particle sizes. It was evidenced that the most active sites in the propane oxidation reaction, consist small RuxOy clusters without well-defined stoichiometry. Such surface species were formed at 100–200°C, and as a result the as prepared Ru/γ-Al2O3 catalyst reached 100% propane conversion below 200°C. Moreover, the Ru nanoparticles under oxidative atmosphere up to 250°C, both in oxygen and in reaction of propane oxidation, possesses good stability and the ruthenium phase was not agglomerated. In consequence, recycling of the supported Ru nanoparticles results only in an insignificant loss of the catalytic activity. The very good catalytic performances of supported Ru nanoparticles prepared under microwave-polyol conditions, preserved after consecutive runs, make them promising for practical application in the purification of environmental pollutions.

Oxygen-atmosphere heat treatment in spin-on doping process for improving the performance of crystalline silicon solar cells

Spin-on doping of phosphorus has been investigated and applied for the emitter fabrication of crystalline Si solar cells. Heat treatment in oxygen atmosphere at relatively low temperature of 550 °C prior to phosphorus diffusion is proved effective for improving solar cell performance, showing a conversion efficiency enhancement of more than 0.2% absolute. Internal quantum efficiency measurements show obvious enhancements at both short and long-wavelength regions. Secondary ion mass spectroscopy and Infrared absorption analysis reveal reduced C impurities after the heat treatment, possibly caused by burning the organic residues in the coated dopant source layer.

Influence of oxygen treatment on transport properties of PbTe:In polycrystalline films

In this work, the oxygen treatment of 1 μm thick n-type PbTe:In films was studied. Two main processes induced during the thermal treatment in oxygen atmosphere were identified. The inversion of the type of electrical conductivity in PbTe:In films from n- to p-type was observed after the thermal treatment in oxygen ( T a=400 °C). This effect is related to indium segregation at the film surface. The photoconductivity demonstrated in PbTe:In films after oxygen treatment is due to oxygen diffusion along the grain boundaries and the creation of potential relief, which separates electron–hole pairs at the boundaries under light illumination.

Influence of thermal annealing treatment in oxygen atmosphere on grain boundary chemistry and non‐ohmic properties of SnO2·MnO polycrystalline semiconductors

AbstractThe present work studied the influence of thermal treatment in oxygen rich atmosphere on heterogeneous junctions in Mn‐doped SnO2 polycrystalline system presenting varistor behavior. The samples were prepared by conventional oxide mixture methodology, and were submitted to heat treatment in oxygen rich atmosphere at 900 °C for 2 h. The samples were characterized by X‐ray diffraction, scanning electron microscopy, dc and ac electrical measurements. The results showed that there is an evident relationship between the microstructure heterogeneity and non‐ohmic electrical properties. It was found that for this SnO2·MnO‐based varistor system the heat treatment in oxygen rich atmosphere does not necessarily increase the varistors' properties, which was related to the decrease in the grain boundary resistance. The results are compared with Co‐doped SnO2 varistors and ZnO based varistors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of CdO films from chemically deposited Cd(OH) 2 films as a precursor

Formation of cadmium hydroxide at room temperature onto glass substrates from an aqueous alkaline cadmium nitrate solution using a simple soft chemical method and its conversion to cadmium oxide (CdO) by thermal annealing treatment has been studied in this paper. The as-deposited film was given thermal annealing treatment in oxygen atmosphere at 450 °C for 2 h for conversion into cadmium oxide. The structural, surface morphological and optical studies were performed for as-deposited and the annealed films. The structural analyses revealed that as-deposited films consists of mixture of Cd(OH) 2 and CdO, while annealed films exhibited crystalline CdO. From surface morphological studies, conversion of clusters to grains after annealing was observed. The band gap energy was changed from 3.21 to 2.58 eV after annealing treatment. The determination of elementals on surface composition of the core–shell nanoparticles of annealed films was carried out using X-ray photoelectron spectroscopy (XPS).

Structural and optical properties of Al-doped ZnO nanowires synthesized by hydrothermal method

The growth of one dimensional Al-doped ZnO nanowires on a silicon substrate with a ZnO seeding layer by using a low temperature hydrothermal method is demonstrated. The structural and optical characteristics of the solution-grown Al-doped ZnO nanowires were studied using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and cathodoluminescence (CL) measurements. The FE-SEM images show that the ZnO nanowires are hexagonal column shaped and stand perpendicularly on the silicon substrate. It is found in XRD patterns that the ZnO nanowires annealed at various temperatures are all wurtzite crystal structure and have (002) preferred orientation. As the annealing temperature changed, the intensity of (100) and (101) peaks reveals distinct change. The CL spectra show the as-grown ZnO nanowires display a weak and narrow UV emission centered at 376 nm. A strong and very broad green–yellow emission band with a center at 575 nm as well as a shoulder like orange–red emission band centering at 625 nm is also demonstrated. It is shown that the luminescence intensity centered at 376 nm increased, the shoulder like emission centered at 625 nm decreased but emission centered at 575 nm disappeared after thermal annealing treatment in oxygen atmosphere.

Particle size dependent adsorption and reaction kinetics on reduced and partially oxidized Pd nanoparticles

Combining scanning tunneling microscopy (STM), IR reflection absorption spectroscopy (IRAS) and molecular beam (MB) techniques, we have investigated particle size effects on a Pd/Fe(3)O(4) model catalyst. We focus on the particle size dependence of (i) CO adsorption, (ii) oxygen adsorption and (iii) Pd nanoparticle oxidation/reduction. The model system, which is based on Pd nanoparticles supported on an ordered Fe(3)O(4) film on Pt(111), is characterized in detail with respect to particle morphology, nucleation, growth and coalescence behavior of the Pd particles. Morphological changes upon stabilization by thermal treatment in oxygen atmosphere are also considered. The size of the Pd particles can be varied roughly between 1 and 100 nm. The growth and morphology of the Pd particles on the Fe(3)O(4)/Pt(111) film were characterized by STM and IRAS of adsorbed CO as a probe molecule. It was found that very small Pd particles on Fe(3)O(4) show a strongly modified adsorption behavior, characterized by atypically weak CO adsorption and a characteristic CO stretching frequency around 2130 cm(-1). This modification is attributed to a strong interaction with the support. Additionally, the kinetics of CO adsorption was studied by sticking coefficient experiments as a function of particle size. For small particles it is shown that the CO adsorption rate is significantly enhanced by the capture zone effect. The absolute size of the capture zone was quantified on the basis of the STM and sticking coefficient data. Finally, oxygen adsorption was studied by means of MB CO titration experiments. Pure chemisorption of oxygen is observed at 400 K, whereas at 500 K partial oxidation of the particles occurs. The oxidation behavior reveals strong kinetic hindrances to oxidation for larger particles, whereas facile oxidation and reduction are observed for smaller particles. For the latter, estimates point to the formation of oxide layers which, on average, are thicker than the surface oxides on corresponding single crystal surfaces.