Oxygen Gas Atmosphere Research Articles

Oxide-Scale and α-Casing Characterization in Ti6Al4V Alloy Oxidised in Oxygen Gas

Abstract Characterization of oxide scale and α-casing in Ti6Al4V titanium alloy oxidized at 1050, 1150, 1250 and 1340 K for 2, 4, 6, 8 and 12 h in a dynamic oxygen gas atmosphere has been analyzed. The oxide scale exhibited a spalling tendency. Its thickness systematically increased with the temperature and the duration of the oxidation. At a later stage the scale exhibited a catastrophic growth due to the increased porosity. The oxygen stabilized α-phase and its volume fraction as well as its hardness decreased with the distance in the metal matrix (α-casing). Estimated oxygen diffusion coefficients based on the hardness profiles across α-casing were 7.0 × 10−14, 8.5 × 10−14, and 1.2 × 10−13, 1.8 × 10−13 m2/s at 1050, 1150, 1250, and 1340 K, respectively. Similarly, the overall activation energy for diffusion of oxygen in the alloy was 105 kJ mol−1. EDS analysis across α-casing in the internal oxidation zone revealed sharp concentration wells for Ti and Al. Titanium concentration decreased and that of aluminum increased in these wells.

Post-growth annealing of zinc oxide thin films pulsed laser deposited under enhanced oxygen pressure on quartz and silicon substrates

Zinc oxide (ZnO) thin films have been prepared by pulsed laser deposition (PLD) technique at room temperature on quartz and single crystal silicon (1 0 0) substrates. The oxygen ambient gas pressure was attained at 6 Torr during the deposition. The deposited films were post-growth annealed in air at various annealing temperatures for 30 min. The X-ray diffraction (XRD), optical and electrical properties have been measured to study the properties of the films as a function of annealing temperatures. XRD has shown the strength of (0 0 2) peak increases and FWHM value decreases as the annealing temperatures increases from 200 to 600 °C. The post-growth annealed at 600 °C show dominant c-axis oriented hexagonal wurtize crystal structure and exhibit high average transmittance about 85% in the visible region and very sharp absorption edge at 376 nm with energy band gap of approximately 3.46 eV. Electrical measurement indicates the resistivity decreases with the annealing temperatures up to 600 °C, after which it increases with higher annealing temperatures at 800 °C. The complex of oxygen vacancy in the ZnO films may be the source of low conductivity in undoped ZnO films.

An investigation of the surface energy and optical transmittance of copper oxide thin films prepared by reactive magnetron sputtering

Copper oxide films have been sputter deposited on glass substrates by reactive radio frequency (rf) magnetron sputtering, using a solid copper target and an argon–oxygen gas atmosphere. The films were characterised by scanning electron microscopy/energy dispersive analysis of X-rays, X-ray photoelectron spectroscopy, atomic force microscopy, profilometry, spectrophotometry and surface energy measurements. The effect of input rf power and oxygen flow rate during deposition on the dispersive, polar and acid–base components of the surface energy of the copper oxide films was investigated. The components of the surface energy were determined by the Owens–Wendt and the Van Oss–Chaudhry–Good method. The Lifshitz–van der Waals dispersive interaction force was found to be the major contributor to the surface energy of the films and the origin of their hydrophobicity. Optical transmission in the prepared films was measured by spectrophotometry in the 400–850 nm wavelength region. We observed a maximum transmission of between 40% and 80% for copper oxide films prepared at a low rf power of 200 W, for the oxygen flow rates investigated. The optical bandgap values of the films ranged between 2.4 and 2.05 eV. The dependence of the optical properties of the films like optical transmittance and optical bandgap on deposition parameters like input rf power and physical properties like thickness and roughness was investigated in the wavelength range 400–850 nm. This information is expected to underlie the successful development of durable copper oxide films for technological applications requiring controlled optical transmission in the visible.

Fabrication of a lotus-like micro–nanoscale binary structured surface and wettabilitymodulation from superhydrophilic to superhydrophobic

We report a simple method for fabricating a lotus-like micro–nanoscale binarystructured surface of copper phosphate dihydrate. The copper phosphate dihydratenanosheets were generated by galvanic cell corrosion of a copper foil with aqueousphosphorus acid solution drops and dried in an oxygen gas atmosphere, and theyself-organized into a film with a lotus-like micro–nanoscale binary structuredsurface. The wettability of this surface can be changed from superhydrophilicto highly hydrophobic or superhydrophobic by heating or modifying it with ann-dodecanethiol monolayer.

Preliminary Investigation of the Supply of Chemical Species to an Aqueous Solution Using a Hydrogen−Oxygen Flame

A new method of supplying radical species to aqueous solutions using a hydrogen-oxygen flame is investigated. When a hydrogen-oxygen flame is directed on the surface of an aqueous solution, hydroxyl radicals (*OH) produced in the flame are extracted into the aqueous phase. The presence of *OH in the aqueous solution was confirmed by electron paramagnetic resonance with spin trapping using 5,5-dimethyl-1-pyrroline-N-oxide. The extraction of *OH into the aqueous solution was monitored using a quantitative analysis of hydrogen peroxide (H2O2). The effects of the hydrogen and oxygen gas flow rates, hydrogen/oxygen ratio, and atmosphere on H2O2 formation were studied. When the hydrogen-oxygen flame blew on a phosphate buffer solution (pH 6.7) under an Ar atmosphere, the concentration of H2O2 increased with the blowing time of the flame and the flow rate of hydrogen gas. Under air, nitrate and nitrite ions were formed in the aqueous phase in addition to H2O2, and the H2O2 concentration was lower than that under argon. The application of this new method to an aqueous solution of Cu(II)-ethylenediaminetetraacetic acid (EDTA) caused a remarkable decrease in the concentration of Cu(II)-EDTA and total organic carbon.

Effect of thermal treatment in oxygen, nitrogen, and air atmospheres on the electrical transport properties of zinc oxide thin films

The effects of thermal treatment in oxygen, air, and nitrogen gas atmospheres, at temperatures ranging from 573 to 1173 K, on the electrical transport properties of thin films of zinc oxide, prepared by sputtering deposition, have been investigated. These experiments have been carried out in preparation for future ion implantation doping studies in zinc oxide. As-prepared samples were slightly oxygen-deficient (Zn: 51%, O: 49%), due to a relatively low concentration of oxygen in the sputtering gas, and exhibited n-type conductivity (sheet resistance ∼3 × 10 2 Ω/square, sheet carrier concentration ∼8 × 10 14 cm − 2 , carrier concentration 4 × 10 19 cm − 3 , and mobility ∼30 cm 2/V s). Heat treatment in oxygen atmosphere led to a decrease in carrier concentration with increasing temperature. Upon annealing at 1173 K the carrier concentration was ∼1 × 10 17 cm − 3 and the mobility was ∼7 cm 2/V s, while heat treatment in nitrogen atmosphere, at the same temperature, resulted in almost no change in carrier concentration but with significant decrease in mobility to ∼1 cm 2/V s. Heat treatment in air led to values of carrier concentration and mobility, intermediate between those observed upon annealing in oxygen or nitrogen gases. These results suggest that the electrical transport properties of zinc oxide thin films are extremely dependent upon deposition conditions and post-deposition treatments and these effects should be carefully considered in any doping attempt by ion implantation.

Survival coefficient of Ga(5s 2S 1/2) sputtered from a GaAs surface

The effect of ambient oxygen gas on the survival probability for an excited Ga(5s) atoms to escape from a mono-crystalline GaAs (100) crystal without suffering tunneling de-excitation was investigated from measurements of photons emitted through the 5s 2S 1/2 → 4p 2P 3/2, 1/2 transition (417.20 nm, 403.3 nm lines) by Ar + bombardment using optical spectroscopic technique. A Doppler analysis of the emitted line profile under an oxygen-free condition gave A/ a = (5.2 ± 0.6) × 10 4 m/s. The transition rate for the resonant de-excitation of Ga(5s) was estimated as R ∼ 1.8 × 10 13 s −1 at atom-surface distance of 2 × 10 −10 m. The experimental result obtained was discussed in connection with the light-intensity dependence of the 417.2 nm spectral line on the distances from the target surface. The experimental result on the ambient oxygen gas effect was also discussed.

Production of gas phase zinc oxide nanoclusters by pulsed laser ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.

The influence of rf power and oxygen flow rate during deposition on the optical transmittance of copper oxide thin films prepared by reactive magnetron sputtering

Copper oxide films have been sputter deposited on glass substrates by reactive rf magnetron sputtering, using a solid copper target and an argon–oxygen gas atmosphere. The films were characterized by SEM/EDAX, XPS, AFM, profilometry and spectrophotometry. Optical transmission in the prepared films was measured by spectrophotometry in the 400–850 nm wavelength region. The optical transmission was found to increase from below 10% to above 80% as the rf power was reduced from 800 to 200 W at a wavelength of 550 nm. The optical bandgap value also increased from 2.05 to 2.4 eV with a reduction in rf power from 800 to 200 W. This bandgap change indicates the possibility of selectively depositing an optically transparent Cu2O-rich film, an absorbing black CuO-rich film or a mixture of both phases by varying the rf power during deposition. The oxygen flow rate during deposition had a less significant effect on the optical transmittance and bandgap of the films. This dependence of the stoichiometry of the copper oxide films on the deposition conditions is explained in terms of the sticking coefficient, nucleation rates and migration of impinging copper and oxygen species on the substrate. This information is expected to underlie the successful development of copper oxide films for technological applications requiring controlled optical transmission in the visible.

Photoinduced Characteristics of Metal-oxide Cosmetic Pigments by Agarose Gel Electrophoresis of DNA Plasmids in vitro under UV-illumination

Photoactive evaluation for cosmetic pigments in sunscreen agents, such as zinc oxide (ZnO), titanium dioxide (TiO2), aluminium oxide (Al2O3) and tungsten oxide (WO3), was carried out by examining DNA damage using agarose gel electrophoresis. Photoinduced DNA damage occurred in the presence of pigments under either aerated condition or oxygen gas atmosphere in the following order: WO3 ≈ Al2O3 ≈ rutile TiO2 < anatase TiO2 « TiO2 (P-25) « ZnO. The photoinduced oxidative activity of various pigments was assessed by the aromatic cleavage rate of phenol as a standard, which corresponds to the degree damaged to the supercoiled configuration of DNA (transformation to the linear form and/or relaxed form). L(+)-ascorbic acid (anti-oxidizing agent) can suppress the formation of photooxidative species such as ·OH radicals and/or ·OOH radicals. DNA damage under UV irradiation even in the presence of highly photocatalytic ZnO pigment was controlled by addition of the anti-oxidative enzyme catalase. DNA damage was depressed with increasing quantity of catalase.

Nitrided Pressureless Sintering에 의해 제조된 Si3N4의 산화거동

Oxidtion behavior of ceramics with the different porosity by the Nitrided Pressureless Sintering (NPS) were investigated in pure oxygen gas atmosphere at 1000 to . The thickness of formed oxide film on the surface of silicon nitride ceramics was increased with oxidation time and temperature. The oxide film thickness of 5A5Y5Si and 5A5Y10Si specimens for 100 h at was about 10 m and 20 m, respectively. The oxidation of 5A5Y5Si and 5A5Y10Si specimens follows the parabolic behavior with an apparent activation energy of 215 kJ/mol and 104 kJ/mol, respectively. The flexural strength of 5A5Y5Si specimens after oxidation test for 500 h at 1300^{circ}C were maintained as-received value of 500 ma. On the other hand, that of 5A5Y10Si specimens were decreased about 100 MPa in as-received value.

Production of ammonia by Tritrichomonas foetus and Trichomonas vaginalis.

Production of ammonia is difficult to find among the various studies of amino acid metabolism in protozoa. Several studies suggest that catabolism of arginine to ammonium is important for the growth of trichomonads. Trichomonads are amitochondriate zooflagellates that thrive under microaerophilic and anaerobic conditions. The authors were able to detect accumulation of ammonium ions and ammonia in cultures of Tritrichomonas foetus and Trichomonas vaginalis, including those resistant to metronidazole. Ammonium ions and ammonia were detected using the indophenol colorimetric method. Cells incubated overnight under an ambient oxygen gas phase had 0.9 mM soluble ammonium (NH(4)(+) and NH(3)) or a 20 % greater concentration of ammonium relative to sterile growth medium that had been incubated similarly. Production of ammonia itself was confirmed by analysis of a wick that was moistened with sulfuric acid (20 mM) and placed above the liquid in sealed cultures of a strain of Trichomonas vaginalis. The wicks from these cultures captured the equivalent of 0.048 mM volatile ammonia (NH(3)) from the liquid as compared to 0.021 mM volatile ammonia from sterile medium after overnight incubation. Intact trichomonads, 0.7 x 10(6) cells ml(-1) equivalent to 0.7 mg protein ml(-1), incubated in Doran's buffer with or without (1 mM) L-arginine produced significant amounts of soluble ammonium (0.07 mM and 0.04 mM, respectively) during 60 min. The results indicate that ammonium ions and the more irritating ammonia are significant metabolites of trichomonads. In addition, based upon end-product amounts, it appears that the rate of arginine metabolism is of the same order of magnitude as that for carbohydrate metabolism by trichomonads.

Optical and Microstructural Properties of TiO&lt;sub&gt;2&lt;/sub&gt;, Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and SiO&lt;sub&gt;2&lt;/sub&gt; Single Layers Deposited by Plasma Assisted E-Beam Evaporation

TiO2, Al2O3 and SiO2 single layer films were deposited in the oxygen gas atmosphere by plasma assisted e-beam evaporation(PAEBE) at various RF power and low temperature on p-type Si wafer(100) and glasses. The effects of plasma assistance on the optical and microstructual properties of three kinds of single layer films were investigated. In addition, those of the films were compared with the films deposited by conventional e-beam evaporation at high temperature(100~ 300 °C) condition. The n-values of TiO2 films gradually increased from 2.405 (λ =550nm) at 150W RF power to 2.54 at 200W. The XPS result indicated that TiO2 films deposited without plasma assistance have Ti2+, Ti3+ and Ti4+ charge states. Whereas the films prepared at 200W, 250W RF power have only Ti3+and Ti4+ charge states. Al2O3 layers had maximum reflective index (n=1.604 at λ =1200nm) at 200W RF power, but slightly decreased to 1.57 at 400W RF power. The measured transmittance spectra show that all the sample deposited by PAEBE are free from absorption and homogenous as well as the surface roughness, packing density and absorption of TiO2, Al2O3 films improved dramatically compared with films deposited conventional e-beam evaporation. However, The reflective index and surface morphologies of SiO2 films had no changed with increasing RF power.

Formation of ohmic contacts to p‐type ZnO

AbstractFormation of ohmic contacts to p‐type zinc oxide (ZnO) was studied. The p‐type ZnO samples were grown by metalorganic molecular‐beam epitaxy with diethylzinc, deionized water vapor and monomethylhidrazine and were annealed under oxygen gas ambient at 650 °C or 700 °C for 20 min to activate doped nitrogen acceptors. Although the current‐voltage characteristics measured through gold p‐contacts were not perfectly ohmic, they showed perfectly ohmic properties after rapid thermal annealing (RTA) in the temperature range of 300 to 520 °C for 2 min. The ohmic contact resistivity was measured with the transmission‐line measurement method and it was decreased to approximately 1/64 with increasing the RTA temperature. The minimum contact resistivity of 3.15 × 10−3 Ω cm2 was observed with RTA at 520 °C for 2 min. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A New Bell-Jar Type Controlled Atmosphere Polishing (CAP) Machine and Its Characteristics

Focusing on the atmospheres around the processing unit, a new CMP machine is developed with a prototype featuring a bell-jar shaped chamber that hermetically contains the entire processing unit. The machine is named “Bell-Jar Type Controlled Atmosphere Polisher” or “CAP” in short. Polishing characteristics of Cu films, silicon and silicon oxide are studied using the CAP under vacuum, or under the pressurized conditions by injecting various gases such as air, oxygen, nitrogen or argon (either individually or in combination) into the bell-jar. Under both vacuum and pressurized conditions, polishing rates of silicon and silicon oxide are 2.5 times higher than those under the conventional polishing that is processed under the atmospheric pressure. Polishing rates of Cu that is easily oxidizable increase under the oxygen gas ambient while it decrease when inert gases are injected. Polishing characteristics vary significantly depending on the types of gases injected into the bell-jar and their pressures as well as chemical properties of the works to be processed. The results confirm the polishing mechanisms that have remained suppositional until now.

Hydrogen Passivation of Er and Si Nanocrystallites in Er-doped SiO2- Increase in Photoluminescence-

ABSTRACTHydrogen passivation effect on the enhancement of photoluminescence (PL) of Er ions in SiO2films contained Si nanocrystallites (nc-Si) has been investigated. Er-doped SiO2films were fabricated by laser ablation of Er-deposited Si substrate in oxygen gas atmosphere. The PL intensity of Er ions and nc-Si were increased by hydrogen gas treatments, while ESR signal intensity of residual defects located at the interfaces between nc-Si and SiO2was decreased. These results indicate that hydrogen passivation of residual defects is useful for the enhancement of the Er PL.

Open atmosphere laser patterning of RBCO high-temperature superconductors

We show that it is possible to use CO2 laser radiation in an open atmosphere to dope high-temperature superconductors with oxygen. We show that, without using a vacuum chamber, high-temperature oxide superconductors can be doped to fabricate devices with electronics applications. The present experimental study shows that, for a given structure of high-temperature superconductor materials, irradiating the samples using an intense laser beam in an inert gas or an oxygen gas atmosphere can change the oxygen content. The reflection infrared spectra show that the laser irradiation of the samples has had suitable results on the samples. The x-ray diffraction spectra of the samples reveal that the intensities of some of the planes change dramatically.

UV-laser-light-produced defects and reversible blue–white photoluminescence change in silica

The photoluminescence (PL) color of silica glass changes from weak blue to intense white under irradiation with 325nm laser light at room temperature in vacuum. Irradiation at room temperature with the same laser light under oxygen gas atmosphere erases the white PL state. Through many successive experiments, it is found that the spectral change is a reversible phenomenon. Such intense white PL state is stored for a long time at room temperature in air under room light after removal of the laser light, in spite of any changes of atmosphere. The observed phenomenon may relate to the photo-induced defect formation at the silica glass surface. Such observed reversible phenomenon may well yield materials for erasable optical information storage, oxygen sensors and white-light emitting devices.

Reversible photoinduced spectral transition in Eu2O3–γAl2O3 composites at room temperature

The photoluminescence (PL) intensity of Eu2O3–γAl2O3 composite has been found to decrease at room temperature with 325nm laser light irradiation in vacuum, without any accompanying white luminescence. Then, under the same laser light irradiation in oxygen gas atmosphere, the PL intensity recovers. Through many successive experiments, it is found that the spectral change is nearly reversible. In spite of the changing atmosphere (for example, oxygen gas and air exposures), each PL state is stored for a long time at room temperature after the removal of the laser light under room light. This phenomenon is interpreted as results of photoinduced valence-number change of europium ions, the oxygen vacancy formation and some excitation energy transfer. Such a reversible phenomenon may well yield materials for erasable optical storage and oxygen sensor.

Thermal oxidation of (0001) 4H-SiC at high temperatures in ozone-admixed oxygen gas ambient

The method of oxidation by atomic oxygen has been developed for gate oxide formation in SiC metal–oxide–semiconductor (MOS) devices. Ozone (O3)–admixed oxygen (O2) gas is introduced into the cold-wall oxidation furnace, where atomic oxygen in a ground state is formed by thermal decomposition of O3 molecules at elevated sample temperatures. The growth rate of oxide in the O3-admixed gas shows a maximum at around 666.4 Pa and 950–1200 °C, whereas the rate in pure O2 gas is negligible below 6664.5 Pa. Interface trap density (Dit) of the MOS capacitors fabricated using atomic oxygen strongly depends on the oxidization temperature; oxidation at 1200 °C results in significant reduction of Dit in comparison with that at 950 °C.