Effect Of O2 Partial Pressure Research Articles

Nanocrystalline Ag–Cu–Al Alloy thin films with densely dispersed alumina particles prepared using reactive sputtering method with Ar–O2 mixed gas

As a first step to challenge the fabrication of highly O2-permeable Ag membranes, thin films of nanocrystalline Ag–Cu–Al alloys with densely dispersed Al2O3 particles were successfully prepared via reactive sputtering using Ar–O2 mixed gas. The effect of O2 partial pressure on the thin film structure during sputtering was investigated. A critical O2 partial pressure was required to obtain a nanocrystalline structure via simultaneous internal oxidation during sputtering. The critical condition was correlated with the flux ratio of O2 to Al impinging on the Ag film surface and the stoichiometric ratio of O to Al in Al2O3.

Effects of O2 Partial Pressure on Composition and Infrared Emissivity of PtO x Films Prepared by Reactive Magnetron Sputtering

PtO x films have been prepared by reactive magnetron sputtering on glass substrates without external heating and characterized by x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The resulting PtO x films mainly consisted of amorphous PtO and PtO2, and the composition largely depended on the O2 partial pressure during sputtering. In this study, the effects of the O2 partial pressure on the deposition rate, composition, surface morphology, structure, electrical resistivity, and infrared emissivity of the as-deposited PtO x films were evaluated. It was found that, with increase in the O2 partial pressure, the O/Pt atomic ratio, resistivity, and infrared emissivity of the as-deposited PtO x film increased, while the deposition rate first increased then decreased with increasing O2 partial pressure. In addition, the O2 partial pressure had little influence on the structure or surface morphology of the as-deposited PtO x film.

(Invited) Ethanol Photoreaction over Anatase TiO2(101) and Rutile TiO2(110) Single Crystals. A Combined STM and Online Mass Spectrometry

The reactions of ethanol have been investigated over anatase TiO2(101) and rutile TiO2 (110) single crystals by STM and on-line mass spectrometry to determine the adsorbate species in the dark and post UV illumination, in the presence and absence of O2 or Au nanoclusters, in order to extract initial reaction parameters under photo-excitation. On anatase (101) TiO2 single crystal the reaction rate for the photo-oxidation of ethanol to acetaldehyde is found to be strongly dependent on O2 partial pressures and surface coverage with an order of the reaction for O2 close to 0.15. Carbon-carbon bond dissociation leading to CH3 radicals in the gas phase was found to be a minor pathway, which is contrary to the case of TiO2 rutile (110) single crystal, as previously reported by our group and others. Our STM images distinguished two types of surface adsorbates upon ethanol exposure that can be attributed to its molecular and dissociative modes. Upon UV exposure at (and above) 3×10-8 mbar O2, a third species is identified as a reaction end-product, which can be tentatively attributed to acetate/formate species, in line with XPS C1s measurements. The room temperature photo-oxidation of ethanol has also been investigated over a rutile TiO2(110) single crystal by STM and on-line mass spectrometry, in the presence of O2 to determine adsorbate species remaining post UV exposure and emitted gas phase products. In addition to acetaldehyde, methyl radical was detected in the mass spectrometry resulting from the photo-fragmentation of an acetaldehyde-O complex. Formic acid species bound to Ti5c in a bi-dentate mode were identified by STM on the surface after the reaction. The effect of O2 partial pressure on the reaction selectivity demonstrated a dominance of the photo-fragmentation process with increasing pressure unlike the case of anatase TiO2(101) single crystal. In addition the effect of Au particles on the reaction of the TiO2(110 rutile has been investigated for hydrogen production under photo-irradiation in UHV conditions. It was found that particle size in the range 4 to 8 nm do not change the reaction rate yet particle density does. Detailed reaction mechanism for both reduction and oxidation reactions are addressed based on structural and kinetic information from the UHV systems and compared to those of their corresponding powder forms in liquid-solid photocatalytic reactions conditions.

Effect of vapor-phase oxygen on chemical vapor deposition growth of graphene

To obtain a large-area single-crystal graphene, chemical vapor deposition (CVD) growth on Cu is considered the most promising. Recently, the surface oxygen on Cu has been found to suppress the nucleation of graphene. However, the effect of oxygen in the vapor phase was not elucidated sufficiently. Here, we investigate the effect of O2 partial pressure (PO2) on the CVD growth of graphene using radiation-mode optical microscopy. The nucleation density of graphene decreases monotonically with PO2, while its growth rate reaches a maximum at a certain pressure. Our results indicate that PO2 is an important parameter to optimize in the CVD growth of graphene.

Effect of O2 partial pressure on optical and electrical properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films were synthesised on single crystal silicon and quartz glass substrates by pulsed laser deposition method at different O2 partial pressure. The structure, composition, optical and electrical properties in AZO thin films were investigated. With the increase in O2 partial pressure, the crystalline quality of AZO thin films becomes poor, and the Al content in the films decreases from 6·3 to 4·3%. The former leads to the enhancement of grain boundary scattering, consequently Hall mobility will decrease. While the latter results in the decrease of carrier concentration. As a result, the electrical resistivity in AZO thin films increases from 2·18×10−4 to 13·40×10−4 Ω cm with increasing the O2 partial pressure. The increase of carrier concentration induces the widening of optical band gap due to the Burstein-Moss effect with the increase of O2 partial pressure. For AZO thin films grown by PLD method, the control of O2 partial pressure is a simple method to adjust the electrical resistivity, optical band gap and UV emission in the films.

The effect of O2 partial pressure on the photoluminescence of ZnO thin films grown by pulsed laser deposition

In this paper, photoluminescence (PL) of ZnO thin films prepared on c-Al2O3 substrates by the pulsed laser deposition (PLD) method at different O2 partial pressures is investigated. For all samples, a narrow ultraviolet (UV) emission and a broad visible emission can be observed at room-temperature (RT). With increasing O2 partial pressures from 0.2 to 5Pa, the intensity ratio of the UV to visible emissions increases, and the energy positions of the UV emission band shift to the high energy side. It is noted that the visible part includes two emission bands of green luminescence (GL) and yellow luminescence (YL), in which the GL emission is strong at low oxygen pressure and the YL emission becomes dominant at high O2 partial pressures. The temperature-dependent PL spectra show that the UV emission is composed of two bands labeled FX and FA. The dependences and possible assignments of these PL bands are briefly discussed.

The use of mixed carbon materials with improved oxygen transport in a lithium-air battery

Two commercial carbon blacks, Ketjen black EC600JD (KB600) and Super P with quite different porosity parameters, are used for the cathode of a lithium-air battery. With high specific pore volume, KB600 shows a higher weight specific capacity. However, Super P exhibits a super high volume specific capacity, about 7 times higher than that of KB600, ascribed to its higher proportion of pores with suitable size for the deposition of solid products. The effects of O2 partial pressure and discharge rate on the specific capacity are investigated, combined with characterizations of contact angle and the structure of the electrodes. It is demonstrated that the Super P electrode possesses better O2 transport that improves the use of the whole electrode volume, and the special mechanism of O2 diffusion in the Super P electrode is proposed. By mixing KB600 with Super P with a weight ratio of 5:1, an electrode is obtained that exhibits increased O2 transport. The weight specific capacity is 1219 mAh g−1, about 1.2 times higher than that of KB600.

Effect of O2 gas partial pressure on mechanical properties of Al2O3 films deposited by inductively coupled plasma-assisted radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of Al2O3 films is studied. Using films prepared by inductively coupled plasma-assisted radio frequency magnetron sputtering, the deposition rate of Al2O3 decreases rapidly when oxygen is added to the argon sputtering gas. The internal stresses in the films are compressive, with magnitude decreasing steeply from 1.6 GPa for films sputtered in pure argon gas to 0.5 GPa for films sputtered in argon gas at an O2 partial pressure of 0.89 × 10−2 Pa. Stress increases gradually with increasing O2 partial pressure. Using a nanoindentation tester with a Berkovich indenter, film hardness was measured to be about 14 GPa for films sputtered in pure argon gas. Hardness decreases rapidly on the addition of O2 gas, but increases when the O2 partial pressure is increased. Adhesion, measured using a Vickers microhardness tester, increases with increasing O2 partial pressure. Electron probe microanalyzer measurements reveal that the argon content of films decreases with increasing O2 partial pressure, whereas the O to Al composition ratio increases from 1.15 for films sputtered in pure argon gas to 1.5 for films sputtered in argon gas at O2 partial pressures over 2.4 × 10−2 Pa. X-ray diffraction measurements reveal that films sputtered in pure argon gas have an amorphous crystal structure, whereas γ-Al2O3 is produced for films sputtered in argon gas with added O2 gas. Atomic force microscopy observations reveal that the surface topography of sputtered Al2O3 films changes from spherical to needlelike as O2 partial pressure is increased. Fracture cross sections of the films observed by scanning electron microscopy reveal that the film morphology exhibits no discernible features at all O2 partial pressures.

Structural and nanomechanical properties of a-plane ZnO thin films deposited under different oxygen partial pressures

The effects of O2 partial pressure during RF magnetron sputtering on the structural and nanomechanical properties of a-plane ZnO thin films were investigated by using X-ray diffraction (XRD) and nanoindentation techniques. The XRD and the transmission electron microscopy (TEM) selected area diffraction results indicate that the epitaxial relationship between ZnO thin films and Al2O3 substrates is ZnO (112¯0)//Al2O3(11¯02). The average values of the hardness and Young’s modulus of the a-plane ZnO films were found to decrease with increasing oxygen partial pressure. The cross-sectional TEM revealing the localized plastic deformation of ZnO thin films beneath the Berkovich indenter, indicating the prominent role played by the threading dislocations in the film deformation behavior. At higher indentation loadings, the sapphire substrate exhibits extensive deformation with narrow slip bands appearing on {0001} plane. However, no evidence of pressure-induced phase transformation, as well as cracking and/or delamination phenomena at the film–substrate interface was observed.

Effect of O<sub>2</sub> Partial Pressure on Magnetic Properties of Alloys CoFe-Rich Nanocrystalline Thin Films

Alloys of CoFe-rich magnetic films are well known as typical soft magnetic alloys. They are used for many kinds of electric and electronic parts such as magnetic recording heads, transformers and inductors. In order to get superior soft magnetic properties of the CoFe-based nanocrystalline thin films, the effect of O2 partial pressure on magnetic properties of Co-Fe-Hf-O nanocrystalline thin films have been investigated. It is found that the soft magnetic properties and electrical property of these films show a dependence on the partial pressure of reactive gases, which presumably changes the microstructure of the films and related magnetic anisotropy. With optimal conditions, thin film exhibit excellent soft magnetic properties: saturation magnetization (4πMs) of 21 kG, magnetic coercivity (Hc) of 0.18 Oe, anisotropy field (Hk) of 49 Oe, and an electrical property is also shown to be as high as 300 μcm. The combination of high 4πMs and relatively high Hk in these films are believed to be partly responsible for the excellent ultra-high-frequency behavior

Effects of O2 Partial Pressure and Ga Atmosphere on the Luminescence of Native Defects in β – Ga2O3 Phosphor

, a native defect luminescent material with blue emission, was fabricated by annealing powders under various partial pressures or in Ga metal atmosphere. Annealing under low partial pressure favors the photoluminescence (PL), which indicates that should be one of the luminescence centers in this phosphor. Annealing in Ga metal atmosphere reduced the PL intensity, which indirectly suggests that or defect cluster might be another luminescent center. Electron paramagnetic resonance (EPR) measurements verified the existence of single ionized oxygen vacancy . An EPR signal with and four hyperfine lines was observed, which is considered to be related to and the hyperfine interaction parameter is . Furthermore, the correlations between PL intensity and the densities of as well as were studied. At present, although we can not clarify whether exists as or , , and may act as donors, whereas or may act as accepters for the luminescence.

Effect of O2 partial pressure and thickness on the gasochromic properties of sputtered V2O5 films

V2O5 thin films were deposited by reactive DC-diode sputtering technique in a mixed atmosphere of O2/Ar gas at room temperature from a high purity target of 99.99% vanadium. For the investigation, the thickness of the films and the O2/Ar ratio during the sputtering process were the parameters. The sputtering rate of the V2O5 films dramatically decreases with increasing the O2/Ar ratio. By X-ray diffraction it was found that films sputtered with 1% O2/Ar ratio grow preferentially in two orientations: the 200 and the 001 orientation. The increase of the O2/Ar ratio enhances the growth preferentially in the c-axis (001) and strongly decreases the growth in the a-axis (200) direction. The scanning electron microscope pictures confirm these results. In the visible region the optical transmittance is increased with increasing the O2/Ar ratio in the sputter gas. Additionally, the optical band gap is slightly larger for the films sputtered with an O2/Ar ratio higher than 5%. Beyond a thickness of about 220 nm and an O2/Ar ratio of 10% the electrical sheet resistance of the films increases dramatically. During the insertion/extraction of hydrogen ions, the change in the optical transmission was investigated. The gasochromism of the V2O5 films was explained by use of the Infra Red (IR) measurements during the insertion/extraction of hydrogen ions.

Effect of O2 partial pressure on YBa2Cu3O7−δ thin film growth by pulsed laser deposition

Abstract YBa 2 Cu 3 O 7− δ thin films were processed by pulsed laser deposition on (1 0 0) LaAlO 3 substrates using O 2 partial pressures from 120 to 1200 mTorr. The effect of O 2 pressure on film properties including room temperature resistivities and microstructures was studied for a unique set of deposition parameters. The film quality was observed to remain high over a wide range of O 2 partial pressures, with much less sensitivity to O 2 pressure than previous studies which are compared. For O 2 pressures from 200 to 1200 mTorr, superconducting transition temperatures consistently reached values >91.5 K and transport critical current densities were 3–5 MA/cm 2 (77 K, self-field). It is proposed that less sensitivity of film properties to O 2 pressure is achieved by: (1) reducing the particle velocity of the plume below a critical threshold, and (2) using a deposition temperature of 785 °C for adequate surface activation.

Effect of O2 gas partial pressure on mechanical properties of SiO2 films deposited by radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of SiO2 films deposited by rf magnetron sputtering is studied. The sputtering rate of SiO2 in argon gas with added O2 gas is lower than that in pure argon gas, whereas the rate is independent of O2 partial pressure. The internal stresses in films are compressive, and the magnitude decreases from 0.8 GPa for films sputtered in pure argon gas to 0.4 GPa for films sputtered in argon gas with O2 gas partial pressure above 9×10−3 Pa. Although the internal stress decreases with increasing O2 partial pressure, the magnitudes of hardness and adhesion increase conversely. X-ray diffraction measurements indicate that the crystal structure of sputtered SiO2 films is amorphous at all O2 partial pressures investigated. The argon content in the film obtained from an electron probe microanalyzer decreases with increasing O2 partial pressure. An atomic force microscopy observation reveals that the surface topography of sputtered SiO2 films show a turnover from needle structure to a spherical structure, and the fracture section varies from columnar to no discernible features as O2 partial pressure is increased.

スパッタ法によるＮｉ‐Ｏ膜の結晶構造と磁気特性

Effects of O2 partial pressure at sputtering on the crystal structures and magnetic properties of Ni-O films werestudied. The film thicknesses were 150 nm for Ni and 500 nm for NiO. The following results were obtained. (1)Below 10% of O2 partial pressure [O2/(Ar+O2)], single-phase Ni films were obtained; above 10%, single-phase NiO films were obtained. (2)Lattice constants of both Ni and NiO were larger than those ofbulk Ni and NiO. (3)The saturation magnetization Ms is 90% that of the bulk. Anisotropy of magnetic susceptibility x was observed, andaverage value is the same as that of the bulk. (4)Coercive force(Hc)of the Ni film at O% is 1.1 kA/m at easy albs and O.9 kA/m at hard axis. (5)Electric resistivity ρ for Ni tends to increase with O2 partial pressure. The ρ of NiO which indicates semiconductor properties is only by four order larger than that of Ni, and is by four order smaller than thatof bulk NiO. It is thought that the NiO film composition is not stoichiometric, and the film is Ni-defect type (P-type) semiconductor.

Influence of O2 availability on NO and N2O release by nitrification and denitrification in soils

AbstractThe availability of O2 is believed to be one of the main factors regulating nitrification and denitrification and the release of NO and N2O. The availability of O2 in soil is controlled by the O2 partial pressure in the gas phase and by the moisture content in the soil. Therefore, we investigated the influence of O2 partial pressures and soil moisture contents on the NO and N2O release in a sandy and a loamy silt and differentiated between nitrification and denitrification by selective inhibition of nitrification with 10 Pa acetylene. At 60% whc (maximum water holding capacity) NO and N2O release by denitrification increased with decreasing O2 partial pressure and reached a maximum under anoxic conditions. Under anoxic conditions NO and N2O were only released by denitrification. NO and N2O release by nitrification also increased with decreasing O2 partial pressure, but reached a maximum at 0.1–0.5% O2 and then decreased again. Nitrification was the main source of NO and N2O at O2 partial pressures higher than 0.1–0.5% O2. At lower O2 partial pressures denitrification was the main source of NO and N2O. With decreasing O2 partial pressure N2O release increased more than NO release, indicating that the N2O release was more sensitive against O2 than the NO release. At ambient O2 partial pressure (20.5% O2) NO and N2O release by denitrification increased with increasing soil moisture content. The maximum NO and N2O release was observed at soil moisture contents of 65–80% whc and 100% whc, respectively. NO and N2O release by nitrification also increased with increasing soil moisture content with a maximum at 45–55% whc and 90% whc, respectively. Nitrification was the main source of NO and N2O at soil moisture contents lower than 90% whc and 80% whc, respectively. Higher soil moisture contents favoured NO and N2O release by denitrification. Soil texture had also an effect on the release of NO and N2O. The coarse‐textured sandy silt released more NO than N2O compared with the fine‐textured loamy silt. At high soil moisture contents (80–100% whc) the fine‐textured soil showed a higher N2O release by denitrification than the coarse‐textured soil. We assume that the fine‐textured soil became anoxic at a lower soil moisture content than the coarse‐textured soil. In conclusion, the effects of O2 partial pressure, soil moisture and soil texture were consistent with the theory that denitrification increasingly contributes to the release of NO and in particular N2O when conditions for soil microorganisms become increasingly anoxic.

Ｂｉ系２２２３相の各種雰囲気下での生成 酸素分圧の影響

The effects of O2-partial pressure on formation of the Bi-2223 phase. The samples were heated at 807°C-850°C under various O2 atmospheres after calination in air or Ar flow. Single phase products of the 2223 phase were obtained by heating in 20%O2 both in Ar and air. The Pb-substituted 2212 phase, (Ca, Sr)2Cu03 and CuO coexist in samples calcined i n Ar. The 2223 phase forms at a markedly lower temperature (807°C) in samples calcined in Ar than in those in air. In samples calcined in Ar, the 2223 phase forms without formation of (Ca, Sr)2PbO4. These results reveal that the formation process of the 2223 phase in samples calcined in Ar is different from that i n thoseinair.

Effect of O2 partial pressure on the myeloperoxidase pathway of neutrophils.

Neutrophils recruited to different tissues undergo respiratory burst activity at widely different PO2 levels. The present study investigated the in vitro effects of PO2 on neutrophil oxidative metabolism. When neutrophils were stimulated with either zymosan or phorbol myristate acetate (PMA) under different PO2's (0-700 Torr), hexose monophosphate shunt activity, H2O2, and hydroxyl radical (OH.) production were directly related to the level of PO2. Neutrophils functioned surprisingly well at PO2's as low as 10 Torr, where metabolic burst activity was prolonged and usually exceeded 50% of maximal values. The production of neutrophil stable oxidants and hypochlorous acid (HOCl) by zymosan-stimulated neutrophils was also directly related to PO2. In contrast, the production of stable oxidants and HOCl by PMA-stimulated neutrophils was significantly higher at 10 Torr compared with 700 Torr. The decrease in stable oxidant production by PMA-stimulated neutrophils at elevated PO2's was explained by both increased destruction of stable oxidant products and by decreased availability of the precursor HOCl. Superoxide dismutase and the OH. scavenger benzoate partially prevented the fall in stable oxidants at elevated PO2's. Measurements of stable oxidants in PMA-stimulated supernates generated at 10 and 700 Torr correlated with the ability of these supernates to decrease the elastase inhibitory capacity of the serum antiprotease alpha 1-antitrypsin. These findings suggest that different PO2's alter the magnitude and pattern of neutrophil oxidative metabolism.

Germination, Respiration, and Adenylate Energy Charge of Seeds at Various Oxygen Partial Pressures

The effect of O(2) partial pressure on the germination and the respiration of 12 cultivated species was studied. The reciprocal of the time necessary to observe rootlet emergence in 50% of the seeds was used to approach the germination rate. The maximum germination and respiration rates were reached in most seeds at O(2) pressures close to that of air. Decreasing the O(2) pressure produced a gradual decrease of the germination rate. The seeds could be classed in two groups according to their response to low O(2) pressures. Group I includes lettuce, sunflower, radish, turnip, cabbage, flax, and soybean: at O(2) pressures close to 2 kilopascals, the germination in this group was stopped and the adenylate energy charge was lower than 0.6. Group II includes rice, wheat, maize, sorghum, and pea. The germination rate of these seeds was also gradually decreased by lowering the O(2) partial pressure but germination still occured, very slowly, at 0.1 kilopascal; the adenylate energy charge remained higher than 0.6. These differences in the germination rates and adenylate energy charge values could not be explained by differences in the sensitivity of respiration to O(2).

Diffusion in polymers: Optical techniques

AbstractOptical techniques have been applied to study gas diffusion in poly(methyl methacrylate) and Lexan polycarbonate resin[poly(diphenyl‐2,2‐propane carbonate)] for temperatures ranging from 20°C. to the glass transition temperatures. One method consists of observing the movement of a sharp colored diffusion boundary which occurs when certain radical scavenging gases (e.g., O2, I2) penetrate a polymer which has been exposed to high energy irradiation. The theoretical basis and physical interpretation of the moving boundary are discussed. In essence, the color center concentration (produced by irradiation) is greater than the normal equilibrium concentration of scavenger molecules in the polymer so that the latter are trapped before they can move very far inward. The result is approximately a step‐function distribution of the remaining color centers. For O2 penetration into Lexan below Tg, D (cm.2/sec.) ⋍ 0.014 exp {7100 cal./mole/RT}. This relation accounts for the effect of O2 partial pressure on the penetration rate. For O2 penetration into PMMA, below Tg, an activation energy of 10 kcal./mole was observed. A spectrophotometric method was used to measure the uptake of J2 vapor in polycarbonate films. The data indicate a large change (∼50 kcal./mole) in apparent activation energy near 114°C. Several possible applications of the moving boundary technique are mentioned and the results of its use to investigate the effect of stress on the diffusion rate in the polycarbonate are presented. Tensile stresses near the yield point produce a two‐fold increase in D, whereas compressive stresses of comparable magnitude cause only a slight reduction.