Removal Of Oxygen Atoms Research Articles

Discharge singlet oxygen generator for oxygen–iodine laser: I. Experiments with rf discharges at 13.56 and 81 MHz

The scaling on pressure for a discharge singlet oxygen generator based on the rf discharge excitation of O2 flow is studied in the context of the problem of oxygen–iodine laser pumping. With this aim, the evolution of O2(a 1 Δg) and molecules as well as O(3P) atoms in 13.56 and 81 MHz discharges at pressures up to 15 Torr has been investigated in detail. It is shown that fast quenching of O2(a1Δg) by atomic oxygen with increasing pressure and energy input causes rapid saturation of the O2(a1Δg) density in the discharge and limits the O2(a 1 Δg) yield on a rather low level of a few per cent. Covering of the discharge tube walls with mercury oxide for fast catalytic removal of oxygen atoms allows us to greatly increase the O2(a 1 Δg) yield as well as to avoid fast quenching of O2(a 1 Δg) in the early afterglow. It enables us to succeed in obtaining the rather high O2(a 1 Δg) yields at such high pressure as 10–15 Torr. So the singlet oxygen yield is ∼10–12% at ∼10 Torr. The transition to the higher frequency of 81 MHz even increases greatly the O2(a 1 Δg) yield up to ∼16%.

Chain Structures of Surface Hydroxyl Groups Formed via Line Oxygen Vacancies on TiO2(110) Surfaces Studied Using Noncontact Atomic Force Microscopy

Structures of surface hydroxyl groups arranged on a reduced TiO2(110) surface that had line oxygen vacancies were studied using noncontact atomic force microscopy (NC-AFM). NC-AFM results revealed that by increasing the density of oxygen vacancies on the TiO2(110) surface, line oxygen vacancies were formed by removal of oxygen atoms in a bridge oxygen row on the TiO2(110) surface. After the TiO2(110) surface with the line oxygen vacancies was exposed to water, the surface showed hydroxyl chain structures that were composed of hydroxyl groups linearly arranged in a form of two rows on the line oxygen vacancies and on a neighboring bridge oxygen row. In-situ NC-AFM measurements of these surfaces exposed to water at room temperature revealed that hydroxyl chain structures were formed at the line oxygen vacancy. Annealing above 500 K was sufficient to remove the hydroxyl chain structures on the TiO2(110) surface and allowed line oxygen vacancies to reappear on the surface. The line oxygen vacancies are active sites for water dissociation. In conclusion, the formation of the hydroxyl chain structure suggests that the surface hydroxyl groups on a TiO2(110) surface can be controlled by preparing oxygen vacancy structures on the surface.

Phase transformation of single crystal β-tungsten nanorods at elevated temperatures

We report the phase transformation of single crystal β-phase W(100) nanorods that occurs at an elevated temperature of ∼950 °C. The β-W nanorods oriented perpendicular to the flat silicon substrate were grown by an oblique angle sputter deposition technique with substrate rotation. The nanorods typically have an average length of ∼450 nm and an average width of ∼75 nm. The phase transformation was investigated by X-ray diffraction measurements of the nanorods vacuum-annealed at various temperatures in the range 700–1000 °C for 30 min at each annealing temperature. As deposited individual nanorods are found to be single crystal, as evidenced from the analysis of transmission electron microscopy diffraction patterns. Our single crystal β-phase W(100) nanorods phase transformation temperature is higher than that of the polycrystalline simple-cubic β-phase (A15) W films. Depending on the deposition conditions, W films generally transform to thermodynamically stable bcc α-phase at temperatures ranging from room-temperature to ∼650 °C. The transformation is accompanied with the removal of oxygen atoms from the β-matrix. However, our results of W rods suggest that the removal of oxygen atoms from the single crystal W nanorods is more difficult due to the absence of grain boundaries that leads to the requirement of higher annealing temperatures for the phase transformation.

Potassium-Selective Membrane Electrodes Based on Macrocyclic Metacyclophanes Analogous to Calixarenes

The tetrabutyl ester derived from 9,16,25,32-tetrahydroxy[3.1.3.1]metacyclophane was an excellent ionophore for constructing a K+-selective membrane electrode. This ionophore exhibited a much higher selectivity toward K+ than the structurally similar potassium ionophore IV commercially available from Fluka. In particular, the interference from organic ammonium ions decreased remarkably. Potassium ionophore IV possessed oxygen atoms in the ring structure, while the present ionophore changed the oxygen atoms to carbon atoms. Thus, the removal of oxygen atoms in ring constituents of the metacyclophane acted to reduce the interaction with the NH3+ group of organic ammonium ions. The size of the cavity of the present ionophore was between those of calix[4]arene and calix[6]arene derivatives, which act as Na+ and Cs+ ionophores, respectively, demonstrating that the ability to recognize alkali metal cations was strongly cavity size-dependent. The present K+-selective electrode had less interference from Rb+ and Cs+ than an electrode constructed using valinomycin, but suffered greater interference from Na+.

Potential barrier formation at a metal-semiconductor contact using selective removal of atoms

The possibility of forming a potential profile in a semiconductor by forming a metal film on its surface via selective removal of oxygen atoms from a deposited metal oxide layer was studied. Selective removal of atoms (SRA) was performed using a beam of accelerated protons with an energy of about 1 keV. Epitaxially grown GaAs films with a thickness of ∼100 nm and an electron concentration of 2×1017 cm−3 were chosen as the semiconductor material, and W obtained from WO3 was used as the metal. The potential profile appeared due to the formation of a Schottky barrier at the metal-semiconductor interface. It was found that the Schottky barrier formed at W/GaAs contacts made by the SRA method is noticeably higher (∼1 eV) than the barrier formed at the contacts made by conventional metal deposition (0.8 eV for W/GaAs). The data presented indicate that there is no damaged layer in the gate region of the structures, which is most strongly affected by the proton irradiation. Specifically, it was shown that the electron mobility in this region equals the mobility in bulk GaAs with the same doping level.

Removal of oxygen atoms from a SiO 2 surface by incoherent vacuum ultraviolet excimer irradiation

Summary form only given. Non-thermal photochemical removal of oxygen atoms from a SiO/sub 2/ layer on a silicon wafer using short wavelength emission has recently attracted much attention in the semiconductor industry and other related areas. It provides not only physics on the interaction between surface and high-energy photons, but also novel engineering aspects such as non-thermal nano-scale materials processing. In addition, the direct removal of oxygen atoms from a SiO/sub 2/ layer could open up the possibility of using a SiO/sub 2/ bulk as an insulator in the recent silicon-on-insulator (SOI) technology. The vacuum ultraviolet emission source was developed by use of a silent discharge, producing 9.8 eV photons with an intensity of 0.3 mWcm/sup -2/. Such high photon energy is larger than the energy gap of the SiO/sub 2/. The high-energy photon, therefore, directly excites the electronic transition in SiO/sub 2/. The emission intensity is so low that a temperature rise of the SiO/sub 2/ surface was estimated of the order of 10/sup -6/ K even during the irradiation. Surface morphology monitored by an atomic force microscope verified the non-thermal no damage processing.

Recovery Treatment of EuBa2Cu3O7-δ Thin Films with Activated Oxygen Plasma

Using high-quality c-axis-oriented EuBa2Cu3O7-δ (EBCO) thin films with transition temperatures (Tce) of about 90 K, a deterioration treatment by removal of oxygen atoms and a recovery treatment were performed in a sputtering chamber. The removal of oxygen atoms by heating in a mixture gas of Ar+7.5%O2 at 7 Pa resulted in an expansion of lattice constants (c0) of about 11.86 Å and semiconductive features. Two recovery methods using pure oxygen and activated oxygen plasma were examined. For the treatment with pure oxygen, signs of recovery in structural and transport properties appeared at annealing temperatures (Tsa) above 300°C at an oxygen pressure (PO2(a)) of 30 Pa, but the as-grown state was not obtained even at PO2(a)=2000 Pa. For the activated oxygen plasma treatment, where the deteriorated films were exposed to oxygen plasma and oxygen gas was subsequently introduced into the chamber, an almost complete recovery of superconducting and structural properties was achieved. The appropriate conditions for the recovery were Tsa's of 500–700°C, plasma exposure time (tp) above 30 min, and oxygen partial pressures (PO2(pc)) above 200 Pa. Atomic force microscope (AFM) images of EBCO films treated at Tsa's below 550°C showed the same spiral structure as those of as-grown films. The image-deformation and growth of outgrowths became obvious with increasing annealing temperature. The change in the surface morphology revealed the substantial movement of constituent atoms from Tsa's of about 600°C. Because the films exhibit optimum superconducting properties in spite of the rapid cooling, it is considered that the movement of constituent atoms induces trilayered perovskite structures with an excess oxygen atom deficiency at high temperatures.

Phases on the ?Perovskite Line? in the La-Sr-Cu-O System

Our recent research in the La-Sr-Cu-O system has revealed the existence of two new oxygendeficient compounds. One is (La1−xSrx)4Cu4O10 (x=0.135–0.15∶ 4-4-10 phase), which has the same structure as CaMnO2.5 and transforms to the well-known (La1−xSrx)8Cu8O20 (x=0.135–0.30∶ 8-8-20 phase) at higher temperature. The other is (La1−xSrx)5Cu5O13 (x=0.125–0.1666∶ 5-5-13 phase), which is synthesized under high oxygen pressure and is isostructural to La4BaCu5O13 (4-1-5 phase). We have also studied the strontium-rich compound (La1−xSrx)8Cu8O16+δ (x=0.7–0.8∶ 8-8-16+δ phase) and isolated the semiconductor-like 8-8-16 phase (δ≈0.0) and the metallic 8-8-18 phase (δ>2.0). Cations (La and Sr) in several of these compounds on the (La+Sr)∶Cu=1∶1 line, which we call the perovskite line, are distributed in a disordered manner and their crystal structures can be explained by the systematic removal of oxygen atoms from an ideal perovskite structure.

XeCl laser ablation of yttria stabilized zirconia

XeCl laser ablation of yttria stabilized zirconia (YSZ) in air and in vacuum (1.3×10−4 Pa) is studied by means of etch depth measurements, scanning electron microscopy, and X-ray photoelectron spectroscopy of ablated surfaces. Results on ablation rate, surface morphology, and surface chemical composition are discussed in terms of the influence of ambient atmosphere on the ablation process, rapid melting and solidification of ablated surfaces, and preferential removal of oxygen atoms from the YSZ surface.

Interface formation between d metals and the Bi 2Sr 2CaCu 2O 8 surface

X-ray photoelectron spectroscopy has been used to investigate the chemical stability of cleaved single-crystal Bi 2 Sr 2 CaCu 2 O 8 surfaces interacting with overlayers of various transition and noble metals ( Ti, Pd, Fe, Cu, Au). Except for gold which is inert, all the other metals are strongly reactive at submonolayer coverages. In general, a thin metal oxide layer (≈ 2 Å thick) forms immediately after deposition through the removal of oxygen atoms from the top Bi - O plane. Chemical shifts and lineshape modifications of core and valence levels result from the disruption of the outermost layers of the superconductor. The structures are subsequently buried as the metal film becomes thicker and surface segregation of metallic bismuth to the surface occurs. The growth mode of the interface is of the Volmer-Weber type with formation of clusters of increasing thickness and size.

The plasticity of titanium at low and medium temperatures

Abstract The slip systems and plastic properties of normal and transition hexagonal metals are briefly reviewed. In the case of titanium, there is strong evidence that the core of screw dislocations has a sessile three-dimensional configuration, so that the lattice friction on screw dislocations governs the low-temperature plasticity. The mechanical behaviour of Ti–Y alloys is explained by the removal of oxygen atoms from the titanium matrix below 400 K, by oxide dispersion strengthening and by dynamic strain ageing caused by the residual interstitial concentration at medium temperatures.

Superconductivity and Magnetic Properties of YBa2(Cu1-xFex)3O7-y

Superconductivity and magnetic properties of YBa 2 (Cu 1- x Fe x ) 3 O 7- y with x =0-0.1 are investigated by the measurements of static magnetic susceptibility, electrical resistance, weight change and lattice parameters. Substitution of Fe atoms for Cu atoms causes orthorhombic to tetragonal phase transition at about x =0.035 and depresses critical temperature T c from 95 K to 32 K at x =0.1. The effective magnetic moment per Fe, about 5.5 µ B below x =0.01 decreases to 3.6 µ B at x =0.1. The removal of oxygen atoms in the specimens of superconducting tetragonal phase with x =0.04 by quenching brings about remarkable expansion of c -axis and decreases T c from 74 K to below 4.2 K. The effective moment per Fe was found to decrease from 4.4 µ B to 3.3 µ B with increase of oxygen deficiency due to quenching. Causes of reduced iron effective moments due to increase of iron concentration and oxygen deficiency are discussed in consideration of superexchange interaction between Fe and Cu spins.

Transient oxidation and reduction of alumina-supported platinum

The oxidation state of alumina-supported Pt following treatment with O2 and the transient reaction between CO and preadsorbed oxygen are reported. Pt/Al2O3 (65%-dispersed) was exposed to O2 (1.23 kPa) at 523 K. The maximum oxygen uptake was obtained within 120 s. Following flushing with inert, a flow of CO (1.23 kPa) was switched over the sample. During the transient reaction, the production of gaseous CO2 was monitored with a mass spectrometer and the absorption of infrared radiation by adsorbed CO was recorded at a fixed wavenumber. The experiments were repeated to obtain the infrared data over a range of wavenumbers. From the complete set of infrared data, spectra were obtained which show how the population of five different CO adsorption states varied with time. The total amount of CO2 produced during the transient reaction corresponds to removal of two O atoms per Pt atom in the sample and, thus, indicates complete oxidation of the Pt. Two peaks in the CO2 production rate are observed: an initial sharp peak lasting for 2.5 s in which about 20% of the preadsorbed oxygen is removed followed by a broad peak lasting for about 120 s in which all of the remaining oxygen is removed. With 30%-dispersed Pt/Al2O3 the relative heights and shapes of the two peaks are slightly different but the same initial O atom to total Pt atom ration is indicated. The first CO2 peak is ascribed to removal of oxygen atoms in the surfaces of supported Pt oxide particles. The second CO2 peak is ascribed to removal of oxygen atoms bound within supported Pt oxide particles. Similar transient reduction behavior was also observed with Rh/Al2O3.

Transient oxidation and reduction of alumina-supported platinum

The oxidation state of alumina-supported Pt following treatment with O 2 and the transient reaction between CO and preadsorbed oxygen are reported. Pt/Al 2O 3 (65%-dispersed) was exposed to O 2 (1.23 kPa) at 523 K. The maximum oxygen uptake was obtained within 120 s. Following flushing with inert, a flow of CO (1.23 kPa) was switched over the sample. During the transient reaction, the production of gaseous CO 2 was monitored with a mass spectrometer and the absorption of infrared radiation by adsorbed CO was recorded at a fixed wavenumber. The experiments were repeated to obtain the infrared data over a range of wavenumbers. From the complete set of infrared data, spectra were obtained which show how the population of five different CO adsorption states varied with time. The total amount of CO 2 produced during the transient reaction corresponds to removal of two O atoms per Pt atom in the sample and, thus, indicates complete oxidation of the Pt. Two peaks in the CO 2 production rate are observed: an initial sharp peak lasting for 2.5 s in which about 20% of the preadsorbed oxygen is removed followed by a broad peak lasting for about 120 s in which all of the remaining oxygen is removed. With 30%-dispersed Pt/Al 2O 3 the relative heights and shapes of the two peaks are slightly different but the same initial O atom to total Pt atom ration is indicated. The first CO 2 peak is ascribed to removal of oxygen atoms in the surfaces of supported Pt oxide particles. The second CO 2 peak is ascribed to removal of oxygen atoms bound within supported Pt oxide particles. Similar transient reduction behavior was also observed with Rh/Al 2O 3.

Resonance absorption measurements of atom concentrations in reacting gas mixtures. VIII. Rate constants for O+H2→OH+H and O+D2→OD+D from measurements of O atoms in oxidation of H2 and D2 by N2O

Resonance absorption spectroscopy has been used to measure O atom concentration in shock treated H2–N2O–Ar and D2–N2O–Ar mixtures. Four compositions were studied over the temperature range 1919–2781 K for the H2-containing mixtures and 2097–2481 K for those containing D2. Only a few elementary reactions exerted any appreciable influence on the total oxidation process so that the rate coefficients of those reactions could be deduced. Primary sensitivity under all conditions was to the rate coefficients of the reactions directly responsible for the formation and removal of oxygen atoms. We find O+H2→OH+H, k = 2.3E14 exp(−57.5 kJ/RT) cm3 mol−1 s−1 and O+D2→OD+D, k = 1.6E14 exp(−59.6 kJ/RT) cm3 mol−1 s−1. Under our conditions the reaction of H or D atoms with N2O was insignificant, in contrast to the observations of Dean at higher concentrations. The isotope effect for this reaction is close to 1.6 throughout our temperature range.

The reaction of atomic oxygen O(3P) with propane

AbstractThe reaction of O(3P) atoms with propanehas been studied at temperatures near 300 K by using a discharge flow system. Oxygen atoms were generated in the absence of molecular oxygen by the reaction N + NO → N2 + O, nitrogen atoms having been generated in a microwave discharge. Rate constants for the reaction were measured in two ways, either by measurement of O‐atom decay in the presence of excess propane or by measuring the change in propane concentration after an appropriate time in the presence of an excess of oxygen atoms. The two methods were in good agreement, and the mean rate constant at 306 K is given by A study of the products of the reaction under conditions corresponding to complete removal of oxygen atoms has shown that an important product of the reaction in the early stages is propene. This is difficult to explain interms of a mechanism involving alkoxy radicals similar to that which has been proposed for some other O(3P)–hydrocarbon reactions. An alternative mechanism is proposed in terms of successive hydrogen abstraction reactions.

Chemical reactions in glow discharges. IV. Production and removal of oxygen atoms in the dc glow discharge

An experimental technique for the measurement of the rate of formation and removal of atomic oxygen in an active glow discharge is described. The concentration of atomic oxygen was monitored with a mass spectrometer by sampling the gases flowing through the discharge. The rate of removal of oxygen atoms was found to be first order in atomic oxygen and 10 to 100 times faster than the corresponding recombination rate in the afterglow region. The measured rates of atom production are in agreement with those calculated by assuming electron impact dissociation of ground state molecular oxygen. The atoms are removed by a wall recombination process.The ability of trace amounts of certain gases to enhance significantly the extent of dissociation in an electric discharge in oxygen has been studied. Only those added gases which contain a hydrogen or nitrogen atom are effective in enhancing the yield of atomic oxygen. For each hydrogen atom introduced into the oxygen stream about 300 extra oxygen atoms could be produced. This 'catalytic' effect is shown to be due to a marked decrease in the rate of recombination of O-atoms at the walls of the discharge tube. Whatever small change that occurs in the rate of O-atom production can be easily accounted for by a change in the energy distribution of the electrons in the discharge due to the effect of the additives.

Effect of Heterogeneous Removal of Oxygen Atoms on Measurement of Nitrogen Dioxide in Combustion Gas Sampling Probes

Abstract Abstract — The gas phase reactions of NO-NO2 and surface effects for oxygen atom recombination in a geometry typical of water-cooled stainless steel aerodynamic sampling probes are considered. The rate equations describing the system are summarized in a set of non-linear ordinary differential equations which are solved numerically. It is shown that the catalytic activity of the probe walls for atom recombination, the available surface to volume ratio, and the pressure are important parameters controlling the extent of NO2/NO reactions in the probe environment.

ESR study of Mo(V) in partially reduced Bi/Mo catalyst

By evacuation of Bi/Mo mixed oxide, removal of oxygen atoms from the surface leads to Mo(V) ions in tetragonal pyramidal structure with approximately C 4v symmetry. The nature of this active center and its bond coefficients are deduced from the ESR parameters.

Reductive radical formation of hetero aromatic N-oxides.

Pyridine 1-oxide gave the 4, 4'-dipyridyl anion radical in 1, 2-dimethoxyethane by reduction with the potassium metal in vacuo. The 3, 5-lutidine, pyrazine and 3-nitropyridine anion radicals were also obtained from the parent N-oxides by the reduction, accompanied with the removal of oxygen atoms, while the 4-nitro- and 4-nitroso-pyridine 1-oxide anion radicals were obtained from the parent compounds without the deoxygenation.