Amount Of Oxygen Atoms Research Articles

On the relationship between atomic oxygen and vertical shifts between OH Meinel bands originating from different vibrational levels

OH Meinel emissions from different vibrational levels are known to occur at slightly different altitudes in the terrestrial airglow. Earlier model studies suggested quenching by atomic oxygen to be a principal cause of these vertical shifts. Here we employ the tropical mesopause region—characterized by pronounced semiannual variations—as a natural laboratory to test the hypothesis that vertical shifts between different OH Meinel bands are a consequence of quenching by atomic oxygen. Nighttime satellite measurements of OH(3–1) and OH(6–2) volume emission rate profiles and atomic oxygen with Scanning Imaging Absorption Spectrometer for Atmospheric Chartography on Envisat are used for this purpose. Upper mesospheric atomic oxygen profiles are retrieved from measurements of the O(1S–1D) green line emission. The results demonstrate that vertical shifts between the OH bands investigated are indeed correlated with the amount of atomic oxygen in the upper mesosphere, corroborating the hypothesis.

Structural and Magnetic Features of Oxygen Inserted [Co–O/Pt]<SUB><I>n</I></SUB> Multi-Layer Matrix for Spin Transfer Torque Memory Applications

We describe the influence of inserted oxygen atoms on the structural and magnetic properties of a [Co/Pt]n multi-layer matrix. The correlation of magnetic properties with oxygen gas flow rate was studied as an alternative perpendicular medium in spin transfer torque magnetic random access memory applications. Experimental analysis suggests that the addition of a small amount of oxygen atoms into the [Co/Pt]n multi-layer matrix leads to a high coercivity and proper magnetization performance, together with high thermal stability. Finally, the nature of the improved perpendicular medium behaviors is also discussed.

Growth, characterization and effect of substrate bias on ZnO prepared by reactive capillaritron ion beam sputtering deposition

ZnO thin films have been deposited on Si substrates by reactive ion beam sputtering deposition utilizing a capillaritron ion source. All the as-deposited ZnO films exhibit a preferred (0 0 2) growth direction while the grain size increases as oxygen partial flow rate increases. An optimum photoluminescence result was achieved using oxygen partial flow rate of ∼40% that the ratio of integrated deep level emission to that of integrated near-band-edge emission is less than 1.5. The atomic percentage ratio of Zn:O remains at 55/45, regardless of oxygen partial flow rates. With the applied substrate bias, the atomic percentage ratio of Zn/O changes to 40/60, indicating that stoichiometric ZnO may be achieved by selecting appropriate substrate bias. With the substrate bias applied, increased amount of oxygen atoms were found located in oxygen deficient matrixes, likely due to the bombardment of secondary ions.

Characteristics of the plasma discharge generated in dielectric capillary at atmospheric pressure

An atmospheric-pressure argon plasma discharge with a length of 63 cm is generated in a quartz capillary by using a pair of hollow needle electrodes. The discharge mode transition from abnormal glow to arc is investigated by means of electrical measurement and optical emission spectroscopy. The effects of the distance between two needle electrodes and the operating frequency of power supply on the voltage-current characteristics are discussed. The plasma electron density was estimated to be the order of 1014 cm-3 in the arc discharge. Moreover, the variation of gas temperature with the applied voltage is also studied, which is closely associated with the power dissipation. Furthermore, in measuring the oxygen atoms generated in argon/oxygen arc plasma discharge by optical actinometry, we found that the amount of oxygen atoms almost does not change with the rise of oxygen concentration.

Transient yielding of CO 2 over oxidized ruthenium surfaces: Monte Carlo simulations

We develop Monte Carlo simulations to study the catalytic oxidation of CO over a surface of ruthenium. The catalyst is exposed to a continuous flux of CO molecules and its surface is pre-covered with an amount of oxygen atoms. Recent experiments performed on this system [R. Blume, W. Christen, H. Niehus, J. Phys. Chem. B 110 (2006) 13912] have shown that three different reaction mechanisms can account for the experimental results. Two of them are based on the Langmuir–Hinshelwood mechanism, where CO molecules are adsorbed at oxygen-free defect sites before reactions take place. The third one proceeds via the Eley–Rideal mechanism, which is almost time independent, and reactions occur at non-defect sites. In our model, we consider a semi-infinite cubic lattice to mimic the surface of the catalyst and oxygen atoms are incorporated into the layers below the surface. A fraction of defects is created at the topmost layer and at the first subsurface layer. Oxygen atoms can diffuse over the surface as well as between adjacent layers of the system. We also assumed a temperature dependent reaction rate that is related to the residence time of CO at the surface. Comparisons are made between the CO 2 yielding at defect-rich and smooth surfaces as a function of temperature.

Contrasting characteristics of pulsed and sinusoidal cold atmospheric plasma jets

Pulsed excitation of cold atmospheric plasmas is commonly believed to offer valuable benefits compared to the mainstream sinusoidal excitation. However, direct comparison of pulsed and sinusoidal atmospheric plasmas remains few, if any, thus casting an uncertainty of whether pulsed excitation facilitates any significant advantage. In this letter, we report a comparison study of pulsed and sinusoidal cold atmospheric plasma jets through electrical characterization, gas temperature measurement, and optical detection of reactive plasma species. An example of pulsed excitation is shown to reduce the electrical energy consumption by a factor of 12 for producing the same amount of oxygen atoms.

Variation of Ozone Reflection Coefficient at a Metal Surface with its Gradual Oxidation

AbstractSummary: Investigation of ozone loss rate in a metallic chamber has been performed paying attention to the wall materials effect. Stainless steel, copper, and aluminum are used in the experiments. Ozone is produced by corona discharge electrode, which was mounted on the secondary electrode of a piezoelectric transformer. The decaying ozone density, which was observed after the corona discharge interruption, was measured using the HgI 254 nm photo absorption method. The temporal decrease of ozone density shows a single‐exponential and the loss rates of ozone, that is, the inverse of ozone lifetimes are determined. During the experiment with repetition using the same surface material, we found a gradual increase of the ozone reflection coefficient in the low‐pressure region. We adopted surface inspection of specimens using electron probe micro analysis (EPMA), Auger electron spectroscopy (Auger), and X‐ray photo‐electron spectroscopy (XPS). The results indicate that some amount of oxygen atoms is detected in the surface layer of the specimen. We consider that the increase of ozone reflection coefficient with the repeated measurement corresponds to gradual oxidation of the surface wall material.Variation of effective lifetime over repeated measurements using same material.magnified imageVariation of effective lifetime over repeated measurements using same material.

Sterilization of dental bacteria in a flowing N/sub 2/-O/sub 2/ postdischarge reactor

Destruction processes of several dental bacteria have been analyzed in a flowing postdischarge reactor. An N/sub 2/-5%O/sub 2/ gas mixture has been chosen to produce a high quantity of oxygen atoms and a UV emission intensity of NO/sub /spl beta// bands in the whole reactor chamber. The first results obtained with Streptococcus mutans (Sm), Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn), Prevotella intermedia (Pi), and Escherichia coli (E. Coli) dental bacteria at initial concentrations from 10/sup 6/-10/sup 10/ colony forming unit per milliliter (CFU/ml) introduced in small cylindrical Al substrates (previously sterilized) are reported. A full destruction of Sm, Pg, and Pi bacteria was obtained after 15-20 min and of Fn after 30 min of treatment. However, the E. coli bacteria, introduced to 10/sup 10/ CFU/ml was still not destroyed after a treatment time of 30 min.

Thin film interaction between low- k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer

The interaction between low- k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer has been studied using four-point-probe sheet resistance measurement, X-ray diffraction, conventional Rutherford backscattering spectrometry (RBS), nuclear resonance analysis (NRA), elastic recoil detection (ERD), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). The conventional intermetal dielectrics SiO 2 and plasma-enhanced tetraethylorthosilicate (PETEOS) have been studied also for the purpose of comparison with HSQ. In the low temperature regime (300–550°C), a considerable amount of oxygen atoms, from various sources, diffuses into Ti film to form a Ti(O) solid solution, raising the resistivity of Ti significantly and causing the expansion of the Ti lattice. A good correlation between the oxygen composition in the Ti film, the sheet resistance variation of Ti and the change of Ti lattice parameter C 0 have been observed. At the same temperature, there are more oxygen atoms incorporated into the Ti film in Ti/HSQ than those for Ti/PETEOS, suggesting that additional HSQ-related oxygen sources, such as the moisture uptake and the conversion reaction of HSQ, may be attributed to this. In the high temperature regime (550–700°C), HSQ reacts with Ti to form a final TiO/Ti 5Si 3/HSQ stack structure. It is assumed that a few competing reactions occur in this regime. At 550–650°C, HSQ reacts directly with Ti; in the meantime, part of HSQ undergoes conversion reactions, with the reaction products SiO 2 and SiH 4 reacting with Ti to form Ti silicide. At 650–700°C, HSQ is almost completely converted into SiO 2, so the dominant mechanism is Ti reaction with SiO 2. Before HSQ is completely turned into SiO 2, the Ti/HSQ system is more reactive than both Ti/PETEOS and Ti/SiO 2. The initiating temperature for the Ti/HSQ reaction exhibits no obvious Ti thickness dependence.

Mechanisms of ligand exchange reactions involving selenite sorption on goethite labeled with oxygen‐stable isotope

A labeled goethite was synthesized, using oxygen‐stable isotope 18O, in order to reveal ligand exchange reactions accompanying selenite sorption on the particles. The 18O isotope ratio of the surface hydroxyl groups on the labeled goethite was estimated to be 3.2% or 4.8% (depending on the assumed cases) by measuring the increase in the 18O isotope ratio of water molecules of the solutions through fluoride sorption on the goethite. The amount of oxygen atoms from surface hydroxyl groups on the labeled goethite released by selenite sorption was estimated, approximately, by the measurement of changes in the oxygen isotope ratio of water molecules in the reaction solutions. The δ18O value of the selenite sorptive solutions was apparently increased, suggesting that ligand exchange reactions occurred between selenite ions and the surface hydroxyl groups on the labeled goethite. The results suggested that the ligand exchange reactions of selenite sorption consisted of 6 to 40% of reaction in which oxygen atoms of the surface hydroxyl groups were released from the particles and of 60 to 94% of the alternative reaction in which oxygen atoms of selenite ions were released into the solutions, if the reaction sites for selenite sorption on the goethite are the samcas for fluoride sorption.

Role of ozone in reactive coevaporation of lead zirconate titanate thin films

The role of ozone in the reactive coevaporation of the lead zirconate titanate thin film was investigated by depositing films at various growth rates with various ozone fluxes or molecular oxygen fluxes on unheated substrates and then crystallizing them using rapid thermal annealing. The oxidation state of lead in the as-deposited film was determined from the ratio of the ozone to the total metal fluxes. The amount of atomic oxygen supplied to the surface of the film was at least 103 times larger when the deposition was done using ozone rather than molecular oxygen. When the ozone flux was more than one-third of the total metal flux, well-oxidized films were obtained. To ensure obtaining well-oxidized film, the ozone flax should be more than twice as much.

Interaction of oxygen with polycrystalline cobalt studied by inverse-photoemission spectroscopy.

We report a room-temperature UV inverse-photoemission study of the early oxidation stages of polycrystalline cobalt within the photon energy range 12-25 eV for exposures between 1 and 10 4 Langmuir (L) (1 L=10 -6 Torr s). The decomposition of each spectrum related to intermediate exposures in terms of bulk Co and oxidized Co, together with the analysis of the relative intensities for the different contributions, shows the stable formation of CoO at the interface for exposures ≥30 L, whereas for lower exposures the oxide stoichiometry depends on the amount of oxygen atoms. In the 5-7-L range, possible Co 3 O 4 formation takes place consistently with a decreased interdiffusion in this regime as compared to the higher exposures regime

Oxidation mechanism of amorphous silicon in air

The pure amorphous silicon (a-Si) films without cracks or pores were prepared by electron beam evaporation, and the oxidation of the resultant films has been studied by electron diffraction and infrared absorption spectroscopy in order to pursue the progress of oxidation. The oxidation proceeds in any depths throughout the film, indicating that the oxygen diffuses through the Si network. The oxidation is found to occur as a result of the breaking of a Si-Si bond by an oxygen, which is inserted between the two Si atoms, making a bridge between them. The amount of oxygen atoms incorporated in a-Si film increases in proportion to the logarithm of the time of exposure to air in a similar way as the oxidation of the c-Si surface. The occurrence of the oxidation is attributed to the presence of dangling bonds in a-Si films.

Rapid Thermal Annealed Undoped LPCVD Si/Single Crystal Si Substrate Structures with an Implant of Si Near Interfaces

ABSTRACTThe breaking up of a native oxide layer of a LPCVD amorphous Si/single crystal n+Si substrate interface by a rapid-thermal annealing was studied from the point of view of oxygen movement and morphological change. Oxygen atoms began to move at 1025 °C. After annealing at 1115 °C for 30sec, the quantity of oxygen atoms near the interface decreased dramatically and a silicon implant near the interface could enhance the decrease. More detailed observation was carried out by cross-section high-resolution transmission electron microscopy. After annealing at 940 °C for 30sec, the native oxide layer was continuous. On the qther hand, with a silicon implant near the interface, it changed into small oxide balls and an epitaxial growth occurred in the LPCVD layer with twins caused by these oxide balls. After annealing at 1115°C for 30sec, even without the silicon implant, a complete epitaxial growth occurred but it seemed that some SiOx particles dissolved into a single crystal Si layer near the interface.