Function Of Oxygen Fraction Research Articles

The transition of heterogeneous–homogeneous ignitions of dispersed coal particle streams

Abstract This work is assessing a study of the collective ignition behaviors of dispersed coal particle streams, with ambience temperature from 1200 K to 1800 K and oxygen mole fractions in the range of 10–30%. The dispersed coal particles of 65–74 μm are injected into an optical Hencken flat-flame burner by a novel de-agglomeration feeder. Three kinds of pulverized coals from different ranks, Hulunbel lignite, high-ash-fusion bituminous and low-ash-fusion bituminous, are considered. The normalized visible light signal intensity, deleting the background noise, is established to characterize the ignition delay of coal particle streams. Firstly, the prevalent transition from heterogeneous ignition to hetero–homogeneous ignition due to ambience temperature is observed. The pure homogeneous ignition rarely occurs, with an exception under high temperature and low oxygen for high-volatile coal. By comparing time scales between pyrolysis and heating processes, the competition of the volatile evolution and heterogeneous surface reaction are discussed. Then, the effects of ambience temperature, oxygen mole fraction and coal rank on the characteristic ignition delay are examined. Finally, the transient mode is developed, which not only well interprets the observed ignition transition phenomena, but also approximately predicts a variation of heterogeneous ignition time as a function of oxygen fraction.

Simultaneous Etching and Deposition Processes during the Etching of Silicon with a Cl2/O2/Ar Inductively Coupled Plasma

AbstractIn this article, surface processes occurring during the etching of Si with a Cl2/O2/Ar plasma are investigated by means of experiments and modeling. Cl2‐based plasmas are commonly used to etch silicon, while a small fraction of O2 is added to protect the sidewalls from lateral etching during the shallow trench isolation process. When the oxygen fraction exceeds a critical value, the wafer surface process changes from an etching regime to a deposition regime, drastically reducing the etch rate. This effect is commonly referred to as the etch stop phenomenon. To gain better understanding of this mechanism, the oxygen fraction is varied in the gas mixture and special attention is paid to the effects of oxygen and of the redeposition of non‐volatile etched species on the overall etch/deposition process. It is found that, when the O2 flow is increased, the etch process changes from successful etching to the formation of a rough surface, and eventually to the actual growth of an oxide layer which completely blocks the etching of the underlying Si. The size of this etch stop island was found to increase as a function of oxygen flow, while its thickness was dependent on the amount of Si etched. This suggests that the growth of the oxide layer mainly depends on the redeposition of non‐volatile etch products. The abrupt change in the etch rate as a function of oxygen fraction was not found back in the oxygen content of the plasma, suggesting the competitive nature between oxidation and chlorination at the wafer. Finally, the wafer and reactor wall compositions were investigated by modeling and it was found that the surface rapidly consisted mainly of SiO2 when the O2 flow was increased above about 15 sccm. magnified image

TiC xO y thin films for decorative applications: Tribocorrosion mechanisms and synergism

Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on various materials are gaining more attention by scientists and engineers due to its practical and economical significances in a wide range of applications. The main objective of the present work were to investigate the tribocorrosion behaviour of single layered titanium oxycarbide, TiC x O y , thin films on a reciprocating sliding tribometer, and in the presence of artificial sweat solution at room temperature, by considering the practical usage of such films as a decorative coating on various components. The films were produced by DC reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O 2 was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, electrochemical impedance spectroscopy (EIS) tests were performed before and after sliding process. The modifications on the “native” coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear–corrosion mechanisms occurring in each system. The corrosion studies, including EIS measurements, exhibited the high corrosion resistance of the TiC x O y films, which is clear from the unchanged/constant values of the polarization resistance, before and after the sliding process, at the evaluated potential. The effects of hardness, thickness and structure of the films on their tribocorrosion performance, as a function of oxygen fraction, were studied and an attempt was made to classify them. Two of the eight films ( f O=0.55 and 0.79), considered in the test, demonstrated better tribocorrosion resistance than others. Further, individual and synergistic effects of wear and corrosion on total wear loss were estimated and correlated with tribocorrosion mechanisms.

Properties of thin films deposited from HMDSO/O 2 induced remote plasma: Effect of oxygen fraction

Thin films deposited from Hexamethyledisiloxane (HMDSO)/O 2 mixture excited in a radio-frequency hollow cathode discharge system have been investigated for their structural, optical and corrosive properties as a function of oxygen fraction χ O 2 ( χ O 2 = 0 , 0.38 , 0.61 , 0.76 and 0.90 ). It is found that the effect of oxygen fraction on films properties is related to O 2 dissociation degree ( α d) behavior in pure oxygen plasma. α d has been investigated by actinometry optical emission spectroscopy (AOES) combined with double Langmuir probe measurements, a maximum of O 2 dissociation degree of 15% has been obtained for 50 sccm flow rate of O 2 ( χ O 2 = 0.61 in HMDSO/O 2 plasma). Fourier transform infrared spectroscopy (FTIR) and optical measurements showed that the behavior of both identified IR group densities and deposition rate as a function of oxygen fraction is similar to that of O 2 dissociation degree. The inorganic nature of the films depends significantly on oxygen fraction, the best inorganic structure of deposited films has been obtained for 62% HMDSO content in the mixture HMDSO/O 2 ( χ O 2 = 0.38 ). The refractive index for deposited films from pure HMDSO ( χ O 2 = 0 ) has been found to be higher than that of films deposited from HMDSO/O 2 mixture. In HMDSO/O 2 plasma, it has a behavior similar to that of deposition rate, and it is comparable to that of quartz. The effect of oxygen fraction on the corrosive properties of thin films deposited on steel has been investigated. It is found that the measured corrosion current density in 0.1 M KCl solution decreases with the addition of O 2 to HMDSO plasma, and it is minimum for χ O 2 = 0.38 .

Growth characteristics and residual stress of RF magnetron sputtered ZnO:Al films

Transparent and conductive ZnO:Al films were deposited by RF reactive magnetron sputtering on glass substrates. The growth characteristics of the films as function of oxygen fraction and RF power were investigated by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy; while the induced residual stress in the films was calculated by the Stoney's equation. It is shown that the deposits were flat and dense with a columnar structure in the cross-section morphology. A ZnO (0002) preferred orientation was obtained when the oxygen fraction used in the deposition process was larger than 12%. The growth rate reveals a maximum value depending on the oxygen fraction and RF power. All the deposits show a compressive stress which increased as the RF power was increased when the oxygen fraction in the deposition process was 8∼10%, while it decreased as the oxygen fraction was 12∼15%.

Comparison of deuterium and hydrogen dissociation with a surface-wave discharge dissociator and a SiO 2 sputtered nozzle

The deuterium dissociation degree has been measured using a new type of dissociator based on a Surface-Wave Discharge (SWD) at 2.45 GHz, equipped with a SiO 2 sputtered conical-shaped aluminum nozzle. Deuterium dissociation measurements are reported as function of oxygen fraction, microwave power and gas throughput, and compared with hydrogen dissociation values obtained with the same dissociator.

The effect of hydrogen content on silicon coordination in silicon oxynitrides: An Auger parameter study

AbstractSilicon oxynitride films prepared by plasma‐enhanced chemical vapour deposition (PECVD), with compositions in the range O/N = 0 to O/N = 0.89, and containing amounts of hydrogen in the range H(H + O + N) = 0.07–0.31, have been studied by measurement of the Auger parameter α = EK(Si KLL) – EK(Si 2s). A pure thermal oxide was also included. Depth profiles using 4 keV argon ions showed that the films were uniform in both composition and silicon coordination. Peak widths of the 2p, 2s and KLL features were measured as a function of oxygen fraction O/(H + O + N); in contrast to the films prepared by low‐pressure chemical vapour deposition (LPCVD) studied by Rivière et al., the widths of the 2p and 2s peaks were constant. However, the width of the KLL Auger peak went through a maximum near O/(H + O + N) = 0.5, as observed previously. The 2p and 2s width invariance is interpreted as being due to the presence of hydrogen, in that the weak hydrogen bonding allows strain due to varying bond angles and distances to be taken up more easily than in SiO and SiN bonds. The KLL variation, on the other hand, is suggested as arising from the effect of the core hole in the L shell, causing instantaneous local strain around the ionized Si atom associated with SiO and SiN bonds.The dependence of the Auger parameter on the oxygen fraction O/(H + O + N) was different from that found for the LPCVD films in that it was accurately linear. As a result, the PECVD films do not obey the random bonding model of progressive substitution of N by O, but consist of a mixture of two phases, in agreement with Claassen and Kuiper who suggested the phases SiO2 and Six Ny Hz. The linear decrease in the Auger parameter is thus due to the proportionate decrease in the Six Ny Hz content. Plots of the Auger parameter as a function of (n2 − 1)/n2 were again linear, confirming the direct relationship between the parameter and the polarization energy found previously.

Silicon oxynitride films: Ion bombardment effects, depth profiles, and ionic polarization, studied with the aid of the Auger parameter

Thin films of Si3 N4, SiO2, and of silicon oxynitrides with compositions in the range 0.3≤O/N≤3.6 were deposited on silicon substrates to thicknesses between 20 and 150 nm by low-pressure chemical vapor deposition. Auger parameters of the films were measured during the study of ion bombardment effects and depth profiling, and as a function of the O/N ratios. The particular parameter used was based on the Si 2s photoelectron, and bremsstrahlung-excited Si KLL Auger lines. When normalized to constant ion dose, no significant differences in the effects of bombardment with argon ions in the energy range 0.5–4.0 keV could be found, and the equilibrium O/N ratio measured by x-ray photoelectron spectroscopy was close to that measured by Rutherford backscattering and elastic recoil detection analysis. During depth profiling no reduction of the oxynitride to elemental silicon was observed, in contrast to previous work using the low-energy Si LVV Auger peak with electron excitation; it is therefore recommended that to perform depth profiling of these materials while retaining artefact-free compositional and chemical information, the high kinetic energy Si spectral features should be used. At the oxynitride/silicon interfaces in some of the films additional features were found corresponding to intermediate Si chemical states. The widths of the Si 2s, 2p and KLL spectral features were measured at the stages in depth profiling at which equilibrium composition had been reached. In every case there was an increase in width as a function of oxygen fraction O/(O+N), from Si3 N4, through a maximum at about O/(O+N)≊0.5, followed by a decrease to SiO2. The maximum increase for the KLL Auger peak was ≊0.9 eV, but for the 2s and 2p only ≊0.35 eV, and the peak broadening was uniformly distributed about the peak centroid. The broadening is attributed to the appearance of a number of additional chemical states of Si too closely spaced to be resolvable, and probably arising from a defective film structure. The Auger parameters of the various films, measured also once equilibrium composition had been reached during profiling, showed what appeared to be a monotonic dependence on O/(O+N), thus supporting the random bonding model in which nitrogen atoms are substituted randomly by oxygen in the SiNz O4−z (z=0, 1, 2, 3, 4) tetrahedra. However, the Auger parameter versus composition plot was displaced slightly from the theoretical one in the direction of higher parameter than expected. When the Auger parameter was plotted against the function (n2−1 )/n2, proportional to the polarization energy, n being the measured refractive index of a film, a linear relationship was found within experimental error, but with a slope different from that for the standards SiO4/2 (silica), SiO6/3 (stishovite), Si3 N4, and Si. This divergence is interpreted in terms of a lower O ionic polarizability in the oxynitrides than in the oxides.

Oxygen effect on secondary ion emission of impurities in GaAs

To investigate quantitatively the effect of oxygen on the ion yields in secondary ion mass spectrometry (SIMS) analysis of impurities in GaAs, oxygen-implanted GaAs crystals were prepared. Oxygen-induced ion yield enhancement was demonstrated by the SIMS analysis of these oxygen-implanted GaAs crystals. B, Cr, Cu, and Mn in these crystals were found to have impurity ion yields 50 times larger than those without oxygen under Ar+ bombardment. The ion yield enhancement of impurities by oxygen has been interpreted by treating ion yields as a function of oxygen fraction, i.e., probability of occupying the adjacent site to the impurities by oxygen atoms. For oxygen fractions, the local thermodynamic equilibrium calculations were carried out to obtain T parameters which enable the impurity ion yields to be estimated only by ionization potentials if the oxygen fraction is given.