Effect Of Ambient Gas Research Articles

The effect of ambient gas on measurements with microwave-assisted laser-induced plasmas in MA-LIBS with relevance for the analysis of nuclear fuel

The effect of ambient gas on measurements with microwave-assisted laser-induced plasma in microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS) was studied with relevance for the analysis of nuclear fuel. A pelletized gadolinium oxide (Gd2O3) sample, which was used as a simulated nuclear fuel, was irradiated by a pulsed Nd:YAG laser (532 nm, 5 mJ) coupled with microwaves (2.45 GHz, 400 W) under various gases of air, Ar, and He. Microwaves can be effectively used to enhance laser-induced plasma emissions. The emission spectrums of Gd obtained by MA-LIBS in Ar and He gases are much better than those of the air case. Namely, the spectral lines can be clearly identified and are far from molecular bands. Furthermore, the emission intensity is highest with low background emissions. Linear calibration curves of Ca in the concentration range between 0 and 500 mg/kg as an impurity in Gd2O3 have been successfully obtained in all gases. The detection limits of Ca impurity in air, Ar and He gases were 2, 0.8 and 0.6 mg/kg, respectively, which are much lower than the required limits of Ca impurity in nuclear fuels.

Study on the effect of ambient gas on nanostructure formation on metal surfaces during femtosecond laser ablation for fabrication of low-reflective surfaces

Nanostructure formation on bulk metals (silver, gold, copper and titanium) by femtosecond Ti-sapphire laser irradiation (775nm, 150fs) is studied aiming the production of low-reflectivity surfaces and the better understanding of the development process. The experiments were performed in nitrogen, air, oxygen and helium environments at atmospheric pressure. The samples were irradiated with fluences in the 0.1–2J/cm2 range and an average pulse number of 100 falling over a given area. The reflectivity of the treated surfaces was determined by a microspectrometer in the 450–800nm range and their morphology was studied by scanning electron microscopy. The gas ambience influenced the results via two effects: formation processes and the chemically-induced modifications of the nanostructures. In case of He the nanoparticle aggregates–otherwise generally present–are predominantly missing, which leads to a lower darkening efficiency. The presence of oxygen enhances the darkening effect for copper mostly at lower fluences, while causes a slow increase in reflectivity in the case of titanium (in case of pure oxygen) in the high fluence range. The surface morphology in case of nitrogen and air were quite similar probably due to their close molecular mass values.

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al2O3 nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N2 as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N2 during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.

Experimental study on primary breakup of diesel spray under cold start conditions

Studies on primary breakup of diesel spray under room temperature (25°C) and low temperature (−2°C), were carried out by mass flow rate measurement and microscopic imaging. It was shown that under low injection pressure and low temperature, raised viscosity and surface tension caused slower penetration and poorer breakup. Under high injection pressure, higher chances of mushroom formation under low temperature due to higher viscosity surprisingly leaded to quicker penetration but still poorer dispersion during the initial spray stage. Low temperature retarded the start of atomization as the needle rose. The end of injection showed a large amount of compact liquid fuel with little dispersion, which was deteriorated by low temperature. In addition, a new equation including the influences of ambient gas on breakup, was proposed to quantify the spray stability, allowing quantitative analysis of the effects of temperature and ambient gas.

High-resolution core-level photoemission measurements on the pentacene single crystal surface assisted by photoconduction

Upon charge carrier transport behaviors of high-mobility organic field effect transistors of pentacene single crystal, effects of ambient gases and resultant probable ‘impurities’ at the crystal surface have been controversial. Definite knowledge on the surface stoichiometry and chemical composites is indispensable to solve this question. In the present study, high-resolution x-ray photoelectron spectroscopy (XPS) measurements on the pentacene single crystal samples successfully demonstrated a presence of a few atomic-percent of (photo-)oxidized species at the first molecular layer of the crystal surface through accurate analyses of the excitation energy (i.e. probing depth) dependence of the C1s peak profiles. Particular methodologies to conduct XPS on organic single crystal samples, without any charging nor damage of the sample in spite of its electric insulating character and fragility against x-ray irradiation, is also described in detail.

Effect of Ambient Gas on Flammability Limit of Flat Materials in Microgravity

Effect of Ambient Gas on Flammability Limit of Flat Materials in Microgravity

Effects of ambient gas on cold atmospheric plasma discharge in the decomposition of trifluoromethane

N2< He < Ar: the order of energy efficiency for CHF3decomposition among these gas discharges.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

Effects of flow rate of atmosphere gases on the characteristics of Zn-doped ITO (ZITO) thin films for organic light emitting diodes

We have investigated the effect of ambient gases on the structural, electrical, and optical characteristics of Zn -doped indium tin oxide (ZITO) thin films intended for use as anode contacts in organic light emitting diodes (OLED) devices. These ZITO thin films are deposited by radio frequency (RF) magnetron sputtering under different ambient gases ( Ar , Ar + O 2 and Ar + H 2) at 300°C. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0.1 sccm to 0.5 sccm and from 0.1 sccm to 1 sccm, respectively. The intensity of the (400) peak in the ZITO thin films increases with increasing H 2 flow rate whilst the (400) peak was nearly invisible in an atmosphere of Ar + O 2. The electrical resistivity of the ZITO thin films increases with increasing O 2 flow rate, whereas the electrical resistivity decreases with increasing H 2 flow rate. The change of electrical resistivity with changes in the ambient gas composition is mainly interpreted in terms of the charge carrier mobility and the charge carrier concentration. All the films show an average transmittance of over 80% in the visible range. The optical bandgap of the ZITO films increases with increasing H 2 flow rates, whereas the optical bandgap of the ZITO films deposited in an O 2 atmosphere decreases with increasing O 2 flow rates. The current density and the luminance of the OLED devices with ZITO thin films deposited in 1 sccm of H 2 ambient gas are the highest among all the films. The optical bandgap energy of ZITO thin films plays a major role in OLED device performance, especially the current density and luminance.

Angular distribution of energetic argon ions emitted by a 90 kJ Filippov-type plasma focus

Characteristics of the energetic argon ions emitted by a 90 kJ Filippov-type plasma focus are studied by employing an array of Faraday cups. The Faraday cups are designed to minimize the secondary electron emission effects on their response. Angular distribution of the ions is measured, and the results indicate a highly anisotropic emission with a dip at the device axis and a local maximum at the angle of 7° with respect to the axis. It has been argued that this kind of anisotropic emission may be related to the surfatron acceleration mechanism and shown that this behavior is independent of the working gas pressure. It has been also demonstrated that this mechanism is responsible for the generation of MeV ions. Measuring the total ion number at different working gas pressures gives an optimum pressure of 0.3 Torr. In addition, the energy spectrum of ions is measured by taking into account of the ambient gas effects on the energy and charge of the ions. The current neutralization effect of electrons trapped in the ion beam as well as the effect of conducting boundaries surrounding the beam, on the detected signals are investigated.

Effects of substrate and ambient gas on epitaxial growth indium oxide thin films

Indium oxide thin films were grown by pulsed electron beam deposition method at 500 °C on c-cut sapphire and (0 0 1) oriented LaAlO3 single crystal substrates in oxygen or argon gas. The effects of ambient gas and substrate symmetry on the growth of indium oxide thin films were studied. Stoichiometric In2O3 films are formed in oxygen, while oxygen deficient In2O2.5 films are grown in argon, with In metallic nanoclusters embedded in a In2O3 matrix (nanocomposite films). In both cases, epitaxial In2O3 films having the bixbyite phase were grown with various orientation relationships, depending upon the substrate symmetry and gas ambient (oxygen or argon). Domain matching epitaxy was used to describe the precise in-plane epitaxial film–substrate relationships. The differences in film texture were correlated to the differences in growth conditions, while the differences in the film properties were correlated to the film oxygen composition.

Effects of flow rate of oxygen and hydrogen gases on characteristics of ITO thin films for OLEDs

We have investigated the effect of ambient gases on the structural, electrical and optical characteristics of indium tin oxide (ITO) thin films intended for use as anode contacts in organic light emitting diode (OLED) devices. These ITO thin films are deposited by radio frequency magnetron sputtering under different ambient gases (Ar, Ar+O2 and Ar+H2) at 300°C. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0·5 to 5 sccm and from 0·1 to 1 sccm, respectively. The intensity of the (400) peak in the ITO thin films increases with increasing H2 flow rate, while the (400) peak was nearly invisible in an atmosphere of Ar+O2. The electrical resistivity of the ITO thin films increases with increasing O2 flow rate, whereas the electrical resistivity decreases sharply under an Ar+H2 atmosphere and is nearly similar regardless of the H2 flow rate. The change of electrical resistivity with changes in the ambient gas composition is mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. All the films show an average transmittance of >80% in the visible range. The optical band gap of the ITO films increases with increasing H2 flow rates, whereas the optical band gap of the ITO films deposited in an O2 atmosphere decreases with increasing O2 flow rates. The current density and the luminance of the OLED devices with ITO thin films deposited in 1 sccm of H2 ambient gas are the highest among all the films. The optical band gap energy of ITO thin films plays a major role in OLED device performance, especially the current density and luminance.

Oxygen-induced bi-modal failure phenomenon in SiOx-based resistive switching memory

The ambient gas effect in SiOx-based resistive switching memory has been studied. After the electroforming process, resistive switching behavior functions in vacuum as well as in nitrogen without dramatic degradation. However, introducing an oxygen-nitrogen ambient suppresses resistive switching behavior at pressures above 1 Torr. Resistive switching is fully reestablished in oxygen-exposed devices after a vacuum recovery step. The failure phenomena can be described by Monte Carlo simulation using bi-modal statistics to enable feature distribution modeling of failure modes. Design criteria and guidelines are identified for packaging of future oxygen-sensor and of nonvolatile memory applications.

Numerical Study on High Prandtl Number Liquid Bridge

The overall numerical analysis of liquid bridge for high Pr number fluid and flow field of ambient air under the zero-gravity environment was carried out in the present paper. The paper used level set method of mass conservation to capture two phase interfaces. Not only the free surface deformation was considered, but also the effect of ambient gas was taken into account. Simultaneously, results of stream function in liquid bridge and ambient gas-phase were given.

Elucidation of ambient gas effects in organic nano-floating-gate nonvolatile memory

Pentacene-based organic field-effect transistor nonvolatile memories employing nano-floating-gate show high performance in vacuum, typically with field-effect mobility of 0.6 cm2/Vs, memory window of 45 V, reading ON/OFF ratio over 106, and excellent retention ability and programming/erasing endurance. The memory performance is unstable in air, which is demonstrated to result mainly from the device operation instability in O2. The O2-induced acceptor-like trap states reduce the electron supply in pentacene during programming, limiting the electron trapping into the nano-floating-gate and thus suppressing the positive threshold voltage shift. The corresponding hole trapping during erasing is not effectively influenced by the ambient gas effects.

Effect of Ultraviolet Illumination and Ambient Gases on the Photoluminescence and Electrical Properties of Nanoporous Silicon Layer for Organic Vapor Sensor

The purpose of this research, the nanoporous silicon layer were fabricated and investigated the physical properties such as photoluminescence and the electrical properties in order to develop organic vapor sensor by using nanoporous silicon. The Changes in the photoluminescence intensity of nanoporous silicon samples are studied during ultraviolet illumination in various ambient gases such as nitrogen, oxigen and vacuum. In this paper, the nanoporous silicon layer was used as organic vapor adsorption and sensing element. The advantage of this device are simple process compatible in silicon technology and usable in room temperature. The structure of this device consists of nanoporous silicon layer which is formed by anodization of silicon wafer in hydrofluoric acid solution and aluminum electrode which deposited on the top of nanoporous silicon layer by evaporator. The nanoporous silicon sensors were placed in a gas chamber with various organic vapor such as ethanol, methanol and isopropyl alcohol. From studying on electrical characteristics of this device, it is found that the nanoporous silicon layer can detect the different organic vapor. Therefore, the nanoporous silicon is important material for organic vapor sensor and it can develop to other applications about gas sensors in the future.

Estimation Method of Spray Diameter and Size Distribution Based on Energy Conservation Law

An analytical method was proposed and validated for droplet diameters and size distributions. The method was developed based on the energy conservation law including surface free energy and Laplace pressure. Under several hypotheses, the law derived an equation indicating that atomization resulted from a kinetic energy loss. Thus, once the amount of loss was obtained, the droplet diameter was able to be calculated without any experimental parameters. When the effects of ambient gas were ignorable, injection velocity profiles of liquid jets were the essential factor for the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization was inversely proportional to the injection Weber number under the conditions of injection velocity profiles with laminar or turbulent. By applying the mean diameter model, a non dimensional distribution function was also derived assuming Nukiyama-Tanasawa's function. The validity of these estimation methods were favorably confirmed by comparisons with corresponding mean diameters and the size distributions, which were experimentally measured under atmospheric pressure.

Preparation and Characterization of Piezoelectric Films of ZnO and AlN by RF Sputtering for RF MEMS Applications

In present work, we report preparation and characterization of piezoelectric films of zinc oxide (ZnO) and aluminum nitride (AlN) by RF magnetron sputtering using respective ceramic targets. The effect of ambient gas, substrate temperature, RF power and sputtering pressure has been studied to get highly c-axis oriented films for potential applications in micro-electromechanical systems. The films were characterized by X-ray diffraction technique to identify the crystallographic orientation. It was observed that the film deposited in pure Argon (Ar) ambient were amorphous or weekly crystallized with no preferred (002) orientation. On the other hand, the films prepared in Ar-O2 for ZnO were highly c-axis oriented. Similarly AlN films were observed to be oriented along c-axis perpendicular to substrate only when deposited in mixture of Ar-N2. To demonstrate the application of piezoelectric properties, an FBAR device (Film Bulk Acoustic Resonator) using ZnO thin film was fabricated. ZnO films are very sensitive to the chemicals used in the micro-electro-mechanical systems (MEMS) fabrication processes which include acids, bases and etchants of different material layers (e.g. SiO2, chromium, gold etc.). A specially designed mechanical jig was used for physically protecting the film during Si anisotropic etching process in potassium hydroxide solution. The potential applications of these films in various RF MEMS devices have been discussed.

Preparation and Characterization of Piezoelectric Films of ZnO and AlN by RF Sputtering for RF MEMS Applications

In present work, we report preparation and characterization of piezoelectric films of zinc oxide (ZnO) and aluminum nitride (AlN) by RF magnetron sputtering using respective ceramic targets. The effect of ambient gas, substrate temperature, RF power and sputtering pressure has been studied to get highly c-axis oriented films for potential applications in micro-electromechanical systems. The films were characterized by X-ray diffraction technique to identify the crystallographic orientation. It was observed that the film deposited in pure Argon (Ar) ambient were amorphous or weekly crystallized with no preferred (002) orientation. On the other hand, the films prepared in Ar-O2 for ZnO were highly c-axis oriented. Similarly AlN films were observed to be oriented along c-axis perpendicular to substrate only when deposited in mixture of Ar-N2. To demonstrate the application of piezoelectric properties, an FBAR device (Film Bulk Acoustic Resonator) using ZnO thin film was fabricated. ZnO films are very sensitive to the chemicals used in the micro-electro-mechanical systems (MEMS) fabrication processes which include acids, bases and etchants of different material layers (e.g. SiO2, chromium, gold etc.). A specially designed mechanical jig was used for physically protecting the film during Si anisotropic etching process in potassium hydroxide solution. The potential applications of these films in various RF MEMS devices have been discussed.

502 岩石のメカノルミネッセンスのスペクトルにおける雰囲気ガスの影響(材料力学V)

502 岩石のメカノルミネッセンスのスペクトルにおける雰囲気ガスの影響(材料力学V)