Ar Gas Mixture Research Articles

Effects of anti-UV film and protective atmosphere on fresh-cut iceberg lettuce preservation

The aim of this research was to study the shelf-life of fresh-cut iceberg lettuce, testing a packaging film manufactured with and without addition of anti-UV compounds, and using two different protective atmospheres (N2/CO2 70/30% and Ar/CO2 80/20%). In order to simulate the most common retail storage conditions, the samples were stored at 6 °C under artificial light by using real supermarket refrigerated exposition stands. The data obtained showed that the use of an anti-UV film always causes a lower quality decay of the product; in any case, the best results were obtained when the anti-UV film was utilized in association with the packaging atmosphere consisting of Ar and CO2 (80/20%) gas mixture.

Influence of Ne sputtering gas on structure and properties of diamond-like carbon films deposited by pulsed-magnetron sputtering

The key process in diamond-like carbon (DLC) film deposition is the formation of sp3-C hybridized bond, which is believed to significantly link to the ionization degrees of the carbon atoms. Ne has a high ionization energy and can facilitate the ionization degree of sputtered carbon. In this paper, Ne and Ar gas mixture was used as the sputtering gas to prepare DLC film by using a pulsed-magnetron sputter. The influences of the Ne fraction in the sputtering gas mixture on the growth character, carbon bond structure, residual stress and mechanical properties of the as-deposited DLC films were studied carefully by using scanning electron microscope, Raman spectroscopy, stress tester and nano-indentation, respectively. The results reveal that the introduction of Ne in sputtering gas mixture can induce the structure densification of the coatings, and significantly increase the sp3 fraction of the DLC films. However, it was found that the sp3 fraction of the films increased little as the Ne fraction exceeded 25%. This phenomenon might be attributed to the reduction of the electron density of the plasma due to the increase of the Ne fraction in the sputtering gas mixture. The residual stress of the DLC films was believed to depend on the sp3 fraction of the films, and thus exhibited a similar changing trend to sp3 fraction as a function of Ne fraction. However, the hardness and elastic modulus of the films increased continuously as the Ne fraction increased. The structure densification and the increase of the sp3 fraction caused by the addition of Ne may be the main factors contributed to the increase of the hardness and elastic modulus of the films.

Non-radioactive Chemical Ionization Mass Spectrometry Using Acetic Acid–Acetate Cluster as a Reagent Ion for the Real-time Measurement of Acids and Hydroperoxides

We have developed a non-radioactive chemical ionization mass spectrometry method using acetic acid–acetate cluster as the reagent ion. By electron impact onto an acetic anhydride–Ar gas mixture, a strong and single ion peak of the acetic acid–acetate cluster was observed. We demonstrated that the reagent ion can ionize carboxylic acids (RC(O)OH) and hydroperoxides (ROOH) produced in ethylene ozonolysis through the formation of adduct ions of these species and acetate. This technique could be used for the detection of various organic hydroperoxides as well as organic and inorganic acids in the atmosphere.

Plasmochemical modification of aluminum-zinc alloys using NH3-Ar atmosphere with anti-wear coatings deposition

This paper constitutes a continuation of studies on modification technologies for 7075 series aluminum alloys (Al-Zn) in plasmochemical conditions using the RF CVD (Radio-Frequency Chemical Vapor Deposition) method. This technique is simultaneously the second stage of alloy ageing. The presented results concern optimization of alloy surface modification using N+ ions (in NH3 or NH3/Ar atmosphere) before obtaining a DLC (Diamond-Like Carbon) layer doped with Si and N.From the results it can be concluded that the most profitable mechanical properties (H, ca. 12 GPa and E, ca. 115 GPa) are obtained when the SiCNH coating process is preceded by Al-Zn alloy surface modification with nitrogen ions. These ions are provided by a flowing NH3 and Ar gas mixture (1:1 ratio). In these process conditions, the lowest tribological wear of the surface is also observed. Furthermore, the obtained coating exhibits a fine-grained structure.

Simulating reduction of in-flight particles of magnetite concentrate by carbon monoxide

In the present study, the reduction of in-flight particles of iron ore concentrate by carbon monoxide has been investigated. A mathematical model was developed for simulating the motion of particles in a CO–Ar gaseous mixture within the reactor. Pre-designed experiments were carried out in a fabricated experimental set-up for validating the model. Excellent agreement between the model predictions and the experimental data approved the accuracy of the model. The nucleation and growth model and the fminsearch optimising method were used for investigating the reaction kinetics. The following equation was obtained relevant to CO reduction of the magnetite concentrate particles:

Structural and Hydrophilic Characteristics of N-doped TiOx Films Deposited by RF-Magnetron Sputtering

Nitrogen doped titanium oxides (N-doped TiO x ) films were deposited by sputtering the TiO 2 target in N 2 /Ar gas mixture to control the doping amount of nitrogen accurately. In order to modify the resultant films, the samples were annealed in air in a temperature range of 300 ∼ 600 ° C, and then they were irradiated under visible-light (VIS) after being placed in dark. X-ray photoelectron spectroscopy (XPS) spectra show that N-Ti-O ( β -N) and hydroxyl form in the films due to nitrogen doped into TiO x lattice. And the content of hydroxyl increases with annealing temperatures increasing, which leads to the better hydrophilicity. X-ray diffraction (XRD) was used to investigate the crystallinity of the films annealed at different temperatures and the results indicate that the amorphous films transform into crystalline phase as a consequence of annealing. Scanning electron microscopy (SEM) results reveal that the particle size becomes bigger at the higher temperature. Hydrophilicity was tested by contact angle meter. The results show that the water contact angle decreases with raising heat treatment temperature due to the change of particle size and the content of −OH. Hydrophilicity is also influenced by the storing process, and the water contact angles increase with time. Furthermore, the hydrophilicity of N-doped TiO x films increases under visible light (VIS) irradiation.

Relationship between formation of surface-reaction layers and flux of dissociated species in C4F8/Ar plasma for SiO2 etching using pulsed-microwave plasma

The mechanism of highly selective etching of SiO2 using pulsed-microwave electron-cyclotron-resonance plasma was investigated by analyzing the relationship between plasma dissociations and fluorocarbon layers formed on surfaces during etching with a cyclo-C4F8/Ar gas mixture. Dissociated molecules of CxFy and CFx species were measured without fragmentations using ion attachment mass spectrometry, and both thicknesses and atomic concentrations of reaction layers formed on etched surfaces were analyzed using x-ray photoelectron spectroscopy. Thus, the impact of CxFy molecules on the formation of fluorocarbon layers were analyzed using this measurement system. The authors found that the process window of highly selective etching of SiO2 over Si was enlarged by using pulsed-microwave plasma because a thinner fluorocarbon layer was formed by controlling C4F8 dissociation by changing the duty cycle of the pulsed-microwaves. With conventional continuous plasma, an etch stop occurred at low wafer bias conditions because a thicker fluorocarbon layer, which protects the SiO2 surface from the ion bombardment, was formed on the SiO2 surface. The thicker fluorocarbon layer was formed from a large amount of CxFy species, such as C2F2, which were generated in the highly dissociated continuous plasma. On the contrary, with pulsed plasma, a thinner fluorocarbon layer was formed due to the lower flux of CxFy species because the dissociation of C4F8 was controlled by reducing the duty cycle of the pulsed-microwave plasma. As a result, the process window was enlarged to the low wafer bias conditions using the pulsed-microwave plasma.

Application of Cl2/BCl3/Ar Plasma Treatment in the Improvement of Ti/Al/Mo/Au Ohmic Contacts

Significant improvement of Ti/Al/Mo/Au ohmic contacts deposited on previously Cl2/BCl3/Ar plasma treated surface was observed. The standard deviation of contact resistance was crucially reduced due to the incorporation of Cl2/BCl3/Ar plasma treatment. The Cl2:BCl3:Ar gas mixture was used in order to thin the top of AlGaN layer prior to deposition of Ti/Al/Mo/Au ohmic contacts. The surface morphology of AlGaN was investigated using scanning electron microscopy and atomic force microscopy. TLM measurements revealed a consequential decrease of contact resistivity.

Impact of high N2flow ratio on the chemical and morphological characteristics of sputtered N-DLC films

Because of their outstanding characteristics, diamond-like carbon (DLC) thin films have been recognized as interesting materials for a variety of applications. For this reason, the effects of the incorporation of different elements on their fundamental properties have been the focus of many studies. In this work, nitrogen-incorporated DLC films were deposited on Si (100) substrates by DC magnetron sputtering of a graphite target under a variable N2 gas flow rate in CH4 + N2 + Ar gas mixtures. The influence of high N2 flow ratios (20, 40 and 60%) on the chemical, structural and morphological properties of N-DLC films was investigated. Different techniques including field emission gun-equipped scanning electron microscope (FEG-SEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), profilometry, Rutherford backscattering spectrometry (RBS) and Raman spectroscopy (325-nm and 514-nm excitation) were used to examine the properties of the N-DLC films. Thus, the incorporation of nitrogen was correlated with the morphology, roughness, thickness, structure and chemical bonding of the films. Overall, the results obtained indicate that the fundamental properties of N-DLC films are not only related to the nitrogen content in the film but also to the type of chemical bonds formed. Copyright © 2016 John Wiley & Sons, Ltd.

Microwave absorption performance enhanced by high-crystalline graphene and BaFe12O19 nanocomposites

The nanocomposites, consisting of BaFe12O19 ferrite and few-layer graphene sheets (FL-GSs) in various weight ratios (1−9 wt. %), were fabricated by a mechanical mixing method. The high-crystalline FL-GSs were prepared by direct current arc discharge evaporation of pure graphite electrodes in an H2–Ar gas mixture. We measured the electromagnetic properties, including effective magnetic permeability and effective permittivity in addition to microwave absorption performance, of the FL-GSs/BaFe12O19 nanocomposites compared with the pristine BaFe12O19 nanoparticles (NPs). The nanocomposite FL-GSs/BaFe12O19 with the optimal performance (6 wt. % FL-GSs) exhibited an effective microwave absorption (<−10 dB) bandwidth of 5.8 GHz with a thickness of 2.2 mm, 53% higher than that of the pristine BaFe12O19 NPs. Meanwhile, this nanocomposite had the minimum reflection loss of −49.7 dB at 8.4 GHz with a thickness of 2.8 mm, three times greater than those without FL-GSs. These performances result from a simultaneous increase in both magnetic and dielectric losses possibly due to synergistic effects of BaFe12O19 and FL-GSs. In such nanocomposites, both magnetic loss from BaFe12O19 and dielectric loss from FL-GSs contribute to the absorbing performances. Adding FL-GSs as dielectric fillers enhances the impedance matching of the nanocomposites compared with the pristine BaFe12O19 NPs based on the magnetic loss alone. Our results indicate that the incorporation of high-crystalline nanocarbon materials into ferrite oxides can provide high microwave absorption intensity and broad effective absorption bandwidth, while maintaining high thermal stability.

Thermal Analysis Simulation of Germanium Zone Refining Process Assuming a Constant Radio-Frequency Heating Source

Three-dimensional thermal analysis simulation of a horizontal zone refining system is conducted for germanium semiconductor materials. The considered geometry includes a graphite boat filled with germanium placed in a cylindrical quartz tube. A flow of Ar and H2 gas mixture is purged through the tube. A narrow section of the boat is assumed to be exposed to a constant heat rate produced by an rf coil located outside the quartz tube. The results of this analysis provide essential information about various parameters such as the shape of the molten zone, required power and temperature gradient in the system.

RT Atomic Layer Deposition of ZrO2 By Using Plasma Excited Water Vapor

Size of semiconductor devices in large-scale integration has reached the submicron range where gate oxide films in metal oxide semiconductor (MOS) devices need to be fabricated at a nanometer scale. Atomic layer deposition (ALD) is a technology for depositing dielectric films with monolayer precision by repeating adsorption of a source gas on substrate that is subsequently reactivated for further adsorption [1]. Zirconium oxide (ZrO2) is believed to be a candidate as the high-k gate oxide material [2]. The growth temperature for the ZrO2 deposition has been desired to be decreased to near room temperature (RT) because the interfacial layer is formed by the solid phase reaction with heating process [3]. In this work, we developed a RT atomic layer deposition of ZrO2 with tetrakis (ethylmethylamino) zirconium (TEMAZ) and a remote-plasma excited water vapor.A p-type Si(100) substrate with a resistivity of 8-12 Ωcm was used as a sample. Prior to the experiment, the sample was cleaned with a buffered HF acid solution and sulfuric acid-hydrogen peroxide mixture. TEMAZ as the zirconium precursor was introduced with a variable leak valve. An induction plasma system generating oxidizing gas was installed to the ALD chamber as shown in Fig.1. The source gas for the oxidizing gas is a mixture of H2O vapor and Ar gas. The plasma was generated in a glass tube with an induction coil with a frequency of 13.56MHz and a RF power of 30 W. Before the ALD process, the substrate surface was treated with the plasma excited water vapor for 5 min to be terminated with OH groups. For the ZrO2 deposition, we repeated the cycle of TEMAZ saturation and the oxidizing gas treatment at RT. The TEMAZ exposure was set to 1.12×10-3 Torr×100 s. The saturation of TEMAZ on the hydroxylated surface has been confirmed by the IR absorption spectroscopy. The plasma excited oxidizing gas was injected for 150 s. The oxidization state of the ZrO2 film was evaluated by X-ray photoelectron spectroscopy (XPS). The thickness of the grown film was measured by spectroscopic ellipsometry.Fig.2 shows Zr3d spectra obtained from ZrO2 on Si grown by the present ALD. According to the increase in the ALD cycles, the Zr3d5/2 peak at around 181.9 eV evolves. The peak position indicates the full oxidized ZrO2 growth on Si [4]. Fig.3 shows the ZrO2 thickness as a function of the ALD cycle. The linear increase of ZrO2 thickness with the ALD cycle indicates that the ZrO2 is grown in the ALD mode. The growth rate is estimated to be 0.14 nm/cycle. This value is comparable with those released in the conventional thermal ALD studies [5].To conclude, we developed the non-heating, RT ALD of ZrO2 with the plasma enhanced technology. We are now investigating the electrical characteristics of ZrO2 MOS on Si and Ge, which will be released elsewhere. The RT grown ZrO2 films might be also applicable for the anticorrosion coatings on plastic material. In the conference, we present not only the details of growth experiment but also discuss the growth kinetics of RT ALD.Acknowledgement This work was partly supported by JST-CREST. We would like to express the deepest appreciation to AIR-LIQUIDE for the high quality precursor of TEMAZ.

A study on the electron transport properties of ZnON semiconductors with respect to the relative anion content.

High-mobility zinc oxynitride (ZnON) semiconductors were grown by RF sputtering using a Zn metal target in a plasma mixture of Ar, N2, and O2 gas. The RF power and the O2 to N2 gas flow rates were systematically adjusted to prepare a set of ZnON films with different relative anion contents. The carrier density was found to be greatly affected by the anion composition, while the electron mobility is determined by a fairly complex mechanism. First-principles calculations indicate that excess vacant nitrogen sites (VN) in N-rich ZnON disrupt the local electron conduction paths, which may be restored by having oxygen anions inserted therein. The latter are anticipated to enhance the electron mobility, and the exact process parameters that induce such a phenomenon can only be found experimentally. Contour plots of the Hall mobility and carrier density with respect to the RF power and O2 to N2 gas flow rate ratio indicate the existence of an optimum region where maximum electron mobility is obtained. Using ZnON films grown under the optimum conditions, the fabrication of high-performance devices with field-effect mobility values exceeding 120 cm2/Vs is demonstrated based on simple reactive RF sputtering methods.

Rate determining steps of fuel oxidation over CeO2 impregnated Ni-YSZ in H2 + H2O + CO + CO2 ambient

Polarization resistance of the Ni-Zr0.84Y0.16O1.92 anode impregnated with cerium oxide in H2+H2O+CO+CO2+Ar gas mixtures of different composition was studied at temperatures of 700–950°C by means of EIS and subsequent DRT and NLLS analysis of EIS spectra. The electrochemical activity of the anode in the H2+H2O+CO+CO2+Ar was found to be defined basically by the hydrogen-containing components (H2 and H2O). The EIS spectra analysis revealed that the anode polarization resistance is determined by three processes, registered at high-, middle- and low-frequencies, respectively. The high-frequency resistance had an activation energy of about −0.93eV and it did not depend on the gas mixture composition. Both the middle-frequency resistance (activation energy of about −1.04eV) and the low-frequency resistance (0.31eV) depended on the gas atmosphere composition. Suggestions about the nature of the rate-determined steps were proposed.

Photochemical Reduction of Low Concentrations of CO2 in a Porous Coordination Polymer with a Ruthenium(II)-CO Complex.

Direct use of low pressures of CO2 as a C1 source without concentration from gas mixtures is of great interest from an energy-saving viewpoint. Porous heterogeneous catalysts containing both adsorption and catalytically active sites are promising candidates for such applications. Here, we report a porous coordination polymer (PCP)-based catalyst, PCP-Ru(II) composite, bearing a Ru(II) -CO complex active for CO2 reduction. The PCP-Ru(II) composite showed improved CO2 adsorption behavior at ambient temperature. In the photochemical reduction of CO2 the PCP-Ru(II) composite produced CO, HCOOH, and H2 . Catalytic activity was comparable with the corresponding homogeneous Ru(II) catalyst and ranks among the highest of known PCP-based catalysts. Furthermore, catalytic activity was maintained even under a 5 % CO2 /Ar gas mixture, revealing a synergistic effect between the adsorption and catalytically active sites within the PCP-Ru(II) composite.

機能性被覆の性状とインピーダンス応答の関係を用いた<i>in-situ</i>評価

The characterization of Zr oxide layer formed in Ar and O2 gas mixture at 973 K on the surface of Zr metal was characterized by electrochemical impedance spectroscopy (EIS). The increase of the layer thickness and the formation of the horizontal crack in the layer were evaluated in-situ using EIS. The thickness of the Zr oxide layer estimated by EIS agreed well with that by EPMA analysis. It was found that the time constant τ of the Zr oxide layer obtained by the EIS increased with the oxidation time. This trend indicated the growth of horizontal crack. The constant phase element (CPE) parameter p was obtained from the results of EIS. The change of p indicated that the Zr oxide layer has the gradient of the chemical composition in its thickness direction. The single horizontal crack and compositionally gradient in the oxide layer was modeled as they electrically functioned in the equivalent circuits. The simulation results indicated that the EIS method can be used as the in-situ monitor the gradient of the chemical composition and the crack formation in the oxide layer.

Synthesis of SiC whiskers by VLS and VS process

This study investigates the mechanisms of SiC whisker formation in the carbothermal reduction of quartz to SiC in different gas atmospheres. Reduction of quartz by graphite was studied in Ar, H2, and CH4–H2–Ar gas mixture in a laboratory fixed bed reactor. The reduction products were characterised by XRD, SEM and TEM. Whiskers were not formed in the carbothermal reduction of quartz in argon. Two types of SiC whiskers were observed in the carbothermal reduction of quartz in H2 and CH4–H2–Ar gas mixture. In the process of reduction at 1400–1600°C in H2 and at 1200–1600°C in CH4–H2–Ar gas mixture, whiskers with hexagonal shape with diameter 100–800nm and length up to tens of microns were formed by the VLS mechanism under catalytic effect of iron. The whiskers with the characteristics of cylindrical shape and high aspect ratio were synthesized in CH4–H2–Ar gas mixture at 1400–1600°C by VS mechanism.

Fabrication of particular structures of hexagonal boron nitride and boron–carbon–nitrogen layers by anisotropic etching

Anisotropic etching of hexagonal boron nitride (h-BN) and boron–carbon–nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H2 and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.

Stopping powers and ranges for the heaviest atoms

Slowing down and stopping of the heaviest atoms, products of the fusion–evaporation nuclear reactions, during their passage through the Dubna gas-filled recoil separator has been studied using TRIM simulations. The study is important for experiments on the synthesis of super-heavy elements (SHEs) with atomic numbers around ZP=114 produced with accelerated heavy ion (HI) beams and extracted with a separator for their detection. The average Mylar stopping power (SP) values obtained with the simulations for HIs with 82⩽ZP⩽92 reveal almost the same magnitudes, allowing extrapolation to the region of ZP>92. Similar extrapolation of the ranges in an He+Ar gas mixture leads to rather small values for the heaviest atoms (ZP⩾102) as compared to the range for U. The extrapolated values have large uncertainties and should be verified with different approaches. Available SP data obtained for HIs with 18⩽ZP⩽92 at energies E<20MeV/u have been analysed within various semi-empirical approaches. The analysis has shown that existing parameterizations give Mylar SP values for ZP⩾82 that are very different from each other at energies of interest (around 0.1MeV/u). We propose to use a general approach based on the HI effective charge parameterization obtained with available SP data for HIs and the hydrogen SP and effective charge corresponding to the same velocity and stopping medium as those for HIs. In this manner, the SPs of the gases H2, He, C4H10, and Ar as well as those of the solids Mylar, C, Al, and Ti have been obtained for any atoms with ZP⩾18 (including the heaviest ones) at their reduced velocities 0.03⩽Vred⩽5.0. The SP values derived in such a way seem to be more reliable compared to the existing semi-empirical calculations and can be used in the conditioning of experiments on the synthesis of SHEs.

Characterization of pure Ni ultrafine/nanoparticles synthesized by electromagnetic levitational gas condensation method

In this work, Ni ultrafine/nanoparticles were directly produced using the one-step, relatively large-scale electromagnetic levitational gas condensation method. In this process, Ni vapors ascending from the levitated droplet were condensed by Ar and He–20%Ar gas mixtures under atmospheric pressure. Effects of type and flow rate of the condensing gas on the size, size distribution and crystallinity of Ni particles were investigated. The particles were characterized by scanning electron microscopy, X-ray diffraction and vibrating sample magnetometer (VSM). The process parameters for the synthesis of the crystalline Ni ultrafine/nanoparticles were determined.