Mixture Of Argon Research Articles

Role of Hydrogen Flow Rate for the Growth of Quality Nanodiamonds via Microplasma Technique

Nanodiamonds (NDs) were prepared by utilizing a microplasma facility. Ethanol and Argon mixture was decomposed in microplasma for the formation of NDs. In order to stabilize the NDs growth, the Hydrogen was added in the mixture during the growth process. Hydrogen flow rate was changed from 1 to 5 L/min to find out the optimum flow rate for the growth of stabilized NDs. The experiments were also performed without the introduction of Hydrogen for the comparison. TEM and Raman analysis confirm that the highest quality diamonds are obtained at Hydrogen flow rate of 3L/min. In the case of Hydrogen, the SAED patterns reveal the presence of pure diamond phases which in turn envisages the etching of graphitic shell. TEM micrographs reveal that the size of NDs produced at 3 L/min Hydrogen flow rate ranges from 1~20 nm which is much smaller than that of without Hydrogen (4-32 nm). EDX spectra also disclose the Carbon peak with a maximum intensity for 3 L/min flow rate. UV-Visible and PL spectroscopy analysis indicate the presence of Nitrogen-Hydrogen defect centers. However, a decrease in defect density at 3L/min indicates the production of improved quality NDs. FTIR also verifies the removal of graphitic shell around NDs at 3 L/min flow rate. Moreover, high hydrogen flow rates effectively incorporate nitrogen vacancy (NV) defects. Prepared NDs offer emerging applications in optoelectronic systems, biomedical nanodevices and nanoscale sensors for electric field, magnetic field & temperature.

Shock structure solutions of Grad 13-moment equations for binary gas mixtures

The presence of sub-shocks within a shock structure solution is discussed for an inert binary mixture of monatomic gases, whose evolution is governed by a Grad 13-moment model. The aim of this paper is to analyse the role of characteristic speeds on the occurrence of jump discontinuities along the wave front. Lax admissible sub-shocks are further examined by geometric arguments on singularity manifolds. Theoretical results are confirmed by numerical simulations in the case of Helium and Argon mixtures.

Synthesis of Cellular Silica Using Microbubbles as Templates.

In this work, cellular silica was synthesized by using microbubbles as templates, which contain a mixture of argon and silicon tetrafluoride (SiF4). The latter is generated from decomposition of hexafluorosilicic acid (H2SiF6) at ambient conditions. The specific surface area of cellular silica can be as high as 130 m2/g, the size of the cavity is hundreds-of-nanometers, and the thickness of the cavity wall is around 30 nm. The cavity size, apparent packing density, and porosity of cellular silica strongly depend on the nature of the aqueous solutions; the cavity size appears to be negatively proportional to the surface tension, but thickness of cavity walls seems to be weakly affected by the aqueous properties. An attempt was made to introduce aluminum atoms in situ in the second-coordination sphere of Si atoms and/or load aluminum into the silica structure. Cellular silica with large pores facilitate the transfer of large molecules, including polymers and enzymes; thus, it could find applications in (bio)catalysis, sorption, controlled release and separations.

Surface processes on thin layers of black aluminum in ultra-high vacuum

Thin films of black aluminum (B–Al) were prepared by pulsed DC magnetron sputtering in a mixture of argon + nitrogen (Ar + N2) gases with concentration of nitrogen 6%. At this concentration the process of anti-reflective surface (UV to near IR diffuse reflectance below 4%) formation is favored. The properties of such layers have been investigated using methods allowing to follow near-surface processes by means of thermally stimulated desorption (TSD) and thermally stimulated exo-electron emission (TSEE) in ultra-high vacuum conditions (p < 2.10−7 Pa). It is shown that at certain temperatures some adsorbed particles are desorbed and at the same time negative charges are emitted. In some cases, the emission sites are common. Comparison of TSEE measurements at three different excitations (α, proton irradiation and UV illumination) was performed. Common measurements together with calculations of the activation energies of desorption as well as electron emission sufficiently describe the centers responsible for these processes. In particular, the atomic oxygen Oat, the AlOH radical and partly the atomic nitrogen Nat together with the AlN radical are shown to play a significant role in this surface process.

Comparative study of Mn-ZIF-67 derived carbon (Mn-Co/C) and its rGO-based composites for the methanol oxidation

In this study, we report the comparative electrocatalytic study of commercial Pt/C with Mn-Co/C and its rGO based composites (i.e., 1–8 wt% rGO @Mn-Co/C) for methanol oxidation. Catalysts were synthesized by a two-step procedure. Firstly, via the solvothermal method, all catalysts were prepared and then pyrolyzed at 700 °C in an argon and hydrogen mixture environment. The characterization of the Mn-Co/C, 1–8 wt% rGO Mn-Co/C catalysts was accomplished by XRD, SEM, EDX, Raman, TEM, BET and XPS. The as-prepared dodecahedron morphology of the initial Mn-based ZIF-67 particles is retained, with the interconnected sheets of reduced graphene oxide after the pyrolysis in a reducing atmosphere (i.e., Ar+H2). Among all the catalysts, the 5 wt% rGO@Mn-Co/C catalyst has shown much higher electrochemical activity (i.e., 235.24 mA/cm2) and stability than other rGO-based Mn-Co/C catalysts and also than commercial Pt/C in 1 M NaOH and 3 M CH3OH. The presence of support materials such as rGO and the availability of nano porous carbon with Mn and Co may contribute to the improved electrocatalytic activity of 5 wt% rGO Mn-Co/C over Mn-Co/C. With a number of beneficial features in structure, composition, and nitrogen doping level, it results in enhanced electrocatalytic activity and stability as well as methanol tolerance when benchmarked with a commercial Pt/C electrocatalyst under the same testing conditions.

Microbulk Micromegas in non-flammable mixtures of argon and neon at high pressure

We report on a systematic characterization of microbulk Micromegas readouts in high-pressure Ar+1%iC4H10 and Ne+2%iC4H10 mixtures. Experimental data on gain, electron transmission and energy resolution are presented for a wide range of drift and amplification voltages and pressures from 1 bar to 10 bar for the argon mixture and from 5 bar to 10 bar in the neon mixture, in steps of 1 bar. Maximum gains higher than 1.7 × 103 (1.7 × 104) in the argon (neon) mixture are measured for all pressures, without the significant decrease with pressure typically observed in other amplification structures. A competitive energy resolution at 22.1 keV, but with a slight degradation with pressure, is observed: from 10.8% at 1 bar to 15.6% FWHM at 10 bar in Ar+1%iC4H10 and from 8.3% at 5 bar to 15.0% FWHM at 10 bar in Ne+2%iC4H10. The experimental setup, procedure and the results will be presented and discussed in detail. The work is motivated by the TREX-DM experiment, that is operating in the Laboratorio Subterráneo de Canfranc with the mentioned mixtures, although the results may be of interest for other applications of time projection chambers at high pressures.

Photoelectron Collection Efficiency Of PDT

Photoelectron collection efficiency for 3-(2-Pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) photocathode in pure Methane and in Argon Methane gas mixtures at different rations i.e. 50:50, 80:20 and 90:10 against decreased electric field and photons of wavelength ranging from 190nm to 230nm has been presented. Maximum QE reaches to ~95%, ~94 and ~95 of vacuum QE respectively in charge multiplication mode. These values are achieved at approximately E/p = 3.5 V/cm.Torr, 2.5 V/cm.Torr and 2 V/cm.Tor at 190 nm respectively. Similar QE are achieved E/p = 4.1 V/cm.Torr, 2.7 V/cm.Torr and 2.2 V/cm.Torr respectively at 230 nm.

The Characteristics of Closed-Loop Inductively Coupled Low Mercury Pressure Discharge

The characteristics of inductively coupled ferrite-free low mercury pressure discharges generated in closed-loop 815-mm-long quartz tubes 16.6 mm in diameter are studied. Discharges were excited at a frequency of 13.56 MHz with plasma power ranging from 10–270 W in a mixture of mercury vapor (~0.01 Torr) and argon (0.5, 1.0 and 2.0 Torr) by means of an induction coil placed over the discharge tube wall external perimeter. With a growth of plasma power, the lower the argon pressure, the faster the growth rates of the RF voltage across the induction coil and the current through it. The plasma impedance as a function of plasma power calculated within the framework of the inductively-coupled discharge transformer model has a minimum, which shifts toward higher plasma power values with increasing the argon pressure. The lower the argon pressure the higher the RF electric field averaged over the plasma cross section, and the lower the plasma power at which the dependence of discharge current on plasma power reaches its maximum.

The Characteristics of Closed-Loop Inductively Coupled Low Mercury Pressure Discharge

The characteristics of inductively coupled ferrite-free low mercury pressure discharges generated in closed-loop 815-mm-long quartz tubes 16.6 mm in diameter are studied. Discharges were excited at a frequency of 13.56 MHz with plasma power ranging from 10–270 W in a mixture of mercury vapor (~0.01 Torr) and argon (0.5, 1.0 and 2.0 Torr) by means of an induction coil placed over the discharge tube wall external perimeter. With a growth of plasma power, the lower the argon pressure, the faster the growth rates of the RF voltage across the induction coil and the current through it. The plasma impedance as a function of plasma power calculated within the framework of the inductively-coupled discharge transformer model has a minimum, which shifts toward higher plasma power values with increasing the argon pressure. The lower the argon pressure the higher the RF electric field averaged over the plasma cross section, and the lower the plasma power at which the dependence of discharge current on plasma power reaches its maximum.

Formation of epitaxial 3C-SiC layers on Si by rapid vacuum thermal processing

The results of a study of the structure and phase composition of epitaxial layers of silicon carbide (SiC) formed on silicon substrate with orientation (100) under rapid vacuum thermal processing are presented. Planar-view transmission electron microscopy investigation revealed the formation of epitaxial layers of cubic polytype SiC (3C-SiC) on silicon in the process of carbidisation at 1100 °C during 30 s, using a gas mixture of propane (10 %) and argon (90 %) as a carbon source. The formation of a monocrystalline 3C-SiC with polycrystalline inclusions and twins on all possible planes {111} was found. A rather narrow band of 793 cm–1 transverse optical phonon mode SiC on Raman spectra confirms the formation of a cubic polytype SiC. It is noted that the presence of a 180 cm–1 spectral line and a 793 cm–1 half-width band on Raman spectra indicate the presence of deformation defects in SiC.

Modelling of dcMS and HiPIMS process with hydrocarbon gas admixture

Magnetron sputtering in an argon and hydrocarbon gas mixture is a complex deposition process exhibiting features of both physical vapour deposition and plasma enhanced chemical vapour deposition. The hydrocarbon gas decomposes within the plasma and then it is able to form a carbide phase with the target metal atoms or to be deposited as amorphous carbon. In this paper, a simple model for both the direct current (dcMS) and the high power impulse magnetron sputtering (HiPIMS) processes with hydrocarbon gas admixture is presented. The sputtered target racetrack is divided into metallic, compound, and carbon fractions to take into account both the carbide formation and the carbon deposition. To simulate the HiPIMS process, the back-attraction of ionised sputtered metal particles is incorporated into the model. The model is cross-validated with the previously published experiments which were conducted using the same deposition apparatus allowing for the direct comparison of the dcMS and HiPIMS processes. The simulated results correlate with the measured dependencies of the deposition rate, the carbon content in deposited films, and the racetrack fractions on the acetylene supply rate. The presented model is further successfully validated with the evolution of the racetrack composition calculated by SDTrimSP.

Work relation for determining the mixing free energy of small-scale mixtures

In thermodynamically characterizing a mixture comprising a finite number of molecules, we consider two kinds of protocol for producing a mixture from a pure substance. The first is a single alchemical operation, whereas the second is a series of processes with feedback control in information thermodynamics and conventional mixing with semipermeable membranes. A comparison of the two numerically determined free-energy changes provides a combinatorial factor that indicates the indistinguishability of the molecules and an alternative Jarzynski equality. The comparison also uncovers a work relation for determining the mixing free energy without using semipermeable membranes. We demonstrate a numerical calculation of applying the work relation to a mixture of argon and krypton. The mixing free energy clearly shows the characteristics of liquid--vapor transition.

Impact of growth atmosphere on langatate (La3Ga5.5Ta0·5O14) crystals grown by czochralski technique and its coloration

Langatate (LGT) crystals of La3Ga5.5Ta0·5O14 composition of diameter 50 mm were grown from the melt by Czochralski technique. Using (1–2 wt %) Ga2O3 excess in the starting charge and growing crystal in mixture argon (0.1–1%O2) gas atmosphere are a good condition to crystallize LGT under stationary stable regime. The LGT crystals grown along Z-axis exhibit strong faceting. The grown crystals were exempt of inclusions, cracks and secondary phases. The presence of oxygen in the growth chamber is necessary to limit gallium oxide evaporation and strongly affect the crystals coloration and the transmission spectra in the range (200–500 nm). The electrical resistivity is sensitive to the oxygen content in the growth environment.

Synthesis of Ag-decorated vertical graphene nanosheets and their electrocatalytic efficiencies

Herein we report the successful preparation of silver (Ag)-decorated vertically oriented graphene sheets (Ag/VGs) via helicon wave plasma chemical vapor deposition (HWP-CVD) and radiofrequency plasma magnetron sputtering (RF-PMS). VGs were synthesized in a mixture of argon and methane (Ar/CH4) by HWP-CVD and then the Ag nanoparticles on the prepared VGs were modified using the RF-PMS system for different sputtering times and RF power levels. The morphology and structure of the Ag nanoparticles were characterized by scanning electron microscopy and the results revealed that Ag nanoparticles were evenly dispersed on the mesoporous wall of the VGs. X-ray diffraction results showed that the diameter of the Ag particles increased with the increase in Ag loading, and the average size was between 10.49 nm and 25.9 nm, consistent with the transmission electron microscopy results. Ag/VGs were investigated as effective electrocatalysts for use in an alkaline aqueous system. Due to the uniquely ordered and interconnected wall structure of VGs, the area of active sites increased with the Ag loading, giving the Ag/VGs a good performance in the oxygen evolution reaction. The double-layer capacitance (C dl) of the Ag/VGs under different Ag loadings were studied, and the results showed that the highest Ag content gave the best C dl (1.04 mF cm−2). Our results show that Ag/VGs are likely to be credible electrocatalytic materials.

Laser induced breakdown spectroscopy for hydrogen detection in molybdenum at atmospheric pressure mixtures of argon and nitrogen

Present study investigated the effect of argon and nitrogen mixtures at atmospheric pressure on the hydrogen Hα line emission intensity during the Laser Induced Breakdown Spectroscopy (LIBS) measurements. LIBS is foreseen for the assessment of the fuel retention in ITER plasma facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or dry air. The use of argon flow during LIBS measurements has shown to increase the LIBS signal at atmospheric conditions which aids the distinguishing of hydrogen isotopes. LIBS was used to ablate a small amount of molybdenum (Mo) target and the development of formed plasma plume was investigated by time-resolved emission spectra and photographs. Spectral measurements showed that the Hα line intensity and electron density decreased faster with the increased fraction of nitrogen in the background atmosphere. The electron temperature of created plasma was also lower in the nitrogen atmosphere. The spatial development of plasma plume was comparable in both argon and nitrogen atmospheres. According to these results, the reduction of Hα line intensity in the presence of nitrogen can be explained by higher fraction of energy consumption in dissociation and excitation processes of molecular gas and increased quenching of excited H states. Furthermore, the results demonstrate that a small amount of N2 impurities in Ar atmosphere does not have detrimental effect on LIBS measurements of hydrogen isotopes. Most of the local thermodynamic equilibrium (LTE) conditions required for the applicability of CF-LIBS were fulfilled in the time-window between 1-5 µs for Ar and 1-3 µs for N2 gas. One notable exception was the time-stability criterion for hydrogen atoms. The effect of this deviation from LTE on the applicability of CF-LIBS requires further studies.

Selected properties of Al x Zn y O thin films prepared by reactive pulsed magnetron sputtering using a two-element Zn/Al target.

AlxZnyO thin films were obtained by reactive pulsed magnetron sputtering. A two-element Zn/Al planar target was used as source material prepared in the form of a Zn disc (100 mm diameter) with Al rings pressed into its surface. The sputtering processes were carried out in a mixture of argon and oxygen. The films were deposited with a discharge power of PE = 400 W, which corresponded to a power density on the target surface of approximately 5 W/cm2. The films were deposited on glass strip substrates, placed symmetrically over the target, making it possible to obtain films with different composition and thickness. The film sheet resistance was measured as a function of the distance from the target axis on both sides (front and back) of the substrate. The lowest measured resistivity was about 4 × 10−3 Ω·cm. Additionally, optical properties, surface topography, and elemental composition were determined in selected areas of the substrate.

Nano-columnar, self-organised NiCrC/a-C:H thin films deposited by magnetron sputtering

Thin films of NiCr–C were deposited by pulse magnetron sputtering of the NiCr20 alloy cathode in an atmosphere containing a mixture of argon and acetylene. Their structure, chemical composition, and magnetic properties were studied using X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, atomic and magnetic force microscopy, and superconducting quantum interference magnetometry methods. Film amorphisation observed upon increasing carbon content was followed by amorphous carbon segregation. As a result of the self-assembly processes during the coating growth, nanostructures were obtained consisting of metallic columns surrounded in carbon sheaths, with axes parallel to the growth direction. The resulting films exhibited weak ferromagnetism in a direction parallel to the axis of the nanocolumns, while the system’s response was superparamagnetic for the direction of magnetisation perpendicular to the nanocolumns.

On the double heat capacity peak of oxygen solid-to-solid transition near 23.8 K

The aim of the paper is to make a summary of INRiM’s most recent results on the α - β solid-to-solid transition (s.s.t.), by reporting the basic details of the findings concerning what looks like a new, and apparently distinct, transition just below the “regular” α - β one. Data are also reported for the temperature changes of the same transitions when measuring certified mixtures of argon in oxygen up to an argon amount concentration x(Ar) = 10–3. The existence of a possible split into two α - β transitions was theoretically predicted by Borovik-Romanov et al. and Kanda et al..

Особенности получения танталосодержащих покрытий на титане методом магнетронного напыления

Tantalum-containing coatings deposited on titanium in vacuum were studied. For deposition of films, a DC magnetron with a balanced magnetic system was used. High purity (99.99 %) tantalum sheet was used as a target. The current density of the glow discharge during the etching of the target was 20.4 A / m2. Plasma-forming gases were argon or a mixture of argon and oxygen. Three types of coatings of tantalum on titanium were obtained: the first one was tantalum oxide on titanium, the second — tantalum on titanium, and the third — tantalum on titanium with a tantalum oxide sublayer. The effect of a pre-deposited sublayer of tantalum oxide on the hardness and morphology of the “base-coating” system was studied. It was found that of the greatest practical interest is an oxygen-saturated tantalum coating with the thickness of 800 nm deposited on a tantalum oxide sublayer with the thickness of 75 – 80 nm. Nanoindentation of samples with a tantalum-containing coating without a tantalum oxide sublayer revealed an increase in hardness up to 39 GPa and in elastic modulus up to 194 GPa. In case of the deposited tantalum oxide sublayer, the nanoindentation hardness reached 60 GPa, and the elastic modulus was 230 GPa. This superhard two-layer structure had a bimodal hardness distribution and contained a Ta2O phase with a cubic crystal lattice. In this case, the proportion of measurements related to superhard inclusions was at least 43 %. The coating had a heterogeneous structure consisting of agglomerates with a size of 0.4 – 0.5 µm. The chemical composition of the surface layer was characterized by an oxygen content of 17.46 at.%, titanium — within 2.00 at.%, and tantalum — 80.54 at.%. An increase in the proportion of coating agglomerates with a size of 0.2 – 0.3 µm was observed from 53.13 to 68.25 % when using a tantalum oxide sublayer. The results make it possible to consider the developed process of obtaining coatings promising for the application of functional layers on titanium medical devices.

Controlled deposition of plasma‐polyaniline thin film by PECVD: Understanding the influence of aniline to argon ratio

AbstractLow pressure capacitively coupled radiofrequency plasmas operated in a mixture of aniline vapor and argon are used for the deposition of thin films on silicon substrates. The influence of the aniline vapor fraction in the gas mixture upon the plasma properties and the characteristics of the deposited thin film is analyzed. Plasmas diagnostics are carried out using mass spectrometry and optical emission spectroscopy and the thin films are characterized by means of Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and near‐edge X‐ray absorption fine‐structure spectroscopy. Experiments highlight that the use of a low aniline/argon ratio leads to the deposition of an amorphous film whereas high‐aniline/argon ratios allow the synthesis of a plasma polymer similar to polyaniline. The properties of such plasmas and the mechanisms involved in the deposition process are discussed in detail.