High-pressure Argon Research Articles

One-step epitaxy of high-mobility La-doped BaSnO3 films by high-pressure magnetron sputtering

As unique perovskite transparent oxide semiconductors, high-mobility La-doped BaSnO3 films have been successfully synthesized by molecular beam epitaxy and pulsed laser deposition. However, it remains a big challenge for magnetron sputtering, a widely applied technique suitable for large-scale fabrication, to grow high-mobility La-doped BaSnO3 films. In this work, we developed a method to synthesize high-mobility epitaxial La-doped BaSnO3 films (with mobility up to 121 cm2 V−1 s−1 at the carrier density of ∼4.0 × 1020 cm−3 at room temperature) directly on SrTiO3 single crystal substrates using high-pressure magnetron sputtering. The structural and electrical properties of La-doped BaSnO3 films were characterized by combined high-resolution x-ray diffraction, x-ray photoemission spectroscopy, and temperature-dependent electrical transport measurements. The room-temperature electron mobility of La-doped BaSnO3 films achieved in this work is two to four times higher than the reported values of the films grown by magnetron sputtering. Moreover, in the high carrier density range (n > 3 × 1020 cm−3), the electron mobility value of 121 cm2 V−1 s−1 achieved in our work is among the highest values for all reported doped BaSnO3 films. It is revealed that high argon pressure during sputtering plays a vital role in stabilizing the fully relaxed films and inducing oxygen vacancies, which facilitates high mobility at room temperature. Our work provides an easy and economical way to massively synthesize high-mobility transparent conducting films for transparent electronics.

Pulsed laser deposition of Au nanoparticles on ZnO nanostructures

Au nanoparticles and ultrathin gold films were obtained on the surface of thin (100 nm) ZnO films on Si (001) by pulsed laser deposition (PLD) at high argon pressure by sputtering a pure gold target with a CL3100 pulsed excimer laser (λ = 248 nm) at room temperature. The dependence of the size and distribution of nanoparticles on the argon pressure in the vacuum chamber (PAr), the power density of laser radiation (j), and the number of laser pulses (N) was investigated. Also, to obtain nanostructures, axial and non-axial deposition was used, where the substrate was located perpendicular and parallel to the plasma torch, respectively. Stable modes of obtaining gold nanoparticles with high uniformity and average size from 4 to 10 nm were demonstrated. The modes of stable and reproducible deposition of ultrathin Au films (23-42 nm) and percolation structures (18-20 nm) were also demonstrated. Thus, PLD is a reliable and flexible tool for obtaining nanoparticles and ultrathin Au films the average size and thickness of which can be predictably controlled by varying the deposition parameters. This technique is well suited for coating with gold nanoparticles the surface of nanostructured materials based on chemically active substances that are particularly sensitive to surface cleanliness, which cannot be coated by standard methods.

Benchmark of the KGMf with a coupled Boltzmann equation solver

The Kinetic Global Model framework (KGMf) is an open-source general-purpose global model (spatially averaged) simulation code developed to explore the reaction kinetics and pathways in plasma discharge systems. It contains species continuity and electron energy balance equations, with a time-dependent evaluated electron energy distribution function (EEDF) for electron impact reactions. The EEDF is utilized to determine the rate coefficients for electron impact reactions, which can have profound impact on the temporal evolutions of plasma parameters. Previously, the EEDF was commonly assumed as Maxwellian or an analytical function of the effective electron temperature. In this work, the KGMf is coupled with a Boltzmann equation (BE) solver to self-consistently compute the EEDF. The EEDF evolution frequency is determined based on relative changes of the reduced electric field. The KGMf is benchmarked with the ZDPlasKin code based on high-pressure low-temperature argon plasma discharge cases. The temporal evolutions of reduced electric field, electron temperature, EEDF, reaction rates, and species densities, are obtained and compared under different discharge conditions, showing good agreement between the KGMf and the ZDPlasKin simulations. The application of the KGMf for predicting breakdown times in high power microwave discharges is also presented, which shows qualitative agreement with particle-in-cell simulations. The KGMf can be further applied for more complicated plasma discharge systems, where the reaction kinetics are more intricate (e.g., plasma-assisted combustion systems).

Improvement of quality and stability of MAPbI3 films grown by post annealing under high pressure argon atmosphere

Organic-inorganic hybrid perovskite MAPbI3 films with large grain size and excellent photoelectric properties are obtained by annealing the precursors at Ar atmosphere with pressure up to 10 MPa. In comparing to the film annealing at Ar with 0.1 MPa, 4 times lager grains are observed with the film annealing at the Ar atmosphere with the pressure of 6 MPa. The structural stability in respect to temperature is confirmed by the temperature dependence of x-ray diffraction. The band gap of MAPbI3 films may be adjusted by varying the annealing pressure. There is one order of magnitude in intensity of photoluminescence (PL) due to annealing at the Ar atmosphere with high pressure, even the intensity of PL increases with increasing the temperature up to 35 °C. Post annealing with high atmosphere pressure may be a new method in fabricating high performance MAPbI3 films.

Distributed Joule-Thomson effects and convective heat transfer of high-pressure argon gas flow in helically coiled mini-tubes

Helically coiled mini-tubes have compact structures and good heat transfer performance which attract wide attentions in applications of compact heat exchangers of miniature thermal systems. In this study, forced convection in the helically coiled mini-tubes is numerically studied for the high-pressure low-temperature argon gas. The distribution of temperature and velocity on the cross-section and the variations of the local Nusselt number along the length and periphery of helical coils are presented. The frictional factors and the average heat transfer coefficients h are obtained for Reynolds number in the range of 22500–82500. In the helical coil with tube diameter of 0.3 mm, the distributed Joule-Thomson effect becomes noticeable, and the secondary flow is more apparent at a large Reynolds number, leading to the enhancement of heat transfer compared with that of 0.5 mm tube. The proposed parametrization of Gnielinski correlation yields good consistency with the numerical results, and the deviations for predictions of friction factor and heat transfer coefficient are within ±10%.

Delayed ionization and excitation dynamics in a filament wake channel in a dense-gas medium

A unified theoretical description is developed for the formation of an ionized filament channel in a dense-gas medium and the evolution of electronic degrees of freedom in this channel in the laser pulse wake, as illustrated on an example of high-pressure argon. During the laser pulse, the emerging free electrons gain energy via inverse Bremsstrahlung on neutral atoms, enabling impact ionization and extensive collisional excitation of the atoms. A kinetic model of these processes produces the radial density distributions in the immediate wake of the laser pulse. After the pulse, the thermalized electron gas drives the system evolution via impact ionization (from the ground and excited states) and collisional excitation of the residual neutral atoms, while the excited atoms are engaged in Penning ionization. The interplay of these three processes determines the electron gas cooling dynamics. The local imbalance of the free-electron and ion densities induces a transient radial electric field, which depends critically on the electron temperature. The evolving radial profiles of the electron, ion, and excited-atom densities, as well as the profiles of electron temperature and induced electric field are obtained by solving the system of diffusion-reaction equations numerically. All these characteristics evolve with two characteristic timescales, and allow for measuring the electronic stage of the wake channel evolution via linear and nonlinear light-scattering experiments.

Identification of the Jahn-Teller active trichlorosiloxy (SiCl3O) free radical in the gas phase.

The Ã2A1-X̃2E electronic transition of the jet-cooled trichlorosiloxy (SiCl3O) free radical has been observed for the first time in the 650-590 nm region by laser induced fluorescence (LIF) detection. The radical was produced by a pulsed electric discharge through a mixture of silicon tetrachloride and oxygen in high pressure argon at the exit of a pulsed molecular beam valve. The LIF spectrum shows low frequency intervals, which we assign as activity in the normally forbidden degenerate v5 ' and v6 ' modes, indicative of a significant Jahn-Teller effect in the ground state. Single vibronic level emission spectra show level dependent spin-orbit splittings in the ground state and Jahn-Teller predictable variations depending on which upper state level is pumped. The measured lower state energy levels have been fitted to a Jahn-Teller model that simultaneously includes spin-orbit coupling and linear and quadratic multimode coupling. In SiCl3O, the Jahn-Teller interaction predominates over spin-orbit effects.

Radio frequency and DC high voltage breakdown of high pressure helium, argon, and xenon

Motivated by the possibility of guiding daughter ions from double beta decay events to single-ion sensors for barium tagging, the NEXT collaboration is developing a program of R&D to test radio frequency (RF) carpets for ion transport in high pressure xenon gas. This would require carpet functionality in regimes at higher pressures than have been previously reported, implying correspondingly larger electrode voltages than in existing systems. This mode of operation appears plausible for contemporary RF-carpet geometries due to the higher predicted breakdown strength of high pressure xenon relative to low pressure helium, the working medium in most existing RF carpet devices. In this paper we present the first measurements of the high voltage dielectric strength of xenon gas at high pressure and at the relevant RF frequencies for ion transport (in the 10 MHz range), as well as new DC and RF measurements of the dielectric strengths of high pressure argon and helium gases at small gap sizes. We find breakdown voltages that are compatible with stable RF carpet operation given the gas, pressure, voltage, materials and geometry of interest.

Experimental characterization of argon/air mixture microwave plasmas using optical emission spectroscopy

The plasma is generated by a microwave (MW) source inside a conditioned cell with an axial gas injection working at high pressure argon with a small admixture of air. Several characterization methods based on the analysis of the optical emission spectra are employed to determine rotational Trot, vibrational Tvib, excitation Tex and electron Te temperatures along the plasma flame axis. The densities of electrons and oxygen and nitrogen atoms are also determined from spectra analysis for the same plasma axis positions. The rotational and vibrational temperatures are simultaneously estimated using a new method based on the analysis of 3 consecutive band heads of the second positive system (SPS) of molecular nitrogen spectra. This new method, based on pre-calculated synthetic spectra databases, leads to Trot varying from about 2000 to 2500 K along the plasma axis while Tvib are higher (around 5000 K and more). Both temperatures are coherent when determined from N2SPS in the case of two distinct wavelength ranges (around 313 nm and 376 nm). These temperatures are in agreement with Trot determined from comparison between synthetic and experimental OH(A-X) spectra and Tvib determined from the first negative system N2+FNS spectra. The estimated electron temperatures Te are around 2.0 eV while the electron densities are in the range 1015to 1016cm−3using a literature method adapted in the present work to air diluted in argon buffer gas. The densities of atomic oxygen are estimated close to 1015cm−3and those of nitrogen close to 1016 cm−3 when using an actinometry method assuming a priori known the density of hot buffer argon gas at Trot temperature and also Tex determined using classical Boltzmann plots based on a chosen series of Ar lines. The significant deviations between the different temperatures Trot, Tvib, Tex and Te clearly underline a pronounced non thermal equilibrium of the present MW argon/air plasma. It is also shown an important chemical non-equilibrium since the measured electron, N and O densities are found much higher than the usual equilibrium densities generated by thermal dissociation and recombination processes. This therefore means that the energetic electron impacts play a significant role on the formation of the present non-equilibrium MW plasma.

DC-Plasma over Aqueous Solution for the Synthesis of Titanium Dioxide Nanoparticles under Pressurized Argon.

Nanomaterials that comprise titanium dioxide (TiO2) nanoparticles have received much attention owing to their wide applications; presently, the green synthesis of TiO2 nanoparticles is a developing research area. In this study, the TiO2 nanoparticles were synthesized through a DC-pulsed discharge plasma over an aqueous solution surface under a high-pressure argon environment. The titanium-rod electrode was utilized as the material source for the TiO2 nanoparticle generation. Experiments were performed at room temperature with pressurized argon at 1–4 MPa. To generate a pulse electrical discharge plasma, a DC power supply of 18.6 kV was applied. The Raman spectroscopy showed that the TiO2 nanoparticle with a brookite structure was formed dominantly. The scanning transmission electron microscopy equipped with energy dispersion spectroscopy (STEM coupled with EDS) indicated that TiO2 coated with carbon and that without carbon coating were successfully produced at the nanoscale. The process presented here is an innovative process and can update the existing information regarding the synthesis of metal-based nanoparticles using pulsed discharge plasma under an argon environment.

The electronic spectrum of the jet-cooled stibino (SbH2) free radical.

The Ã2A1-X̃2B1 electronic transition of the jet-cooled stibino (SbH2 and SbD2) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH3 or SbD3) in high pressure argon at the exit of a pulsed molecular beam valve. SbH2 exhibits only three LIF bands, assigned as 21 0, 00 0, and 20 1, with a fluorescence lifetime (τ), which decreases from ∼50 ns for 00 to <10 ns for 21. LIF transitions to the 00 (τ ∼ 2 µs), 21 (τ ∼ 400 ns), and 22 (τ ∼ 75 ns) upper vibronic states of SbD2 were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r0 ″ = 1.724(2) Å, θ0 ″ = 90.38(7)° and r0 ' = 1.693(6) Å, θ0 ' = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm-1) in SbH2 and 12 quanta (6853 cm-1) in SbD2 were measured from dispersed fluorescence spectra. All indications are that SbH2 undergoes a dissociative process at low vibrational energies in the excited electronic state.

Synthesis of Ar@C60 using molecular surgery.

Synthesis of Ar@C60 is described, using a route in which high-pressure argon filling of an open-fullerene and photochemical desulfinylation are the key steps for >95% encapsulation of the noble gas. Enrichment by recycling HPLC leads to quantitative incorporation of argon in the product endofullerene, with a mass recovery of tens of milligrams, allowing the first characterisation of fine structure in the solution 13C NMR spectrum.

Predictive analysis of surface roughness in argon-assisted EDM using semiempirical and ANN techniques

This experimentation explores the utilization of argon-assisted electrical discharge machining (AAEDM) of high-carbon high-chromium die steel. High-pressure argon gas in conventional EDM was utilized to assess the surface roughness (SR). Analysis of variance was connected to decide the critical parameters influencing SR. In this study, a mathematical model has been instigated to get to know SR by using Buckingham pi-theorem while applying the AAEDM process. The fit summary confirmed that the quadratic model is statistically appropriate, and the lack-of-fit is insignificant. Root-mean-square error and absolute standard deviation, obtained through response surface method, were also used for developing the model and for its predicting abilities through ANN. The experiment and anticipated estimates of SR during the process, obtained by dimensional analysis and ANN, were found to be in accord with each other. However, the ANN technique proved to be more fitting to the response as compared to the dimensional analysis.

Growth controlling behavior of vertically aligned MoSe2 film

Vertical layered MoSe2 nanosheets have been synthesized via rapid selenization of a magnetron sputtered Mo film with a large number of penetrating microcracks. The phase microstructure and morphologies of Mo and MoSe2 films were evaluated by X-ray diffractometer, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The results indicate that a relatively high argon pressure during the sputtering process allows Mo films to deposit with a multi-crack structure. The microcracks increase the inner surface area of Mo films and provide a rapid transmission tunnel for selenium diffusion, which allows MoSe2 nanosheets to grow vertically with a c-axis // substrate texture. The growth mechanism for vertically aligned MoSe2 films has been proposed based on the experimental results. The growth orientation of MoSe2 film can be precisely controlled by adjusting the density of Mo film precursor under the same selenization condition. These findings provide a new strategy for the preparation and application of highly orientated MoSe2 film.

First measurement of the Ar(e,e′)X cross section at Jefferson Laboratory

The success of the ambitious programs of both long- and short-baseline neutrino-oscillation experiments employing liquid-argon time-projection chambers will greatly rely on the precision with which the weak response of the argon nucleus can be estimated. In the E12-14-012 experiment at Jefferson Lab Hall A, we have studied the properties of the argon nucleus by scattering a high-quality electron beam off a high-pressure gaseous argon target. Here, we present the measured $^{40}$Ar$(e,e^{\prime})$ double differential cross section at incident electron energy $E=2.222$~GeV and scattering angle $\theta = 15.541^\circ$. The data cover a broad range of energy transfers, where quasielastic scattering and delta production are the dominant reaction mechanisms. The result for argon is compared to our previously reported cross sections for titanium and carbon, obtained in the same kinematical setup.

The high-resolution LIF spectrum of the SiCCl free radical: Probing the silicon-carbon triple bond

A rotationally resolved spectrum of a band of the A∼2Σ+ − X∼2Π electronic transition of the SiCCl free radical has been obtained for the first time. The radical was produced in an electric discharge jet using 1,1-dichlorosilacyclobutane vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the band system in the 610–550 nm region was recorded and the 2Π3/2 spin component of the 0–0 band was studied at high resolution. Rotational analysis gave the B values for the combining states and by fixing the CCl bond lengths at ab initio values we obtained r″ (SiC) = 1.692(1) Å and r' (SiC) = 1.594(1) Å. The bond lengths correspond to a silicon-carbon double bond in the ground state and an unusual SiC triple bond in the excited state. Single vibronic level emission spectra yielded the ground state bending and stretching energy levels up to energies near 5000 cm−1. These were satisfactorily fitted to a Renner-Teller model that included spin–orbit and vibrational anharmonicity effects.

High-pressure optical floating-zone growth of Li2FeSiO4 single crystals

We report the growth of mm-sized Pmnb-Li2FeSiO4 single crystals by means of the optical floating-zone method at high argon pressure and describe the conditions required for a stable growth process. The crystal structure is determined and refined by single-crystal X-ray diffraction. The lattice constants amount to a = 6.27837(3) Å, b = 10.62901(6) Å and c = 5.03099(3) Å at 100 K. In addition, we present high-resolution neutron powder diffraction data that suggest that the slight Li – Fe site exchange seems to be intrinsic to this material. High quality of the crystal is confirmed by very sharp anomalies in the static magnetic susceptibility and in the specific heat associated with the onset of long-range antiferromagnetic order at TN = 17.0(5) K and pronounced magnetic anisotropy for the three crystallographic axes. Furthermore, magnetic susceptibility excludes the presence of sizable amounts of magnetic impurity phases.

Optical measurement of the high temperature ballooning of nuclear fuel claddings.

During the last decades, several experiments revealed interesting details about the ballooning and burst of nuclear cladding tubes in accident conditions involving high temperature and high pressure. A new set of experiments was conducted at MTA EK to further improve our understanding of this phenomenon. The research goal was to determine the pressure of the burst at different temperatures. These data represent a durability and usability limit of fuel cladding tubes under loss of coolant accident conditions. A large tube furnace was fitted with two optical telescopes on opposite sides to observe the ballooning and burst of zirconium alloy fuel cladding samples. These telescopes gave an opportunity to capture the ballooning and also to use a high-speed camera to record details of the crack formation and crack propagation during the burst. A precise pressurization system was constructed to feed high-pressure argon into the samples at a given pressurization rate. The previous data were reproduced accurately in this new apparatus with further insight into the phenomena. The change in tube diameter was observed using regular HD cameras. Based on the captured images, an algorithmic method was developed to separate the contours of the cladding tubes from the background and the diameter increase was measured. It was found to be mostly uniform at lower pressures. The formation of a bulge started at 85% of actual burst pressure. Crack formation at high temperature was recorded using a high-speed camera at speeds up to 100.000 fps. The details of the planning, facility construction, and gauge calibration are detailed in this article.

High voltage insulation and gas absorption of polymers in high pressure argon and xenon gases

High pressure gas time projection chambers (HPGTPCs) are made with a variety of materials, many of which still await proper characterization in high pressure noble gas environments. As HPGTPCs increase in size toward ton-scale detectors, assemblies become larger and more complex, creating a need for detailed understanding of how structural supports and high voltage insulators behave. This includes identification of materials with predictable mechanical properties and without surface charge accumulation that may lead to field deformation or sparking. This paper explores the mechanical and electrical effects of high pressure gas environments on insulating polymers PTFE, HDPE, PEEK, POM and UHMW in argon and xenon, including studying gas absorption, swelling and high voltage insulation strength.

A novel method using MOS electronic nose and ELM for predicting postharvest quality of cherry tomato fruit treated with high pressure argon

Flavor characteristic, caused by a series of physicochemical changes, is an important part of fruit quality and freshness. The purpose of this study was to investigate the reliability and validity of using electronic nose (e-nose) technology to evaluate the quality and freshness of cherry tomatoes after high pressure argon treatments. Extreme learning machine (ELM) and Partial least squares (PLS) were applied for quality parameters prediction. The results showed that freshness of cherry tomatoes based on flavor characteristic over the entire storage time displayed four groups (fresh, acceptable, stale and very stale, respectively). High pressure argon at 0.8 MPa significantly maintained the freshness and quality of cherry tomatoes during cold storage. ELM models showed better performance than PLS models for evaluating the firmness, SSC and pH values according to their higher fitting correlation coefficients (R2 > 0.9500). The results demonstrated e-nose technology combined with ELM provided a reliable and valid method for evaluating quality and freshness of cherry tomatoes during cold storage.