Gas Inlet System Research Articles

Thermogravimetric study of metal–organic precursors and their suitability for hybrid molecular beam epitaxy

Although metal–organic (MO) precursors are widely used in technologically relevant deposition techniques, reports on their temperature-dependent evaporation and decomposition behaviors are scarce. Here, MO precursors of the metals Ti, V, Al, Hf, Zr, Ge, Ta, and Pt were subjected to thermogravimetric analysis to experimentally determine their vapor pressure curves and to gain insight into their temperature-dependent decomposition kinetics. Benzoic acid was used as a calibration standard and vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The obtained data is used to discuss the suitability of these MO precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular. All MOs, except for Ta- and one Ti-based MOs, were deemed suitable for gas inlet systems. The Ta-based MO demonstrated suitability for an effusion cell, while all MOs showed compatibility with cracker usage.Graphical

An innovative gas inlet design in a microwave plasma chemical vapor deposition chamber for high-quality, high-speed, and high-efficiency diamond growth

A novel design of the gas inlet system in a diamond microwave plasma chemical vapor deposition growth chamber has been reported in this paper. The design is targeting for high-quality, high-speed, and high-efficiency diamond material fabrication. By introducing a gas inlet hole into the susceptor, we expand the ways of gas introduction for diamond growth. After extensive numerical and experimental investigation, we have found that the introduction of methane and doping gas inlet from the hole of below while the hydrogen from the top is feasible for realizing the target. The growth and doping species could be confined around the substrate, making efficient usage of the precursors. The plasma state change caused by the difference of the gas inlet modes has been ascribed to the resulted gas distribution in the chamber. The measured growth rate has been increased to 32 μm h−1, which is 16 times higher than traditional gas inlet configuration. Meanwhile, a large improvement of the nitrogen doping concentration has been achieved. Besides, with the increase of growth rate and nitrogen incorporation efficiency, the crystal quality and surface morphology keep in an acceptable degree. In this mode, the dual gas flow system can perfectly solve the contradiction among the crystal quality, growth rate, and doping efficiency, commonly existing during the material fabrication process, the chamber contamination could be significantly suppressed due to the constrained distribution of methyl and doping species, making the fabrication cost much lower. The results of repetitive experiments indicate that other residual impurities present in the chamber of microwave plasma chemical vapor deposition could likely regulate the threshold concentration of nitrogen required for accelerating the growth rate during the nitrogen doped diamond growth, which have a significant effect on the diamond growth.

A rapid high‐precision analytical method for triple oxygen isotope analysis of CO2 gas using tunable infrared laser direct absorption spectroscopy

RationaleThe simultaneous analysis of the three stable isotopes of oxygen—triple oxygen isotope analysis—has become an important analytical technique in natural sciences. Determination of the abundance of the rare 17O isotope in CO2 gas using magnetic sector isotope ratio mass spectrometry is complicated by the isobaric interference of 17O by 13C (13C16O16O and 12C16O17O, both have mass 45 amu). A number of analytical techniques have been used to measure the 17O/16O ratio of CO2 gas. They either are time consuming and technically challenging or have limited precision. A rapid and precise alternative to the available analytical methods is desirable.MethodsWe present the results of triple oxygen isotope analyses using an Aerodyne tunable infrared laser direct absorption spectroscopy (TILDAS) CO2 analyzer configured for 16O, 17O, and 18O combined with a custom gas inlet system. We evaluate the sensitivity of our results to a number of parameters. CO2 samples with a wide range of δ18O values (from −9.28‰ to 39.56‰) were measured and compared to results using the well‐established fluorination‐gas source mass spectrometry method.ResultsThe TILDAS system has a precision (standard error, 2σ) of better than ±0.03‰ for δ18O and ±10 per meg for Δ′17O values, equivalent to the precision of previous analytical methods. Samples as small as 3 μmol CO2 (equivalent to 300 μg CaCO3) can be analyzed with a total analysis time of ~30 min.ConclusionsWe have successfully developed an analytical technique for the simultaneous determination of the δ17O and δ18O values of CO2 gas. The precision is equal to or better than that of existing techniques, with no additional chemical treatments required. Analysis time is rapid, and the system is easily automated so that large numbers of samples can be analyzed with minimal effort.

Helium Suicide, a Rapid and Painless Asphyxia: Toxicological Findings

Suicide by helium inhalation has become increasingly common in the last few decades in Europe and the US because it produces a quick and painless death. Inhaled-gas suicides can easily be assessed through death scene investigation and autopsy. However, helium is a colorless and odorless inert gas that unfortunately cannot be detected using standard toxicological analysis. A successful gas analysis was performed following the suicide of a 17-year-old female. For the detection of helium, central/peripheral blood samples and gaseous samples from the esophagus, stomach, and upper and lower respiratory airways (from the trachea and the primary left and right bronchia) were collected with a gastight syringe, ensuring minimal dilution. Qualitative analyses were positive in all gaseous samples. Quantitative analyses were performed using a special gas-inlet system with a vacuum by which the sample can be transferred to a mass spectrometer, reducing the risk of contamination. Helium concentrations were 20.16% from the trachea, 12.33% from the right lung, and 1.5% from the stomach. Based on the high levels of helium, the cause and manner of death were assessed as asphyxia suicide by inhalation of helium. Therefore, toxicological analyses should always be applied in order to gain evidence of inhaled gas in gaseous samples.

Impurity temperatures measured via line shape analysis in the island scrape-off-layer of Wendelstein 7-X

Impurity temperatures have been determined by a spectroscopic line shape analysis for several species in the divertor scrape-off-layer of the stellarator Wendelstein 7-X (W7-X). Examples include spectral lines from intrinsic elements (C II and C III, He I) as well as from seeded impurities (Ar II, N II) through the divertor gas inlet system. Both Doppler broadening and Zeeman splitting are found to contribute significantly to the impurity line shapes. Zeeman splitting arises due to the confining magnetic field in W7-X and complicates the line shape appearance. By attributing Doppler widths to each of the various Zeeman components, however, we demonstrate that reliable ion temperature values can be derived provided that the presence of the magnetic field is properly accounted for. The spectrally highly resolved lines are analyzed by means of a multi-parameter, least-squares fit routine, which accounts for Doppler broadening, Zeeman splitting, as well as the instrumental broadening of the spectrometer used to measure the spectral line shapes. By spectral fitting of the Zeeman features, it is also found that the line shape analysis can yield values for the local magnetic field, which can be used to localize the impurity radiation approximately provided that the line emission is dominant in a small area intersected by the lines of sight of the spectrometer.

In situ synchrotron x-ray diffraction studies monitoring mechanochemical reactions of hard materials: Challenges and limitations.

In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, γ-AlOOH, to corundum, α-Al2O3, was chosen as a model system. The modifications of the mill's clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shakermill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup.

The Polaris Linear Plasma Device

We report the construction of Polaris, a new linear plasma device with an axial magnetic field dedicated to research and education at the American University of Beirut in Lebanon. The goal is to initiate the investigation of topics related to basic magnetized plasma physics and nuclear fusion. We discuss the novel technical solutions found to set up various components of the device. We start with the magnetic coils where we use power cables to generate the required axial magnetic field. They are included in a stainless steel case for water-cooling. Then, we present the vacuum and the gas inlet systems with which we control the neutral pressure. The way we manufacture the water-cooled radio frequency (RF) antenna allows the production of a variety of designs. Polaris is thus built to operate in a steady state. Using a reciprocating Langmuir probe, we determine the plasma properties as a function of the various control parameters. As the plasma remains in the “blue mode,” we show that the increase in the main magnetic field leads to an increase in the density but a decrease in the plasma temperature. The increase in neutral pressure yields the same effects. However, the increase in RF power leads to an increase in both density and temperature. Finally, plans for future investigations are briefly described.

Evolved gas analysis-mass spectrometry in an oxidative atmosphere using a temperature-programmable furnace-type pyrolyzer

Evolved gas analysis-mass spectrometry (EGA-MS) has been used to characterize the effect of heating a material in an oxidative or non-oxidative environment. Measurements in an oxidative environment are usually done by using the mixture of air and helium (He) as the carrier gas; however, ionization efficiency of evolved gases in a mass detector (MSD) decreases in such an environment, resulting in a corresponding decrease in sensitivity. The drop in sensitivity can be reduced by diluting the air in the carrier gas with He after evolving gases from a sample and before the evolved gases flow to the MSD. This study reports on a simple modification of the gas inlet system so that experiments requiring oxidative conditions in an air atmosphere can be routinely performed without loss of the MSD sensitivity. The impact of using this modification on the data is demonstrated using polystyrene (PS) as a test sample. EGA curves were acquired in two flow configurations: (1) adding He to the carrier gas immediately after the furnace, which reduces the concentration of nitrogen and oxygen in the carrier gas; thus, minimizing the quenching of the ionization and the associated decrease in signal-to-noise ratio (S/N) and (2) the standard configuration which simply uses a mixture of He and air as the carrier gas. Data obtained using the modified method had a much high S/N than that obtained using a gas mixture (He and air or He and oxygen) as a carrier gas. The RSD (n = 5) values for the peak area and the peak temperature of the EGA curve of PS were 1.6 and 0.60 % respectively, and these values were comparable with those obtained using a He carrier gas. The modified gas inlet system was also applied to the analysis of isotactic polypropylene.

Adoption of the ASDEX Upgrade pumping to hydrogen released by an in-vessel cryopump

Detached divertor scenarios at ASDEX Upgrade (AUG) need high gas fluxes, which are mainly pumped with the gas binding in-vessel cryopump (CP). To cope with the large quantities of hydrogen released from the CP during regeneration, a hydrogen compatible pumping system (HCPS), which is built to comply with safety regulations for explosion protection, has been built up in parallel to the already existing gas transfer pumping system (TPS). The amount of gas injected in the vacuum vessel (VV) is limited by an additional volume added to the gas inlet system. A fully automated procedure has been implemented for comprise with safety regulations. This includes daily tests of the components and communications with other relevant systems.

Express Analysis of Natural Gas and Gas Mixtures Using a Portable Raman Spectrometer Coupled to a Hollow Photon-Crystal Light Guide

A means of express gas analysis is developed that meets all necessary requirements for determining the partial composition of natural gas and derivatives of gas mixtures using a portable Raman spectrometer with an excitation wavelength of 532 nm, rigidly coupled to a hollow crystalline light guide and equipped with a gas inlet system.

Residual gas analysis in vacuum insulation panel (VIP) with glass fiber core and investigation of getter for VIP

Vacuum insulation panel (VIP) based on glass fiber core material has attracted considerable attention in building insulation due to lower core material cost than fumed silica. The insulation performance and service life of VIP are significantly dependent on the residual gas pressure and gas composition in VIP. Residual gas composition is measured using a newly-developed test apparatus that contains quadrupole mass spectrometer (QMS) and gas inlet system (GIS) in this paper. The results indicate that the main residual gases are nitrogen (N2), oxygen (O2) and water vapor (H2O) in the initial stage of VIP with thermal conductivity 1.52 mW m−1 K−1, while nitrogen (N2), oxygen (O2) hydrogen (H2) and water vapor (H2O) become the main residual gases after two years with thermal conductivity 6.80 mW m−1 K−1. Correspondingly, a composite getter for VIP is investigated, sorption capacities of which for hydrogen (H2), oxygen (O2) and water vapor (H2O) are measured in this paper. It is predicted that the central thermal conductivity of VIP with getter increases to 15 mW m−1 K−1 after 25 years, which is one step towards a future recommendation for building sectors.

Negative Ion Formation by Thermal Surface Ionization of Sulfur Dioxide.

The generation of negative ions from SO2 in the gas phase was studied using the thermal surface ionization method. Six anion types were measured: O- , S- , SO- , and SO2- and anions with m/z=96 and m/z=128. The most abundant anion formed was S- and the formation routes are discussed for each of the six anions. O- , S- , and SO- are formed via dissociative electron attachment to the molecule, whereas the generation of SO2- and anions with m/z=96 and m/z=128 are probably associated with the formation of H2 SO4 in the gas inlet system and the ion source. Using statistical thermodynamics the dissociation temperatures of SO2 and SO in the gas phase are calculated and values of above 1800 °C are obtained for both molecules. We also estimated the optimal filament temperatures for the formation of all anions measured, indicating that for SO2 the optimal temperature is related to the electron affinity of the molecules: the optimal temperature increases with decreasing value of the electron affinity for the molecule corresponding to the respective anion.

The gas supply and gas inlet control systems of the fusion experiment Wendelstein 7-X

After a detailed commissioning process the fusion experiment Wendelstein 7-X (W7-X) was ready to operate in December 2015. The gas supply system and the gas inlet system are two important technical systems of the W7-X device, offering a wide spectrum of functions for plasma vessel conditioning, and plasma operation as well as for diagnostic and calibration purposes.A brief overview is given of the structure of both gas supply and gas inlet systems. The design of the control systems of the gas supply and the gas inlet are introduced and described. The application of the W7-X gas inlet system is explained during an experiment discharge.

Upgrading the ECR ion source within FAMA

Recent upgrading of the Facility for Modification and Analysis of Materials with Ion Beams - FAMA, in the Laboratory of Physics of the Vinca Institute of Nuclear Sciences, included the modernization of its electron cyclotron resonance ion source. Since the old ion source was being extensively used for more than 15 years for production of multiply charged ions from gases and solid substances, its complete reconstruction was needed. The main goal was to reconstruct its plasma and injection chambers and magnetic structure, and thus intensify the production of multiply charged ions. Also, it was decided to refurbish its major subsystems - the vacuum system, the microwave system, the gas inlet system, the solid substance inlet system, and the control system. All these improvements have resulted in a substantial increase of ion beam currents, especially in the case of high charge states, with the operation of the ion source proven to be stable and reproducible.

Development of a gas-inlet system into the ion source of an atom injector of Globus-M tokamak and the optimization of the atomic beam parameters

A new gas-inlet system in the gas-discharge chamber of an ion source has been developed that makes it possible to adjust the arc discharge burning mode and the parameters of the plasma ion emitter. The measurements of the main electrotechnical parameters of the ion source and signals of secondary-emission probes have been performed. Based on the obtained data, the profile of power distribution in a beam has been restored. The optimum form of the control signal for the gas inlet valve of the atom injector of the spherical Globus-M tokamak has been selected.

Status and perspectives of the ASDEX Upgrade gas inlet system

Installed in the late 1980s the gas inlet system of ASDEX Upgrade was state of the art at the time of commissioning. However, after more than 20 years of operation a redesign was needed to take the growing complexity of experimental scenarios into account and to replace out-dated components.A conceptual design based on a study of operational requirements as well as available resources was developed and the gas inlet system was renewed step by step during planned maintenance shutdowns of AUG over the last years. The improvement comprises the building of a gas supply station, construction of a system for the gas assignment, relocation of the operational gas inlet and inside-vessel gas guiding as well as a redesign of the communication with the control system. Since the campaign 2014 the renewed system is in routine operation.

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings based on the carbon-13 isotope breath test has been designed and constructed. Important stages of the work included (i) calculating a low-aberration mass analyzer, (ii) manufacturing and testing special gas inlet system, and (iii) creating a small-size collector of ions. The proposed instrument ensures 13C/12C isotopic ratio measurement to within 1.7‰ (pro mille) accuracy, which corresponds to requirements for a diagnostic tool. Preliminary medical testing showed that the mass spectrometer is applicable to practical diagnostics. The instrument is also capable of measuring isotopic ratios of other light elements, including N, O, B (for BF2+ ions), Ar, Cl, and S.

Pulsed rotating supersonic source for merged molecular beams

We describe a pulsed rotating supersonic beam source, evolved from an ancestral device [M. Gupta and D. Herschbach, J. Phys. Chem. A 105, 1626 (2001)]. The beam emerges from a nozzle near the tip of a hollow rotor which can be spun at high-speed to shift the molecular velocity distribution downward or upward over a wide range. Here we consider mostly the slowing mode. Introducing a pulsed gas inlet system, cryocooling, and a shutter gate eliminated the main handicap of the original device in which continuous gas flow imposed high background pressure. The new version provides intense pulses, of duration 0.1-0.6 ms (depending on rotor speed) and containing ∼10(12) molecules at lab speeds as low as 35 m/s and ∼10(15) molecules at 400 m∕s. Beams of any molecule available as a gas can be slowed (or speeded); e.g., we have produced slow and fast beams of rare gases, O(2), Cl(2), NO(2), NH(3), and SF(6). For collision experiments, the ability to scan the beam speed by merely adjusting the rotor is especially advantageous when using two merged beams. By closely matching the beam speeds, very low relative collision energies can be attained without making either beam very slow.

ECR-Ectching of Submicron and Nanometer Sized 3C-SiC(100) Mesa Structures

Anisotropic etching processes for mesa structure formation using fluorinated plasma atmospheres in an electron cyclotron resonance (ECR) plasma etcher were studied on Novasic substrates with 10 µm thick 3C-SiC(100) grown on Si(100). To achieve reasonable etching rates, a special gas inlet system suitable for injecting SF6 into the high density downstream Ar ECR plasma was designed. The influence of the etching mask material on the sidewall morphology was investigated. Masking materials with small grain sizes are preferable to achieve a desired shape. The evolution of the mesa form was investigated in dependence on the gas composition, the applied bias, the pressure and the composition of the gas atmosphere. The achieved sidewall slope was 84.5 deg. The aspect ratios of the fabricated structures in the developed residue free ECR plasma etching process were between 5 and 10. Mesa structures aligned to [100] and [110] directions were fabricated.

Piezo-valve controller for the gas inlet system of the fusion experiment Wendelstein 7-X

The gas inlet system of the fusion experiment Wendelstein 7-X (W7-X) comprises eleven gas inlets around the torus for controlled provision with working gases in the torus. This fast gas inlet system is designed for different operating modes of W7-X, from short discharges with only a few seconds durations to steady state plasma operation with operation time of 30min. Piezo valves of type FGIS (FGIS: Fast Gas Injection System from General Atomics) are used as actuators for the W7-X gas inlet system.The design of an intelligent control unit for the FGIS Piezo valves are introduced and discussed. The integration of the valve controller units into the W7-X control component “W7-X gas inlet” and their planned application in an experiment run is described.