Torr Pressure Research Articles

Detection of X-ray Radiations from Low Energy Focus Plasma Using Thermoluminescence Dosimeter TLD-500A

The present plasma focus device (0.1 kJ Mather type) is powered by a capacitor bank of 1 μF at 15 kV maximum charging voltage. The radiations emission was investigated using time-integrated thermoluminescence TLD-500. These detectors have been calibrated against standard X-ray machine (VIC model 4000M+) as well as standard gamma sources (Co60 and Cs137) to identify the dose from X-ray delivered to the dosimeter. It is found that from the results of time-integrated detectors, the maximum radiation dose obtained at 0.1 Torr pressure and charging voltage 15 kV for different gases. At this pressure, the device favours a proper discharge dynamics so as to form a strong pinching i.e. transferring maximum energy into plasma.

Numerical analysis of ion-funnel transmission efficiency in an API-MS system with a continuum/microscopic approach.

A multi-step numerical approach is used to analyze the efficiency of an ion-funnel to transport ions over a wide range of m/z. A continuum approach based on the solution of the Navier-Stokes equations is applied to model the gas flow through a capillary connecting the atmospheric and subatmospheric sections of a mass spectrometer. A microscopic, fully kinetic approach based on the solution of the Boltzmann equation is used to examine the ion and gas transport through an ion-funnel kept at a 0.1-3 Torr pressure to the quadrupole section kept at a 0.01 Torr pressure. In addition to aerodynamic drag, the developed approach takes into account the combined effect of the DC field driving the ions downstream toward the funnel exit, the rf field confining the ions in radial direction, and the space charge causing ion repulsion. The sensitivity of the ion transmission to the gas pressure in the ion-funnel, the rf, and the total ion current injected to the funnel from capillary nozzle is shown. Graphical Abstract ᅟ.

Studies on AC Response of MPc Thin Films Molecular Materials

GRAPHICAL ABSTRACT

Improving Bond Strength at Propellant–Liner Interfaces

In solid rocket motors, a strong bond at the propellant–liner interface ensures that the propellant functions as designed. If the interface degums, the propellant burn surface area will change and the performance of internal ballistics will be adversely affected. In this study, two cases of motor failure are considered to investigate methods for improving the bond strength between the propellant grain and the liner interface, with the aim of achieving a tensile strength exceeding the requirement. Hydroxyl-terminated polybutadiene was used as the liner material. This hydroxyl-terminated-polybutadiene-based material was conditioned and processed under the conditions of 5–20 torr pressure and 60–70°C temperature. Further, toluene diisocyanate was considered as the hardener and its contents were increased in the liner by 0 (i.e., original content), 2, 5, 10, and 15% to obtain diisocyanate NCO/OH equivalence ratios of 1.035, 1.057, 1.087, 1.144, and 1.187, respectively. Thereafter, bond strength tests and analyses were conducted. The tensile strength gradually increased with increasing toluene diisocyanate content in the liner. The bond strength was found to increase after improving the liner, performing hydroxyl-terminated polybutadiene heating and vacuum extraction pretreatments, and increasing the toluene diisocyanate content by 10%.

Determining the microwave coupling and operational efficiencies of a microwave plasma assisted chemical vapor deposition reactor under high pressure diamond synthesis operating conditions.

The microwave coupling efficiency of the 2.45 GHz, microwave plasma assisted diamond synthesis process is investigated by experimentally measuring the performance of a specific single mode excited, internally tuned microwave plasma reactor. Plasma reactor coupling efficiencies (η) > 90% are achieved over the entire 100-260 Torr pressure range and 1.5-2.4 kW input power diamond synthesis regime. When operating at a specific experimental operating condition, small additional internal tuning adjustments can be made to achieve η > 98%. When the plasma reactor has low empty cavity losses, i.e., the empty cavity quality factor is >1500, then overall microwave discharge coupling efficiencies (η(coup)) of >94% can be achieved. A large, safe, and efficient experimental operating regime is identified. Both substrate hot spots and the formation of microwave plasmoids are eliminated when operating within this regime. This investigation suggests that both the reactor design and the reactor process operation must be considered when attempting to lower diamond synthesis electrical energy costs while still enabling a very versatile and flexible operation performance.

Structural, Field Emission and Ammonia Gas Sensing Properties of Multiwalled Carbon Nanotube-Graphene Like Hybrid Films Deposited by Microwave Plasma Enhanced Chemical Vapor Deposition Technique

This paper reports the direct deposition of multiwalled carbon nanotube (MWCNT)-graphene like hybrid films on nickel substrate using a 2.45 GHz microwave plasma enhanced chemical vapor deposition (MW PECVD) system in the temperature range of 500-700 degrees C at 20 Torr pressure. The films have been characterized by Raman spectra, high resolution transmission electron microscope (HRTEM), scanning electron microscope, high resolution X-ray diffraction and contact angle measurement. Raman spectroscopy and HRTEM reveal the formation of MWCNT and graphene like hybrid carbon sheet structures. The effect of processing temperature on the field emission properties of MWCNT-graphene like hybrid films has been investigated. Field emission measurement reveals that the turn-on field decrease and the emission current density increase with the increase of deposition temperature. The rambutan structure of MWCNT formed at 700 degrees C is responsible for the improvement in the field emission properties. The film deposited at 700 degrees C shows fast response and recovery time of 40 and 96 s, respectively, for ammonia gas sensing due to the high surface area of the film. It has also been found that the hydrophobic surface of the film helps to perform the gas sensing in the humid environment.

Unexpected Spin-Crossover and a Low-Pressure Phase Change in an Iron(II)/Dipyrazolylpyridine Complex Exhibiting a High-Spin Jahn–Teller Distortion

The synthesis of 4-methyl-2,6-di(pyrazol-1-yl)pyridine (L) and four salts of [FeL2]X2 (X(-) = BF4(-), 1; X(-) = ClO4(-), 2; X(-) = PF6(-), 3; X(-) = CF3SO3(-), 4) are reported. Powder samples of 1 and 2 both exhibit abrupt, hysteretic spin-state transitions on cooling, with T1/2↓ = 204 and T1/2↑ = 209 K (1), and T1/2↓ = 175 and T1/2↑ = 193 K (2). The 18 K thermal hysteresis loop for 2 is unusually wide for a complex of this type. Single crystal structures of 2 show it to exhibit a Jahn-Teller-distorted six-coordinate geometry in its high-spin state, which would normally inhibit spin-crossover. Bulk samples of 1 and 2 are isostructural by X-ray powder diffraction, and undergo a crystallographic phase change during their spin-transitions. At temperatures below T1/2, exposing both compounds to 10(-5) Torr pressure inside the powder diffractometer causes a reversible transformation back to the high-temperature crystal phase. Consideration of thermodynamic data implies this cannot be accompanied by a low → high spin-state change, however. Both compounds also exhibit the LIESST effect, with 2 exhibiting an unusually high T(LIESST) of 112 K. The salts 3 and 4 are respectively high-spin and low-spin between 3 and 300 K, with crystalline 3 exhibiting a more pronounced version of the same Jahn-Teller distortion.

Kinetics of Several Oxygen-Containing Carbon-Centered Free Radical Reactions with Nitric Oxide.

Kinetics of four carbon-centered, oxygen-containing free radical reactions with nitric oxide (NO) were investigated as a function of temperature at a few Torr pressure of helium, employing flow tube reactors coupled to a laser-photolysis/resonance-gas-discharge-lamp photoionization mass spectrometer (LP-RPIMS). Rate coefficients were directly determined from radical (R) decay signals under pseudo-first-order conditions ([R]0 ≪ [NO]). The obtained rate coefficients showed negative temperature dependences, typical for a radical-radical association process, and can be represented by the following parametrizations (all in units of cm(3) molecule(-1) s(-1)): k(CH2OH + NO) = (4.76 × 10(-21)) × (T/300 K)(15.92) × exp[50700/(RT)] (T = 266-363 K, p = 0.79-3.44 Torr); k(CH3CHOH + NO) = (1.27 × 10(-16)) × (T/300 K)(6.81) × exp[28700/(RT)] (T = 241-363 K, p = 0.52-3.43 Torr); k(CH3OCH2 + NO) = (3.58 ± 0.12) × 10(-12) × (T/300 K)(-3.17±0.14) (T = 221-363 K, p = 0.50-0.80 Torr); k(T)3 = 9.62 × 10(-11) × (T/300 K)(-5.99) × exp[-7100/(RT)] (T = 221-473 K, p = 1.41-2.95 Torr), with the uncertainties given as standard errors of the fits and the overall uncertainties estimated as ±20%. The rate of CH3OCH2 + NO reaction was measured in two density ranges due to its observed considerable pressure dependence, which was not found in the studied hydroxyalkyl reactions. In addition, the CH3CO + NO rate coefficient was determined at two temperatures resulting in k298K(CH3CO + NO) = (5.6 ± 2.8) × 10(-13) cm(3) molecule(-1) s(-1). No products were found during these experiments, reasons for which are briefly discussed.

Hydrogenated silicon oxycarbonitride films. Part III. Thermodynamic modeling of the Si-C-N-O-H system

The thermodynamic modeling of the deposition of the condensed phase of a complex composition has been performed in the Si-C-N-O-H system in the broad temperature range of 300–1300 K under total pressure Ptotal0 = 6−7×10−2 Torr and residual air pressure in reactor Pres = 5 × 10−3 Torr using the initial gas mixtures of organosilicon compound, hexamethyldisilazane (HMDS), with nitrogen, oxygen, air mixture (O2 + 4N2), and a variable mixture of oxygen with nitrogen (O2 + xN2). The temperature boundaries of multiphase ranges, where one can anticipate the deposition of silicon oxycarbonitride, silicon oxycarbides, and silicon oxynitride, have been determined.

Reaction of CO with Preadsorbed Oxygen on Low-Index Copper Surfaces: An Ambient Pressure X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Study

The reaction of CO with chemisorbed oxygen on three low-index faces of copper was studied using ambient pressure X-ray photoelectron spectroscopy (XPS) and high-pressure scanning tunneling microscopy. At room temperature, the chemisorbed oxide can be removed by reaction with gas-phase CO in the 0.01–0.20 Torr pressure range. The reaction rates were determined by measuring the XPS peak intensities of O and CO as a function of time, pressure, and temperature. On Cu(111) the rate was found to be one order of magnitude faster than that on Cu(100) and two orders of magnitude faster than that on Cu(110). The apparent activation energies for CO oxidation were measured as 0.24 eV for O/Cu(111), 0.29 eV for O/Cu(100), and 0.51 eV for O/Cu(110) in the temperature range between 298 and 473 K. These energies are correlated to the oxygen binding energies on each surface.

Catalytic Decomposition of Methane and Ethylene into the Carbon and Hydrogen

The role of nickel as catalyst on the conversion of methane and ethylene in a gas phase flow reactor in the absence of oxygen is studied. In this study, nickel in its different forms is used as catalyst. The role of pressure, flow rate, and temperature on the conversion of feed gases is investigated. The experiments have been carried out in the presence and absence of the catalysts to measure the efficiency of the catalyst activity towards the conversion of the feed gases. Major products have been found to be carbon as soot or coke and hydrogen when methane is used as feed gas. Up to 97% conversion of the ethylene to methane, ethane, hydrogen, and carbon soot were achieved on the surface of the honeycomb nickel catalyst at 900 ± 10 K and 415 ± 5 Torr pressure, while the conversion of methane to hydrogen and carbon on the surface of NiO/SiO2 catalyst was found to be up to 36% at 930 ± 10 K and 490 ± 5 Torr pressure with no sign of C2 or C3 formation. The carbon buildup on the surface of the prepared catalysts is also investigated.

Synthesis, structural and field emission properties of multiwall carbon nanotube-graphene-like nanocarbon hybrid films grown by microwave plasma enhanced chemical vapor deposition

Multiwall carbon nanotube (MWCNT)-graphene-like nanocarbon hybrid films were directly deposited on nickel substrate without any pre-treatment in a single-step by microwave plasma enhanced chemical vapor deposition (MW PECVD) technique at 600 °C. The effects of hydrogen partial pressure on the growth of MWCNT-graphene-like nanocarbon hybrid films and their structural, morphological and field emission properties were investigated. High resolution scanning electron microscope revealed MWCNT structure. High resolution transmission electron microscope images and Raman spectra revealed graphene-like nanocarbon film. Raman spectra showed 2D, G, D and D + G peaks at approximately 2690, 1590, 1350 and 2930 cm−1, respectively. The minimum threshold field for electron emission was found to be 3.6 V/μm corresponding to 1 μA/cm2 current density for the MWCNT-graphene-like nanocarbon hybrid film deposited at 20 Torr pressure whereas the maximum current density of 0.12 mA/cm2 and field enhancement factor of ∼3356 was obtained for the sample deposited at 5 Torr pressure.

Enhanced simulation of an RF ion funnel including gas turbulence.

Electrodynamic ion funnels are used to enhance the transmission of ions in electrospray-based ion injection systems in 0.1 to 30 Torr pressure range. Jet disrupters are commonly employed to prevent droplets and high pressure jets from entering subsequent vacuum regions. This study presents the simulation and testing of an ion funnel containing a jet disrupter using computational fluid dynamics (CFD) and SIMION ion trajectory simulations. Traditional modeling approaches have utilized approximations for the bulk fluid flow fields without including the time-varying nature of the turbulent flow present in the system, thus yielding idealized results. In this study, the fluid flow fields are calculated using CFD. In an effort to include time dependence, a random velocity vector, whose magnitude is proportional to the square root of the turbulence kinetic energy, was calculated at each time step and added to the velocity of the background gas. These simulations predicted that the transmitted ion current is effectively modulated by the variation of the jet disrupter voltage. The addition of the random velocity vector produced results that closely matched the experiments. The simulations yielded the dependence of the transmission on the jet disrupter voltage, and the voltage necessary for maximum ion throughput was accurately predicted. In addition, the magnitude of the predicted transmission closely matched that of the experimental results. This modeling approach could be extended to similar ion transport and filtering systems in which the effects of turbulent fluid flow cannot be ignored.

Catalyst-free vapour–solid technique for deposition of Bi2Te3and Bi2Se3nanowires/nanobelts with topological insulator properties

We present a simple two-stage vapour-solid synthesis method for the growth of bismuth chalcogenide (Bi2Te3, Bi2Se3) topological insulator nanowires/nanobelts by using Bi2Se3 or Bi2Te3 powders as source materials. During the first stage of the synthesis process nanoplateteles, serving as "catalysts" for further nanowire/nanobelt growth, are formed. At a second stage of the synthesis, the introduction of a N2 flow at 35 Torr pressure in the chamber induces the formation of free standing nanowires/nanobelts. The synthesised nanostructures demonstrate a layered single-crystalline structure and Bi : Se and Bi : Te ratios 40 : 60 at% for both Bi2Se3 and Bi2Te3 nanowires/nanobelts. The presence of Shubnikov de Haas oscillations in the longitudinal magneto-resistance of the nanowires/nanobelts and their specific angular dependence confirms the existence of 2D topological surface states in the synthesised nanostructures.

Measurement of the branching fractions and lifetime of the5D5/2level ofBa+

We present a measurement of the branching fractions for decay from the long-lived $5D_{5/2}$ level in \Ba. The branching fraction for decay into the $6S_{1/2}$ ground state was found to be $0.846(25)_{\mathrm{stat}}(4)_{\mathrm{sys}}$. We also report an improved measurement of the $5D_{5/2}$ lifetime, $\tau_{5D_{5/2}}=31.2(0.9)$~s. Together these measurements provide the first experimental determination of transition rates for decay out of the $5D_{5/2}$ level. The low ($<7 \times 10^{-12}$~Torr) pressure in the ion trap in which these measurements were made simplified data acquisition and analysis. Comparison of the experimental results with theoretical predictions of the transition rates shows good agreement.

Effect of the Gas Pressure and the Charging Voltage on the Plasma Current Density Distribution in Conical Z Pinch Plasma Thruster

Plasma current density is measured inside the chamber of a conical z-pinch device using helium as the working gas. The gas pressure and the charging voltage are the major factors affecting the magnitude of the plasma current, pinching time, and the pinch duration. Calculations are carried out at different radial positions between the pin electrode and the chamber wall. The experimental results show that the current density reaches a maximum value of about 8.7 kA/cm2 above the pin electrode for 7 kV charging voltage and 1 Torr pressure, and this value decreases toward the chamber wall. The gas pressure has a significant effect on the current density at radial position of 0.5 cm from the pin indicating that the plasma could not be confined to a radius less than that. This result is confirmed by the recorded plasma current signal in which one peak only is recorded at the pin and two or three are recorded near the wall as a result of sequent compression and expansion. The experimental results show that a time of 2–2.5 μs is needed for the pinch to occur. Increasing the discharge voltage decreases both pinch time and the pinch duration due to the faster confinement process.

Ion Energy Threshold in Low-Temperature Silicon Epitaxy for Thin-Film Crystalline Photovoltaics

Plasma-enhanced chemical vapor deposition (PECVD) enables epitaxial silicon deposition for up to several micrometers and at low temperatures (as low as 150 °C). We present herein a detailed study of the effect of ion energy at high (above 2 torr) and low (below 1 torr) pressure, where the plasma and surface reactions are expected to be different, i.e., driven, respectively, by high-order and low-order silane precursors. We find a sharp energy threshold at low pressure, above which no epitaxy can be obtained, but this threshold is relaxed at high pressure. The occurrence of epitaxy breakdown is studied and compared in detail for these two different pressure regimes.

Effect of annealing with pressure on tungsten film properties fabricated by atmospheric plasma spray

In this study, the effects of various annealing conditions on tungsten film fabricated by atmospheric plasma spraying (APS) were studied to analyze the APS tungsten film and an adequate strategy for the improvement of the mechanical properties of the tungsten film. In general, the use of the APS method to create tungsten films results in splat boundaries in an oxidized state not unlike semi-cracks. We therefore conducted vacuum annealing of the tungsten film at 800 °C and 950 °C under less than 0.1 Torr pressure to strengthen the binding force between splats. Additionally, we conducted press annealing in order to achieve a more dramatic improvement. The micro-hardness of the as-sprayed tungsten film, the vacuum-annealed tungsten film, and the press-annealed tungsten film were 1.55, 1.52, and 2.19 GPa respectively. By utilizing analysis methods such as electron back-scatter diffraction, scanning electron microscopy, Raman spectroscopy, and nano-indentation, we found that filling the gap between the splats, while eliminating the oxides, played a critical role in enhancing the mechanical properties of the tungsten film fabricated by means of the APS method.

Influence of magnetic field on laser-produced barium plasmas: Spectral and dynamic behaviour of neutral and ionic species

The expansion dynamics and spectral behaviour of plasma produced by a Nd:YAG laser (λ = 1.064 μm, pulse width: 8 ns) from barium target and expanding in 0.45 T transverse magnetic field in vacuum (10−5 Torr pressure) are investigated using time-of-flight optical emission spectroscopy. The experiments are carried out at various laser fluences from 12 to 31 J/cm2. The temporal profiles of neutral (Ba I 553.5 and 577.7 nm) lines are temporally broadened, while that of ionic (Ba II 413.0 and 455.4 nm) lines show strong confinement in the presence of a magnetic field. In the absence of magnetic field, the temporal profile of Ba I 553.5 nm is exactly reproduced by fitting with two Shifted Maxwell Boltzmann (SMB) Distribution components, while in the presence of a magnetic field the profile could only be fitted with three components. The field enhanced and field induced SMB components of neutral profile are correlated with populations of ground state, metastable states, and long-lived Rydberg states present in the barium plasma, while SMB components of ionic lines are explained on the basis of the presence of super-elastic collisions among the excited species in the plasma. The spatial variation of electron temperature and temporal variation of electron density are deduced and correlated to the different collisional processes in the barium plasma. The ionic profiles show efficient confinement in the presence of a magnetic field at higher fluences.

Surface structure and chemistry of Pt/Cu/Pt(1 1 1) near surface alloy model catalyst in CO

Near surface alloy (NSA) model catalyst Pt/Cu/Pt(111) was prepared on Pt(111) through a controlled vapor deposition of Cu atoms. Different coordination environments of Pt atoms of the topmost Pt layer with the underneath Cu atoms in the subsurface result in different local electronic structures of surface Pt atoms. Surface structure and chemistry of the NAS model catalyst in Torr pressure of CO were studied with high pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In Torr pressure of CO, the topmost Pt layer of Pt/Cu/Pt(111) is restructured to thin nanoclusters with size of about 1nm. Photoemission feature of O 1s of CO on Pt/Cu/Pt(111) suggests CO adsorbed on both edge and surface of these formed nanoclusters. This surface is active for CO oxidation. Atomic layers of carbon are formed on Pt/Cu/Pt(111) at 573K in 2Torr of CO.