Small Amount Of Argon Research Articles

Particle in cell/Monte Carlo collision analysis of the problem of identification of impurities in the gas by the plasma electron spectroscopy method

The work deals with the Particle in Cell/Monte Carlo Collision (PIC/MCC) analysis of the problem of detection and identification of impurities in the nonlocal plasma of gas discharge using the Plasma Electron Spectroscopy (PLES) method. For this purpose, 1d3v PIC/MCC code for numerical simulation of glow discharge with nonlocal electron energy distribution function is developed. The elastic, excitation, and ionization collisions between electron-neutral pairs and isotropic scattering and charge exchange collisions between ion-neutral pairs and Penning ionizations are taken into account. Applicability of the numerical code is verified under the Radio-Frequency capacitively coupled discharge conditions. The efficiency of the code is increased by its parallelization using Open Message Passing Interface. As a demonstration of the PLES method, parallel PIC/MCC code is applied to the direct current glow discharge in helium doped with a small amount of argon. Numerical results are consistent with the theoretical analysis of formation of nonlocal EEDF and existing experimental data.

Effect of argon on the performance of a fast-axial flow CO2 laser

The performance characteristics of a fast-axial flow (FAF) cw CO2 laser are described. The dependences of the output power, efficiency, and discharge voltage on the discharge current of a FAF cw CO2 laser with optimised composition of the CO2:N2:He=1:4.4:7.6 gas mixture with a small amount of argon are studied experimentally at two pressures of 50 and 60 mbar in open and closed cycle regimes of the laser system.

Determination of K‐Ar ages in milligram samples using an infrared laser for argon extraction

The K-Ar dating method has been used for decades to decipher the ages of terrestrial and extraterrestrial minerals and rocks. The natural radioactive decay of a metal to a rare gas is an advantage that allows the determination of very small amounts of argon by mass spectrometry. Although the Ar-Ar method has superseded K-Ar, the latter is still used and it has room for improvement. One of these is the reduction of the analyzed sample mass, a desideratum of any current analytical technique. I report here our experience in K-Ar geochronology of milligram-sized samples using laser heating and melting for gas extraction. This modification of the classical K-Ar technique has not been, to my knowledge, used in any other laboratory in the world and deserves a detailed description of its advantages and limitations.

Gas temperature measurement in CF4, SF6, O2, Cl2, and HBr inductively coupled plasmas

Neutral gas temperature (Tg) is measured in an industrial high-density inductively coupled etch reactor operating in CF4, SF6, O2, Cl2, or HBr plasmas. Two laser diodes are used to deduce Tg from the Doppler widths of 772.38 and 811.5nm lines absorbed by Ar*(P23) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5nm beam passing parallel to the wafer, Tg near the wafer surface is obtained by laser absorption technique. With the 772.38nm beam entering the top of the reactor perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged Tg increases with radio frequency power and with pressure, although the temperature near the walls is only weakly dependent on gas pressure. The main effect of increasing the pressure is an enhancement of the temperature gradient between the discharge center and the wall boundary. Due to the thermal accommodation, the authors always observe a significant temperature jump between the surface and the gas in its vicinity. This gap is typically about 200K. Gas temperatures for a wide range of pressure and rf powers are reported. These data will be useful to validate and improve numerical models of high-density reactive plasmas.

Improvement of Tear Strength using Dielectric Barrier Discharge Plasma

In the our study, an improvement of the tear strength of the bonded resin material using an atmospheric dielectric barrier discharge plasma treatment is described. The surface treatment experiments were carried out on the surface of the polyimid films with the air and the air with an argon as a operation gas for various treatment times. The 20 kVP-P, 2 AP-P and 45 kHz power supply was used to produce an atmospheric discharge plasma with the mixture of air and small amount of argon. The contact angle on the treated surface was significantly decreased from 40-50 degree to less than 10 degree by the this plasma treatment. This suggested the removal of the organic contaminant and the enhancement of the wettability to an adhesive. The peeling test of the bonded resin materials was adopted to study the tear strength in both cases with and without plasma treatment. The results showed that the tear strength was successfully improved by more than 3 times of that measured for the bonded un-treated films. We could conclude that the surface of the polyimid film was successfully treated by the atmospheric dielectric barrier discharge plasma and that the organic contaminants which inhibited the adhesion was removed. In addition, the adhesive property also affects rough surface effect and active effect of the surface(1)-(3). And the adhesive property can be improved by them. As a result, a significant improvement of the tear strength of the resin materials was achieved.

Structural and optoelectronic properties of silicon germanium alloy thin films deposited by pulsed radio frequency plasma enhanced chemical vapor deposition

Hydrogenated amorphous silicon germanium (a-SiGe:H) alloy films are still under study to improve their incorporation into tandem solar cells. In this paper we have investigated the quality of films deposited in a radio frequency powered plasma enhanced chemical vapor deposition unit. Two series of samples were prepared either from a mixture of silane and germane diluted into hydrogen or from the same mixture to which a small amount of argon was added. The applied rf power at 13.56 MHz was either continuous or modulated by a square wave pulse at a frequency of 1356 kHz. Different films were deposited in the two series controlling the time the plasma was “on.” The ratio of the on time to the total period of the modulation, the duty cycle, was varied between 100% (continuous mode) and 50%. The plasma during deposition as well as structural and optoelectronic properties of the resulting films was studied with several techniques. We found an optimum in the transport properties for a duty cycle of 75%: an ambipolar diffusion length of the order of 100 nm for a material presenting a bandgap of 1.44 eV. To explain this promising result, we present a discussion on the growth mechanisms of such layers linking the structural results to the transport data.

Characterization of sputtered and annealed niobium oxide films using spectroscopic ellipsometry, Rutherford backscattering spectrometry and X-ray diffraction

Niobium oxide films were prepared by radio frequency sputtering using Nb 2O 5 crystalline powder. The thickness and the complex dielectric functions of the as-prepared films were determined by spectroscopic ellipsometry using the Tauc–Lorentz oscillator model. The as-deposited films were amorphous, their refractive index varies between 2.26 and 2.30 at wavelength of 550 nm and the optical band gap varies between 3.29 and 3.46 eV depending on the sputtering conditions. The composition of the layers was studied using Rutherford backscattering spectrometry with 2 MeV 4He + ion beam. The Nb/O ratio was found in the close vicinity of the stoichiometric one. The films contained small amount of argon. Annealing in air (500 °C, 24 h) causes crystallization and changes in the refractive index and in the extinction coefficient of the film. The optical properties of the sputtered films were compared with those of layers prepared by plasma enhanced chemical vapor deposition, reactive dc sputtering and low frequency magnetron sputtering in other laboratories.

PYROLYSIS OF WOOD IN ARC PLASMA FOR SYNGAS PRODUCTION

Plasma pyrolysis and gasification for production of syngas is an alternative to convential methods of biomass treatment. Basic analysis of energy balances of plasma gasification of wood is presented in the paper. The experimental reactor equipped with the hybrid gas-water stabilized torch with arc power up to 160 kW has been used in experiments with wood gasification and pyrolysis. The hybrid torch, producing steam plasma with small amount of argon, is characterized by extremely low plasma flow rate and high plasma enthalpy, which results in high process efficiency and optimal composition of produced syngas. The experimental results proved that homogeneous heating of the volume of plasma reactor and proper mixing of plasma with treated material was ensured despite of low plasma mass flow rate and constricted form of plasma jet. The conditions within the reactor ensured complete destruction of tested substance. Depending on operation conditions, the main components of produced syngas were hydrogen (28−46% vol.), CO (44−68%), CO2 (2−8%) and Ar(0.2−8%). No presence of complex hydrocarbons or tar was detected.

THIXOMOULDING INJECTION MOULDING OF SEMI-SOLID MAGNESIUM ALLOYS

The thixomoulding technology, i.e. the injection moulding of thixotropic, semi-solid magnesium, represents a new, innovative and fully automated processing technique for magnesium alloys, which combines substantial processing elements of the magnesium die casting and the conventional plastics injection moulding. The process technology is very similar to the injection moulding of thermoplastics, except magnesium is being moulded. The two objectives pursued by thixomoulding are the process substitution of die casting of certain component parts on the one hand and the material substitution in special fields of plastics injection moulding on the other hand. Magnesium offers a considerable potential for material and structural lightweight construction. Thus, by means of the thixomoulding technology, a multitude of lightweight and mechanically high-grade net or near net shape parts can be manufactured, requiring no or very little finishing. Thixomoulded parts can be found in the areas of consumer electronics (for example housings for cell phones, laptops, cameras etc.) and in the fields of the automotive industry (in the form of thin-walled structural components). The thixomoulding process is environmentally friendly, since small amounts of argon can be used for an inert gas atmosphere in the mostly encapsulated plasticising unit, instead of ozone depleting gases, such as SF 6 , generally used in die-casting. At the same time, the process is operator friendly as well, since the danger of exposure to molten magnesium is minimised due to the closed machine.

Au-II 282 nm segmented hollow-cathode laser-parametric studies and modeling

Laser operation on the Au-II 282.3 nm ultraviolet transition is obtained using a high-voltage segmented hollow-cathode discharge tube. The metal vapor is produced by means of cathode sputtering. A small amount of argon is added to the helium buffer gas in order to achieve higher sputtering yield. Measurements of the laser power and small signal gain indicate that the optimal partial concentration of argon is in the range of 0.25%–0.75%. Quasi-continuous wave output power of 100 mW is obtained from a 34-cm-long active region while the highest small-signal gain is 52% m−1. To explain the basic features of the laser operation we present a model of the segmented hollow-cathode discharge. All the discharge characteristics are calculated in a self-consistent way except the temperature of slow electrons. The trajectories of fast electrons emitted from the cathode are followed by Monte Carlo simulation. Rate equations of ion, metastable and metal atom densities are solved in the negative glow, while another Monte Carlo code is applied for the fast heavy particles in the cathode sheath. The spatial distribution of the gas temperature and the thermalization of sputtered metal atoms are calculated as well. The laser characteristics predicted by the model are in reasonable agreement with the experimental results.

Growth of microcrystalline β-SiC films on silicon by ECR plasma CVD

We have investigated the growth of microcrystalline β-SiC films grown by ECR plasma CVD for application as a solar cell window material. The main reactant gases used were silane and methane. Hydrogen has been employed as the plasma gas with phosphine as the dopant gas. Film growth and properties have been investigated over a wide range of process parameters. This paper presents results on the structural and compositional properties of the films as a function of these process parameters, particularly growth temperature, ECR microwave power and reactant gas composition. The primary analysis techniques employed have been Rutherford Backscattering using the Simulated Annealing algorithm and X-ray diffractometry. We have found the grain size in our films to be limited to values less than 10 nm. Both growth rate and crystallite size increase with sample temperature. In addition, the growth rate increases with power while crystallite size reaches a maximum between 800 and 900 W. Small amounts of argon added to the reactant gases have a significant effect on the deposition kinetics and have produced the largest grain size in our material. An analysis of these findings is presented.

Excitation of singly ionized argon species in helium-matrix glow discharge plasma—role of the energy transfer from helium metastables

When a small amount of argon is added to the helium plasma in a Grimm-type glow discharge radiation source, the interaction between helium and argon species is investigated from analyzing the intensities of emission lines of of argon ion (ArII). The excitation energy as well as the term multiplicity concerning the optical transitions to which the ArII emission lines are identified are significant factors for determining their emission intensities in the helium-matrix plasma. In the case where the excitation energy of ArII lines is higher than the internal energy of the helium metastable states, the emission intensity in the helium-matrix plasma is observed to be much weaker than that obtained only with argon gas. On the other hand, the intensity is enhanced when the excitation energy is slightly lower. In the excited levels of argon ion having quartet multiplicity, closer interactions with the triplet rather than the singlet metastable level of helium atom are recognized, with the singlet helium metastable in the argon excited levels having doublet multiplicity.

Atomic hydrogen concentrations in pulsed microwave discharges used for diamond synthesis

Pulsing of a microwave discharge is a promising new technique to improve the control of the diamond deposition process. A small amount of argon (5% Ar) was added to the usual feed stock (0.5% methane in hydrogen) to act as an actinometer. Plasma emission was observed during the pulse on-times for pulse repetition rates from 50 Hz to 10 kHz by time-resolved optical spectroscopy. Determined relaxation time constants for atomic hydrogen are on the order of 1 ms. Thus, the atomic hydrogen concentrations do not vary very much at a pulse repetition rate of 20 kHz, whereas at 50 Hz the radical concentrations vary between a saturation value and zero. The saturation value of atomic hydrogen increases with increasing peak power, but mean values are generally lower as in the continuous wave mode with the same average power and decrease with decreasing duty cycles and pulse repetition rates. The results are consistent with deposition experiments.

Nitrogen in Spray Formed Superalloys

AbstractSpray forming is of considerable interest for potential commercial production of superalloy forging and rolling preforms. The low degree of macro segregation and the relatively small grain size (25–40 μm) make this process look attractive for compositionally complex modern day nickel based superalloys. Both argon and nitrogen have been used successfully as the atomising gas. Argon atomisation has been used when little or no oxygen or nitrogen pickup is desired and when a small amount of argon filled porosity (∼1 vol.-%) can be tolerated. Nitrogen atomization has been used when a decrease in porosity is desired and when a small amount of nitrogen pickup can be tolerated. In this case, rather than staying in the pores, the nitrogen gas dissolves into the alloy and precipitates as submicrometre titanium and niobium carbonitrides. These precipitates have been observed to have little effect on key mechanical properties (tensile, creep, and fatigue). PM/0649

The role of argon in yttrium aluminates

AbstractSpectral properties of YAG and YAP grown in vacuum or under ArH2 protective atmosphere were compared. The latter contained small amounts of argon which was detected by a laser mass spectral analysis. Ar impurity evokes brown colour of unannealed crystals and strenghtens anomalous red colour of annealed (Particularly in O2) YAP crystals doped with Nd + Cr or Nd + Mo. The same red coloration of the doped YAGs is less stable.

Spectroscopic study of chemical composition of high-frequency glow-discharge in halogen-containing gas mixtures

This paper presents a spectroscopic study of high-frequency (HF) gas discharge in mixtures of fluorine- and chlorine-containing gases: trichlorotrifluoroethane (C/sub 2/F/sub 3/Cl/sub 3/), sulfur hexafluoride (SF/sub 6/), and tetrafluoromethane (CF/sub 4/). The optical emission spectrum of the plasma was recorded in the range of 200-800 nm by the photoelectric method, using an MDR-23 monochromator, FEU-79 and FEU-39A radiation dectectors. A small amount of argon was added to the plasma-forming gas to determine the concentration of atoms and radicals and change in the plasma parameters when the discharge burning regimes are changed. The experiments showed that the most probable molecule emitting the 280-335-nm band with a maximum at lambdamax = 306 nm is si /SUB x/ S /SUB y/ Fz. It can be formed as a result of the interaction of sulfur-fluorine containing radicals with the silicon surface, or in the bulk of the material, due to the reaction of SiF /SUB m/ and SF /SUB n/ radicals.

Evaluation of a liquid-helium cryopumping system operating with an electron beam gun

A recently developed 14-kW 240 ° electron beam gun was installed in an 18-in. glass belljar pumped by a liquid-helium cryopumping system made by Air Liquide, a French supplier of cryogenic pumps. The cryogenic pump has a speed of 6000 liter/sec for air. Pumping of hydrogen and helium is accomplished by bleeding in a small amount of argon which freezes on the helium reservoir and has a gettering effect on these gases. Experiments were conducted to determine the operating characteristics of this type of system when evaporating various materials such as aluminum, copper, and tantalum. Data taken during the evaporation runs consisted of major gases evolved, time for belljar pressure to recover to 10−7 Torr range, pressure during evaporation, effectiveness of argon sublimator in reducing pressure, and pumpdown curves. It was found that using a liquid-helium cryopumping system in conjunction with an electron beam gun gives exceptional results. It would be particularly advantageous in the fabrication of MOS devices where extreme cleanliness is required.

Nuclear Capture of Muons in Argon and Neon

The total nuclear capture rates of muons by argon and neon have been measured. The experiment was performed by stopping negative muons in a target of ultrapure gaseous deuterium (at 6 atm pressure and 293\ifmmode^\circ\else\textdegree\fi{}K) separately contaminated by small amounts of argon and neon, and observing the differential time distribution of the decay electrons coming from muons stopped within the gaseous mixture. The results are ${\ensuremath{\lambda}}_{c,\mathrm{Ar}}=(1.20\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}{10}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and ${\ensuremath{\lambda}}_{c,\mathrm{Ne}}=(0.30\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}{10}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$.

A flame sensor for high-temperature ambients

The flame sensor consists of a photoelectric counter tube which is triggered by ultraviolet photons emitted by flames in the spectral region beyond the solar cutoff. Tubes of this type have been made previously, but this new tube differs in being able to operate in ambient temperatures up to and in excess of 1000°F. The new tube has high sensitivity and a lower operating voltage than older tubes. The flame sensor is encapsulated in a titanium and forsterite ceramic envelope and uses a sapphire window to admit the ultraviolet photons. The photocathode consists of a molybdenum rod which has been cleaned by heating and sputtering. The anode is a molybdenum hemisphere, which also serves as a mirror to concentrate the light from the flame on the photocathode. The gas-fill is 100 torr of a helium-argon mixture, where the small amount of argon is used to help remove helium metastables following a count. The sensor operating voltage is about 150 V, and a dead time of 1 ms or more is used to avoid multiple counting. Typical counting rates obtained with a small methane flame at 12 ft are 60 per second. A sensor was life-tested at 1000°F in air for longer than 2000 hours.

Radioactive ages of micas from granitic rocks by Rb‐Sr and K‐A methods

Analytical data and ages are given for K‐A, Rb‐Sr, U‐Pb and Th‐Pb ages from a number of locations. Comparisons of the ages obtained indicate (a) that K‐A and Rb‐Sr ages of mica usually agree when modern laboratory determined values of the decay constants of K40 and Rb87 are used; (b) that the K‐A and Rb‐Sr ages of micas agree with the U‐Pb ages of cogenetic uraninite, zircon, and monazite when the U‐Pb ages are concordant; (c) that when the U‐Pb ages of these uranium minerals are discordant, the mica ages agree best with the Pb207‐Pb206 age; (d) that the pattern of K‐A and Rb‐Sr ages of micas can be most simply explained by postulating the loss of variable but small amounts of argon from the mineral.