High-pressure Argon Research Articles

Use of emissive probes in high pressure plasma

The characteristics of emissive probes in unmagnetized high pressure (≤1 Torr) argon and helium plasmas, produced by inductively coupled 13.56 MHz rf power, are studied. A procedure is given for interpreting emissive probe current–voltage (I–V) characteristics. The I–V curves indicate the amplitude of the rf fluctuation of the plasma potential. They also show ionization near the emissive probe when the potential drop between the emissive probe and the plasma potential is more than the ionization potential. Experiments show that when the temperature of the emissive probe wire and/or the neutral pressure is increased, ionization becomes significant. An increase in the local ion density due to the additional ionization was demonstrated by the I–V curves of an emissive probe and a nearby Langmuir probe. A simple procedure is presented for interpreting these results.

Growth characteristics and magnetic properties of sputtered NdFeB thin films

Thin NdFeB films (200 to 2000 nm) with good hard magnetic properties have been produced by magnetron sputtering in UHV. We have investigated the influence of substrate temperature and sputtering gas pressure on the structural and magnetic properties of the films. It was found that the composition of the films strongly depends on the argon pressure. This gives us the possibility to vary the Nd content in the range of 13 to 32 at%. Highly textured films can be produced at low gas pressure (0.03 mbar) and low substrate temperatures (≈ 675 K). These films exhibit a low coercivity (100 to 300 kA/m) and low remanence, but have a high saturation polarization of about 1.5 T, measured vertical to the film plane. High coercive films ( H cj ≈ 800–1200 kA/m) with a remanence of about 1.05 T can be achieved through sputtering at high argon pressures (0.1 to 0.2 mbar) and a substrate temperature in the range of 800 to 900 K.

Superconductivity in (Gd 1.85 − xPr xCe 0.15)CuO 4

We have carried out a systematic study of structural and superconducting characteristics of the system (Gd 1.85 − x Pr x Ce 0.15)CuO 4 over the entire composition range. Superconductivity was observed for Gd 0.75Pr 1.10Ce 0.15 CuO 4 at 6.5 K. Superconducting transition temperature ( T c) in this compound was found to increase to 18 K by subjecting it to high Ar pressure annealing. However, attempts to induce superconductivity in the undoped Gd 1.85Ce 0.15CuO 4 did not succeed. The results are explained as due to the increased lattice parameters of the doped compound, consequent upon the replacement of Gd 3+-ion by larger Pr 3+-ion, and the increase in the charge carrier concentration as a result of high pressure argon annealing.

Improvement of Co71Cr19Pt10/Ti90Cr10 perpendicular recording media by independent optimization of film nucleation and growth processes

CoCrPt/TiCr perpendicular recording media having independently optimized nucleation and growth conditions have been prepared by changing the argon pressure during sputter deposition of each film. A low argon pressure CoCrPt nucleation layer produces strong c-axis perpendicular orientation that can be maintained during continued CoCrPt deposition at high argon pressure. The two-layer media combines increased particle separation from high pressure growth and strong orientation to produce higher signal to noise ratio than either high pressure or low pressure single layer CoCrPt media. TiCr underlayers, despite poor orientation and a noncolumnar structure, improve CoCrPt c- axis perpendicular orientation. Low argon pressure during TiCr deposition maximizes CoCrPt orientation. A TiCr bilayer having a low pressure nucleation layer followed by a high pressure growth layer improves performance of the subsequent CoCrPt layer. A TiCr bilayer having a high pressure growth layer followed by a thin low pressure template produces even greater recording performance enhancement. This media has Hc=2560 Oe, D50=90 kfci and S0/Nd at 240 kfci=4.0. An identical CoCrPt layer deposited on the low pressure TiCr underlayer has Hc=1850 Oe, D50=80 kfci and S0/Nd at 240 kfci=2.4.

Raman spectroscopy and theoretical modeling of HCl vibrational frequency shifts in high pressure argon

Raman vibrational frequencies of HCl in argon were measured at pressures up to 110 MPa. The mean frequency of the asymmetric Q-branch is shown to accurately measure vibrational shifts through a density region where line shape changes due to motional narrowing render the peak maximum an inaccurate measure of pressure induced frequency shifts. A semiclassical, analytical expression utilizing Hutson’s HCl–Ar pair-potentials is used to determine the derivative of the HCl vibrational frequency with respect to Ar density in the limit of zero density. The predictions are in reasonable agreement with experimental results, although the experimental frequency shifts are about 20% smaller (less redshifted) than theoretical predictions, which may represent the influence of multibody interactions. Experimental HCl Raman Q-branch and S-branch linewidths and peak shifts are compared qualitatively with previous R-branch (IR absorption) results. Separation of the vibrational (Q-branch) and rotational parts of the frequency shift suggest that the rotational contribution is positive (blueshifted) for all J values and approaches zero with increasing J.

The argon gas detectors for the fission measurement in the FEAT

A fission detector developed for the first energy amplifier test made at CERN-PS during the period September–October 1994 [1,2] will be described. The device is a small dimension high pressure argon gas ionization chamber with high background rejection and very high efficiency on 2π for fission fragments. The number of fissions produced in a fissile target allows the neutron flux measurement.

The electrical resistance versus temperature dependence of single amorphous CrNi (40:60) thin films r.f.-sputtered in high argon pressure

The application of thin CrNi films as resistor networks in microelectronics has generated a spate of studies designated to promote a better understanding of the relationships among the deposition conditions, film structure and resulting electrical properties [1-29]. Among the papers that had a particular significance was Campbell and Hendry's study [1] of how the electrical properties depended on CrNi alloy composition, which led to mainly restricting the choice of the thin-film resistor composition in the range from 40 to 60at% Cr. They also tried to explain the electrical properties by a macroscopic two-phase model characterized by the mixture of an oxygenfree CrNi metal phase and the Cr203 oxide phase. Most of the earlier papers dealing with CrNi thin-film resistors [2-5, 8, 9, 12, 14, 15, 22] also adopted this model to explain the electrical behaviour of asdeposited and also annealed thin films. Mooij and De Jong [6], summarizing their experimental results on triode-sputtered CrNi thin films on glass substrates at temperatures below 80 °C, noticed that: (i) in CrNi thin films the electrical resistivity is constant and the temperature coefficient of electrical resistivity (TCR) is low in the composition range 20-80% Cr, as in bulk CrNi alloys; and (ii) the electrical resistivity appears to be insensitive to changes in the crystallographic structure (£c.c., b.c.c., X phase or amorphous). In a tentative explanation of these electrical conduction properties, they have assumed that the disorder in these alloys leads to a minimum mean free path of the conduction electrons which is close to the interatomic distance. Recently, Dintner et al. [23,24] carried out measurements of the d.c. conductivity at low temperatures of NiCr-O thin films reactively sputtered under various deposition conditions. They concluded that the disorder was mainly chemical as a result of oxygen incorporation, and the d.c. conductivity at low temperatures could be interpreted in terms of weakly localized electrons and their interaction in a highly disordered metallic system. Our recent [25, 26,28] TED and TEM structural investigations performed on r.f.-sputtered CrNi (65:35, 50:50 and 20:80) thin films revealed a complex dependence of the resulting phases (single amorphous phase, two amorphous phases, nanocrystalline multiphase stable solid solutions, nanocrystalline multiphase segregated solid solutions, etc.) on the chosen deposition parameters (substrate tempera

On the use of the line-to-continuum intensity ratio for determining the electron temperature in a high-pressure argon surface-microwave discharge

This work presents an experimental study of argon microwave discharges maintained by a surface wave at 2.45 GHz, at atmospheric pressure and under low flow, in a capillary tube. Emission spectroscopy techniques are used to characterize these discharges. Special attention is paid to the determination of the electron temperature by using the line-to-continuum intensity ratio method. We show that, even in situations very close to local thermal equilibrium, simple substitution of the excitation temperature Texc by the electron temperature Te in the equation governing the line radiation emitted by a plasma should not be done. Causes for such an assertion are analysed and a parametric study is conducted to determine the sensitivity of the proposed method. This method is then applied to provide Te from experimental data corresponding to an atmospheric pressure argon plasma produced by a surface microwave.

Sputtered molybdenum bilayer back contact for copper indium diselenide-based polycrystalline thin-film solar cells

A method is described for fabricating low-resistivity molybdenum films on soda-lime glass substrates with good adhesion. Films are sputtered onto substrates nominally held at room temperature in a cryo-pumped d.c. magnetron system in a partial pressure of argon. 1-μm-thick films sputtered at low argon pressure were found to have low resistivity (10–15 μΩ cm), were under compressive stress, and suffered from poor adhesion. Films sputtered with high argon pressure had high resistivity (50–250 μΩ cm), were under tensile stress, but adhered well to the glass. By varying argon pressure during deposition, 1-μm-thick molybdenum bilayers have been fabricated with both low resistivity (12–14 μΩ cm) and good adhesion. These films are being used as back contacts for the National Renewable Energy Laboratoy's state-of-the-art polycrystalline copper indium gallium diselenide solar cells with good results.

High Pressure Supercritical PVT‐Data of Water‐Sodium Hydroxide Mixtures and of Liquid Sodium Hydroxide to 673 K and 400 MPa

AbstractThe density of homogeneous fluid mixtures of water and sodium hydroxide has been measured from 293 to 673 K and at pressures from 10 to 400 MPa. Measurements were performed at eight compositions between 10 and 90 weight percent NaOH and with pure molten NaOH. At sufficiently high pressure complete miscibility of NaOH and H2O exists above the melting temperature of NaOH at 595 K. A differential autoclave with internal heating within a space filled with high pressure argon and with an internal nickel bellows cell for the H2O–NaOH mixtures is described. Immediate results are given as specific mixture volumes and molar volumes. Molar volumes in dependence of composition have distinct minima near 30 mole percent NaOH. All excess volumes are negative. A semiempirical equation is proposed on the basis of a hydration model to describe molar and excess volumes. Partial molar volumes and estimated activity coefficients are given for 673 K and pressures at 100 and 400 MPa.

New diagnostic features in the laser implosion of argon-filled targets

Argon-filled-target implosions on the OMEGA laser system were analyzed and compared to code predictions. For the case of high-pressure argon the diagnostic signatures used were absorption lines of Ar16+ transitions as well as of lower ionizations (shifted Kα lines). The measurements indicate deviations from predictions, which are attributed to a cooler than predicted core.

New diagnostic features in the laser implosion of argon-filled targets

Argon-filled-target implosions on the OMEGA laser system were analyzed and compared to code predictions. For the case of low-pressure argon in an Ar-DD mixture, the diagnostic signatures used were Stark broadening, reduction in ionization energy, continuum slope, and continuum jump. For the case of high-pressure argon the diagnostic signatures used were absorption lines of Ar 16+ transitions as well as of lower ionizations (shifted K α lines), K-shell photoelectric absorption, and the absolute magnitude of core emission. The measurements indicate deviations from predictions, which are attributed to imperfect implosion symmetry.

Xenon atomic-like 3P 2 radiative decay in cold and high-pressure argon

The decay channels of Xe *( 3P 2) in low-temperature and high-pressure argon gas doped with ppm levels of Xe are reported. At low temperatures the argon perturbed Xe *( 3P 2) decays radiatively in addition to the decay channel observed at room temperature, i.e. through 3P 1 by means of endothermal collisions. The lifetime of the argon perturbed Xe *( 3P 2) is found to be several microseconds. The nature of the emitting level is discussed.

Zn1−xCdx polytype single crystals with various degree of order

AbstractThe results of X‐ray investigations of the polytype structures formed in solid solutions of Zn1–xCdxSe are presented. For compositions of 0.22 < x < 0.35 polytypes 8H, 6H, 4H, and DS (disordered structure) are present. The Zn1–xCdxS single crystals of 0 ≦ x ≦ 0 were obtained by Bridgman's method under high protective argon pressure from the melt. The structures are characterised by FARKASZ‐JAHNKE statistical parameters π(m,p), and by parameters PLH of the polytype unit cell formation probability.

Production of Bulk Amorphous Mg<SUB>85</SUB>Y<SUB>10</SUB>Cu<SUB>5</SUB> Alloy by Extrusion of Atomized Amorphous Powder

Amorphous Mg85Y10Cu5 powders with a particle size fraction less than 25 μm were produced by using a newly designed high-pressure argon atomization-consolidation equipment in which each content of oxygen and moisture was controlled to be less than 1 ppm. The extrusion of the amorphous powders at 373 K causes the formation of a bulk alloy having the nonequilibrium structure which is the same as that for the as-atomized powders. The thermal stability of the extruded alloy is also the same as that for the as-atomized powders. The Young’s modulus, compressive fracture strength and fracture elongation at R.T. for the bulk alloy are 46 GPa, 750 MPa and 1.8%, respectively, which are nearly the same as those for the melt-spun amorphous ribbon with the same alloy composition. The fracture surface of the bulk alloy consists mainly of a vein pattern. No appreciable trace of the original boundaries between the powders is seen and hence the powders seem to have a truely bonding state. The good consolidation tendency is presumably because of the clean surface state for the atomized powder by the use of the closed preparation equipment.

Mg-based amorphous alloys

Recent progress in Mg-based amorphous alloys has been reviewed in the framework of the results obtained by the present authors. The amorphous alloys are formed in wide composition ranges in a number of Mg-based alloy systems by melt spinning. The amorphous alloys in MgLnTM (Ln ≡ lanthanide metal, TM ≡ transition metal) system exhibit a wide supercooled liquid region before crystallization and have large glass-forming ability which enables the production of bulk amorphous alloys with thickness below 7 mm by the high pressure die casting process. The bulk amorphous alloys were also found to exhibit high tensile strength above 600 MPa. Furthermore, by using the newly developed high pressure argon atomization equipment in which oxygen and moisture contents can be controlled to be below 1 ppm, Mg-based amorphous powders were produced in various alloy systems. The consolidation of the Mg-based amorpous powders resulted in finely mixed structures of Mg and compounds. The mixed phase alloys exhibit high tensile strengths at room and elevated temperatures for MgCuY and MgCaAl alloys and high corrosion resistance for MgCaAl alloys. The large glass-forming ability and these excellent properties for the Mg-based amorphous alloys are very attractive in applications for the subsequent development of the new alloys.

Xenon luminescence in high pressure argon: spectroscopy and kinetics

The luminescence associated with selective excitation of the three lowest xenon resonant levels ( 3P 1/6s[ 3 2 ] 0 1, 1P 1/6s′[ 1 2 ] 1 and 5d[ 3 2 ] 0 1) in high pressure (14–71 bar) argon doped with minimal amount of xenon is reported. Under these conditions the decay channels specific to Xe*Ar were obtained without Xe* 2 formation. In particular, it is demonstrated that the part of the 3P 1 level excitation population which is not radiated “immediately” is first transferred to the 3P 2 metastable level. Subsequently a long 3P 1 decay also occurs via its formation by the reverse reaction. An analogous behavior is found for the upper 1P 1/ 3P 0 levels showing that most of the fluorescence is retarded with in this case transfers of population to the close 6p[ 1 2 ] 1 and to 6s( 3P 1/ 3P 2) levels. The behavior found after 5d[ 3 2 ] 1 level excitation is quite diferent, with in parallel a fast direct fluorescence and a quenching into the 1P 1/ 3P 0 levels but not directly into the 3P 1/ 3P 2 levels. A kinetic analysis is developed according to these schemes. Particularly, the 3P 1 to 3P 2 quenching is found to depend linearly on the density with the rate k 2=(4.5±0.5) × 10 −13 cm 3 s −1. The more complicated description of the 1P 1 clearly indicates the necessity of using selective excitation to succeed in a self-consistent interpretation.

High-resolution transmission electron microscopic (HRTEM) studies of Tl 2Ba 2CuO 6±x

High resolution transmission electron microscopy (HRTEM) and diffraction techniques were used to characterize Tl 2Ba 2CuO 6 specimens prepared using a variety of new synthetic paths. Thus the degree of crystalline perfection, at atomic resolution, of the tetragonal phase, which usually has a superconducting transition in the range 0–90K, could be characterized and compared with that of the orthorhombic phase. Excellent quality Tl 2Ba 2CuO 6 crystals, with Tc = 92K, were obtained under high pressure of argon to minimize Tl-loss. In the best quality material there were no extended defects. The application of computer-simulation and image-matching techniques allowed the CuO 2 layers of the structure to be located on the HRTEM images. High-Tc materials showed typically perfect order for the CuO 2 and adjacent Ba-O sheets : for non-superconducting orthorhombic crystals fluctuations of image intensity and contrast for the CuO 2 sheets were observed. It is suggested that such fluctuations, associated with variations of Tl occupancy, including vacancies and/or Cu substituting for Tl, are responsible for the variability of Tc exhibited by this cuprate material.

Hyperfine interaction and structure of a gallium arsenide cluster: Ga2As3

Vapor species produced by laser heating of gallium arsenide crystals were allowed to aggregate in a relatively high pressure of argon or krypton before condensation of the matrices at 4 K. Electron-spin resonance (ESR) identified the spectrum of the S=1/2 Ga2As3 cluster via the 69,71Ga (I=3/2) and 75As (I=3/2) hyperfine structure as containing two equivalent Ga and three equivalent As nuclei. Its geometry is therefore trigonal bipyramid and its ground state probably 2A2″, as obtained by Lou et al., from local-spin-density theory. The observed hyperfine parameters indicate that the unpaired spin is confined almost entirely to the two axial gallium atoms.

Influence of the Argon Pressure at dc Magnetron Sputtering on Contaminations in CrSi Thin Films

AbstractThis paper deals with the influence of process parameters, especially of argon pressure, power, and target‐substrate spacing on impurity content and properties of Cr‐Si thin films deposited by dc magnetron sputtering in a non‐heated high vacuum apparatus. The results confirm the well‐known fact that in such a unit by means of a magnetron pure films can be produced without any difficulties. However, this has proved to be possible only in the case of low argon pressure being preferentially employed in magnetron sputtering. Boosting the argon pressure yields drastic film contaminations by oxygen and hydrogen, which are caused by a reinforced release of adsorbats from the apparatus walls under these operating conditions. A high argon pressure effects simultaneously a change in the film microstructure resulting together with the contaminants in modified electrical properties.