High-pressure Argon Research Articles

The VUV emissivity of a high-pressure cascade argon arc from 125 to 200 nm

We have investigated the vacuum ultraviolet (VUV) emissivity of a cascade arc in argon from 125 to 200 nm. The temperature and pressure dependences of this emissivity are the subject of this paper. Enhancement of the emissivity has been obtained by adding nitrogen to the argon. In some wavelength ranges, the increase of the emissivity due to broadened lines is more than a factor of 10 in a spectral range of several nanometers. These lines reach the blackbody limit, corresponding to the electron temperature of the plasma inside the arc. The electron temperature has been varied between 12,200 and 14,500 K. The relative temperature dependence of the free-bound Biberman factor as a function of wavelength in this temperature range has been determined from continuum measurements and compared to the theoretical temperature dependence of the free-bound Biberman factors according to Hofsaess. The agreement is good.

Growth and microstructural study of radio frequency magnetron sputtered MgO films on silicon

Microstructure of magnesium oxide films radio frequency (rf) sputtered on 〈100〉 silicon substrates at various argon: oxygen (9:1) gas pressures in the range 1–6.7 Pa and at various substrate temperatures up to 700 °C have been studied using x-ray diffraction and scanning electron microscopy. The films have shown a tendency for oriented structure with growth orientation perpendicular to the 〈200〉 planes. The tendency for columnar growth has been found to be strong at high argon pressures and has been found to persist to higher substrate temperatures. This observation is consistent with the structure zone model proposed by Movchan and Demchishin [Phys. Met. Mettallogr. 28, 83 (1969)] and later studied by Thornton [J. Vac. Sci. Technol. 11, 666 (1974)]. Annealing of films at 900 °C in oxygen which is needed to reduce oxygen deficiencies and strain generated during growth, and to improve crystallinity by increasing grain size, has been found to cause microcracks in the films depending upon the microstructure and thickness. Films with columnar structure have shown microcracks and the threshold thickness at which microcracks develop has been found to be strongly dependent on the nature of the columnar structure. Dense MgO films deposited at 600 °C at a low pressure of 1 Pa have not shown microcracks upto a thickness of 600 nm. Such films should be potentially applicable as buffer layers for the growth of high quality Y1Ba2Cu3O7−δ films on silicon.

Vibrational structure in the laser excitation spectrum of nickel dichloride at 360 nm

Nickel dichloride has been formed “cold” in the vapor phase by heating the solid to about 750°C, entraining the vapor in a high pressure of argon and expanding it supersonically through a small hole into a vacuum chamber. The laser excitation spectrum of the sample prepared in this way has been recorded in the region of 360 nm. Under these conditions, it is possible to resolve both vibrational and rotational fine structure. The same spectrum was recorded when carbon tetrachloride vapor was passed over the hot metal and expanded through the nozzle. Some “hot” bands have been identified by dispersing the fluorescence with a small monochromator. Virtually no chlorine isotope structure could be identified, even when isotopically enriched samples were used. A partial analysis of the vibrational structure has been achieved in which several progressions in the symmetric stretching vibration have been identified. These progressions are consistent with a value for v ̃ 1 of 360 cm −1 for the lower electronic state and 345 cm −1 for the upper electronic state. The complications in the observed spectrum may be caused by two or more upper electronic states being involved in the band system.

Length of Laser-Produced Dense Plasma in High Pressure Argon Gases

When a high pressure gas was irradiated by a focused ruby laser light, a hot and dense plasma was produced, and moved towards the lens under the action of the laser radiation. The length of the laser-produced plasma was calculated on the basis of a breakdown wave and a radiation supported shock wave processes. The plasma length is experimentally observed in high pressure argon gas up to 200 atm, which agrees with the calculated one. At high pressure, the breakdown wave is dominant, while the radiation supported shock wave is predominant at low pressure.

Depth analysis of nickel thin films on silicon by glow discharge spectroscopy: The interface region

AbstractDepth profiles of nickel thin films on silicon obtained with a Grimm glow discharge lamp operating at various conditions were compared. The best conditions for the profile analysis are: high argon pressure, high discharge current and low discharge voltage. The signal response at the interface was described quantitatively using piecewise linear model functions. Influence of the discharge parameters on the signal response at the interface was discussed. Interface broadening was confirmed to be caused by the crater effect, with a non‐uniform removal rate distribution across the analysed spot that does not depend on the total sputtered depth in the analysis of a homogeneous sample.

Thin film structure and adhesion of sputtered TiNi layers on silicon

Thin film stress, adhesion and structure at different argon pressures have been investigated in the system Ni(200–800 nm)/Ti(100–400 nm)/Si, prepared in a d.c. planar magnetron sputtering apparatus. The adhesion between titanium and silicon has been found to decrease at low argon pressure (0.67 Pa (5 mTorr)) and to increase at high argon pressure (2.67 Pa (20 mTorr)) X-ray diffraction analysis revealed a highly oriented Ni(111) layer near the boundary between nickel and titanium, and the X-ray fluorescence method showed that the density was higher at an argon pressure of 0.67 Pa. The adhesion change is considered to be influenced mainly by the change in stress of the nickel film; that is, the modulus of elasticity seems to vary with crystalline orientation and density, which are affected by the argon pressure.

Formation of the 124-phase superconductor YBa2Cu4O8 by retaining oxygen in a reaction HIP sintering process

The ceramic superconductor YBa2Cu4O8 has been produced by high temperature sintering of a mixture of CuO and YBa2Cu3O7 in a glass capsule under high hydrostatic argon pressure. The resulting highly dense material is investigated by X-ray diffraction, optical and electron microscopy, resistance measurements and hardness measurements, and shown to be a homogeneous High transition temperature superconductor.

Sputtered tungsten for deep submicroncomplementary metal-oxide-semiconductor technology

Tungsten gate metal-oxide-semiconductor capacitors formed by 6.5 nm ofthermal SiO 2 and 150 nm of sputtered tungsten have been characterized. The gate metal was deposited using high argon pressure (55 mTorr) to obtain a deposit with a low residual internal stress. To avoid tungsten oxidation and to remove the oxide damage caused by the sputtering deposition process, thermal treatments (500°C ⩽ T ⩽ 800°C) were performed in a silicide oxygen-free furnace. The electrical characterization has shown the efficacy of the low temperature anneal and the onset of gate oxide degradation on treatments at T ⩾ 700°C. There is experimental evidence that this degradation can be attributed, at least partially, to the oxygen depletion that characterizes the environment inside the silicide anneal furnace.

TiAlOn black decorative coatings deposited by magnetron sputtering

Black decorative coatings with improved mechanical properties (wear resistance) were deposited from TiAlON source material. A composite ceramic Al 2O 3 + 1.5TiN has been used as a target in a planar magnetron rf sputtering system (13.56 MHz, 1200 W). A non-reactive process at high argon pressure yielded black, shiny coatings with deposition rates above 0.5 μm h −1. In this study we report on the structural analyses as well as on the high temperature stability of such coatings. Transmission electron microscopy studies on very thin films (50 nm) have given evidence of a two-phase microstructure: crystallized grains of average size 10 nm are embedded in an amorphous matrix. X-ray diffraction has shown that these grains had the cubic B1 structure of TiN, with a lattice constant of 0.413 nm for as-sputtered films. Post-deposition thermal treatment under vacuum up to 900°C for 5 h affected only the lattice parameter which decreased to 0.409 nm. At 1000°C, the amorphous matrix decomposed into two crystalline phase: α-Al 2O 3 and TiO 2 (rutile). The present investigation has shown that stable black decorative coatings can be deposited by a simple PVD process from a single target.

R.f.-diode sputtered amorphous rare earth-transition metal films: Microstructure, stability, and magneto-optical properties

We report the strong correlation of deposition parameters, microstructure and stability of r.f.-diode sputtered magneto-optical thin films studied by transmission electron microscopy and a magneto-optical hysteresis loop tracer. Both argon bleeding pressure and substrate bias strongly affect the microstructure and oxidation resistance of the films. Films sputtered using moderate argon pressures and substrate bias voltages are dense, smooth and morphologically featureless. They are strongly resistant to oxidation. In contrast, low or high argon pressures and substrate bias result in films of high porosity, columnar island-like structure or “sponge-like” morphology. They degrade rapidly in air.

Stress and microstructure in tungsten sputtered thin films

Tungsten films, 0.05–1 μm thick, were deposited on silicon wafers by rf magnetron sputtering. Induced film stresses were investigated as a function of substrate temperature and background pressure in connection with microstructural observations and limited compositional analysis. Homologous substrate temperatures Ts/Tm, where Tm is the melting point of tungsten (3683 K), ranged from 0.08 to 0.15. Argon pressures investigated ranged from 1 to 7 Pa. This corresponds to the low-temperature part of Thornton’s microstructure model, within zones I and T. Two regions were distinguished for increasing values of the homologous temperature and/or decreasing values of argon pressure: (i) The first region, observed for low substrate temperature and high argon pressure, was a voided zone I microstructure with small grain size (200–400 Å). Film stresses increased from zero towards tensile values as voids disappeared. (ii) The second region, observed for higher values of Ts/Tm and/or low pAr, was a denser zone T structure, with a bimodal grain distribution (<3000 Å). After reaching a maximum tensile value σ=2×103 MPa, corresponding to the transition from zone I to zone T microstructure, the stress decreased abruptly to a constant value σ=−2.7×103 MPa. All stress values were found to be quite independent of thickness in the range from 0.05 to 1 μm. Even though β metastable phase is usually observed for zone I deposits, a quasipure α film was obtained at low temperature and high pressure (within zone I) under especially clean conditions. Independent of phase composition (α or β phase) the voided zone I was observed to be highly reactive in air. The shift with time toward compressive stress for the zone I structure was attributed to oxygen absorption in the pores. For 3-month-old films, a high oxygen content of ∼20% was measured by nuclear reaction analysis. In the denser zone T films without voids, no change in film stresses was observed over time, and oxygen content was negligible (<1%) after 3 months.

Measurements of gain, saturation, and line competition in an electron beam pumped high-pressure Ar/Xe laser

Using a small electron beam device, we have observed time-dependent competition among the 1.73, 2.03, 2.63, and 2.65 μm lines of the xenon laser in a high-pressure argon buffer. The small-signal gain and saturation intensity for each of these lines have also been measured. The maximum specific energy output of the laser was 1.7 J/ℓ and the efficiency was 2.3%.

The kinetics of growth and the morphological instability of zinc single crystals

The effect exerted by diffusion upon the kinetics and morphological stability of zinc single crystals during growth from vapour phase in the presence of argon is studied. The shift of the basal face in normal direction and the growth of the edge of the same face as a function of time is checked at constant temperature and constant supersaturation at high vacuum or argon pressure 666-33330 Pa. Linear and parabolic dependences of the crystal sizeR as a function of the timet, respectively of the length of the basal edgea as a function of the time as well as the kinetic critical sizeRk, respectivelyak are established. In agreement with the isotropic theory of Chernov and Cahn, zinc single crystals with sizesR smaller thanRk grow in a kinetic regime, while those with sizesR larger thanRk grow in a diffusion regime. It is shown that the results of the kinetic investigations are in good agreement with data obtained by morphological studies.

Production of Nd-Fe-B alloy powders using high-pressure gas atomization and their hard magnetic properties

Fine spherical Nd−Fe−B powders with a tetragonal Nd2Fe14B phase have been produced by high pressure argon or helium atomization. The average size defined by 50 pct cumulative weight fraction is as small as about 25 μm. The Curie temperature of the powders is about 580 K and the intrinsic coercivity (iH c ) of the bonded products made from the powders increases with decreasing particle size and reaches about 0.581 MA/m for the powder below 25 μm diameter. TheiH c value increases with an increase in the cooling rate by helium atomization as well as with an increase in neodymium and boron content to 18 at. pct Nd and 12 at. pct B with the highestiH c value reaching 0.716 MA/m. Annealing in the range of 773 to 1073 K gives rise to a further increase ofiH c to 1.035 MA/m. The highiH c value is promising for practical use as isotropic bonded powder magnets. The increase of magnetization for the bonded powder magnets takes place rapidly and the behavior is similar to that for sintered Nd−Fe−B magnets, in goods contrast to a sluggish increase of magnetization for the bonded Nd−Fe−B powder magnets made from the comminuted powders of melt-spun ribbon. From the magnetization behavior, it was presumed that the generation of the large intrinsic coercivity is due to the difficulty of the nucleation of reverse domain rather than the pinning of domain walls.

Continuous-wave dye laser pumped by a high-pressure argon arc

Continuous-wave operation of a Rhodamine 6G dye laser, incoherently pumped by a high-pressure argon arc, has been achieved. A special electrode design reduces melting of the electrode tips, and thus the arc provides the necessary brightness for periods of the order of hours.

Swelling and gas release in UO2 and comparisons with FASTGRASS and OGRES code predictions

The results of experiments on the swelling of UO2 under known pressure driving forces are reviewed. High-pressure argon was entrapped during sintering which then caused swelling when the ambient pressure was reduced. The swelling strains rates before interconnection could be expressed as V̇ = AFn exp(−Q/RT), where A is a structural constant, F is the net pressure driving force for swelling, n ≈ 1.5, and Q = 200 kJ/mol. The results are consistent with models for the growth of pores controlled by diffusion of atoms along grain boundaries from pore surfaces. For the conditions investigated, pore interconnection begins at ~ 91% TD and is associated with a decrease in strain rates and concurrent gas release. Interconnection occurs first along grain edges and corners. Pores maintain equilibrium shape prior to interconnection, but are not able to do so after interconnection. Resintering and densification follows gas release. Under conditions of rapid microstructural change during sintering where pores are coalescing and “pinching-off”, the subsequent swelling rates show considerable scatter. For more stable structures, the swelling rates also become more reproducible for the same conditions.The relevant portions of the FASTGRASS and OGRES codes were benchmarked against the experimental results along with a mathematical model for diffusive pore growth. Both codes required adjustments using measured parameters to approximate the data. Since the codes are based on diffusive pore growth models, they describe the almost linear dependence of swelling rates on pressure at the low pressures investigated, but are not expected to do so at higher pressures, where deformation mechanisms may control. The relaxation time approach in FASTGRASS appears to be inappropriate for large swelling transients. The codes do not describe resintering accurately.

Microstructure and stability of rf-diode sputtered GdTbFeCo thin films

The correlation of deposition parameters, microstructure, and stability of rf-diode sputtered magneto-optical thin films has been studied by using transmission electron microscopy and a magneto-optical hysteresis loop tracer. Among the sputtering parameters, we found that both argon bleeding pressure and substrate bias have strong influences on microstructure and consequently the oxidation resistance of the films. Sputtering using moderate argon pressure and substrate bias produces dense and smooth films. The bare films are strongly resistant to oxidation. In contrast, low or high argon pressure and substrate table bias result in films of high porosity, columnar ‘‘islandlike’’ structure, or ‘‘spongelike’’ morphology. They degrade rapidly in air.

The effects of deposition conditions on microstructure and magnetic properties of TbFeCo

Transmission electron microscopy (TEM) has been employed to characterize micro/magnetic structural details of magneto-optical (MO) recording TbFeCo thin films as a function of dc-magnetron sputtering parameters using bright/dark field imaging, selected area diffraction, convergent beam electron diffraction, and Lorentz electron microscopy. It is found that the preparation conditions have a strong impact on both microstructure and magnetic properties of the films. The microstructures of the films deposited at low argon bleeding pressures (<10 mTorr) are featureless, and their magnetic domains are of the ‘‘stripe’’ type with a perpendicular anisotropy. In contrast, high argon pressures (>20 mTorr) give rise to microvoids surrounding ‘‘honeycomblike’’ networks and in-plane domains with ‘‘ripple type’’ contrast. The microstructure and magnetic domain structures are related to the films’ magnetic properties as characterized by a MO loop tracer.

A spectroellipsometric investigation of the effect of argon partial pressure on sputtered palladium films

The microstructure of palladium thin films prepared by dc planar magnetron sputtering at low deposition temperatures was investigated as a function of the argon partial pressure. The films were characterized by spectroellipsometry, electron microscopy, and x-ray diffraction. Below a transition pressure Pt≂15 mTorr, the films consisted of densely packed grains, corresponding to the zone T region in Thornton’s structure zone model. Above this transition pressure the films developed into a more voided columnar structure, characteristic of a zone 1 region. A microstructural analysis of the spectroellipsometric data indicated a general trend to increased porosity and microroughness of the films with higher argon pressures. Furthermore, the effective medium theory of Sen, Scala, and Cohen (SSC), relevant for a random coated-particle microstructure where the grains are optically isolated from each other, was required to describe the films prepared with argon pressures above Pt. The zone 1 region was therefore best described optically as a random coated-particle microstructure where the microroughness and porosity varied with the argon pressure. Spectroellipsometry, which is sensitive to the film microstructure, was able to identify the zone T/zone 1 transition through the changes in the pseudodielectric function of the Pd films. Electron microscopy confirmed that for the thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries, thus further supporting the random coated-particle basis of the SSC theory.

Effects of argon pressure and substrate heating on the chromium underlayer used for high-density longitudinal CoNiCr media

Sputtered CoNiCr on Cr is one of the preferred material systems for high-density longitudinal recording media. dc magnetron sputtered Cr films, on Al substrates, were investigated for the effects of argon pressure and substrate temperature on the microstructure. High-resolution scanning electron micrographs reveal that the films made at lower argon pressures have acicular-shaped grains changing to faceted grain structures at higher argon pressures. The effect of substrate heating prior to deposition was to change the structure from acicular shape to cubic shape. X-ray diffraction work reveals a bcc(110) orientation for films deposited at lower argon pressures changing to a mixed phase at higher argon pressures. Increased substrate temperature caused a mixture of (110) and (200) orientation.