Secondary Vacuum Research Articles

Preparation and characterisation of tin-doped indium oxide films

Tin-doped In2O3 (ITO) thin films were prepared by reactive evaporation from new pulverulent mixture of indium oxide, tin oxide and metallic indium at different partial pressures of oxygen. The films were annealed in a secondary vacuum just after deposition. Under optimal conditions of evaporation, these films are stoichiometric, show a good crystallinity and feature high transmission in visible region (T>90%) and high reflection in near IR region versus oxygen pressure.

Effect of environment on the mechanical behavior of Ni–20Cr thin strip

The tensile and creep behavior of a Ni–20Cr thin strip was investigated in air and vacuum in order to determine the constitutive equations of the material and to study the effect of environment. Tensile tests were performed in air in isothermal conditions between room temperature and 900°C. A dramatic loss in ductility was observed around 800°C. Incremental loading tests were performed in air and secondary vacuum at 500–900°C. While the alloy tends to be more creep resistant in vacuum than in air at 500°C, there is no difference at higher temperatures. The effect of environment on the mechanical behavior was attributed to two competing mechanisms, a softening mechanism related to a vacancy flux toward the bulk of the alloy, as a consequence of the NiO cationic growth and a strengthening effect due to the formation of Cr 2O 3 as internal particles or as a continuous layer, acting as vacancy sinks.

Influence of the deposition parameters on the characteristics of Cu xMo 6S 8 thin films in situ grown by pulsed laser deposition

Cu x Mo 6S 8 thin films have been grown in situ by pulsed laser deposition (PLD) on R-cut Al 2O 3 single-crystal substrates. Under selected deposition conditions, they are oriented and present epitaxial relationships with the in-plane substrate directions. The influence of deposition parameters on composition or epitaxial quality has been studied in detail. In most samples, an excess of metallic molybdenum has been detected by X-ray diffraction and quantified by Rutherford backscattering spectrometry (RBS). The deposition under argon (8.10 −2 mbar) at 870°C with a target–substrate distance of 38 mm and an average laser fluence of 5 J cm −2, has entailed a significant reduction of this secondary phase. Moreover, using a small-sized, home made vacuum chamber, single-phased Cu x Mo 6S 8 films have been in situ grown for the first time. The epitaxial relations have been investigated by X-ray diffraction in various modes (namely θ-2θ, θ-scans and ϕ-scans) and by scanning electron microscopy. Under secondary vacuum, (100) Rh oriented thin films are obtained above 820°C and a progressive improvement of the epitaxial growth has been observed up to 890°C. The superconducting critical temperature T c, measured by the a.c. susceptibility method, appears insensitive to the microstructural modifications. Such deposition conditions have been applied to other substrates like Al 2O 3C, (100) MgO or (100) Y: ZrO 2 and have led to new complex epitaxial growth relations.

Commissioning and initial operation of a radioactive beam ion source at ISAC

In November of 1998, the ISAC radioactive beam facility at TRIUMF started delivering on-line isotope separated radioactive beams to experiments. A surface ionization source developed for ISAC has been used to commission the mass separator and beam transport systems and is providing radioactive beams to the first generation of ISAC experiments. The ion source is integral with the radioactive beam production target and is designed to be simple, radiation hard, inexpensive, and easily exchanged by remote-handling techniques. The ion source and its extraction column are suspended at the bottom of ∼2 m of steel shielding incorporated in the target module. The module is suspended in a vacuum tank with primary and secondary vacuum systems. All services for the target/ion source and beam extraction system are ducted through the module shielding. The first sets of beam transport elements and beam diagnostic devices are similarly suspended in vacuum at the bottom of two additional shielded modules. Ion beam characteristics can be routinely monitored during on-line operation by a system of Faraday cups, wire scanners, “harp” monitors, and a novel emittance measurement apparatus that can measure beam emittance in both horizontal and vertical planes. The diagnostics devices are capable of resolving beam signals down to the 10 pA range.

三極管形電離真空計の電極変位と感度係数の関係

Secondary standard ionization vacuum gauge VS-1 is a triode gauge. Simulation of the electrical potential profile of the gauge, electron trajectory emitted from a hot filament, and ion current produced by ionization of gas by the electron assuming a simple electrode geometry was done. The increase in sensitivity coefficient depending on grid potential and the decrease in that depending on filament potential agreed with experimental results by 5%. The increase in sensitivity coefficient depending on filament displacement and ion collector tilting from its regular position was also explained by simulation.

Subcritical Crack Propagation in 3Y‐TZP Ceramics: Static and Cyclic Fatigue

A detailed analysis of crack propagation in tetragonal zirconia polycrystals doped with 3 mol% of Y2O3 (3Y‐TZP) ceramics is presented. Crack propagation tests have been conducted for crack velocities of 10‐12‐10‐3 m/s in several environments, including air, water (in the temperature range of 3°‐85°C), secondary vacuum (10‐5 mbar), and silicon oil. Analysis of the experimental results‐three propagating regimes that are dependent on the environment and a marked threshold below which no propagation occurs‐shows that stress corrosion by water molecules is the key mechanism for crack propagation. The effect of grain size on the crack velocity is quantified and analyzed in terms of transformation toughening. Experiments under cyclic loading have been conducted to quantify the effects of cyclic fatigue. Crack velocities are higher under cyclic loading than that predicted by stress corrosion alone, and the threshold is lower. Experiments that have been conducted at two different frequencies (0.1 and 1 Hz) and static‐fatigue/cyclic‐fatigue sequences show that both stress corrosion by water and pure cyclic‐fatigue effects are operative under alternative stresses.

Unipolar arc simulation device

We describe a simple laboratory device for establishing a vacuum arc plasma discharge that can serve to simulate a unipolar arc. The technique makes use of a triggered vacuum arc plasma gun to generate a plasma plume that in turn causes breakdown of a secondary discharge. The device is in fact a secondary vacuum arc discharge that is triggered by a primary vacuum arc discharge, with some of the features of the secondary plasma discharge having similarities with a unipolar arc configuration. Here we describe the experimental setup and outline how the device can be used for some areas of unipolar arc materials research.

A tangentially viewing vacuum ultraviolet TV system for the DIII–D divertor

A video camera system capable of imaging vacuum ultraviolet emission in the 120–160 nm wavelength range, from the entire divertor region in the DIII–D tokamak, was designed. The new system has a tangential view of the divertor similar to an existing tangential camera system [M. E. Fenstermacher et al., Rev. Sci. Instrum. 68, 974 (1997)] which has produced two-dimensional maps of visible line emission (400–800 nm) from deuterium and carbon in the divertor region. However, the overwhelming fraction of the power radiated by these elements is emitted by resonance transitions in the ultraviolet, namely the C IV line at 155.0 nm and Ly-α line at 121.6 nm. To image the ultraviolet light with an angular view including the inner wall and outer bias ring in DIII–D, a six-element optical system (f/8.9) was designed using a combination of reflective and refractive optics. This system will provide a spatial resolution of 1.2 cm in the object plane. An intermediate UV image formed in a secondary vacuum is converted to the visible by means of a phosphor plate and detected with a conventional charge injection device (CID) camera (30 ms framing rate). A single MgF2 lens serves as the vacuum interface between the primary and secondary vacuums; a second lens must be inserted in the secondary vacuum to correct the focus at 155 nm. Using the same tomographic inversion method employed for the visible TV, we will reconstruct the poloidal distribution of the UV divertor light. The grain size of the phosphor plate and the optical system aberrations limit the best focus spot size to 60 μm at the CID plane. The optical system is designed to withstand 350 °C vessel bakeout, 2 T magnetic fields, and disruption-induced accelerations of the vessel.

Neutron diffraction studies of Zr-containing intermetallic hydrides with ordered hydrogen sublattice. II. Orthorhombic Zr 3FeD 6.7 with filled Re 3B-type structure

Zr 3FeD 6.7 was obtained by deuteration of the Zr 3Fe binary intermetallic compound with Re 3B-type structure at temperatures near 273 K and D 2-pressures below 0.25 bar, and was characterised by Thermal Desorption Spectroscopy and powder X-ray diffraction. Crystal structure data (new structure type of intermetallic hydrides) were derived at 7 K and 293 K from Rietveld refinements of high-resolution powder neutron diffraction data. The orthorhombic symmetry of Zr 3Fe (space group Cmcm) is retained during hydrogen absorption; however, there is an anisotropic expansion in the unit cell dimensions. At 293 K a=3.5803(3); b=11.059(1); c=9.6486(8) Å (Δ a/ a=7.7%, Δ b/ b=0.8%, Δ c/ c=9.4%). The deuterium atoms take an ordered structure with near complete filling of four different types of interstices, one trigonal bipyramidal Zr 3Fe 2 interstice and three types of tetrahedral interstices of Zr 3Fe (one) and Zr 4 (two). Metal–deuterium bond distances are in the range Zr–D=2.058–2.204 Å, Fe–D=1.713–1.791 Å (293 K). All D–D distances in the completely ordered hydrogen sublattice exceed 2.01 Å. The sublattice is built from two types of polyhedra which surround zirconium atoms, consisting of deformed cubes with an additional ninth vertex [Zr1D 9] and deformed cubes [Zr2D 8]. These polyhedra form a spatial framework by sharing vertexes and edges. There are no indications for magnetic long range order in the powder neutron diffraction data at 7 K. A multistaged deuterium desorption starts just above room temperature for Zr 3FeD 6.7. At 448 K the less saturated deuteride Zr 3FeD ∼5, with a reduced unit cell volume, is obtained. Deuteration, when performed at 873 K and 1 bar D 2, results in disproportionation of Zr 3Fe into ZrD 2 and ZrFe 2. Both for Zr 3FeD 6.7 and the disproportionated phase mixture, deuterium desorption under secondary vacuum conditions is completed below 973 K and results in a full recovery of the Zr 3Fe intermetallic. Zr 3Fe presents a new example of successful application of the Hydrogenation–Disproportionation–Desorption–Recombination process to intermetallic phases of zirconium.

The JET soft x-ray diagnostic systems

A new multicamera soft x-ray detector system has been constructed for the pumped divertor phase of JET to provide improved spatial and temporal resolution. It is based on 12 compact pinhole cameras each of which uses a 35 element PIN photodiode array. The cameras are housed in a secondary vacuum and view the plasma through beryllium windows 250-μm-thick which absorb x rays with energies below ∼2 keV. The front-end electronics, located up to 10 m away from the detectors, sample data at 250 kHz, with a 100 kHz passband. The diodes are operated at zero bias voltage. The system ran successfully during the 1995 phase of JET operation with poloidal mode numbers up to m=5 being successfully reconstructed. Detector noise levels (<1 nA) were small compared to signal statistical noise. Some deterioration in diode performance was observed after exposure to an integrated neutron fluence of ∼1013 n. cm−2. Tests have shown that operating with 3 V reverse bias can offset much of the fall in performance from radiation damage. Using a similar 16 element PIN photodiode, a windowless camera has been developed for installation in the JET primary vacuum, to investigate fast XUV/x-ray events which develop at lower energies near the plasma edge or in the divertor. Finally, a radiation hardened system is being developed for D-T operation.

Influence of the annealing atmosphere on the formation of Al–Cu–Fe quasicrystals

Icosahedral samples of nominal composition Al63.5Cu24Fe12.5, which normally grow a rhombohedral approximant crystal, were submitted to heat treatments of various durations. The atmosphere in contact with the surface of the specimens was either dry air or secondary vacuum in order to test whether the formation of the icosahedral phase is sensitive or not to the nature of the atmosphere. Materials annealed in air showed a very thin surface layer of oxide which contained hydrogen. Beneath this oxide layer, small quantities of oxygen and hydrogen were also detected within the underlying lattice. This contamination was sufficient to shift the composition of the samples out of the stability domain of the icosahedral phase and has induced formation of a significant amount of the cubic phase. In contrast, the rhombohedral compound no longer appeared. This behavior goes along with the great sensitivity of the icosahedral phase stability to a sharply denfined electron to atom ratio.

A Temperature-Programmed Desorption Technique for Studying Surface Contamination and Acid-Base Properties of Thick Metal Sheets

Abstract This paper describes how the temperature-programmed desorption (TDP) technique, which is widely used in the fields of surface science and catalysis, has been newly adapted to investigate the thick metallic sheet samples of about 10cm2 area used in adhesion studies. A high frequency induction system has been designed in order to achieve a high heating rate (up to 200 K.s_1) without creating substantial temperature gradients in the sheet. The sample is placed in a secondary vacuum reactor and the gas desorbed is analysed by means of a quadrupole mass spectrometer. The results presented deal with stainless steel and chromium surfaces, subjected to various chemical treatments. The sensitivity and the resolution of the technique presented are shown to be sufficient to study metallic surface contamination and to characterise the acid sites at the surface by desorption of a basic probe molecule such as ammonia.

Solid-state bonding of single-crystals of Ni(111)/Al2O3(0001)

Some fundamental aspects of the solid state bonding process between single crystals of alumina and nickel were studied. It was shown that a model formerly developed to account for the kinetics of diffusion bonding between two metals can be adapted to the case of a metal-ceramic couple. A coincidence site lattice calculation proved that one of the crystallographic relative orientations often mentioned in literature was certainly energetically favourable. With this relative orientation, several nickel-alumina bicrystals have been produced by solid state bonding under secondary vacuum. The influence of operating conditions such as contact pressure and annealing duration has been explored and compared with the calculated results of the bonding kinetics model. Characterization of the solid-state bonded interface was undertaken by optical microscopy and scanning as well as transmission electron microscopy. Observations prove that the initial imposed crystallographic relative orientation was maintained during the solid-state bonding process, and that the synthetic alumina-nickel interface obtained by this technique was free from reaction layer at the usual TEM scale.

Primary and secondary vacuum measurements

Primary, transfer and working instruments and systems for pressure determination from the barometric range down to low pressures are examined on the basis of the measurement uncertainty level attained at IMGC. In low-pressure primary measurements over the 10 5–10 2 Pa range, relative uncertainties from ± 1.5×10 −5 to +1×10 −2 can be obtained. At lower pressures a relative uncertainty of a few parts in 10 3 is considered satisfactory; it increases to 10 −2 for 10 −5 Pa pressures. Calibration results concerning transfer gauges, as well as short- and long-term repeatability of the most widely used working gauges are reviewed.

Oxidizing-reducing effects in yttrium doped Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) superconductor

A polycrystalline sample of Bi 2Sr 2Ca 0.8Y 0.2Cu 2O 8+δ was prepared by a solid state reaction method. The effect of annealing temperatures on T c both in oxygen flow and secondary vacuum were investigated using a.c. susceptibility measurements. The onset of T c increases from 60 K to 82 K as a result of oxygen annealing. The results obtained are explained on the basis of a small change in oxygen content and/or average oxidation state of copper.

High-throughput continuous cryopump

A cryopump with a unique method of regeneration which allows continuous operation at high throughput has been constructed and tested. Deuterium was pumped continuously at a throughput of 30 Torr l/s at a speed of 2000 l/s and a compression ratio of 200. Argon was pumped at a throughput of 60 Torr l/s at a speed of 1275 l/s. To produce continuous operation of the pump, a method of regeneration that does not thermally cycle the pump is employed. A small chamber (the ‘‘snail’’) passes over the pumping surface and removes the frost from it either by mechanical action with a scraper or by local heating. The material removed is topologically in a secondary vacuum system with low conductance into the primary vacuum; thus, the exhaust can be pumped at pressures up to an effective compression ratio determined by the ratio of the pumping speed to the leakage conductance of the snail. The pump, which is all-metal sealed and dry and which regenerates every 60 s, would be an ideal system for pumping tritium. Potential fusion applications are for pump limiters, for repeating pneumatic pellet injection lines, and for the centrifuge pellet injector spin tank, all of which will require pumping tritium at high throughput. Industrial applications requiring ultraclean pumping of corrosive gases at high throughput, such as the reactive ion etch semiconductor process, may also be feasible.

Additives to biological substances. III. The moisture content and moisture uptake of commonly used carrier agents undergoing processing conditions similar to those used in the preparation of international biological standards

Aqueous solutions of the carbohydrates alpha alpha'-trehalose, mannitol and lactose, human serum and human albumin were freeze-dried in ampoules and part of each batch was further desiccated over phosphorus pentoxide in a manner similar to that used to prepare international biological standards and related materials. The residual moisture present in the preparations and their uptake of moisture was then measured by Karl Fischer titration. In ampoules open to atmosphere [22 degrees C, 34% relative humidity (RH)] freeze-dried serum, albumin, lactose and alpha alpha'-trehalose all exhibited hygroscopic properties, their moisture contents rising over a period of 24 h, to 10%, 8%, 8% and 7%, respectively. Mannitol when dried to low moisture levels did not exhibit hygroscopic properties, but the residual moisture in different freeze-dried batches was very variable, possibly as a result of that solid's sponge-like and/or crystalline microstructure. When exposed to the same conditions, dried materials in ampoules fitted with polythene capillary leak plugs (used routinely at this Institute during the preparation of Biological Standards) exhibited a considerably reduced rate of moisture uptake. The effect of secondary vacuum drying over phosphorus pentoxide on the moisture content of these preparations is also reported.

Electrical and optical properties of sputtered amorphous silicon films prepared under a reduced pumping speed

A series of amorphous silicon (a-Si) films have been deposited by dc sputtering. We have found a new preparation parameter, namely, the pumping speed of the secondary vacuum pump which has a considerable influence on the electronic properties of the material. Samples deposited under a reduced pumping speed possess electrical properties which are extremely sensitive to the presence of hydrogen. Conductivity and photoconductivity may increase over several orders of magnitude with the addition of a relatively small amount of hydrogen.

The flavouring of the pomeron and reggeon field theory with thresholds

The flavoured pomeron is introduced into reggeon field theory to show that, in the absence of a secondary vacuum trajectory P′, the critical solution is in fair agreement with experimental data.

Abstract: Thermogravimetric device operating up to 2300 °C under controlled atmospheres

A very‐high‐temperature furnace has been combined with an upper‐holder microbalance resulting in an apparatus which can be used under neutral or nitriding atmospheres and static or dynamic conditions. The furnace is a muffled type with a tungsten cylindrical‐mesh heating element, electrically heated by a low‐voltage transformer and programmable controller. Water‐cooled copper electrical connections and a furnace–balance connecting bellows are at the lower water‐cooled cover plate. A sight window at the upper water‐cooled cover plate permitted temperature measurements in good black body conditions with an optical pyrometer at 0.65 μ. A secondary vacuum pump is connected to the water jacket of the furnace allowing a pressure of 5×10−6 Pa in the furnace. The upper sample holder was used to prevent attack of the crucible suspension wire of a conventional balance by the corrosive vapors from samples. Applications and performances of this apparatus are illustrated by examination of the ternary Ti–O–N in the solid and liquid phase.