Browse - Journal of Vacuum Science & Technology Archives 1964-1982

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New Hot-Filament Ionization Gauge with Low Residual Current

P. A. Redhead

J. Vac. Sci. Technol. 3, 173 (1966); http://dx.doi.org/10.1116/1.1492470 (8 pages) | Cited 23 times

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The design and performance of a new type of hot-filament ionization gauge is described. The ions are extracted from the ionization region, focused through an aperture in a shield electrode, and then collected on a short, fine wire. The sensitivity factor of this gauge is about 13 Torr⁻¹ for nitrogen. The ratio of the soft x-ray flux reaching the collector of the new gauge to that of a Bayard-Alpert gauge is calculated, and the x-ray limit of the new gauge estimated to be 3×10⁻¹³ Torr. Measurements at low pressures indicate that the x-ray limit cannot be greater than 7×10⁻¹³ Torr and may be considerably less. False pressure indications, caused by the electronic desorption of positive ions from chemisorbed gases on the grid (in particular, oxygen), are at least 500 times smaller in the new gauge than in the Bayard–Alpert gauge.

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07.30.Dz

Vacuum gauges

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Implications of High Vacuum on the Characteristics of the Lunar Surface

Peter E. Glaser

J. Vac. Sci. Technol. 3, 181 (1966); http://dx.doi.org/10.1116/1.1492471 (6 pages)

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The pressure on the lunar surface, which may be no higher than 10⁻¹³ terrestrial atmospheres, has already been shown to have an important effect on the behavior of postulated lunar surface materials. The observational evidence on the nature of the lunar atmosphere is summarized and the implications of the low pressure on lunar surface structural and physical properties are discussed. Lunar environmental effects including micrometeoroid impact and solar radiation are shown to be contributing to the surface characteristics. The effects of low pressures on the vesiculation of lava are used to illustrate structural features which may be present on the lunar surface. Consolidation phenomena, which are expected to produce adhesion of particles on the lunar surface, and the rôles of chemical bonds and van der Waals and electrostatic forces are discussed. The effects of the high vacuum on heat-transfer phenomena on the surface are examined and the required characteristics of postulated materials, ranging from a lightweight interconnected structure to a vesicular low-density foam, are listed. The restraints imposed on lunar exploration by the absence of the atmosphere and the expected contamination caused by lunar probes and future lunar-landing vehicles are considered.

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96.20.Dt

Features, landmarks, mineralogy, and petrology

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Increase of Residual Background Gases During Ultrahigh-Vacuum Mass Spectroscopic Analysis

G. A. Rozgonyi

J. Vac. Sci. Technol. 3, 187 (1966); http://dx.doi.org/10.1116/1.1492472 (5 pages) | Cited 2 times

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It has been observed that anomalously high residual background-gas pressures will occur in an ultrahigh-vacuum mass spectrometer exposed to increasing argon pressure. The gases have been identified as hydrogen, helium, neon, carbon monoxide, methane, and ethane. The vacuum system is bakeable, with sputter-ion and cryogenic sorption pumps. Vacua of less than 1×10⁻¹⁰ Torr are routinely obtained. A mechanism is described to account for the appearance of the above gases based on the vacuum-system components. The gases either evolve from the sputter-ion pump or are inefficiently pumped by it. These gases migrate through the system and are adsorbed on the various internal surfaces when the pressure is below 10⁻⁹ Torr. They are subsequently desorbed by argon bombardment, most likely in the vicinity of the total- and partial-pressure gauges, as the argon pressure is increased. In a static system, the residual gases will increase to as ranch as 1% of the argon pressure. In a dynamic system, the gases are still observed, but at lower concentrations.

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07.30.Bx	Degasification, residual gas
07.75.+h	Mass spectrometers

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Experimental Conditions for Effective Glow-Discharge Bombardment of Vacuum Deposition Substrates

W. E. Isler and L. H. Bullis

J. Vac. Sci. Technol. 3, 192 (1966); http://dx.doi.org/10.1116/1.1492473 (4 pages) | Cited 1 time

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Glow-discharge bombardment is widely used in vacuum practice as the final step in the preparation of substrates prior to the deposition of thin films. Work carried out at these laboratories has shown that the effectiveness of the technique is highly dependent upon the experimental arrangement used. In these experiments, the heating effect upon a glass substrate was taken as a measure of the effectiveness of the bombardment, and a systematic investigation was made of the effects of such parameters as type of discharge, accelerating voltage, electrode size and placement, and residual pressure. The results for direct current (dc) showed that for constant discharge current the heating increased with decreasing pressure and electrode diameter. A maximum was reached at a pressure of 9 mTorr below which, owing to power source limitations, the increase in carrier energy was insufficient to compensate for the decrease in carriers. Grounded-center-tap alternating current (ac) glow discharge, sometimes used for glow-discharge bombardment, was shown to be relatively ineffective as compared with the dc glow discharge.

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81.40.Wx	Radiation treatment (particle and electromagnetic)
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy

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Physisorption of Xenon and Krypton on Glass and on Molybdenum Films

N. Endow and R. A. Pasternak

J. Vac. Sci. Technol. 3, 196 (1966); http://dx.doi.org/10.1116/1.1492474 (6 pages) | Cited 3 times

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Physisorption of room temperature xenon and krypton at low pressures (10⁻⁹−10⁻⁴ Torr) on Pyrex® and on molybdenum films at 77 ° and 87 °K has been investigated. The initial sticking probabilities are close to unity, and the adsorbate shows high surface mobility. The steady-state data, which can be shown to differ little from equilibrium data, fit the Polyani potential theory and the Dubinin-Radushkevich isotherm. For the films, the isotherm slopes (which are related to the isosteric heats of adsorption) increase with film age; for old films, they approach the values found for physisorption of xenon and krypton on Pyrex and on zirconium films. Constancy of isotherm slopes for argon on widely different adsorbents has been noted previously. Thus, the physisorption forces in these systems appear to be unrelated to specific properties of the sorbing surfaces, except in the case of highly porous adsorbents.

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68.03.Fg	Evaporation and condensation of liquids
68.43.Mn	Adsorption kinetics

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Approximate Calculation of Expansion of Gas from Nozzles into High Vacuum

H. G. Nöller

J. Vac. Sci. Technol. 3, 202 (1966); http://dx.doi.org/10.1116/1.1492475 (6 pages) | Cited 2 times

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The exact calculation of the density of a steady-state gas flow by means of the Boltzmann function generally leads to great mathematical difficulties, in the case of an expanding gas passing from the viscous flow region into the molecular flow region. An approximate solution can be found by replacing the actually continuous transition from viscous to molecular flow with a suitably defined discontinuity surface. Molecules that leave the viscous region through this surface continue to fly in straight lines with their respective velocities. By adopting this conception, the density at each point of the molecular-flow region can be found by integration. The general procedure is specialized for the case of the two-dimensional flow and can be applied to the supersonic flow around a corner in vacuum.

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47.60.-i	Flow phenomena in quasi-one-dimensional systems
47.45.Dt	Free molecular flows

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Isothermal Release of Ionically Pumped Inert Gases

G. P. Smeaton and G. Carter

J. Vac. Sci. Technol. 3, 208 (1966); http://dx.doi.org/10.1116/1.1492476 (6 pages)

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The release of He, Ar, and Xe, ionically pumped into Pyrex glass surfaces, is studied as a function of time after the cessation of pumping. Both pumping and release are conducted at room temperature. The parameters of pumping pressure and pumping time are varied in a dynamic system so that the pressure during pumping is maintained constant. A general release-rate function of the form Rate proportional to Time raised to the —m is obtained, the index m depending upon the pumping time, pressure, and gas species; and the results are interpreted in terms of release of gas from capture sites in the glass that possess a spectrum of activation energies for desorption.

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07.30.Cy

Vacuum pumps

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Some Effects of Surface Layers on the Degassing Properties of Copper

T. D. Kirkendall, P. F. Váradi, and H. D. Doolittle

J. Vac. Sci. Technol. 3, 214 (1966); http://dx.doi.org/10.1116/1.1492477 (7 pages)

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The effects of pretreatment and surface layers on the degassing properties of OFHC copper were investigated. With the use of a radiofrequency mass spectrometer, the throughput method of analysis was employed to measure the evolution characteristics of H₂, H₂O, N₂, CO, and CO₂. Pretreatments such as hydrogen and vacuum firing, as well as surface layers on the metal, influence the quantity and rate of gas evolution at elevated temperatures. Surface layers of copper oxide, nickel, gold, and titanium accelerate degassing. A layer of vapor-deposited titanium on the copper greatly reduces the quantity of evolved gases.

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07.30.Bx

Degasification, residual gas