Hydrogen adsorption and its effect on the resistance of evaporated nickel films-an application of ultra-high vacuum

First International Congress on Vacuum Techniques 22.5. lonen-Getterpumpe fiir Niedrige Drucke: G. REICH. E. Leybold's Nachfolger, K61n, Deutschland. An Ionen-Getterpumpen, die beispielsweise ftir grosse Kernmaschinen eingesetzt werden sollen, werden zwei wesentliche Forderungen gestellt : (1) Nicdriger Enddruck. (2) Betriebssichere Arbeitsweise tiber mehrere Monate. Es wird eine grosse Pumpe mit Sauggeschwindigkeiten zwischen 500 und 5000 l/s beschrieben, die diese Forderungen dadurch erftillt, dass der Gettcrmetallvorrat vor lnbetriebnahme ausgeheizt wird und dass durch eine automatische druckabh/ingige Steuerung des Verdampfers der Gettermetallverbrauch auf ein Minimum herabgesetzt wird. Es wird welter tiber Ergebnisse eingehender Untersuchungen tiber den Aufzehrmechanismus berichtet, die durch Partialdruckanalysen mit dem Omegatron gcwonnen wurden. 22.6. Sur un Principe Nouveau de R6alisation de la " Pompe /I l~vaporation de T i t a n e " : A. SCHRAM. Compagnie G6n6rale de Radiologie, Paris, France. L'6vaporation de titane dans une pompe pose des probl6mes difficiles et dont les solutions apport6es jusqu'aujourd'hui restent plus ou moins d6licates, en particulier : le creuset ou le support sur lequel le titane s'6vapore, le syst6me d'alimentation en fil de titane, et le syst6me de chauffage du titane. A partir des syst6mes g cathode froide, on peut obtenir des d6charges 61ectriques si intenses et si courtes qu'une cible massive de titane soit port6e superficiellement, sans 6chauffement notable de la masse, h des temp6ratures dbpassant de loin le point de fusion. De telles d6charges p6riodiques permettent d'obtenir une importante 6vaporation de titane, sans qu'aucun 616ment soit port6 ~ haute temp6rature, sans creuset et en utilisant du titane sous forme massive, en cylindre ou plaques par exemple. Par un tel proc6d6, une evaporation de 15 mg de titane par rain avec 200 W a 6t6 obtenuc. 23.1. Adsorption and Desorption of Positive Ions on Glass and Metal Surfaces: J. H. LECK. University of Liverpool, Liverpool, United Kingdom. Observations have been made of the amount of the inert gases adsorbed on to glass and metal surfaces in high vacuum systems. In the case of the metals adsorption was brought about by bombarding the surfaces with ions of the inert gases with energies up to 5000 eV. Subsequently the surfaces were degassed by heating. The total quantity of gas desorbed was measured by using a mass-spectrometer as the detecting element. The mass-spectrometer enables accurate measurements of small desorption transients to be made against a large and fluctuating background pressure. Results obtained for tungsten, nickel and platinum show the total quantity of gas taken up to increase with increasing energy of the bombarding ions to such a value as to be equivalent to a complete surface layer for an energy of 5000 eV. Temperatures of the order of 800°K are required to remove the gas, thus showing binding energies much higher than for physical adsorption. It has also been noted that the ions can dislodge, and take the place of, molecules already adsorbed at the surface. The ion bombardment was also found to allow the release of impurities such as potassium and sodium from the metal targets. This was especially true for tungsten, where after a bombardment of ions a subsequent heating produced a short burst of potassium and sodium positive ions from the target surface. No quantitative measurements of the intensities or energies of the incident ions o n to glass surfaces have yet been undertaken ; all the measurements have been made at the glass envelope of the Bayard-Alpert type ionization gauges. It has been shown, however, that stable adsorption takes place, again with a comparatively large binding energy, which does not appear to be constant over all the adsorption sites. For example, for argon, in order to release all the inert gas molecules from the surface baking temperatures in the range 500-600°K must be used.

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*23.2. The Attainment of Clean Surfaces by Breaking Crystals in Ultra-high Vacuum: P. C. BANBURY, G. A. BARNES, D. HANEMAN and E. W. J. MITCaELL. University of Reading, Reading, United Kingdom. 23.3. Hydrogen Adsorption and its Effect on the Resistance of Evaporated Nickel films--An Application of Ultra-high Vacuum : T. ICHIMIYA and Z. ODA. Nippon Telegraph and Telephone Public Corporation, Tokyo, Japan. The gas adsorption phenomena on metal surfaces are very sensitive to the cleanliness of the surface. Therefore, in order to investigate the interactions between gas and metal surface fundamentally, it was required to attain the ultra-high vacuum and carry out the experiment in it. As an example of the application of ultra-high vacuum technique, the change of electric resistance of evaporated nickel films due to the adsorption of hydrogen under various conditions is investigated. By gas adsorption the resistance increases on very clean films, while it decreases on contaminated films. Experiments show that this decrease is due not to the oxygen pre-adsorbed on the surface, but to that which has diffused into nickel lattice. There are two sorts of reversal in resistance change during adsorption : one occurs on a very clean film at --183°C and the other on a film containing a small amount of oxygen at 0°C. The former is considered to be an inherent property on nickel film connected to adsorption mechanism, while the latter is a spurious one due to oxygen. The degree of vacuum which can guarantee the cleanliness of the film will be discussed. 31.11. Factors Controlling the Ultlmate Pressures Obtainable in Large Nuclear Physics Vacuum Systems : J. BLEARS, E. J. GREER and J. NIGHTINGALE. Metropolitan-Vickers Electrical Co., Manchester, u n i t e d Kingdom. The paper presents new data on the rates of degassing and thermal decomposition of the more commonly used high vacuum materials, including synthetic resins. It gives an account of an investigation of the relative performance of large cold traps, activated carbon and alumina adsorption traps and refrigerated baffles. Observations on transient pressure changes following changes in system temperature are compared with analogous phenomena observed during the baking of vacuum gauges. 31.12. Some Vacuum Problems at Low Temperatures : R. BUDDE. CERN, Geneva, Switzerland. There will be discussed some sealing techniques for metalmetal and metal-glass seals that have been developed and tested for the use at high vacuum and low temperatures. Hand- and pneumatically-operated valves for liquefied gases have been designed, and are now in use in a vacuum system. Some equipment industrially available has been used with or without having been adapted, and will be discussed, as well as the properties of some materials which were found to be useful in the vaccum-low temperature range. 31.13. Vacuum Techniques in Mass Spectrometry: J. BisHop. United Kingdom Atomic Energy Authority, Capenhurst, United Kingdom. This paper gives a survey of some of the vacuum techniques used and experience gained in a laboratory engaged on design, operation and development of high-precision mass spectrometers. The performance of the mass spectrometer is critically dependent on both the quantity and the type of the residual gases in the vacuum system and the developments in vacuum techniques have been aimed at reducing these. Illustrations are given of types of gaskets which can permit brake-out temperatures of the vacuum system to be extended up to 450°C, together with a suitable copper analyser tube. Designs of improved baffles for the reduction of back-streaming from mercury pumps a n d of greaseless seals for rotating shafts are given. 31.2 I. Automatische Steuerung in der Hochvakuumtechnik : K. H. MIRGEL. E. Leybold's Nachfolger, K6ln, Deutschland.