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Sorption pumping of hydrogen by cryodeposits: Sorption capacity measurement
Classified abstracts 52-62 tested. It ~s found that the ultimate pressure in the vacuum system and the adsorption rate may be influenced by modifications of the X-type zeohte. Zeolite m Ca -°+ form is more advantageous for attaining low pressure in the system m comparison to the Na+-X-type, when the air is the pumped gas. V Bosacek, Czech JPhys, B20 (8), 1970, 912-916. 21 52. Calculation of the performance chart for Roots-type pumps. (W Germany) The influence of the design prinoples on the pumping speed of a Roots-type pump were investigated and compared. A method is given for the analytical determination of the performance chart for cases where the backstreaming within the axial clearances has boundary layer characteristics and the results are compared with experimental data. H Hamacher, Rep DLR-FB-69-88, Dec 1969, 118 pages (m German) (Set Tech Aerospace Reps, 8 (12), 2216, N70-26326). 21 53. Design and testing of a 9000 I./sec turbomolecular pump. (France) A turbomolecular pump which can produce an ultrahigh vacuum in a large vessel was developed. The theory of molecular pumps, outgassing, desorption, etc are reviewed, and a detailed description of the pump is gwen. The pump is capable of producing 1.4 × 10-11 torr. L Rubert, PhD Thesis, Paris Umv Fac Sciences, 1969, 99 pages (Set Tech Aerospace Reps, 8 (13), 2392, N70-27556). 21 54. Sorption pumping of hydrogen by cryodeposits: Sorption capacity measurement. (USA) The state-of-the-art of cryosorptlon of Ha and He by cold cryodeposited frost is reviewed and summarized and the results of addit,onal measurements of the sorption of Ha by COn frost are reported. It is shown that the sorption capacity of the frost depends upon the conditions at which the frost was formed and upon its temperature history. Frosts formed in a manner to make them porous or disordered are shown to possess greater sorpt~on capacities. It appears that surface diffusion of adsorbed molecules into a disordered frost structure is the basic pumping mechanism. Isotherms for H~ sorbed by COn frosts over a wide range of conditions are presented. As a result of the present tests, it is now possible to understand the confllctmg results of previous experimental investigations. K E Templemeyer, Rep AD-700980, Feb 1970, 64 pages (Sci Tech Aerospace Reps, 8 (13), 2335, N70-26919). 22. GAUGES 22 55. Development of ultrahigh vacuum measurements. (USA) Ultrahigh vacuum measuring techmques employing both the buried collector and the orbitron gauge designs have been studied. These studies include the determination of the hmiting background currents to the ion collector, pressure to ion collector response and the effects of varying the operational parameters on the gauge response. C M Gosselin and G A Beitel, Rep NASA-CR-1600, May 1970, 61 pages (Sci Tech Aerospace Reps, 8 (13), 2380, N70-26582).
22 56. An ionization gauge for the pressure range 10 ~-10 torr. (W Germany Two ionization gauges are described which allow pressure measurements to be made with high reproducibility (better than 10 per cent) in the region 10 ~-10 tort even after an electrode has been changed. Four or six equal, parallel wires are used as electrodes, the wires being loosely hung m electrode mountings, which in turn are bonded to ceramic discs. The effects on the ion current of varying the pressure, electrode distance, electrode potential and electrode current were measured A linear relation between the pressure and pressure display, was obtained up to about 0.5 torr. Deviations from lineanty at high pressures are ascribed to multiple ionization by the same electron and increasing energy losses due to electron scattering from gas atoms at low energies. The measurements were made with rare gases, hydrogen, nitrogen and oxygen. H G Schaeffer et al, Rep 1PP-2/75, July 1969, 37 pages (m German) (Set Tech Aerospace Reps, 8 (12), 2213, N70-26422). 22 57. Electron trajectories in ionization gauges. (Great Britain) When optimizing iomzatlon gauge sensitivity the efficient use of the ionizing electrons is one of the important requirements. Recent designs of extractor gauge retain the cylindrical grid structure, external
electron emitting filament and coaxial screen cyhnder currently used m the Bayard-Alpert gauge. The motion of electrons in this type of electrode system is described and the dependence of gauge sensitivity on the resulting trajectories is analyzed. The relationship is dlustrated between the average number of electron passes through the grid region and the electron capture probabdity of the grid, showing the advantage of a high grid transparency. The results of the study show that a considerable variation in gauge sensitivity can occur depending on the extent to which the electrons are focussed mto diametric paths across the grid region. L G Pittaway, JPhys D, ApplPhys, 3 (7), 1970, 1113-1121. 23. P U M P I N G 2~ 58. A new flange design for O-ring seals. (USA) A tn-contact O-ring seal flange was designed to provide a vacuum tight cover for a large wide-mouth cylindrical Dewar. The new design forces the O-ring outwards against the inner wall of the vessel to be sealed. W J Foote, Rev scient lnstrum, 41 (8), 1970, 1237. 23 59. A versatile vacuum manipulator. (USA) The manipulator which is described, provides motion for a sample in ultrahigh vacuum. It consists of a rotary drive, a feedthrough collar and a three dimensional translator. The sealing is provided by metal and bellows. T A Calcott and R G Oswald, Rev scient Instrum, 41 (8), 1970, 12491251. 24. VALVES 24 60. Improved liquid-metal glass vacuum valve. (USA) A magnetically actuated glass valve is described. The scaling of the valve is based on indium-tin eutect~c. C Veillon, Rev sctent Instrum, 41 (7), 1970, 1094.
III. Vacuum applications 30. EVAPORATION AND SPUTTERING 30 61. Photoelectric properties of amorphous and crystalline films of antimony. (Germany) Films of antimony are evaporated from an outgassed tungsten boat on cleaned quartz substrates. Experiments are carried out in a mercury-pumped glass system and in an ion-pumped stainless steel vacuum system. The pressure during antimony evaporation is always less than 5 × 10-s tort. It is found that for the thinnest films the amorphous state is stable, and at a critical thickness corresponding to an optical transmission of about 30 per cent the film crystalhzes spontaneously. The phase transition between amorphous and crystalhne films of antimony may be detected by an abrupt increase of about an order of magmtude in the photoelectric yield. A sudden decrease m the electrical resistance of the film, previously taken as an indication of the phase transition, occurs at a rather greater film thickness It is suggested that the thinnest films are made up of islands of amorphous antimony, at the critical thickness crystallization occurs, but the island structure is still retained. The decrease m resistance at greater thickness is probably due to coalescence of the islands. The photoelectric threshold of crystalhne films of antimony thicker than about 15 nm is 4.52 eV Amorphous films have a threshold m the region of 4.7 eV. In the amorphous region the photoelectric yield is related to the photon energy by the empxrical relation, which has been found to apply to a number of semiconductors. (England) T W Hall ef al, Phys Status Sohdi (a), 2 (2), June 1970, 327-334. 30 62. Conductivity of CdSe, CdSe-SiO x thin films. (Poland) Changes m conductivity of CdSe, CdSe-SiO x layers on glass substrate are investigated during thermal evaporation m vacuum at a pressure of 3 × 10 -6 torr. Ohmic contacts to CdSe are produced by gold with an mdmm admixture. The thickness of CdSe layers is 8001000 A at the evaporation rate of 2-5 A,/sec. After evaporation a slow increase of layer resistance is observed. CdSe layers deposited on substrates at a higher temperature of 90 to 160°C are characterized by smaller resistance changes due to residual gas ambient. Some layers with high cadmmm excess show rapid decrease of resistance after 65
22 56. An ionization gauge for the pressure range 10 ~-10 torr. (W Germany Two ionization gauges are described which allow pressure measurements to be made with high reproducibility (better than 10 per cent) in the region 10 ~-10 tort even after an electrode has been changed. Four or six equal, parallel wires are used as electrodes, the wires being loosely hung m electrode mountings, which in turn are bonded to ceramic discs. The effects on the ion current of varying the pressure, electrode distance, electrode potential and electrode current were measured A linear relation between the pressure and pressure display, was obtained up to about 0.5 torr. Deviations from lineanty at high pressures are ascribed to multiple ionization by the same electron and increasing energy losses due to electron scattering from gas atoms at low energies. The measurements were made with rare gases, hydrogen, nitrogen and oxygen. H G Schaeffer et al, Rep 1PP-2/75, July 1969, 37 pages (m German) (Set Tech Aerospace Reps, 8 (12), 2213, N70-26422). 22 57. Electron trajectories in ionization gauges. (Great Britain) When optimizing iomzatlon gauge sensitivity the efficient use of the ionizing electrons is one of the important requirements. Recent designs of extractor gauge retain the cylindrical grid structure, external
electron emitting filament and coaxial screen cyhnder currently used m the Bayard-Alpert gauge. The motion of electrons in this type of electrode system is described and the dependence of gauge sensitivity on the resulting trajectories is analyzed. The relationship is dlustrated between the average number of electron passes through the grid region and the electron capture probabdity of the grid, showing the advantage of a high grid transparency. The results of the study show that a considerable variation in gauge sensitivity can occur depending on the extent to which the electrons are focussed mto diametric paths across the grid region. L G Pittaway, JPhys D, ApplPhys, 3 (7), 1970, 1113-1121. 23. P U M P I N G 2~ 58. A new flange design for O-ring seals. (USA) A tn-contact O-ring seal flange was designed to provide a vacuum tight cover for a large wide-mouth cylindrical Dewar. The new design forces the O-ring outwards against the inner wall of the vessel to be sealed. W J Foote, Rev scient lnstrum, 41 (8), 1970, 1237. 23 59. A versatile vacuum manipulator. (USA) The manipulator which is described, provides motion for a sample in ultrahigh vacuum. It consists of a rotary drive, a feedthrough collar and a three dimensional translator. The sealing is provided by metal and bellows. T A Calcott and R G Oswald, Rev scient Instrum, 41 (8), 1970, 12491251. 24. VALVES 24 60. Improved liquid-metal glass vacuum valve. (USA) A magnetically actuated glass valve is described. The scaling of the valve is based on indium-tin eutect~c. C Veillon, Rev sctent Instrum, 41 (7), 1970, 1094.
III. Vacuum applications 30. EVAPORATION AND SPUTTERING 30 61. Photoelectric properties of amorphous and crystalline films of antimony. (Germany) Films of antimony are evaporated from an outgassed tungsten boat on cleaned quartz substrates. Experiments are carried out in a mercury-pumped glass system and in an ion-pumped stainless steel vacuum system. The pressure during antimony evaporation is always less than 5 × 10-s tort. It is found that for the thinnest films the amorphous state is stable, and at a critical thickness corresponding to an optical transmission of about 30 per cent the film crystalhzes spontaneously. The phase transition between amorphous and crystalhne films of antimony may be detected by an abrupt increase of about an order of magmtude in the photoelectric yield. A sudden decrease m the electrical resistance of the film, previously taken as an indication of the phase transition, occurs at a rather greater film thickness It is suggested that the thinnest films are made up of islands of amorphous antimony, at the critical thickness crystallization occurs, but the island structure is still retained. The decrease m resistance at greater thickness is probably due to coalescence of the islands. The photoelectric threshold of crystalhne films of antimony thicker than about 15 nm is 4.52 eV Amorphous films have a threshold m the region of 4.7 eV. In the amorphous region the photoelectric yield is related to the photon energy by the empxrical relation, which has been found to apply to a number of semiconductors. (England) T W Hall ef al, Phys Status Sohdi (a), 2 (2), June 1970, 327-334. 30 62. Conductivity of CdSe, CdSe-SiO x thin films. (Poland) Changes m conductivity of CdSe, CdSe-SiO x layers on glass substrate are investigated during thermal evaporation m vacuum at a pressure of 3 × 10 -6 torr. Ohmic contacts to CdSe are produced by gold with an mdmm admixture. The thickness of CdSe layers is 8001000 A at the evaporation rate of 2-5 A,/sec. After evaporation a slow increase of layer resistance is observed. CdSe layers deposited on substrates at a higher temperature of 90 to 160°C are characterized by smaller resistance changes due to residual gas ambient. Some layers with high cadmmm excess show rapid decrease of resistance after 65