The second international congress of the international organization for vacuum science and technology and the eighth national vacuum symposium of the american vacuum society, Washington, October, 1961
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Conferences and Symposia
The Second International Congress of The International Organization
for Vacuum Science and Technology and The Eighth National Vacuum
Symposium of The American Vacuum Society, Washington, October, 1961
THE largest vacuum congress that has ever been held took place at Washington during the four days from 16th to 19th October, 1961. About 1800 people were present and, in a total of 22 sessions, 204 papers were read. The object of this report is to discuss the proceedings in a way which will point to the main trends in development and research.
The subject is considered here under the following headings, arranged alphabetically for convenience : (1) adsorption and gettering ; (2) components ; (3) gauges ; (4) general topics; (5) getter-ion pumps, cryopumps and diffusion pumps ; (6) mass spectrometry ; (7) mechanical pumps and sorption pumps ; (8) space simulators ; (9) sputtering ; (10) thin films ; (11) ultra-high vacuum ; (12) vacuum metallurgy ; (13) vacuum systems.
It must be stressed that parallel sessions of two or three were held which, combined with the sheer physical effort of attending lectures all day for four days, made it impossible to appreciate more than about fifty of the papers presented. To that extent this account is biased ; further, to avoid an over-long report, review papers receive less attention than those reporting new work.
(I) Adsorption and gettering B. M. W. Trapnell surveyed the chief features of the
experimental and theoretical work on chemisorption and physical adsorption ; recent measurements on the velocities and heats of chemisorption were described and an appeal was made for further work on carbon. Adsorption of semi-conductors, especially in relation to the effects of charge transfer between an adsorbing particle and the semi- conductor, was discussed by J. T. Law. The preparation of initially atomically clean single crystal surfaces, including those of semi-conductors, in ultra-high vacuum was described by J. A. Dillon. The interaction of gas atoms with surfaces and molecular processes in adsorption on metals were the subject of papers by G. D. Kalsey and G. Ehrlich respectively. J. P. Hobson reported work on physical adsorption in which pressures of the order of lo-20 Torr were achievable by cooling ultra-high vacuum systems to liquid helium tem- peratures. Sticking probability measurements were described by D. Lee, H. Tomaschke and D. Alpert. In a study of the desorption of gas by photons, W. J. Lange and H. Riemersma found that about 10-s gas particles were released per photon (of energy a few electron-volt) for the system carbon monoxide on nickel. A new method of recording and displaying by
electronic means the variation of temperature with time of an initially flashed tungsten filament was described by A. E. Saunders and J. Yarwood in connection with work on the measurement of accommodation coefficients. The gettering efficiency of titanium was shown to be adversely influenced by carbon impurity because of the formation of hydrocarbon vapours and carbon oxides when hydrogen or oxygen are being sorbed respectively (L. Holland, L. Laurenson and P. G. W. Allen). The extraordinary efficiency of bulk getters consisting of an alloy zirconium with 16 per cent aluminium at about 300C was the chief feature of the exten- sive investigation of getters from metals of the 4th A group and thorium by P. della Porta, T. Giorgi and S. Origlio.
(2) Components K. S. Balain reported his work on epoxy resin seals for
high and low temperature work. Epoxy resin Stycast 285GT (Technical Bulletin 7-2-7, Emerson and Cuming, Inc. Canton, Mass., U.S.A.) was chosen for copper potentials leads out of high vacuum at liquid helium temperatures ; epoxy resin Stycast 2762 was successful for lead-ins in high temperature (up to 250C) vacuum systems. W. R. Wheeler and M. A. Carlson compared four seal designs for ultra-high vacuum flanges and concluded that the so-called Conflat sealwas the best: this consists of conical sealing surfaces and a flat metallic gasket. R. A. Haefer described an ion baflle for reducing back-streaming of oil from a mechanical or vapour pump : a cold cathode magnetron or inverted magnetron electrode arrangement is used in the pump inlet line ; the decomposed hydrocarbon molecules have an extraordinary tendency to recombine to solid polymers, preferentially at the electrodes. J. Hengevoss and W. K. Huber described ultra-high vacuum experiments in which residual gas analysis was by a cycloidal type mass spectrometer. A special study was made of the liquid nitrogen trap : in ultra-high vacuum, it was shown that the action consists of adsorption of permanent gases at well baked-out surfaces of trap.
(3) Gauges An ultra-high vacuum gauge of better sensitivity than the
Bayard-Alpert type and based on the omegatron electrode structure (but without mass spectrometer action) was described by A. Klopfer. Though having a very low X-ray limit, the complex electrode structure would be difficult to
162 Conferences and Symposia
de-gas readily. A. van Oostrom described a design of Bayard-Alpert gauge with an extremely thin ion collector wire and a special grid structure with optimum potential distribution for which the X-ray limit was about 6 x lo-13 torr. A hot-cathode magnetron ionization gauge was described by J. M. Lafferty. In the most recent development, the low pressure limit has been extended below 4 x lo-14 torr by use of an electrostatic .lens system that focuses ions on the first dynode of an electron multiplier. A special Geiger- Mtiller tube which counts U.V. photons from electron-excited residual gas was used as a vacuum gauge by I. Alexeff ; this should theoretically measure pressures down to lo-13 torr. Susceptibility to cathode contamination would probably lead to considerable sensitivity variations. H. Schwarz described a resonance vacuum gauge of which the operation depends on the damping of a light vibrating membrane by the surrounding gas ; it is alleged to cover the range from 760 to 10-s torr.
(4) General topics
Papers presented included subjects of vacuum spectroscopy (B. Rosen), an ultra-high vacuum U.V. monochromator (L. Marton, J. A. Simpson, J. A. Suddeth and L. B. Leder), apparatus for measuring gas evolution rates (M. L. Hill), distillation (E. Heunecke and W. Nerge), molecular dis- tillation of rice oil (K. Sakutai), steam sterilizers (T. W. G. Rowe, R. Kusay and E. Skelton) and reactions of silica glass with metals (H. Okamoto).
(5) Getter-ion pumps, cryopumps and diffusion pumps One of the most interesting contributions was that of
K. C. D. Hickman on high vacuum with the polyphenyl ethers . These consist of chains of benzene radicals inter- bonded by oxygen and have exceptional stability and resis- tance to radiation damage. The isomer mixture, bis (phenoxy-phenoxy) phenyl ether has a vapour pressure of about 10-g torr at 25C and yields vacua approaching 10-g torr in the unrefrigerated condensation pump. This fluid can also be applied to gaskets, valves, joints, and as a coating to large inside metal surfaces. Tests of this fluid on modified commercial vapour pumps were described ; new designs of pumps to take full advantage of these fluids were called for and their desirable features outlined.
J. Grobman reported on a catalytic method for cryo- pumping hydrogen . In research on electric thermal rockets, hydrogen has been proposed as a propellant. Vacuum chambers for testing these rockets could be reduced in size and cost if condensers for hydrogen could be incorporated. Large-scale helium refrigeration is possible but very costly. An alternative is a catalytic surface reaction whereby hydro- gen is chemically converted into water which will condense readily on a liquid-nitrogen cooled surface. Catalyst studied was palladium-coated alumina pellet. Catalyst support geometries were considered.
New work on cryopumping was also reported in the
session on space simulators, and is included under that heading here.
The object of the research reported by N. Milleron and L. L. Levenson was to achieve the highest possible pumping speed for hydrogen and helium compatible with negligible oil contamination rate in the optimization of oil diffusion pump systems for ultra-high vacuum. A new diffusion pump was designed with Hickmans new oils in mind. Quick-acting boiler heaters were designed to produce super- heated oil vapour whilst maintaining relatively low-tempera- ture liquid in the boiler, to supply each jet of a diffusion pump with an independent vapour source, to minimize oil cracking, to maximize efficiency of conversion of electrical energy to vapour energy at jets and to eliminate eruptive boiling. The oil boiler designed was so effective in producing a directed stream of vapour that the same basic design was used for the top jet. The heater used was nichrome ribbon 0.001 in. thick and 1 in. wide, corrugated transversely and coiled into spiral with glass tape separating turns.
A. R. Hamilton presented a paper on some experimental data on parameter variations with a triode ion pump . This consists of two cathodes with a central egg-box shape anode ; the cathodes are at -3500 V and the anode at +3500 V with the collector surfaces and pump casing earthed; a magnetic field is provided perpendicular to the plane of the electrodes. The search for a new sputter cathode material or combination of materials which might be more efficient than titanium was unsuccessful. Other points brought out were (i) thorough baking is essential to remove water vapour; (ii) new gas releases molecules of previously pumped gas; (iii) foreign gases are produced in the pump as a result of outgassing and re-emission of previously pumped gas, (iv) as gas composition is