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New vacuum-evaporated cermet resistor and insulator mixtures
Abstracts
of the papers presented
at the Thirteenth
National
12 in practice) and a very weak function of the sweep rate. Using a knowledge of the desorption kinetics, a spectrometer of arbitrarily slow sweep rate, and hence arbitrarily high resolving power, has been simulated on a digital computer. Resolving power can be increased to the point where magnification of noise in the data becomes intolerable. Increases by a factor of two or more are evident in examples presented. B A Wightman, Radio and Electrical Engineerirzg Division, National Research
Council, Ottawa,
Ontario.
Canada.
The resolving power of the monopole mass spectrometer The monopole, in contrast to the quadrupole mass filter, is an instrument whose performance at high resolving power depends importantly on entrance and exit aperture dimensions. Yet none of the theoretical expressions developed to predict resolving power includes these aperture dimensions as basic instrument parameters. In addition, aberrations caused by energy and angular spread in the ion beam must be explicitly accounted for if accurate estimates of performance are to be made. An analysis of the factors entering into monopole resolving power is made with respect to the recently proposed mode of operation wherein an integral number of rf cycles occurs during passage of an ion through the analyzer. A simple closed expression is developed for resolving power, and in application predicts values intermediate between the expression of von Zahn and the estimate of Lever. Stanley S Grossel, Veeco Instruments, Terminal Drive, Plainview, New
York 11803.
Improved qnadrnpole mass filter The transmission of ions through a conventional quadrupole mass filter is severely attenuated by the impulses which the ions receive as they traverse the fringing field. A computer study has been made to evaluate this phenomenon. Serious losses are indicated. The computer was also used to explore the effectiveness of a proposed scheme for eliminating these undesired radially directed impulses. The results were encouraging, and an experimental apparatus was built to evaluate the scheme in the laboratory. Preliminary results indicate that, at the higher resolving powers, the transmission of ions through the quadrupole is increased by factors of ten to one hundred without loss of resolving power. Wilson M Brubaker. Bell & Howell Research Center. 360 Sierra Madre
Villa, Pasadena,
California.
The behaviour of background hydrogen below 1O-10 torr A I-litre ultrahigh vacuum system with many valves, and with an envelope of aluminosilicate glass and stainless steel, has been tested. Gauges were (a) modulated Bayard-Alpert, (b) modulated suppressor, and (c) 90” mass spectrometer, all having hot filaments. The residual pressure was dominated by hydrogen, and this background hydrogen has been studied. The main findings have been: (1) Theory postulating a fixed source and pumping rate was not applicable. (2) Local pressures of hydrogen appeared in each gauge, making uncertain the assignment of a unique pressure to the whole system. A single gauge has measured a total pressure of 6 x lo-i3 torr. (3) The equilibrium ratio of masses 1 to 2 varied between 5 and 0.2 under various conditions of system processing. (4) A hypothesis that the primary source of hydrogen was atomic hydrogen coming out of solution in the filaments and recombining on nearby electrodes to yield molecular hydrogen, described most of the observations made. J P Hobson and J W Karnsbaw, Radio and Electrical Engineering Division.
National
Research
Council,
Ottawa
7, Ontario,
Canada.
Partial pressure analyses in the presence of a cold surface at a temperature variable between 3°K and 77°K The mouth of an omegatron tube is directed towards the cold surface SO that all gas molecules entering the gauge head have their starting point at the cold surface. The device is fitted in an ultrahigh vacuum system with a container having a volume of 250 litres. It provides (a) information about the potential sources of residual gases (b) a considerable increase of sensitivity as compared with static methods of mass spectroscopy, due to the accumulation of gases at a low temperature and subsequent re-evaporation. W Bachler, H Hoch and H G Niiller, E Leybold’s Nachfolger, 5 K&zBayenthal, 166
Bonner Str 504, Germany.
Vacuum Symposium
Thin-film
techniques
III-V Compound semiconductors prepared by multisource thermal evaporation techniques A wide variety of semiconductor films has been prepared with principal emphasis on InSb, InAs, GaAs and GaSb. One of the principal advantages of the method is that it allows mixtures of these materials to be formed in a rapid and convenient manner and specimens composed of InAs,Sb,., and GaAs,Sb,_, and Ga,In,_,Sb have been prepared. These systems appeared to be miscible m all proportions as indicated by their x-ray diffraction patterns. The use of optical techniques to study the dispersion and absorption in films of these materials indicates that optical properties behave similarly to those of the bulk materials. However, thoseabsorption processes which are determined by excess carrier scattering can become much larger than in the bulk. Roy F Potter, Infrared Division, US Naval Ordnance Laboratory, Corona,
California.
Film deposition by exploding wires The use of the exploding wire phenomena as a source of vapor for depositing thin films in vacuum is discussed. A capacitor discharge system capable of delivering 1500 J of energy at 15 kV with a rise time of 5 ,tsec for generating exploded wire films is described. Gross distribution of the deposited material and the microstructure of the resulting films are discussed in terms of the deposition variables: (1) residual gas pressure, (2) energy input, (3) wire material, (4) wire size and length, and (5) source to substrate distance. It is found possible to obtain films with a reasonably uniform thickness when using materials such as aluminium which are easily vaporized. The films formed in this manner have a very fine grained structure and exhibit nucleation and growth stages similar to those reported for vacuum evaporation. D M Mattox, A W Mullendore and F N Rebarchik, Sandia Corporation, PO Box 5800, Albuquerque,
New Mexico
87115.
Ion-beam deposition of metal films By using both the ion-beam deposition technique and the electronbeam scanning method, the maskless deposition process is possible. The process is as follows: the ion-beam is controlled such that it passes just above the substrate to collector and the substrate is scanned by the electron beam. The thin films are deposited on the substrate with the negatively charged pattern which is written by electron beam scanning. Structures and electrical properties of the ion-beam deposited metal films are reported. Susumu Namba, Pil Hyon Kim and Norio Kanekama, D’zeInstitute of Physical
and Chemical
Research,
Bunkyo-ka,
Tokyo, Japan.
Thin films of metals and inorganic compounds vacuum deposited by high energy laser A laser beam capable of energy outputs up to 500 J was directed through a glass window into a vacuum system, so that it could impinge onto fine grain powder of Cr, W, Ti, C, Sb,S,, ZnS, SrTiO,, BaTiO, and others. Special vacuum treatment was necessary to avoid splashing. The laser, a neodymium doped glass laser, of 1.06 /,rn wavelength was mostly used without Q-spoiling. Pulse burst duration was 2 to 4 msec, energy outputs 80 to 150 J. Deposition rates up to 100,000 A/set were obtained. The substrate was positioned between vapor source and laser, so that the laser beam passed through it. Electron micrographs and diffraction patterns showed that under certain conditions films were obtained without changing the original chemical composition of the source materials. Helmut Schwarz and H A Tourtellotte, Rensselaer Polytechnic Institute, 06028.
Harrford
Graduate
Center,
East
Windsor
Hill,
Connecticut
New vacuum-evaporated cermet resistor and insulator mixtures In the investigation of possible resistive materials for application as thin-film integrated-circuit components, new useful cermet mixturecompounds were discovered. These mixtures can be co-evaporated from the same crucible, eliminating the necessity of using simultaneous evaporation from two sources with all the attendant problems of dual monitoring and control. A simple relationship has been found between crucible soaking temperature and film composition control. Compounds are formed by in situ reactions of the mixture constituents. A simple mixture of germanium and chromium,
Abstracts
of the papers presented
at the Thirteenth
National
an aluminium-aluminium-oxide compound-mixture, (the composition of which is expected to be Also), Al-SiO and Si-SiOrCr mixtures are discussed. Data on temperature, resistivities, and temperature coefficients of these compounds are presented. Grant C Riddle, ITT Semiconductors Product Laboratory, Palo Alto, California. Resistivity and structure of Cr-SiO cermet tilms Resistivities of cermet films have previously been reported as a function of the Cr:SiO ratio in the source material. Film analysis by x-ray fluorescence has shown that the widely used flash evaporation technique of mixed powders leads to films of markedly different composition. The resistivities of films with 0 to 50 atmospheres % SiO and their changes during post-deposition heat treatment have been re-investigated. Cr and Cr,Si have been determined by electron diffraction. The well-known decrease of film resistivities during annealing is accompanied by grain growth of the metallic constituents. R Glang, R A Holmwood and S Clarke, IBM Corp, East Fishkill Facility, Route 52, Hopewell Junction, NY. An investigation of sputtered @tantalum thin 6lms Sputtered ,4 tantalum thin films were produced in a two chamber vacuum system (entrance chamber and sputtering chamber) with typical background pressure of 1 x lo-’ torr. Both the resistivity and sheet resistance uniformity were almost entirely dependent on cathode voltage. The application of negative anode bias voltage was found to control @ tantalum film resistivity. A relationship between resistivity and plasma potential was found which unifies both cathode voltage and anode bias voltage effects. Continuous sputtering over a period of several days was required to initially achieve equilibrium conditions in the sputtering chamber. The application of direct substrate negative bias voltage during cleanup reduced the B tantalum resistivity and, in some cases, produced a mixed structure of both bee and p tantalum. H C Cook, Western Electric Company, Engineering Research Center, PO Box 900, Princeton, NJ. A study of thin lilm interconnects between dissimilar materials Three organic materials and five inorganic materials were investigated for mounting “chip” parts and silicon parts into recesses in microcircuit wafers of glass and alumina to assess their feasibility as suitable surfaces for subsequent deposition of an electrical conductor. On the basis of preliminary thermal cycling tests, a lithium silicate filled diphenyl ,oxide varnish was selected for the next step in the study. Experimental models were subsequently fabricated with a variety of materials for pads. Samples were exposed to low temperature aging, moisture cycling, and thermal shock. An evaluation was made for adhesion of deposited conductors and interconnection resistance. M Lauriente, R Geisler, S Bassler and J M Winter, Westinghouse Electric Corporation, Defense and Space Center, Aerospace Division, Baltimore, Maryland.
Outgassing The causes of pressure fluctuations above oil diffusion pump This paper describes a systematic programme of experiments made to isolate the various causes, and attempts to summarize practical remedies. Sources outside the pump itself can he very severe, and those already known include gas bursts from the elastometer seals, and the effect of high forepressures, particularly of light gases. A new explanation of the latter effect is put forward in some detail. Sources associated with the pump are usually smaller in magnitude, but harder to eliminate. Returning fluid which tends to boil outside the jet assembly can be controlled by careful design. Experiments show that eruptive boiling may not always be a serious problem, unless it is associated with wet running of the top stage; a theory for the mechanism involved is proposed, and cures indicated. E D Tolmie and D J Crawley, Edwards High Vacuum Ltd, Manor Royal, Crawley, Sussex, England. The thermal re-emission of inert gas ions from tungsten and gold Inert gas ions of energy in the range 100 eV to 2 KeV were injected into polycrystalline tungsten and gold targets and upon subsequently
Vacuum Symposium heating the targets the rate of release of the previously entrapped gas was observed as a function of target temperature. The release rate-temperature spectra from tungsten reveal peaks, the details of which are ion type independent from He+ to Xe+ but sensitively dependent upon ion dose and energy. The variation of the magnitudes of the peak release rates with ion energy and dose suggests that the bombardment can simultaneously release trapped gas by vacancy production. The peak structure in gold is less well developed than in tungsten, but the energies associated with the peaks can be compared with normal diffusional processes in the target. K Erents. R P W Lawson and G Carter, Department of Electrical Engineering and Electronics, The Universiiy, Liverpool, Ekgland. Diffusion of hydrogen and nitrogen in tungsten and molybdenum Permeation and diffusion of hydrogen and nitrogen in tungsten and molybdenum have been measured at temperatures between 1100 and 2400°K and for pressures between 10-O and 500 torr. The data are based on three wrought tungsten tubes and one drawn molybdenum tube. Over large ranges in temperature and pressure, permeation rates follow Arrhenius plots and are proportional to the square root of the driving pressure. These results are believed to have direct bearing on flash filament experiments and pressure measurements using hot filament gauges. R Frauenfelder, Westinghouse Research Laboratories, Pittsburgh, Pennsylvania 15235. Temperature effects on outgassing A new technique is presented utilizing a series of nomographs to aid the engineer in predicting outgassing rates as a function of time and temperature. Surface as well as bulk processes are treated. A nomograph is given which inter-relates quantity of gas left in a material, outgassing rate, time, temperature and original gas content. The use of the technique presented makes possible an accurate prediction of system gas load as a function of temperature and time. In addition, by analyzing the gas load, the type of process and the gas source can be made. Frank Pagano, Aero Vat Corp, PO Box 448, Troy, New York 12181. Thermodesorption studies of carbon dioxide and oxygen from silver The thermodesorption of carbon dioxide and oxygen from a silver powder has been studied using a vacuum ultramicrobalance from 25 to 300°C. Three maxima were obtained when the desorption velocity was plotted versus temperature. These are related semiquantitatively to the activation energy of desorption and correspond to molecularly adsorbed carbon dioxide, molecularly adsorbed oxygen, and automatically adsorbed oxygen. A W Czanderna, Institute of Colloid and Surface Science and Department of Physics, Clarkson College of Technology, Potsdam, New York 13676 Reduction of stainless steel outgassing in ultrahigh vacuum The gassing rate of a 2 mm thick stainless steel sheet was measured in ultrahigh vacuum at constant pressure to avoid the readsorption occurring in a “rate of pressure rise” determination. The rate was typically 10-l* torr litre/cn? set and about 99% or more of the gas w& hydrogen. Since stainless steel usually contains large amounts of hvdroaen and the diffusion coefficient of hydrogen for stainless steel- is high, it was suspected that the hydrogen- diffuses to the surface from the interior of the metal and is released into the vacuum. Calculations indicated that the observed gassing rate could be explained by such a process and should be reduced several orders of magnitude by a high temperature treatment. Measurements are in reasonable agreement with these calculations. R Calder and G I.&n, CERN, Geneva, Switzerland. Outgassing of Al,O, and Be0 in vacuum at 540°C and 870°C A mass spectrometer study was carried out to determine the amount of gase&s oxygen compounds remaining in sapphire, a 99.8% ALO. bodv and a 99.8 “/, Be0 body after selected cleaning and firing s&edules.Partial pres&e plots oi evolved gases versus time for 26 minute outgassing runs at 871°C are presented, as well as total evolved gas quantities for the same period. R McRae and H Lloyd, Eimac, Division of Varian Associates, 301 Industrial Way, San Carlos, California. 167
of the papers presented
at the Thirteenth
National
12 in practice) and a very weak function of the sweep rate. Using a knowledge of the desorption kinetics, a spectrometer of arbitrarily slow sweep rate, and hence arbitrarily high resolving power, has been simulated on a digital computer. Resolving power can be increased to the point where magnification of noise in the data becomes intolerable. Increases by a factor of two or more are evident in examples presented. B A Wightman, Radio and Electrical Engineerirzg Division, National Research
Council, Ottawa,
Ontario.
Canada.
The resolving power of the monopole mass spectrometer The monopole, in contrast to the quadrupole mass filter, is an instrument whose performance at high resolving power depends importantly on entrance and exit aperture dimensions. Yet none of the theoretical expressions developed to predict resolving power includes these aperture dimensions as basic instrument parameters. In addition, aberrations caused by energy and angular spread in the ion beam must be explicitly accounted for if accurate estimates of performance are to be made. An analysis of the factors entering into monopole resolving power is made with respect to the recently proposed mode of operation wherein an integral number of rf cycles occurs during passage of an ion through the analyzer. A simple closed expression is developed for resolving power, and in application predicts values intermediate between the expression of von Zahn and the estimate of Lever. Stanley S Grossel, Veeco Instruments, Terminal Drive, Plainview, New
York 11803.
Improved qnadrnpole mass filter The transmission of ions through a conventional quadrupole mass filter is severely attenuated by the impulses which the ions receive as they traverse the fringing field. A computer study has been made to evaluate this phenomenon. Serious losses are indicated. The computer was also used to explore the effectiveness of a proposed scheme for eliminating these undesired radially directed impulses. The results were encouraging, and an experimental apparatus was built to evaluate the scheme in the laboratory. Preliminary results indicate that, at the higher resolving powers, the transmission of ions through the quadrupole is increased by factors of ten to one hundred without loss of resolving power. Wilson M Brubaker. Bell & Howell Research Center. 360 Sierra Madre
Villa, Pasadena,
California.
The behaviour of background hydrogen below 1O-10 torr A I-litre ultrahigh vacuum system with many valves, and with an envelope of aluminosilicate glass and stainless steel, has been tested. Gauges were (a) modulated Bayard-Alpert, (b) modulated suppressor, and (c) 90” mass spectrometer, all having hot filaments. The residual pressure was dominated by hydrogen, and this background hydrogen has been studied. The main findings have been: (1) Theory postulating a fixed source and pumping rate was not applicable. (2) Local pressures of hydrogen appeared in each gauge, making uncertain the assignment of a unique pressure to the whole system. A single gauge has measured a total pressure of 6 x lo-i3 torr. (3) The equilibrium ratio of masses 1 to 2 varied between 5 and 0.2 under various conditions of system processing. (4) A hypothesis that the primary source of hydrogen was atomic hydrogen coming out of solution in the filaments and recombining on nearby electrodes to yield molecular hydrogen, described most of the observations made. J P Hobson and J W Karnsbaw, Radio and Electrical Engineering Division.
National
Research
Council,
Ottawa
7, Ontario,
Canada.
Partial pressure analyses in the presence of a cold surface at a temperature variable between 3°K and 77°K The mouth of an omegatron tube is directed towards the cold surface SO that all gas molecules entering the gauge head have their starting point at the cold surface. The device is fitted in an ultrahigh vacuum system with a container having a volume of 250 litres. It provides (a) information about the potential sources of residual gases (b) a considerable increase of sensitivity as compared with static methods of mass spectroscopy, due to the accumulation of gases at a low temperature and subsequent re-evaporation. W Bachler, H Hoch and H G Niiller, E Leybold’s Nachfolger, 5 K&zBayenthal, 166
Bonner Str 504, Germany.
Vacuum Symposium
Thin-film
techniques
III-V Compound semiconductors prepared by multisource thermal evaporation techniques A wide variety of semiconductor films has been prepared with principal emphasis on InSb, InAs, GaAs and GaSb. One of the principal advantages of the method is that it allows mixtures of these materials to be formed in a rapid and convenient manner and specimens composed of InAs,Sb,., and GaAs,Sb,_, and Ga,In,_,Sb have been prepared. These systems appeared to be miscible m all proportions as indicated by their x-ray diffraction patterns. The use of optical techniques to study the dispersion and absorption in films of these materials indicates that optical properties behave similarly to those of the bulk materials. However, thoseabsorption processes which are determined by excess carrier scattering can become much larger than in the bulk. Roy F Potter, Infrared Division, US Naval Ordnance Laboratory, Corona,
California.
Film deposition by exploding wires The use of the exploding wire phenomena as a source of vapor for depositing thin films in vacuum is discussed. A capacitor discharge system capable of delivering 1500 J of energy at 15 kV with a rise time of 5 ,tsec for generating exploded wire films is described. Gross distribution of the deposited material and the microstructure of the resulting films are discussed in terms of the deposition variables: (1) residual gas pressure, (2) energy input, (3) wire material, (4) wire size and length, and (5) source to substrate distance. It is found possible to obtain films with a reasonably uniform thickness when using materials such as aluminium which are easily vaporized. The films formed in this manner have a very fine grained structure and exhibit nucleation and growth stages similar to those reported for vacuum evaporation. D M Mattox, A W Mullendore and F N Rebarchik, Sandia Corporation, PO Box 5800, Albuquerque,
New Mexico
87115.
Ion-beam deposition of metal films By using both the ion-beam deposition technique and the electronbeam scanning method, the maskless deposition process is possible. The process is as follows: the ion-beam is controlled such that it passes just above the substrate to collector and the substrate is scanned by the electron beam. The thin films are deposited on the substrate with the negatively charged pattern which is written by electron beam scanning. Structures and electrical properties of the ion-beam deposited metal films are reported. Susumu Namba, Pil Hyon Kim and Norio Kanekama, D’zeInstitute of Physical
and Chemical
Research,
Bunkyo-ka,
Tokyo, Japan.
Thin films of metals and inorganic compounds vacuum deposited by high energy laser A laser beam capable of energy outputs up to 500 J was directed through a glass window into a vacuum system, so that it could impinge onto fine grain powder of Cr, W, Ti, C, Sb,S,, ZnS, SrTiO,, BaTiO, and others. Special vacuum treatment was necessary to avoid splashing. The laser, a neodymium doped glass laser, of 1.06 /,rn wavelength was mostly used without Q-spoiling. Pulse burst duration was 2 to 4 msec, energy outputs 80 to 150 J. Deposition rates up to 100,000 A/set were obtained. The substrate was positioned between vapor source and laser, so that the laser beam passed through it. Electron micrographs and diffraction patterns showed that under certain conditions films were obtained without changing the original chemical composition of the source materials. Helmut Schwarz and H A Tourtellotte, Rensselaer Polytechnic Institute, 06028.
Harrford
Graduate
Center,
East
Windsor
Hill,
Connecticut
New vacuum-evaporated cermet resistor and insulator mixtures In the investigation of possible resistive materials for application as thin-film integrated-circuit components, new useful cermet mixturecompounds were discovered. These mixtures can be co-evaporated from the same crucible, eliminating the necessity of using simultaneous evaporation from two sources with all the attendant problems of dual monitoring and control. A simple relationship has been found between crucible soaking temperature and film composition control. Compounds are formed by in situ reactions of the mixture constituents. A simple mixture of germanium and chromium,
Abstracts
of the papers presented
at the Thirteenth
National
an aluminium-aluminium-oxide compound-mixture, (the composition of which is expected to be Also), Al-SiO and Si-SiOrCr mixtures are discussed. Data on temperature, resistivities, and temperature coefficients of these compounds are presented. Grant C Riddle, ITT Semiconductors Product Laboratory, Palo Alto, California. Resistivity and structure of Cr-SiO cermet tilms Resistivities of cermet films have previously been reported as a function of the Cr:SiO ratio in the source material. Film analysis by x-ray fluorescence has shown that the widely used flash evaporation technique of mixed powders leads to films of markedly different composition. The resistivities of films with 0 to 50 atmospheres % SiO and their changes during post-deposition heat treatment have been re-investigated. Cr and Cr,Si have been determined by electron diffraction. The well-known decrease of film resistivities during annealing is accompanied by grain growth of the metallic constituents. R Glang, R A Holmwood and S Clarke, IBM Corp, East Fishkill Facility, Route 52, Hopewell Junction, NY. An investigation of sputtered @tantalum thin 6lms Sputtered ,4 tantalum thin films were produced in a two chamber vacuum system (entrance chamber and sputtering chamber) with typical background pressure of 1 x lo-’ torr. Both the resistivity and sheet resistance uniformity were almost entirely dependent on cathode voltage. The application of negative anode bias voltage was found to control @ tantalum film resistivity. A relationship between resistivity and plasma potential was found which unifies both cathode voltage and anode bias voltage effects. Continuous sputtering over a period of several days was required to initially achieve equilibrium conditions in the sputtering chamber. The application of direct substrate negative bias voltage during cleanup reduced the B tantalum resistivity and, in some cases, produced a mixed structure of both bee and p tantalum. H C Cook, Western Electric Company, Engineering Research Center, PO Box 900, Princeton, NJ. A study of thin lilm interconnects between dissimilar materials Three organic materials and five inorganic materials were investigated for mounting “chip” parts and silicon parts into recesses in microcircuit wafers of glass and alumina to assess their feasibility as suitable surfaces for subsequent deposition of an electrical conductor. On the basis of preliminary thermal cycling tests, a lithium silicate filled diphenyl ,oxide varnish was selected for the next step in the study. Experimental models were subsequently fabricated with a variety of materials for pads. Samples were exposed to low temperature aging, moisture cycling, and thermal shock. An evaluation was made for adhesion of deposited conductors and interconnection resistance. M Lauriente, R Geisler, S Bassler and J M Winter, Westinghouse Electric Corporation, Defense and Space Center, Aerospace Division, Baltimore, Maryland.
Outgassing The causes of pressure fluctuations above oil diffusion pump This paper describes a systematic programme of experiments made to isolate the various causes, and attempts to summarize practical remedies. Sources outside the pump itself can he very severe, and those already known include gas bursts from the elastometer seals, and the effect of high forepressures, particularly of light gases. A new explanation of the latter effect is put forward in some detail. Sources associated with the pump are usually smaller in magnitude, but harder to eliminate. Returning fluid which tends to boil outside the jet assembly can be controlled by careful design. Experiments show that eruptive boiling may not always be a serious problem, unless it is associated with wet running of the top stage; a theory for the mechanism involved is proposed, and cures indicated. E D Tolmie and D J Crawley, Edwards High Vacuum Ltd, Manor Royal, Crawley, Sussex, England. The thermal re-emission of inert gas ions from tungsten and gold Inert gas ions of energy in the range 100 eV to 2 KeV were injected into polycrystalline tungsten and gold targets and upon subsequently
Vacuum Symposium heating the targets the rate of release of the previously entrapped gas was observed as a function of target temperature. The release rate-temperature spectra from tungsten reveal peaks, the details of which are ion type independent from He+ to Xe+ but sensitively dependent upon ion dose and energy. The variation of the magnitudes of the peak release rates with ion energy and dose suggests that the bombardment can simultaneously release trapped gas by vacancy production. The peak structure in gold is less well developed than in tungsten, but the energies associated with the peaks can be compared with normal diffusional processes in the target. K Erents. R P W Lawson and G Carter, Department of Electrical Engineering and Electronics, The Universiiy, Liverpool, Ekgland. Diffusion of hydrogen and nitrogen in tungsten and molybdenum Permeation and diffusion of hydrogen and nitrogen in tungsten and molybdenum have been measured at temperatures between 1100 and 2400°K and for pressures between 10-O and 500 torr. The data are based on three wrought tungsten tubes and one drawn molybdenum tube. Over large ranges in temperature and pressure, permeation rates follow Arrhenius plots and are proportional to the square root of the driving pressure. These results are believed to have direct bearing on flash filament experiments and pressure measurements using hot filament gauges. R Frauenfelder, Westinghouse Research Laboratories, Pittsburgh, Pennsylvania 15235. Temperature effects on outgassing A new technique is presented utilizing a series of nomographs to aid the engineer in predicting outgassing rates as a function of time and temperature. Surface as well as bulk processes are treated. A nomograph is given which inter-relates quantity of gas left in a material, outgassing rate, time, temperature and original gas content. The use of the technique presented makes possible an accurate prediction of system gas load as a function of temperature and time. In addition, by analyzing the gas load, the type of process and the gas source can be made. Frank Pagano, Aero Vat Corp, PO Box 448, Troy, New York 12181. Thermodesorption studies of carbon dioxide and oxygen from silver The thermodesorption of carbon dioxide and oxygen from a silver powder has been studied using a vacuum ultramicrobalance from 25 to 300°C. Three maxima were obtained when the desorption velocity was plotted versus temperature. These are related semiquantitatively to the activation energy of desorption and correspond to molecularly adsorbed carbon dioxide, molecularly adsorbed oxygen, and automatically adsorbed oxygen. A W Czanderna, Institute of Colloid and Surface Science and Department of Physics, Clarkson College of Technology, Potsdam, New York 13676 Reduction of stainless steel outgassing in ultrahigh vacuum The gassing rate of a 2 mm thick stainless steel sheet was measured in ultrahigh vacuum at constant pressure to avoid the readsorption occurring in a “rate of pressure rise” determination. The rate was typically 10-l* torr litre/cn? set and about 99% or more of the gas w& hydrogen. Since stainless steel usually contains large amounts of hvdroaen and the diffusion coefficient of hydrogen for stainless steel- is high, it was suspected that the hydrogen- diffuses to the surface from the interior of the metal and is released into the vacuum. Calculations indicated that the observed gassing rate could be explained by such a process and should be reduced several orders of magnitude by a high temperature treatment. Measurements are in reasonable agreement with these calculations. R Calder and G I.&n, CERN, Geneva, Switzerland. Outgassing of Al,O, and Be0 in vacuum at 540°C and 870°C A mass spectrometer study was carried out to determine the amount of gase&s oxygen compounds remaining in sapphire, a 99.8% ALO. bodv and a 99.8 “/, Be0 body after selected cleaning and firing s&edules.Partial pres&e plots oi evolved gases versus time for 26 minute outgassing runs at 871°C are presented, as well as total evolved gas quantities for the same period. R McRae and H Lloyd, Eimac, Division of Varian Associates, 301 Industrial Way, San Carlos, California. 167