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681. Ultra-high vacuum
Classified Abstracts 678--683
Classified
Abstracts
General Vacuum Science and Engineering 10.
is that of thermodynamic equilibrium in the system, which does not always hold. The author points out that in many cases it is not the total density but the partial density of certain gaseous constituents which is of interest. For this purpose special instruments, so called partial density meters, have been developed, which are in effect miniature mass spectrometers.
V a c u u m S c i e n c e and T e c h n o l o g y
10 : 11 : 12 678. Basic vacuum physics and technology. U.S.A. During the past few years, considerable progress has been made in the techniques for producing and for measuring ultra-high vacuum. There still remain, however, quite a number of problems which are not properly understood. These are discussed by the author in some detail. Foremost is the question of how a vacuum gauge acts as a source of gas and what is the pumping speed of the gauge for various gases. This brings in the general problem of interaction of neutral gases with surfaces and the effects of adsorption on pressure measurements. Attempts have been made in the case of ionization gauges to lower the temperature of the electron source so as to reduce the disturbing effects of such gauges on the pressure measurement. Finally the relation of adsorption measurements to getter pump and getter ion pump characteristics is discussed. It is very important to take into account not only the mechanisms inside a gauge which act as a gas source, but also those which cause it to act as a pump. Such processes not only affect the total gas pressure, but also the composition as recorded in a mass spectrometer. New tools for studying gas surface reactions are required and the greatest need is an ultra-high vacuum electron microscope of very high resolving power. Typical vacuum conditions in present day instruments are so poor that many layers of hydrocarbons are deposited during the course of a single observation.
W . J. S.
H. G. Noller, Le Vide, 17 (97), Jam/Feb. 1962, 36-52. 10:30 680. The history and progress of the vacuum deposition processes. Great Britain. The author has divided his paper into 3 parts, the first dealing with the history of vacuum evaporation and cathodic sputtering, whilst the second treats of the effect of deposition conditions on the structure and purity of the evaporated film. The third part covers recent advances in techniques. One of the earliest attempts to produce thin metal films by physical rather than chemical means was that of Faraday's who prepared thin coatings of metal by passing the spark from a Leyden battery between the points of metal wires near glass plates in an inert atmosphere. Subsequent to Faraday's work investigators of electrical discharges at reduced pressures began to observe coatings on the glass envelope of the discharge tube, obviously produced by disintegration of the electrodes. The author traces the development of sputtering techniques from the early work of Grove and Edison, to later developments by Knudsen and Langmuir. Special mention is made of the present day large scale employment of vacuum evaporation to produce anti-reflecting coatings and front surface mirrors. In the second part of his paper, the author deals with the effect of deposition conditions in the resultant product. These conditions are treated under several headings, such as vapour intensity, incidence angle, substrate temperature etc. Interesting electron micrographs show resultant variation in film structure. In the last part of the paper, the author deals with such modern developments as electron bombarded vapour sources and reactive sputtering. Finally a modern high vacuum plant for film deposition at 10 " to 10 s torr is described. An extensive bibliography is provided, w.J.s.
W . J. S.
D. Alpert, Le Vide, 17 (97), Jam/Feb. 1962, 19-35. 10 : 11 : 12 679. Method for producing and measuring a vacuum. Germany. Two fundamental methods are available for producing a vacuum. In the first, gas molecules are extracted from the recipient by means of a pump and discharged bodily into the free atmosphere. In the second method, the molecules are attached to a wall or surface inside the recipient either by condensation or adsorption. The gas pressure is thus reduced but the molecules are not transferred into the outer atmosphere. An important class of pumps of the first kind are the oil or mercury diffusion pumps. When provided with suitable baffles and low temperature traps, such pumps can produce terminal pressure of the order of 10 -9 torr (oil diffusion) and 10 -11 torr (mercury diffusion) respectively. Examples of pumps of the second kind making use of absorption or condensation are provided by getter and getter ion pumps. A characteristic of the latter is the very strong dependence of pumping speed on the nature of gas being pumped. Thus a pump with a pumping speed of 1000 l./sec for hydrogen will manage only about 10 1./sec in the case of argon. Terminal pressure of the order of 10 s torr are obtained with pumps of this type. After discussing the basic principles of the two classes of pumps referred to above, the author turns his attention to the measurement of a vacuum. Pressures less than 10 3 torr cannot be measured directly in mechanical units and it has become necessary to estimate lower pressures indirectly in term of number of particles present per unit volume, assuming that the Maxwellian distribution is applicable. A further assumption
L. Holland, Le Vide, 17 (97), Jam/Feb. 1962, 83-106. 10 681. Ultra-high vacuum. (U.S.A.) P. A. Redhead et al., Advances in Electronics and Electron Physics 1962, 17, 323-432. 10:22 682. Ultra-high vacuum use of Bayard-Alpert ionization gauges. (U.S.A.) T. E. Hartman, Rev. Sci. Instrum., 34 (3), March 1963, 281-285. 11.
P r o d u c t i o n o f L o w Pressures
11 : 21 : 25 683. Performance of diffusion pumps in the ultra-molecular domain. France. The author describes a pump assembly for obtaining and maintaining vacua of the order of 10 7-10-1° torr. Starting 283
Classified
Abstracts
General Vacuum Science and Engineering 10.
is that of thermodynamic equilibrium in the system, which does not always hold. The author points out that in many cases it is not the total density but the partial density of certain gaseous constituents which is of interest. For this purpose special instruments, so called partial density meters, have been developed, which are in effect miniature mass spectrometers.
V a c u u m S c i e n c e and T e c h n o l o g y
10 : 11 : 12 678. Basic vacuum physics and technology. U.S.A. During the past few years, considerable progress has been made in the techniques for producing and for measuring ultra-high vacuum. There still remain, however, quite a number of problems which are not properly understood. These are discussed by the author in some detail. Foremost is the question of how a vacuum gauge acts as a source of gas and what is the pumping speed of the gauge for various gases. This brings in the general problem of interaction of neutral gases with surfaces and the effects of adsorption on pressure measurements. Attempts have been made in the case of ionization gauges to lower the temperature of the electron source so as to reduce the disturbing effects of such gauges on the pressure measurement. Finally the relation of adsorption measurements to getter pump and getter ion pump characteristics is discussed. It is very important to take into account not only the mechanisms inside a gauge which act as a gas source, but also those which cause it to act as a pump. Such processes not only affect the total gas pressure, but also the composition as recorded in a mass spectrometer. New tools for studying gas surface reactions are required and the greatest need is an ultra-high vacuum electron microscope of very high resolving power. Typical vacuum conditions in present day instruments are so poor that many layers of hydrocarbons are deposited during the course of a single observation.
W . J. S.
H. G. Noller, Le Vide, 17 (97), Jam/Feb. 1962, 36-52. 10:30 680. The history and progress of the vacuum deposition processes. Great Britain. The author has divided his paper into 3 parts, the first dealing with the history of vacuum evaporation and cathodic sputtering, whilst the second treats of the effect of deposition conditions on the structure and purity of the evaporated film. The third part covers recent advances in techniques. One of the earliest attempts to produce thin metal films by physical rather than chemical means was that of Faraday's who prepared thin coatings of metal by passing the spark from a Leyden battery between the points of metal wires near glass plates in an inert atmosphere. Subsequent to Faraday's work investigators of electrical discharges at reduced pressures began to observe coatings on the glass envelope of the discharge tube, obviously produced by disintegration of the electrodes. The author traces the development of sputtering techniques from the early work of Grove and Edison, to later developments by Knudsen and Langmuir. Special mention is made of the present day large scale employment of vacuum evaporation to produce anti-reflecting coatings and front surface mirrors. In the second part of his paper, the author deals with the effect of deposition conditions in the resultant product. These conditions are treated under several headings, such as vapour intensity, incidence angle, substrate temperature etc. Interesting electron micrographs show resultant variation in film structure. In the last part of the paper, the author deals with such modern developments as electron bombarded vapour sources and reactive sputtering. Finally a modern high vacuum plant for film deposition at 10 " to 10 s torr is described. An extensive bibliography is provided, w.J.s.
W . J. S.
D. Alpert, Le Vide, 17 (97), Jam/Feb. 1962, 19-35. 10 : 11 : 12 679. Method for producing and measuring a vacuum. Germany. Two fundamental methods are available for producing a vacuum. In the first, gas molecules are extracted from the recipient by means of a pump and discharged bodily into the free atmosphere. In the second method, the molecules are attached to a wall or surface inside the recipient either by condensation or adsorption. The gas pressure is thus reduced but the molecules are not transferred into the outer atmosphere. An important class of pumps of the first kind are the oil or mercury diffusion pumps. When provided with suitable baffles and low temperature traps, such pumps can produce terminal pressure of the order of 10 -9 torr (oil diffusion) and 10 -11 torr (mercury diffusion) respectively. Examples of pumps of the second kind making use of absorption or condensation are provided by getter and getter ion pumps. A characteristic of the latter is the very strong dependence of pumping speed on the nature of gas being pumped. Thus a pump with a pumping speed of 1000 l./sec for hydrogen will manage only about 10 1./sec in the case of argon. Terminal pressure of the order of 10 s torr are obtained with pumps of this type. After discussing the basic principles of the two classes of pumps referred to above, the author turns his attention to the measurement of a vacuum. Pressures less than 10 3 torr cannot be measured directly in mechanical units and it has become necessary to estimate lower pressures indirectly in term of number of particles present per unit volume, assuming that the Maxwellian distribution is applicable. A further assumption
L. Holland, Le Vide, 17 (97), Jam/Feb. 1962, 83-106. 10 681. Ultra-high vacuum. (U.S.A.) P. A. Redhead et al., Advances in Electronics and Electron Physics 1962, 17, 323-432. 10:22 682. Ultra-high vacuum use of Bayard-Alpert ionization gauges. (U.S.A.) T. E. Hartman, Rev. Sci. Instrum., 34 (3), March 1963, 281-285. 11.
P r o d u c t i o n o f L o w Pressures
11 : 21 : 25 683. Performance of diffusion pumps in the ultra-molecular domain. France. The author describes a pump assembly for obtaining and maintaining vacua of the order of 10 7-10-1° torr. Starting 283