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Effects of the evaporation technique on optical glass
Vacuum,
October, 1951
Vol. I No. 4
LETTERS
TO
THE
EDITOR
Effects of the Evaporation Technique on Optical Glass Sommaire fit remarquer dans un article precedemment publie dans ce journal, qu’il avait observe que des surfaces optiquement planes en verre ou quartz etaient uarfois deteriorees oendant la deuosition d’un film L’auteur signale une metalli&e par projection cathodique. observation semblable qu’il fit dans des cas oii le procede d’evaporation normal pour l’argentage de surfaces optiques Dans un cas une convexite de 1 a 23 s’etait etait utilise. form&e dans le verre. LE PROFESSEUR
TOLANSKY
Fag. I. IT IS OF INTEREST to read that Professor Tolanskyl has found that permanent damage to glass or quartz optical flats sometimes occurs during cathodic sputtering of a metallic film on to the surface. Some time ago a similar effect was observed at this laboratory when using the normal evaporation technique. A silver film was evaporated on to the surface of a 6-inch diameter optical flat. The surface was cleaned initially in the usual manner with soapy water, nitric acid and hydrogen peroxide. The surface was finally subjected to ionic bombardment at 3,300 volts for 6 minutes. The silver was evaporated from a molybdenum boat at a current rating of 55 amperes in a chamber evacuated to 10-5mm. Hg by oil diffusion pumping. This silvered optical flat, which was originally flat to 7~120 (A=S,OOO A) was examined using a The interferomaster optical flat of knbwn flatness. grams obtained are shown in Plate I Figures 1 and 2. Figure 2 is just a different arrangement of the fringes to that in Figure 1 showing very vividly the nature The hill is and location of the ‘ hill ’ on the surface. clearly between h and 2h high. The-silvered flat was then thoroughly cleaned of all the visible coating of silver and resilvered by evaporation. The hill remained and continuous soaking in nitric acid for hours did not remove it. The flat was examined in white light by eye at oblique incidence and a ‘ burnt ’ region is clearly visible extending over an area of about Q in. Figure 3 of Plate I shows a picture of this area taken in
green light. The inner part of the area is red to yellow changing to blue-violet in colour at the outer edge. There was some slight evidence of a small distortion effect on the non-silvered side of the flat. It would appear that silver or molybdenum or impurities in the evaporation chamber have been Fig.’ 2.
October,
1951
Vacuum.
BOOK
Vol. I No. 4
REVIEWS
Industrial High Vacuum. Bv T. R. DAVY. (Sir Isaac Pitman &3ons Ltd.. London: 1951.) PD. 243. Price EI 5s. od. WHEN WRITING A BOOK which
Fig. 3.
driven into the surface from a sudden but unnoticed burst of ions or particles during the bombardment or evaporation. It is proposed to remove the top surface layer of the flat chemically and have this examined by micro-analysis. It is worth noting that a 3-inch diameter flat made of optical glass was affected similarly a short time later. Further experiments were done with a test piece of optical glass using deliberately excessive bombardment rates and heating currents but the effect could not be repeated. Examination of the glass with polarised light during bombardment and evaporation showed no evidence of strain taking place in the glass. Further investigation of the exact nature of the material deposited on a surface by evaporation seems desirable when effects such as those described above can occur. C. F. Bruce. National Standards Laboratory, University Grounds, Sydney, Australia. 1st October, l Tolansky,
1951. S., Vacuum 1, (1951), 75.
deals with the industrial applications of a scientific technique there are three possibilities afforded to the author. Firstly, he may decide to cover the subject fully, in which case he is very unlikely to be thoroughly familiar with more than a small part of the whole technology, consequently he has to digest other books and many papers recording original work relating to subjects of which his knowledge is not gained from first hand experience. This method leads to a good book if the author has wide experience, a strong critical faculty, good imagination and infinite patience. Secondly, he may collect together a team of writers who have, collectively, a comprehensive knowledge gamed from practical experience. This approach is becoming more and more widely adopted, especially in America, but it often results in a work lacking homogeneity. Thirdly, the author may write fully about those aspects of the subject of which he has great experience, and neglect or deal summarily, with technologies outside his special province. This last course has apparently been adopted by the author of Industrial High Vacuum. As a result the work is out of balance and might even be said to have a misleading title. Nevertheless, it is a valuable book. The author is manifestly an authority on the deposition of metals and salts in vacuum, and at least half the book is devoted to detailed accounts of this work. The information given on this subject is first-class : a great deal of data is given in book form for the first time, and many results of the author’s own experimental work are included. On the other hand, despite the rapid growth of vacuum science in many new fields of technology in recent years, the manufacturers of electron tubes are surely still the largest users of vacuum apparatus. This book, however, confines the details of this vast use of vacuum to a few miscellaneous details here and there in the text, supplemented by a three page appendix called ‘ Emission of Electrons : Cathodes.’
301
October, 1951
Vol. I No. 4
LETTERS
TO
THE
EDITOR
Effects of the Evaporation Technique on Optical Glass Sommaire fit remarquer dans un article precedemment publie dans ce journal, qu’il avait observe que des surfaces optiquement planes en verre ou quartz etaient uarfois deteriorees oendant la deuosition d’un film L’auteur signale une metalli&e par projection cathodique. observation semblable qu’il fit dans des cas oii le procede d’evaporation normal pour l’argentage de surfaces optiques Dans un cas une convexite de 1 a 23 s’etait etait utilise. form&e dans le verre. LE PROFESSEUR
TOLANSKY
Fag. I. IT IS OF INTEREST to read that Professor Tolanskyl has found that permanent damage to glass or quartz optical flats sometimes occurs during cathodic sputtering of a metallic film on to the surface. Some time ago a similar effect was observed at this laboratory when using the normal evaporation technique. A silver film was evaporated on to the surface of a 6-inch diameter optical flat. The surface was cleaned initially in the usual manner with soapy water, nitric acid and hydrogen peroxide. The surface was finally subjected to ionic bombardment at 3,300 volts for 6 minutes. The silver was evaporated from a molybdenum boat at a current rating of 55 amperes in a chamber evacuated to 10-5mm. Hg by oil diffusion pumping. This silvered optical flat, which was originally flat to 7~120 (A=S,OOO A) was examined using a The interferomaster optical flat of knbwn flatness. grams obtained are shown in Plate I Figures 1 and 2. Figure 2 is just a different arrangement of the fringes to that in Figure 1 showing very vividly the nature The hill is and location of the ‘ hill ’ on the surface. clearly between h and 2h high. The-silvered flat was then thoroughly cleaned of all the visible coating of silver and resilvered by evaporation. The hill remained and continuous soaking in nitric acid for hours did not remove it. The flat was examined in white light by eye at oblique incidence and a ‘ burnt ’ region is clearly visible extending over an area of about Q in. Figure 3 of Plate I shows a picture of this area taken in
green light. The inner part of the area is red to yellow changing to blue-violet in colour at the outer edge. There was some slight evidence of a small distortion effect on the non-silvered side of the flat. It would appear that silver or molybdenum or impurities in the evaporation chamber have been Fig.’ 2.
October,
1951
Vacuum.
BOOK
Vol. I No. 4
REVIEWS
Industrial High Vacuum. Bv T. R. DAVY. (Sir Isaac Pitman &3ons Ltd.. London: 1951.) PD. 243. Price EI 5s. od. WHEN WRITING A BOOK which
Fig. 3.
driven into the surface from a sudden but unnoticed burst of ions or particles during the bombardment or evaporation. It is proposed to remove the top surface layer of the flat chemically and have this examined by micro-analysis. It is worth noting that a 3-inch diameter flat made of optical glass was affected similarly a short time later. Further experiments were done with a test piece of optical glass using deliberately excessive bombardment rates and heating currents but the effect could not be repeated. Examination of the glass with polarised light during bombardment and evaporation showed no evidence of strain taking place in the glass. Further investigation of the exact nature of the material deposited on a surface by evaporation seems desirable when effects such as those described above can occur. C. F. Bruce. National Standards Laboratory, University Grounds, Sydney, Australia. 1st October, l Tolansky,
1951. S., Vacuum 1, (1951), 75.
deals with the industrial applications of a scientific technique there are three possibilities afforded to the author. Firstly, he may decide to cover the subject fully, in which case he is very unlikely to be thoroughly familiar with more than a small part of the whole technology, consequently he has to digest other books and many papers recording original work relating to subjects of which his knowledge is not gained from first hand experience. This method leads to a good book if the author has wide experience, a strong critical faculty, good imagination and infinite patience. Secondly, he may collect together a team of writers who have, collectively, a comprehensive knowledge gamed from practical experience. This approach is becoming more and more widely adopted, especially in America, but it often results in a work lacking homogeneity. Thirdly, the author may write fully about those aspects of the subject of which he has great experience, and neglect or deal summarily, with technologies outside his special province. This last course has apparently been adopted by the author of Industrial High Vacuum. As a result the work is out of balance and might even be said to have a misleading title. Nevertheless, it is a valuable book. The author is manifestly an authority on the deposition of metals and salts in vacuum, and at least half the book is devoted to detailed accounts of this work. The information given on this subject is first-class : a great deal of data is given in book form for the first time, and many results of the author’s own experimental work are included. On the other hand, despite the rapid growth of vacuum science in many new fields of technology in recent years, the manufacturers of electron tubes are surely still the largest users of vacuum apparatus. This book, however, confines the details of this vast use of vacuum to a few miscellaneous details here and there in the text, supplemented by a three page appendix called ‘ Emission of Electrons : Cathodes.’
301