Patent GB-771231-A (GB)
Title: Improvements in and relating to the froduction of thin layers
IPC: H01B1/00
Filed: 1950-10-13
Abstract: 771,231. Coating by vapour deposition. VESZI, G. A., and MARKUS, P. Oct. 9, 1951 [Oct.13, 1950], No. 25057/50. Class 82(2) [Also in Group XL(a)] A process for coating a transparent support comprises forming a thin layer of transparent electrically conducting cadmium oxide by cathode sputtering and an additional layer of transparent material in contact with the cadmium oxide by cathode sputtering or vacuum evaporation, The additional layer, e.g. of sodium iodide or arsenic trioxide, can be provided between the layer of cadmium oxide and the support, e.g. of glass, and can have a refractive index intermediate between those of the cadmium oxide and the support and a further additional layer can be applied to the external surface of the. cadmium oxide, the further additional layer being of: a material, e.g. silicon monoxide, magnesium fluoride or cryolite, having a refractive index intermediate the refractive indices of cadmium oxide and air. Alternatively the additional layer can be applied to the external surface of the cadmium oxide and can be silicon monoxide, magnesium fluoride or cryolite. The additional layers approach a quarter wave length thickness. Apparatus for carrying out the process is shown in Figs. 1 and 2 and comprises a cylindrical chamber 10 closed at its ends by removable plates 11, 12 and wing nuts 13, 14 and containing a carriage 16, 17 for the plate 15 to be coated moved by motor driven screw-threaded rods 19, 20. The evaporation materials are contained in removable crucibles 23 electrically heated by elements 24 and separated by baffles. 25. Removable cathode sputtering elemeats 28 separated by a baffle 29, are provided at the other end of the chamber 10. Gases can be admitted to the chamber through connections 32, 33, 34 controlled by cocks as described in Specification 732,891. The plate 15 to be coated can be inspected through glass-covered openings 38 and the light transmission of the plate can be determined by light source 44, glasscovered openings 40, 41 and a photo-cell 45. In a specific example a glass plate 15 is degreased and cleaned by chalk powder and ammonium hydroxide, rinsed in distilled water and air dried and then placed in the carriage 16, 17. The chamber 10 is then evacuated to a pressure of 10<SP>-4</SP> to 10<SP>-5</SP> mms, the plate moved to opposite the cathode sputtering means 28, hydrogen admitted to the chamber at a pressure of about 10-' to 10-<SP>2</SP> nuns, and the plate subjected to a discharge using an aluminium cathode for a period of about 10 secs. to effect cleaning. The plate 15 is then moved opposite the evaporation means 23 and a layer of blooming material applied for about 2 to 3 minutes. The layer of cadmium oxide is then deposited by the sputtering means 28 as described in Specification 732,891, and the final blooming layer then deposited. The plate 15 should be moved during both the evaporation and cathode sputtering processes. In order to leave uncoated marginal portions of the plate 15 masks 46, 47 carried on and movable by rods 48. 49 extending through the end plates 11 and 12 are provided.