GB523982A - Improvements in secondary electron emission layers for use in electron discharge devices - Google Patents

Abstract

523,982. Electrode materials. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 18, 1939, No. 1765. Convention date, Jan. 18, 1938. [Class 39 (i)] A secondary emitting layer for the electrodes of an electron multiplier is formed of a film of beryllium vaporized in vacuo on to a foundation metal such as molybdenum or nickel, and the film and foundation metal are then subjected to a heat treatment. This heat treatment may be carried out in the presence of oxygen, the greater the oxygen pressure the lower the temperature required. In one method, the beryllium vaporized layer having been formed in vacuo on the foundation metal, the whole is exposed to air and heated to 350‹C. Alternatively, after formation and exposure to air the foundation and layer may be heated, e.g. by high frequency current, in vacuo to a temperature between 600‹C. and 800‹C. for a few minutes. The resulting multiplication ratio is about 4 to 5. A further increase of emissivity may be obtained by a subsequent heating to about 1,000‹C. in vacuo. These beryllium films are not impaired by the presence of oxygen or by heavy electron bombardment, and are useful for electron multipliers where the electrodes are raised to temperatures above 150‹C. by electron bombardment. The first stages of a multiplier in which the heating effect results in temperatures of less than 150‹C. may be caesium on oxidized silver films of high emissivity.