LARGE-AREA BERYLLIUM METAL FOILS

To manufacture beryllium filters having diameters up to 82 mm and thic knesses in the range 0.1-1 mu m, it was necessary to construct apparat us in which the metal could safely be evaporated, and then to find an acceptable substrate and evaporation procedure. The metal was evaporat ed resistively from a tantalum dimple boat mounted in a baffled enclos ure that could be placed in a conventional vacuum bell jar, obviating the need for a dedicated complete vacuum system. Substrates were 102 m m x 127 mm x 0.05 mm cleaved mica sheets, coated with 0.1 mu m of NaCl , then with approximately 50 mu g/cm(2) of cellulose nitrate. These we re mounted on poly(methyl methacrylate) sheets 3 mm thick that were in turn clamped to a massive aluminum block for thermal stability. Detai ls of the processes for evaporation, float off, and mounting are given , and the resulting foils described.