Abstract
High-vacuum techniques made electron microscopy possible. In the 1930s vacuum evaporators with glass or metal chambers, diffusion pumps and oil sealed mechanical pumps were used in Europe and the U.S. The earliest systems used mercury pumps with liquid air traps. Oil diffusion pumps were manufactured in the U.S. by D.P.I. from glass or metal. In 1940 the first RCA TEM went into production as the EMB. First shadow casting in the U.S. was by Williams and Wycoff in 1944 and in Europe by Műller in 1942. Due to war secrecy, neither knew about the other. In 1944 RCA built the first production evaporator for EM under the direction of Bob Picard. The system had an 18" dia. glass bell jar and a metal baseplate with an oil diffusion pump backed by a Cenco Hypervac 20 mechanical pump. In 1948 Optical Film Engineering designed a 12" dia. bell jar evaporator for EM. This SC-3 employed a Welch 5 cfm mechanical pump and a 3" diffusion pump. Carbon evaporation for substrates or replicas was invented by D.E. Bradley in England and published in 1954.
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