R.D. Mathis Resistively heated evaporation sources are made from high purity, minimum 99.95%, refractory metals which have high melting points and low vapour pressures. The most commonly used \ refractory materials are tungsten, molybdenum and tantalum. There are a number of evaporation source designs - multi-strand filaments, wire baskets, boats and crucibles. An electric power source with low voltage tappings and high currents will be needed. The boat evaporation sources are usually more demanding in their power requirements.
Multi-strand (often three strand) tungsten filaments are typically used to evaporate metals such as aluminium or platinum. Tungsten wire baskets can be employed to evaporate chips or pellets of metals or dielectrics which either sublime or do not wet the basket when melting. They can also hold and heat crucibles containing the evaporant. Boat sources are also fabricated from tungsten, molybdenum and tantalum. Most elements and compounds can be evaporated from the standard boat sources, but where the material "wets" the complete boat (such as nickel) an aluminium oxide coated source may be considered. For highly dense uniform chromium films, chromium plated tungsten rods are available and baffle sources for materials such as silicon monoxide and zinc sulphide.