Thermal vaporization sources sublimation

Vacuum evaporation (including sublimation) is a PVD process where material from a thermal vaporization source reaches the substrate without collision with gas molecules in the space between the source and substrate. The vacuum is required to allow the molecules to evaporate freely in the chamber and then subsequently condense on all surfaces... 

Sublimation source (vaporization) A vaporization source for heating materials, such as chromium, that sublime rather than evaporate. The subUmation source can function best by ensuring good thermal contact between the heater and the solid. Examples Electroplated chromium on a tungsten heater heating by radiation in an oven-like structure direct e-beam heating of the surface of a solid. 

Many solids do not develop enough vapor pressure at atmospheric pressure (760 mm Hg) to be purified by sublimation, but they frequently can be sublimed at reduced pressure. Thus, most sublimation equipment has provision for connection to an aspirator or other vacuum source. Reduction of pressure also helps to prevent thermal decomposition of substances that would require high temperatures to sublime at ordinary pressures. 

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