E-beam evaporation is performed using a electron beam that scan the surface of the sample and then evaporate or sublimate the material just from its surface, without melting it in the crucible. In general, the crucible is cooled down using a water cooled circuit. this way the impurities located in the crucible do not diffuse in the charge and thus do not contaminate the very pure piece of material used for evaporation.
Evaporation is performed by heating a piece of material in a crucible, both the crucible and the charge inside are heated to the desired temperature, thus the crucible may contaminate the charge due to impurity diffusion from the crucible to the charge. However, some crucible such as PBN-made crucibles, are now of good purity, but if you do not want to contaminate your charge you should use each crucible to evaporate only one type of material. Contamination-free crucibles are expensive and they all have a range of temperature of use. for very high temperature evaporation sometime the only choice of crucible is graphite and thus there is a significant probability to find carbon in the material you evaporate.
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