The thickness of physically vapor deposited copper and chromium specimens was measured as a function of position on a flat substrate situated above an electron-beam-heated evaporation source. The resulting profiles deviated from analytically predicted profiles based on the integrated mass flux from a flat surface of infinitesimal, directed surface sources. This deviation has been noted in the past and has been attributed to molecular interaction above the source. However, we show that the calculated molecular mean free path is much too long to allow any appreciable interaction of the evaporating molecules. Further, curva¬ture of the molten source, arising from the surface recoil from evaporating molecules, is likely to be responsible for the difference between the observed and predicted profiles.
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