Flash Evaporation

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Abstract
A study has been made of the behavior of thin metallic films when subjected to rapid heat pulses. Cadmium metal films, vapor deposited upon a tungsten ribbon, have been caused to evaporate in the form of a vapor pulse by rapidly heating the ribbon to temperatures in excess of the conventional boiling point of cadmium. The velocity of the emitted vapor pulse has been measured, in vacuum, using a time‐of‐flight technique involving the sequential scattering of two fixed electron beams. The dependence of the velocity has been measured as a function of a calculated tungsten‐ribbon temperature. A detailed study of the shape of the observed scattering signal due to the vapor pulse suggests that the condensed phase of cadmium is superheated to the ribbon temperature. Further, the pulse so formed has a temporal distribution in density, at some distance from the ribbon, which is equivalent to a molecular velocity distribution of a modified Maxwell—Boltzmann type, characteristic of an equilibrium molecular beam of cadmium at the tungsten‐ribbon temperature.

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