Thermal Emission of Electrons from Liquid Helium

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Abstract
The free surface of liquid helium acts as an energy barrier for electrons crossing the surface from the liquid into the vapor. The barrier is shown to be induced by the dielectric image-potential acting on the electrons below the liquid vapor interface. The application of an extracting electric field across the surface reduces the barrier and leads to a potential well below the surface which traps the electrons for extended periods of time. The escape into the vapor phase is shown to be dominated by thermal diffusion from the potential well according to Smoluchowski's equation. By measuring the escape rate a barrier height of 43.8 ± 0.7 K has been found. The top of the well lies 25 Å below the liquid vapor interface. Close to the λ-point and at higher temperatures the escape rate deviates from the theory. The relevancy of the present work for previous and further investigations of thermal eelctron emission from liquid helium is discussed.

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