Low-Energy Electron Beam Studies in Thin Aluminum Foils

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Abstract
The transmission of normally incident electrons through aluminum, which has been vacuum deposited on a 75-Å aluminum oxide insulator has been measured for electrons of energy between 1 eV and 4 keV. Currents to the top layer (65 to 525 Å) and to the metallic bottom layer underlying the insulator were monitored with operational amplifiers in obtaining the transmission characteristic. Below 50 eV the transmission is apparently controlled by the aluminum oxide insulator. Above this energy the absorption increases rapidly until the entire beam current is absorbed in the top layer. At still higher energies the current to the top layer decreases through zero to a value of − 1 (normalized). The energy at which the top current goes to zero was found to increase as the thickness of the top layer was increased. These data were analyzed to yield the electron stopping power which was found to vary from about 3.1 eV/Å at 300 eV to about 4.5 eV/Å at 950 eV when the raw data were corrected for nuclear scattering by a modified version of the Yang scattering theory.