Electron Emission from a (100) Tungsten Surface under Proton Bombardment

Abstract

The yield of electrons from a clean (100) surface of tungsten under bombardment by protons at normal incidence is reported as a function of proton energy in the range 50 to 225 keV. The maximum value of the yield is 1.51\ifmmode\pm\else\textpm\fi{}0.03 electrons per incident proton at a proton energy of 125 keV. The yield from the (100) plane surface fell (10\ifmmode\pm\else\textpm\fi{}2)% below the yield from a polycrystalline surface. This difference can be attributed to the higher work function of the (100) surface. The tungsten surface was cleaned by flash-heating a single-crystal tungsten ribbon to 2400\ifmmode^\circ\else\textdegree\fi{}K in a vacuum chamber in which the total pressure was about 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ Torr. The yield was measured with the surface at room temperature, about 2 min after the surface was cleaned, while the time for a monolayer of residual gases to form on the surface was greater than 2 h.