Electron-stimulated desorption of sodium atoms initiated by their reverse motion

This paper reports on the first measurement of the yield and energy distributions of sodium atoms in electron-stimulated desorption at T = 160 K from sodium layers adsorbed on tungsten with a gold film atop. The Na atom yield has a resonant pattern with an appearance threshold of 30 eV, which can be attributed to exciton excitation in the Na 2p level. The Na yield is associated with the formation of a semiconducting Na _x Au _y film at T ∼ 300 K and sodium and gold coverages in excess of one monolayer. Sodium atoms are desorbed through Auger neutralization of Na²⁺ ions in their reverse motion toward the surface and is limited by the resonant ionization of Na atoms as they pass through the adsorbed layer of Na⁺ ions. The energy distributions of Na atoms are bell shaped with a maximum at about 0.56 eV.