Energy distribution in field emission from adsorbate-covered surfaces

A calculation of the total energy distribution of field-emitted electrons in the presence of chemisorbed atoms shows that [j(ω)-j0(ω)]j0(ω)=u(ω)2 ImGaa(ω) if the adsorbate resonance level lies within the conduction band of the metal. j(ω) and j0(ω) are the current densities per unit energy in the presence and absence of the adsorbate, respectively; the energy ω is measured from the vacuum level; xa is the surface-adsorbate distance; and (1πImGaa is the local density of states at the adsorbate. u(ω)2exp{2(-2mω2)12xa+[43(2m2)12(-ω)32(eF)-1×(v(y)-1)]}, where F is the electric field and v(y) is the image-potential correction factor. The expression given above for the tunneling current is general and independent of the explicit form of Gaa. if the adsorbate resonance lies below the bottom of the conduction band, then [j(ω)-j0(ω)]j0(ω)<0, in agreement with the results of Duke and Alferieff.