The total energy distributions (TEDs) of the emission currents in field
emission and surface photofield emission and the overlayer-induced
modifications in the surface electronic structures from the technologically
important W surfaces with the commensurate W(100)/Na c(2x2), W(110)/Na (2x2)
and W(111)/Na (1x1) overlayers are calculated. The TEDs obtained by our recent
numerical method that extends the full-potential linear augmented plane wave
method for the electronic structures to the study of field and photofield
emission are used to interpret the shifts of the peaks in the experimental TEDs
in field emission and photofield emission from the W(100) and W(110) surfaces
at sub-monolayer and monolayer Na coverage. Hybridization of the 3s Na states
with the pairs of dz2-like surface states of the strong Swanson hump in clean
W(100) and surface resonances in clean W(111) below the Fermi energy shifts
these W states by about -1.2 eV and -1.0 eV, thus stabilizing these states, to
yield new strong peaks in the TEDs in field emission and photofield emission
from W(100)/Na c(2x2) and W(111)/Na (1x1) respectively. The effect of Na
intralayer interactions are discussed and are shown to shift the strong s- and
p-like peaks in the surface density of states of W(110) below and above the
Fermi energy respectively to lower energy with increased Na coverage, in
agreement with experiments.Comment: 12 page
