  The local density of states of Ag(111) has been probed in detail on
disordered terraces of varying width by dI/dV-mapping with a scanning tunneling
microscope at low temperatures. Apparent shifts of the bottom of the
surface-state band edge from terrace induced confinement are observed.
Disordered terraces show interesting contrast reversals in the dI/dV maps as a
function of tip-sample voltage polarity with details that depend on the average
width of the terrace and the particular edge profile. In contrast to perfect
terraces with straight edges, standing wave patterns are observed parallel to
the step edges, i.e. in the non-confined direction. Scattering calculations
based on the Ag(111) surface states reproduce these spatial oscillations and
all the qualitative features of the standing wave patterns, including the
polarity-dependent contrast reversals.
