NaCl films on Cu(311) exhibit a remarkably strong and localized binding bet
ween adlayer and substrate. The binding sites of the ions in the NaCl film
with respect to the Cu surface are determined from atomically resolved scan
ning tunneling microscopy images. A new model is proposed in which the bind
ing mechanism is controlled by the charge modulation of a regularly stepped
surface due to the Smoluchowski effect. This model can be extended to expl
ain the growth of ionic adlayers on regularly stepped and kinked metal surf
aces in general.