In this work we investigate the growth of tris(8-hydroxyquinoline) aluminium (Alq₃) on single-crystal Ag(111) substrates partially covered by an ultrathin KBr film. Noncontact atomic force microscopy is used to determine the molecular ordering of 0.8 monolayer Alq₃ evaporated onto these substrates. The simultaneous measurement of the local surface potential by means of Kelvin probe force microscopy yields the local workfunction difference between the pure Ag(111) surface and the one covered by an ultrathin KBr film, by pure Alq₃, or by both (KBr|Alq ₃). The molecular ordering and the interface dipole formation are discussed with respect to experiments described in the literature in which electron diffraction and photoelectron spectroscopy were used, respectively.