Ultrathin epitaxial films of the ionic insulators KCl and Rbl on Cu(211) were investigated by high-resolution low-energy electron diffraction (SPALEED). The Cu template employed is a vicinal surface which consists of (111)terraces separated by intrinsic monatomic (100) steps along the [011] direction (step distance 6.25 Angstrom). The resulting uniaxial substrate corrugation forces row matching between the intrinsic step separation and the characteristic lattice parameters along low-indexed azimuthal directions of the alkali halide layer. In this way, single-crystalline (100)-terminated films whose azimuthal orientations correspond to KCI[010] \\ Cu[011] and RbI[011] \\ Cu[011], respectively, are obtained.