Atomically resolved force microscopy images of complex surface unit cells: Ultrathin alumina film on NiAl(110)

In this Brief Report we present atomically resolved images of the ultrathin alumina film on NiAl (110). For the first time detailed images of the complex microstructure for both reflection domains have been obtained by frequency modulation dynamic force microscopy using a very stable, custom built, dual mode scanning force and scanning tunneling microscope. Measurements have been performed under ultrahigh vacuum conditions at 5 K with a quartz tuning fork as a force sensor. The high spatial resolution allows to derive 28 atomic positions in real space in the surface unit cell by simple graphical analysis. This has been successful without application of filtering or correlation methods, emphasizing the potential of this force microscopy method on complex oxide surfaces. With respect to topographic height even quantitative agreement with theory could be achieved, here shown for selected structural elements within the unit cell. Furthermore, deeper insight into a wavelike morphological feature could be obtained. Consistency with a published density-functional theory model and connections to other data from the literature are discussed.