Structure of atomically smoothed LiNbO3(0001) surface

LiNbO3 (LN) is a substrate material used extensively for various optical or piezoelectric devices. We investigated an atomic-scale smoothing process of a LN single-crystal (0001) surface. Atomic force microscopy (AFM) observation revealed a surface morphology flattened from threefold symmetry to a step-terrace structure. The marked change of the surface was found to be dominated by a balance of surface diffusion and crystal growth within a period of 1-5 hours. An atomically flat surface with a straight and single-step height of 0.22 nm was obtained for a conventional LN substrate on the market. Next, we evaluated the surface composition and structure of the atomically flat LN (0001) surface by coaxial-impact collision ion scattering spectroscopy (CAICISS). We found that the atomically smoothed surface was terminated by a Nb atomic layer in which the Nb atoms were not shifted from the bulk position.