Unraveling the LiNbO 3 X-cut surface by atomic force microscopy and density functional theory

Abstract

The LiNbO3(21̄1̄0) surface, commonly referred to as X-cut, is investigated by means of atomic force microscopy and first-principles calculations. Atomically resolved atomic force microscopy images show geometrical patterns not compatible with truncated bulk terminations. Fast Fourier transformation of the real-space images shows an oblique surface unit cell with lattice parameters of a=0.75±0.02 nm, b=0.54±0.02 nm, and α=94.8â̂̃. Comparing these experimental results with the theoretical models of stable surface terminations provides clear evidence for the formation of a -Li12 termination. The LN X-cut is, thus, characterized by a nonstoichiometric and Li-enriched composition. An analysis of the surface electronic charge indicates that the atomic force microscopy contrast is governed by the charge accumulation at the oxygen ions. © 2014 American Physical Society.