Surface termination and stoichiometry of LaAlO₃(001) surface studied by HRTEM

As an important topic of condensed matter physics, metal oxide surfaces often exhibit exotic properties such as high catalytic activity, enhanced ferroelectricity and electronic phase transition, originating from the different local symmetry with respect to the bulk. As the structure determination of oxide surfaces presents challenges to conventional surface science techniques like scanning tunneling microscopy, aberration-corrected transmission electron microscopy (TEM) has been increasingly used to solve structures of oxide surfaces. In this work, the (001) surface of LaAlO₃, one of the most used components of oxide heterostructures, has been investigated. Our TEM experiments and extensive image simulations show that the La-O terminated LaAlO₃(001) surface undergoes significant reconstructions, forming La vacancies on the surface layer. Energetically, the LaAlO₃(001) surface is stable with the reconstructed La-O termination in a wide range of oxygen chemical potentials. Polarity compensation, reduced density of states at the Fermi level and bond enhancement of subsurface oxygen anions all contribute to the stabilization of the reconstructed surface.