Stability of Rocksalt (111) Polar Surfaces: Beyond the Octopole

Abstract

Stable polar oxide surfaces must be simultaneously electrostatically compensated and in thermodynamic equilibrium with the environment. As a paradigm, the MgO(111)-p(2x2) reconstructed surface is shown to involve combinations of Mg-covered terminations with peculiar insulating electronic structure, favored in O-poor conditions, and the O-terminated octopole, stabler in more O-rich environments. Such a picture, which could not have been foreseen by either experiments or simulations separately, goes beyond the Wolf model and reconciles the theory with the experimental data taken in variable thermodynamic conditions.

Effects of unreconstructed and reconstructed polar surface terminations on growth, structure, and magnetic properties of hematite films

“…Different surface stabilization models have been proposed and studied, with reconstruction [7][8][9][10][11][12][13][14] and hydrogen adsorption [12][13][14][15][16][17] being the two relevant mechanisms for the present study of growth on the prototypical MgO(111) polar oxide surface with the rock-salt structure. This surface has been shown to display (√3×√3)R30° [7,10,11,13] and (2×2) [10,12,13] surface reconstructions upon high temperature annealing, and (1×1)-OH termination when prepared at lower temperatures [13,16,17]. Water evolution appears to play an important role in the structures of the reconstructed surfaces even when these are prepared in UHV [14].…”

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…The best studied example is the octopolar reconstruction of the rocksalt (111) surface that was predicted by Wolf 273 and later verified experimentally for NiO(111) 34 and MgO (111) surfaces. 274 The octopolar reconstruction comprises two surface layers with 75% and 25% atom filling with respect to the ideal plane, residing on top of a bulk-truncated oxide layer. The dipole compensation in this case is so effective that the free-energy of the reconstructed surface drops even below the value for comparable non-polar oxide planes.…”

A brief introduction to the ABINIT software package

“…Also, some capabilities of ABINIT, less relevant for crystallographic and mineralogical studies, have been omitted. To complete the present paper, the interested reader might consult an earlier description of the project [1], visit the Web site [2], or examine recent selected papers [3][4][5][6][7][8][9][10].…”