Understanding the Role of Oxygen Vacancies in the Stability of ZnO(0001)-(1 x 3) Surface Reconstructions

The atomic-scale explanation of ZnO surface reconstructions is relevant to strengthen its use in technological applications and to guide experimental efforts in improving the growth techniques. Several surface reconstructions have been observed for both ZnO polar surfaces, the so-called (0001) and (000 (1) over bar), which correspond to the Zn and O terminations. The experimental evidence for the (0001) surface reconstructions brings an insight into the stabilization mechanisms vital for surface processes. This work explores the stability between the previously reported reconstructions (2 x 2), (4 x 4) pit, and (4 x 4) pit + Zn, against the (1 x 3) reconstruction found experimentally by Torbrugge et al. [J. Phys. Chem. C 2009, 113, 4909-4914]. It is found that the original Zn-vacancy model is not favorable in any range of oxygen chemical potential. We report two stable reconstructions for the oxygen-poor limit associated with O vacancies. Models with one and two oxygen vacancies arise as candidates to explain the (1 x 3) reconstruction. We present theoretical Tersoff-Hamann scanning tunneling microscopy images for both reconstructions and compare them with the experimental atomic force microscopy images. The striped pattern composed of single and double Zn rows, obtained from the two oxygen vacancy model, is consistent with the experimental measurements. Density of states of the stable models depicts metallic character, where the typical sp(3) bulk hybridization is preserved in the upper layers. Charge density plots confirm the formation of Zn atomic wires in the [1000] direction.

Automated summary

Theoretical models identified two stable reconstructions for oxygen-poor limits with oxygen vacancies, potentially explaining the experimentally observed (1 x 3) reconstruction. The striped pattern from the double oxygen vacancy model is consistent with experimental measurements, supporting the formation of Zn atomic wires in the [1000] direction.