Tracking the atomic structure evolution of ZnO(0001¯) polar surface via carbon dioxide infrared probe

So far, the clear periodic structures of ZnO polar surfaces and their depolarization stabilization mechanism have not yet been clarified because of the structural complexity and inferior conductivity of these surfaces. Here, we combined microchannel plate low-energy electron diffraction (MCP-LEED), CO2 molecule probe based on polarization-resolved infrared reflection adsorption spectra (PR-IRRAS) and first-principles calculations to systematically study the ZnO(0001¯) polar surface. Five clear periodic surface structures including 3×3R30°, (1×1), (1×2), (43×43)R30° and (3×3) were achieved depending on hydrogen coverage. These surfaces appear in sequence with reducing hydrogen coverage, and vice versa. The CO2 infrared probe tracked these surface atomic configuration evolutions. First-principles calculations revealed that the role of surface hydrogens is to fully fill the partially filled O-2p band at surface while retaining the compensation of surface polarity. Our works reveal the stabilization mechanism of hydrogen covered ZnO(0001¯) polar surface, clarify the long-standing controversy on such surface, and also supply a novel approach for investigating some complex surfaces.