Atomic structure of the polar NiO(111)- p(2x2) surface

Area of Science:

• Surface science
• Materials science
• Solid-state physics

Background:

• Nickel oxide (NiO) is a crucial transition metal oxide with diverse applications.
• Understanding NiO surface structure is key to controlling its properties.
• Octopolar reconstruction is a theoretically predicted surface phenomenon.

Purpose of the Study:

• To investigate the surface structure of single crystal NiO(111) and a NiO(111) thin film.
• To compare the experimental findings with theoretical predictions of octopolar reconstruction.
• To assess the reactivity of these NiO surfaces towards hydroxylation.

Main Methods:

• Grazing-incidence x-ray diffraction (GIXRD) was employed to probe surface structures.
• Analysis focused on the p(2x2) surface reconstructions.
• Experimental observations were correlated with theoretical models.

Main Results:

• Both single crystal NiO(111) and a 5-monolayer NiO(111) film on Au(111) exhibited octopolar reconstruction locally.
• Significant differences were noted: the single crystal had Ni termination and double steps, while the film showed both O and Ni terminations with single steps.
• Neither surface demonstrated reactivity towards hydroxylation.

Conclusions:

• Experimental evidence supports the theoretical octopolar reconstruction model for NiO(111) surfaces.
• Surface termination and step morphology vary between single crystals and thin films.
• The nonreactive nature of these surfaces towards hydroxylation has implications for their use in certain environments.