The formation of nickel oxide nanolayers by oxidizing Ni overlayers on Rh(111) has been investigated and their
structures are reported as a function of the nickel coverage and oxygen pressure. Scanning tunneling microscopy
(STM), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and diffraction (XPD), and
high-resolution electron energy loss spectroscopy (HREELS) have been applied to characterize the structure and
stoichiometry of the nickel oxide nanolayers. Several different phases have been observed depending on the strain
state of themetallicNi overlayers. For the pseudomorphicNimonolayer, two distinctly different oxide phaseswith
(6×1)-Ni5O5 and (2√3×2)-Ni8O10 structures have been identified at oxygen-poor (p=5×10−8 mbar) and
oxygen-rich (p≥1×10−6 mbar) conditions, respectively. Above one monolayer, where the Ni layers are relaxed,
bulk-like NiO(100) films form at the O-rich conditions, whereas chemisorbed-type p(2×2)O\Ni(111) layers
develop in the O-poor regime. X-ray photoelectron diffraction analysis has provided additional insight into the
relaxation mechanism and the detailed atomic structure of the Ni-oxide nanolayers.
