Formation of a faceted MoO2 epilayer on Mo(1 1 2) studied by XPS, UPS and STM

The open trough and row Mo(1 1 2) surface serves as substrate for the epitaxial growth of MoO2. XPS, UPS and STM studies of the oxygen adsorption allow to monitor step-by-step the transformation of the electronic and morphological properties during this process. XPS and UPS spectra reveal that a stable oxygen chemisorbed state precedes the formation of MoO2. STM topographs identify this oxygen chemisorbed phase as an oxygen-induced p(2 × 3) reconstruction of the missing row type. This precursor state evolves into a flat p(1 × 3) reconstructed (0 1 0) MoO2 layer which roughens by the formation of (1 1 0) facets under further oxygen exposure.