CO adsorption on Fe₃O₄(111) with regular and biphase terminations

We present studies on CO adsorption on an Fe3O4(1 1 1) surface with a regular tetrahedral termination (Fe-tet1) and with different hexagonal superstructures called `biphase' structures. All these terminations were precisely controlled on a 70 angstrom magnetite layer epitaxially grown on a Pt(1 1 1) single crystal. The experiments, including low energy electron diffraction, scanning tunnelling microscopy (STM) and temperature-programmed desorption (TPD), were carried out in situ under ultrahigh vacuum conditions. During the TPD measurements, the Fe3O4(1 1 1) surfaces were exposed to 0.1-20 L of CO at 105 K, and then the samples were heated with a linear temperature rise to 600 K. We found that as the Fe-tet1-terminated area decreases, as confirmed by STM observations, the surface becomes less active in CO adsorption. This means there are fewer adsorption states on the biphase structure than on Fe3O4(1 1 1) with regular termination.