EPITAXIAL-GROWTH OF CO3O4 ON COO(100)

Under mildly oxidizing ultrahigh vacuum conditions, it is possible to form on top of CoO(100) single crystal substrates, thin films that hav e higher oxygen content but that preserve the overall symmetry of the CoO(100) low-energy electron diffraction pattern. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectrosco py (HREELS) data indicate that the epitaxial film grown on CoO(100) at 625 K and 5x10(-7) Torr is Co3O4-like in both oxygen content and XP/H REEL spectroscopic characteristics. Both materials are closest packed in lattice oxygen, with the mismatch of bulk O2--O2- distances of appr oximately 5%. However, the Co3O4 is only able to grow to a thickness o f approximately 5 Angstrom before the oxidation process halts. It is p roposed that the orientation of Co3O4 that forms most readily on the C oO(100) surface does not present a thermodynamically stable orientatio n of the bulk Co3O4 substrate but is that which grows under the constr aint of the best CoO(100)/Co3O4 epitaxial arrangement. While the misma tch in lattice parameters may in part be to blame for the limitation o f higher oxide thickness, thicker oxide films have been grown under co nditions with significantly larger mismatch. (C) 1996 American Vacuum Society.