Chemical and spectroscopic surface science investigation of MoO3 and MoO3/Al2O3 ultrathin films

The nature of MoO3 and MoO3/Al2O3 ultrathin films supported on Mo~110! and their interactions with CH3OH have been investigated using surface science techniques. The ultrathin (,50 Å) films were characterized by Auger electron spectroscopy, low energy electron diffraction, and high resolution electron energy loss spectroscopy ~HREELS! of their phonon vibrational modes and electronic transition regions. The activity toward oxidation by the surfaces was investigated using temperature programmed desorption of methanol. The vibrational features associated with the terminal Mo5O and the bridging Mo–O–Mo in tetrahedral molybdate have been identified by HREELS. The intensity of the Mo5O loss (;1000 cm) of unsupported molybdate decreases after several runs of methanol adsorption/desorption. The M5O feature appears in the MoO3/ alumina system only after annealing to .800 K, apparently as a function of auto-oxidation. Simultaneous with the rise of the vibrational loss at 1000 cm is a feature in the ELS spectrum which appears at ;1.8 eV associated with d–d transitions in MoO2 . © 1997 American Vacuum Society. @S0734-2101~97!53003-X#