ABSTRACT
A question may be raised as to what extent the idealized ture of the surfaces of Mo03 crystallites represent the real structure of Mo03 samples used in catalytic research. A detailed study of Mo03 single crystals with many sophisticated physical techniques such as LEED, XPS, UPS, and EELS revealed [73] that the basic (010) crystal plane of the oxidized sample is indeed stoichiometric and shows the same periodicity as that of the bulk. Heating Mo03 in vacuum to 600 K reduces the surface region, the O/Mo atomic ratio decreasing to 2.85. On sputtering the Mo03 lattice disorders, oxygen is lost and the final product is Mo02' as determined by XPS and electron diffraction. Annealing above 770 K causes the reappearance of the LEED pattern of the (010) plane of Mo03' and the valence band structure becomes indistinguishable from that of stoichiometric Mo03. As the only source of oxygen to replenish the surface is the bulk of the sample, so oxygen diffusion must be rapid. Recently it was claimed that very thin steps on the (010) plane of Mo03 platelets may be visible by the electron microdiffraction technique [70].
