Abstract:

Metal oxides are useful catalytic materials but are not well understood due to a scarcity of fundamental studies. They are rarely available as single crystals and their insulator nature causes charging problems when electrons or ions are probes. We report the use of a technique to overcome these problems by anepitaxial growth onto a dissimilar metal to study the solid add niobium oxide. The model niobium oxide grew epitaxially on a single crystal Pt(111) substrate. The growth mode of the niobium oxide overlayers indicates that the overlayer grows as a 2D monolayer on the Pt substrate followed by the development of a high density of small 3D crystallites. LEED patterns from the niobium oxide overlayer indicate that the small crystallites of niobium oxide grew with the (111) structure of the Pt(111) substrate. The valence states of Nb of our model niobium oxide were determined from AES and ILS (ionization loss spectroscopy, which gives information similar to XPS) chemical shifts. Nb oxide overlayers could segregate into bulk Pt and decompose at high tempetature. This Nb oxide overlayers will be used as a model Nb oxide catalyst.

Key words: Eqitaxial growth, Nb oxide, Model catalyst, Crystal film