Catalytic oxidation of solid materials.

摘要

One or more monolayers of cerium arrayed on the surface of a niobium metal acts as a catalyst to oxidation of the niobium at ambient temperature and results in a very thin, very high quality insulating layer which may be configured by patterning of the catalyst. Significant amounts of Nb<Sub>2</Sub>0<Sub>5</Sub> are formed at pressures as low as 6.6x 10<Sup>-6</Sup>Pa, promoted by the

presence of the cerium. This catalytic activity is related to the trivalent to tetravalent valence change of the cerium during oxidation. The kinestics of Nb<Sub>2</Sub>0<Sub>5</Sub> formation beneath the oxidation cerium shows two stages:
<UnorderedLists id="ula01" listStyle="none"><ListItem>the first stage is fast growth limited by ion diffusion;</ListItem><ListItem>the second stage is slow growth limited by electron tunnelling.</ListItem></UnorderedLists>

Other catalytic rare earths usable instead of cerium are terbium and praseodymium; other substrate materials usable instead of niobium are aluminium, hafnium, silicon and tantalum, or oxidizable alloys thereof.