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 Nb2O5 are formed at pressures as low as 6.6x10-6Pa, 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 kinetics of Nb2O5 formation beneath the oxidized cerium shows two stages: the first stage is fast growth limited by ion diffusion; the second stage is slow growth limited by electron tunneling. Other catalytic rare earths usable instead of cerium are terbium and praseodymium; other substrate materials usable instead of niobium are aluminum, hafnium, silicon and tantalum, or oxidizable alloys thereof.