Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9594512 | Surface Science | 2005 | 10 Pages |
Abstract
The heating temperature dependence of Sc-O/W(1Â 0Â 0) surface properties and the effects of oxygen exposure on these properties were investigated. A (2Â ÃÂ 1)-(1Â ÃÂ 2)-Sc-O/W(1Â 0Â 0) surface having a high work function was formed by heating at â¼1500Â K with a sufficient provision of oxygen. Oxygen exposure was required for surface Sc atoms to form Sc-O complexes and diffuse into the W(1Â 0Â 0) substrate at â¼1500Â K. By heating at â¼1700Â K, a (1Â ÃÂ 1)-Sc-O/W(1Â 0Â 0) surface having a low work function was formed and found to be very stable at â¼1500Â K, the operating temperature of the Sc-O/W(1Â 0Â 0) emitter. In contrast, the (1Â ÃÂ 1)-Sc-O/W(1Â 0Â 0) surface was converted to the (2Â ÃÂ 1)-(1Â ÃÂ 2)-Sc-O/W(1Â 0Â 0) surface by heating at â¼1500Â K with oxygen exposure. Moreover, it was confirmed that the (1Â ÃÂ 1)- and (2Â ÃÂ 1)-(1Â ÃÂ 2)-Sc-O/W(1Â 0Â 0) surfaces were alternately formed by heating at â¼1700Â K and â¼1500Â K with oxygen exposure, indicating that a reversible phase transition occurs on the Sc-O/W(1Â 0Â 0) surface at high temperatures. The present results reveal that the optimization of both the heating temperature during the pretreatment and operation of the Sc-O/W(1Â 0Â 0) emitter and the pressure around the tip is important for the practical use of the Sc-O/W(1Â 0Â 0) emitter.
Keywords
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Y. Nakanishi, T. Nagatomi, Y. Takai,