dc.description.abstract | When the planar surface is covered by certain adsorbate and annealed, facets with lower surface energy will be exposed and pyramids with different size will be formed on the surface. This phenomenon is called adsorbate induced faceting. The adsorbate induced faceting can be used to fabricate single atom tip, which has applied potential for high resolution microscopy, field emission electron source, and ion source. Pd on W(111) can induce surface transition from planar(111) to faceting{112}, which has been researched a lot in our laboratory. However, since the work function of W is large, the emission current of W tip is small. On one hand the work function of Nb (4.87eV) is lower than that of W (5.25eV) [11], and on the other Nb is one of superconductive materials [18]. In superconducting state, the electron intensity of field emission energy distribution has an extra peak near the Fermi level. Thus, if the faceting of Nb(111) can be induced. The performance of single atom Nb tip will be better than W tip in many applications. In our experiments, we found that oxygen can induce complex faceting on Nb(111). Moreover, by Temperature Programmed Auger (TPA), we can trace real-time reversible diffusion and segregation of oxygen with temperature variation. We also deposited Pt on oxidized surface and found that aggregation or wetting of Pt would depend on the variation of oxide. Pd is more stable than Pt on oxidized surface, and the coverage of Pd has significant effect on diffusion of oxygen. We also tried Au, Pt, and Pd to induced Nb faceting, but we haven’t observed any faceting structure in these systems so far. | en |
dc.relation.reference | References
[1] T.E. Madey, C.-H. Nien, K. Pelhos, J.J. Kolodziej, I.M. Abdelrehim, H.-S. Tao, Surf. Sci. 438 (1999) 191.
[2] C.-H. Nien, T.E. Madey, Y.W. Tai, T.C. Leung, J.G. Che, C.T. Chan, Phys. Rev. B 59 (1999) 10335.
[3] T.E. Madey, J. Guan, C.-H. Nien, C.-Z. Dong, H.-S. Tao, R.A. Campbell, Surf. Rev. Lett. 3 (1996) 1315.
[4] C.-Z. Dong, J. Guan, R.A. Campbell, T.E. Madey, in: X. Xie, S.Y. Tong, M.A. van Hove (Eds.), The Structure of Surface IV, World Scientific, Singapore, 1994, p. 328.
[5] C.-H. Nien, T.E. Madey, Surf. Sci. 380 (1997) L527.
[6] C.-Z. Dong, L. Zhang, U. Diebold, T.E. Madey, Surf. Sci. 322 (1995) 221.
[7] K.-J. Song, J.C. Lin, M.Y. Lai, Y.L. Wang, Surf. Sci. 327 (1995) 17.
[8] For reviews, see, E.H. Conrad, Prog. Surf. Sci. 39 (1992) 65; G.A. Somorjai and M.A. Van Hove, Prog. Surf. Sci. 30 (1989) 201; M. Flytzani-Stephanopoulos and L.D. Schmidt, Prog. Surf. Sci. 9 (1979) 83.
[9] E.D. Wi lliams and N.C. Bartelt, Ultramicroscopy 31 (1989) 36.
[10] Tsu-Yi Fu, Lung-Chieh Cheng, C.-H. Nien, and Tien T. Tsong, Phys. Rev. B 64, 113401 (2001)
[11] H. L. Skriver, and N. M. Rosengaard, Phys. Rev. B 46, 7157 (1992)
[12] Jacek Brona, and Antoni Ciszewski, Phys. Rev. B 69, 115408 (2004)
[13] H. H. Farrell, H.S. Isaacs, and Myron Strongin, Surf. Sci.38 (1973) 18-52
[14] R. Franchy, T.U. Bartke, and P.Gassmann, Surf. Sci.366 (1996) 60-70
[15] T.W. Haas, A.G. Jackson, and M.P. Hooker, J. Chem. Phys. 46 (1967) 3025
[16] R. Pantel, M. Bujor, and J.Bardolle, Srf. Sci. 62 (1977) 589
[17] L.H Rovner, A. Drowart, F.Degreve, and J. Drowart, AFML-TR-68-200, 1968.
[18] C. Oshima, J. Phys. Soc. Jpn. Vol. 72 (2003) Suppl. C 24-29 | en |