AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM6
Pyramidal Faceted Ni Nanocrystals on W(111)

Tuesday, November 4, 2003, 10:00 am, Room 328

Session: Nucleation and Growth
Presenter: Q. Wu, Rutgers University
Authors: Q. Wu, Rutgers University
J. Kolodziej, Rutgers University
H. Wang, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
Nanoscale features formed by nucleation of ultrathin Ni films on W(111) are studied by means of ultrahigh vacuum-STM, soft X-ray photoemission spectroscopy (SXPS) using synchrotron radiation, LEED, and AES. Whereas a single monolayer (ML) of Ni covers planar W(111) uniformly, we find that multilayers of Ni (~5 ML) follow the Stranski-Krastanov growth mode, and form clusters and islands on the Ni-covered W(111). Upon heating to ~600K, Ni clusters are found to aggregate into nanoscale pyramidal facets, which coexist with planar regions of Ni-covered W(111). This type of faceting is different from the monolayer-induced faceting of W(111) seen for Pt, Pd, Ir, and Rh: a single ML of Ni does not cause faceting of W(111). Thermal stability of Ni films on W(211) and W(111) is studied by SXPS and AES, which indicates that alloy formation between Ni and W occurs at temperatures @>=@700K. Further annealing of faceted Ni nanocrystals also leads to Ostwald ripening. Reactivity of Ni nanoclusters with adsorbates (e.g. oxygen and thiophene) is also investigated. The nucleation and growth of nanocrystals are discussed in terms of overlayer strain due to lattice mismatch.