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O: Oberflächenphysik
O 19: Epitaxie und Wachstum (IV)
O 19.7: Talk
Tuesday, March 28, 2000, 17:45–18:00, H36
Novel Mechanism for Strain Relaxation in Ni/Ru(0001) Heteroepitaxy — •Y. Shingaya, S.M. Shivaprasad, and R.J. Behm — Abteilung Oberflächenchemie und Katalyse, Universität Ulm, 89069 Ulm
STM observations on the epitaxial growth of Ni
on Ru(0001) reveal that for submonolayer coverages a highly
strained pseudomorphic structure is thermodynamically stable. For
coverages exceeding that of the (1×1) phase, the Ni adlayer
incorporates additional Ni atoms by forming a triangular
dislocation network, which relieves part of the lattice strain.
Due to kinetic constraints this phase can be formed at lower
coverages; more importantly, a third phase is also formed, which
is characterized by triangular islands with an orientation
opposite to that of the (1×1) islands. Atomic resolution
images of these islands reveal a (2×2) structure with an
atomic density identical to the (1×1) structure, but with
groups of four nickel atoms clustering now to form a quartet
arrangement. The change in island orientation can be understood
from the fcc stacking in this phase, while in the (1×1)
phase Ni atoms occupy the hcp positions. The formation of this
phase was found to strongly depend on small CO pre-coverages. The
(2×2) phase with its local contraction can be considered as
a novel way for (local) strain relaxation. Energetic, structural
and kinetic aspects of this structure and its formation will be discussed.