Regensburg 2000 – scientific programme

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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.