Step energies and equilibrium shape of strained monolayer islands
1 Centro de Microanálisis de Materiales, Departamento de Física de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto “Nicolás Cabrera”, Universidad Autónoma de Madrid - E-28049 Madrid, Spain
2 Institute of Physical Chemistry, Bulgarian Academy of Sciences - 1113 Sofia, Bulgaria
Received: 3 July 2014
Accepted: 4 November 2014
Using a simple atomistic model of anharmonic nearest-neighbors interaction, we have calculated the step energies of strained hexagonal monolayer islands. These have been found to decrease with the absolute value of the misfit due to the strain relaxation at steps. The effect is significantly more pronounced in the case of positive misfit owing to the stronger repulsive interatomic forces. Furthermore, (111)-faceted steps are favored at positive misfit (compressed islands) and, to a lesser extent, (100)-faceted steps at negative misfits (tensile islands). The result is rationalized in terms of the different bonding geometries at step edges and a comparison with experiments is included. Thus, the equilibrium shape transforms from regular hexagons at zero misfit to threefold symmetric hexagons with increasing misfit.
PACS: 68.35.Md – Surface thermodynamics, surface energies / 81.10.Aj – Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation / 68.43.Hn – Structure of assemblies of adsorbates (two- and three-dimensional clustering)
© EPLA, 2014