Stability and Rupture of Alloyed Atomic Terraces on Epitaxial Interfaces

The detailed knowledge of the fine atomic structure of epitaxial interface is of fundamental importance for design and fabrication of electronic devices with exotic physical properties. Recently, it has been shown that accounting for diffusion energy barriers at specific sites on the epitaxial interface (atomic terraces, steps, kinks and imperfections), allows fine tuning of the adatom thermal energy which opens up a way for specific nanoscale surface design. Hence, through simple temperature variation, the surface migration of foreign atoms and clusters leads to formation of a variety of alloyed or pure terraces, alloyed islands and alloyed atomic stripes thus forming nanoscale surface patterns. A key role in this scenario plays the density of steps and kinks at the epitaxial interface. On that physical background, in the present paper we discuss the structure, stability and rupture of alloyed terraces as a first step towards the formation of alloyed two-dimensional islands on pure, non-alloyed substrate. The atomistic simulational model reveals a temperature-dependent critical terrace width for rupture and specifies criteria for thermodynamic stability. In the case of incomplete alloying we analyze the competition and overlapping of the elastic strain fields generated by opposite terrace edges. The specific atomic ordering in alloyed islands is also discussed. The simulation results frame the limits of incomplete surface-confined intermixing and point to a path to nanoscale surface design.