Computational study of stripe alloy formation on stepped surfaces

Abstract

The present study deals with two-dimensional ͑2D͒ surface alloy formation on stepped crystal surfaces. In specific temperature range, the high diffusion barrier for direct atomic exchange between adsorbed layer and substrate, completely block 2D intermixing on smooth, step-free surface domains. Hence, in a given energy gap the diffusion takes place exclusively via step terrace mechanism. In such systems, the dynamic competition between energy gain by mixing and substrate strain energy results in diffusion scenario where adsorbed atoms form alloyed stripes in the vicinity of terrace edges. The stripe width, L S , is step-anisotropy dependent and correlates with the relaxation ability of the terraces in specific direction. Atomic terraces having a critical width L T Ͻ 3L S are completely transparent for the adsorbed atoms. This phenomenon, considered as incomplete 2D alloying, opens up a way various surface pattern to be configured at different atomic levels on the crystal surface. Refining important details of diffusion behavior of adsorbed atoms and accounting for the energy barriers at specific atomic sites ͑smooth domains, terraces, and steps͒ located on the crystal surface, the presented computational model reveals a classification order of surface alloying: blocked, incomplete, and complete. Being in agreement with experimental findings, the observed stripe alloy formation could be applied to nanoscale surface design in volume-immiscible systems.

Computer modelling of nanoscale diffusion phenomena at epitaxial interfaces

“…It is essential to point out that the final configuration seen in figure 1b represents a close-to-equilibrium state and does not change during the subsequent time evolution of the interface. The results presented reveal a classification order of surface-confined intermixing (blocked, incomplete and complete, see figure 3) and open a way for the formation of a variety of nanoscale surface patterns via fine tuning of the system temperature [9]. …”

“…This semi-empirical TB SMA potential has been extensively applied in contemporary atomistic simulations of transition metals and intermetallic alloys [7][8][9][10]. Its advantage relates to the ability of reproducing real physical properties of surfaces and interfaces including point defects, dislocations, vacancies, grain boundaries [8,9]. Depending on the specific diffusion problem, we also apply an external field to direct the cluster migration in a specific direction and to evaluate the cluster stability.…”

“…The atomic-scale surface morphology provides a variety of energy barriers for surface diffusion [3,9]. For volume-immiscible systems, the migration of a single atom on the surface evolves in two diffusion scenarios.…”

“…On an atomically smooth interface, this scenario leads to formation of a stable two-dimensional (2D) surface alloy and can be realized if the energy of migrating atoms is higher than the energy barrier for incorporation inside the substrate [4]. Refining the classical diffusion model, we showed that on vicinal surfaces, the intermixing could take place even in the case when the adatom energy is lower than that for direct incorporation inside the first atomic layer [3,9]. This effect, known as incomplete alloying, is realized exclusively via surface diffusion through the steps of atomic terraces.…”

Atomic Scale Design, Structure and Stability of Quantum Nanowires Located on Epitaxial Interfaces and Free‐Standing in Space

“…Hence, the epitaxial nanowires located at the step edges could be disintegrated, depending on the interface temperature, in two ways: 1) by generation of atomic vacancies along the steps and 2) by atomic exchange with steps and formation of linearly ordered surface alloyed chains or stripes. The formation of 1D and 2D surface alloyed atomic configurations, considered here as nanowires breakdown, has been studied in detail in our previous studies . This scenario of breakdown and disintegration of step‐supported heteroepitaxial nanowires has to be evidenced by further experimental researches.…”