Chemistry Reference
In-Depth Information
Chapter 6
Classification Order of Surface-Confined
Intermixing at Epitaxial Interface
M. Michailov
Abstract
The self-organization phenomena at epitaxial interface hold special atten-
tion in contemporary material science. Being relevant to the fundamental physical
problem of competing, long-range and short-range atomic interactions in systems
with reduced dimensionality, these phenomena have found exacting academic inter-
est. They are also of great technological importance for their ability to bring sponta-
neous formation of regular nanoscale surface patterns and superlattices with exotic
properties. The basic phenomenon involved in this process is surface diffusion. That
is the motivation behind the present study which deals with important details of dif-
fusion scenarios that control the fine atomic structure of epitaxial interface. Consist-
ing surface imperfections (terraces, steps, kinks, and vacancies), the interface offers
variety of barriers for surface diffusion. Therefore, the adatoms and clusters need a
certain critical energy to overcome the corresponding diffusion barriers. In the most
general case the critical energies can be attained by variation of the system tempera-
ture. Hence, their values define temperature limits of system energy gaps associated
with different diffusion scenarios. This systematization imply classification order of
surface alloying: blocked, incomplete, and complete. On that background, two dif-
fusion problems, related to the atomic-scale surface morphology, will be discussed.
The first problem deals with diffusion of atomic clusters on atomically smooth inter-
face. On flat domains, far from terraces and steps, we analyzed the impact of size,
shape, and cluster/substrate lattice misfit on the diffusion behavior of atomic clusters
(islands). We found that the lattice constant of small clusters depends on the number
N
of building atoms at 1
10. In heteroepitaxy, this effect of variable lattice
constant originates from the enhanced charge transfer and the strong influence of
the surface potential on cluster atomic arrangement. At constant temperature, the
variation of the lattice constant leads to variable misfit which affects the island
migration. The cluster/substrate commensurability influences the oscillation behav-
ior of the diffusion coefficient caused by variation in the cluster shape. We discuss
<
N
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