Classification Order of Surface-Confined Intermixing at Epitaxial Interface - Nanophenomena at Surfaces - page 146

layer, Fig. 6.1 . Hence, the migration of adatoms is confined in specific energy gaps
imposed by the dominant surface morphology. Determined by the site-dependent
values of E DB , the diffusion in each of the above scenarios could generate com-
pletely different, stable atomic arrangements of the epitaxial interface. That is why,
detailed analysis of the specific energy barriers for atomic migration on the crystal
surface might reveal new mechanisms for fine-tuning of diffusion processes and
for generation of nanoscale surface patterns with variable size and geometry [ 4 ].
The native interface structure consists of islands and terraces with steps and smooth
domains. Therefore, a random walking adatom with energy E ATOM meets different
energy barriers shown in Fig. 6.1 :(i) E DB

SMOOTH - the barrier for diffusion on top of

smooth domains; (ii) E DB

DIRECT - the barrier for direct incorporation inside the sub-

strate; and (iii) E DB

STEP - the barrier for diffusion inside the terrace for atoms passing
through the steps. On that physical background we consider diffusion scenarios in
specific energy regions. Being correlated with the system temperature, these regions
are defined by the following equations:

E ATOM < E DB E DB

DIRECT

STEP <

(6.1)

(i) The diffusion behavior in this energy region is typical for low temperatures at
which the adatom energies are below the diffusion barriers for direct incorporation
into the substrate, as well as for penetration in the terrace by passing through the
steps. This case is relevant to a simple random walk of adatoms exclusively on top
of the interface layer (the yellow atoms in Fig. 6.1 ). It will be considered as atomic
diffusion at blocked surface intermixing.

E DB E ATOM < E DB

DIRECT

STEP ≤

(6.2)

Fig. 6.1 Principal view of basic types of energy barriers for surface diffusion on stepped or vicinal
epitaxial interface: (i) the barrier for diffusion on top of smooth domains - E DB

SMOOTH ( yellow balls ),
( 6.1 ); (ii) the barrier for diffusion into the terrace across the atomic steps - E DB

STEP ( red balls ), ( 6.2 );
(iii) the barrier for diffusion into the terrace or substrate by direct incorporation, E DB

DIRECT ( black

balls ), ( 6.3 )