Chemistry Reference
In-Depth Information
Fig. 6.14
Time evolution of the interface atomic configuration for initial terrace of 6 atomic rows.
(
a
) Non-equilibrium configuration with terrace width comparable with the size of alloyed stripe.
(
b
) Close to equilibrium configuration resulting from (
a
). Completely alloyed Pb-Cu islands are
formed. (see also Fig.
6.9
curve II)
6.5.4 Terrace Stability
The problem of terrace stability directly relates to the surface pattern formation at
different atomic levels at epitaxial interface. The decrease of terrace width below a
given critical value causes overlapping of elastic strain fields generated by the left
and right alloyed stripes, Fig.
6.14
a. The smooth, non-alloyed area inside the terrace
disappears. As a result, the terrace entirely releases the elastic strain and forms 2D
homogeneously alloyed islands on top of pure, non-alloyed substrate, Fig.
6.14
b.
By variation of the initial terrace width, we found that the stripe width
L
S
does
not depend on the terrace width
L
T
at
L
T
>
3
L
S
. The decrease of
L
T
more than
three times
L
S
makes the terrace unstable and completely transparent for Pb atoms
[
4
,
43
]. On Cu substrate with initial terrace width
L
T
of six atomic rows we observed
totally alloyed Pb-Cu domains. Therefore, at constant
T
, the variation of
L
T
gives
the opportunity to form various surface patterns: (i) one-level patterns at
L
T
>
3
L
S
,
i.e., alloyed stripes followed by smooth, pure terrace areas Fig.
6.8
; (ii) two-level
patterns at
L
T
<
3
L
S
, i.e., totally alloyed terraces (islands) and pure non-alloyed
substrate domains, Fig.
6.14
b.
Fig. 6.15
The atomic configuration of epitaxial interface at high coverage (0.7ML) at complete
wetting of the substrate by adsorbed layer. Even being entirely alloyed, the terrace retains its linear
shape and dimension. This is in contrast to the low-coverage case where the terrace destroys and
forms 2D-alloyed islands, Fig.
6.14
b
