Chemistry Reference
In-Depth Information
practical development of novel surface nanoobjects in which quantum effects can
be observed.
In studies of the surface and bulk structure of crystalline objects, the most com-
plete and adequate information is obtained by various methods of electron and scan-
ning probe microscopies. These methods make it possible to study the structure of
the surface, bulk, and interface at an atomic level by means of direct resolution of
the atomic structure. The use of mutually complementary high-resolution diagnostic
methods adapted to materials under study, in combination with unique objects of
analysis, gives us new knowledge on their structure, morphology, defect formation
and will extend the possibility of controlling the structural quality of epitaxial and
low-dimensional systems [
3
].
An important aspect of contemporary and future technologies is the design of
novel materials with tailored properties. Such new materials are produced using
atomic assembly methods, which allow controlled association of atoms into isolated
nanoclusters, layer-by-layer growth of various coatings, self-assembly, and self-
ordering of nanoobjects. In this case, understanding of atomic-level structural reac-
tions is of primary and crucial importance in the development of low-dimensional
systems with quantum-size electronic properties. To solve such problems, high-
resolution methods of nanomaterial characterization should be developed, prefer-
ably in situ diagnostic during nanostructure formation [
4
,
5
].
Structural perfection and properties of stepped Si(111) surfaces depend crucially
on the surface roughness that basically defined by spatial distribution of atomic
steps. Generally the step allocation may be altered through surface morphology
instability due to thermodynamic or kinetic reasons [
6
]. Thermodynamic instabil-
ity deals with adsorption of impurity atoms on the surface, which may change the
surface energy producing surface reconstruction, faceting, and/or step bunching.
Atomic step distribution can be also changed during superstructural phase transi-
tions. For example, during the
phase transition that takes place
on clean Si(111) surface at 830
◦
C, atomic step shifts due to changing of the adatom
density at the terraces [
7
]. During submonolayer deposition of foreigner atoms on
Si(111) the formation of new surface phases occurs too. It was shown that nucleation
and growth of the superstructural domains also can modify atomic step distribution
forming step bunches. Detailed investigation of instability of the silicon (111) sur-
face morphology induced by polycentric nucleation of reconstructed domains at
adsorption of Ge [
8
], Au [
9
,
10
], Ca [
11
], and Cu [
12
,
13
] indicates that step bunch-
ing occurs during enlarging the reconstructed domains longer than the step-step
width. Similar step bunching occurs during the
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transition on
clean Si(111) surface on cooling when reconstructed domains cover non-uniformly
the stepped surface [
14
].
The dramatic changes in step spatial distribution on Si(111) surface governed by
direct electric current used for sample heating have been revealed first by Latyshev
et al. [
15
] and latter confirmed by many others [
16
-
20
] and discussed theoretically in
detail [
21
-
26
]. They have investigated in detail the kinetic instability of atomic steps
on silicon surface during sublimation caused by direct electrical current heating. As
a result of this instability the reversible transition from regular steps (RS) to step
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