11.5 Surface Morphology
343
(a)
c(4 4)
2(2 4)
2(2 4)
(4 2)
(2 6)
mixed dimer
[110]
[110]
(b)
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
Energy (eV)
Ga chemical potential
(eV)
0
-0.5
GaAs(100)
Fig. 11.4 a Various reconstructions of the GaAs(100) surface. Filled (empty) circles represent As (Ga) atoms. Atom
positions in the top two atomic layers are indicated by larger symbols. b The relative formation energy per (1 × 1) unit
cell of various reconstructions as a function of the Ga chemical potential. Vertical dashed lines mark the approximate
anion- and cation-rich limits of the thermodynamically allowed range of Adapted from [1065]
(a)
[112]
[110]
[111]
1nm
(b)
Fig. 11.5 a Schematic drawing of the 7 × 7 reconstruction of Si(111) surface. The large grey circles represent adatoms,
the small balck circles rest atoms. Adapted from [1066] b STM image (empty states) of such surface. Adapted from [1067]
11.5 Surface Morphology
The surface reconstruction is related to the local atomic arrangement of the surface atoms. On larger
length scales, surfaces can exhibit roughness in general and various specific morphologies, among
them steps, step bunches, facets, hillocks or pits. When atomically flat terraces are separated by steps
of equal heights, the surface is termed vicinal. The step height can be an atomic monolayer or more.
The step edges can be straight, smoothly curved or rugged, depending on the formation energy of
kinks. If the substrate surface is inclined by a small ‘off-cut’ angle θ with respect to a low index plane,
for a step height h the average terrace width L is given by
L =
h
tan θ
≈
h
θ
.
(11.2)
The Si(001) surface (under certain conditions) exhibits monoatomic steps between the A-type 1×2 and
B-type 2 × 1 terraces [1069]; clearly also the step edges between A–B and B–A are quite different, one
being much rougher than the other (Fig. 11.6). The surface is thus a two domain surface, the symmetry
of both A- and B-type terraces being 2 mm, rotated by 90
◦ against each other.
343
(a)
c(4 4)
2(2 4)
2(2 4)
(4 2)
(2 6)
mixed dimer
[110]
[110]
(b)
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
Energy (eV)
Ga chemical potential
(eV)
0
-0.5
GaAs(100)
Fig. 11.4 a Various reconstructions of the GaAs(100) surface. Filled (empty) circles represent As (Ga) atoms. Atom
positions in the top two atomic layers are indicated by larger symbols. b The relative formation energy per (1 × 1) unit
cell of various reconstructions as a function of the Ga chemical potential. Vertical dashed lines mark the approximate
anion- and cation-rich limits of the thermodynamically allowed range of Adapted from [1065]
(a)
[112]
[110]
[111]
1nm
(b)
Fig. 11.5 a Schematic drawing of the 7 × 7 reconstruction of Si(111) surface. The large grey circles represent adatoms,
the small balck circles rest atoms. Adapted from [1066] b STM image (empty states) of such surface. Adapted from [1067]
11.5 Surface Morphology
The surface reconstruction is related to the local atomic arrangement of the surface atoms. On larger
length scales, surfaces can exhibit roughness in general and various specific morphologies, among
them steps, step bunches, facets, hillocks or pits. When atomically flat terraces are separated by steps
of equal heights, the surface is termed vicinal. The step height can be an atomic monolayer or more.
The step edges can be straight, smoothly curved or rugged, depending on the formation energy of
kinks. If the substrate surface is inclined by a small ‘off-cut’ angle θ with respect to a low index plane,
for a step height h the average terrace width L is given by
L =
h
tan θ
≈
h
θ
.
(11.2)
The Si(001) surface (under certain conditions) exhibits monoatomic steps between the A-type 1×2 and
B-type 2 × 1 terraces [1069]; clearly also the step edges between A–B and B–A are quite different, one
being much rougher than the other (Fig. 11.6). The surface is thus a two domain surface, the symmetry
of both A- and B-type terraces being 2 mm, rotated by 90
◦ against each other.