342
11 Surfaces
bonds such as dimers along the surface, lowering the total energy. This surface reconstruction displays
two-dimensional periodicity of a surface unit cell.
Since the forces from the split-away half-space are missing, the atomic planes will rearrange vertically
1 and the surface-near layers will exhibit slightly different lattice spacing than in bulk. In [1062]
the surface reconstructions of many semiconductors are reviewed. In Fig. 11.3a the rearrangement of
surface atoms on GaAs(110) is depicted as an example. The anion is moved up, the cation moved
down, preserving the bond length, rotating the bond by about γ = 30
◦ for various III–V semiconductors [1063] (Fig. 11.3b). The height difference of the top anion and cation 1 scales with the bulk
lattice constant (Fig. 11.3c). The details are specific to materials and orientations.
Different reconstructions occur for different thermodynamical conditions, some of them being
metastable, as depicted for GaAs(100) in Fig. 11.4. Several different surface reconstructions can also
be present simultaneously at a surface within different domains.
The stable reconstruction of the Si(111) surface is the somewhat complicated 7 × 7 reconstruction
which is schematically depicted in Fig. 11.5a as proposed in [1066] (‘DAS’ dimer-adatom-stacking
fault model’). A STM image of this surface has been reported first in [1067] and is depicted in Fig. 11.5b.
Details of this surface are also recently a subject of interest [1068].
(a)
Ga As
ideal
reconstructed
(b)
[100]
[110]
(c)
Fig. 11.3 a Schematic drawing of the GaAs(110) surface after cutting bonds (‘ideal’) and actual atomic rearrangement
with asymmetric dimer in the reconstructed state. Adapted from [1064]. b Schematic of the III–V (110) surface relaxation
(red circles: anions, blue circles: cations) with bond rotation ω and atom shift c Experimental values for he relaxation
1 as shown in panel (b) for various semiconductors vs. their bulk lattice constant a 0 ; dashed line is straight line as
guide to the eye. Data from [1063]
1 Typically the distance between the first and second layer is reduced, and the distance between the second and third layer
a little bit increased.
11 Surfaces
bonds such as dimers along the surface, lowering the total energy. This surface reconstruction displays
two-dimensional periodicity of a surface unit cell.
Since the forces from the split-away half-space are missing, the atomic planes will rearrange vertically
1 and the surface-near layers will exhibit slightly different lattice spacing than in bulk. In [1062]
the surface reconstructions of many semiconductors are reviewed. In Fig. 11.3a the rearrangement of
surface atoms on GaAs(110) is depicted as an example. The anion is moved up, the cation moved
down, preserving the bond length, rotating the bond by about γ = 30
◦ for various III–V semiconductors [1063] (Fig. 11.3b). The height difference of the top anion and cation 1 scales with the bulk
lattice constant (Fig. 11.3c). The details are specific to materials and orientations.
Different reconstructions occur for different thermodynamical conditions, some of them being
metastable, as depicted for GaAs(100) in Fig. 11.4. Several different surface reconstructions can also
be present simultaneously at a surface within different domains.
The stable reconstruction of the Si(111) surface is the somewhat complicated 7 × 7 reconstruction
which is schematically depicted in Fig. 11.5a as proposed in [1066] (‘DAS’ dimer-adatom-stacking
fault model’). A STM image of this surface has been reported first in [1067] and is depicted in Fig. 11.5b.
Details of this surface are also recently a subject of interest [1068].
(a)
Ga As
ideal
reconstructed
(b)
[100]
[110]
(c)
Fig. 11.3 a Schematic drawing of the GaAs(110) surface after cutting bonds (‘ideal’) and actual atomic rearrangement
with asymmetric dimer in the reconstructed state. Adapted from [1064]. b Schematic of the III–V (110) surface relaxation
(red circles: anions, blue circles: cations) with bond rotation ω and atom shift c Experimental values for he relaxation
1 as shown in panel (b) for various semiconductors vs. their bulk lattice constant a 0 ; dashed line is straight line as
guide to the eye. Data from [1063]
1 Typically the distance between the first and second layer is reduced, and the distance between the second and third layer
a little bit increased.