Chemistry Reference
In-Depth Information
Fig. 4.30
STM images revealing the quantum growth mode of Pb
0
.
89
Bi
0
.
11
alloy films, with bilayer
growth (
a
) for 4 and 6ML thicknesses and (
b
) for 7 and 9ML thicknesses. In these images, the
black pores
are uncoated regions extending down to the substrate; in films used for study of super-
conductive properties, we verified the films to be simply connected and fully covering the substrate.
Image (
c
) shows bilayer growth in a thicker film (also with a 1ML terrace from the substrate), while
(
d
) illustrates single layer growth near the even-odd crossover thickness. Reproduced from. [
31
]
DFT calculations for different Bi doping concentrations of Pb
1
−
x
Bi
x
alloy films
have been carried out [
31
,
75
]. Figure
4.31
shows the surface energy of Pb
89
Bi
11
alloy films as a function of thickness for both freestanding films and films on a
rotated Si(111) substrate. Note that for calculations performed on the substrate, both
the beating periodicity and the location of the even-odd crossovers are in excellent
agreement with the experimental result. Further calculations have been carried out
Fig. 4.31
(
a
) Surface energy of a Pb
0
.
89
Bi
0
.
11
freestanding alloy slab obtained from first-principles
DFT calculations. The
black curve
(
circles
) represents the surface energy for maximum Bi-Bi
separation (within the constraints of a supercell calculation). The
red curve
(
squares
) represents
the surface energy of a slab in which Bi atoms all have Bi nearest neighbors in the adjacent (111)
layers; (
b
) surface energy of a Pb
89
Bi
11
thin film alloy on a Si(111) substrate together with the
second-order derivation of surface energy as a function of thickness (inset). Reproduced from [
31
]
