Chemistry Reference
In-Depth Information
Figure 5.3. TMAFM images taken in ambient conditions of a thin film of EDT-
TTF grown on KCl(100) by PVD. (a) 2D representation, 15
µ
m
×
15
µ
m, (b) 3D
representation, 3.5
m. The walls in (b) are approximately 300 nm high
and the plateaus inside exhibit heights of
c
. 100-150 nm.
µ
m
×
3.5
µ
formation of larger isolated microcrystals on complete coverage of two strained
layers (Stranski-Krastanov mode) with increasing
T
sub
between 180 and 420 K
(Chkoda
et al
., 2003). This morphology transformation is observed for nominally
∼
5 ML min
−
1
. When grown under certain experi-
10 nm thick films with
D
t
∼
0
.
mental conditions (
T
sub
<
350 K) the PTCDA/Ag(111) system shows a morphology
transition as a function of
T
ann
. This transition, which in reality consists in a wetting-
dewetting transformation, induces evolution from an initial (as-grown) pseudo-2D
morphology (a smooth film) towards a final 3D morphology, where regions of the
substrate become uncovered. This transition is thus of a different nature and simply
reveals that the as-grown films are unstable against annealing (Krause
et al
., 2003).
On the other hand,
n
-alkanes (
n
=
,
,
7) adsorbed from the vapour phase
on Ag(111) surfaces also grow following the Stranski-Krastanov mechanism
(Wu
et al
., 2001).
Figure 5.3 gives an example of the Volmer-Weber mechanism of growth. The
figure shows TMAFM images of an EDT-TTF film grown under a base pressure
of
4
6
10
−
5
mbar on KCl(100) surfaces held at RT, taken after interruption of the
growth process and exposure to air. It cannot be directly concluded that this corre-
sponds to a snapshot of the growth process, although it is tempting to propose it,
since the sample was exposed to air after stopping the molecular beam flux. From
the images it becomes clear that the film is not continuous but instead formed
by isolated microcrystals oriented along well-defined surface crystallographic
∼
