Chemistry Reference
In-Depth Information
Figure 3.7. TMAFM images of a (001) surface of an as-received EDT-TTF-
(CONHMe)
2
single crystal measured under ambient conditions (2.5
m
×
2.5
µ
m): (a) topography and (b) phase. The phase angle is defined as the phase shift
observed between the cantilever oscillation and the signal sent to the piezo-scanner
driving the cantilever.
µ
ambient conditions using microfabricated silicon cantilevers with ultrasharp silicon
tips (tip radius
R
10 nm).
Let us analyse the TMAFM images in some detail. The topography image of
Fig. 3.7(a) depicts circular features with higher (brighter) central parts, which in
turn show large phase contrasts of about 40 degrees (dark regions) in Fig. 3.7(b).
The exception is the larger feature at the centre of the image inside the large cir-
cle. The large phase contrast along with the amplitude images strongly suggest
that the structures exhibit clearly differentiated adhesion in comparison with the
regions outside these features, thus suggesting a liquid or liquid-like nature in
the form of droplets. Those features exhibiting low phase contrast show relatively
high protrusions (
c
. 40 nm in height) indicating that for some reason spontaneous
crystallization has occurred within the initial droplets. Confinement is achieved
with the more external and lower circles surrounding the features, with heights of
c
. 7 nm, which we will term nanobeakers and which act as nanocontainers. The
large circle in Fig. 3.7 is likely to have grown upon coalescence of smaller droplets.
Nanobeakers originate from droplets of a saturated solution of EDT-TTF-
(CONHMe)
2
in CH
3
CN, the crystallization solvent, which remain in air at the
crystal surface after the synthesis process and undergo an outward capillary flow
in which pinning of the drop-surface contact line of the drying drop ensures that
solvent evaporating from the edge is replenished by solution from the interior,
thus originating an EDT-TTF-(CONHMe)
2
-rich edge (Fraxedas
et al.
, 2005). The
microscopic picture of this process is exemplified by the formation of ring stains
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