Chemistry Reference
In-Depth Information
Fig. 5.18
Side view SEM
image of core-shell SiC-SiO2
nanowires: It is hard to define
the exact average length since
nanowires form a dense
bundle, but it exceeds 100
μ
m
5.5.1
Experimental Procedure
Experiments were carried out in an open tube reactor placed with a conventional
horizontal tube furnace with a constant temperature region 10 cm long. (100) silicon
is used as substrate as well as silicon source for the growth.
After catalyst deposition and drying (as explained before), the samples are placed
in an open tube reactor purged with vacuum-nitrogen cycles to remove oxygen from
the growth chamber.
The temperature is then raised to the synthesis setting (1100
◦
C) and CO is pro-
vided under a constant flow (4
10
−
6
m
3
/s) for 30 min. at atmospheric pressure in
nitrogen carrier gas flow. Subsequently the sample is brought to ambient temperature
during 10 min.
After the cooling step, the sample is covered with a white coloured deposit
indicating the presence of a dense wires network all over the surface.
Using gaseous CO as precursor instead of a solid state reaction between C and
WO
3
as proposed by Park et al. (
2004
) allows a continuous control over CO flow, so
the concentration during the growth, and prevent tungsten contamination inside the
chamber.
·
5.5.2
Morphological, Structural and Compositional Analysis
The shape of the wires is cylindrical, the average diameter is 60 nm and the length
is more than 100
m.
From SEM observation it is possible to see the dense nanowire bundle forming a
layer of about 100
μ
μ
m on the substrate (Fig.
5.18
) the shape of the wires is curvilinear
(Fig.
5.19
) but it is rare to spot abrupt folds.
