A typical product obtained by such a process resembles a disordered ball of wool,
as shown in Figure 5.34; this is a typical example of a carbon nanotube product made
from methane as precursor and an iron-containing catalyst. By correctly selecting
the catalyst it is possible to adjust the diameter of the nanotubes.
Instead of using randomly placed catalyst particles, it is possible to prepare clearcut patterns of catalyst particles, either by printing or vapor deposition. With regard
to the application (e.g., as a field electron emitter), this allows nanotubes to be grown
exactly at the places where they are needed. This ability is of particular importance in
the production of field emission displays.
So, the question arises: “How does the catalyst work?” In an effort to provide an
answer to this problem, a model of the growth of nanotubes, supported by a catalyst,
is shown in Figure 5.35.
The production of nanotubes or nanorods begins with a droplet of liquid catalyst.
The precursor is gaseous, and the precursor and catalyst are selected in such a way
Figure 5.34 Carbon nanotubes made in a tubular furnace as shown in Figure 5.33. Methane was
used as the carbon precursor and iron as catalyst. The reaction temperature was approximately
1300 K. (Reproduced with permission by Hampel and Leonhardt, IFW Dresden; unpublished results).
Figure 5.35 Model of the catalytic action
during the synthesis of nanotubes or nanorods.
Initially, the precursor for the product reacts
with the catalyst metal. It is advisable to select a
metal as precursor that forms a liquid phase
together with the material for the nanotube or
nanorod. After exceeding the maximum
solubility, the nanorod or nanotube is
precipitated. The one-dimensional product will
grow as long as the precursor is supplied.
5.2 Nanostructures Related to Compounds with Layered Structures j115
as shown in Figure 5.34; this is a typical example of a carbon nanotube product made
from methane as precursor and an iron-containing catalyst. By correctly selecting
the catalyst it is possible to adjust the diameter of the nanotubes.
Instead of using randomly placed catalyst particles, it is possible to prepare clearcut patterns of catalyst particles, either by printing or vapor deposition. With regard
to the application (e.g., as a field electron emitter), this allows nanotubes to be grown
exactly at the places where they are needed. This ability is of particular importance in
the production of field emission displays.
So, the question arises: “How does the catalyst work?” In an effort to provide an
answer to this problem, a model of the growth of nanotubes, supported by a catalyst,
is shown in Figure 5.35.
The production of nanotubes or nanorods begins with a droplet of liquid catalyst.
The precursor is gaseous, and the precursor and catalyst are selected in such a way
Figure 5.34 Carbon nanotubes made in a tubular furnace as shown in Figure 5.33. Methane was
used as the carbon precursor and iron as catalyst. The reaction temperature was approximately
1300 K. (Reproduced with permission by Hampel and Leonhardt, IFW Dresden; unpublished results).
Figure 5.35 Model of the catalytic action
during the synthesis of nanotubes or nanorods.
Initially, the precursor for the product reacts
with the catalyst metal. It is advisable to select a
metal as precursor that forms a liquid phase
together with the material for the nanotube or
nanorod. After exceeding the maximum
solubility, the nanorod or nanotube is
precipitated. The one-dimensional product will
grow as long as the precursor is supplied.
5.2 Nanostructures Related to Compounds with Layered Structures j115