5.3 Nanostructures Related to Compounds with Layered Structures 105
• GaN nanorods: Ga-dimethyl amide (Ga 2 [N(CH 3 ) 2 ] 6 ) as gallium source. Iron,
applied as catalyst is provided as iron carbonyl, Fe(C 5 H 5 ) 2 vapor. The reaction
is performed in a nitrogen–ammonia gas mixture.
Looking at nanotubes, typically, the reaction product looks like a disordered ball
of wool. As an example, Figure 5.29 displays carbon nanotubes synthesized with
methane as precursor and an iron-containing catalyst. The diameter of the nanotubes is adjusted by selection of the catalyst.
To produce arrays of carbon nanotubes, as are needed, for example, for electron
field emission displays, tiny droplets of a catalyst are arranged on a substrate either
by printing or by a vapor process. After producing these substrates, the following
process is similar to that described above, with just one difference: Now, the
carbon nanotubes grow perpendicularly to the substrate. This process is, in a
simplified manner, depicted in Figure 5.30.
The formation of the one-dimensional nanoparticle, nanotube or nanorod is
connected to a process of dissociation, dissolution, and precipitation at the surface
of the catalyst. First, the gaseous precursor is dissociated by reaction with the catalyst and partly dissolved. Here, one realizes a first criterion for the selection of the
catalyst: It must be able to dissolve the material for the intended nanoparticle.
After exceeding the maximal solubility, precipitation starts. The precipitation
takes place as nanorods or nanotubes. This one-dimensional object will continue
growing as long as the precursor is supplied. For example, looking at the synthesis
of carbon nanotubes using methane, CH 4 , as precursor, one observes dissociation
of the methane at the surface of the iron catalyst particle. The released carbon
dissolves in the catalyst particle and precipitates after exceeding the solubility limit.
This precipitation is the intended carbon nanotube. The length of this nanotube
is controlled by the supply of the precursor. As diffusion processes are significantly
faster and solubilities are higher in liquids as compared to solids, the catalyst
Figure 5.29 Carbon nanotubes synthesized in a tubular furnace as shown in Figure 5.26 at a
temperature around 1300 K. CH 4 was used as carbon precursor and iron as catalyst. (Ritschel,
M., Leonhardt, A., (2007) IFE Dresden, Germany; private communication.)
500 nm
• GaN nanorods: Ga-dimethyl amide (Ga 2 [N(CH 3 ) 2 ] 6 ) as gallium source. Iron,
applied as catalyst is provided as iron carbonyl, Fe(C 5 H 5 ) 2 vapor. The reaction
is performed in a nitrogen–ammonia gas mixture.
Looking at nanotubes, typically, the reaction product looks like a disordered ball
of wool. As an example, Figure 5.29 displays carbon nanotubes synthesized with
methane as precursor and an iron-containing catalyst. The diameter of the nanotubes is adjusted by selection of the catalyst.
To produce arrays of carbon nanotubes, as are needed, for example, for electron
field emission displays, tiny droplets of a catalyst are arranged on a substrate either
by printing or by a vapor process. After producing these substrates, the following
process is similar to that described above, with just one difference: Now, the
carbon nanotubes grow perpendicularly to the substrate. This process is, in a
simplified manner, depicted in Figure 5.30.
The formation of the one-dimensional nanoparticle, nanotube or nanorod is
connected to a process of dissociation, dissolution, and precipitation at the surface
of the catalyst. First, the gaseous precursor is dissociated by reaction with the catalyst and partly dissolved. Here, one realizes a first criterion for the selection of the
catalyst: It must be able to dissolve the material for the intended nanoparticle.
After exceeding the maximal solubility, precipitation starts. The precipitation
takes place as nanorods or nanotubes. This one-dimensional object will continue
growing as long as the precursor is supplied. For example, looking at the synthesis
of carbon nanotubes using methane, CH 4 , as precursor, one observes dissociation
of the methane at the surface of the iron catalyst particle. The released carbon
dissolves in the catalyst particle and precipitates after exceeding the solubility limit.
This precipitation is the intended carbon nanotube. The length of this nanotube
is controlled by the supply of the precursor. As diffusion processes are significantly
faster and solubilities are higher in liquids as compared to solids, the catalyst
Figure 5.29 Carbon nanotubes synthesized in a tubular furnace as shown in Figure 5.26 at a
temperature around 1300 K. CH 4 was used as carbon precursor and iron as catalyst. (Ritschel,
M., Leonhardt, A., (2007) IFE Dresden, Germany; private communication.)
500 nm