Page 163 - Carbon Nanotubes

I54 Y. SAITO
Table 1. Formation of filled nanocapsules. Elements in shadowed boxes are those which were encapsu-
lated so far. M and C under the chemical symbols represent that the trapped elements are in metallic and
carbide phases, respectively. Numbers above the symbols show references.

7, 8 11, 12 lJ,-!2 11,)2 II, 12 11, 12 11, I2 II, 12 II, 12 12 II, 12
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
c c c c c c c c c c C

tubes, gave dooz = 0.344 nm[14], being consistent nally observed. The structure of the particles at this
with the result of electron diffraction. The interlayer stage may be “quasi-liquid” or amorphous with high
spacing is wider by a few percent than that of the ideal structural fluidity because of the high temperature
graphite crystal (0.3354 nm). The wide interplanar (=3500 K)[17] of the electrode and ion bombardment.
spacing is characteristic of the turbostratic graphite[ 151. Ion bombardment onto the electrode surface seems to
Figure 2 illustrates a proposed growth process[3] of be important for the growth of nanoparticles, as well
a polyhedral nanoparticle, along with a nanotube. as tubes. The voltage applied between the electrodes
First, carbon neutrals (C and C,) and ions (C+)[16] is concentrated within thin layers just above the surface
deposit, and then coagulate with each other to form of the respective electrodes because the arc plasma is
small clusters on the surface of the cathode. Through electrically conductive, and thereby little drop in volt-
an accretion of carbon atoms and coalescence between age occurs in a plasma pillar. Near a cathode, the volt-
clusters, clusters grow up to particles with the size fi- age drop of approximately 10 V occurs in a thin layer
of to lop4 cm from the electrode surface[l8].
Therefore, C+ ions with an average kinetic energy
of - 10 eV bombard the carbon particles and enhance
the fluidity of particles. The kinetic energy of the car-
bon ions seems to affect the structure of deposited car-
bon. It is reported that tetrahedrally coordinated
amorphous carbon films, exhibiting mechanical prop-
erties similar to diamond, have been grown by depo-
sition of carbon ions with energies between 15 and
70 eV[ 191. This energy is slightly higher than the present
case, indicating that the structure of the deposited ma-
terial is sensitive to the energy of the impinging car-
bon ions.
The vapor deposition and ion bombardment onto
quasi-liquid particles will continue until the particles
are shadowed by the growth of tubes and other par-
ticles surrounding them and, then, graphitization oc-
curs. Because the cooling goes on from the surface to
the center of the particle, the graphitization initiates
on the external surface of the particle and progresses
Fig. 1. TEM picture of a typical nanoparticle. toward its center. The internal layers grow, keeping