Carbon ion bombardment

Figure 7 shows a multiwalled carbon nanotube produced by electron beam evaporation [72]. Carbon ion bombardment processes using either electron beam [72] or electrical heating [17] afford multi- and single shell carbon nanotubes by vaporizing carbon in a vacuum. These processes show promise but still need to be fully developed. 

The technology of growing carbon nanotubes from the vapor phase dates back to 1991 when they were first found [11] in arc discharge experiments. Nanotubes can be obtained by chemical vapor deposition, laser evaporation, arc discharge, and carbon ion bombardment [62], Addition of particulate metal catalysts creates a more controlled growth habitat and helps growth of whiskers with greatly enhanced dimensional uniformity. 

The size of the nanoparticles was determined with TEM after the final ion bombardment on the same sample. The samples for TEM investigation were prepared by extraction replica method. The particles were stripped off the substrate surface by means of collodion which was covered by carbon film. The collodion was dissolved after carbon deposition. 

SIMS is a technique of direct mass analysis where the ion sputter is removed from the surface and, as a result of the ion bombardment, it is analyzed. By measuring both positive and negative ions, two different types of mass spectra are obtained. Positive SIMS is especially sensitive to low Z elements, which have low electronegative and ionization potential, while the negative SIMS is most sensitive to low Z elements with high electronegativity. The SIMS spectrum shown in Fig. 2.14 (Denison et al., 1988a, b) as a function of mass number is typical of that obtained from a carbon fiber surface. 

Wong, D.C.L. van Compemolle, R. Nowlin, J.G. O Neal, D.L. Johnson, G.M. Use of supercritical fluid extraction and fast ion bombardment mass spectrometry to identify toxic chemicals from a refinery effluent adsorbed onto granular activated carbon. Chemosphere 1996, 32, 621. 

Recent investigations in the field of plasma etching have almost universally found that surfaces subjected to ion bombardment (e.g., the target surface in Fig. 1) react (i.e., etch) much more rapidly than those which are held near plasma potential. Examples of this type have been reported by Hosokawa et al. for the halocarbon etching of silicon and by Holland and Ojha for the oxygen plasma-etching of carbon. Several systems exhibiting this type of behavior have also been observed in our laboratory . 

Finally, one must consider the possibility of an involatile residue being formed by one or more of the atomic species present in the molecular gas, e.g., adsorbed carbon from CF. Unless this residue is removed by some mechanism (step 5), it will terminate the etching reaction. Electron and ion bombardment could enhance residue removal by many of the same mechanisms mentioned above in connection with steps 2-4. 

A schematic illustration of the model is shown in Figure 10.2.12, together with that of polyhedral nanoparticles which grow as byproducts of MWNTs (see Fig. 10.2.3). An initial seed of an MWNT is the same as that of a polyhedral nanoparticle. Carbon neutrals [C, C2 (19)] and ions (C+) deposit and coagulate with each other to form atomic clusters and fine particles on a surface of the cathode. Structures of the particles at this stage may be amorphous with high fluidity (liquidlike) because of the high temperature ( 3500 K) of the electrode surface and ion bombardment. 

Figure 28.13 XPS spectrum of a H2 activated sample subjected to 45 h of reaction in syngas at 523 K. The Fe 2p region and the C Is region is shown (a) before and (b) after Ar ion bombardment. The carbide present in the sample is seen only after the carbon overlaycr is...

Fig. 16.6. Predicted NT/NS ratio (solid curve) for three incident angles and measured Knoop hardness as a function of nitrogen ion bombarding energy for carbon nitride film [56]. Hardness data O and obtained from References [18] and [57], respectively.

---