OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 269

of stainless steel (SS) surfaces has shown eficient deposition of catalyst to
support growth of CNTs through water-assisted catalytic chemical vapour
deposition (Fig. 9.16). 107 In all cases of Fe-containing materials abraded on
Al 2 O 3 substrates, CNT growth was observed, demonstrating a method that is
(i) simple, (ii) accurate in catalyst patterning and also (iii) proicient for large
area catalyst deposition. An additional advantage is represented by the high
quality of the tubes, as demonstrated by Raman spectroscopy. Interestingly,
the same procedure of chemical vapour deposition can be exploited to
enable the reuse of the catalyst for multiple regrowths of vertically aligned
CNT arrays (carpets). 108 The as-produced CNTs could be transferred from
the growth substrate, while the catalyst and the substrate are reactivated by
annealing in air, which controls length and diameter distribution of nanotubes
accurately due to an additional size-dependent process of iron carbide
particle reoxidation. However, a limitation of this study was the inability to
achieve indeinite regrowth due to catalyst dynamics taking place during the
growth and regrowth processes. Conversely, the high density and continued
growth of CNTs were achieved by cutting the SWCNT ibres with a focused
ion beam technique followed by etching for removing amorphous carbon and
opening the ends of the SWCNTs. 109 Through this procedure, nanoscopically
lat open-ended SWCNT substrates were eficiently prepared.
Figure 9.16 . Scheme that describes catalyst deposition through abrasion. Any object
with Fe metal content abrades a catalyst in the form of particles that can be used as
nucleation sites for CNT growth. Reproduced from Alvarez et al . 107 with permission.
Another example of CNT “lying carpets” has been recently described by
the research group at the Smalley Institute, where chemical vapour deposition
(CVD) with roll-to-roll e-beam deposition was employed to produce the
lakes on which dense and aligned tubes were able to grow. 110 A theoretical
study regarding nanotubes' growth has been developed at Rice University
by Yakobson and collaborators, 111 who proved that a CNT's growth rate is
proportional to the chiral angle of the tube, as shown by ab initio energy
calculations. The predicted values were in full agreement with experimental
measurements, thus strengthening the solid consistency of the study.