Bundle of nanotubes

The fractal-like organization led, therefore, to conductivity measurements at three different scales (1) the macroscopic, mm-size core of nanotube containing material, (2) a large (60 nm) bundle of nanotubes and, (3) a single microbundle, 50 nm in diameter. These measurements, though they do not allow direct insights on the electronic properties of an individual tube give, nevertheless, at a different scale and within certain limits fairly useful information on these properties. 

A cylindrical hard deposit, which is grown on the tip of a cathode (A in Fig. 10.2.2), consists of two regions an inner fibrous black core and an outer gray hard shell (15). The inner core had a columnar structure that was made up of bundles of nanotubes and flocks of polyhedral graphitic particles (32). On the other hand, the hard shell was made of stacked graphitic flakes. 

Experiment. The sample was scanned in a direction crossing a bundle of nanotubes. The gradient maps represented at Fig. 2a, 2b show relief of a bundle and... 

Methods of AFM, by means of a new method of calibration of lateral forces, allow to quantitavely investigate various mechanical characteristics of nanotubes. We have demonstrated one of applications of this method and determined critical lateral force that displace bundle of nanotubes over HOPG surface. The advantage of the work is possibility of real time observation of moment of nanotubes displacement, so relatively exact value of the lateral force caused such event can be estimated. 

In some cases, the bundles of nanotubes grow beyond the zeoUte s surface and form a pattern that is defined by the pore distribution. An example for this type of MWNT arrangement is found in the chemical vapor deposition of acetylene on anodic alumina with a pore size of ca. 25 nm. The resulting multiwalled nano tubes can be isolated by chemical removal of the template with chromic and phosphoric acid (Figure 3.26). 

It would surely be attractive for a variety of examinations and appUcations to avoid bundle formation immediately at production. As for the time being this has not succeeded, a postprocessing is required in aU cases. This is aimed at removing impurities from production (e.g., catalyst) as well as at dissolving the bundles of nanotubes. These efforts result in stable solutions of carbon nanotubes. Still the obtainable concentrations are not very high and range about a few milligrams per milUUter. 

The mechanical properties of isolated SWNT in particular (Section 3.4.3) turn them into nothing short of a fiUer par excellence for polymer composites. However, the embedding of individual, completely debundled carbon nanotubes in the polymer matrix still poses large problems. This is why, for the time being, the materials produced do by far not reach the envisaged improvement of characteristics Bundles of nanotubes feature much worse mechanical properties as there... 

Figure 3.93 Possible sites for the intercalation of small particles or atoms inlude the tube s inner void (a) as well as the interstitial space In multiwalled tubes (b) and the hollow space within bundles of nanotubes (c).

FIGURE 18.11 Bundle of nanotubes (view along the tube axes) after the impact of 500 eV Ar ion beam (a) and a multiwalled nanotube after 300 eV Ar ion beam irradiation with a dose of 2 x 10 cm" (b). (Reprinted from AmcZ. Instrum. Methods Phys. Res. B, 216, Krasheninnikov, A.V. and Nordlund, K., Irradiation effects in carbon nanotubes, 355-366, Copyright 2004, with permission from Elsevier.)... 

Depending on the amount of rolled sheets, the CNTs can be divided into two categories those with only one wall, called single wall (SWNT—Single-Wall Nanotubes) or multi-wall (MWNT— Multi-WaU Carbon Nanotnbes). The latter is the result of several coaxial cylinders with a distance similar to the distance between the walls of graphene sheets that make np graphite (0.335 nm [34]).The number of sheets or walls of MWNTs can vary widely, from two (also eaUed DWNT, Double-Wall Carbon Nanotubes) to dozens of walls [35, 36]. MWNTs are usually isolated in synthesis products, while SWNTs are usually produced in the form of bundles of nanotubes [37]. 

Figure 8.77 shows the experimental adsorption isotherm data for the Electric-arc discharged SWNTs purified by the wet oxidation method (Fig. 8.77a) and HiP Q SWNTs purified by the two-stage purifieation step (Fig. 8.77b) and the MD simulation results (Fig. 8.77c). The simulations were performed assuming heterogeneous bundle of nanotubes that included large interstitial sites due to imperfect packing of the nanotubes. The bundle consisted of 45 nanotubes of various diameters. The mean diameter of the tubes in the bundle is about 13. 6 A, whieh is the diameter...

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