Incomplete bonding defects

Defects in MWCNTs are always present. We can briefly differentiate between topological defects which lead to rehybridization (C5 and C7 rings instead of C6 lead to rehybridization between sp2 and sp3) and incomplete bonding defects (vacancies, dislocation) (Fig. 16.2). Functionalization or doping with heteroelements may add further modifications with respect to the ideal ordered structure, but are also the sites which allow for anchoring supported metals or metal oxides, or to functionalize the CNTs with organic groups. 

The presence of defects caused by incomplete reaction in the particles has been found while comparing intra- and intermolecular reaction rates in polycomplexes obtained by mixing polymer solutions, and by matrix polymerization 461. In the latter case a polycomplex is formed simultaneously with the chain growth which is connected with the complementary macromolecule, the matrix. This process of polycomplex formation is closer to the equilibrium one — in any case there are considerably fewer obstacles here for forming an uninterrupted sequence of intermolecular bonds. That is why the rate and conversion of thermochemical reactions (which are connected with the presence or absence of defects — loops or tension in double-stranded chains of the polycomplex) depend on how the polycomplex have been obtained. After its destruction and reconstruction (e.g., by increasing and then decreasing of pH in the case of p.c. (PMA — PVPD)) the matrix polycomplex does not differ from the one obtained by mixing 46). 

Based on this model, the hyperfine spectra for the defect can be related to the s- and p- components of the wavefunction (Stutzmann and Biegelsen, 1988). Table 4.1 shows the results and compares them with the silicon defects which are known to be of the dangling bond type in other materials. An sp dangling bond has J s-like and p-like character, so should have a = 0.5 and p = 0.87. In practice, all the defects in Table 4.1 have a slightly smaller s-character and larger p-character and also incomplete localization, compared to the sp dangling bond model. 

Si(II) defect, especially at its internal surfaces, which in turn gives rise to the observed bright photoluminescence. Further reduction of oxygen due to incomplete oxidation could result in the fromation of Si-Si bonding across the oxygen vacancies. Indeed, the Raman spectrum of our Si02 particles shows a sharp band at 520 cm" ... 

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