Electron-positron annihilation in carbon nanotubes

Carbon nanotubes (CNTs) are investigated using the method of angular correlation of annihilation radiation (ACAR). Three centers of positron annihilation are revealed: (1) with π electrons in interlayer spacings; (2) with electrons of unsaturated covalent σ bonds in the region of defects; (3) with quasi-free electrons. An increase in defectiveness of carbon nanotubes yields an increase in the localization radius rm1 of the wave function of π electrons in interlayer spacings and an increase in the share of quasi-free electrons. Edge dislocations in multilayered CNTs result in a twofold (up to 0.25 nm) increase in rm1 and hybridization of unsaturated σ and stretched π bonds. This yields an increase in the concentration of conduction electrons. High sensitivity of positrons to defects can be used for developing methods for assessment and identification of defects in CNTs. © 2011 Pleiades Publishing, Ltd.