No abstract

Raman spectroscopy study of multi‐wall carbon nanotubes (MWNTs) of different diameters (with a small controllable number of walls) produced using Fe–Co catalyst with a variable size of the same active component has been performed. We have characterized as produced MWNTs with different diameters (series 1) and two types of tubes with fixed mean diameters (∼10 and 20 nm) heated in a flow of pure argon at various temperatures (2200, 2600 and 2800 °C – series 2). The Raman spectra of MWNTs have been registered in three spectral regions, corresponding to D (disorder‐induced), G (graphite) and 2D (two‐phonon scattering) bands. A ratio of intensities I2D/ID for tubes of series 1 has demonstrated almost a linear dependence on the nanotube diameter. After heating (series 2), D (disorder‐induced) Raman band has shown a substantial decrease in intensity. The variation of the Raman spectra parameters is discussed in terms of defectiveness of nanotubes.

We report on the increase of the Young's modulus (E) of chemical vapor deposition (CVD) grown multi-walled carbon nanotubes (MWNTs) upon high temperature heat treatment. The post heat-treatment at 2200–2800ºC in a controlled atmosphere results in a considerable improvement of the microstructure, chemical stability and electro-physical properties of the nanotubes. The Young's modulus of MWNTs of different diameters was measured by the deflection of a single tube suspended across the hole of silicon nitride membrane and loaded by an atomic force microscope tip. Contrary to previous reports, a strong increase of E was feasible due to the improved growth conditions of pristine carbon nanotubes and to the improved heat treatment conditions. However, the elastic modulus of CVD grown MWNTs still shows strong diameter dependence resulting from the remaining structural inhomogeneities in large diameter nanotubes.