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The synthesis of single-walled carbon nanotubes (SWCNTs) with the narrowest possible diameter distribution is a challenging undertaking in carbon nanoscience, which can be overcome through the fabrication of monodisperse catalytic nanoparticles. A technique is presented here to approach the diameter control of SWCNTs using a chemisorbed nickel acetylacetonate monolayer at the surface of silica. We show by Fourier transform infrared spectroscopy and thermogravimetry coupled with mass spectroscopy that a monolayer of nickel acetylacetonate is anchored with the silanol groups at the surface of the substrate. After thermal decomposition, the nickel remains bonded with these silanol groups, resulting in a good dispersion of the nickel over the silica surface. Using this catalyst, SWCNTs with a narrow diameter distribution were synthesized at moderate temperature. This opens new perspectives for the fabrication of uniform-diameter carbon nanotubes.

In the current work, we show that it is possible to favor the selective growth of single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution on supported catalyst particles with a broad size distribution. Carbon nanotubes were grown at 600 °C on silicon substrates. The structure of carbon deposits was controlled by managing the carbon feedstock for adjusting the rate of carbon nanostructures formation on the surface of catalyst particles. Either carbon nanofibers (CNFs) carpets or isolated SWCNTs were obtained. With the fine tune of carbon feedstock, small isolated SWCNTs with a narrow diameter distribution were obtained by limiting the catalytic activity of the largest catalyst particles. HRTEM observations of nanotube embryos have suggested a possible mechanism of multi-walled carbon nanotubes (MWCNTs) formation that can explain why the growth of MWCNTs with parallel walls seems to be more difficult than SWCNTs or CNFs at low temperature.

Double wall carbon nanotubes (DWCNTs) have proven to have a very good structural stability when exposed to high static pressures. We report here on the study of DWCNTs after application of shock wave (dynamic) compression up to 36 GPa in a recovery assembly. TEM images of so-treated samples reveal a threshold between 19 and 26 GPa of shock wave compression above which significant structural damage is induced whereas only minor damage can be detected below. The threshold detected with TEM coincides well with the collapse pressure of DWCNTs previously reported [You et al., High Press. Res. 31, 186 (2011); Aguiar et al., Phys. Chem. C 115, 5378 (2011)]. Raman data demonstrate a gradual accumulation of structural defects via an increase in D-band to G-band intensity ratio (ID/IG-ratio) from ∼0.2 to ∼0.8 in going from the source CNT material to the nanotubes after compression to 36 GPa. Despite severe damage; the DWCNTs exposed to 36 GPa of shock wave compression survived which is evidenced by Raman spectra. The DWCNTs demonstrate a higher susceptibility to structural damage under dynamic than static pressure.

We report on a systematic study of the influence of laser irradiation on the Raman spectra of HiPco-produced single-wall , CNTS. Specifically, we have examined the Raman response of bundled CNTs to: i) laser power density; ii) exposure time and iii) photon energy (1.96 and 2.33 eV). Our results show that irreversible destruction of CNTs in the bundles can occur at even low laser power density (0.15 kW/cm2). The tubes with smaller diameters are influenced first and the rate of CNT destruction increases with photon energy. Finally, we determined that when investigating destruction of CNT bundies, the use of a low laser power density is required because changes in the structure of the bundles can lead to sample temperature changes for otherwise identical measurement parameters.

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