Fabrication of free-standing vertically aligned carbon nanotubes structures by pyrolysis of ferrocene in conditions of low to high local ‘carbon-to metal’ ratio

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We report the observation of selective fabrication of carbon nano-onions (CNOs) and carbon nanotubes (CNTs) films in an advanced chemical vapour deposition (CVD) approach. Selective formation of these nanostructures is triggered by a residence-time induced variation of carbon to metal ratios in the atomic species of the pyrolyzed ferrocene vapour. The use of high sublimation temperatures is found to play a crucial role in reducing such residence time. Due to this effect, free standing vertically aligned CNTs films could be nucleated in the outer zone of the CVD reactor. The characteristics of these structures were investigated using multiple characterization techniques, namely: TEM, SEM, XRD, UV–vis and Raman spectroscopy.