Influence of carbon source and synthesis temperature on structural and morphological properties of carbon nanofibers synthesized on tubular porous ZrO2 layers

This work presents a systematic study on structural details of carbon nanofibers and their dependency on substrate material, carbon source and synthesis temperature. Carbon nanostructures were grown by chemical vapor deposition on the inner surface of porous ceramic substrates in single channel geometry. The structural details, in particular the interlayer spacing, the apex angle and the undulation of the carbon layers were quantified from high resolution transmission electron microscopy images in a statistical manner, allowing a detailed evaluation of the structure processing relationship. The interlayer spacing decreases with increasing synthesis temperature, irrespective of carbon source and substrate material. The carbon source mainly affects the fiber diameter, showing opposed temperature dependences for methane and ethylene. Additionally, by using ethylene smaller apex angles were obtained. The carbon products were also characterized by field emission scanning electron microscopy, Raman spectroscopy and thermal analysis. Raman spectroscopy data suggested that best structural properties of the fibers were obtained at 800 °C with methane and at 750 °C with ethylene as carbon source. Simultaneously, these fibers possess highest thermal stability. A correlation between undulation of carbon layers and ID/IG ratios calculated from Raman spectroscopy data was found, suggesting undulation as a measure of crystallinity.