Quantitative crystallographic analysis of individual carbon nanofibers using high resolution transmission electron microscopy and electron diffraction

High resolution transmission electron microscopy (HRTEM) and electron diffraction allow for a thorough crystallographic characterization of the herringbone structure of carbon nanofibers (CNF). A newly developed method for an extended quantitative structural evaluation of single carbon nanofibers is applied. The method is based on quantitative analysis of radial and azimuthal profiles extracted from selected area electron diffraction (SAED) patterns, nano beam electron diffraction (NBED) patterns or power spectra obtained by Fourier transformation of HRTEM images. Precise quantification of structural parameters, in particular cone apex angle, interlayer spacing and undulation of graphene layers is carried out. For the first time a profound interpretation of CNF diffraction patterns is given, proving the rotational disorder of the turbostratic structure and suggesting a random rotation between successive graphene cones. A series of crystallographic analyses along the axis of a single CNF reveal a continuous increase of the interlayer spacing during CNF growth. Additionally, the different techniques HRTEM, SAED, and NBED are evaluated in terms of attainable structural information, precision and applicability to different diameters of CNFs.