A method for diffraction-based identification of amorphous sp2 carbon materials

A method is suggested for estimation of structural properties of amorphous sp2 carbon and applied to amorphous fullerene and its derivatives produced by vacuum annealing. The method is based on the fitting of the neutron or x-ray powder diffraction patterns for scattering wave vector's modulus in the range from few units to several tens of inverse nanometers. The respective inverse problem assumes that the nanostructure of a sample is representable by a limited number, Nstr, of candidate structures (e.g. fullerenes, carbon flakes with graphene-like atom arrangement) of a limited number of atoms, Natom. These structures are packed heterogeneously, in the domains with various average densities of atoms and various total potential energy, using the rigid body molecular dynamics with variable parameter of pair interaction of atoms in the neighboring nanostructures. The method is applied to interpreting the data of neutron diffraction by an amorphous C60 fullerene annealed at 600, 800, 850, 900 and 1000 °C. The results for Nstr = 36 and Natom = 14 ÷ 285 enabled us to quantify structural properties of the samples in terms of the average size and curvature of the sp2 carbon structures, and analyze sensitivity of results to the layout of these structures in the domains.