Structural studies of nano-structured carbons: complementary x-ray and neutron techniques using short wavelengths

Carbon materials have a wide range of structural characteristics that can be studied by diffraction and small-angle scattering techniques using either synchrotron x-rays and/or neutrons. In order to obtain good spatial resolution in the pair correlation functions [g(r)], it is necessary to measure the structure factor [S(Q)] over a wide range of Q-values, requiring the use of short wavelength beams (with λ ∼ 0.1-0.2 A). During recent years, the use of pulsed neutrons from spallation sources such as ISIS (at RAL) and high energy x-ray beams from third generation sources (such as the ESRF) have allowed the development of powerful new methods for studying these materials. This brief review focuses on the properties of various carbon materials using a range of modern diffraction techniques:- Activated carbons made from saccharose and anthracene precursors, showing different ''graphitisng'' features, Diamond nanoparticles (∼ 50 A) convert to carbon onions and facet ted graphitic particles on heat treatment, Carbon nanotubes show detailed in-plane structure of curved graphene sheets in single and multi-walled nanotubes Carbon nanotubes grown in restricted geometry show partial orientation. Carbon nanohorns reveal detailed structural features for opened and unopened nanotubes. For these ''homonuclear'' systems the techniques of reactor neutrons, pulsed neutrons and synchrotron x-rays (normal and high energy) are seen to be complementary. Optimal measurements depend on sample quantity, Q-range and texture (orientational dependence). The review concludes with a speculation on likely future developments. (author)