Structural characterization of carbon nanosheets via x-ray scattering

The structure of carbon nanosheets deposited by radio frequency plasma-enhanced chemical-vapor deposition at different substrate temperatures is investigated via x-ray scattering. Carbon nanosheets consist of vertically aligned graphene-layer stacks, one to nine layers thick, which can attain micron-scale lengths. Histograms of both molecule length and thickness are generated by fitting the experimental data with a linear combination of x-ray scattering intensities, which are calculated for rhombus-shaped molecules of different dimensions. These histograms show that the average uncorrugated length within a nanosheet decreases from 107 A at a 670 degrees C deposition temperature to 50 A at 950 degrees C. The distribution of nanosheet thickness remains qualitatively similar at each deposition temperature, but decreases from an average of eight graphene layers at 670 degrees C to about six layers at 950 degrees C. With increasing temperature large nestlike structures are observed, but are found to consist of the same nanosheet constituents in a more corrugated and bunched form. These changes are accompanied by the transition from a primarily turbostratic structure with some ordered graphite crystallites at 670 degrees C to a completely turbostratic structure with amorphous content at 950 degrees C. All x-ray scattering results are explained in the context of the nanosheet morphology observed with scanning electron microscopy, and corroborating structural information is provided by Raman spectroscopy. (C) 2005 American Institute of Physics.