Structural characterization of carbon nanosheets via x-ray scattering

Abstract

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 107Å at a 670°C deposition temperature to 50Å at 950°C. The distribution of nanosheet thickness remains qualitatively similar at each deposition temperature, but decreases from an average of eight graphene layers at 670°C to about six layers at 950°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°C to a completely turbostratic structure with amorphous content at 950°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.