Variable step radial ordering in carbon onions

We analyse the radial distribution of atoms in carbon onions optimised using a combination of classical molecular dynamics and density functional theory. X-ray diffractograms of thermally annealed nanodiamonds are also exploited together with high-resolution transmission electron microscopy data published elsewhere. The internal radial ordering of atoms inside the onions was determined showing a gradual change of intershell separation as a function of radius. This change may result in a twisted internal structure of the onions. The influence of atomic defects appearing in the shells altering their curvature on the formation of twisted onions is discussed.

► Experimental data are compared with theory for the layer spacing in carbon onions.
► X-ray pattern broadening can be related to the internal ordering of the onion shells.
► Spirally twisted onions are predicted theoretically after annealing nanodiamonds.
► The data suggest carbon particles transitional between nanodiamonds and onions.
► The spirally twisted onions have a shape similar to a marine mollusc.