Fig. 6.

HAADF images of graphene and graphene oxide samples with varying degrees of purity. a–e Varying contamination degree on GO synthesised from various graphite feedstocks (of differing purity) along with a commercially purchased material: a commercially sourced GO; b natural graphite flake (98% purity); c natural graphite flake (99% purity); d natural graphite flake (99.9% purity); e natural graphite powder (99.9999% purity). f Typical solvent-exfoliated graphene synthesised from graphite with 99.9% purity showing a very clean surface with almost no contamination. Numbers of layers are marked on the image. Scale bars in the images are 5 nm. g–l Comparison of the EDS spectra of the samples shown at a–f, respectively. The panels are colour-coded for clarity