Few-layer graphene sheets are prepared by splitting the expanded graphites using a high-power sonication. Atomic-level quantitative scanning transmission electron microscopy (Q-STEM) is employed to carry out the efficient layer statisticsm, enabling global optimization of the experimental conditions. A two-step splitting mechanism is thus revealed, in which the mean layer number was firstly reduced to less than 20 by heating to 1100{\deg}C and then tuned to the few-layer region by a 5-minute 104W/litre sonication. Raman spectroscopic analysis confirms the above mechanism and demonstrates that the sheets are largely free of defects and oxides.
@article{arxiv.1009.0059,
title = {Two-step splitting the expandable graphite for few-layer graphene},
author = {Kaiming Liao and Wangfeng Ding and Yuyuan Qin and Zhaoguo Li and Taishi Chen and Jianguo Wan and Fengqi Song and Min Han and Guanghou Wang and Jianfeng Zhou},
journal= {arXiv preprint arXiv:1009.0059},
year = {2011}
}