Department of Chemistry, the Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005, United States.
ACS Nano. 2012 Sep 25;6(9):7842-9. doi: 10.1021/nn3020147. Epub 2012 Aug 22.
Graphite intercalation compounds (GICs) can be considered stacks of individual doped graphene layers. Here we demonstrate a reversible formation of sulfuric acid-based GICs using ammonium persulfate as the chemical oxidizing agent. No covalent chemical oxidation leading to the formation of graphite oxide occurs, which inevitably happens when other compounds such as potassium permanganate are used to charge carbon layers. The resulting acid/persulfate-induced stage-1 and stage-2 GICs are characterized by suppression of the 2D band in the Raman spectra and by unusually strong enhancement of the G band. The G band is selectively enhanced at different doping levels with different excitations. These observations are in line with recent reports for chemically doped and gate-modulated graphene and support newly proposed theories of Raman processes. At the same time GICs have some advantageous differences over graphene, which are demonstrated in this report. Our experimental observations, along with earlier reported data, suggest that at high doping levels the G band cannot be used as the reference peak for normalizing Raman spectra, which is a commonly used practice today. A Fermi energy shift of 1.20-1.25 eV and ∼1.0 eV was estimated for the stage-1 and stage-2 GICs, respectively, from the Raman and optical spectroscopy data.
石墨插层化合物（GICs）可以被认为是单个掺杂石墨烯层的堆叠。在这里，我们展示了使用过硫酸铵作为化学氧化剂来可逆地形成基于硫酸的 GICs。不会发生导致氧化石墨形成的共价化学氧化，当使用其他化合物如高锰酸钾来给碳原子层充电时，必然会发生这种情况。由此产生的酸/过硫酸盐诱导的阶段 1 和阶段 2 GICs 的特征是在拉曼光谱中抑制 2D 带，并且 G 带异常增强。在不同的掺杂水平下，通过不同的激发，G 带选择性地增强。这些观察结果与最近关于化学掺杂和栅极调制石墨烯的报道一致，并支持新提出的拉曼过程理论。同时，GICs 与石墨烯相比具有一些有利的差异，本报告对此进行了演示。根据拉曼和光谱数据，我们的实验观察结果以及之前报道的数据表明，在高掺杂水平下，G 带不能用作归一化拉曼光谱的参考峰，这是当今常用的做法。分别估计出阶段 1 和阶段 2 GICs 的费米能级位移为 1.20-1.25 eV 和 1.0 eV。
