Aqueous-Phase Oxidation of Epitaxial Graphene on the Silicon Face of SiC(0001)

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• 作者：Md. Zakir Hossain ; Maisarah B. A. Razak ; Shinya Yoshimoto ; Kozo Mukai ; Takanori Koitaya ; Jun Yoshinobu ; Hayato Sone ; Sumio Hosaka ; Mark C. Hersam
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 16, 2014
• 年：2014
• 卷：118
• 期：2
• 页码：1014-1020
• 全文大小：400K
• ISSN：1932-7455

文摘

To explore the chemical and electronic states of oxidized epitaxial graphene (EG) grown on the Si face of SiC(0001), we employ the Hummers oxidizing agents (H₂SO₄ + NaNO₃ + KMnO₄) under different reaction conditions that oxidize the graphene layer. The resulting material is characterized with scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). A mild 鈥渄rop-cast鈥?procedure at 60 掳C is found to be equally effective at oxidizing EG as the conventional Hummers procedure. This aqueous-phase oxidation reaction appears to proceed in an autocatalytic manner as indicated by the concurrent observation of patches of oxidized and clean graphene areas in atomically resolved STM images on partially oxidized EG. STS further reveals substantial changes in electronic structure for oxidized EG including the opening of a local band gap of 0.4 eV. The oxidation is confined to the graphene layers as verified by XPS characterization of the underlying SiC substrate. In contrast to EG oxidized in ultrahigh vacuum that contains only epoxy groups and can be fully reverted back to pristine EG following annealing at 260 掳C, aqueous-phase oxidized EG possesses carbonyl and hydroxyl groups in addition to the dominant epoxy groups and thus remains partially oxidized even following annealing at 1000 掳C.