International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
ACS Nano. 2011 Jun 28;5(6):4401-6. doi: 10.1021/nn103200t. Epub 2011 May 16.
A suspended graphene oxide device is fabricated and investigated using a transmission electron microscope (TEM) scanning tunneling microscope (STM) setup. A detailed study of step-by-step reduction of an individual graphene oxide sheet under current flow and Joule heating in tandem with conductivity measurements, atomic structure imaging, chemical composition, and bonding alternations tracing is performed. As monitored by electron energy loss spectroscopy, the oxygen content is tuned from that peculiar to a pristine graphene oxide (i.e., 23.8 at %) to oxygen-free pure graphene. Six orders of magnitude conductance rise is observed during this process with the final conductivity reaching 1.5 × 10(5) S/m. Quantification of plasma energy losses of the starting graphene oxide shows that ∼40% of the oxygen atoms are in the form of epoxy, and ∼60% oxygen atoms are in the form of hydroxyl. The total portion of sp(3) bonds in pristine graphene oxide is estimated to be ∼45%. The epoxy groups show a larger influence on the conductivity of graphene oxide than hydroxyl ones. Through analyzing consecutive plasma-loss energy spectra under gradual graphene oxide to graphene transformation, it is found that the oxygen atoms in epoxy groups decompose prior to those in hydroxyl groups.
采用透射电子显微镜（TEM）扫描隧道显微镜（STM）装置制备并研究了悬浮氧化石墨烯器件。通过对电流和焦耳热作用下单个氧化石墨烯片的逐步还原进行详细研究，同时进行了导电性测量、原子结构成像、化学成分和键合变化追踪。通过电子能量损失光谱监测，氧含量从原始氧化石墨烯（即 23.8 at%）调谐至无氧纯石墨烯。在此过程中观察到 6 个数量级的电导上升，最终电导率达到 1.5×10(5) S/m。对起始氧化石墨烯的等离子体能量损失进行定量分析表明，约 40%的氧原子以环氧基的形式存在，约 60%的氧原子以羟基的形式存在。原始氧化石墨烯中 sp(3)键的总比例估计约为 45%。环氧基团对氧化石墨烯的导电性影响大于羟基基团。通过分析逐步氧化石墨烯到石墨烯转变过程中的连续等离子体损耗能谱，发现环氧基团中的氧原子先于羟基基团中的氧原子分解。
