Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
Nano Lett. 2010 Nov 10;10(11):4600-6. doi: 10.1021/nl1026452.
Atomic-resolution imaging of discrete [γ-SiW10O36]8- lacunary Keggin ions dispersed onto monolayer graphene oxide (GO) films by low voltage aberration corrected transmission electron microscopy is described. Under low electron beam dose, individual anions remain stationary for long enough that a variety of projections can be observed and structural information extracted with ca. ± 0.03 nm precision. Unambiguous assignment of the orientation of individual ions with respect to the point symmetry elements can be determined. The C2v symmetry [γ-SiW10O36]8- ion was imaged along its 2-fold C2 axis or orthogonally with respect to one of two nonequivalent mirror planes (i.e., σv). Continued electron beam exposure of a second ion imaged orthogonal to σv causes it to translate and/or rotate in an inhibited fashion so that the ion can be viewed in different relative orientations. The inhibited surface motion of the anion, which is in response to H-bonding-type interactions, reveals an important new property for GO in that it demonstrably behaves as a chemically modified (i.e., rather than chemically neutral) surface in electron microscopy. This behavior indicates that GO has more in common with substrates used in imaging techniques such as atomic force microscopy and scanning tunneling microscopy, and this clearly sets it apart from other support films used in transmission electron microscopy.
采用低电压像差校正透射电子显微镜，对分散在单层氧化石墨烯（GO）薄膜上的离散[γ-SiW10O36]8-缺位 Keggin 离子进行原子级分辨成像。在低电子束剂量下，单个阴离子停留时间足够长，可以观察到各种投影，并以约 0.03nm 的精度提取结构信息。可以确定各个离子相对于点对称元素的取向的明确分配。C2v 对称的[γ-SiW10O36]8-离子沿其 2 重 C2 轴或与其两个不等价的镜像平面之一（即σv）正交成像。继续用电子束照射与 σv 正交成像的第二个离子，会使其以受抑制的方式平移和/或旋转，从而可以以不同的相对取向观察该离子。阴离子的受抑制的表面运动，这是对氢键型相互作用的响应，揭示了 GO 的一个重要新特性，即它在电子显微镜中明显表现为化学改性（即，而不是化学中性）的表面。这种行为表明，GO 与原子力显微镜和扫描隧道显微镜等成像技术中使用的衬底更具相似性，这显然使它与透射电子显微镜中使用的其他支撑膜区别开来。
