Stolyarova Elena, Rim Kwang Taeg, Ryu Sunmin, Maultzsch Janina, Kim Philip, Brus Louis E, Heinz Tony F, Hybertsen Mark S, Flynn George W
Department of Chemistry and Center for Electron Transport in Molecular Nanostructures, Columbia University, New York, NY 10027, USA.
Proc Natl Acad Sci U S A. 2007 May 29;104(22):9209-12. doi: 10.1073/pnas.0703337104. Epub 2007 May 21.
We present scanning tunneling microscopy (STM) images of single-layer graphene crystals examined under ultrahigh vacuum conditions. The samples, with lateral dimensions on the micrometer scale, were prepared on a silicon dioxide surface by direct exfoliation of crystalline graphite. The single-layer films were identified by using Raman spectroscopy. Topographic images of single-layer samples display the honeycomb structure expected for the full hexagonal symmetry of an isolated graphene monolayer. The absence of observable defects in the STM images is indicative of the high quality of these films. Crystals composed of a few layers of graphene also were examined. They exhibited dramatically different STM topography, displaying the reduced threefold symmetry characteristic of the surface of bulk graphite.
我们展示了在超高真空条件下检测的单层石墨烯晶体的扫描隧道显微镜（STM）图像。这些样品的横向尺寸为微米级，通过对结晶石墨进行直接剥离在二氧化硅表面制备而成。利用拉曼光谱法识别出了单层薄膜。单层样品的形貌图像展现出了孤立石墨烯单层完整六边形对称性所预期的蜂窝状结构。STM图像中未观察到明显缺陷，这表明这些薄膜质量很高。我们还对由几层石墨烯组成的晶体进行了检测。它们呈现出截然不同的STM形貌，显示出块状石墨表面所特有的降低的三重对称性。
