Kavli Nanoscience Institute and Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
J Am Chem Soc. 2011 Mar 2;133(8):2334-7. doi: 10.1021/ja108554p. Epub 2011 Feb 4.
We report on the use of graphene templating to investigate the room-temperature structure and dynamics of weakly bound adlayers at the interfaces between solids and vapors of small organic molecules. Monolayer graphene sheets are employed to preserve and template molecularly thin adlayers of tetrahydrofuran (THF) and cyclohexane on atomically flat mica substrates, thus permitting a structural characterization of the adlayers under ambient conditions through atomic force microscopy. We found the first two adlayers of both molecules adsorb in a layer-by-layer fashion, and atomically flat two-dimensional islands are observed for both the first and the second adlayers. THF adlayers form initially as rounded islands but, over a period of weeks, evolve into faceted islands, suggesting that the adlayers possess both liquid and solid properties at room temperature. Cyclohexane adlayers form crystal-like faceted islands and are immobile under the graphene template. The heights of the second adlayers of THF and cyclohexane are measured to be 0.44 ± 0.02 and 0.50 ± 0.02 nm, respectively, in good agreement with the layer thicknesses in the monoclinic crystal structure of THF and the Phase I "plastic crystal" structure of cyclohexane. The first adlayers appear slightly thinner for both molecules, indicative of interactions of the molecules with the mica substrate.
我们报告了使用石墨烯模板来研究固体和小分子蒸气界面上弱束缚吸附层在室温下的结构和动力学。单层石墨烯片被用来在原子级平坦的云母衬底上保存和模板化四氢呋喃（THF）和环己烷的分子层薄吸附层，从而通过原子力显微镜在环境条件下对吸附层进行结构表征。我们发现这两种分子的前两层吸附层以逐层的方式吸附，并且对于第一层和第二层吸附层都观察到原子级平坦的二维岛。THF 吸附层最初形成圆形岛，但在数周内演变成有面的岛，这表明吸附层在室温下同时具有液体和固体的性质。环己烷吸附层形成类似晶体的有面岛，在石墨烯模板下不移动。THF 和环己烷的第二层吸附层的高度分别测量为 0.44±0.02nm 和 0.50±0.02nm，与 THF 的单斜晶结构和环己烷的 I 相“塑料晶体”结构中的层厚度非常吻合。对于这两种分子，第一层吸附层看起来稍微薄一些，这表明分子与云母衬底之间存在相互作用。
