Department of Chemical Engineering, Stanford University, Stanford, California, 94305, USA; Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea.
Small. 2015 May 6;11(17):2037-43. doi: 10.1002/smll.201403006. Epub 2015 Jan 7.
Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.
有机 - 石墨烯系统已成为各种应用的新平台，例如柔性有机光伏和有机发光二极管。由于其在电荷输运中的重要意义，研究和可靠控制石墨烯 - 分子界面处的分子组装结构对于成功将石墨烯纳入相关有机器件非常重要。在这里，利用悬浮石墨烯的理想膜作为分子组装模板来研究薄膜外延行为。通过透射电子显微镜，发现了在石墨烯上的并五苯的两种不同的分子组装结构。一种观察到的组装结构类似于众所周知的体相，在石墨烯衬底上采用面内分子取向。另一方面，确定了并五苯晶体的一种罕见多晶型，其沿 c 轴表现出明显的应变。特别是，应变膜表现出特定的分子取向和与底层石墨烯的强烈方位相关。通过包括范德华相互作用在内的第一性原理电子结构计算，将这种不寻常的多晶型归因于石墨烯与并五苯的强相互作用。在石墨烯上观察到的应变有机薄膜生长表明通过石墨烯 - 分子相互作用来调节分子组装的可能性。
