Shen Tian-Zi, Hong Seung-Ho, Lee Jae-Hyun, Kang Seog-Gyun, Lee Bomi, Whang Dongmok, Song Jang-Kun
Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do, 16419, Korea.
Department of Energy Systems Research and Department of Materials Science and Engineering, Ajou University, Suwon, Gyeonggi-do, 16499, Korea.
Adv Mater. 2018 Aug 2:e1802441. doi: 10.1002/adma.201802441.
Epitaxial alignment of organic liquid crystal (LC) molecules on single-crystal graphene (SCG), an effective epitaxial molecular assembly template, can be used in alignment-layer-free liquid crystal displays. However, selectivity among the threefold symmetric easy axes of LCs on graphene is not well understood, which limits its application. Here, sixfold symmetric radial LC domains are demonstrated by dropping an LC droplet on clean SCG, which reveals that the graphene surface does not have an intrinsic preferential direction. Instead, the first contact geometry of the LC molecules determines the direction. Despite its strong anchoring energy on graphene, the LC alignment direction is readily erasable and rewritable, contrary to previous understanding. In addition, the quality of the threefold symmetric alignment is sensitive to alien residue and graphene imperfections, which can be used to detect infinitesimal impurities or structural defects on the graphene. Based on this unique epitaxial behavior of LCs on SCG, an alignment-layer-free electro-optical LC device and LC alignment duplication, which can result in practical graphene-based flexible LC devices, are realized.
有机液晶（LC）分子在单晶石墨烯（SCG）上的外延排列，作为一种有效的外延分子组装模板，可用于无取向层的液晶显示器。然而，人们对石墨烯上液晶三重对称易轴之间的选择性了解不足，这限制了其应用。在此，通过将液晶液滴滴落在干净的单晶石墨烯上，展示出了六重对称的径向液晶畴，这表明石墨烯表面没有固有的优先方向。相反，液晶分子的首次接触几何形状决定了方向。尽管液晶在石墨烯上具有很强的锚定能，但与之前的认识相反，液晶的取向方向很容易擦除和重写。此外，三重对称取向的质量对外来残留物和石墨烯缺陷很敏感，这可用于检测石墨烯上的微小杂质或结构缺陷。基于液晶在单晶石墨烯上这种独特的外延行为，实现了一种无取向层的电光液晶器件和液晶取向复制，这可能会带来实用的基于石墨烯的柔性液晶器件。
