Selectivity of Threefold Symmetry in Epitaxial Alignment of Liquid Crystal Molecules on Macroscale Single‐Crystal Graphene. Issue 40 (2nd August 2018)

• Record Type: Journal Article
• Authors: Shen, Tian‐Zi; Hong, Seung‐Ho; Lee, Jae‐Hyun; Kang, Seog‐Gyun; Lee, Bomi; Whang, Dongmok; Song, Jang‐Kun
• Is Part Of: Advanced materials. Volume 30:Issue 40(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-08-02
• Subjects: liquid crystals -- molecular assembly -- single‐crystal graphene; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.201802441
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: 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. Abstract : A sixfold symmetric molecular assembly on clean, large, single‐crystal graphene is presented, which directly proves that the molecular‐ordering direction is determined by the first contact direction of the LC molecules on the graphene surface. Epitaxial molecular assembly along one direction is erasable and rewritable to another direction, unlike in previous reports. The findings remedy misleading knowledge regarding epitaxial molecular assembly on graphene.