title: Monitoring defects on monolayer graphene using nematic liquid crystals.
abstract: Defects in graphene governs electrical and optical properties. Although grain boundaries in graphene inevitably formed during large area synthesis process, which act as scattering centers for charge carriers to degrade mobility, have been studied extensively, point defects have been rarely investigated mainly due to the absence of facile observation tools. Here, we report polarized optical microscopy to observe defect distributions in monolayer graphene. This was realized by aligning liquid crystal s (LC) on graphene where the defect population was modulated by irradiating ultraviolet (UV) light directly on graphene surface under moisture condition. Aromatic rings in LC molecules are oriented with hexagonal rings in graphene to have preferred orientation, providing a way to identify relative orientations of graphene domains and point defects. Our studies show that point defects generated by prolonged UV irradiation time give rise to irregular LC alignment with disclination lines on the graphene surface and a large-size LC domain associated with graphene single domain eventually disappeared. This indicates that defects associated with oxygen-containing functional groups cause to reduce the strong stacking interaction between graphene and LC molecules.
authors.forename: Young Jin
authors.initials: YJ
authors.lastname: Lim
authors.forename: Byung Hoon
authors.initials: BH
authors.lastname: Lee
authors.forename: You Ri
authors.initials: YR
authors.lastname: Kwon
authors.forename: Young Eun
authors.initials: YE
authors.lastname: Choi
authors.forename: G
authors.initials: G
authors.lastname: Murali
authors.forename: Joong Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Van Luan
authors.initials: VL
authors.lastname: Nguyen
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee
authors.forename: Seung Hee
authors.initials: SH
authors.lastname: Lee