title: Observing grain boundaries in CVD-grown monolayer transition metal dichalcogenides.
abstract: Two-dimensional monolayer transition metal dichalcogenides (TMdCs), driven by graphene science, revisit optical and electronic properties, which are markedly different from bulk characteristics. These properties are easily modified due to accessibility of all the atoms viable to ambient gases, and therefore, there is no guarantee that impurities and defects such as vacancies, grain boundaries, and wrinkles behave as those of ideal bulk. On the other hand, this could be advantageous in engineering such defects. Here, we report a method of observing grain boundary distribution of monolayer TMdCs by a selective oxidation. This was implemented by exposing directly the TMdC layer grown on sapphire without transfer to ultraviolet light irradiation under moisture-rich conditions. The generated oxygen and hydroxyl radicals selectively functionalized defective grain boundaries in TMdCs to provoke morphological changes at the boundary, where the grain boundary distribution was observed by atomic force microscopy and scanning electron microscopy. This paves the way toward the investigation of transport properties engineered by defects and grain boundaries.
authors.affiliation: IBS Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University , Suwon 440-746, Korea.
authors.forename: Thuc Hue
authors.initials: TH
authors.lastname: Ly
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Chiu
authors.forename: Ming-Yang
authors.initials: MY
authors.lastname: Li
authors.forename: Jiong
authors.initials: J
authors.lastname: Zhao
authors.forename: David J
authors.initials: DJ
authors.lastname: Perello
authors.forename: Magdalena Ola
authors.initials: MO
authors.lastname: Cichocka
authors.forename: Hye Min
authors.initials: HM
authors.lastname: Oh
authors.forename: Sang Hoon
authors.initials: SH
authors.lastname: Chae
authors.forename: Hye Yun
authors.initials: HY
authors.lastname: Jeong
authors.forename: Fei
authors.initials: F
authors.lastname: Yao
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee
keywords: STEM; TEM; atomic force microscopy; sapphire grain boundary; scanning electron microscopy; selective oxidation; transition metal dichalcogenides