title: Vertical Single-Crystalline Organic Nanowires on Graphene: Solution-Phase Epitaxy and Optical Microcavities.
abstract: Vertically aligned nanowires (NWs) of single crystal semiconductors have attracted a great deal of interest in the past few years. They have strong potential to be used in device structures with high density and with intriguing optoelectronic properties. However, fabricating such nanowire structures using organic semiconducting materials remains technically challenging. Here we report a simple procedure for the synthesis of crystalline 9,10-bis(phenylethynyl) anthracene (BPEA) NWs on a graphene surface utilizing a solution-phase van der Waals (vdW) epitaxial strategy. The wires are found to grow preferentially in a vertical direction on the surface of graphene. Structural characterization and first-principles ab initio simulations were performed to investigate the epitaxial growth and the molecular orientation of the BPEA molecules on graphene was studied, revealing the role of interactions at the graphene-BPEA interface in determining the molecular orientation. These free-standing NWs showed not only efficient optical waveguiding with low loss along the NW but also confinement of light between the two end facets of the NW forming a microcavity Fabry-Pérot resonator. From an analysis of the optical dispersion within such NW microcavities, we observed strong slowing of the waveguided light with a group velocity reduced to one-tenth the speed of light. Applications of the vertical single-crystalline organic NWs grown on graphene will benefit from a combination of the unique electronic properties and flexibility of graphene and the tunable optical and electronic properties of organic NWs. Therefore, these vertical organic NW arrays on graphene offer the potential for realizing future on-chip light sources.
authors.forename: Jian-Yao
authors.initials: JY
authors.lastname: Zheng
authors.forename: Hongjun
authors.initials: H
authors.lastname: Xu
authors.forename: Jing Jing
authors.initials: JJ
authors.lastname: Wang
authors.forename: Sinéad
authors.initials: S
authors.lastname: Winters
authors.forename: Carlo
authors.initials: C
authors.lastname: Motta
authors.forename: Ertuğrul
authors.initials: E
authors.lastname: Karademir
authors.affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
authors.forename: Weigang
authors.initials: W
authors.lastname: Zhu
authors.forename: Eswaraiah
authors.initials: E
authors.lastname: Varrla
authors.forename: Georg S
authors.initials: GS
authors.lastname: Duesberg
authors.forename: Stefano
authors.initials: S
authors.lastname: Sanvito
authors.affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.|Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Science, Tianjin University and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) , Tianjin 300072, China.
authors.forename: Wenping
authors.initials: W
authors.lastname: Hu
authors.forename: John F
authors.initials: JF
authors.lastname: Donegan
keywords: Vertical; graphene; optical microcavity; organic nanowire; solution; van der Waals epitaxy