title: Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence.
abstract: Oriented assemblies of small crystals forming larger structures are common in nature and crucial for forthcoming technologies as they circumvent the difficulties of structural manipulation at microscopic scale. We have discovered two distinctive concentric assemblies of zinc oxide rods, wherein each rod has an intrinsically positive and a negative polar end induced by the noncentrosymmetric arrangement of Zn and O atoms. All the rods in a single assembly emanate out of a central core maintaining a single polar direction. Due to growth along the two polar surfaces with different atomic arrangements, these assemblies are distinct in their intrinsic properties and exhibit strong UV luminescence in the exterior of Zn-polar assemblies, unlike the O-polar assemblies. Although novel applications can be envisioned, these observations suggest that hierarchical organization with respect to internal asymmetry might be widespread in natural crystal assemblies.
authors.affiliation: International Center for Materials Nanoarchitectonics, National Institute for Materials Science Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. guatam.ujjal@nims.go.jp
authors.forename: Ujjal K
authors.initials: UK
authors.lastname: Gautam
authors.forename: Masataka
authors.initials: M
authors.lastname: Imura
authors.forename: Chandra Sekhar
authors.initials: CS
authors.lastname: Rout
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Bando
authors.forename: Xiaosheng
authors.initials: X
authors.lastname: Fang
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dierre
authors.forename: Leonid
authors.initials: L
authors.lastname: Sakharov
authors.forename: A
authors.initials: A
authors.lastname: Govindaraj
authors.forename: Takashi
authors.initials: T
authors.lastname: Sekiguchi
authors.forename: Dmitri
authors.initials: D
authors.lastname: Golberg
authors.forename: C N R
authors.initials: CN
authors.lastname: Rao