title: Ultrathin topological insulator Bi2Se3 nanoribbons exfoliated by atomic force microscopy.
abstract: Ultrathin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi(2)Se(3)), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi(2)Se(3) nanoribbons (>50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultrathin nanoribbons, showing drastic difference in sheet resistance between 1-2 QLs and 4-5 QLs. Transport measurement carried out on an exfoliated (<or=5 QLs) Bi(2)Se(3) device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states.
authors.affiliation: Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: Seung Sae
authors.initials: SS
authors.lastname: Hong
authors.forename: Worasom
authors.initials: W
authors.lastname: Kundhikanjana
authors.forename: Judy J
authors.initials: JJ
authors.lastname: Cha
authors.forename: Keji
authors.initials: K
authors.lastname: Lai
authors.forename: Desheng
authors.initials: D
authors.lastname: Kong
authors.forename: Stefan
authors.initials: S
authors.lastname: Meister
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kelly
authors.forename: Zhi-Xun
authors.initials: ZX
authors.lastname: Shen
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui