title: Two-dimensional vanadium-doped ZnO nanosheet-based flexible direct current nanogenerator.
abstract: Here, we report the synthesis of lead-free single-crystalline two-dimensional (2D) vanadium(V)-doped ZnO nanosheets (NSs) and their application for high-performance flexible direct current (DC) power piezoelectric nanogenerators (NGs). The vertically aligned ZnO nanorods (NRs) converted to NS networks by V doping. Piezoresponse force microscopy studies reveal that vertical V-doped ZnO NS exhibit typical ferroelectricity with clear phase loops, butterfly, and well-defined hysteresis loops with a piezoelectric charge coefficient of up to 4 pm/V, even in 2D nanostructures. From pristine ZnO NR-based NGs, alternating current (AC)-type output current was observed, while from V-doped ZnO NS-based NGs, a DC-type output current density of up to 1.0 μAcm(-2) was surprisingly obtained under the same vertical compressive force. The growth mechanism, ferroelectric behavior, charge inverted phenomena, and high piezoelectric output performance observed from the V-doped ZnO NS are discussed in terms of the formation of an ionic layer of [V(OH)4(-)], permanent electric dipole, and the doping-induced resistive behavior of ZnO NS.
authors.affiliation: School of Advanced Materials Science and Engineering, ‡SKKU Advanced Institute of Nanotechnology (SAINT), Center for Human Interface Nanotechnology (HINT), and §IBS Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University (SKKU) , Suwon 440-746, Republic of Korea.
authors.forename: Manoj Kumar
authors.initials: MK
authors.lastname: Gupta
authors.forename: Ju-Hyuck
authors.initials: JH
authors.lastname: Lee
authors.forename: Keun Young
authors.initials: KY
authors.lastname: Lee
authors.forename: Sang-Woo
authors.initials: SW
authors.lastname: Kim