title: Hollow ZnO nanofibers fabricated using electrospun polymer templates and their electronic transport properties.
abstract: Thin (0.5 to 1 microm) layers of nonaligned or quasi-aligned hollow ZnO fibers were prepared by sputtering ZnO onto sacrificial templates comprising polyvinyl-acetate (PVAc) fibers deposited by electrospinning on silicon or alumina substrates. Subsequently, the ZnO/PVAc composite fibers were calcined to remove the organic components and crystallize the ZnO overlayer, resulting in hollow fibers comprising nanocrystalline ZnO shells with an average grain size of 23 nm. The inner diameter of the hollow fibers ranged between 100 and 400 nm and their wall thickness varied from 100 to 40 nm from top to bottom. The electronic transport and gas sensing properties were examined using DC conductivity and AC impedance spectroscopy measurements under exposure to residual concentrations (2-10 ppm) of NO(2) in air at elevated temperatures (200-400 degrees C). The inner and outer surface regions of the hollow ZnO fibers were depleted of mobile charge carriers, presumably due to electron localization at O(-) adions, constricting the current to flow through their less resistive cores. The overall impedance comprised interfacial and bulk contributions. Both contributions increased upon exposure to electronegative gases such as NO(2) but the bulk contribution was more sensitive than the interfacial one. The hollow ZnO fibers were much more sensitive compared to reference ZnO thin film specimens, displaying even larger sensitivity enhancement than the 2-fold increase in their surface to volume ratio. The quasi-aligned fibers were more sensitive than their nonaligned counterparts.
authors.affiliation: Center for Energy Materials Research, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul, Republic of Korea.
authors.forename: Seung-Hoon
authors.initials: SH
authors.lastname: Choi
authors.forename: Guy
authors.initials: G
authors.lastname: Ankonina
authors.forename: Doo-Young
authors.initials: DY
authors.lastname: Youn
authors.forename: Seong-Geun
authors.initials: SG
authors.lastname: Oh
authors.forename: Jae-Min
authors.initials: JM
authors.lastname: Hong
authors.forename: Avner
authors.initials: A
authors.lastname: Rothschild
authors.forename: Il-Doo
authors.initials: ID
authors.lastname: Kim
mesh_terms: D000327:Adsorption; D004553:Electric Conductivity; D017097:Electric Impedance; D004581:Electronics; D049329:Nanostructures / Q000737:chemistry*; D009585:Nitrogen Dioxide / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry*; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D011145:Polyvinyls; C013215:polyvinyl acetate; D009585:Nitrogen Dioxide; D015034:Zinc Oxide