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.

Recent advances in large-scale assembly of semiconducting inorganic nanowires and nanofibers for electronics, sensors and photovoltaics

“…134 Besides solid nanofibers, hollow semiconductor fibers with high orientation can also be fabricated by combination of this gapping method with coaxial electrospinning 138 or electrospun polymer nanofiber templates method. [139][140][141] For example, Li and Xia 138 prepared hollow TiO 2 nanofibers by electrospinning two immiscible liquids (e.g. heavy mineral oil and ethanol solution containing poly(vinyl pyrrolidone) and Ti(OiPr) 4 ) through a coaxial, two-capillary spinneret, followed by calcining to selectively remove the cores (Fig.…”

Hierarchically Structured Electrospun Fibers

“…Choi et al generated hollow ZnO fiber sensors by coating a sacrificial electrospun fiber template with ZnO followed by calcination. The hollow ZnO fiber membrane showed enhanced sensitivity for NO 2 compared to a ZnO thin film [104]. Gao et al prepared polyaniline tubes using electrospun PVA as a template.…”

Morphology‐Controlled Aluminum‐Doped Zinc Oxide Nanofibers for Highly Sensitive NO2 Sensors with Full Recovery at Room Temperature

“…The surface‐adsorbed oxygen molecules (from air) pull electrons, leading to the formation of a potential barrier that is sensitive to the electron carrier concentration in the SMO layer. When an SMO (n‐type) is exposed to the oxidizing gas, NO 2 , it extracts electrons from the surface resulting in further decrease in the current and increase in the potential barrier height30 (Supporting Information). The same mechanism may be applied to the AZO nanofiber.…”