We are the first group to use a simple direct ultraviolet light (UV, λ=365 nm, I=76 mW cm(-2)) in a decomposition process to fabricate ZnO nanowires on a flexible substrate using a zinc acetylacetonate hydrate precursor in ambient air. ZnO nanocrystal (or nanowire) production only requires three to ten minutes. A field emission scanning electron microscopy (FESEM) image reveals a high aspect ratio of the ZnO nanowires, which are grown on a substrate with a diameter of ∼50-100 nm, and a length of up to several hundred microns. High resolution transmission electron microscopy (HRTEM) images reveal that the nanowires consist of many single crystalline ZnO nanoparticles that grow along the c axis, which suggests an oriented attachment process. A potential application for flexible UV photodetectors was investigated using a UV lamp (λ=365 nm, I=2.34 mW cm(-2)). A significant ratio of photocurrent to dark current--around 11,300%--was achieved.

In ambient air, zinc acetylacetonate hydrate precursor was directly decomposed to fabricate large-area ZnO nanowires on a substrate using ultraviolet-light- (λ = 350−380 nm, I = 76 mW cm−2) assisted thermal decomposition processes at 200 °C. The growing process required 5 min. High-resolution transmission electron microscopy images revealed that the ZnO nanowires consisted of fine single-crystal nanoparticles. The particle size was calculated to be ∼8−9 nm using the Debye−Scherrer equation. The photocatalytic activities of ZnOnonUV (without UV-light assistance) nanowires were found to be superior to those of ZnOUV (with UV-light assistance) nanowires and commercial TiO2 P25 nanoparticles. The oxygen defects (i.e., oxygen vacancies and interstitials) acted as key components for a photodegradation process in the ZnO nanowires. The oxygen defects are attributed to the presence of zinc hydroxide [Zn(OH)2] on the surface of the ZnO nanocrystallites. For the photoresponsive activities, no significant photocurrent-to-dark-current ratio was observed in ZnOnonUV nanowires using UV-light (λ = 365 nm, I = 2.33 mW cm−2), whereas the ratio of ZnOUV nanowires was high, reaching a maximum of 91. As-synthesized ZnOUV nanowires exhibited a relatively good crystallinity and superior photoresponsive properties when compared with ZnOnonUV nanowires based on the characterizations of the materials and sensor properties. Detailed mechanisms of the photoresponsive and photocatalytic properties were investigated.

The ultrafine ZnO nanoparticles/nanowires were successfully synthesized on a flexible and transparent substrate by an ultraviolet-light decomposition process. We demonstrate that water molecules can affect the morphology of ZnO nanostructures. An ultraviolet lamp (λ ~ 380 nm, 75 mW cm(-2)) can be used to irradiate Zn(AcAc)2 and Zn(AcAc)2·H2O precursors, which rapidly synthesize ZnO nanoparticles and nanowires, respectively. High-resolution transmission electron microscopy (HRTEM) images and a selected-area electron diffraction pattern revealed that the single-crystal nanoparticles were comprised of wurtzite structure ZnO. The nanowires consisted of ultrafine nanoparticles. On the basis of the Debye-Scherrer formula, the particle size of ZnO was calculated as ~6-9 nm. The more water molecules the precursor had, the more OH(-) and Zn[(OH)4](2-) it put out. Moreover, due to the Zn[(OH)4](2-) and Zn(OH)2 species formed on the surface of the ZnO nanocrystals, they facilitated the one-dimensional nanowires during the crystal growth process. On the basis of our investigations, oxygen vacancies, hydroxyl, and zinc hydroxide all acted as key components in the formation processes that determined photoresponsive properties.

Bismuth-doped ZnO nanowires were synthesized by a vapor transfer process at 600 degrees C. Raman spectra revealed that a slight blueshift occurred in ZnO:Bi (438 cm(-1)) nanowires in contrast to ZnO (436 cm(-1)) nanowires. The X-ray photoelectron spectrum showed that the ZnO: Bi nanowires contained the Bi dopant as Bi(0) and Bi(3+). The turn-on fields of the ZnO: Bi and ZnO nanowires were similar to 4.19 and 6.57 V/mu m, respectively. Because the ZnO:Bi nanowires exhibited a redshift of absorbance spectrum with a high ratio in the UV range, the photocatalytic activities of ZnO: Bi nanowires were considered superior to those of ZnO nanowires. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3387638] All rights reserved