Growth Mechanism, Photoluminescence, and Field-Emission Properties of ZnO Nanoneedle Arrays

Abstract

ZnO nanoneedle arrays have been grown on a large scale with a chemical vapor deposition method at 680 degrees C. Zn powder and O(2) gas are employed as source materials, and catalyst-free Si plates are used as substrates. Energy-dispersive X-ray and X-ray diffraction analyses show that the nanoneedles are almost pure ZnO and preferentially aligned in the c-axis direction of the wurtzite structure. The growth mechanism of ZnO nanoneedle arrays is discussed with the thermodynamic theory and concluded to be the result of the co-effect of the surface tension and diffusion. Photoluminescence spectrum of the as-grown products shows a strong emission band centering at about 484 nm, which originates from oxygen vacancies. Field-emission examination exhibits that the ZnO nanoneedle arrays have a turn-on voltage at about 5.3 V/microm.

Optical properties of ZnO nanoparticles synthesized by varying the sodium hydroxide to zinc acetate molar ratios using a Sol-Gel process

“…The green emission is also known to be a deep level emission which is caused by the impurities and structural defects in the crystal such as oxygen vacancies, zinc interstitials, etc. Vanheusden et al [22] proposed the mechanism of green emission and reported that green emission is due to the recombination of the electrons in singly occupied oxygen vacancies in ZnO and that the emission results due to the recombination of a photo-generated hole with an electron occupying the oxygen vacancies. It is also reported that particles surface depletion plays a major role in the density of singly ionized oxygen vacancies and the charge state of this defect and thus is controlling the green emission intensity [23,24].…”

“…Regarding the appearance of blue emission in ZnO nanomaterials, Dai et al reported that blue emission at 460 nm might be due to intrinsic defects such as oxygen and zinc interstitials [22]. However, the exact mechanism behind this emission is still unclear.…”

Three-dimensional six-fold symmetry ZnO sub-microstructures

“…The reaction given in Eq. (3), i.e., the growth and the dissolving of the ZnO, is reversible [25]. With the KOH additive, the OH À concentration was increased, in which the chemical equilibrium tends to proceed towards the right.…”

Optical Properties of ZnO Nanoparticles Synthesised from a Polysaccharide and ZnCl2

“…It has also attracted attention as a promising phosphor for field emission displays (FEDs) [2] compared with the conventional sulfide phosphors. The biggest users of ZnO are manufacturers of rubber; the content of ZnO in vulcanized rubber can be reduced to 10 times if nanosized ZnO is used instead of the conventional micro ZnO [3].…”