Synthesis of novel ZnO hexagonal nanocones by direct thermal evaporation method.

Novel ZnO hexagonal nanocones have been synthesized on Si(100) substrate by directly evaporating zinc acetate dihydrate, at a low temperature of 400 degrees C, without using any carrier gas and catalyst. Clear formation of hexagonal nanocones was confirmed by high resolution scanning electron microscopy. Size of the hexagonal nanocones was found to be 600 nm. Structural analysis by X-ray diffraction pattern revealed that most of the nanocones were aligned along the c-axis (002). Chemical composition analysis by energy dispersive X-ray spectroscopy shows both zinc and oxygen are nearly equal in stoichiometry. Vapor-liquid-solid (VLS) mechanism was used to explain the growth of ZnO hexagonal nanocones. Diffused reflectance spectroscopy confirms the band gap of ZnO hexagonal nanocones as 3.34 eV. Photoluminescence of the ZnO hexagonal nanocones shows a near band-edge emission at 398 nm. No observable green-yellow emission, which corresponds to oxygen vacancies, was observed.

Effect of running water on the predatory efficiency of the larvivorous fish Gambusia affinis.

Effects of standing and running water on the predatory efficiency of the larvivorous fish Gambusia affinis was tested at 6 different current speed: 0.0, 0.8, 2.4, 4.5, 8.5 and 10.2 ml/sec. G. affinis predated 25 Anopheles stephansi or 21 Culex fatigans (IV instar) during the test period of 10 hours. The predatory efficiency of G. affinis decreased remarkably to about 60% and thereafter gradually to about 30% in aquaria containing running water at the speed of 2.4 and 10.2 ml/sec, respectively.