Morphology engineering of ZnO nanostructures

Nanosized ZnO structures were grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD) in the temperature range 200–500 °C at variable precursor pressure. Temperature induced evolution of the ZnO microstructure was observed, resulting in regular transformation of the material from conventional polycrystalline layers to hierarchically arranged sheaves of ZnO nanowires. The structures obtained were uniformly planarly located over the substrate and possessed as low nanowires diameter as 30–45 nm at the tips. The observed growth evolution is explained in terms of ZnO crystal planes free energy difference and growth kinetics. For comparison, the convenient growth at constant precursor pressure on Si and SiC substrates has been performed, resulting in island-type grown ZnO nanostructures. The demonstrated nanosized ZnO structures may have unique possible areas of application, which are listed here.     

Comparative PL study of individual ZnO nanorods,grown by APMOCVD and CBD techniques

The photoluminescence properties of individual ZnO nanorods, grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCV) and chemical bath deposition (CBD) are investigated by means of temperature dependent micro-PL. It was found that the low temperature PL spectra are driven by neutral donor bound exciton emission D⁰X, peaked at 3.359 and 3.363 eV for APMOCVD and CBD ZnO nanorods, respectively. The temperature increase causes a red energy shift of the peaks and enhancement of the free excitonic emission (FX). The FX was found to dominate after 150 K for both samples. It was observed that while APMOCVD ZnO nanorods possess a constant low signal of visible deep level emission with temperature, the ZnO nanorods grown by CBD revealed the thermal activation of deep level emission (DLE) after 130 K. The resulting room temperature DLE was a wide band located at 420–550 nm. The PL properties of individual ZnO nanorods can be of importance for their forthcoming application in future optoelectronics and photonics.