Effect of substrate position on the formation of ZnO nanostructures synthesized by thermal evaporation of ZnO-CNTs mixture

In this work, the effect of substrate position on the formation of ZnO nanostructures synthesized by thermal evaporation of zinc oxide (ZnO) and carbon nanotubes (CNTs) on silicon substrate is investigated. The multi-wall CNT powder made by chemical vapor deposition was mixed with ZnO powder with a molar ratio of 1:1. The source material was put into the middle of chamber while Si substrates were placed at various locations from the center to the end of the tube furnace. The evaporation took place at 950°C and 2 Torr under argon gas flow rate of 500 seem and the system was vented at this temperature at the end of process. Structural characterization by scanning electron microscopy showed that ZnO tetrapod-like structures are formed in samples at different positions but they have different densities, sizes and morphologies. The density and size of ZnO nanotetrapods are found to decrease as the distance from source powder increases and substrate temperature decreases. In addition, considerable carbon content and high crystallinity of wurtzite ZnO nanostructure were observed by energy dispersive x-ray spectrometry and x-ray diffraction. Moreover, ZnO nanostructures have a wide blue-green luminescent band between 380 and 600 nm.