Morphology Control of Zinc Oxide Nanocrystals via Hybrid Laser/Hydrothermal Synthesis

Abstract

We introduce a hybrid growth method for the rapid synthesis of ZnO nanocrystals with controllable morphologies through incorporating laser heating along with the traditional hydrothermal synthesis. The crystals are formed using a 248 nm KrF excimer laser irradiation of hydrothermal mixtures. Characterization of samples carried out using transmission electron microscopy, absorption spectroscopy, and photoluminescence spectroscopy indicate a critical fluence at which the reaction kinetics can be controlled to synthesize nanoparticles with a narrow size distribution while fluences above or below this value leads to nanocrystals with a range of morphologies and a broad size distribution.. A growth model is presented in order to explain the observed trend with varying laser fluence. At low fluence, Ostwald ripening is thought to control the growth process, while at the critical fluence a competing photothermal breakdown effect is thought to explain the size controlled formation of nanoparticles. At higher fluences, Ostwald ripening is thought to proceed at a rate higher than the photothermal breakdown leading to the formation of bi-, tri-, or tetrapod-like structures. The possibility of the photothermal breakdown process at the critical fluence is also supported through computational results.