Self-assembly of ZnO Particles and Subsequent Hydrothermal Crystal Growth to Produce ZnO Urchin-like Structure and Its Application to Gas Sensor

Abstract

Zinc oxide (ZnO) has semiconductor properties and is applicable to gas sensors. The principle of gas sensing is the exchange of electrons between ZnO structure and gas molecules. Thus, effective passageway of electrons in the structure is required in the structure in addition to the increase in surface area. Gathered urchin-like structure will makes many contacts points utilizing their needles. This paper proposes a two-step fabrication process. In the first step, ZnO particles (φ100 nm) were dispersed in aqueous suspension and a substrate was drawn up from it to produce self-assembly structure as nuclei. In the second step, ZnO needles were synthesized or grown on each ZnO particle of the assembly by hydrothermal method in which source materials were filled in an autoclave together with water. The morphology changed drastically depending on the conditions. Thus, systematic experiments were carried out and the appropriate conditions were made clear. Finally, gas sensing property of the structure was examined and higher sensitivity of the urchin-like structures compared to ZnO assembled particles was confirmed.