The effect of hydrothermal grown zinc oxide nanoparticles as seeds on the properties of nanoripples in zinc oxide thin films

Abstract

This work reports on a simple approach to improving the optoelectronic properties of Wurtzite ZnO nanoripples by means of incorporating hydrothermally synthesised ZnO nanoparticles under controlled synthesis temperature. Initially, ZnO nanoparticles were investigated and subsequently utilised as seeds to induce ripple growth in spin-coated ZnO thin films. TEM images illustrated the development of nanospheres at 140°C. The yield of ZnO NPs at 180°C increased and consisted of a combination of nanorods and nanospheres. Morphologically, seedless ZnO nanoripples showed rugged ends of the nanoripple structures. The SEM images illustrated that the layers uniformly formed on the substrates, and seeding the ZnO nanoripples caused the nanoripples to elongate. The thickness of the nanoripples thin films showed a decrease with the incorporation of hydrothermally synthesised ZnO seeds from 134 nm for unseeded ZnO nanoripples to 96 nm at 180°C. The incorporation of ZnO NPs seeding treatment increased the transmission of ZnO nanoripples from 82% to 92%, leading to untreated ZnO nanoripples exhibiting a direct band gap of 3.19 eV that increased after seeding to 3.36 eV. The change in the band gap to a higher value(s) and increased transparency confirms the progressive improvement of the thin films due to incorporating ZnO seeding for optoelectronic and photovoltaic applications.