Effect of Sol Strength on Growth, Faceting and Orientation of Sol-Gel Derived ZnO Nanostructures

ZnO thin films are used for a number of MEMS-based sensors because of the piezoelectric and semiconducting properties. In certain class of devices, especially those using surface acoustic wave (SAW) technology on a layered substrate (such as ZnO on Si), it is a requirement to grow several micron thick ZnO layer which must be highly c axis oriented. In this attempt, we have deposited ZnO films by sol-gel spin process and using three different concentrations of 10%, 12.5%, and 25% of sol using zinc acetate as the precursor material and characterized for their thickness and other associated characteristics. The XRD pattern showed diffraction peaks of the hexagonal ZnO phase. The intensity of the 002 peak was much low for low-strength sols indicating substantial preferred orientation of the crystallites perpendicular to the sample surface. The crystallite size was estimated to be about 45 nm from the 100 diffraction peak. For the sample with 25% strength of the sol, the XRD pattern showed diffraction peaks of the hexagonal ZnO phase. The crystallite size was estimated as about 60 nm from the 100 peak and about 145 nm from the 002 peak. The TEM results showed fine nanoparticles with hexagonal ZnO crystal structure and morphology dependence upon the sol strength. Faceted morphology of hexagonal ZnO nanostructures has been obtained. The results would find application in nanoelectronic piezoelectric sensors.