Zinc oxide (ZnO), a representative of II–VI semiconductor compounds, is a very versatile and important material. ZnO has a unique position among semiconducting oxides due to its piezoelectric and transparent conducting properties. It has a high electrical conductivity and optical transmittance in the visible region. Zinc oxide (ZnO) has extensive commercial use during the past 100 years. It has useful optical, chemical and electrical properties, and is nontoxic, inexpensive and chemically stable. ZnO, a semiconductor with a direct wide band gap of 3.37 eV at room temperature and large exciton binding energy of 60 meV, is one of the most promising materials for the fabrication of optoelectronic devices operating in the blue and ultraviolet (UV) regions and gas sensing applications (Djurisic et al., 2010 and Michelle, 2012). It has a wide range of technological applications including transparent conducting electrodes of solar cells, flat panel displays, surface acoustic devices, chemical and biological sensors and UV lasers (Zhong Lin Wang, 2004; http://www.chemistry.ohio-state.edu/~woodward/ch754/struct/ZnO.htm; Zhiyong Fan and Jia G. Lu, 2005; Baruah and J Dutta, 2009). Controlled synthesis of semiconductor nanostructures in terms of size and shape has strong motivation to researchers because their properties can be controlled by shape and size. Novel applications can be investigated and are dependent of their structural properties. As the morphology of nano-materials is one of the key factors that affect their properties. ZnO nano-structures with novel morphologies are therefore needed urgently. To date, ZnO with different nanostructures, such as nanotetrapods, combs-like, nanoneedles, nano-flowers, nanorods, nanowires, nanobelts, nanotubes, nanorings and nanosheets (Baruah and J Dutta, 2009; Ahsanulhaq Qurashi, 2013; Xiaobin Xu, 2012; Juan Xie et al., 2009; Fanfei Bai et al., 2005; Xudong Wang, 2007, Zhong Lin Wang, 2014 and Wang et al., 2011), have been successfully synthesized. During the past few years, attention has been focused on the research field of one-dimensional (1D) nanostructure materials, such as nanowires and nanorods, because of their fundamental importance and the wide range of potential applications for nanodevices (Djurisic, 2010). One-dimensional (1D) ZnO have been prepared by various methods such as thermal evaporation, cyclic feeding chemical vapor deposition, chemical vapor deposition (CVD), metal–organic CVD, vapor–liquid–solid (VLS), metal organic chemical vapor deposition (MOCVD), arc discharge and laser ablation (Chen et al., 2004; Sekar et al., 2005; Zhang, 2005 and Subramanyam, 2000). However, these methods involve special equipment, complex process controlling or high temperature as unfavorable for industrialization. As a result; it is conceived that the preparation of 1D ZnO nano/micro structures via wet chemical routes such as template-based method, hydrothermal process, solvothermal process, microwave-heating route, ultrasonic technique (Tian et al., 2011; Law et al., 2005; Saito and Haneda, 2011 and Ghule, 2011) can produce such structures, with better crystal quality preferably at lower growth temperature. It works out to be an easier and economical process as well. For the present research, ZnO nanocrystals were synthesized using microwave and ultrasonic radiations. A number of reaction conditions for example solvents, surfactants, precursors, acidity and basicity were used to synthesize ZnO nanocrystal with difference morphologies. The effects of the reaction conditions on the final products were systematically investigated.
Prof. Dr. Bilal BİLGİN