Growth morphology and optical properties of ZnO nanostructures on different substrates

Growth of ZnO nano and microstructures were carried out by low temperature hydrothermal method on glass and silicon substrates without seed layer. Crystallographic orientation and morphology of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The transmittance measurements were done by Fourier transformed infrared (FTIR) spectroscopy and a Raman spectrometer was also deployed to understand the vibrational properties of ZnO nanocrystals. XRD and Raman studies showed the formation of hexagonal wurtzite phase of ZnO on both the substrates. Cactus and needle like nanostructures forming rosette superstructure were observed for ZnO on glass substrate. On Si(100), nanorods, tetrapods and multipodes were found with smaller crystallite size. More preferential growth and crystalline nature of ZnO on silicon substrate is discussed on the basis of lattice compatibility between ZnO and Si. The role of interface SiO2 layer, the effective growth mechanism and properties of these nanostructures are also discussed.