Three Dimensional Spherically Evolved Nanostructures of ZnO Comprised of Nanowires and Nanorods for Optoelectronic Devices

摘要

Novel spherically evolved nanostructures of ZnO comprised of nanowires and nanorods in large quantity are synthesized from ZnO/Graphite powders in one step at similar to 900 degrees C +/- 50 degrees C and collected over a 4 inch x 1 inch long strip of Si/SiO2 substrate placed at 700 degrees C-500 degrees C temperature gradient zone for 3 hours. The deposited nanostructures look off-white thick layered material sticking hard to the substrate under the above condition. Scanning electron microscopy images show that all sample decorated densely with the nanowires and nanorods populated with the spherically evolved nanostructures. Energy Dispersive X-Ray spectra (EDX) spectra reveal that as-grown material has pure Zn and O composition with no carbon or other impurities in the sample. The XRD spectra of the sample show perfectly matched wurtzite crystal structure with c/a = 1.60 and Raman Spectra also show strong E-2 peak at 437 cm(-1) (Raman-active optical phonon mode) considered a signature of hexagonal phase of ZnO crystal. Photoluminescence (PL) spectra obtained at room temperature from the two ends of the sample (grown at 700 degrees C and 500 degrees C) show sharp near band edge peak at 381 nm in the UV regime and a broad wide peak in the green/blue regime mainly attributed to the intrinsic defects in the ZnO crystal structure. The growth of such novel nanostructures would be of immense interest in future to better understand the formation and evolution of three dimensional morphologies of materials specially of ZnO at the nano and micro scale as well as for useful application in luminescent devices and optoelectronics.