Synthesis, growth mechanism, photoluminescence and field emission properties of metal-semiconductor Zn-ZnO core-shell microcactuses

Metal-semiconductor Zn-ZnO core-shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH₃ as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65-75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor-liquid-solid (VLS) based growth mechanism was proposed for the formation of Zn-ZnO core-shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn-ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn-ZnO core-shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices.