Synthesis of ZnO eggshell-like hollow spheres via thermal evaporation at low temperature

Hollow zinc oxide microspheres have been successfully synthesized on silicon substrate via simple thermal evaporation of pure zinc powder without any catalyst or template material at a relatively low temperature of 550 deg. C. The morphologies, chemical composition and crystal structure are characterized using x-ray powder diffraction, transmission electron microscopy and scanning electron microscopy. A smooth surface and rough ones with many nanopores are observed. The difference in the structures of the shells is discussed and a possible growth mechanism is proposed in detail. The room-temperature photoluminescence spectrum reveals a peak at 380 nm corresponding to free exciton emission and a strong green emission at ∼ 525 nm associated with defect-related emission