Effect of catalyst layer on morphology and optical properties of zinc-oxide nanostructures fabricated by carbothermal evaporation method

Zinc-oxide nanostructures were synthesised by carbothermal evaporation of ZnO+C at elevated temperatures. Substrates were silicon wafers, and different materials such as SiO₂, Al₂O₃, Au and silica-gel were used as the catalyst layer. Characterisation of morphology by scanning electron microscopy showed that the catalyst layer has a major role in controlling of geometrical shape and dimensions of the resultant nanostructures. The long and narrow nanowires with a regular cross-section were formed on the substrate coated by Au particles. On the substrate coated by silica-gel, the authors achieved the capillary microtubes with the hexagonal cross-section, nanometre-thick walls and also radial sheets inside them. Such nanostructures are believed to be reported for the first time. The electro-optical specifications of the samples were investigated by measurement of their optical absorption spectra using ultraviolet/visible (UV/VIS) spectrophotometry. Determination of the optical band gap from Tauc´s plot showed that, in contrary to different shapes, the samples have identical band gap energy. This phenomenon revealed that the optical behaviour of the nanostructures grown by the proposed method does not depend to their morphology.