Here I am trying to synthesize ZnO NRs on different metal sheets. Initially, the ZnO seed layers were electrochemically deposited using zinc acetate and hexamethyletetramine mixed solution. Deionized water is used as solvent. After mild annealing, the samples were used for ZnO NRs growth using the zinc nitrate hexahydrate and hexamethyletetramine equimolar solution at the temperature of 70 oC. After this stage I have noticed black spots (there is no growth) along with ZnO NRs. Now my doubt is what could be the reason for the formation of black spots on the substrates and how to avoid them?
Fast of all black spots are copper oxide and may be degasation procedure before experiment will help you
Is it essential to keep the deposition technique(electrochemically)?
You used deionized water as solvent.But the surface tension of water is very high and may be you can not fully cover the surface of your substrate(seed layer).You should try to reduce the surface tension of water by using another solvent.Prepare new seed layer:2-methoxyehanol+zinc acetate+monoethanoamine.
Perhaps it might help to solve the problem.
Its a big problem of Sample Preparation Procedures and Measurement Conditions.Thermal annealing can improve the crystal and optical
qualities of the grown ZnO NRs.The dark spots show the void distributions under different annealing conditions. please referthis article " Void Structures in Regularly Patterned ZnO Nanorods Grown with the Hydrothermal Method" by Yu-Feng Yao et al., 2013.
You may increase the annealing temperature (150-200 C), annealing time is also important. and also you can pay attention to pHfor the formation of ZnO.
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