| Zinc oxide(ZnO)has attracted considerable attention as one of the most promising field emission materials,due to its wide direct band gap,large exciton binding energy,low electron affinity,ideal thermal conductivity and carrier mobility,high mechanical and chemical stabilities,as well as significant band bending under high electric field strength.The morphology of tetrapod-like zinc oxide(T-ZnO)is conducive to field electron emission,and the electron concentration could be improved by doping with metal,which is expected to further improve its field emission properties.This thesis focuses on the growth and field emission properties of Sn-doped T-ZnO nanostructures and tetrapod like Al2O3/ZnO composite nanostructures.The results are as follows:Firstly,T-ZnO nanostructures were successfully synthesized via thermal evaporation,and the effects of growth temperature on the morphology and field emission properties of T-ZnO were studied.It was found that when the growth temperature is 950?,the sample with better morphology consistency and the best field emission properties was obtained,which had turn-on field of 2.45 V·?m-1 and field enhancement factor of 3977.Appropriate Sn doping can further improve the whisker aspect ratio,thus to improve their field emission properties.The aspect ratio of the whiskers increases first and then decreases with the increase of doping concentration.On the contrary,the turn-on field decreases first and then increases with the Sn doping concentration.When the Sn doping concentration is larger than 5 at.%,un-tetrapod-shaped impurities such as nanosheet appears,thus the performance of field emission further declines.The samples had the best comprehensive performance,with the lowest turn-on field of 1.95V·?m-1 and the field enhancement factor of 9556,when the Sn doping concentration was 1 at.%.Combined with the analysis result of SEM,XRD,PL,XPS,the improvements of the field emission properties of Sn-doped T-ZnO nanostructures can be attributed to the increases of the aspect ratio and conductivity.Effects of growth times on the whisker aspect ratio and field emission properties of tetrapod shaped Sn doped ZnO nanostructured are further studied.The experimental results showed that there is a significant impact of the growth time on the morphology of the Sn-doped T-ZnO nanostructures,especially the aspect ratio of the whiskers.The aspect ratio of the whiskers increases with the growth time increases when grown time is shorter(<90 s),and had a high aspect ratio of 16.5 and the best field emission properties which meant that the turn-on field was 1.82 V·?m-1 and the field enhancement factor was 4664,when the growth time was 90 s.The field emission properties of sample are decrease further over time for the emergence of different series of T-ZnO nanostructures and other impurities such as nano-sheet.To achieve precise control over the amount of metal doping,tetrapod Al2O3/ZnO nano composite structure were synthesized by growing Al2O3 film on the surface of T-ZnO via atomic layer deposition.For the realization of Al doping,we adopt thermal annealing process to effect the A1 element diffusion.The study found that the field emission properties of the samples prepared by atomic layer deposition with 3 cycles were the best whose turn-on field was 1.59 V·?m-1 and field enhancement factor reached 5618.Also,the stability of electron emission current have been greatly improved,showing good field emission properties.After the thermal annealing process,the turn-on field of the sample decreased from 1.59 V·?m-1 t0 1.32 V·?m-1 and the field enhancement factor increased from 5618 to 8130. |
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