Growth And Field Emission Properties Of ZnO Composite Nanostructures

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.Many kinds of ZnO nanostructures have been found and their combinations can break the limitation of simple structure and realize the outstanding field emitters.Therefore,it is of importance to study the growth and field emission properties of ZnO composite nanostructures.Firstly,tetrapod-shaped ZnO nanostructures were successfully synthesized via chemical vapor deposition method(CVD).The effects of ZnO powder pretreatment by H2O2 on the growth and field emission properties of tetrapod-shaped ZnO were studied.It was found that when the H2O2 volume concentration was 0.5%,the sample with moderation whisker and the best field emission properties was obtained,which had tun-on field of 4.60 V·?gm-1 and field enhancement factor of 3243.In order to get tetrapod-shaped/nanowires ZnO composite nanostructure,ZnO nanowires were subsequently grown on the surface of tetrapod-shaped ZnO by CVD method.The effects of growth time and O2 flux on the morphology and field emission properties of the composite were investigated,respectively.The results indicated that the ZnO composite nanostructure had the best filed emission properties with the turn-on field of 3.37 V·?m-1 and field enhancement factor of 3790 when the growth time was 20 min and the flow of O2 was 20 sccm.Additionally,Sn-doped ZnO composite with tetrapod-shaped/nanowires ZnO structures were also prepared by the two-step CVD method.The effects of Sn doping amount on the morphology and field emission properties of the prepared ZnO composites were investigated.The results showed that the samples with Zn:Sn weight ratio of 1:0.5 presented the best filed emission properties with turn-on field of 2.61 V·?m-1 and field enhancement factor of 6940.Compared to the pure ZnO composites,Sn dopant could improve the field emission properties of ZnO composite nanostructures.Finally,ZnO ridge and nanorods were prepared by sol-gel method and hydrothermal method,respectively.Then the composite nanostructures of ridge/nanowires ZnO and nanorods/nanowires ZnO were fabricated through growing ZnO nanowires on ZnO ridge and nanorod by CVD method,too.Field emission measurements were carried out for the two ZnO composite nanostructures,respectively.The turn-on field of nanorods/nanowires ZnO was 3.63 V·?m-1 which was lower than ZnO nanorods,and its field enhancement factors was 3814,which was higher than ZnO nanorods.Moreover,the turn-on field of ridge/nanowires ZnO was 5.57 V·?m-1,which was lower than ZnO ridge,and its field enhancement factors was 1749,which was higher than ZnO ridge.It could be found that ZnO composite nanostructures would have better field emission properties than that of the single ZnO structure.In conclusion,various ZnO composite nanostructures were fabricated and their field emission properties with different technological parameters were also studied using scientific methods.In addition,ZnO composite nanostructures with admirable field emission properties had been obtained,and the results would provide references for the application of ZnO nanostructures in field emission devices.