| The flame pyrolysis method used to synthesize carbon nanotubes was applied in this work.In order to improve the quality of synthesized carbon nanotubes,it is important to change the corresponding natures of the catalyst.Two catalyst preparation methods,namely,the sol-gel method and the impregnation method,were compared in this experiment.The composition,content and morphology of the catalyst were analyzed systematically by energy dispersive spectrometer(EDS),x-ray diffraction(XRD),temperature program reduction(TPR).The generation of carbon nanotubes was systematically analysed through scanning electron microscope(SEM),molecule dynamics(MD),raman spectroscopy and transmission electron microscope(TEM).The results show that the catalysts prepared by the impregnation method are stickier,dispersed and easier to attach to the probe or substrate,which is beneficial for the large-scale production of carbon tubes.The specific surface area of alumina is larger and the iron and molybdenum oxide are more evenly dispersed on the surface of alumina,so catalyst particle size is smaller.The carbon nanotubes have less interlaced bending and less impurity in SEM diagram,the ratio of ID/IG is 29.7%lower than that of the sol-gel method in the Raman spectra,the TEM statistics show that the average diameter of the carbon tubes decreases by 23.3%,these indicate that the synthesized carbon nanotubes have higher graphitization degree,less impurity and smaller diameter.Therefore,the impregnation method can improve the quality of carbon nanotubes in the case of a similar degree of difficulty in the preparation of the catalyst.The wide application of carbon nanotubes depends not only on the improvement of their quality,but also on their properties,so the first principles study on the effect of co-doping on various optical spectra of a zigzag single-walled carbon nanotube(SWCNT)is introduced in this paper.Optical spectra of a pristine SWCNT,SWCNT co-doped with Aluminum(Al)&Sulphur(S),SWCNT co-doped with Ferrum(Fe)&Sulphur(S),SWCNT co-doped with Al,S and Nitrogen(N)and another one co-doped with Fe,S and N have been calculated using density functional theory(DFT).Polarized and unpolarized light as well as light through polycrystalline media have been considered,the dependence of various spectra on the status of incident light provides a clear evidence for the anisotropicity of the optical properties.Analysis of the simulated spectra of the pristine and co-doped SWCNTs involves calculation and comparison of different optical properties like dielectric function,refractive index,reflectivity,absorption,conductivity and loss function.For dielectric function,refractive index and reflectivity,the degree of anisotropy is the highest for Al-S co-doped SWCNT while lowest for Fe-S co-doped SWCNT.In addition,when nitrogen is added to two kinds of co-doping SWNTs,the optical properties are almost the same,this phenomenon shows that the nitrogen element can weaken the influence of other co-doped elements.For absorption,conductivity and loss function,a reduction is observed as a result of co-doping irrespective of the status of the incident light and the variety of doping element.It is also observed that the presence of polycrystalline media has an influence on the optical properties.It can be concluded that co-doping can be used as a new,effective tool for controling optical properties of modified carbon nanotubes as the requirements while designing an optical device,this is of great value for the effective design of sensitive optical devices based on SWCNT. |
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