Preparation Of Aligned Carbon Nanotube Materials And Their Optical Response In Terahertz Range

CNTs have natural quasi-one-dimensional structure and excellent physical properties,and are expected to be used in terahertz waveband.However,current research on the generation of carbon nanotubes in terahertz has focused on the theoretical stage,with minimal experimental research,and there is no conclusion as to whether the response of carbon nanotubes in terahertz waveband is due to differences in structural parameters(such as diameter,length,etc.)or to interactions between carbon tubes.There is also a lack of systematic research on the optical response mechanism of carbon nanotubes,especially multiwalled carbon nanotubes in terahertz band.Therefore,in order to solve the problems encountered in terahertz research,we have prepared array multi-walled carbon nanotubes and polymer coated carbon nanotube composites with different parameters.The details are as follows:Firstly,the vertically aligned carbon nanotubes were prepared by chemical vapor deposition(CVD)under different parameters.The parameters change during growth respectively,growth time,growth temperature,catalyst concentration and gas ratio(Ar:H2).Through characterization,we found that when the growth time,growth temperature,catalyst solution concentration and gas ratio were 6min,750 ?,0.06g/ml and Ar:H2=8:2 respectively,the alignment and array properties of CNTs were the best.Secondly,we use the uniform and good array of carbon nanotubes in the terahertz band to study the photoelectric response in this band.First,we measured the terahertz generation of carbon nanotubes.By changing the optical parameters(sample angle,pump power and pump polarization angle),we got different terahertz pulse waveforms.It is found that there exists a certain rule in terahertz wave.We have used the theoretical and experimental interpretation of light traction effect on carbon nanotubes in terahertz,and the optical rectification effect was excluded.In this effect,the carrier plays a major role,and the carrier can not only along the axial transmission,but also the transmission between the carbon nanotubes.Secondly,we use the carbon nanotube in the terahertz time domain spectroscopy test,and get the time domain waveform.The frequency domain spectrum is obtained by Fourier transformation.Through the analysis,we have obtained the refractive index,absorption coefficient,conductivity,dielectric constant and other optical parameters of the carbon nanotube.Finally,in order to better explain and understand the photoelectric response of carbon nanotubes in terahertz band,we use epoxy polymer to coat it and get composite material,and composite material is also applied to produce terahertz and time-domain spectroscopy test.During the terahertz generation test,we found that when the pump polarization angle was changed,the result obtained was completely opposite to that of pure carbon nanotubes.This phenomenon is also explained by the effect of photon drag effect.In this process,the carrier also plays a leading role.However,when the carbon nanotubes are coated to form composite materials,the carrier transport between the tubes is isolated,leaving only the carrier transmission along the axial direction of the carbon tube.Therefore,when the polarization angle of the pump is changed,there is a contrary phenomenon to the pure carbon tube.Next we use composite materials to time-domain spectroscopy test,through the analysis we also obtained the optical parameters of composite materials.At the same time,we compared the waveform of pure carbon nanotubes and composite materials,and through the Drude-Lorentz theoretical model fittingthe experimental results.We found that the fitting results are in good agreement with the experimental results.This research can theoretically deepen the understanding of the terahertz radiation mechanism of the aligned CNTs materials,and provide technical support for the new terahertz radiation source device from the application,which has certain practical application value.