Research On Near Field Optical Properties Of Carbon Nanotubes

A single-walled carbon nanotube(CNT)can be simply understood as a hollow cylinder formed by a single layer of graphene curled at a certain angle.Because of their unique nano-scale structure,they have been favored by scientists since they were discovered in the 1990 s.There has been a great deal of research and ongoing work on the use of carbon nanotubes(CNTs)in fundamental science and technology devices.Carbon nanotubes are the preferred platform for the study of electron-electron interactions in solid state systems.The unique electrical,optical and thermal properties of single-walled CNTs enable them to be used in a variety of applications,such as nanoelectronics,energy storage and nanomedicine.Digital circuits based on carbon nanotube field effect transistors could be the next generation of electronic systems beyond silicon.Despite extensive research on CNTs,their emerging properties have never ceased to emerge,and there are always some surprising potential applications that attract researchers.In the last decade,with the development of material synthesis and processing technology,high quality,ultra-long single-walled carbon nanotubes have been successfully prepared.And characterization,detection methods technology also rapid development,has been achieved on the electrical and optical properties of single nanotube detection.A spin-coating machine was used to spin the ultra-pure CNTs solution onto the desired substrate,and then the surface plasmon polaritons of the CNTs were investigated by using a scattering near-field optical microscope and a Raman Spectrometer.The thesis consists of three parts: 1.Regulation of the properties of plasmons in carbon nanotube is studied.First,we use the commercial software COMSOL based on the finite element method to simulate the nanotubes,and calculate the effects of the diameter,dielectric environment and excitation frequency on the properties of the plasmon.Then,the scattering scanning near-field optical microscope(s-SNOM)is used to detect and test the same nanotube by changing the excitation frequency.The real-space imaging of nanotube plasmons is realized,and the function of plasmon wavelength with respect to excitation frequency is obtained.The results show that the wavelength of the surface plasmon polaritons increases with the increase of the diameter of the nanotubes,which is consist with the numerical simulation results.Finally,we detected the same diameter nanotubes on silicon dioxide and boron nitride substrates respectively,and found that the dispersion behavior of plasmons could be controlled by changing the dielectric environment.2.The coupling effect of plasmons in double nanotube system is studied.The near field optical fourier transform of plasmons in double nanotubes shows that there are two plasmonic hybrid modes that can be excited,namely symmetric and anti-symmetric modes.Based on the finite element method,the charge distribution,dispersion relation and coupling length of the two modes are studied.It is also predicted that the coupling can be controlled by changing the distance between the two nanotubes and the excitation frequency.The excited plasmons in the double nanotubes exhibit low energy loss,strong spatial confinement and extremely small coupling length.3.The chiral plasmon in carbon nanotubes is studied.In the near-field optical detection of nanotubes,it is found that the chiral plasmons can be excited.When the angle between the excitation polarization and the nanotubes axis is changed,the rotation direction of the helical plasmons also changes.Then the occurrence and formation mechanism of this phenomenon are investigated by numerical simulation.It is also found that the diameter of the nanotubes can modulate the plasmonic mode.Finally,the influencing factors of the plasmonic pitch are studied.In summary,we have conducted a systematic and in-depth study on the properties of plasmons in carbon nanotube,and revealed their formation mechanism.It is believed that our research results can bring new inspiration to the application of plasmons in carbon nanotubes.