Properties Of DMSO-doped-PEDOT:PSS Films And Their Applications In The Terahertz Range

Terahertz(THz)radiation is situated between the microwave and infrared regions of the electromagnetic spectrum,in the intersection of electronics and photonics.The special frequency position makes the THz system both the advantages of the electronic system and the optical system.THz wave has a strong application prospect in biomedical imaging,material characterization,high speed communication and homeland security.In recent years,there has been a dramatic increase in demand for THz-band optoelectronic devices,which can be seen from the development of THz optical elements.However,compared to laser technology,many of the key devices required for THz technology are limited,and the techniques for manipulating THz waves are still lagging behind.Further research in THz filtering,phase control and modulation has yet to be further improved.The lack of fast response,ease of production and integration modulation devices and high-performance functional materials is one of the important reasons for the rapid development of THz technology.Many of the THz devices and functional materials reported are currently in the experimental stage,they usually have shortcomings such as complex production,poor stability and narrow bandwidth.Therefore,the THz band functional materials and modulation devices are studied in this thesis.Firstly,the THz multi-functional materials DMSO-doped-PEDOT:PSS films were prepared,and their physical properties were characterized.The method of improving the conductivity of PEDOT: PSS was analyzed.The conductivity of PEDOT: PSS films was improved by DMSO doping method.The reason why DMSO doping improves the conductivity of the film was explained.A series of PEDOT: PSS films with different concentrations of DMSO were prepared by spin coating method.The surface morphology of the films was characterized by atomic force microscopy(AFM).The conductivity of the films was characterized by four-probe method.The transmittance of the films in the THz range was measured by the THz-TDS system.The film quality,conductivity and transmittance of the THz transparent electrode were investigated in three aspects.Secondly,terahertz anti-reflective coatings and ND filters based on DMSOdoped-PEDOT:PSS films were developed.A series of DMSO-doped-PEDOT:PSS films were prepared to explore their potential as anti-reflection and filtering materials in THz range.The antireflection properties of DMSO-PEDOT:PSS films were analyzed by THz-TDS.The antireflection principle of DMSO-doped-PEDOT:PSS films was analyzed.The filter properties of PEDOT: PSS films were analyzed by THz-TDS.The transmittance and optical density of DMSO-doped-PEDOT:PSS films based ND filters were calculated at THz frequencies.Thirdly,the THz liquid crystal phase modulator,the THz blue phase liquid crystal modulator and the THz blue phase liquid crystal grating were designed and fabricated.The basic properties of nematic liquid crystal and the working principle of liquid crystal phase modulator were introduced.The THz liquid crystal phase modulator based on 15 vol% DMSO-doped-PEDOT:PSS transparent electrodes was designed and fabricated.According to the theory,the phase shift of the phase modulator with the electric field was given,and the phase modulation ability was experimentally measured by THz-TDS.The basic properties of PS-BPLC were introduced.The THz PS-BPLC modulator based on 15 vol% DMSO-doped PEDOT: PSS transparent electrode was designed and fabricated.The performance of PS-BPLC modulator was tested by continuous THz laser.The modulation principle was explained by electronically controlled scattering performance.A THz PS-BPLC onedimensional grating based on 15 vol% DMSO-doped-PEDOT:PSS transparent electrode was designed and fabricated.The striped structure electrode was etched by ion beam sputtering method.The diffraction effect of the grating was tested by a THz imaging system.Finally,the dielectric properties of DMSO-doped PEDOT: PSS films were analyzed in detail,and a THz frequency selective surface(FSS)was designed based on the films.The complex refractive index and complex permittivity of PEDOT:PSS films doped with different concentrations of DMSO in the THz range were calculated by the time domain information measured by THz-TDS system.The classical generalization of the Drude formula was introduced,and the dielectric properties of PEDOT: PSS films were analyzed in detail by using the Drude – Smith model.The values of carrier concentration,carrier mobility and Drude – Smith model were obtained by fitting the dielectric coefficient with Drude – Smith formula.A THz cross-dipole FSS was designed according to the Drude – Smith model parameters of PEDOT: PSS films,and the resonant frequency response of the FSS were simulated by CST Microwave Studio software.