Research On The Flexible Near-infrared Plasmonic Materials

Materials science has always played an important role in the study of plasmonics.The range of plasmonic materials is expanding,from the traditional noble metals Au and Ag to transparent conductive oxides(TCO),heavily doped semiconductors,and novel two-dimensional materials such as graphene,etc..Researchers have been trying to solve the problems in practical device applications by seeking novel materials with low loss,tunable optoelectronical characteristics,mechanical-,chemical-and temperature-stability.Besides,to achieve a breakthrough of consumption level industrial productization,it is essential to weigh the costs of preparation and processing,complementary metal oxide semiconductor(CMOS)process compatibility and biological compatibility.With the development of research,optoelectronic devices begin to extend from the traditional inorganic and rigid materials to organic,flexible and two-dimensional unique materials.Conventional visible-near infrared(Vis-NIR)inorganic noble metals such as Ag,Au and TCO have been difficult to meet the requirements of organic flexible optoelectronics and many other emerging applicationsBased on the above considerations,this paper will be dedicated to a new research topic of flexible plasmonic materials and its application exploration,and propose two novel flexible plasmonic materials:modified PEDOT:PSS and two-dimensional MXene.Especially for the first time,the surface plasmon characteristics of organic modified PEDOT:PSS are compared with those of inorganic structures,which provide the possibility for the research of other organic plasmonic materialsIn this thesis,we focus on the study of the Vis-NIR characteristics of high conductivity acidified organic PEDOT:PSS film and two-dimensional MXene film,including the following aspects:(1)The optical and electrical properties of high conductivity PEDOT:PSS and two-dimensional MXene films prepared by spin coating process were deeply characterized.It is found that the carrier concentration of MXene film is as high as 2.8×1021cm-3;the carrier concentration of the modified PEDOT:PSS film is increased to the order of～1022cm-3,and the carrier can be freely tuned in the range of 3 × 1022cm-3～4.5 × 1022cm-3 by adjusting the acidification temperature,the type and concentration of acid;at the same time,the transmittance of modified PEDOT:PSS film is up to 70%at 400 nm,and that of MXene film is up to 55%at 600 nm.(2)Based on the unique dispersion model of Drude+three Lorentz oscillators,the dielectric permittivity dispersion curves of modified PEDOT:PSS film and two-dimensional MXene film are obtained by ellipsometry and transmittance spectroscopy.By changing the carrier concentration,the dielectric permittivity cross-over wavelength λC and the surface plasmon wavelength λsp of the modified PEDOT:PSS film are tunable in the range of 650-900 nm,and the surface plasmon wavelength λsp of the two-dimensional MXene film is 1278 nm.(3)The surface plasmon polariton(SPP)propagation mode of the modified PEDOT:PSS and MXene films was excited effectively in the spectral range of 1050-1550 nm by the prism coupling configuration.When the localized surface plasmon resonance(LSPR)occurs in the cylindrical antenna array based on the modified PEDOT:PSS,with the of field enhancement in electromagnetic hot spot could be reach up to 13 times(4)Based on the frequency-dependent average electron scattering rate Γ’(ω)and SPP two-dimensional figures of merit(FOM),the effective loss of plasmons and SPP field propagation and confinement ability of the modified PEDOT:PSS,two-dimensional MXene,Ag,Au and indium tin oxide(ITO)films were compared and summarized.The activation,propagation and field confinement of plasmons on the surface of modified PEDOT:PSS and two-dimensional MXene are comparable to those of ITO,and have a wider tuning range of plasmon wavelength.Compared with the traditional plasmonic materials Ag and Au,it has the characteristics of wide tuning of dielectric constant and strong localization of surface plasmons(the ability of plasmon localization on the dielectric side is 3-4 times higher),which brings more flexibility in the design of devices.