Study On Preparation And Optoelectronic Properties Of DAST-graphene Composite Films

In recent years, the rapid development of new technology and new materials make the terahertz(THz) sources become a conventional technology. As a result, many research institutions in the world begin to pay more attention to THz and the uncooled THz detectors. However, the inorganic sensitive materials are utilized widely. Such materials respondweekly to THz signals, which cannot meet the device requirements.So, we first synthesized DAST. Based on it,in-situ and ex-situ DAST-graphene composite materials were synthesized. Accordingly, DAST films, in-situ composite films, and ex-situ composite filmswere further prepared. The resulting filmswere systematically investigated with metallographic microscope, scanning electron microscope(SEM), fourier transform infrared spectroscopy, UV-vis spectroscopy, Raman spectroscopy, and high resistance meter, respectively. The main results of this thesis are listed below:(1) In in-situ process, graphene is mixed with DAST during the DAST synthesis. The products are characterized by elemental analysis and fourier transform infrared spectroscopy, both of which prove that the products are DAST.(2) A new reduction of graphene oxide(GO) by DAST at a low temperature of 80 oC was discovered, which is essentially triggered by withdrawing of electrons from the H atoms in the rings of DAST to the O atoms in the C=O groups of GO.The interactions between DAST and graphene are enhanced in the in-situ process, thus resulting in higher film quality, as well as superior optical and electrical properties.Incontrast, the number ofhydrogen bond in ex-situcomposite is lower, which make the interactions between DAST and graphene weaker and thus lead to poor electrical and optical propertiesfor the ex-situ composite films. In optics, graphene addition leads toenhancedabsorption from visible light to THz band.Importantly, blue-shifts of IR signals of DAST and red-shifts of Raman signals of graphene are simultaneously observed in this work.The resistances of room temperature(RRT)for thein-situcomposite filmsaredecreased significantly to7.6×106Ω, a decrease which is four or five orders of magnitude compared with that of the DAST films. The conductivitiesof in-situ composite films arehighand theabsolute values of TCR(-0.0279 K-1) arelarge, which meet the requirements of micro-bolometers.(3) Finally, the composite films with different graphene concentrations were also prepared, which morphologies, optical and electrical properties were investigated. Results indicate that the composite films with 5% graphene exhibit optimal comprehensiveproperties. In contrast, alot of crystals will appear in composite film if the concentration of graphene is below 5%, whileweak IR absorption will be observedif the concentration of graphene is exceeded 5%. The electrical properties of DAST-5% graphene composite films arehigher than those of others. The conductivity become poorerif the concentration of graphene is low, while the film quality turns bad if the concentration of graphene is high. Accordingly, the optimal concentration of graphene in the DAST-graphene composite film is 5%.