The Preparation And Property Studies Of Graphene-based And ZnO-based Multilayer Films

A thin film is a layer of material ranging from fractions of a nanometer to severalmicrometers in thickness, and the main applications are benefit from thin-filmconstruction. In recent years, graphene, graphene-based composite and ZnO-basedfilms are attracting tremendous attention because of their remarkable properties whichmake them useful for extensive applications such as transparent electrodes, solar cells,electronic devices, energy storage devices, sensors and catalysts.In our work, graphene, graphene-TiO2and ZnO/Cu/ZnO films were prepared byPECVD and physical vapor deposition (magnetron sputtering). The structure,morphology, electrical and optical properties were investigated using Ramanmicroscope, X-ray diffraction (XRD), transmission electron microscopy (TEM),atomic force microscopy (AFM), scanning electron microscope(SEM), fiber opticalspectrometer, four-point probe. The main research work is as follows:(1) A monolayer graphene film with high quality was synthesized using PECVDtechnique at substrate temperature as relatively low as800oC on Cu foil substrate.The changes in growth temperature, CH4flow rate and H2flow rate were found toaffect the quality and layer number of the graphene. With increasing the growthtemperature, the layer number of graphene was decreased, the quality of graphene wasimproved, and the sheet resistance was rapidly decreased. The graphene film withhigh quality could be synthesized at a low CH4flow rate of1sccm, and the qualitydecreased with increasing the CH4flow rate. Defects could be brought into grapheneat a low or high H2flow rate, the graphene had a higher quality at H2flow rate of10sccm in our experiment.(2) We prepared high-quality graphene films using PECVD and directlydeposited TiO2onto the obtained graphene to fabricate graphene-TiO2multilayerfilms. The charge transfer between TiO2and graphene was investigated by comparingRaman spectra of pristine graphene and TiO2-deposited graphene. The surface morphology was investigated using AFM, suggesting that the insertion of grapheneleaded to increased specific surface area. The adsorption capacity and UVphotocatalytic activity of the samples were investigated in the process of methylorange (MO) decomposition and it was found that graphene-TiO2multilayer filmsexhibited improved photodegradation efficiency compared to pure TiO2film. Thegraphene layers in the multilayer films not only served as electron-acceptor materialwhich separated the photoexcited electron-hole pairs then hindered the chargerecombination, but also acted as substrates which induced enhanced specific surfacearea of the upper TiO2films.(3) The ZnO/Cu/ZnO multilayer films had been fabricated by simultaneous RFand DC magnetron sputtering at room temperature. Numerical simulation of theoptical properties of the multilayer films had been carried out in order to guide theexperimental work. The influences of the ZnO and Cu layer thicknesses, and of O2/Arratio on the photoelectric and structural properties of the ZnO/Cu/ZnO films wereinvestigated. When the thickness of the ZnO layers changed in the range of40–70nm,the multilayer films presented a better optical property, their transmittance spectra hada relatively flat plateau in the entire visible region. And before the Cu layer wascontinuous, the sheet resistance decreased rapidly as the Cu layer thickness increased;however, the transmittance decreased in both UV and visible regions. The multilayerfilm prepared at O2/Ar ratio of1:4exhibited higher sheet resistance, and as the O2/Arratio further increased, the sheet resistance of the multilayers decreased. Wespeculated that the change of sheet resistance with O2/Ar ratio could be attributed tothe interface effect.