Controllable Synthesis And Spin Transport Of Graphene

Graphene and its related materials are widely used in the field of high-speed computing chips,composite materials,transparent conducting electrodes,field effect transistors and spin valves due to their superior physical and chemical properties.The.demand for large-area and high-quality graphene has increased unabated.At present,copper-based chemical vapor deposition(CVD)is the most systematic approach to prepare graphene.The growth mechanism of graphene on the surface of Cu is"self-limited surface deposition",which greatly limits the growth of bilayer and multilayer graphene.This work focuses on the preparation,characterization and application of graphene.Combining with chemical vapor deposition,Raman characterization,electron beam lithography and electron beam evaporation,a comprehensive study on the preparation graphene,synthesis of tungsten disulfide(WS2),and application of graphene field effect transistor(GFET)and spin valve is carried out.The major results are as follows:The transition metal nano-powders were introduced to the low pressure CVD to assist the synthesis of bilayer and multilayer graphene for the first time.The oxygen-assisted technique was applied to synthesis the large single crystalline graphene rapidly through the atmospheric pressure CVD.Back gate GFETs were fabricated in batch by using CVD graphene.The relationship between the mobility and the channel length,and the influence of residual adhesive doping on the devices were discussed.The metal lateral spin valve was prepared by shadow evaporation technique,and the spin polarization current was injected into the non-magnetic metal Ag at room temperature.The spin accumulation in Ag was detected,and the thermal stability of metal lateral spin valve was investigated.Spin accumulation in mechanical exfoliation graphene and CVD graphene was further studied.The spin current was successfully injected into the two kinds of lateral spin valves.The relationship between spin accumulation signal and the number of graphene layers was discussedWS2 was synthesized on Au foil by atmospheric pressure CVD.The controllable synthesis of oriented single crystal WS2 as well as fully covered monolayer WS2 films was achieved by adjusting the growth parameters.