Synthesis,Mechanism And Property Research Of Graphene And 2D MoO₂ By Chemical Vapor Deposition

2D materials,with the thickness smaller than 100 nm,is a branch of nanomaterials.The thickness of some 2D materials is atomic level,which is widely researched recent years.The thickness of some 2D materials is even smaller than 1 nm,such as single-layer graphene.2D material has widely potential application in electronic devices,conducting films,sensors,energy storage,catalytic,etc.Considering the chemical component,2D materials can be divided into several categories,including unitary 2D material like graphene,Transition-metal dichalcogenides like MoS2,metal caibides or carbide nitrides,metal oxides,etc.Chemical vapor deposition(CVD)is an effective method to large scale synthesis of 2D materials.In this paper,the CVD growth of graphene is systematically studied with carbon source,substrate,structure,and the growth mechanism and the electronic property of synthesized graphene is also researched.Otherwise,2D MoO2 synthesized by CVD is also researched.The mechanism and the electronic property of 2D MoO2 is also studied.The specific content of this paper is as follows.(1)Micrometer-scale 2D MoO2 single crystals have been successfully synthesized directly on SiO2/Si substrate by chemical vapor deposition.The chemical component of MoO2 has been revealed by Raman spectroscopy,the cystal structure and the single crystal nature have been revealed by highe resolution transimittance microscope.The smallest thickness is 3.8 nm,and the lateral size is several micrometers.The shape of 2D MoO2 single crystals has three types,including standard parallelogram,parallelogram with two angles missed and hexagonal.The growth model of three shape type is discussed,and the difference of growth velocity of two growth directions is the key factor of the final shape.The theoretical calculation confirmed the metallic property of as-synthesized 2D MoO2 and its conductivity is 5×103 S/cm,indicating it has excellent conductivity and may have potential application in conducting films.(2)Large area few layer graphene films have been successfully synthesized on silicon dioxide/Si substrates by chemical vapor deposition with ethylene glycol as carbon source.Pseudo-dual temperature zone is constructed by a block,and the growth temperature of graphene and the temperature of the carbon source are synchronization controlled.The smallest thickness of obtained graphene films is nearly 2nm,measured by atominc force microscope.The orientation of SiO2 layer can obviously influence the thickness of graphene.The thickness of graphene with SiO2 layer at bottom is much smaller than on top.T While the temperature higher than the optimized value,the thickness of graphene will increase with the increase of temperature.While the temperature is lower than the optimized value,the thickness of graphene will increase with the decrease of the temperature.The graphene can't grow if the growth temperature is lower than special value.The field effect transistor with graphene film as channel material is fabricated,and the carrier mobility is 707 cm2 V-1S-1,better than the values of much similar works.This work offers a new strategy to directly grow graphene on silicon dioxide/Si substrates,and the as-synthesized graphene films may have potential applications in conducting films,electronic devices,etc.(3)Uniform and large area bi-layer graphene film is direct synthesized on silicon substrate by chemical vapor deposition with methane as carbon source.Raman spectra indicate that the bi-layer graphene is AB-stacked.Raman mapping indicates that the graphene films are large area uniformity and the area ratio of bi-layer graphene is>95%.The growth temperature and the hydrogen flow will influence the thickness of graphene.The X-ray photoelectron spectroscopy measurement indicates that the surface of the Si substrate is partially oxidized and a thin oxidized layer is formed.This oxidized layer is a key factor to the growth of bi-layer graphene.The graphene film can be transferred to SiO2/Si substrate by thermal release tape and the graphene-based electronic device is fabricated and the measured mobility of the directly grown graphene film is 343.3 cm2V-1S-1.These as-synthesized graphene films may have potential applications in conducting films,electronic devices,etc.(4)Uniform and large area bi-layer graphene films on MgO(100)substrates have been successfully synthesized by chemical vapor deposition with methane as carbon source,without the aid of any metal catalysts.The graphene film is AB-stacked bi-layer graphene revealed by Raman spectroscopy and atomic force microscope.Raman mapping indicates that the graphene films are large area uniformity and the area ratio of bi-layer graphene is>95%.The growth temperature will obviously influence the growth of graphene.The thickness will increase while the temperature increase upon the optimized temperature or decrease below the optimized temperature.The H2/CH4 flow ratio will also influence the quality,thickness and lateral size of graphene.The graphene film can be transferred to SiO2/Si substrate by thermal release tape and the electronic device is fabricated.The measured mobility of these directly grown graphene films is 130 cm2 V-1S-1 and they may have potential applications in transparent conducting coatings and electronic devices.(5)Large scale graphene is synthesized on MgO powder by chemical vapor deposition with methane as carbon source.Three dimensional graphene composed by 2D graphene sheets is obtained with the dissolve of MgO powder by hydrochloric acid.The observation of high resolution transmittance microscope indicated that the layer number of major graphene sheets is three to five.There are plenty of channals benefits for the diffusion of inons in the 3D graphene.The hydrocarbons decomposed from methane under high temperature will coat at the surface of MgO grain to form graphene film.The room of MgO grains will be partially keeped after the grains dissolved and the three dimensional structure of graphene will form naturally.The synthesized 3DG was used as counter electrode of quantum dots sensitization solar cell.The performance is better than the solar cell with CuS as counter electrode,while other conditions are the same.The 3DG synthesized with this method is simple,low cost.The synthesized 3DG may have potential application in quantum dots sensitization solar cell and energy storage.