Growth Of Graphene On 4H-SiC By Joule Heat Thermal Decomposition And The Synthesis And Application Of Ag-Au-Pt Trimetallic Nanoparticles

The thesis is mainly consisted of two parts.In chapter 1 to 3,the study of growing graphene on 4H-SiC by Joule Heat Thermal Decomposition and the application of graphene on 4H-SiC(0001)are introduced.From chapter 4 to 6,the synthesis and application of Ag-Au-Pt trimetal nanoparticles are discussed.Graphene is a two-dimentional singal-layer material composed of carbon atoms with honeycomb structure.Due to its excellent characteristics:carrier mobility as high as?200,000 cm2V-1s-1 at room temperature,nonreactivity,high heat conductivity(?5300 W/mK),monolayer graphene having a light transmittance of?97.7%,excellent mechanical properties(young's modulus?1.1 TPa,tensile strength 125 GPa)and nanoscale high hydrophobicity,etc.,graphene has been widely applied in field effect transistor,transparent electrode,sensor and so on.In this dissertation,the experimental method of growing graphene on 4H-SiC by Joule Heat Thermal Decomposition is studied,and the application of graphene in photoelectric detector is discussed.The achieved results are as follows:1.Graphene is grown with a customized designed experimental platform.At the pressure of 10-6 Torr,highly doped n-type 4H-SiC is heated by applying a direct current.When heated at 1470? for 5 min,multi-layer low-defect uniform graphene with an area?12mm×5mm is obtained.2.Linear transmission line model(LTLM)is used to characterize the graphene-gold contact.It is found that the specific contact resistance of graphene-gold is 5.03 × 10-5 ?·cm2,and the sheet resistance of graphene is 52.36 ?/sq.Noble metal nanocrystals have a wide range of application prospects.Silver and gold nanoparticles both are good in local surface plasma(LSPR)and surface-enhanced Raman spectroscopy(SERS)but have few catalytic applications.Palladium and platinum nanoparticles are widely applied in catalysis,but their LSPR are relatively weak,therefore hard to characterize by UV-vis spectra.In order to possess LSPR,SERS and catalytic properties,the study of bimetallic and polymetallic alloy nanocrystals has become popular.Among all the noble metals,silver has become the best choice of material for plasmonics and related applications owing to its abundant reserves and low price,but its application is greatly restricted due to its high susceptibility in the oxidative environment.The synthesis of bimetallic and polymetallic nanoparticles using silver nanoparticles as seeds has attracted lots of interests.The main contributions are as follows:1.Using Ag@Au core-shell nanocubes as the seeds,for the first time Ag@Au-Pt trimetallic nanocubes with platinum deposited on {110} surfaces,gold deposited on{100} surfaces and silver deposited on {111} surfaces are synthesized by seeded growth method.In situ SERS is used to observe the reaction of 4-nitrothiophenol(4-NTP)t reduced by sodium borohydride with Ag@Au-Pt nanocubes as a catalyst,which is found that it is 3.5 times stronger than that of Ag@Au nanocubes.Ag-Au-Pt nanoboxes with openings?2-3 nm at the corners and shell thickness of?2 nm are obtained by wet etching for the first tiem.2.The effect of reducing agent ascorbic acid(H2Asc)on the synthesis of Ag@Au-Pt nanoparticles is studied.Without H2Asc,the main reaction is galvanic replacment reaction(GRR),and nanoboxes are obtained.With H2Asc,both GRR and reduction raction occur simultaneously.TEM characterization show that the surface of the nanoparticles is rough and covered with small nanocrystals.Finally,their catalytic performance is studied.The results show that the nanoparticles with H2Asc involved have better catalytic properties,which is 8 times stronger than that of Ag-Au nanoboxes,and 2 times stronger than that of the nanoparticles synthesized without H2Asc involved.