纳米材料和纳米结构第七讲

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,第七讲,Physical Vapor Deposition,物理气相沉积,纳米材料和纳米结构,Physical Vapor Deposition(PVD),Definition,Film,deposition by condensation from vapor phase,Three Steps of PVD,Generating a vapor phase by evaporation or sublimation,Electron-beam evaporation,Molecular-beam,epitaxy,Thermal evaporation,Sputtering,Cathodic,arc plasma deposition,Pulsed laser deposition,Transporting the material from the source to the substrate,Formation of film by nucleation and diffusion,Application,Coatings of electronic materials,Insulator,Semiconductor,Conductor,Superconductor,Nanometer scale multilayer structures,Advanced electronic devices,Abrasion resistant coatings,Concerned Problems and Challenges,Contamination at the interfaces or intermixing,Multi-material systems involved,Cost of equipment and maintenance,Complexion of operation,Systems Described in This Section,Sputtering,Pulsed laser deposition,1,Sputtering,（溅射）,1-1 Principle of Sputtering,1-2 Sputtering System,1-3 Preparing Multilayer Structures by Sputtering,1-4 Current Status of Sputtering,1,-1 Principle of Sputtering,Ejection of Atoms from the Target,Energetic particles bombarding a target surface with sufficient energy(50,eV,1000,eV,),Target,Cathode,connected to a negative voltage supply,Composed of the materials to be deposited,Substrate,Anode,May be grounded,floated,or biased,Glow Discharge Medium in Sputtering Chamber,A gas or a mixture of different gases,most commonly,Ar,or He,In reactive sputtering:introduce reactive gases such as O,2,or N,2,Pressure:a few,mTorr,to several hundreds,mTorr,Procedure,Generation of positive ions:ionizing the sputtering gas by glow discharge,Bombarding:accelerated positive ions to strike the target surface and remove mainly neutral atoms,Condensation:neutral atoms leave the target and condense on the substrate surface,and form into thin films,An Important Concept:Sputtering,Yield,A measurement of the efficiency of sputtering,Ratio of the number of emitted particles to the number of bombarding ones,1,-2 Sputtering System,Typical Types of Sputtering Systems,Direct current(dc)diode sputtering,Used for sputtering conducting materials,Radio frequency(,rf,)diode sputtering,Used for sputtering insulating materials,Magnetron diode sputtering,Most commonly used today,Plasma be confined around the target surface by a magnet field,Advantages of using magnetron sputtering,Feasibility of large cathode size,High sputtering yield,Less bombardment to the substrate,用于制备,TiN,/VN,多层膜的磁控溅射系统,氩气,流量表,流量控制阀,压力传感器,低温泵,低温泵,靶,1,靶,2,旋转衬底支架,衬底,流量表,阀门,流量表,流量控制阀,1,流量控制阀,2,主流量控制阀,质谱仪,阀门,锁定装置,Ways to reduce the damage and re-sputtering of growing film,Damage caused by negative ion effect and radiation enhanced diffusion,Improvement method,Use high gas pressure:to reduce the energy of the negative ions,Use off-axis sputtering:to avoid the substrate directly facing the cathode,Disadvantage of off-axis sputtering:,low deposition rate,small deposition area,Deposition of magnetic materials:facing target sputtering systems,偏轴溅射系统,示意图,Schematic of off-axis sputtering system,可,360,度旋转的衬底支架,陶瓷加热器,负离子撞击区,衬底,靶,溅射枪,溅射源,屏蔽闸,空间屏蔽区,正面溅射系统,示意图,Schematic of the facing target sputtering system,衬底,靶,磁体,冷却水,氩气,1-3 Preparing Multilayer Structures by Sputtering,Types and Properties of Multilayer Structures,Types of architectures,Metal/metal,Ceramic/ceramic,Metal/ceramic,Semiconductor/semiconductor,Structural and physical properties,With structurally modulated architectures,With compositionally modulated architectures,High interface volume fraction,Large intrinsic stress,With structural and/or compositional gradient,Exhibiting unique and enhanced electric,dielectric,magnetic,and mechanic properties,BaTiO,3,Nanolayer,Ferroelectric Thin Film Capacitors,Advantage:higher relative dielectric constant,Disadvantage:high leakage current,Electrical properties strongly depending upon the processing condition,microcrystal structure,and choice of bottom electrode,Amorphous:low dielectric constant(16 at 105 V/cm),low leakage current,Polycrystalline:high dielectric constant(400 at 105 V/cm),high leakage current,Aim of,nanolayer,structure BaTiO3 film capacitor:high dielectric constant and low leakage current,Realization and effects,Substrate:Ru/SiO2/Si,Technique:,rf,magnetron sputtering,sputtering interruption between layers to change the substrate temperatures(680,C,60,C,),Layer structure:n-cycle alternate layers of amorphous and polycrystalline BaTiO3(microcrystalline be obtained by annealing amorphous layer),Results obtained,Leakage current density be considerably reduced,and the effect becoming better with increasing cycle number,Dielectric constant be two or three times higher than single amorphous layer but lower than a single polycrystalline layer,具有纳米多层结构的,BaTiO,3,薄膜电容器横截面示意图,Nanolayer,MoSi,2,/SiC,Substrate:single crystal silicon(,sc,-Si),Techniques:,Magnetron sputtering for deposition of MoSi2,rf,sputtering for deposition of,SiC,MoSi2/SiC layered composites be pr