第一章_真空技术基础.docxVIP

第一章真空技术基础本章主要内容：1.真空的基本知识2.真空的获得3.真空的测量4.稀薄气体的基本性质5.真空配件、检测1§1-1气体与真空Air, as a gas, is composed of molecules that you can imagine as round elastic balls.Molecules move in straight lines until they collide with neighboring molecules or the container wall.2THE ATMOSPHERE IS A MIXTURE OF GASESPARTIAL PRESSURES OF GASES CORRESPOND TO THEIR RELATIVE VOLUMESGASSYMBOLPERCENT BY VOLUMEPARTIAL PRESSURE TORRPASCALNitrogenN,000OxygenO,000ArgonAr0.937.1940Carbon DioxideCO20.030.2533NeonNe0.00181.4 x 10-21.8HeliumHe0.00054.0 x 10-35.3 x 10-1KryptonKr0.00018.7 x 10-41.1 x 10-1HydrogenH20.000054.0 x 10-45.1 x 10-2XenonXe06 x 10-58.7 x 10-3WaterH2OVariable5 to 50665 to 66503PressureP = F / A=nMvrms2/3NAItcomesfromthestrikingofgasmoleculesonthewalls.Partial Pressure4VAPOR PRESSURE OF WATERT (O C) 100250-40-78.5-196(BOILING)(FREEZING)(DRY ICE) (LIQUID NITROGEN)P (mbar) 1013326.40.136.6 x 10 -410 -245Pressures ofgases67Vapor Pressure of some SolidsTHE VACUUM·定义 真空：低于一个大气压的气体状态。 “相对真空”，“绝对真空”?特点：压强(Pressure)低，分子稀薄， 分子的平均自由程长。电学特性输运特性真空的性质可由压强、单位体积分子个数、气体的密度等表示8Relative PressureAbsolute Pressure用“真空度”及“压强”两个参量来衡量真空的程 度。帕斯卡（pascal）=1牛/米2，国际单位制托（Torr）=133.322Pa=1/760atm单位，描述 真空的独特单位此外，mmHg、atm、bar等。The only onewhich is legal9Pressure unitPaBarAtmTorr10.000019.869×10-67.501×10-9.869×10-17.501×10.0.320.0013331.316×10-31Pressure unitPaBarAtmTorr105. Why is a Vacuum Needed?To move a particle in a (straight) line over a large distance115. Why is a Vacuum Needed?1. 颗粒可以做直线运动2. 为薄膜生长提供洁净表面Atmosphere(High)VacuumContamination (usually water)Clean surface126. 真空的划分粗真空 105－102Pa : 目的是获得压差vacuum cleaner, vacuum-filter，CVD低真空 102－10-1Pa:气体分子运动特征改 变，电场下具有导电特征 vacuum-bottle, vacuum- desiccator, vacuum-impregnation，Sputtering, LPCVD高真空 10-1－10-6Pa :Evaperation, Ion source超高真空 ＜10-6Pa ：Surface analysis，Particle Physics13§1-2稀薄气体的基本性质1. Ideal gas equation低压状态下，可用理想气体的状态方程（波 义尔定律、盖·吕萨克定律、查理定律）来描 述，遵守麦克斯韦——玻尔兹曼分布。PV＝nmolRT=nmolecularkT=nMvrms2/3NA nmol=m/Mnmolecular =7.2*1022P/T142. 气体分子的速度分布· 麦克斯韦