照明系统 ·电子枪 Units Tungsten LaB Schottky FEG Cold FEG Operating temperature K 2700 1700 1700 300 Work function,Φ eV 4.5 2.4 3.0 4.5 Current density A/m2 5 102 105 106 Crossover size nm >105 104 15 2~3 Brightness A/m2sr 1010 5x1011 5x1012 1013 Energy spread eV 3 1.5 0.7 0.3 Emission current stability %/hr <1 <1 <1 5 Vacuum Pa 10-2 104 10-6 109 Lifetime hr 100 1000 >5000 >5000 6
Units Tungsten LaB6 Schottky FEG Cold FEG Operating temperature K 2700 1700 1700 300 Work function, Φ eV 4.5 2.4 3.0 4.5 Current density A/m2 5 102 105 106 Crossover size nm >105 104 15 2~3 Brightness A/m2sr 1010 5x1011 5x1012 1013 Energy spread eV 3 1.5 0.7 0.3 Emission current stability %/hr <1 <1 <1 5 Vacuum Pa 10-2 10-4 10-6 10-9 Lifetime hr 100 1000 >5000 >5000 6 照明系统 • 电子枪
Structure of a TEM Example TEM schematic One of many types of TEMs Filament PHILIPS Wehnelt "Gun" Anode Gun deflectors 照明系统 Condensor aperture 1 (may be adustable by user depending on TEM type) C J Condensor lens 1 Condensor stigmator Fixed aperture Condensor lens 2 Beam deflectors Condensor aperture 2 Objective stigmator Sample holder Objective lens upper Objective lens lower 样品室 Objective aperture Image deflectors Selected area aperture (or immediate aperture) Intermediate lens Diffraction stigmator 成像系统/ 11 Projector lens 1 Projector lens 2 图像观察 CCD camera Beam axis Viewing screen 7
7 Structure of a TEM 照明系统 成像系统/ 图像观察 样品室
照明系统 聚光镜：会聚电子枪射出的电子束，以最小的损失照 明样品，调节照明强度、孔径角和束斑大小 第1聚光镜 第2聚光镜 光阑 会聚小透镜 (CM透镜) 物镜 前置磁场 试样 后置磁场 (a)TEM模式 (b)EDS模式(C)NBD模式(d)CBED模式 8
8 照明系统 • 聚光镜：会聚电子枪射出的电子束，以最小的损失照 明样品，调节照明强度、孔径角和束斑大小 (a) TEM模式 (b) EDS模式 (c) NBD模式 (d) CBED模式
照明系统 聚光镜：利用磁偏转器可使电子束平移、偏转 平移：上、下偏转线圈偏转角相等，但方向相反 倾斜：上线圈偏0转角，下线圈反方向偏转0+β角，则倾斜了角β 上偏转线圈 ∽ 下偏转线圈 L +B 聚光镜电子束对中系统工作原理图 9
9 照明系统 • 聚光镜：利用磁偏转器可使电子束平移、偏转 聚光镜电子束对中系统工作原理图 平移: 上、下偏转线圈偏转角相等，但方向相反 倾斜: 上线圈偏θ转角，下线圈反方向偏转 θ+β角，则倾斜了角β
Structure of a TEM Example TEM schematic One of many types of TEMs Filament PHILIPS Wehnelt "Gun" Anode 照明系统 Condensor aperture 1 8日 Gun deflectors (may be adustable by user depending on TEM type) 1 Condensor lens 1 Fixed aperture Condensor stigmator Condensor lens 2 Beam deflectors Condensor aperture 2 Obiective stiamator Sample holder Objective lens upper Objective lens lower 样品室 Objective aperture Image deflectors Selected area aperture (or immediate aperture) Intermediate lens Diffraction stigmator 成像系统/ Projector lens 1 Projector lens 2 图像观察 CCD camera Beam axis Viewing screen 10
10 Structure of a TEM 照明系统 成像系统/ 图像观察 样品室