分析电子显微镜AEM.ppt

3.2.5 The limitations in EELS analysis 1. Detection limits MDM: In 500? Fe foil, 103 atoms for Li and Al 3 x 104 atoms for O (k - edge) MDF: C in 300? steel : 3at% (100 atoms) O in 600? steel : 6at% 2. Specimen thickness 3. Spatial resolution Phase identification 4、Micro Diffraction 4.1 Limit of the Selected area electron diffraction (SAD) 4.2 Micro diffraction 4.2.1 the Ricke method 4.2.2 convergent beam micro diffraction 4.1 Limit of the Selected area electron diffraction (SAD) 3.2.3 Optimization of the AEM for microanalysis 3.2.4 X-Ray microanalysis Cliff and Lorimer : CA+CB=100% Limit for microanalysis by EDS 1. Absolute accuracy 2 Minimum detectable mass: MDM ? 10-20g 3 Minimum mass fraction: MMF ? 0.1wt% 4 Spatial resolution: 10 ～20 nm 5 Low Z limit 6 Practical limitations : (1) contamination (2) Embedded particales 3.2 EELS - Electron Energy Loss Spectroscopy 3.2.1 energy loss process in thin foil TEM specimens 3.2.2 Where to find the energy loss electrons? 3.2.3 Electron energy loss spectrometer 3.2.4 Comparison of the signal generating process for EDS and EELS 3.2.5 The energy loss spectrum 3.2.6 EELS Microanalysis and the limit of analysis 3.2.7 Conclusion remarks 3.2.2 Where to find the energy loss electrons? 3.3.3 EELS Spectrometer 3.2.4 Comparison of the signal generating and collection process for EDS and EELS 1. Signal generation EDS - secondary event High energy incident electrons excitation of atoms characteristic X-rays or Auger electrons EELS - primary event 2. Collection efficiency EDS - very low !! X-Ray generation: for carbon: 1 in every 400 k-shell ionization for Na, 1 in 40 Collection efficiency: WDS: 10-3 - 10-4 EDS: