1、Part III Analytical Electron Microscopy in Materials Science1.Introduction2.Image mode in AEM3.Microanalysis in AEM 3.1 X-ray Energy Dispersive Spectroscopy (EDS) 3.2 Electron Energy Loss Spectroscopy (EELS) 3.3 Microdiffraction 3.4 Convergent beam diffraction 1、Introduction1.Signals generated in th

2、e interaction between the incident high energy electron beam and the thin crystalline specimen2.How to form a probe3.Relationship between TEM, SEM and AEM 3.1 TEM Image mode Diffraction mode 3.2 SEM Image mode: SE, BSE, X-Ray Mapping Microanalysis: WDS, EDS 3.3 AEM Imaging mode: TEM, STEM, SEM, Mapp

3、ing (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, micro-diffraction, convergent beam diffraction How to form a probe ?Detectors needed for an AEM3.Relationship between TEM, SEM and AEM 3.1 TEM Image mode Diffraction mode 3.2 SEM Image mode:

4、SE, BSE, X-Ray Mapping Microanalysis: WDS, EDS 3.3 AEM Imaging mode: TEM, STEM, SEM, Mapping (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, micro-diffraction, convergent beam diffraction3.2 SEM Image mode: SE, BSE, X-Ray Mapping Microanalysis

5、: WDS, EDS3.3 AEM Imaging mode: TEM, STEM, SEM, Mapping (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, Micro-diffraction, Convergent beam diffraction2、Imaging in AEM2.1.TEM2.2.STEM - Scanning transmission electron microscopy2.3.STEM/SEM imagi

6、ng2.4.Signal mixing - Hybrid imaging2.5.X-Ray and EELS mapping 3、Microanalysis in AEM3.1 X-Ray quantitative microanalysis 3.1.1 X-Ray signal generation in TEM thin foil specimens 3.2.2 Identification and elimination of spurious signals 3.2.3 Optimization of the AEM for microanalysis 3.2.4 X-Ray micr

7、oanalysis 3.2.5 Microanalysis limit3.2 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 ene

8、rgy loss spectrum 3.2.6 EELS Microanalysis and the limit of analysis 3.2.7 Conclusion remarks 3.3 Comparison between EDS and EELS X-Ray signal generation in TEM thin foil specimensFluorescence yield (w):w = 0 for Z 5 (Boron k shell ionization) Z 27 (Cobalt L shell) Z 57 (lathanlum M shell)3.2.3 Opti

9、mization of the AEM for microanalysis3.2.4 X-Ray microanalysisCliff and Lorimer :CA+CB=100%Limit for microanalysis by EDS1. Absolute accuracy 2 Minimum detectable mass: MDM 10-20g 3 Minimum mass fraction: MMF 0.1wt%4 Spatial resolution: 10 20 nm5 Low Z limit6 Practical limitations : (1) contaminatio

10、n (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

11、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 Spectrometer3.2.4 Comparison of the signal generating and collection process for EDS and EELS 1. Signal generation EDS - secondary event High energy incident

12、electrons excitation of atoms characteristic X-rays or Auger electrons EELS - primary event2. 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: 10-2 Gold layer (20nm): only allow 67% be

13、transmitted ! The Dead layer below the gold layer: 37% of the 67% be transmitted! EELS: very high! 75% of the energy loss electrons with a collection angle of 10 mrad 100% when collection angle is 30 mrad 3.2.5 The energy loss spectrum(1) The zero loss peak(2) The low loss region of the spectrum DE=

14、 50eV energy loss peak - ionization edges pre-edge and post-edge structureMicroanalysis using ionization peaks (edges)3.2.5 The limitations in EELS analysis1. 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

15、steel : 6at%2. Specimen thickness3. Spatial resolutionPhase identification4、Micro Diffraction4.1 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)5、Conver

16、gent beam diffraction5.1 Terminology5.2 How to get a CBDP5.3 ZOLZ - the Zero Order Laue Zone5.4 Thickness Measurement by CBDP5.5 HOLZ - Higher Order Laue Zone5.6 HOLZ Lines - Higher Order Laue Zone Lines5.7 ZAPS - the zone Axis Patters5.8 Acquiring 3-D symmetry information5.9 Phase identification5.1

17、0 summary 5.1 TerminologyZOLZ - Zero Order Laue ZoneHOLZ - Higher Order Laue ZoneFOLZ - First Order Laue ZoneSOLZ - Second Order Laue ZoneKikuchi LinesHOLZ LinesDynamical EffectK- M PatternKossel Pattern5.2 How to get a CBDP5.3 ZOLZ - the Zero Order Laue Zone5.4 Thickness Measurement by CBDP5.5 HOLZ

18、 - Higher Order Laue Zone5.5.1 Higher order Laue zone5.5.2 Determination of interplanar spacings parallel to the electron beam direction5.5.3 Indexing of the HOLZ maxima hu + kv + lw = 1 for FOLZ maxima hu + kv + lw = 2 for SOLZ maximaFor fcc :When U+V+W oddWhen U+V+W evenFor bcc :When UVW all oddWhen U