1. 电子能量损失谱
Electron Energy Loss Spectroscopy (EELS)
张 庶 元

2. 入射高能电子与样品的相互作用

3. Atomic-scale view of electron energy loss in TEM
Incident beam electron
E0 (100 to 1000 keV)
Excited specimen electron
EB + E
Scattered beam electron
E0 - E 3 3

4. Electron energy loss (eV)
What is an EELS spectrum?
Elastic scattering
Inelastic scattering L L K
Carbon
atom K
Zero loss
Electrons count
1 eV
C K
290
Electron energy loss (eV)

5. 电子能量损失谱信息 非弹性散射过程: 声子激发 (<0.1eV) 等离子激发 (<30eV) 内壳层电子激发 (＞13eV)
自由电子激发
(二次电子)
(<50eV)
(背底)
韧致辐射 (背底)
∙∙∙ ∙∙∙

6. 根据等离子激发能量的大小，即谱峰的位置，可以确定物质的种类和他的组成。
Na： ev(一次激发) ev(二次激发)

7. 随试样厚度的增加，电子在试样中可能产生二次，甚至多次等离子激发，其峰位出现在第一次激发峰的两倍或多倍能量的位置。
Al: ev ev ev ev

8. 表中列出了几种物质的等离子激发峰的理论值和实测值

9. Specimen thickness measurement
λ 为电子非弹性散射的平均自由程
IT 为第一个等离激发峰的强度
Io 为零损失峰的强度
Rough estimate of λ :
λ ~ 0.8Eo nm
so for 100-keV electrons
λ is nm various materials

10. 内壳层电子激发
偶极跃迁：Δl = ±1

11. Correlation between EELS and specimen feature11

12. Magnetic prism spectrometer

13. EELS spectrometer Optical configuration at entrance
Dispersion and focusing section
Projection section
Spectrum plane 13

14. In-column omega-filter
Inserted in the imaging lens system
Energy-filter imaging and electron diffraction, CBED

15. Post-column imaging filter
Gatan (Tridiem) imaging filter (GIF).
Attached to the TEM column below the viewing chamber

16. Energy-loss spectroscopy (EELS - low loss)
Spectrum is enlarged and optimally coupled to detector
Final EELS readout
EELS spectrum projected onto CCD 16

17. Energy-loss spectroscopy (EELS - core loss)
The spectrum is shifted
Best to do by changing prism current preserve probe focus
Final EELS readout
O K edge
Mn L edge
Spectrum offset via prism current
EELS spectrum projected onto CCD 17

18. EFTEM: Energy Filtered TEM: GIF only
Projection section operates in imaging mode
Spectrum is projected back to an image
Just like forming an image from a diffraction pattern in TEM
Unfiltered image projected onto CCD detector 18

19. Energy-filtered TEM imaging (EFTEM - core loss)
The spectrum is shifted relative to the slit opening
Best to do by increasing beam energy to preserve image focus
Core-loss image projected onto CCD detector
Spectrum offset via high tension
image mode 19

20. EFTEM - a five-stage process20 20

21. Spectrum Imaging – EFTEM mode
Collects detailed spatial and spectroscopy information
Allows processing decisions after acquisition
Spectrum imaging can create quantitative images / profiles
Can confidently locate artifacts & understand image contrast Dx Dy
image at DE1
image at DE2 . . . . . . . . .
Dx, Dy spatial dimensions
DE energy-loss dimension
image at DEi DE
spectrum at Dxi , Dyi 21

22. Spectrum imaging - STEM EELS mode22

23. Spectrum imaging - STEM EELS mode23

24. Elemental Mapping Using Energy Filtered Imaging
SiC/Si3N4

25. Atomic Resolved EELS of GaAs in the bulk
HAADF survey image
Analysis was carried out using the facilities at Florida State University
System: ARM200 with cold FEG equipped with GIF Quantum heavily upgraded
Sample was provided by Glasgow University and Sample was observed along the [110] direction
Sample is 4 years old and shows some oxidation 25

26. Atomic Resolved EELS of GaAs in the bulk
EELS spectrum extracted from the region in the red box in the EELS SI
EELS SI
Ga L2,3-edges
As L2,3-edges
Convergence angle: 25mrad
Collection angle120mrad
EELS data was acquired in single range mode
Exposure time per pixel: 50ms
Dataset size: 26x25x2048
Total number of pixels: 650
Total acquisition time: 51seconds 26

27. Atomic Resolved EELS of GaAs in the bulk
As elemental map
EELS colorized elemental map
Ga: Green
As: Red
Ga elemental map
The GaAs dumbbell is clearly resolved with high contrast 27

28. Elemental maps EDS Pd EELS Pd
Intensity line profiles extracted from the region in the blue in the Pd maps
The EELS elemental map for the Pd looks much sharper and shows higher contrast than the same map obtained using EDS. This can be directly attributed to the strong forward scattering of the EELS signal and the nearly 100% collection efficiency of detector.
The high signal to noise ratio in the data is evident from intensity line profiles extracted from the region indicated in the box in the EDS and EELS Pd elemental maps. 28

29. Elemental maps Mean signal Std. Dev. SNR Au M EELS Map 14468 856 17:1
Au EDS
Au EELS
Mean signal
Std. Dev.
SNR
Au M EELS Map
14468
856
17:1
Au M EDS Map
79.9
10.1
7.9:1
The signal intensity was analyzed from a uniform region of a Au particle. This 16x16 pixel region is show by the red box in the Au elemental maps
The SNR for the EELS data is ~17 while that for the EDS data is ~8 giving about a 2x improvement for the EELS data.
the EELS signal is more than twice as sensitive than the EDS data 29

30. Colorized Elemental Maps
EDS
EELS
Red: Pd
Green: Au
Despite the presence of heavy elements involved in the analysis, EELS maps show better contrast
Some details in the maps can be observed only in the EELS elemental maps

31. State of the Art SrTiO3 Example
Acknowledgements: Julia Mundy, Carolina Adamo, Darrell Schlom, David Muller, Cornell University
2012
(1024x1024)
10nm
Mn L
La M
Ti L
LaMnO3/SrMnO3 superlattice grown on SrTiO3
NION UltraSTEM with Enfinium ER
250pA
8GB of data!
2008
(64x64) 31

32. STEM-EELS Atomic-Resolution Electron Energy Loss Spectroscopy
La-doped CaTiO3
M.S. Varela, et al., Phy. Rev. Lett. 92 (2004)

33. 谢 谢 !