电子能量损失谱

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

4. What is an EELS spectrum? Elastic scattering Inelastic scattering L L K Carbon atom K Zero loss Electrons count C K 1 eV Electron energy loss (eV) 290 0

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。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： 5.70ev(一次激发) 11.4ev(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。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: 14.95ev 29.9ev 44.35ev 59.8ev

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 80-120 nm various materials

10. 内壳层电子激发 偶极跃迁：Δl = ±1

11. Correlation between EELS and specimen feature 11

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) Final EELS readout • Spectrum is enlarged and optimally coupled to detector EELS spectrum projected onto CCD 16

17. Energy-loss spectroscopy (EELS - core loss) Final EELS readout Mn L edge O K edge • The spectrum is shifted • Best to do by changing prism current preserve probe focus 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 process 20

21. Spectrum Imaging – EFTEM mode 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 • 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

22. Spectrum imaging - STEM EELS mode 22

23. Spectrum imaging - STEM EELS mode 23

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 EELS colorized elemental map As elemental map Ga: Green As: Red Ga elemental map • The GaAs dumbbell is clearly resolved with high contrast 27

28. EELS Pd EDS Pd Elemental maps 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 Au EDS Au EELS • 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 2012 (1024x1024) Mn L La M Ti L 2008 (64x64) 10nm 31 • LaMnO3/SrMnO3 superlattice grown on SrTiO3 • NION UltraSTEM with Enfinium ER • 2msec/pixel @ 250pA • 8GB of data! Acknowledgements: Julia Mundy, Carolina Adamo, Darrell Schlom, David Muller, Cornell University

32. Atomic-Resolution Electron Energy Loss Spectroscopy STEM-EELS La-doped CaTiO3 M.S. Varela, et al., Phy. Rev. Lett. 92 (2004) 095502

33. 谢 谢 !