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Electron Microscopy for Catalyst Characterization Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology.

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Presentation on theme: "Electron Microscopy for Catalyst Characterization Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology."— Presentation transcript:

1 Electron Microscopy for Catalyst Characterization Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology CENG 511 Lecture 3

2 Electron-Specimen Interaction e-e- e-e- e-e- backscattered e - elemental contrast secondary e - surface topography Primary or unscattered e - projected sample image transmission electron microscopy

3 Specimen Interaction Volume (V i ) Auger secondary e- backscattered e- K X-ray L X-ray increasing depth surface information bulk information V i  when accelerating  V i  when incident angle  V i  when atomic number 

4 Electron-Specimen Interaction Backscattered electrons Topography (A-B) Composition (A+B)

5 Electron-Specimen Interaction Secondary electrons

6 Electron-Specimen Interaction Ugly BUGS

7 Electron-Specimen Interaction Surface Topography of Catalyst-related Materials

8 Electron-Specimen Interaction Primary or unscattered electrons diamond gold TEM

9 Electron-Specimen Interaction e-e- e-e- e-e- X-rays bulk elemental composition Auger electrons surface elemental composition Cathodaluminescence band-gap energy, electronic property

10 Electron-Specimen Interaction Cathodaluminescence

11 Electron-Specimen Interaction Cathodaluminescence Ion implanted silicon patterns

12 Electron-Specimen Interaction X-rays Sampling volume for X-ray X-rays Si(Li) detector

13 Electron-Specimen Interaction Si(Li) Detector   E   Ne -  PULSE 1 PULSE 2

14 Electron-Specimen Interaction Si(Li) Detector Window

15 Electron-Specimen Interaction Energy Dispersive X-ray Spectroscopy Si (bright)Al (bright)

16 Electron-Specimen Interaction Auger Electron WKWK WLWL WMWM WNWN WGWG KK KK LL Auger e - or Auger e -   Z 

17 Scanning Electron Microscopy specimen Electron gun

18 SEM - Electron Gun

19 SEM - Electromagnetic Condenser Lenses

20

21 Figure C-8. The light optics (4) and scanning coils (1) are located inside the minicoil probe- forming lens (2) at the base of the electron column. The pole piece (7) is one solid piece of metal and protects the sample from stray magnetic fields. The x-ray beams (3) are collimated by small apertures (6), and pass through an electron trap (5) that prevents backscattered electrons from entering the x-ray pectrometers. SEM - Objective Len

22 SEM - Electron Probe

23 SEM - Image Formation-1

24 SEM - Image Formation-2

25 Scanning Electron Microscopy high voltage low voltage Effect of accelerating voltage

26 Scanning Electron Microscopy Effect of accelerating voltage

27 Scanning Electron Microscopy Effect of beam current and spot size

28 Scanning Electron Microscopy Effect of accelerating voltage

29 Scanning Electron Microscopy Effect of accelerating voltage

30 Scanning Electron Microscopy Incorrect alignment of objective aperture

31 Scanning Electron Microscopy Effect of specimen tilt Stereo microscopy

32 Scanning Electron Microscopy Effect of accelerating voltage (1) (2) (3)

33 Scanning Electron Microscopy Contrast and brightness

34 Scanning Electron Microscopy Astigmatism

35 Scanning Electron Microscopy Sample charging

36 Scanning Electron Microscopy Preventing charging by thin film coating

37 Scanning Electron Microscopy Electron beam damages and contamination Carbon contaminant deposited by electron beam Electron beam damage on a fly’s compound eye

38 Scanning Electron Microscopy Sources of image distortions

39 Scanning Electron Microscopy Influence of external disturbances

40 Scanning Electron Microscopy Importance of sample preparation

41 Electron-Specimen Interaction e-e- e-e- e-e- backscattered e - elemental contrast secondary e - surface topography Primary or unscattered e - projected sample image transmission electron microscopy

42 Electron-Specimen Interaction Principle of E. M. lithography Polymer resist Substrate

43 Electron Beam Lithography Micropatterning and Microfabrication PMMA resist E-beam develop resist selectively etch substrate

44 Microfabricated Catalysts deposit alternate layers of catalyst and inert micropattern and etch undercut and remove 50 nm nickel, 50 nm SiO 2

45 Supported Catalysts Metal supported on metal oxide Coarsening

46 Microfabricated Catalysts Zeolite micropatterned catalysts Zeolite Grids (200)/(020)(101) Zeolite Grids

47 Electron-Specimen Interaction Electron beam Thin sample Unscattered electrons

48 Different Types of Electron Microscopy SEM TEM Ultra-TEM HREM

49 Transmission Electron Microscopy Au/SiO 2

50 Electron-Specimen Interaction

51 Transmission Electron Microscopy Au

52 Transmission Electron Microscopy Primary or unscattered electrons diamond gold TEM

53 Transmission Electron Microscopy Catalyst particle size distribution

54 Transmission Electron Microscopy Catalyst particle shape and morphology

55 Particle Morphology Selected zone dark field imaging (SZDF) ? ?

56 Particle Morphology Selected zone dark field imaging (SZDF)  (100) (110)

57 Particle Morphology Weak beam dark field (WBDF) 

58 Particle Morphology SZDF and WBDF techniques

59 Electron-Specimen Interaction

60 Transmission Electron Microscopy Distribution of crystallographic planes

61 Electron-Specimen Interaction

62 High Resolution Electron Microscopy Bismuth molybdates (Bi 2 Mo 3 O 12 -  )

63 High Resolution Electron Microscopy Bismuth molybdates (Bi 2 MoO 6 -  )

64 High Resolution Electron Microscopy Platinum on Alumina hydrogen Hydrogen sulfide

65 High Resolution Electron Microscopy 2 x 1 reconstruction of (110) surface of Au particle

66 High Resolution Electron Microscopy Rh/SiO 2 Reduced Oxidized

67 High Resolution Electron Microscopy Rh particles

68 High Resolution Electron Microscopy Electron-beam induced reduction of RuCl 3 on MgO

69 High Resolution Electron Microscopy Hydrogen reduced Rhodium-TiO 2

70 Electron-Specimen Interaction


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