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 http://www.jeol.com/sem_gde/imgchng.html http://www.unl.edu/CMRAcfem/ http://www.ou.edu/research/electron/www-vl/ http://www.mwrn.com/guide/electron_microscopy/microscope.htm

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 http://jan.ucc.nau.edu/~wittke/Microprobe/ProbeNotes.html

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 http://jan.ucc.nau.edu/~wittke/Microprobe/Interact.html#Aug 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 http://www.jeol.com/sem_gde/imgchng.html

26 Scanning Electron Microscopy Effect of accelerating voltage http://www.jeol.com/sem_gde/imgchng.html

27 Scanning Electron Microscopy Effect of beam current and spot size http://www.jeol.com/sem_gde/imgchng.html

28 Scanning Electron Microscopy Effect of accelerating voltage http://www.jeol.com/sem_gde/imgchng.html

29 Scanning Electron Microscopy Effect of accelerating voltage http://www.jeol.com/sem_gde/imgchng.html

30 Scanning Electron Microscopy Incorrect alignment of objective aperture http://www.jeol.com/sem_gde/imgchng.html

31 Scanning Electron Microscopy Effect of specimen tilt http://www.jeol.com/sem_gde/imgchng.html Stereo microscopy

32 Scanning Electron Microscopy Effect of accelerating voltage http://www.jeol.com/sem_gde/imgchng.html (1) (2) (3)

33 Scanning Electron Microscopy Contrast and brightness http://www.jeol.com/sem_gde/imgchng.html

34 Scanning Electron Microscopy Astigmatism http://www.jeol.com/sem_gde/imgchng.html

35 Scanning Electron Microscopy Sample charging http://www.jeol.com/sem_gde/imgchng.html

36 Scanning Electron Microscopy Preventing charging by thin film coating http://www.jeol.com/sem_gde/imgchng.html

37 Scanning Electron Microscopy Electron beam damages and contamination http://www.jeol.com/sem_gde/imgchng.html Carbon contaminant deposited by electron beam Electron beam damage on a fly’s compound eye

38 Scanning Electron Microscopy Sources of image distortions http://www.jeol.com/sem_gde/imgchng.html

39 Scanning Electron Microscopy Influence of external disturbances http://www.jeol.com/sem_gde/imgchng.html

40 Scanning Electron Microscopy Importance of sample preparation http://www.jeol.com/sem_gde/imgchng.html

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 http://www.jeol.com/sem_gde/imgchng.html http://www.unl.edu/CMRAcfem/ http://www.ou.edu/research/electron/www-vl/ http://www.mwrn.com/guide/electron_microscopy/microscope.htm

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 http://www.cnf.cornell.edu/SPIEBook/spie5.htm#2.5.3.1

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 http://www.mwrn.com/guide.htm http://www.hei.org/research/depts/aemi/micro.htm

50 Electron-Specimen Interaction

51 Transmission Electron Microscopy Au

52 Transmission Electron Microscopy Primary or unscattered electrons diamond gold TEM http://em-outreach.sdsc.edu/web-course

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 http://bnlstb.bio.bnl.gov/biodocs/stem/interactive.htmlx 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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