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CENG 511 Lecture 3. Electron Microscopy for Catalyst Characterization Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology. Electron-Specimen Interaction. backscattered e - elemental contrast. e -. e -. secondary e -

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CENG 511

Lecture 3

Electron Microscopy for Catalyst Characterization

Dr. King Lun Yeung

Department of Chemical Engineering

Hong Kong University of Science and Technology


Electron-Specimen Interaction

backscattered e-

elemental contrast

e-

e-

secondary e-

surface topography

e-

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


Auger

secondary e-

backscattered e-

K X-ray

L X-ray

surface information

increasing depth

bulk information

Specimen Interaction Volume (Vi)

Vi when accelerating 

Vi when incident angle 

Vi when atomic number 


Topography (A-B)

Composition (A+B)

Electron-Specimen Interaction

Backscattered electrons


Electron-Specimen Interaction

Secondary electrons



Electron-Specimen Interaction

Surface Topography of Catalyst-related Materials


Electron-Specimen Interaction

Primary or unscattered electrons

diamond

TEM

gold


Electron-Specimen Interaction

e-

Cathodaluminescence

band-gap energy, electronic property

X-rays

bulk elemental composition

e-

Auger electrons

surface elemental composition

e-

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


Electron-Specimen Interaction

Cathodaluminescence


Electron-Specimen Interaction

Cathodaluminescence

Ion implanted silicon patterns


Electron-Specimen Interaction

X-rays

Si(Li) detector

X-rays

Sampling volume

for X-ray


Electron-Specimen Interaction

Si(Li) Detector

l  E   Ne- 

PULSE 2

PULSE 1


Electron-Specimen Interaction

Si(Li) Detector Window


Electron-Specimen Interaction

Energy Dispersive X-ray Spectroscopy

Si (bright)

Al (bright)


Ka

WK

Kb

La

WL

or

Auger e-

WM

WN

WG

Electron-Specimen Interaction

Auger Electron

Auger e-  Z 

http://jan.ucc.nau.edu/~wittke/Microprobe/Interact.html#Aug


Electron gun

specimen

Scanning Electron Microscopy





SEM - Objective Len

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.





high voltage

low voltage

Scanning Electron Microscopy

Effect of accelerating voltage

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Effect of accelerating voltage

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Effect of beam current and spot size

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Effect of accelerating voltage

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Effect of accelerating voltage

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Incorrect alignment of objective aperture

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Effect of specimen tilt

http://www.jeol.com/sem_gde/imgchng.html

Stereo microscopy


Scanning Electron Microscopy

(1)

Effect of accelerating voltage

(2)

(3)

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Contrast and brightness

http://www.jeol.com/sem_gde/imgchng.html


http://www.jeol.com/sem_gde/imgchng.html

Scanning Electron Microscopy

Astigmatism


Scanning Electron Microscopy

Sample charging

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Preventing charging by thin film coating

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Electron beam damages and contamination

Carbon contaminant deposited by

electron beam

http://www.jeol.com/sem_gde/imgchng.html

Electron beam damage on a

fly’s compound eye


Scanning Electron Microscopy

Sources of image distortions

http://www.jeol.com/sem_gde/imgchng.html


Scanning Electron Microscopy

Influence of external disturbances

http://www.jeol.com/sem_gde/imgchng.html


http://www.jeol.com/sem_gde/imgchng.html

Scanning Electron Microscopy

Importance of sample preparation


Electron-Specimen Interaction

backscattered e-

elemental contrast

e-

e-

secondary e-

surface topography

e-

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


Electron-Specimen Interaction

Principle of E. M. lithography

Polymer resist

Substrate


Electron Beam Lithography

Micropatterning and Microfabrication

E-beam

develop resist

selectively etch

substrate

PMMA resist

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


Microfabricated Catalysts

50 nm nickel, 50 nm SiO2

deposit alternate layers

of catalyst and inert

micropattern and etch

undercut and remove


Supported Catalysts

Metal supported on metal oxide

Coarsening


Microfabricated Catalysts

Zeolite micropatterned catalysts

Zeolite Grids

Zeolite Grids

(200)/(020)

(101)


Electron beam

Thin sample

Unscattered

electrons

Electron-Specimen Interaction



Transmission Electron Microscopy

Au/SiO2

http://www.mwrn.com/guide.htm

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




Transmission Electron Microscopy

Primary or unscattered electrons

diamond

TEM

gold

http://em-outreach.sdsc.edu/web-course


Transmission Electron Microscopy

Catalyst particle size distribution


Transmission Electron Microscopy

Catalyst particle shape and morphology


Particle Morphology

Selected zone dark field imaging (SZDF)

?

?


Particle Morphology

Selected zone dark field imaging (SZDF)

(100)

(110)


Particle Morphology

Weak beam dark field (WBDF)


Particle Morphology

SZDF and WBDF techniques



Transmission Electron Microscopy

Distribution of crystallographic planes



High Resolution Electron Microscopy

Bismuth molybdates (Bi2Mo3O12-a)

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


High Resolution Electron Microscopy

Bismuth molybdates (Bi2MoO6-g)


High Resolution Electron Microscopy

Platinum on Alumina

hydrogen

Hydrogen sulfide


High Resolution Electron Microscopy

2 x 1 reconstruction of (110) surface of Au particle


High Resolution Electron Microscopy

Rh/SiO2

Oxidized

Reduced



High Resolution Electron Microscopy

Electron-beam induced reduction of RuCl3 on MgO


High Resolution Electron Microscopy

Hydrogen reduced Rhodium-TiO2



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