Electron Microscopy for Catalyst Characterization
Dr. King Lun Yeung
Department of Chemical Engineering
Hong Kong University of Science and Technology
CENG 511
Lecture 3
Electron-Specimen Interaction
e-
backscattered eelemental contrast
e- secondary esurface topography
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
ePrimary or unscattered eprojected sample image
transmission electron microscopy
Auger
secondary ebackscattered eK X-ray
L X-ray
increasing depth
Specimen Interaction Volume (Vi)
surface information
bulk information
Vi  when accelerating 
Vi  when incident angle 
Vi  when atomic number 
Electron-Specimen Interaction
Backscattered electrons
Topography (A-B)
Composition (A+B)
Electron-Specimen Interaction
Secondary electrons
Electron-Specimen Interaction
Ugly BUGS
Electron-Specimen Interaction
Surface Topography of Catalyst-related Materials
Electron-Specimen Interaction
Primary or unscattered electrons
diamond
TEM
gold
Electron-Specimen Interaction
eCathodaluminescence
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)
Electron-Specimen Interaction
Auger Electron
Ka
WK
WL
Auger e-   Z 
Kb
La
or
Auger e-
WM
WN
WG
http://jan.ucc.nau.edu/~wittke/Microprobe/Interact.html#Aug
Scanning Electron Microscopy
Electron gun
specimen
SEM - Electron Gun
SEM - Electromagnetic Condenser Lenses
SEM - Electromagnetic Condenser Lenses
SEM - Objective Len
Figure C-8. The light optics (4) and scanning
coils (1) are located inside the minicoil probeforming 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 - Electron Probe
SEM - Image Formation-1
SEM - Image Formation-2
Scanning Electron Microscopy
Effect of accelerating voltage
high voltage
low 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
Effect of accelerating voltage
(1)
(2)
http://www.jeol.com/sem_gde/imgchng.html
(3)
Scanning Electron Microscopy
Contrast and brightness
http://www.jeol.com/sem_gde/imgchng.html
Scanning Electron Microscopy
Astigmatism
http://www.jeol.com/sem_gde/imgchng.html
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
Scanning Electron Microscopy
Importance of sample preparation
http://www.jeol.com/sem_gde/imgchng.html
Electron-Specimen Interaction
e-
backscattered eelemental contrast
e- secondary esurface topography
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
ePrimary or unscattered eprojected sample image
transmission electron microscopy
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-Specimen Interaction
Electron beam
Thin sample
Unscattered
electrons
Different Types of Electron Microscopy
SEM
TEM
HREM
Ultra-TEM
Transmission Electron Microscopy
Au/SiO2
http://www.mwrn.com/guide.htm
http://www.hei.org/research/depts/aemi/micro.htm
Electron-Specimen Interaction
Transmission Electron Microscopy
Au
Transmission Electron Microscopy
Primary or unscattered electrons
diamond
TEM
gold
http://em-outreach.sdsc.edu/web-course
Transmission Electron Microscopy
Catalyst particle size distribution
Size (nm)
Transmission Electron Microscopy
Catalyst particle shape and morphology
Particle Morphology
Selected zone dark field imaging (SZDF)
?
?
(100)
Particle Morphology
Selected zone dark field imaging (SZDF)
(100)
(110)
(100)

Particle Morphology
Weak beam dark field (WBDF)
(100)

Particle Morphology
SZDF and WBDF techniques
Electron-Specimen Interaction
Transmission Electron Microscopy
Distribution of crystallographic planes
Electron-Specimen Interaction
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
Reduced
Oxidized
High Resolution Electron Microscopy
Rh particles
High Resolution Electron Microscopy
Electron-beam induced reduction of RuCl3 on MgO
High Resolution Electron Microscopy
Hydrogen reduced Rhodium-TiO2
Electron-Specimen Interaction