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Electron Microscopy for Catalyst Characterization
Dr. King Lun YeungDepartment of Chemical Engineering
Hong Kong University of Science and Technology
CENG 511 Lecture 3
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Electron-Specimen Interaction
e-
e-
e-
backscattered e-
elemental contrast
secondary e-
surface topography
Primary or unscattered e-
projected sample image transmission electron microscopyhttp://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
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Specimen Interaction Volume (Vi)
Augersecondary e-
backscattered e-
K X-rayL X-ray
incr
easi
ng d
epth surface information
bulk information
Vi when accelerating Vi when incident angle Vi when atomic number
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Electron-Specimen Interaction
Backscattered electrons Topography (A-B)
Composition (A+B)
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Electron-Specimen Interaction
Secondary electrons
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Electron-Specimen Interaction
Ugly BUGS
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Electron-Specimen Interaction
Surface Topography of Catalyst-related Materials
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Electron-Specimen Interaction
Primary or unscattered electronsdiamond
gold
TEM
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Electron-Specimen Interaction
e-
e-
e-
X-raysbulk elemental composition
Auger electronssurface elemental composition
Cathodaluminescenceband-gap energy, electronic property
http://jan.ucc.nau.edu/~wittke/Microprobe/ProbeNotes.html
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Electron-Specimen Interaction
Cathodaluminescence
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Electron-Specimen Interaction
Cathodaluminescence
Ion implanted silicon patterns
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Electron-Specimen Interaction
X-rays
Sampling volumefor X-ray
X-rays
Si(Li) detector
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Electron-Specimen Interaction
Si(Li) Detector
E Ne-
PULSE 1PULSE 2
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Electron-Specimen Interaction
Si(Li) Detector Window
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Electron-Specimen Interaction
Energy Dispersive X-ray Spectroscopy
Si (bright) Al (bright)
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Electron-Specimen Interaction
http://jan.ucc.nau.edu/~wittke/Microprobe/Interact.html#Aug
Auger Electron
WK
WL
WM
WN
WG
K
K
L
Auger e-or
Auger e- Z
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Scanning Electron Microscopy
specimen
Electron gun
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SEM - Electron Gun
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SEM - Electromagnetic Condenser Lenses
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SEM - Electromagnetic Condenser Lenses
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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
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SEM - Electron Probe
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SEM - Image Formation-1
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SEM - Image Formation-2
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Scanning Electron Microscopy
high voltage
low voltage
Effect of accelerating voltage
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyEffect of accelerating voltage
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyEffect of beam current and spot size
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyEffect of accelerating voltage
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyEffect of accelerating voltage
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyIncorrect alignment of objective aperture
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyEffect of specimen tilt
http://www.jeol.com/sem_gde/imgchng.html
Stereo microscopy
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Scanning Electron MicroscopyEffect of accelerating voltage
http://www.jeol.com/sem_gde/imgchng.html
(1)
(2)
(3)
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Scanning Electron MicroscopyContrast and brightness
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyAstigmatism
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopySample charging
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyPreventing charging by thin film coating
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyElectron beam damages and contamination
http://www.jeol.com/sem_gde/imgchng.html
Carbon contaminant deposited by electron beam
Electron beam damage on afly’s compound eye
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Scanning Electron MicroscopySources of image distortions
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyInfluence of external disturbances
http://www.jeol.com/sem_gde/imgchng.html
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Scanning Electron MicroscopyImportance of sample preparation
http://www.jeol.com/sem_gde/imgchng.html
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Electron-Specimen Interaction
e-
e-
e-
backscattered e-
elemental contrast
secondary e-
surface topography
Primary or unscattered e-
projected sample image transmission electron microscopyhttp://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
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Electron-Specimen Interaction
Principle of E. M. lithography
Polymer resist
Substrate
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Electron Beam Lithography
Micropatterning and Microfabrication
PMMA resist
E-beam develop resist selectively etchsubstrate
http://www.cnf.cornell.edu/SPIEBook/spie5.htm#2.5.3.1
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Microfabricated Catalysts
deposit alternate layers of catalyst and inert
micropattern and etch
undercut and remove
50 nm nickel, 50 nm SiO2
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Supported Catalysts
Metal supported on metal oxide
Coarsening
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Microfabricated CatalystsZeolite micropatterned catalysts
Zeolite Grids
(200)/(020) (101)
Zeolite Grids
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Electron-Specimen Interaction
Electron beam
Thin sample
Unscatteredelectrons
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Different Types of Electron Microscopy
SEM TEM Ultra-TEM
HREM
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Transmission Electron Microscopy
Au/SiO2
http://www.mwrn.com/guide.htmhttp://www.hei.org/research/depts/aemi/micro.htm
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Electron-Specimen Interaction
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Transmission Electron Microscopy
Au
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Transmission Electron Microscopy
Primary or unscattered electronsdiamond
gold
TEM
http://em-outreach.sdsc.edu/web-course
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Transmission Electron Microscopy
Catalyst particle size distribution
Size (nm)
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Transmission Electron Microscopy
Catalyst particle shape and morphology
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Particle MorphologySelected zone dark field imaging (SZDF)
(100)
??
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Particle MorphologySelected zone dark field imaging (SZDF)
(100)
(100)
(110)
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Particle MorphologyWeak beam dark field (WBDF)
(100)
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Particle MorphologySZDF and WBDF techniques
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Electron-Specimen Interaction
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Transmission Electron Microscopy
Distribution of crystallographic planes
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Electron-Specimen Interaction
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High Resolution Electron Microscopy
http://bnlstb.bio.bnl.gov/biodocs/stem/interactive.htmlx
Bismuth molybdates (Bi2Mo3O12-)
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High Resolution Electron Microscopy
Bismuth molybdates (Bi2MoO6-)
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High Resolution Electron Microscopy
Platinum on Alumina
hydrogen
Hydrogen sulfide
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High Resolution Electron Microscopy
2 x 1 reconstruction of (110) surface of Au particle
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High Resolution Electron Microscopy
Rh/SiO2
Reduced Oxidized
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High Resolution Electron Microscopy
Rh particles
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High Resolution Electron Microscopy
Electron-beam induced reduction of RuCl3 on MgO
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High Resolution Electron Microscopy
Hydrogen reduced Rhodium-TiO2
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Electron-Specimen Interaction