Electron Microscopy for Catalyst Characterization

Dr. King Lun YeungDepartment of Chemical Engineering

Hong Kong University of Science and Technology

CENG 511 Lecture 3

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

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

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 electronsdiamond

gold

TEM

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

Electron-Specimen Interaction

Cathodaluminescence

Electron-Specimen Interaction

Cathodaluminescence

Ion implanted silicon patterns

Electron-Specimen Interaction

X-rays

Sampling volumefor X-ray

X-rays

Si(Li) detector

Electron-Specimen Interaction

Si(Li) Detector

E Ne-

PULSE 1PULSE 2

Electron-Specimen Interaction

Si(Li) Detector Window

Electron-Specimen Interaction

Energy Dispersive X-ray Spectroscopy

Si (bright) Al (bright)

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

Scanning Electron Microscopy

specimen

Electron gun

SEM - Electron Gun

SEM - Electromagnetic Condenser Lenses

SEM - Electromagnetic Condenser Lenses

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

SEM - Electron Probe

SEM - Image Formation-1

SEM - Image Formation-2

Scanning Electron Microscopy

high voltage

low voltage

Effect of accelerating voltage

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

Scanning Electron MicroscopyEffect of accelerating voltage

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

Scanning Electron MicroscopyEffect of beam current and spot size

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

Scanning Electron MicroscopyEffect of accelerating voltage

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

Scanning Electron MicroscopyEffect of accelerating voltage

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

Scanning Electron MicroscopyIncorrect alignment of objective aperture

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

Scanning Electron MicroscopyEffect of specimen tilt

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

Stereo microscopy

Scanning Electron MicroscopyEffect of accelerating voltage

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

(1)

(2)

(3)

Scanning Electron MicroscopyContrast and brightness

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

Scanning Electron MicroscopyAstigmatism

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

Scanning Electron MicroscopySample charging

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

Scanning Electron MicroscopyPreventing charging by thin film coating

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

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

Scanning Electron MicroscopySources of image distortions

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

Scanning Electron MicroscopyInfluence of external disturbances

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

Scanning Electron MicroscopyImportance of sample preparation

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

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

Electron-Specimen Interaction

Principle of E. M. lithography

Polymer resist

Substrate

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

Microfabricated Catalysts

deposit alternate layers of catalyst and inert

micropattern and etch

undercut and remove

50 nm nickel, 50 nm SiO2

Supported Catalysts

Metal supported on metal oxide

Coarsening

Microfabricated CatalystsZeolite micropatterned catalysts

Zeolite Grids

(200)/(020) (101)

Zeolite Grids

Electron-Specimen Interaction

Electron beam

Thin sample

Unscatteredelectrons

Different Types of Electron Microscopy

SEM TEM Ultra-TEM

HREM

Transmission Electron Microscopy

Au/SiO2

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

Electron-Specimen Interaction

Transmission Electron Microscopy

Au

Transmission Electron Microscopy

Primary or unscattered electronsdiamond

gold

TEM

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 MorphologySelected zone dark field imaging (SZDF)

(100)

??

Particle MorphologySelected zone dark field imaging (SZDF)

(100)

(100)

(110)

Particle MorphologyWeak beam dark field (WBDF)

(100)

Particle MorphologySZDF and WBDF techniques

Electron-Specimen Interaction

Transmission Electron Microscopy

Distribution of crystallographic planes

Electron-Specimen Interaction

High Resolution Electron Microscopy

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

Bismuth molybdates (Bi2Mo3O12-)

High Resolution Electron Microscopy

Bismuth molybdates (Bi2MoO6-)

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