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-e- e-e- e-e- backscattered e - elemental contrast secondary e - surface topography Primary or unscattered e - projected sample image transmission electron microscopy
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
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 gold TEM
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
Electron-Specimen Interaction Cathodaluminescence
Electron-Specimen Interaction Cathodaluminescence Ion implanted silicon patterns
Electron-Specimen Interaction X-rays Sampling volume for X-ray X-rays Si(Li) detector
Electron-Specimen Interaction Si(Li) Detector E Ne - PULSE 1 PULSE 2
Electron-Specimen Interaction Si(Li) Detector Window
Electron-Specimen Interaction Energy Dispersive X-ray Spectroscopy Si (bright)Al (bright)
Electron-Specimen Interaction Auger Electron WKWK WLWL WMWM WNWN WGWG KK KK LL Auger e - or Auger e - Z
Scanning Electron Microscopy specimen Electron gun
SEM - Electron Gun
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
Scanning Electron Microscopy Effect of accelerating voltage
Scanning Electron Microscopy Effect of beam current and spot size
Scanning Electron Microscopy Effect of accelerating voltage
Scanning Electron Microscopy Effect of accelerating voltage
Scanning Electron Microscopy Incorrect alignment of objective aperture
Scanning Electron Microscopy Effect of specimen tilt Stereo microscopy
Scanning Electron Microscopy Effect of accelerating voltage (1) (2) (3)
Scanning Electron Microscopy Contrast and brightness
Scanning Electron Microscopy Astigmatism
Scanning Electron Microscopy Sample charging
Scanning Electron Microscopy Preventing charging by thin film coating
Scanning Electron Microscopy Electron beam damages and contamination Carbon contaminant deposited by electron beam Electron beam damage on a fly’s compound eye
Scanning Electron Microscopy Sources of image distortions
Scanning Electron Microscopy Influence of external disturbances
Scanning Electron Microscopy Importance of sample preparation
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
Electron-Specimen Interaction Principle of E. M. lithography Polymer resist Substrate
Electron Beam Lithography Micropatterning and Microfabrication PMMA resist E-beam develop resist selectively etch substrate
Microfabricated Catalysts deposit alternate layers of catalyst and inert micropattern and etch undercut and remove 50 nm nickel, 50 nm SiO 2
Supported Catalysts Metal supported on metal oxide Coarsening
Microfabricated Catalysts Zeolite micropatterned catalysts Zeolite Grids (200)/(020)(101) Zeolite Grids
Electron-Specimen Interaction Electron beam Thin sample Unscattered electrons
Different Types of Electron Microscopy SEM TEM Ultra-TEM HREM
Transmission Electron Microscopy Au/SiO 2
Electron-Specimen Interaction
Transmission Electron Microscopy Au
Transmission Electron Microscopy Primary or unscattered electrons diamond gold TEM
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
Electron-Specimen Interaction
Transmission Electron Microscopy Distribution of crystallographic planes
Electron-Specimen Interaction
High Resolution Electron Microscopy Bismuth molybdates (Bi 2 Mo 3 O 12 - )
High Resolution Electron Microscopy Bismuth molybdates (Bi 2 MoO 6 - )
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/SiO 2 Reduced Oxidized
High Resolution Electron Microscopy Rh particles
High Resolution Electron Microscopy Electron-beam induced reduction of RuCl 3 on MgO
High Resolution Electron Microscopy Hydrogen reduced Rhodium-TiO 2
Electron-Specimen Interaction