1. 1
Electron Microscopy II
Transmission - , Scanning Transmission - and
Analytical Electron Microscopy
krumeich@inorg.chem.ethz.ch
www.microscopy.ethz.ch
Electron Microscopy Methods
Transmission Electron Microscopy (TEM)
Bright / Dark Field (BF/DF)
High-Resolution Transition Electron Microscopy (HRTEM)
Energy-Filtered (EFTEM)
Electron Diffraction (ED)
Scanning Transmission Electron Microscopy (STEM)
Bright / Dark Field (BF/DF-STEM)
High-Angle Annular Dark Field (HAADF-STEM)
Analytical Electron Microscopy (AEM)
X-ray Spectroscopy
Electron Energy-Loss Spectroscopy (EELS)
Electron Spectroscopic Imaging (ESI)
Scanning Electron Microscopy (SEM)
Secondary Electrons (SE)
Back-Scattered Electrons (BSE)

2. 2
Development of the First Transmission
Electron Microscope
Knoll, Ruska, Z. Phys. 78 (1932) 318
1927 Hans Busch: Electron beams
can be focused in an inhomogeneous
magnetic field.
1931 Max Knoll and Ernst Ruska
built the first TEM.
1986 Nobel prize for Ruska
History of Electron Microscopy
1938 First Siemens electron microscope (resolution ca. 13 nm)
History of Electron Microscopy

3. 3
1939: first TEM serially
produced by Siemens
resolution ca. 7 nm
History of Electron Microscopy
Transmission Electron Microscopes
∼1970: HRTEM
Philips EM400, V = 120 kV
resolution ca. 0.35 nm
∼1990
Philips CM30, V = 300 kV
resolution ca. 0.2 nm
Transmission Electron Microscopy
Magnetic Lens
An electron in a magnetic
field (here: inhomogeneous,
but axially symmetric)
experiences the Lorentz
force F:
F = -e (E + v x B)
|F| = evBsin(v,B)
E: strength of electric field
B: strength of magnetic field
e/v: charge/velocity of electrons

4. 4
Transmission Electron Microscopy
Magnetic Lens
Lens
Back focal plane
Image plane
Object plane
Light optical analogue
Lens equation: 1/u + 1/v = 1/f
Magnification M = v/u
Lens problems:
spherical aberation Cs
chromatic aberation Cc
astigmatism
Transmission Electron Microscopy
Cross-Section of the Column of a CM30 Microscope
accelerator
electron gun
condenser system
objective lenses
sample
diffraction lens
intermediate lens
projector lenses
viewing screen
photo camera
TV, SlowScan
CCD Camera

5. 5
Electron Guns
Thermoionic Guns
Electron emission by heating
Transmission Electron Microscopy
Field Emission Guns
(FEG)
Electron emission by applying
an extraction voltage
W
W
LaB6
>1000500100Lifetime / h
10135x1010109Brightness / A/m2sr
(30-)3005001000Maximum current / nA
3-20500030000Source size / nm
0.4-1.51.5-33-4Energy spread / eV
(300-)180020002700Temperature / K
4.52.44.5Work function / eV
FEGLaB6WProperties
TEM – Imaging and Diffraction
Optic axis
Objective lens
Back focal plane
Image plane
Object plane
↓
Diffraction pattern
Transmission Electron Microscopy

6. 6
TEM – Imaging and Diffraction
Optic axis
Image plane
Diffraction pattern
Transmission Electron Microscopy
Diffraction and Imaging Mode
Transmission Electron Microscopy

7. 7
TEM – Imaging and Diffraction
Optic axis
Diffraction pattern
Image
Bright field image
- mass-thickness contrast
- Bragg contrast
Transmission Electron Microscopy
TEM – Imaging and Diffraction
Optic axis
Diffraction pattern
Image Dark field image
Transmission Electron Microscopy

8. 8
Elastic Scattering of Electrons by an Atom
Transmission Electron Microscopy
Weak Coulomb interaction within the
electron cloud
⇒ low-angle scattering
Strong Coulomb interaction with the
nucleus
⇒ scattering into high angles or even
backwards (Rutherford scattering)
⇒ atomic-number (Z) contrast
Types of Image Contrast
Mass-Thickness contrast
Transmission Electron Microscopy
Bragg contrast
Coherent scattering
Diffracted beams do not pass through the
objective aperture leading to a decreased
intensity of crystalline areas

9. 9
BF Images
Transmission Electron Microscopy
Amorphous SiO2 on C foil
Mainly thickness contrast
Au particles (black) on TiO2
Mainly mass contrast
Increasing thickness
BF Images
Transmission Electron Microscopy
ZrO2 micro crystals; crystals orientated close
to zone axis appear dark
Mainly Bragg contrast
Increasing thickness

10. 10
BF and DF imaging
Pt-Particles in SiO2 nanotubes
Transmission Electron Microscopy
BF DF conical DF
TEM – Imaging and Diffraction
Optic axis
Image plane
Diffraction pattern
Transmission Electron Microscopy

11. 11
TEM – Imaging and Diffraction
Optic axis
Diffraction pattern
Image
High-resolution image
Interference of several
diffracted beams with the
direct beam
Transmission Electron Microscopy
TEM – Imaging and Diffraction
Optic axis
Diffraction pattern
Image
Mathematics
+
-2i qx
-
{f(x)} ( ) e dx
∞
π
∞
= ∫F f x
Fourier Transform
Fourier analysis
Fourier synthesis
Transmission Electron Microscopy

12. 12
TEM – Imaging and Diffraction
Optic axis
Diffraction pattern
HRTEM image
Image Processing
Fourier Transform
Fourier Transform
Filtered image
Transmission Electron Microscopy
ED + HRTEM
Nb8W9O47 – threefold TTB
superstructure
Transmission Electron Microscopy

13. 13
HRTEM: Detection of Defects
Planar defect in ZnNb14O35F2
Transmission Electron Microscopy
HRTEM: Detection of Defects
Grain boundary between differently
ordered areas in a Nb-W oxide
Transmission Electron Microscopy
10 nm

14. 14
HRTEM and ED of Aperiodic Structures
Dodecagonal quasicrystal in the system Ta-Te
Transmission Electron Microscopy
HRTEM: Imaging Single Atoms
Gd@C82 in SWCNT
Suenaga et al, Science 290 (2000) 2280
3 nm
3 nm
Transmission Electron Microscopy

15. 15
Transmission Electron Microscopy
Contrast:
• Mass-thickness (BF/DF)
• Bragg (BF/DF)
• Phase (HRTEM)
Determination of
• Structure: HRTEM
• Defects: HRTEM, TEM
• Lattice constants and symmetry: ED
• Particle size: TEM, HRTEM
Transmission Electron Microscopy
Scanning Transmission Electron
Microscopy (STEM)
Scanning Transmission Electron Microscopy
From: Williams, Carter: Transmission Electron Microscopy

16. 16
BF and DF Imaging in STEM
Au islands
on a C film
DF image
recorded by the
annular dark
field detector
BF image
recorded by the
bright field
detector
Scanning Transmission Electron Microscopy
From: Williams, Carter: Transmission Electron Microscopy
STEM
Detectors
BF: Bright Field detector
ADF: Annular Dark Field detector
HAADF: High Angle Annular Dark Field detector
Scanning Transmission Electron Microscopy
10 mrad ≈ 0.57°
From: Williams, Carter: Transmission Electron Microscopy

17. 17
BF and DF Imaging in STEM
Scanning Transmission Electron Microscopy
Pt Particles in SiO2 nanotubes
BF ADF HAADF
BF DF conical DF TEM
HAADF-STEM or Z contrast Images of
Au Particles on Titania
Scanning Transmission Electron Microscopy
50 nm
10 nm

18. 18
High-Resolution HAADF-STEM
WO3 segregations in a
bronze-type Nb-W oxide
Scanning Transmission Electron Microscopy
HRTEM
2 nm
HAADF-STEM of Nb8W9O47
Information about Elemental Distribution
in HAADF-STEM or Z contrast images
Single-crystal X-ray structure
of Nb8W9O47
ca. 80% Nb 100% W
P21212 a=12.26, b=36.63, c=3.95 Å
ca. 80% Nb100% W

19. 19
Scanning Transmission Electron
Microscopy
Contrast:
• Mass-thickness (BF/DF)
• Bragg (BF/DF)
• Z2 (HAADF)
Determination of
• Particles on support: HAADF
• Structure and defects : HR
Important: Combination with EDXS or EELS
Scanning Transmission Electron Microscopy
Interactions of Electrons with Matter
XEDS (EDX, EDS),
WDS, EPMA
SEM
SEM
AES
elastic scattering:
TEM, HRTEM,
STEM, SAED, CBED
inelastic scattering:
EELS, ESI
specimen
electron
beam
scattered
electrons
direct
beam
X rays
backscattered
electrons
Auger
electrons
secondary
electrons

20. 20
Generation of X-rays
1. Ionization
2. X-ray emission
Analytical Transmission Electron Microscopy
Generation of X-rays
1. Ionization
2. X-ray
emission
Inelastic interactions
α1 α2
β1
α1

21. 21
Electron Configuration of Ti: 1s2 2s2 2p6 3s2 3p6 4s2 3d2
energy
1s
2s
3s
4s
2p
3p
4p
3d
K
L
M
N
Kα
Kβ
Inelastic interactions
Energy-Dispersive X-ray Spectroscopy (EDXS)
Analytical Transmission Electron Microscopy
Au-Particles on TiO2
Intensity/counts
Energy / keV
Deceleration of incident
electrons by interaction
with Coulomb field of
nucleus leads to
uncharacteristic
spectrum background
(bremsstrahlung).
Ti L

22. 22
Possible Transitions Between Electron Shells
causing characteristic K, L, M X-rays
Analytical Transmission Electron Microscopy
Quantitative EDXS
Cliff-Lorimer Equation:
NA/NB = kAB IA/IB
NA,NB: atomic % of element A,B
IA/IB: measured intensity of element A,B
kAB: Cliff-Lorimer factor
Analytical Transmission Electron Microscopy

23. 23
X-ray Spectrometer
Analytical Transmission Electron Microscopy
Schematic representation of a energy-dispersive spectrometer with
electronic units. Spectrometers can be attached to TEMs and SEMs.
STEM @ EDXS: Point Analyses
HAADF-STEM of Pd/Pt
particles on alumina
Analytical Transmission Electron Microscopy
Pt
Pd
Pt
Pt
Cu
Al
O
C
Pt
Pd
Pt Pt
Cu
Al
O
C

24. 24
STEM @ EDXS: Point Analyses
500 nm
1
HAADF Detector
Energy (keV)
Counts
20151050
60
40
20
0
W
W
W WW
W
Mo
MoM
Mo
Mo MoMo
Cu
Cu
EDX HAADF Detector Point 1
Analytical Transmission Electron Microscopy
(Mo,W)Ox or
MoOx and WOx?
Interactions of Electrons with Matter
XEDS (EDX, EDS),
WDS, EPMA
SEM
SEM
AES
elastic scattering:
TEM, HRTEM,
STEM, SAED, CBED
inelastic scattering:
EELS, ESI
specimen
electron
beam
scattered
electrons
direct
beam
X rays
backscattered
electrons
Auger
electrons
secondary
electrons
Phonons: lattice vibrations (sample
heating)
Plasmons: electron gas oscillations
Cathodoluminescence: electron-
holes in semiconductors

25. 25
Electron Energy Loss Spectroscopy (EELS)
Analytical Transmission Electron Microscopy
Electron Energy Loss Spectroscopy
Analytical Transmission Electron Microscopy
Relationship between the EEL Spectrum and a Core-Loss
Exication within the Band Structure
ELNES:
Electron Energy Loss Near
Edge Structure
reflects local density of
unoccupied states corresponds
to XANES
EXELFS:
EXtended Energy Loss Fine
Structure
information on local atomic
arrangements corresponds to
EXAFS
Filled states Empty states
EF E
N(E)
Extended fine
structure
Near edge
fine structure

26. 26
Fine structures in EELS
Analytical Transmission Electron Microscopy
Characteristics of the C_K edge
depending on hybridization
Characteristics of the Cu_L2,3
edges depending on oxidation
state of Cu
HRTEM and EELS: Imaging and Detection of
Single Atoms
Gd@C82 in SWCNT
Suenaga et al, Science 290 (2000) 2280
3 nm
3 nm
Transmission Electron Microscopy

27. 27
Elemental Maps by Electron
Spectroscopic Imaging (ESI)
Post-column filter
gun
round lens
sample holder
aperture (objective and sel. area)
aperture (filter entrance)
prism (with straight edges)
prism (with curved edges)
energy-selecting slit
quadrupole lens
sextupole lens
CCD camera
Energy-filtered image
EELS (section) of VOx-NTs
3 window method
Analytical Transmission Electron Microscopy
Elemental Maps by Electron
Spectroscopic Imaging (ESI)
TEM image Vanadium map Carbon map
V and C, respectively, are located at the
sites appearing with bright contrast.
Analytical Transmission Electron Microscopy

28. 28
Imaging of Elemental Distribution
TEM image Ag_M map
M edge: 367 eV
Au_M map
M edge: 2206 eV
Ag/Au Particles on Silica
Analytical Transmission Electron Microscopy
EELS (EFTEM) versus EDXS (x-ray mapping)
Slow technique; only simple
processing required
Fast technique; but complex
processing required
Inefficient signal generation, collection
and detection
=> inefficient x-ray mapping
Very efficient and higher sensitivity to
most elements
=> very efficient mapping technique
Energy resolution > 100 eV causes
frequent overlaps
Energy resolution 0.3-2 eV results in
far fewer overlaps; fine structures
X-rays provide elemental information
only
Elemental, chemical and dielectric
information
High detection efficiency for high Z
elements
High detection efficiency for low Z
elements
EDXSEELS
Analytical Transmission Electron Microscopy

29. 29
Analytical Electron Microscopy
• Qualitative and quantitative information about
the composition: EDXS, EELS
• Bonding, coordination, interatomic distances:
Fine structure in EELS (ELNES, EXEFS)
• Locally resolved information about composition
1. STEM + EDXS and/or EELS
2. ESI
Analytical Transmission Electron Microscopy
Analytical Electron Microscopy
- Restrictions
• Electron-matter interactions are mostly elastic
⇒ high electron dose necessary
• Long recording times
⇒ high sample stability and absence of drift
• Ionization edges occur at different energies and
are of different shape
⇒ not all methods are equally suitable for
all elements
Analytical Transmission Electron Microscopy

30. 30
Analytical Electron Microscopy
- Restrictions
signal/noise measuring time
spatial resolution
Analytical Transmission Electron Microscopy