Title: Transmission Electron Microscopy (TEM)
1Transmission Electron Microscopy (TEM)
- Hendrik O. Colijn
- OSU Campus Electron Optics Facility
- colijn.1_at_osu.edu
- 292-0674
- www.ceof.ohio-state.edu/classes/MSE605.ppt
2TEM
- CM12 TEM/STEM
- CM200 LaB6 TEM
- Tecnai F20 (S)TEM
- Titan 80-300 (S)TEM
3Why EM?
Let msinb 1, then d ? 300nm for light
4Why EM?
- Rayleigh Criterion for electrons (small b)
l ? 0.003nm for electrons compared to 500nm for
light over 100,000x smaller! However, b is
smaller too.
5EM vs. LM
- Electrons vs. photons different interaction
- Strong e- interactions require a thin sample.
- Possible radiation damage.
- Vacuum environment.
- Magnetic lenses -- charged particles wont go
through glass.
6Sample constraints
- Vacuum compatible
- Electron-sample interaction different than for
light. Biological samples (and polymers) often
need stained. - Able to withstand radiation dose, needs to be
somewhat conductive.
7TEM is a projection device
8Similarity of LM and TEM
9SEM
10Illumination sources
- Thermionic
- Tungsten
- LaB6
- Field Emission
- Cold FEG
- Schottky FEG
11Probe Currents vs. E0
12TEM
13TEM Schematic (CM12/EM400)
14TEM Imaging
Remember -- you are looking at a 2D projection of
a 3D object.
15Image vs. Diffraction
16TEM Imaging
- In most cases, you are using amplitude contrast
rather than phase contrast. - Like light microscopy, you can do BF and DF
imaging. - You can also do diffraction from sub micron areas
to examine crystal structure.
17STEM in a TEM
18STEM detectors
19STEM
TEM
STEM
20HAADF STEM NiPt Catalyst
21 HAADF STEM NiPt catalyst
22Ni3Al Z-contrast STEM
23EDS unit
Oxford Instruments EDSHardwareExplained.pdf
Image courtesy of Oxford Instruments
24EDS detector
Image courtesy of Oxford Instruments
25TEM detector
26EDS detector
27Relative resolution
28SEM EDS
29TEM EDS - NiAl
Al Ka
Ni La
Ni Ka
Ni Kb
30Ionization Cross-section, Q
- Probability of an electron ionizing an atom.
- Overvoltage U E0/Ec
- Bethe cross-section model
31Cross-section vs. overvoltage
32Fluorescence yield, w
- Probability of generating an X-Ray from an
ionized atom. - w a 1
- For k shell ionizations
- C 0.0013, S 0.06, Fe 0.3
33Fluorescence Yield
34UTW vs. Be Window
35Cliff-Lorimer equation
Ca Cb are in weight percent (a tradition
started by Castaing)
36Cliff-Lorimer equation
- C-L equation describes relative concentrations
and gives only n-1 equations for n elements - The nth equation is to require the sum of the
concentrations 1. If you neglect an element,
the calculated concentrations will vary from the
true concentrations though the relative amounts
are OK. - The C-L equation neglects absorption and
fluorescence. It is exactly valid only in the
thin film limit (i.e. at t 0).
37k-factors
- kab-factors are relative sensitivity factors.
Always reported with respect to another (usually
common) element. - The original reference element was Si because
Cliff and Lorimer were geologists. Metallurgists
will often use Fe. - We can use theoretical k-factors, but
38Theoretical k-factors
39Electron Energy Loss
- GIF (Gatan Image Filter)
- In-column filter
- EELS spectrum
- Energy filtered imaging
40EELS Post-Column Spectrometer
41GIF spectrometer
42In-Column Spectrometer
43In-column energy filter
44EELS Spectrum
45Zero-loss image
Unfiltered
Filtered
46EELS Spectrum
47N background 1
48N background 2
49N background extrapolation
50N gross peak intensity
51N net EELS image
52TEM techniques
- BF/DF
- Stain specificity
- Low dose
- Diffraction
- Selected Area
- Convergent Beam
- HREM
- Weak phase object
- Aberration correctors
- STEM
- Tomography
- Elemental Info
- EDS
- EELS
- Electron Spectroscopic Imaging
- Holography
53References
- TEM (materials) Williams, D.B. and Carter,
C.B., Transmission Electron Microscopy A
Textbook for Materials Science, Kluwer/Plenum,
1996 - SEM Goldstein, J., Newbury, D., et al, Scanning
Electron Microscopy and X-Ray Microanalysis, 3rd
ed., Kluwer/Plenum, 2003