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Do it with electrons !
II
Do it with electrons !
II
TEM - transmission electron microscopyTEM - transmission electron microscopy
Typical accel. volt. = 100-400 kV (some instruments - 1-3 MV)
Spread broad probe across specimen - form image from transmitted electrons
Diffraction data can be obtained from image area
Many image types possible (BF, DF, HR, ...) - use aperture to select signal sources
Main limitation on resolution - aberrations in main imaging lens
Basis for magnification - strength of post- specimen lenses
Typical accel. volt. = 100-400 kV (some instruments - 1-3 MV)
Spread broad probe across specimen - form image from transmitted electrons
Diffraction data can be obtained from image area
Many image types possible (BF, DF, HR, ...) - use aperture to select signal sources
Main limitation on resolution - aberrations in main imaging lens
Basis for magnification - strength of post- specimen lenses
TEM - transmission electron microscopyTEM - transmission electron microscopy
Instrument components
Electron gun (described previously)
Condenser system (lenses & apertures for controlling illumination on specimen)
Specimen chamber assembly
Objective lens system (image-forming lens - limits resolution; aperture - controls imaging conditions)
Projector lens system (magnifies image or diffraction pattern onto final screen)
Instrument components
Electron gun (described previously)
Condenser system (lenses & apertures for controlling illumination on specimen)
Specimen chamber assembly
Objective lens system (image-forming lens - limits resolution; aperture - controls imaging conditions)
Projector lens system (magnifies image or diffraction pattern onto final screen)
TEM - transmission electron microscopyTEM - transmission electron microscopy
Instrument components
Electron gun (described previously)
Condenser system (lenses & apertures for controlling illumination on specimen)
Specimen chamber assembly
Objective lens system (image-forming lens - limits resolution; aperture - controls imaging conditions)
Projector lens system (magnifies image or diffraction pattern onto final screen)
Instrument components
Electron gun (described previously)
Condenser system (lenses & apertures for controlling illumination on specimen)
Specimen chamber assembly
Objective lens system (image-forming lens - limits resolution; aperture - controls imaging conditions)
Projector lens system (magnifies image or diffraction pattern onto final screen)
TEM - transmission electron microscopyTEM - transmission electron microscopy
ExamplesExamples
Matrix - '-Ni2AlTi
Precipitates - twinned L12 type '-Ni3Al
Matrix - '-Ni2AlTi
Precipitates - twinned L12 type '-Ni3Al
TEM - transmission electron microscopyTEM - transmission electron microscopy
ExamplesExamples
Precipitation in anAl-Cu alloyPrecipitation in anAl-Cu alloy
TEM - transmission electron microscopyTEM - transmission electron microscopy
ExamplesExamples
dislocationsin superalloydislocationsin superalloy
SiO2 precipitate particle in SiSiO2 precipitate particle in Si
TEM - transmission electron microscopyTEM - transmission electron microscopy
ExamplesExamples
lamellar Cr2N precipitates in stainless steel
lamellar Cr2N precipitates in stainless steel
electron diffraction pattern
electron diffraction pattern
TEM - transmission electron microscopyTEM - transmission electron microscopy
Specimen preparationSpecimen preparation
Foils3 mm diam. disk very thin (<0.1 - 1 micron - depends on
material, voltage)
Foils3 mm diam. disk very thin (<0.1 - 1 micron - depends on
material, voltage)
Typesreplicasfilmsslices
powders, fragmentsfoils
Typesreplicasfilmsslices
powders, fragmentsfoils
as is, if thin enough ultramicrotomy
crush and/or disperse on carbon film
as is, if thin enough ultramicrotomy
crush and/or disperse on carbon film
TEM - transmission electron microscopyTEM - transmission electron microscopy
Specimen preparationSpecimen preparation
Foils3 mm diam. disk very thin (<0.1 - 1 micron - depends on
material, voltage)
mechanical thinning (grind)chemical thinning (etch)ion milling (sputter)
Foils3 mm diam. disk very thin (<0.1 - 1 micron - depends on
material, voltage)
mechanical thinning (grind)chemical thinning (etch)ion milling (sputter)
examine region
around perforationexamine region
around perforation
TEM - transmission electron microscopyTEM - transmission electron microscopy
DiffractionDiffraction
Use Bragg's law - = 2d sin
But much smaller
(0.0251Å at 200kV)
if d = 2.5Å, = 0.288°
Use Bragg's law - = 2d sin
But much smaller
(0.0251Å at 200kV)
if d = 2.5Å, = 0.288°
TEM - transmission electron microscopyTEM - transmission electron microscopy
DiffractionDiffraction
2 ≈ sin 2 = R/L = 2d sin ≈ d (2)
R/L = /d
Rd = L
2 ≈ sin 2 = R/L = 2d sin ≈ d (2)
R/L = /d
Rd = L
L is "camera length"
L is "camera constant"
L is "camera length"
L is "camera constant"
image planeimage plane
specimenspecimen
TEM - transmission electron microscopyTEM - transmission electron microscopy
DiffractionDiffraction
Get pattern of spots around transmitted beam from one grain (crystal)Get pattern of spots around transmitted beam from one grain (crystal)
TEM - transmission electron microscopyTEM - transmission electron microscopy
DiffractionDiffraction
Symmetry of diffraction pattern reflectssymmetry of crystal around beam direction
Symmetry of diffraction pattern reflectssymmetry of crystal around beam direction
Why does 3-fold diffraction pattern look hexagonal?Why does 3-fold diffraction pattern look hexagonal?
[111] in cubic [001] in hexagonal
Example: 6-fold in hexagonal, 3-fold in cubic
Example: 6-fold in hexagonal, 3-fold in cubic
TEM - transmission electron microscopyTEM - transmission electron microscopyDiffractionDiffraction
Note: all diffraction patterns are centrosymmetric, even if crystal structure is not centrosymmetric (Friedel's law)
Note: all diffraction patterns are centrosymmetric, even if crystal structure is not centrosymmetric (Friedel's law)
Some 0-level patterns thus exhibit higher rotational symmetry than structure has
Some 0-level patterns thus exhibit higher rotational symmetry than structure has
P cubic reciprocal latticelayers along [111] direction
0-level
l = +1 level
l = -1 level
TEM - transmission electron microscopyTEM - transmission electron microscopy
DiffractionDiffraction
Cr23C6 - F cubica = 10.659 Å
Cr23C6 - F cubica = 10.659 Å
Ni2AlTi - P cubica = 2.92 Å
Ni2AlTi - P cubica = 2.92 Å
TEM - transmission electron microscopyTEM - transmission electron microscopy
Diffraction - Ewald constructionDiffraction - Ewald construction
Remember crystallite size?
when size is small, x-ray reflection is broad
To show this using Ewald construction, reciprocal
lattice points
must have a size
Remember crystallite size?
when size is small, x-ray reflection is broad
To show this using Ewald construction, reciprocal
lattice points
must have a size
TEM - transmission electron microscopyTEM - transmission electron microscopy
Diffraction - Ewald constructionDiffraction - Ewald construction
Also, very small, 1/ very largeAlso, very small, 1/ very large
Many TEM specimens are thin in one direction - thus,
reciprocal
lattice points elongated in one direction to rods
- "relrods"
Many TEM specimens are thin in one direction - thus,
reciprocal
lattice points elongated in one direction to rods
- "relrods"
Ewald sphere
Only zero level in position to reflect
Only zero level in position to reflect
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patternsIndexing electron diffraction patterns
Measure R-values for at least 3 reflectionsMeasure R-values for at least 3 reflections
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patternsIndexing electron diffraction patterns
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patternsIndexing electron diffraction patterns
Index other reflections by vector sums, differencesIndex other reflections by vector sums, differences
Next find zone axis from cross product of any two (hkl)s
(202) x (220) ——> [444] ——> [111]
Next find zone axis from cross product of any two (hkl)s
(202) x (220) ——> [444] ——> [111]
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patternsIndexing electron diffraction patterns
Find crystal system, lattice parameters, index pattern, find zone axisFind crystal system, lattice parameters, index pattern, find zone axis
ACTF!!!ACTF!!! Note symmetry - if cubic, what direction has this symmetry (mm2)?
Note symmetry - if cubic, what direction has this symmetry (mm2)?
Reciprocal lattice unit cell for cubic lattice is a cube
Reciprocal lattice unit cell for cubic lattice is a cube
TEM - transmission electron microscopyTEM - transmission electron microscopy
Why index?Why index?
Detect epitaxyOrientation relationships at grain boundariesOrientation relationships between matrix & precipitatesDetermine directions of rapid growthOther reasons
Detect epitaxyOrientation relationships at grain boundariesOrientation relationships between matrix & precipitatesDetermine directions of rapid growthOther reasons
TEM - transmission electron microscopyTEM - transmission electron microscopy
Polycrystalline regionsPolycrystalline regions
polycrystalline BaTiO3 spotty Debye rings
polycrystalline BaTiO3 spotty Debye rings
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patterns - polycrystalline regionsIndexing electron diffraction patterns - polycrystalline regions
Same as X-rays – smallest ring - lowest - largest dSame as X-rays – smallest ring - lowest - largest d
Hafnium ( 铪 )
TEM - transmission electron microscopyTEM - transmission electron microscopy
Indexing electron diffraction patterns - commentsIndexing electron diffraction patterns - comments
Helps to have some idea what phases present
d-values not as precise as those from X-ray data
Helps to have some idea what phases present
d-values not as precise as those from X-ray data
Systematic absences for lattice centering and other translational symmetry same as for X-rays
Intensity information difficult to interpret
Systematic absences for lattice centering and other translational symmetry same as for X-rays
Intensity information difficult to interpret
TEM - transmission electron microscopyTEM - transmission electron microscopy
Sources of contrastSources of contrast
Diffraction contrast - some grains diffract more strongly than others; defects may affect diffraction
Diffraction contrast - some grains diffract more strongly than others; defects may affect diffraction
Mass-thickness contrast - absorption/ scattering. Thicker areas or mat'ls w/ higher Z are dark
Mass-thickness contrast - absorption/ scattering. Thicker areas or mat'ls w/ higher Z are dark
TEM - transmission electron microscopyTEM - transmission electron microscopy
Bright field imagingBright field imaging
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
TEM - transmission electron microscopyTEM - transmission electron microscopy
Bright field imagingBright field imaging
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
TEM - transmission electron microscopyTEM - transmission electron microscopy
Bright field imagingBright field imaging
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
TEM - transmission electron microscopyTEM - transmission electron microscopy
Bright field imagingBright field imaging
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
Only main beam is used. Aperture in back focal plane blocks diffracted beams
Image contrast mainly due to subtraction of intensity from the main beam by diffraction
TEM - transmission electron microscopyTEM - transmission electron microscopy
What else is in the image?What else is in the image?
Many artifacts surface films local contamination differential thinning others
Many artifacts surface films local contamination differential thinning others
Also get changes in image because ofannealing due to heating by beam
Also get changes in image because ofannealing due to heating by beam
TEM - transmission electron microscopyTEM - transmission electron microscopy
Dark field imagingDark field imaging
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
TEM - transmission electron microscopyTEM - transmission electron microscopy
Dark field imagingDark field imaging
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
strain field contrast
TEM - transmission electron microscopyTEM - transmission electron microscopy
Dark field imagingDark field imaging
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
Instead of main beam, use a diffracted beam
Move aperture to diffracted beam or tilt incident beam
TEM - transmission electron microscopyTEM - transmission electron microscopy
Lattice imagingLattice imaging
Use many diffracted beams
Slightly off-focus
Need very thin specimen region
Need precise specimen alignment
Use many diffracted beams
Slightly off-focus
Need very thin specimen region
Need precise specimen alignment
See channels through foil
Channels may be light or dark in image
Usually do image simulation todetermine features of
structure
See channels through foil
Channels may be light or dark in image
Usually do image simulation todetermine features of
structure
铝 钌 铜 合金
TEM - transmission electron microscopyTEM - transmission electron microscopy
ExamplesExamples
M23X6 (figure at top left).
L21 type '-Ni2AlTi (figure at top center).
L12 type twinned '-Ni3Al (figure at bottom center).
L10 type twinned NiAl martensite (figure at bottom right).