THE UNIVERSITYOF BIRMINGHAM
Centre for Electron Microscopy
Defect and chemicalanalysis in the TEM
I.P. Jones
1. Defect analysis: diffraction contrast
2. Defect analysis: phase contrast
3. Chemical analysis: EDX
4. Chemical analysis: PEELS
Defect and chemical analysis in the TEM
1. Defect analysis: diffraction contrast
2. Defect analysis: phase contrast
3. Chemical analysis: EDX
4. Chemical analysis: PEELS
Defect and chemical analysis in the TEMMode 1
(SAD)
Mode 2
(imaging)
Diffraction
contrast
Phase
contrast
Contrast mechanisms in the TEM
• absorption contrast
• strain contrast
1. Defect analysis: diffraction contrast
• Secondary defects only
• Two beam conditions
• Origin of contrast: movement of atoms perpendicular to reflecting
planes. Movement of atoms within planes gives no change of
intensity (contrast)
Analysing
stacking faults using
diffraction contrast
R
Stacking fault
Stacking faults
Stacking fault fringes
nRg =!
Sometimes stacking faults disappear …..
Stacking faults and APB in Fe3Ge
Why stacking faults are invisible when g.R = integer :
|g.R| = 0 |g.R| = 0.25
|g.R| = 0.5 |g.R| = 0.75
|g.R| = 1 |g.R| = 1.25
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
3 4 5 6 7 8 9 10 3 4 5 6 7 8 9 10
3 4 5 6 7 8 9 10 3 4 5 6 7 8 9 10
3 4 5 6 7 8 92 3 4 5 6 7 8 92
Note that:
1. When g and R are perpendicular (|g.R| = 0) the stacking fault has no effect on the reflecting
planes: it is invisible.
2. |g.R| = 0 and |g.R| = 1 are exactly equivalent, as are |g.R| = 0.25 and |g.R| = 1.25: |g.R| is only
defined modulo 1. The usual range chosen for |g.R| is -0.5 to +0.5.
Analysing stacking faults using diffraction contrast
• Use a series of two beam conditions
• Only displacements perpendicular to the
reflecting planes give diffraction contrast
Other aspects of SFcontrast:
(i) Nature of outerfringes gives sign of
g.R
(ii) Similarity BF-DFgives top/bottom of
foil.
Analysing
dislocations using
diffraction contrast
Screw dislocation
Edge dislocation
Burgers vector
Analysing dislocations using diffraction contrast
Dislocation defined by Burgers vector b and line direction u
b: most displacement parallel to b, so invisibility for g.b = 0
(edge dislocations give weak g.bxu contrast)
u measured by
•Stereographic projection
•Stereoviewer
•Tomography
Electropolishing
TEM foil prepared byElectropolishing. Longitudinalsection of the 10% cold rolledInterstitial free steel.
g.b analysis in Al-2%Mg
Burgers vector analysis with the help of a computer
To make the images narrower and show more detail of thedislocation core,
dark field weak beam imaging
is used. The weak beam is a diffracted beam, severalBragg angles away from its Bragg position.
1. Defect analysis: diffraction contrast
2. Defect analysis: phase contrast
3. Chemical analysis: EDX
4. Chemical analysis: PEELS
Defect and chemical analysis in the TEM
Defect analysis: phase contrast
The principles are the same, but the way they are exploited is
rather different.
Analysing dislocations using phase contrast
A Burgers circuit in TiAl
(M. Aindow et al. Int. Sc. 12, 293 (2004)
Projected b =
!
1
61 1 2[ ] Projected b =
!
1
61 21 [ ]
Total b =
!
1
32 11[ ]
(Aindow et al. Int. Sc. 12, 293 (2004.)
Thin γ lamellae in a TiAl alloy
(Zhang et al. Acta Mat. 52, 191 (2004)
1. Defect analysis: diffraction contrast
2. Defect analysis: phase contrast
3. Chemical analysis: EDX
4. Chemical analysis: PEELS
Defect and chemical analysis in the TEM Chemical analysis: EDX
Same as SEM except:
1. No WDX.
2. Quantification: ratios only (no single element standards).
Calculation or standards.
1. Spatial resolution controlled by beam rather than kV and
4. Surfaces usually have wrong composition.
!
Z
Stacking fault
[001]
[010]
!! ! !
!
!
!
! !! !
"" " "
"
"
"
" " ""# # # #
#
#
##
# ##
16
18
20
22
24
26
28
30
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
nm
Measurement 1
Measurement 2
!
"
# Measurement 3
X-ray profile across a stacking fault in Nb3Al
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
P profile
P c
oncentr
ation, w
t.%
Distance, nm
0 10 20 30 40 50 600
1
2
3
4
Mo Profile
Cr Profile
Mo a
nd
Cr co
nce
ntr
atio
n,
wt.
%
Distance, nm
Image of grain boundary and variation in P, Cr and Moconcentration across the boundary in 2.25Cr1Mo steel.Quantmap. Beam FWHM ~ 1nm (Ding, Rong, and Knott)
Drift detectors in the TEM: fast maps
High Resolution - when countsare limited
• Size of the detector is limiting, for example, for:– Small specimens– High spatial resolution
DTTran Exploiting high count rates when
mapping
• SDD sensors can deal with high count rateswhere generated
• This can often be very useful in TEM!
Chemical mapping of a 64MB DRAM inChemical mapping of a 64MB DRAM ina TEM using SDDa TEM using SDD
1. Defect analysis: diffraction contrast
2. Defect analysis: phase contrast
3. Chemical analysis: EDX
4. Chemical analysis: PEELS
Defect and chemical analysis in the TEM
Schematic diagram of PEELS Schematic diagram of EELS Spectrum
Typical spectrum from an MgO grainExamples of EELS analysis
i. Size of edges
ii. Shape of edges
iii. Low energy region
Examples of EELS analysis
i. Size of edges
ii. Shape of edges
iii. Low energy region
(from Williams and Carter)
Examples of EELS analysis
i. Size of edges
ii. Shape of edges
iii. Low energy region
Determination of Ni valence
870 880 890 900 910 920
Inte
nsity (
arb
.un
its)
Energy Loss (eV)
From CePd3
From CePd7
850 860 870 880 890 900 910 920
Ce4+
Inte
nsity (
arb
.units)
Energy Loss (eV)
Ce3+
Edges from standards. Ce3+
from CePO4.xH2O and Ce4+
from CeO2.
Edges from Pd3Ce andPd7Ce.
Examples of EELS analysis
i. Size of edges
ii. Shape of edges
iii. Low energy region
Five steps to get the dielectric function and DOS
Interband transition strength of matrix and Σ13 grain boundary
Bulk and many grain boundaries ΣΣ1313 grain boundaryA’: O2p-Ti; A: O2p-Ti; B: O2p-Ti; C: O2p-Sr; D: O2p-Sr; E: Sr4p-Ti; E’: Sr4p-Ti 3d t2g 3d t2g 3d eg 3d eg 4d 3d eg 3d t2g
The end