Defect and chemical analysis in the TEM Defect and ... · PDF fileTHEUNIVERSITY OFBIRMINGHAM Centre for Electron Microscopy Defect and chemical analysis in the TEM I.P. Jones 1.Defect

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





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


• 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.






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)





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






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


(from Williams and Carter)


i. Size of edges

ii. Shape of edges


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.


i. Size of edges

ii. Shape of edges


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

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Defect and chemical analysis in the TEM Defect and ... · PDF fileTHEUNIVERSITY OFBIRMINGHAM Centre for Electron Microscopy Defect and chemical analysis in the TEM I.P. Jones 1.Defect