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A.E. Gunns MENA3100 V10

Sample preparation for TEM Crushing

Cutting

saw, diamond pen, ultrasonic drill, FIB

Mechanical thinning

Grinding, dimpling

Electrochemical thinning

Ion milling

Coating

Replica methods

FIB

Plane view or cross section sample?

Is your material brittle or ductile?

Is it a conductor or insulator?

Is it a multi layered material?


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Grind down/

dimple

TEM sample preparation: Thin films

Top view

Cross section

or

Cut out a cylinder

and glue it in a Cu-tube

Grind down and

glue on Cu-rings

Cut a slice of the

cylinder and grind

it down / dimple

Ione beam thinning

Cut out cylinder

Ione beam thinning

Cut out slices

Glue the interface

of interest face toface together with

support material

Cut off excess

material

Focused Ion Beam

(FIB)


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Basic principles, first TEM

Wave length:

= h/(2meV)0.5 (NB non rel. expr.)

= h/(2m0eV(1+eV)/2m0c2)0.5(relativistic expression)

200kV: = 0.00251 nm (v/c= 0.6953, m/m0= 1.3914)

Electrons are deflected by bothelectrostatic and magnetic fields

Force from an electrostatic field (in the gun)

F= -e E

Force from amagnetic field (in the lenses)

F= -e (v x B)

Nobel prize lecture: http://ernst.ruska.de/daten_e/library/documents/999.nobellecture/lecture.html

a) The first electron microscope built by Knoll

and Ruska in 1933, b) The first commercial

electron Microscope built by Siemens in 1939.
http://ernst.ruska.de/daten_e/library/documents/999.nobellecture/lecture.htmlhttp://ernst.ruska.de/daten_e/library/documents/999.nobellecture/lecture.htmlhttp://ernst.ruska.de/daten_e/library/documents/999.nobellecture/lecture.html


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Basic TEM

Electron source:

Tungsten, W

LaB6

FEG

Electron gun


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Electron guns

Thermionic gunField emission gun (FEG)


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Technical data of different sourcesTungsten LaB6 Cold

FEG

Schottky Heated

FEG

Brightness

(A/m2/sr)

(0.3-2)109 (0.3-2)109 1011-1014 1011-1014 1011-1014

Temperature

(K)

2500-3000 1400-2000 300 1800 1800

Work function

(eV)

4.6 2.7 4.6 2.8 4.6

Source size

(m)

20-50 10-20


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Basic TEM

Electron gun

Vacuum requirements:

- Avoid scattering from residual gas inthe column.

- Thermal and chemical stability of the

gun during operation.

- Reduce beam-induced contamination

of the sample.

LaB6: 10-7torr

FEG: 10-10torr

Electron source:

Tungsten, W

LaB6

FEGCold trap

Sample position


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The lenses in a TEM

Sample

Filament

Anode

1. and 2. condenser lenses

Objective lens

Intermediate lenses

Projector lens

Compared to the lenses in an

optical microscope they are verypoor!

The point resolution in a TEM is

limited by the aberrations of the

lenses.

The diffraction limit on resolution

is given by the Raleigh criterion:

d=0.61/sin, =1, sin~

-Spherical

- Chromatic

-Astigmatism


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Spherical aberrations

Spherical aberration coefficient

ds= 0.5MCs3

M: magnification

Cs:Spherical aberration coefficient

: angular aperture/

angular deviation from optical axis

2000FX: Cs= 2.3 mm

2010F: Cs= 0.5 nm

r1

r2

Disk of least confusion

Cscorrected TEMs are now available

The diffraction and the spherical aberration limits on resolution

have an opposite dependence on the angular aperture of the objective.


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Aberrations in a nutshell

Core of the M100 galaxy seen through

Hubble (source: NASA)

Before Cscorrection

After Cscorrection

Q.M. Ramasse


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Resolution limit

Year Resolution1940s ~10nm1950s ~0.5-2nm1960s 0.3nm (transmission)

~15-20nm (scanning)1970s 0.2nm (transmission)

7nm (standard scanning)

1980s 0.15nm (transmission)5nm (scanning at 1kV)

1990s 0.1nm (transmission)3nm (scanning at 1kV)

2000s


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Chromatic aberration

v

v -vdc= Cc((U/U)

2+ (2I/I)2+ (E/E)2)0.5

Cc: Chromatic aberration coefficient

: angular divergence of the beam

U: acceleration voltage

I: Current in the windings of the objective lens

E: Energy of the electrons

2000FX: Cc= 2.2 mm

2010F: Cc= 1.0 mm

Chromatic aberration coefficient:

Thermally emitted electrons:E/E=KT/eV

Force from amagnetic field:F= -e (v x B)

Disk of least confusion


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Lens aberrations

Lens astigmatismLoss of axial asymmetry

y-focus

x-focusy

xThis astigmatism can not be

prevented, but it can be

corrected!


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Operating modes

Convergent beam Parallel beam

Can be scanned

(STEM mode)

Specimen

Imaging mode

orDiffraction mode

Spectroscopy and mapping

(EDS and EELS)


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Image or diffraction mode

1. and 2. condenser

lenses

Objective lens

Intermediate lenses

Projector lens

Spesimen

Filament

Anode

Diffraction plane

Image plane

Objective aperture

Selected area aperture

Image or diffraction patternSTEM detectors (BF and HAADF)

Bi-prism

Viewing screen


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Advanced nanotool

JEOL 2010F FEGTEMUltra high resolution version with analytical possibilities


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Imaging / microscopy

200 nm

Si

SiO2

TiO2

Pt

BiFeO3

Glue

TEM

- High resolution (HREM)- Bright field (BF)

- Dark field (DF)

- Shadow imaging

(SAD+DF+BF)

STEM

- Z-contrast (HAADF)

- Elemental mapping

(EDS and EELS)

GIF

- Energy filtering

Holography


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Simplified ray diagram

Objective lense

Diffraction plane

(back focal plane)

Image plane

Sample

Parallel incoming electron beamSi

c

ow

erCell2.0

1,1 nm

3,8

Objective aperture

Selected area

aperture


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Apertures

Selected area aperture

Condenser aperture

Objective aperture


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Use of apertures

Condenser aperture:Limits the number of electrons hitting the sample (reducing the intensity),

Reducing the diameter of the discs in the convergent electron diffraction pattern.

Selected area aperture:Allows only electrons going through an area on the sample that is limited by the SAD aperture

to contribute to the diffraction pattern (SAD pattern).

Objective aperture:Allows certain reflections to contribute to the image. Increases the contrast in the image.

Bright field imaging (central beam, 000), Dark field imaging (one reflection, g), High resolution

Images (several reflections from a zone axis).


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Objective aperture: Contrast enhancement

All electrons contributes to the image. A small aperture allows only electrons in the

central spot in the back focal plane to contribute

to the image.Intensity: Thickness and density

dependence

Mass-thickness contrast

Si Ag and Pb

glue(light elements)

hole

50 nmOne grain seen along a

low index zone axis.

Diffraction contrast(Amplitude contrast)

Diffraction contrast: B i ht fi ld (BF)


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Diffraction contrast: Bright field (BF),dark field (DF) and weak-beam (WB)

BF image

Objective

aperture

DF image Weak-beam

Dissociation of pure screw dislocation

In Ni3Al, Meng and Preston, J.

Mater. Scicence, 35, p. 821-828, 2000.


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Bending contours

BF image

DF image

DF image

Obj. aperture

Obj. lens

sample


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Thickness fringes/contours

Sample (side view)

e

000 g

t

Ig=1- Io

In the two-beam situation the intensity

of the diffracted and direct beamis periodic with thickness (Ig=1- Io)

Ig=(t/g)2(sin2(tseff)/(tseff)

2))

t = distance traveled by the diffracted beam.

g= extinction distance

Sample (top view)Hole

Positions with max

Intensity in Ig


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Thickness fringes,bright and dark field images

Sample Sample

DF imageBF image


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Phase contrast: HREM and Moire fringes

2 nm

http://www.mathematik.com/Moire/

A Moir patternis an interferencepattern created, for example, when

two grids are overlaid at an angle, or

when they have slightly different mesh

sizes (rotational and parallel Moire

patterns).HREM image

Long-Wei Yin et al., Materials Letters, 52, p.187-191

200-400 kV TEMs are mostcommonly used for HREM

Interference pattern
http://www.mathematik.com/Moire/http://www.mathematik.com/Moire/


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Moire fringe spacing

Parallel Moire spacingdmoire= 1 / IgI = 1 / Ig1-g2I = d1d2/Id1-d2I

Rotational Moire spacing

dmoire= 1 / IgI = 1 / Ig1-g2I ~1/g= d/

Parallel and rotational Moire spacing

dmoire= d1d2/((d1-d2)2+ d1d2

2)0.5

g1

g2

g

g1g2 g

Simulating HREM images


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Simulating HREM imagesContrast transfer function (CTF)

CTF (Contrast Transfer Function) is the function which

modulates the amplitudes and phases of the electron

diffraction pattern formed in the back focal plane of theobjective lens. It can be represented as:

k = u

The curve depend on:

Cs (the quality of objective lens)l(wave-length defined by accelerating voltage)

Df(the defocus value)

u(spatial frequency)

In order to take into account the effect of the

objective lens when calculating HREM images, the

wave function (u) in reciprocal space has to be

multiplied by a transfer function T(u).

In general we have:

(r)= (u) T(u) exp (2iu.r)

T(u)= A(u) exp(i), A(u): aperture function 1 or 0

(u)= fu2+1/2Cs3u4 : coherent transfer function

Si l ti HREM i


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Simulating HREM images

Contrast transfer function (CTF)

Effect of the envelope functions can be represented as:

where Ecis the temporal coherency envelope(caused by

chromatic aberrations, focal and energy spread,instabilities in thehigh tension and objective lens current), and Eais spatial

coherencyenvelope(caused by the finite incident beam

convergence).

http://www.maxsidorov.com/ctfexplorer/webhelp/background.htm
http://www.maxsidorov.com/ctfexplorer/webhelp/spatial_coherency.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/spatial_coherency.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/background.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/background.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/spatial_coherency.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/spatial_coherency.htm


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Scherzer defocus

http://www.maxsidorov.com/ctfexplorer/webhelp/effect_of_defocus.htm

f = - (Cs)1/2

f = -1.2(Cs)1/2

Scherzer condition Extended Scherzer condition
http://www.maxsidorov.com/ctfexplorer/webhelp/effect_of_defocus.htmhttp://www.maxsidorov.com/ctfexplorer/webhelp/effect_of_defocus.htm


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HREM simulations

One possible model for which the simulated HREM images match rectangular region I

HREM simulation along [0 0 1] based on the above structures. The numbers before and after the slash

symbol / represent the defocus and thickness (nm), respectively

The assessment of GPB2/S structures in AlCuMg alloys

Wang and Starink, Mater. Sci. and Eng. A, 386, p 156-163, 2004.


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HAADF image of an icosahedral FePt particle (false colors): thanks to the small

probe size, it is possible to probe precisely the chemical structure of samples atthe atomic level, revealing here a small crystalline layer of iron oxide

surrounding the outermost shell of the particle.

Combined HAADF and EELS


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Energy filtering

A. Thgersen et al., Collaboration with Prof. T. Finnstad, UiO, S. Diplas, SINTEF and

UniS, UK and NIMS, Japan

Documents

TEM Imaging WWW