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Analytics with

Scanning Electron Microscopy

A. Danilewsky

Energy Dispersive X-Ray Analysis EDX

Electron Back Scatter Diffraction EBSD


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Depth of Signals

Auger - elektrons

Secondary electrons SE

Back scatter electrons BSE

X rays:

- Characteristic X - rays

- Continuum X- rays

Sample surface


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Topographic contrast

Electron beam

Electron beam

Many

secondary

electrons

leave the

sampleFew

secondary

electrons

leave thesample


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Characteristic X - Rays

k 1: LIII Kk 2: LII K

k : MIII K

keV


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Relative Intensity of Characteristic X - Rays

L shell consists of 3 subshells with quantum numbers n, l, j and spin m:

lI: 2s orbital n = 2, l = 0, j = , m = max. 2 electrons

=> forbidden transition

lII: 2p orbital n =2, l = 1, j = , m = => max. 2 electrons=> k2 line

lII: 2p orbitals n = 2, l = 1, j = 3/2, m = , 3/2 max. 4 electrons=> k1 - line

Intensity k

1

: k

2

= 2 : 1


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Characteristic X - Rays

Characteristic X rays Continuum X- rays

k : L K

k : M K


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X Ray Detector

Si crystal drifted by Li with

FET (field effect transistor)

Be window

collimator

cooling by liquid N2 (77 K)

dewar

liq. N2

Be - window

collimator

Si - crystal

cold finger

distance

adjustment

preamplifier

sensor


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X Ray Detector: Si crystal drifted by Li

X-ray photons generate

electron hole pairs


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Semiconductor X Ray Detector

Valence band of an intrinsic semiconductor is fully occupied Conduction band of an intrinsic semiconductor is largely unoccupied

X-rays raise electrons from valence to conduction band (photo- and

Auger electrons)

Electron hole pairs move free in the crystal during their lifetime

Bias voltage across the detector moves charge carriers to opposite

electrodes

=> signal/pulse

The number of electron hole pairs is proportional to the energy of

X-ray photons

Minimum energy is the energy gap of the semiconductor (Si: 1.1 eV)

+ energy of lattice vibrations + other physical effects => about 3.8 eV

Multi-channel analyser: 1024 channels set to 10 eV/channel

=> 0.5 10 keV


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Semiconductor X Ray Detector:

Silicon drifted by Li

Low leakage current => high resistivity Si (ultra pure)

Li as a donor compensates p-type conduction of Si at low temperature

Li stabilises the Si structure against X- ray radiation damage

p n - junction from undoped to Li doped area

Only one pulse is is processed at a time. To many X-ray photons during the

anlyser is busy:

=> dead time: no other photons are counted ! Timescale: nano seconds

e.g. 30 seconds counting time at 10% dead time needs

33 seconds real time measurement

X-rays generated in the Si detector crystal it-self: escape peak

Ti Si = 2.77.keV

Si = 1.74 keV

Ti = 4.51 keV

keV


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L - linesK 1 K 2

X Ray Spectra

Energy of of photons: Characteristic X-ray lines

Number of photons: Concentration of element

M -lines

L -lines

K lines at 80.8. keV

keV


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X Rays:

Absorption and Fluorescence

e.g. Fe - Mn

electron beam

Fek

Mnk

SE

SE

ZAF Correction:

Z = atomic numberA = absorption

F = fluorescence


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X Rays: Background Corrections

Continuum spectrum:

Calculation from elements

Subtraction


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Energy dispersive X-ray analysis (EDX)

Oxford - Link System ISISat Zeiss DSM 960

Acceleration voltage: 20 kV

Magnification: x200 x1000

Detector: Si:Li

Qualitative mapping of elements:

Al, Si, Ti, Ca, Fe, Mn

BSE


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Energy dispersive X-ray analysis (EDX)

200 m

200 m

Si

200 m

200 m 200 m

AlFe

Ti


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Geometrie EBSD

Bragg: n = 2d sin


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Electron Backscatter Diffraction EBSDOxford - Link System


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Crystal

Homogenous, anisotropic discontinuum with three-dimensional

periodical arrangement of lattice elements

Crystal Lattice


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Crystal Lattice

br

cr

231

r

straight line through the points 000 and 231: [231]

c1b3a2cwbvaur

r

rr

r

rr

++=++=

ar

[231]

,,Angles

,,sBasevector cba r

r

r

Atomic Plane


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Atomic Plane

ar

br

cr

Indices to Wei reciprocal Miller

plane I 111 111 (111)

plane II 122 1 (211)


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Zone and Zone Axis

Zone axis

Plain of the

surface normal


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Crystal Structure

Gitter

Basis

Lattice

Base

Crystal

structure


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Crystal Systems

Cubic

Hexagonal

Tetragonal

Rhombohedral

Orthorhombic

Monoclinic

Triclinic

C b i


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14 Bravais

Lattices

C u b i c

H e x a g o n a l T e t r a g o n a l

O r t h o r h o m b i c

M o n o c l i n i c T r i c l i n i c


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Unit CellSmallest assembly, which expresses the metric and includes all

symmetry elements

z.B.: F 4 3 m,

Zinkblende structure


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Symmetry

Deckoperationen

im

Kontinuum

Diskontinuum

Symmetry elements in two-dimensions

Mirror plane m

Rotation axis

2-fold 4-fold

3-fold6-fold

Glide reflection

Translation

Symmetry

Transformations:

Continuum

and

Discontinuum


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Space Groups

Tabulated in:

International Tables

for

Crystallography, Vol A

Asymmetric unit:

Smallest portion of a crystal

structure to which crystallo-

graphic symmetry can be

applied to generate one unit cell.By application of all symmetry

operations of the space group,

the whole space is filled.

11 Laue - Groups


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11 Laue - Groups

Due to the phase problem, all diffraction patterns include an inversion center.

=> Centro- and noncentrosymmetric groups can not be distinguished

Crystal system Laue - Group Acentric subgroups

triclinic 1

monoclinic 2/m 2, m

orthorhombic mmm 222, mm2

tetragonal 4/m

4/mmm

4, 4

4mm, 4m2, 422

trigonal

m

3

3m, 32hexagonal 6/m

6/mmm

6, 6

6mm, 6m2, 622

cubic m

m m

23

43m, 432

1

3

3

3

3


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Structure Data


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Information of EBSD Pattern


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Information of EBSD - Pattern

EBSD of Ge


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EBSD of Ge


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Demonstration of Sample Orientation


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Demonstration of Sample Orientation

Projection of the

surface normal in atwo-dimensional

plain occurs analog-

ous to the stereo-

graphic projection:

=> Pole Figure

Pole Figure Corresponding to ~ [111]


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Pole Figure Corresponding to [111]

with Slightly Tilt and Rotation

Inverse Pole Figure


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Polycrystalline Sample


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y y pFew Alignment of Crystallites

Polycrystalline SampleAli t f C t llit C di t [101]


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Alignment of Crystallites Corresponding to [101],

Inverse Pole Figure

Polycrystalline Sample


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Alignment of Crystallites, Inverse Pole Figure

Reference System


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Reference System

Demonstration of Orientation


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Euler angleOrientation:

Rotation of the sample-fixed coordinate system (Cartesian!) into the crystal-

fixed system of the discrete crystallite.

a) Sample orientation

1 - Rotation on perpendicular direction

- Rotation on longitudinal direction

2 - Rotation on transversal direction

b) Crystal orientation

1 - Rotation in (001)

- Rotation on [100]

2 - Rotation in (001)

Convention according to Bunge:

Mechanical Sample Preparation


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Mechanical Sample Preparation

Mechanochemical Sample Preparation


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Sample Preparation


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Sample Preparation

Depth of penetration 10 - 100 nm

Good polish Bad polish

Sample Preparation by Ion Abrasion


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Polycrystalline Si


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rolling directionback scatter electrons (BSE)quality pattern

transverse directionnormal direction

x 200 pixel size 24 m

Polycrystalline Si:

Preferential growth direction


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Preferential growth direction

5 - 7 deviation from [110]

Literature to Scanning Electron Microscopy

L. Reimer, G. Pfefferkorn: "Rasterelektronenmikroskopie", Springer 1977


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H. R. Wenk (Ed.): "Electron Microscopy in Mineralogy", Springer Verlag 1976

L. Reimer: "Scanning Electron Microscopy", Springer 1983

L. Reimer: "Elektronenmikroskopische Untersuchungs- und Prparationsmethoden",

Springer 1967

Schmidt, Peter FritzPraxis der Rasterelektronenmikroskopie und Mikrobereichsanalyse / Peter

Fritz Schmidt - Renningen-Malmsheim : Expert-Verlag, 1994 (Kontakt &

Studium ; 444 : Metechnik)

Joy et al.: "Electron Channeling Pattern in the Scanning Electron Microscope",J. Appl. Phys. Vol 53, No 8 (1982) 439 - 461

U. Holzhuser: "Charakterisierung von Einkristallen mittels Electron Channeling

Pattern", Diplomarbeit Universit@t Freiburg 1992 Flegler, Heckmann, Klomparens, Elektronenmikroskopie, Spektrum

Akademischer Verlag Berlin und Heidelberg, 1993

Humphreys, "Reviw: Grain and subgrain characterisation by electron backscatter

diffraction, J. of Mat. Sci. 36 (2001), 3833 3854

Literature to Scanning Electron Microscopy


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and online:

"Grundlagen der Raster-Elektronenmikroskopie" http://www.reclot.de

by Alexander Fels

"SEM Electron Backscattered Diffraction" by Dr Geoff Lloyd

"Crash Kurs Textur" http://www.texture.de/Multex-Dateien/crash.htm

by Kurt Helming

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