K

L

auger electrons

• Pierre Auger, 1923

• Atom response to deep-lying hole:

– Excitation (create hole)– Relaxation (emit electron)

Ekin=EA-EB-EC

KLL transition:

Auger animation

Ekin=EA-EB-EC

x-ray emission

• Atom response to deep-lying hole:

– Excitation (create hole)– Relaxation (emit x-ray)

Ex-ray=EA-EB

Comparison

K

L

Auger electron emission:KLL transition

K

L

x-ray emission:

XYZ = Initial hole – decay level – emission level

Different transitions

N1-7

M1-5

L1-3

K

4s,4p1/2,4p3/2,4d3/2,4d5/2 ,4d7/2

3s,3p1/2,3p3/2,3d3/2,3d5/2

2s,2p1/2,2p3/2

1s

KLL

LMM

MNN

Splitting:

KLL = KL1L1, KL1L2, KL1L3

KL2L3, KL2L2, KL3L3

Measurement

• Measure N(E)

• Report dN(E)/dE– Small peaks– Large background– Background increases with energy

• Peak height in dN(E) spectrum peak area in N(E)

Ag (2keV electrons incident)

Variation with element number• Increase in binding energies with atomic

number

• Increase in Auger electron energies for

the same transition

27Co

28Ni

29Cu

775 eV

848 eV

920 eV

LMMKLL

N1-7

M1-5

L1-3

K

KLL

LMM

Variation in periodic table

LMMKLL

MNN

N1-7

M1-5

L1-3

K

KLL

LMM

MNN

Energi of the strongest Augertransition for all elements:

Nomenclature

Notation/levels:l : orbital angular momentum s : electron spin momentumj = l + s

n l j X-ray level

Spec.

level

1 0 ½ K 1s1/2

2 0 ½ L1 2s1/2

2 1 ½ L2 2p1/2

2 1 3x½ L3 2p3/2

3 0 ½ M1 3s1/2

3 1 ½ M2 3p1/2

3 1 3x½ M3 3p3/2

3 2 3x½ M4 3d3/2

3 2 5x½ M5 3d5/2

Notation/transitions: (2S+1)LJ

S=sL=lJ=j

Transition End config. Interme-diate

KL1L1 2s02p6 1S0

1P1

KL1L2,3 2s1p5 3P0

3P1

3P2

1S0

3P0

KL2,3L2,3 2s2p4 3P1 (-)3P2

1D2

Magnesium KLL• Figure 5.4:

N1-7

M1-5

L1-3

K

KLL

Splitting into 6 linesKLL = KL1L1, KL1L2, KL1L3,KL2L3, KL2L2, KL3L3

+ spin-orbit coupling (total 9 lines)

Kinetic energy• Ekin = EA – EB - E C

= Einitial – Efinal

~ ZEinitial - ZEfinal1 - ZEfinal2

~ ZEinitial - ½(ZEfinal1 + Z+1Efinal1) - ½(ZEfinal2 + Z+1Efinal2)

M1-5

L1-3

K

KLL

Initial state Final stateZEinitial

Z+1Efinal1

Z+1Efinal2

• Electrons evaporate from hot filament

• Focused with lenses etc.• Electron beams can be

moved and focused easily

• Spot-size down to 200 Å

Producing the electronsElectron gun:

Measuring the electron energy

• Pass energy given by V• Resolution E/E ~ 1%

– V– ()3

• Double-pass CMA

Cylindrical mirror analyser (CMA):

V < 0

• Pass energy constant (small)

• Resolution E/E ~ 1%– ()2

Hemispherical Analyser (HSA):

V2

V1 V0

CMA

HSA

Electron counter• Channeltron :

– Surface emits electrons when hit by an electron cascade effect

– 106-107 multiplication

– A current can be measured

~2 cm

Energy of the strongest Auger transition

LMM

KLL

MNNInformation from peak

position

But you can also get

information from the

peak shape on chemical

changes....

Change in surroundings

LMM ~ LVV(V=valence band)

KLL and plasmon losses

C O

•First clean aluminium:

Bulk and surface plasmons of Al

B2 B1 S KL2,3L2,3

KL1L2,3

KL1L2,3

KL1L1

KL2,3L2,3Splitting into 6 Auger lines

KLL =

KL1L1, KL1L2, KL1L3, KL2L3, KL2L2, KL3L3

Excitation of plasmons

Bulk plasmons ~ 15 eV

Surface plasmons ~11 eV

Oxidation to Al2O3

KLL but NO plasmon losses(Al2O3 is an isolator)

More fine structure• Carbon @ 272 eV

– SiC– Graphite– Ni-C– Ti-C– V-C– Cr-C

• The shape and the fine structure of a peak is related to the local density of states adjacent to the atom

Qualitative analysis

• Peak position

– Compare to table:

– Check by changing the primary energy (does the peak shift?)

– Primary energy > Auger energies

• Peak shape

– compare to handbookA

tom

ic n

um

ber

LMM

KLL

MNN

Auger electron energy [eV]

What is this ?

529 eV703 eV

848 eV

Chromium

529 eV

Iron

703 eV

Nickel

848 eV

Stainless Steel!

Cr529 eV Fe

703 eV

Ni848 eV

What is the composition?

Quantitative analysis• XA = IA/ IA

• IA is measured

• XA is then the mole fraction of element X

• dI = (exp(-d/)) T i N dz• Probabilities for

• creating the initial hole ()• Decay via the Auger process ()• Auger electron making it out of the surface ()

• Detection probability• Number of incident electrons• Atom density (atoms/m3)

• Integrate dI I = S . N• Sensitivity factor (S)• Atom density (N) - related to molar fraction (C)

dz

dI

• Sensitivity factors :

• 5%

Sensitivity factors

N1-7

M1-5

L1-3

K

KLL

LMM

MNN

relative to AgRelative Auger Sensitivities of the Elements

KLL LMM MNN

Composition of stainless steel ?

Cr529 eV

Fe703 eV

Ni848 eV

• I = Sensitivity factor . N

• More components: C =

Ix/Sx

i Ii/Si

Handbook

CrS=0.3

FeS=0.2

NiS=0.28

Composition of stainless steel sample

Known mole fractions of this sample: Cr= 0.205

Fe= 0.702

Ni= 0.093

Cr529 eV Fe

703 eV

Ni848 eV

Other applications• Determine growth-mode• Determine mean free path,

Attenuation of intensity:

I = Iexp(-d/)ln(I/I= (-1/) d

= -d / ln(I/I

I

I0d

52 eV

1147 eV

~2 MLAssume (for Si):

1 ML ~ 1.5.1015 1/cm2, thickness ~2 Å

Mean free path

@ 52 eV:~6 Å

@ 1147 eV:~13 Å

Identification of growth mode

2D

2D-3D

3D

I

I0d

2D: I/I=exp(-n.d/)

3D: I/I=(1-) + exp(-m.d/)

...alloying!

Sputtering Samples

Al/Pd/GaN Thin Film Example

(cross section)

Al/Pd/GaN Profile Data

Al/Pd/GaN Atomic Concentration Data

Area Specific Depth Profile Example

SP UTTER T IM E (M IN .)

PE

AK

-TO

-PE

AK

Fracture surface of Carbon fibers in BN matrix - analysis area outlined in black

Depth profile on fiber to determ ine point of fracture. Variations in fracture surfaceinterface for d ifferent sam ple treatments w ill be reflected in depth profile.

From research by C . C ofer/J. Econom y, M aterials Science D ept.