Aes
-
Upload
cynon -
Category
Technology
-
view
870 -
download
6
Transcript of Aes
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.