auger electron spectroscopy mahboob alam, ca12m004 nccr, iit-m
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AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
MAHBOOB ALAMCA12M00415/04/2013
AUGER ELECTRON SPECTROSCOPY
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Pronunciation and history
The Auger effect, pronunciated as AW-zhar.
The name Auger effect comes from one of its
discoverers Pierre Victor Auger.
Although auger emission is intense, it was not
used until 1950’s.
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
What is Auger ?
Auger Electron Spectroscopy (AES) is a widely used technique to investigate the chemical composition of surfaces.
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Auger Electron Spectroscopy Auger Electron Spectroscopy (AES), is a
widely used technique to investigate the composition of surfaces.
First discovered in 1923 by Lise Meitner and later independently discovered once again in 1925 by Pierre Auger.
Lise Meitner Pierre Victor Auger
1. P. Auger, J. Phys. Radium, 6, 205 (1925).
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-MCATSYMP19 PRESCHOOL
Particle-Surface Interactions
Vacuum
electronelectron
IonsElectronsPhotons
IonsElectronsPhotons
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Basic theoryAuger spectroscopy can be considered as involving
three basic steps :
Atomic ionization (by removal of a core electron) Electron emission (the Auger process) Analysis of the emitted Auger electrons
7
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Equation
KE ===== Kinetic Energy (measure in the XPS spectrometer).
hv ===== photon energy from the X-Ray source (controlled).
Ø ===== spectrometer work function. It is a few eV, it gets more complicated because the materials in the instrument will affect it. Found by calibration.
BE ==== is the unknown variable.
KE=hv-BE-Ø
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Remove adsorbed gases from the sample.
Eliminate adsorption of contaminants on the sample.
Prevent arcing and high voltage breakdown.
Increase the mean free path for electrons, ions and photons.
Degree of Vacuum10
10
10
10
10
2
-1
-4
-8
-11
Low Vacuum
Medium Vacuum
High Vacuum
Ultra-High Vacuum
PressureTorr
Why UHV for Surface Analysis?
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AUGER PARAMETER
Primary Beam=3-20KeV electrons
Detection Sensitivity=1%
Sampling Distance(depth)=2to4nm
Analysis Diameter=80nm to several millimeter
Element Detectable=Li and above
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Atomic number
Auger
yie
ld
Probabilities of X-rays Fluorescence and Auger emission
0 15
30 45 60 75 90
.5
1
.5
1
Fluore
scence
yie
ld
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
BE
WO
RK
FU
NC
TIO
N
PHOTO ELECTRON VS AUGER ELECTRON EMISSION
KE=hv-BE-Work function
Incident Xrays
Photo electron Emitted Auger e
L2,
3L1
Emitted X-rays
Fermi Level
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Characterstics AES
Primary beam Electron
Analyzed beam Electron
Types of sample conductive
Area of analysis 10nm
Surface selectivity 1to5nm
Elemental identification All except H and He
Sensitivity .10%
Nature of chemical bombarding
Shift and shape
Depth profiling Elemental,chemical
Destructive nature none
Characteristic of AES
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
X-rays vs. electron BeamX-Rays
Hit all sample area simultaneously permitting data
acquisition that will give an idea of the average
composition of the whole surface.
Electron Beam
It can be focused on a particular area of the sample
, determine the composition of selected areas of
the sample surface.
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AUGER ELECTRONS ARE PRODUCED IN TWO DIFFERENT WAYS
1. The X-Ray source can irradiate and remove the e- from the core level causing the e- to leave the atom.
A higher level e- will occupy the vacancy. The energy released is given to a third
higher level e-. This is the Auger electron that leaves the
atom.
2. The electron gun can irradiate and remove the core e- by collision. Once the core vacancy is created, the Auger electron process occurs the same way.
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AES INSTRUMENT CONFIGURATION
Elements of Auger System
Electron gun
Analyser
Secondary Electron Detector
Ion Gun
Sample Stage
Intoduction System
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
ANALYSER CONFIGURATION
Generally Two Types
Cylindrical Mirror Analyzer(CMA)
Hemisphericalsector Analyzer(HAS)
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Salient features
Resolution scales with
Ep.
Coaxial design eliminates
topography shadowing.
Better transmission than
an HSA
Relatively short working
distance
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Salient feature Better energy resolution
Longer working distance
possible
Angle dependent
measurement possible
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Kinetic energy of each Auger electron (EAUG):
Core hole of ionization of K electron BE in O =532
eV(EA)
BE of L1 electron in O=24eV(EB)
BE of L2,3 electron in O=7eV(EC)
Auger electron Kinetic Energy
(EKLL) in O=532-24-7=501eV
EAUG=ECore-EB-EC
http://mse.hanyang.ac.kr/SNE/
Calculation of Auger electron spectroscopy
ECore State: the core level electron energiesEB : first outer shell electron energiesEC* : second outer shell electron energies
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
KE versus BE
E E E
KE can be plotted depending on BE
Each peak represents the amount of e-s at a certain energy that is characteristic of some element.
1000 eV 0 eV
BE increase from right to left
KE increase from left to right Binding energy
No o
f ele
ctr
on
s
(eV)
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
FOUR ways to represent Auger spectra
a)N(E) vs E b)dN(E)/d(E)vs E c)d(E.N(E)vs E d) E.N(E)vs E
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AES is one of the best complementary technique for XPS in the chemical analysis. Depending on the kinetic energy of the Auger electrons, AES is much more sensitive to the surface.
Chemical shifts and Auger line shape can be used to determine the chemical state for a given element in the sample, and is studies as charge transfer in alloys.
Chemical AnalysisExamples for AES:
Differences in the line shape and peak Position for the C Auger (KVV) in different CxHy compounds
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Auger chemical state information for a Ge single crystal with layer of oxide
Ge(4)
Ge(0)
Ge(4)
Ge(0)
1130 1150 1170 1190
Kinetic Energy(eV)
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
SiO Si-Si
1600 1610 1620 1630
Auger spectral from element silicon and oxidized silicon showing the chemical shift which occur in the oxide
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Sources of artifacts sample charging
topographical features resulting of non-uniform sputtering of
the sample
preferential sputtering
beam effects
Ion beam mixing
Auger depth profiling
R.Nix, http://www.chem.qmw.ac.uk/surfascc/ces/
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Quantification of the different element on the surface
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Identify surface contaminants and composition.
Study composition as a function of depth.
Analyze sample features as small as 80nm.
Using an electron gun for the primary beam allows small analysis spot sizes.
Corrosion Adhesion Catalysis Chemical Characterization Surface reaction
APPLICATION OF AUGER ELECTRON SPECTROSCOPY
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
It is extremely reliable and reproducible
Need UHV
Standard surface analysis technique
Only surface sensitive
More spatial resolution Need careful calibration
Can even do depth profiling with light ion sputtering
Somewhat difficult to calibrate for adsorbates on surface
ADVANTAGE AND LIMITATION OF AES
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
Comparison of the main characteristics of AES, XPS and SIMS
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
References Handbook of auger electron spectroscopy, Physical Electronics
Industries
Chung and Jenkins, Surface Science,21,253(1970)
F. P. Larkins, Application of Surface, Science 13,1982,4-34.
ASM. Vol.10 Material Characterization
www.wikipedia.org
Introduction to Surface science and thin films – J. Venables
D. Briggs and M.P. Seah, ‘Practical Surface Analysis. Volume 1 – Auger
and
X-ray Photoelectron Spectroscopy’, Second Edition, John Wiley and
Sons,
Chichester, 1990
T.A. Carlson, ‘Photoelectron and Auger Spectroscopy’, Plenum Press,
New
York, 1975
J.F. Watts, ‘An Introduction to Surface Analysis by Electron
Spectroscopy’,
Oxford University Press, Oxford, 1990
AUGER ELECTRON SPECTROSCOPY
Mahboob Alam, CA12M004 NCCR, IIT-M
THANK YOU
If we knew what we were doing, It wouldn't be research, now would it?
Albert Einstein (1879-1955)