AUGER ELECTRON
SPECTROSCOPY
PRINCIPLES AND APPLICATIONS
http://203.199.213.48/1386/1/AUGER_ELECTRON_SPECTROSCOPY_FOR_17TH.ppt.
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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 [1]
Lise Meitner
Pierre Victor Auger
1. P. Auger, J. Phys. Radium, 6, 205 (1925). 2
Particle-Surface Interactions
Auger Electron Spectroscopy
Ions Ions
Electrons Electrons
Photons Photons
Vacuum
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Basic theory
Auger spectroscopy can be considered as involving three basic steps :
(1) Atomic ionization (by removal of a core
electron)
(2) Electron emission (the Auger process)
(3) Analysis of the emitted Auger electrons
This last stage is simply a technical problem of detecting charged particles with high
sensitivity, with the additional requirement that the kinetic energies of the emitted
electrons must be determined.
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Photoelectron vs. Auger Electron Emission
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Auger Electron Spectroscopy
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Physics basis
An Auger transition is therefore characterized primarily by :-
1. the location of the initial hole
2. the location of the final two holes
In general, since the initial ionisation is non-selective and the initial hole may therefore be in various shells, there will
be many possible Auger transitions for a given element - some weak, some strong in intensity. AUGER
SPECTROSCOPY is based upon the measurement of the kinetic energies of the emitted electrons . Each element in
a sample being studied will give rise to a characteristic spectrum of peaks at various kinetic energies.
This is an Auger spectrum of Pd metal - generated using a 2.5 keV electron beam to produce the initial core vacancies and hence to stimulate
the Auger emission process. The main peaks for palladium occur between 220 & 340 eV. The peaks are situated on a high background which
arises from the vast number of so-called secondary electrons generated by a multitude of inelastic scattering processes.
Auger spectra are also often shown in a differentiated form : the reasons for this are partly historical, partly because it is possible to actually
measure spectra directly in this form and by doing so get a better sensitivity for detection. The plot below shows the same spectrum in such a
differentiated form.
High secondary electron background
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INSTRUMENTATION
Main Features of the Laboratory's JAMP 9500F AES Capability
•Quantitative analysis of elements except hydrogen and helium
•Typical element detection limits are 0.1 atomic% from the top few nm (2-5)
•SEM (scanning electron microscopy)
•Scanning Auger Microscopy (SAM) allows surface chemical maps to be collected with lateral resolutions better than 10nm.
•Chemical state information of certain elements (particularly Al, Mg, Si etc.) can be obtained
•Sputter depth profiling reveals chemical depth information
•Samples can be conductors and semiconductors. Analysis of insulators is more difficult but possible
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The System available at VUB-SURF
JEOL9500 F Capabilities
● Elemental composition in a sampling depth that can attain 20 Å.
● Detection of elements heavier than Li. Very good sensitivity for light elements.
● Depth profiling, with depth resolution around 20 Å.
● Spatial distribution of the elements (Auger maps or analysis in lines, points and areas)
● Secondary electron images with spatial resolution down to 10 nm.
● Backscattered electrons imaging.
Energy resolution : 0.06 % compared to 0.1% for most systems
Limitations:
● Samples must be conductive.
● Possibility of beam damage of some surfaces
● Hydrogen and helium are not detectable.
● Quantitative detection is dependent on the element: light elements > 0.1%; heavier elements > 1%.
● Accuracy of quantitative analysis depending on the availability of adequate sensitivity factors. Best accuracy ± 10%.
Analysis requirements:
● AES - Conductive materials. Flat specimens: max. diameter 2 cm and max. height 1 cm;
● Specimen surface not handled. Samples must be clean and free of organics or high vapour pressure contaminants.
● Samples are first analysed “as received” and after a short etching to ensure that all contaminants are removed.
● Surface elemental composition and quantification takes less than 1 hour.
● Depth profiling, Auger imaging with high-resolution curve fitting require analysis time between 1 and 5 hours.
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SITE DIFFERENTIATION
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Surface Analysis Depths
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Scanning Auger Electron Spectrometer
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Elemental Shifts
L. E. Davis, N. C. MacDonald, Paul W. Palmberg, G. E. Riach, R. E. Weber, Handbook of Auger Electron Spectroscopy,
2nd Edition, Physical Electronics Division, Perkin-Elmer Corp., Eden Prairie, MN 1976. 15
Quantitative surface analysis: AES
By assuming the concentration to be a relative ratio of atoms,
we can neglect the terms that depend only on the instrument:
The values of S are determined theoretically or empirically with
standards.
AES is considered to be a semi-quantitative technique
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Quantitative surface analysis: AES
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Auger Analysis Examples
A - Chemical composition, thickness and spatial distribution of the elements on
cerium conversion layers deposited on galvanised steel. Effect of the treatment time
(30 minutes and 24 hours)
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AES Depth Profiling: An Example
(cross section)
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AES Depth Profiling: An Example
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Imaging
Electron Beam in combination with
an SED detector allows for imaging
of the sample to select the area for analysis
Fracture surface of Carbon fibers
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Chemical Shift
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Semiconductor Doping Shift in AES
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Doping Map by AES
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THANK YOU
If we knew what we were doing,
It wouldn't be research, now would it?
Albert Einstein (1879-1955)
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