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Auger Electron Spectroscopy

(AES)

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Brief History

• Auger Effect discovered in 1920’s

• Meitner published first journal

• Auger transitions considered noise at first

• 1953-JJ Lander• Characterization of solids

today

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Three Steps of Auger Electron Spectroscopy

• Note: Solid Samples• 1) Atomic ionization• 2) Electron emission• 3) Analysis

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Atomic Ionization

• “Core Hole”• Electron Beam• Core hole probability:σ=Constant x C(Ei/EA)/EA^2

http://pages.jh.edu/~chem/fairbr/surfacelab/aes.html

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The Auger Process

http://pages.jh.edu/~chem/fairbr/surfacelab/aes.html

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Important Nomenclatures• Electron orbitals and principle quantum number (n)

• Given subscripts based off spins

http://pages.jh.edu/~chem/fairbr/surfacelab/aes.html

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Auger Transissions

• KE of Auger Electron=E(A)=EK-(EL1+EL2)Ex: Silicon K1=1600L1=60, L2=30E(A)=?• Rough Estimate of KE

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Auger Electron Spectra

Direct Spectra• 1x zoom (bottom)• 10x zoom (top)

newton.phys.uaic.ro/data/ppt/L5(AES).ppt

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Auger Electron Spectra

dN(E)/dE Plot d[E*N(E)]/dE plot

Density of States= N(E)=(4π/h3)(2mh*)3/2(Ev-E)1/2

newton.phys.uaic.ro/data/ppt/L5(AES).ppt

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Qualitative Analysis

Elemental Identification Procedure

• Main Auger Peaks ID’d• Values compared to table• ID’d elements labeled on

spec• Repeat procedure until

peaks found

Auger Sample

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Qualitative Analysis

http://www.eag.com/cmss_files/imagelibrary/auger-electron-energies.gif

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Electron Beam/Sample Interaction

• Penetrates 1-3µm• Mean-free path 5-50

angstroms• Backscattered electrons• Secondary electrons• X-Rays from sample• Auger Electron

http://en.wikipedia.org/wiki/Scanning_electron_microscope#Detection_of_backscattered_electrons

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Sample Prep

• Sample 1mm thickness, 1 cm diameter

• Mounted in Ultra-High Vacuum

• Sputtering• Annealing

http://wwwold.ece.utep.edu/research/webedl/cdte/Fabrication/sputtering.gif

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Electron Beam

• Monochromatic electrons• Beam 0.1mm-0.5mm wide• Scans surface

http://www.bing.com/images/search?q=Electron+Beam+Tube&view=detailv2&&&id=4CF43715C2DE021317F945D9A8206DE75B473527&selectedIndex=9&ccid=k%2fBps2H4&simid=608029209144657635&thid=JN.jnUWfUaASQqjpf3KGWNidQ&ajaxhist=0

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Analyzers

• Grid Purposes• Low Energy Electron

Diffraction (LEED)

Retarding Field Analyzer (RFA)

http://www.udel.edu/pchem/C874/LEED_lecture.pdf

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Non-Retarding Mode

• Applied Voltage without suppressor

• Broader energy absorbed• More imaging per run• Less luminescence• Less angular contact

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RFA LEED optics

• Low-energy electrons strike screen (30-300eV)

• De Broglie relationship λ A = (150/E eV)1/2 • Spacing between atoms• Fluoresce when strike

screen

http://www.udel.edu/pchem/C874/LEED_lecture.pdf

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Data Analysis

• XY-Recorder-intensities• Video Camera• Collects all energies• Single points collected• Produces spectra• Compared to Calculated

http://www.matscieng.sunysb.edu/leed/dataacquire.html

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Cylindrical Mirror Analyzer

• Two concentric metal cylinders

• Different V on each cylinder• e- fired from gun to sample• e- of certain energies

analyzed

Double Pass Design

http://uksaf.org/tech/cma.html

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Hemispherical Analyzer• Concave and Convex Hemisphere• Centers of curvature are coincident

so electrons come to a point at detector

• Electric Field-varying voltages• Pass electrons to analyzer• Series of lenses before detector• Constant Retard Ration (CRR)• Constant Analysis Energy (CAE)

http://uksaf.org/tech/cha.html

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Advantages and Disadvantages

• Advantages• Surface Sensitive• Elemental and Chemical composition and

analysis by comparing sample to known samples

• Quantitative composition information as a function of depth below the surface

• Good for spatial distribution of elements in sample (structure).

• I will fix this slide tomorrow just haven’t found out what to do yet about it.

• Disadvantages• Samples must be able to compatible with

ultra high vacuum• Samples must be conductive• Possibility of beam damage for organic

molecules• Cannot detect hydrogen or helium• Quantitative detection is dependent on

the element, but accurate to high sensitivity

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