Electron Spectroscopy for chemical analysis, ESCA and Auger Electron Spectroscopy, AES,
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Transcript of Electron Spectroscopy for chemical analysis, ESCA and Auger Electron Spectroscopy, AES,
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Electron Spectroscopy for
chemical analysis, ESCA and Auger
Electron Spectroscopy, AES,
Emre Ertuğrul20824006
Emin Şahin20824259
Seçkin Gökçe20824044
KMU 396 Material Science and Technology
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Outline of Lecture
Introduction -advantages, -disadvantagesPrinciples of ESCAThe photoelectron effectInstrumentation Analysis Capabilities
-Elemental analysis-Chemical state analysis -More complex effects
Surface Sensitivity
•Introduction -History of AES -General Uses
•Principles of Operation
•Instrumentation
•Auger Spectrum
•Common Applications
•Advantages & Disadvantages of AES
ESCA AES
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IntroductionESCA provides unique information about chemical composition
And chemical state of a surface
useful for biomaterials
advantages-- surface sensitive (top few monolayers)-- wide range of solids-- relatively non-destructive
disadvantages-- expensive, slow, poor spatial resolution, requires high vacuum
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Principles of ESCAESCA is based on the photoelectron effect. A high energy X-ray photon can ionize an atom
Detecting electrons ejected from higher orbitals
producing an ejected free electron with kinetic energy KE:
KE=hv-BE
*BE=energy necessary to remove a specific electron from an atom. BE ≈ orbital energy*h=Planck Constant*v=frequency of light
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InstrumentationEssential components:Sample: usually 1 cm2
X-ray source: Al: 1486.6 eV; Mg 1256.6 eV
Electron Energy Analyzer: 100 mm radius concentric hemispherical analyzer; vary voltages to vary pass energy.
Detector: electron multiplier (channeltron)
Electronics, ComputerNote: All in ultrahigh
vacuum (<10-8 Torr) (<10-11 atm)
State-of-the-art small spot ESCA: 10 mm spot size.
Figure A
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http://www.sphysics.com/
AES in Laboratory
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Analysis CapabilitiesElemental Analysis: atoms have valence
and core electrons: Core-level Binding energies provide unique signature of elements.
Quantitative analysis: measure intensities, use standards or sensitivity factor
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Applications-- Surface contamination-- Failure analysis-- Effects of surface treatments-- Coating, films-- Tribological effects-- Depth Profiling (Ar+ sputtering)
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ESCA studies of polyimidePyromellitic dianhydride -- oxydianiline PMDA - ODA
Figure B
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Introduction to Auger Electron Spectroscopy (AES)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 MeitnerPierre Victor Auger
1. P. Auger, J. Phys. Radium, 6, 205 (1925).
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General Uses Surface composition analysis for metals,
powders, insulators, Identification of particulates, localized
dopants or contaminants, visual defectsInvestigation of submicrometer dimension
structuresGrain boundary investigations, e.g.
intergranular corrosion Analysis of surface coatings and thin filmsWhen combined with ion sputtering,
elemental depth profiling of surface and/or interfacial layers
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Principles of OperationAuger Electron Spectroscopy
IonsElectronsPhotons
Vacuum
IonsElectronsPhotons
• sample bombardment by electrons
•core electron removed
• electron from a higher energy level fall into the vacancy
•release of energy.
•measured energy and defined sample
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AES Instrument Configuration
Elements of Typical Auger System: Electron Gun Analyzer Secondary Electron Detector Ion Gun Sample Stage Introduction System
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Auger Spectrum
Figure C
http://mee-inc.com/sam.html
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Advantages• Monolayer-sensitive surface analysis with high spatial resolution
•Elemental mapping across surface
•Elemental depth profiling with uniform sensitivity
• It is sensitive to light elements (except H and He).
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Limits of Technique and Disadvantages•Surface Sensitivity: < 1 nm
•Lateral Resolution: < 50 nm
•Analytical Volume: 10-18 cm3
•Insulators are difficult to study due to surface charging.
•Surface may be damaged by the incident electron beam.
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Summary
ESCA & AES is very important analytical techniques used in
materials science to investigate molecular surface structures and
their electronic properties.
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References•http://www.rci.rutgers.edu/.../LECTURE5•http://nanoall.blogspot.com/2011/10/auger-electron-spectrometry-aes.html•http://www.orlabs.com/AugerElectronSpectroscopy.php•http://www.wellesley.edu/Chemistry/Chris/AES.html •http://www.Ism.rutgers.edu/esca/principles.html •http://www.jhu.edu/chem/fairbr/surfacelab/aes.html
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Thank You All …