Electron Spectroscopy for

chemical analysis, ESCA and Auger

Electron Spectroscopy, AES,

Emre Ertuğrul

20824006

Emin Şahin

20824259

Seçkin Gökçe

20824044

KMU 396 Material Science and Technology

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

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

Principles of ESCA

ESCA 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

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

http://www.sphysics.com/

AES in Laboratory

Analysis Capabilities

Elemental 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

Applications-- Surface contamination

-- Failure analysis

-- Effects of surface treatments

-- Coating, films

-- Tribological effects

-- Depth Profiling (Ar+ sputtering)

ESCA studies of polyimidePyromellitic dianhydride -- oxydianiline PMDA - ODA

Figure B

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).

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

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

AES Instrument Configuration

Elements of Typical Auger System: Electron Gun Analyzer Secondary Electron Detector Ion Gun Sample Stage Introduction System

Auger Spectrum

Figure C

http://mee-inc.com/sam.html

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).

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.

Summary

ESCA & AES is very important analytical techniques used in

materials science to investigate molecular surface structures and

their electronic properties.

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

Thank You All …