Electron Spectroscopy for chemical analysis, ESCA and Auger Electron Spectroscopy, AES,

1. Electron Spectroscopy for chemical analysis, ESCAandAuger Electron Spectroscopy, AES, • KMU 396 Material Science and Technology Emre Ertuğrul 20824006 Emin Şahin 20824259 Seçkin Gökçe 20824044

2. Outline of Lecture ESCA AES • Introduction • -History of AES • -General Uses • Principles of Operation • Instrumentation • Auger Spectrum • Common Applications • Advantages & Disadvantages of AES • Introduction -advantages, -disadvantages • Principles of ESCA • The photoelectron effect • Instrumentation • Analysis Capabilities -Elemental analysis -Chemical state analysis -More complex effects • Surface Sensitivity

3. Introduction • ESCA 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

4. Principles of ESCA • ESCA is based on the photoelectron effect. • A high energy X-ray photon can ionize anatom • 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

5. Instrumentation • Essential 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, Computer • Note: All in ultrahigh vacuum (<10-8 Torr) (<10-11 atm) • State-of-the-art small spot ESCA: 10 mm spot size. Figure A

6. http://www.sphysics.com/ AES in Laboratory

7. 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

8. Applications -- Surface contamination -- Failure analysis -- Effects of surface treatments -- Coating, films -- Tribological effects -- Depth Profiling (Ar+ sputtering)

9. ESCA studies of polyimide Pyromellitic dianhydride -- oxydianiline PMDA - ODA Figure B

10. 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 Meitner Pierre Victor Auger 1. P. Auger, J. Phys. Radium, 6, 205 (1925).

11. General Uses • Surface composition analysis for metals, powders, insulators, • Identification of particulates, localized dopants or contaminants, visual defects • Investigation of submicrometer dimension structures • Grain boundary investigations, e.g. intergranular corrosion • Analysis of surface coatings and thin films • When combined with ion sputtering, elemental depth profiling of surface and/or interfacial layers

12. Principles of Operation Auger Electron Spectroscopy Ions Electrons Photons Ions Electrons Photons • samplebombardment by electrons • core electron removed • electron from a higher energy level fall into the vacancy • release of energy. • measured energy anddefinedsample Vacuum

13. AES Instrument Configuration • Elements of Typical Auger System: • Electron Gun • Analyzer • Secondary Electron Detector • Ion Gun • Sample Stage • Introduction System

14. Auger Spectrum Figure C http://mee-inc.com/sam.html

15. 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).

16. Limits of Techniqueand 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.

17. Summary ESCA & AES is very important analytical techniques used in materials scienceto investigate molecular surface structures and their electronic properties.

18. 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

19. ThankYouAll …