Emre Ertuğrul Emin Şahin Seçkin Gökçe KMU 396 Material Science and Technology

Outline of Lecture Introduction -advantages, -disadvantages Principles of ESCA The photoelectron effect Instrumentation 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 ESCAAES

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

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

Instrumentation Essential components: Sample: usually 1 cm 2 X-ray source: Al: eV; Mg 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) (< atm) State-of-the-art small spot ESCA: 10  m spot size. Figure A

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 polyimide Pyromellitic 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 Meitner Pierre 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 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

Principles of Operation Auger Electron Spectroscopy Ions Electrons Photons Vacuum Ions Electrons Photons 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: Ê Electron Gun Ë Analyzer Ì Secondary Electron Detector Í Ion Gun Î Sample Stage Ï Introduction System

Auger Spectrum Figure C

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: 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 spectrometry-aes.html

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