Auger Electron Spectroscopy, AES, and Electron Spectroscopy for chemical analysis, ESCA
Transcript of Auger Electron Spectroscopy, AES, and Electron Spectroscopy for chemical analysis, ESCA
Emre Ertuğrul
20824006
Emin Şahin
20824259
Seçkin Gökçe
20824044
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
ESCA AES
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 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
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)
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: Electron Gun Analyzer Secondary Electron Detector Ion Gun Sample Stage Introduction System
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