Auger Electron Spectroscopy, AES, and Electron
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Transcript Auger Electron Spectroscopy, AES, and Electron
Emre Ertuğrul
20824006
Emin Şahin
20824259
Seçkin Gökçe
20824044
KMU 396
Material Science and Technology
Outline of Lecture
ESCA
Introduction
-advantages,
-disadvantages
Principles of ESCA
The photoelectron effect
Instrumentation
Analysis Capabilities
-Elemental analysis
-Chemical state analysis
-More complex effects
Surface Sensitivity
AES
•Introduction
-History of AES
-General Uses
•Principles of Operation
•Instrumentation
•Auger Spectrum
•Common Applications
•Advantages & Disadvantages of
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
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 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
• sample bombardment
by electrons
•core electron removed
Ions
Electrons
Photons
Ions
Electrons
Photons
• electron from a higher
energy level fall into the
vacancy
•release of energy.
•measured energy and
defined sample
Vacuum
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-electronspectrometry-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 …