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 …