AUGER ELECTRON SPECTROSCOPY Mahboob Alam, CA12M004 NCCR, IIT-M

AUGER ELECTRON SPECTROSCOPY

Mahboob Alam, CA12M004 NCCR, IIT-M

MAHBOOB ALAMCA12M00415/04/2013




Pronunciation and history

The Auger effect, pronunciated as AW-zhar.

The name Auger effect comes from one of its

discoverers Pierre Victor Auger.

Although auger emission is intense, it was not

used until 1950’s.



What is Auger ?

Auger Electron Spectroscopy (AES) is a widely used technique to investigate the chemical composition of surfaces.



Auger Electron Spectroscopy 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.

Lise Meitner Pierre Victor Auger

1. P. Auger, J. Phys. Radium, 6, 205 (1925).


Mahboob Alam, CA12M004 NCCR, IIT-MCATSYMP19 PRESCHOOL

Particle-Surface Interactions

Vacuum

electronelectron

IonsElectronsPhotons

IonsElectronsPhotons





Basic theoryAuger spectroscopy can be considered as involving

three basic steps :

Atomic ionization (by removal of a core electron) Electron emission (the Auger process) Analysis of the emitted Auger electrons

7





Equation

KE ===== Kinetic Energy (measure in the XPS spectrometer).

hv ===== photon energy from the X-Ray source (controlled).

Ø ===== spectrometer work function. It is a few eV, it gets more complicated because the materials in the instrument will affect it. Found by calibration.

BE ==== is the unknown variable.

KE=hv-BE-Ø



Remove adsorbed gases from the sample.

Eliminate adsorption of contaminants on the sample.

Prevent arcing and high voltage breakdown.

Increase the mean free path for electrons, ions and photons.

Degree of Vacuum10

10

10

10

10

2

-1

-4

-8

-11

Low Vacuum

Medium Vacuum

High Vacuum

Ultra-High Vacuum

PressureTorr

Why UHV for Surface Analysis?



AUGER PARAMETER

Primary Beam=3-20KeV electrons

Detection Sensitivity=1%

Sampling Distance(depth)=2to4nm

Analysis Diameter=80nm to several millimeter

Element Detectable=Li and above



Atomic number

Auger

yie

ld

Probabilities of X-rays Fluorescence and Auger emission

0 15

30 45 60 75 90

.5

1

.5

1

Fluore

scence

yie

ld



BE

WO

RK

FU

NC

TIO

N

PHOTO ELECTRON VS AUGER ELECTRON EMISSION

KE=hv-BE-Work function

Incident Xrays

Photo electron Emitted Auger e

L2,

3L1

Emitted X-rays

Fermi Level



Characterstics AES

Primary beam Electron

Analyzed beam Electron

Types of sample conductive

Area of analysis 10nm

Surface selectivity 1to5nm

Elemental identification All except H and He

Sensitivity .10%

Nature of chemical bombarding

Shift and shape

Depth profiling Elemental,chemical

Destructive nature none

Characteristic of AES



X-rays vs. electron BeamX-Rays

Hit all sample area simultaneously permitting data

acquisition that will give an idea of the average

composition of the whole surface.

Electron Beam

It can be focused on a particular area of the sample

, determine the composition of selected areas of

the sample surface.



AUGER ELECTRONS ARE PRODUCED IN TWO DIFFERENT WAYS

1. The X-Ray source can irradiate and remove the e- from the core level causing the e- to leave the atom.

A higher level e- will occupy the vacancy. The energy released is given to a third

higher level e-. This is the Auger electron that leaves the

atom.

2. The electron gun can irradiate and remove the core e- by collision. Once the core vacancy is created, the Auger electron process occurs the same way.



AES INSTRUMENT CONFIGURATION

Elements of Auger System

Electron gun

Analyser

Secondary Electron Detector

Ion Gun

Sample Stage

Intoduction System



ANALYSER CONFIGURATION

Generally Two Types

Cylindrical Mirror Analyzer(CMA)

Hemisphericalsector Analyzer(HAS)



Salient features

Resolution scales with

Ep.

Coaxial design eliminates

topography shadowing.

Better transmission than

an HSA

Relatively short working

distance



Salient feature Better energy resolution

Longer working distance

possible

Angle dependent

measurement possible



Kinetic energy of each Auger electron (EAUG):

Core hole of ionization of K electron BE in O =532

eV(EA)

BE of L1 electron in O=24eV(EB)

BE of L2,3 electron in O=7eV(EC)

Auger electron Kinetic Energy

(EKLL) in O=532-24-7=501eV

EAUG=ECore-EB-EC

http://mse.hanyang.ac.kr/SNE/

Calculation of Auger electron spectroscopy

ECore State: the core level electron energiesEB : first outer shell electron energiesEC* : second outer shell electron energies



KE versus BE

E E E

KE can be plotted depending on BE

Each peak represents the amount of e-s at a certain energy that is characteristic of some element.

1000 eV 0 eV

BE increase from right to left

KE increase from left to right Binding energy

No o

f ele

ctr

on

s

(eV)



FOUR ways to represent Auger spectra

a)N(E) vs E b)dN(E)/d(E)vs E c)d(E.N(E)vs E d) E.N(E)vs E



AES is one of the best complementary technique for XPS in the chemical analysis. Depending on the kinetic energy of the Auger electrons, AES is much more sensitive to the surface.

Chemical shifts and Auger line shape can be used to determine the chemical state for a given element in the sample, and is studies as charge transfer in alloys.

Chemical AnalysisExamples for AES:

Differences in the line shape and peak Position for the C Auger (KVV) in different CxHy compounds



Auger chemical state information for a Ge single crystal with layer of oxide

Ge(4)

Ge(0)

Ge(4)

Ge(0)

1130 1150 1170 1190

Kinetic Energy(eV)





SiO Si-Si

1600 1610 1620 1630

Auger spectral from element silicon and oxidized silicon showing the chemical shift which occur in the oxide



Sources of artifacts sample charging

topographical features resulting of non-uniform sputtering of

the sample

preferential sputtering

beam effects

Ion beam mixing

Auger depth profiling

R.Nix, http://www.chem.qmw.ac.uk/surfascc/ces/



Quantification of the different element on the surface



Identify surface contaminants and composition.

Study composition as a function of depth.

Analyze sample features as small as 80nm.

Using an electron gun for the primary beam allows small analysis spot sizes.

Corrosion Adhesion Catalysis Chemical Characterization Surface reaction

APPLICATION OF AUGER ELECTRON SPECTROSCOPY



It is extremely reliable and reproducible

Need UHV

Standard surface analysis technique

Only surface sensitive

More spatial resolution Need careful calibration

Can even do depth profiling with light ion sputtering

Somewhat difficult to calibrate for adsorbates on surface

ADVANTAGE AND LIMITATION OF AES



Comparison of the main characteristics of AES, XPS and SIMS



References Handbook of auger electron spectroscopy, Physical Electronics

Industries

Chung and Jenkins, Surface Science,21,253(1970)

F. P. Larkins, Application of Surface, Science 13,1982,4-34.

ASM. Vol.10 Material Characterization

www.wikipedia.org

Introduction to Surface science and thin films – J. Venables

D. Briggs and M.P. Seah, ‘Practical Surface Analysis. Volume 1 – Auger

and

X-ray Photoelectron Spectroscopy’, Second Edition, John Wiley and

Sons,

Chichester, 1990

T.A. Carlson, ‘Photoelectron and Auger Spectroscopy’, Plenum Press,

New

York, 1975

J.F. Watts, ‘An Introduction to Surface Analysis by Electron

Spectroscopy’,

Oxford University Press, Oxford, 1990



THANK YOU

If we knew what we were doing, It wouldn't be research, now would it?

Albert Einstein (1879-1955)

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AUGER ELECTRON SPECTROSCOPY Mahboob Alam, CA12M004 NCCR, IIT-M