1

An Introduction to AugerElectron Spectroscopy

Spyros Diplas

spyros.diplas@sintef.no

spyros.diplas@smn.uio.no

SINTEF Industry, Materials Physics-Oslo &

Centre of Materials Science and Nanotechnology, Department of Chemistry, UiO

MENA 3100 ‐ May 2018

2

Contents

• Background

• An Auger microprobe

• The Auger process

• Auger spectroscopy

• Auger mapping

• Depth profiling

3

The Auger process

• Named after Pierre Auger• 1925

• Actually discovered by Lise Meitner• 1922

• Emission of an intial electron leads to the emission of a characteristic (Auger) electron.

Auger Electron Spectroscopy (AES)Exciting radiationElectron beam (Scanning)

SignalElectrons(Spectrometer)

UHV vacuum

Analysis depth(typically a few nm) SAMPLE

Auger emission

EKL2,3 L2,3 ≈ EK – EL2,3 – EL2,3

E = energy of emitted electronEK = K‐shell ionisation energyEL2,3 = L‐shell electron energies

4

5

Auger electron vs x‐ray emission yield

5

B Ne P Ca Mn Zn Br Zr

10 15 20 25 30 35 40 Atomic Number

Elemental Symbol

0

0.2

0.4

0.6

0.8

1.0Pr

obab

ility

Auger Electron Emission

X-ray Photon Emission

6

Auger ‐ lateral resolution

160 kX SEM

160 kX Auger Maps

4m at 20kV

0,1m 2kV

n.b. much better than EDS in bulk samples

7

Auger Electron Spectroscopy

Basic Specification• 3nm SEI resolution • 8nm probe diameter for Auger analysis • Variable energy resolution from 0.05% 

to 0.6% • Chemical state analysis in several 10nm 

areas • Ion gun for sputter depth profiling 

Allows some charge neutralisation for analysis of insulating materials

UHV Chamber FE‐SEM quality electron column nm‐scale depth resolution Depth profiling

Additional capabilities:EDS system

•”Bulk” composition analysis.Backscattered electron detector

•Atomic number contrast.Heating stage

•Diffusion experiments.Liquid nitrogen fracture stage

•Grain boundary and interface studies.Electron Beam Induced Current (EBIC)

•Recombination centre mapping in solar cells, etc.

The JEOL JAMP-9500F FE Auger Microprobe

8

Origin of Auger signal

Auger electron generation

An  Auger electron is emitted. The Auger electron is named after the shells involved in its generation. 

Here L3M1M23

Internal transition: An electron from M1 fills a hole in L3

1st step:

2nd step:

9

Electron spectrometerHemispherical spectrometers often used.

Tend to be used in constant retard ration mode (CRR), as this supresses the strong low energy signal.

Constant analyser energy (CAE) also has uses.

Cylindrical mirror analyser used to be most common, still in use.

10

Auger spectrum ‐ typical

It is quite common to deal with the differential form of the spectrum.

11

Chemical shift in Si compounds

Comparison of Si, SiNxand SiO2

12

Auger spectrum ‐ quantification

Can use peak areas or peak-to-background ratios

13

Auger spectrum ‐ quantificationConcentration of element NA is:

NA = IA/(IA + FABIB+FACIC+....)

I is the element intensity

F is a sensitivity factor determined from binary standards such that:

FAB = (IA/NA/IB/NB)

This is highly simplified but can work reasonable well.

14

Auger mapping

Pixel-by-pixel, typically calculate;

(peak-background)/background

15

Combined SEM/Auger analysis

200nm

Carburised alloy

Combined Auger EDS mapping

16

17

Auger mapping of Si p and n type

AES – nm lateral and depth resolution

18

Chromated aluminium alloy surface• Chromating pretreatment

– corrosion protection– before coating, painting, 

bonding, etc• Does the chromate ”passivate” 

intermetallic particles?

430 450 470 490 510 530 550 570 590Electron kinetic energy / eV

1

2

Cr metal reference

1

2 • Auger spectra show that the intermetallic particles are covered by a thin layer of Cr‐oxide that is invisible in the SEM images.

O

19

Depth profiling ‐ schematic

Process is fully automated, sample can be rotated (Zalar rotation).

N.B. Can also perform angle-resolved analysis.

Electron beam

Argon ion gun

Sample

20

Depth profiling CeO2 buffer layer

21

Potential Auger Applications• Conducting / semiconducting materials • Corrosion studies• Coatings• Depth profiling• Catalysis• Carbon/other material fibres• Metallurgy

• Grain boundaries in steels• Can be extended to low conductivity materials

• Use low energy ion gun to flood surface• Probably not polymers

22

Summary• Combine SEM and electron spectroscopy

• High lateral and depth resolution

• Chemical state information• Need to explore the possibilities

• Depth profiling• ”Bread and butter” applicaion.

• Segregation and interface studies• Surfaces and internal interfaces

• Complementart with other techniques• XPS/TEM…… 

23

References• Scanning Auger Electron Microscopy;

M. Prutton and M. M. El. Gomati, Eds., John Wiley and sons,  2006.

• Practical Surface Analysis by Auger and PhotoelectronSpectroscopy; 

D. Briggs and M. Seah, John Wiley, 1983

• An Introduction to Surface Analysis by XPS and AES; J. F. Watts and J. Wolstenholme, Wiley, Chichester, 2003.

• Surface analysis by Auger and x‐ray photoelectron spectroscopy; 

D. Briggs, J. T. Grant, Eds.; IM: Chichester, 2003