Introduction to Introduction to Auger Electron Auger Electron

Spectroscopy (AES)Spectroscopy (AES)MATSE 305 - November 23, 1998MATSE 305 - November 23, 1998

Center for Microanalysis of MaterialsCenter for Microanalysis of Materials

Frederick Seitz Materials Research Frederick Seitz Materials Research LaboratoryLaboratory

University of Illinois at Urbana-University of Illinois at Urbana-ChampaignChampaign

What is Auger?What is Auger?

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

The M ach ine

The M an

Auger (as in ‘Pierre’)

1923:Pierre Auger

d iscovers

the A uger process

Electron Spectroscopy

Why the Odd Name?Why the Odd Name?

W hy is A uger so surface sensitive?

Re f: C ha rle s Eva ns & Asso c . we b p a g e tuto ria l b y Ro n Flle m ing http ://www.c e a .c o m

Surface SensitivitySurface Sensitivity

IncidentElectron

STEP 3(alternative)an x-ray is emittedto conserve energyreleased in step 2

STEP 3KLL Auger electronemitted to conserveenergy released instep 2

STEP 2L electron fallsto fill vacancy

STEP 1Ejected electron

-or-

K

L1

L2

L3

1s

2s

2p

CONDUCTION BAND

VALENCE BAND

FREEELECTRONLEVEL

FERMILEVEL

E(Auger)=E(K)-E(L2)-E(L3)

E(X-ray)=E(K)-E(L2)

Auger Transition Named:KLL

The Auger ProcessThe Auger Process

Auger Energy ScaleAuger Energy Scale

The AES instrument measures The AES instrument measures the kinetic energy of all collected the kinetic energy of all collected electrons.electrons.

AES Electron vs. X-ray PhotonAES Electron vs. X-ray Photon

Relative Probabilities of RelaxationRelative Probabilities of Relaxationof a K Shell Core Holeof a K Shell Core Hole

5

B Ne P Ca M n Z n Br Z r

10 15 20 25 30 35 40 Atom ic Number

Elem en ta l Sym bol

0

0.2

0.4

0.6

0.8

1.0

Pro

ba

bili

ty

Note: The lightNote: The lightelements have aelements have alow cross sectionlow cross sectionfor X-rayfor X-rayemission.emission.

Auger ElectronAuger ElectronEmissionEmission

X-ray PhotonX-ray PhotonEmissionEmission

Auger StatsAuger Stats

Primary Beam = 3 - 20 KeV electrons

Detection Sensitivity = ~1 atomic %

Sampling Distance (depth) = 2 to 4 nm

Analysis Diameter = 80nm to several mm

Elements Detectable = Li and above

Auger Data FormatsAuger Data Formats

Raw Data Differentiated Data

AES Can Identify ElementsAES Can Identify Elements

E lem enta l varia tion in sensitiv ity factors

3kV P rim ary B eam Vo ltage

5kV P rim ary B eam Vo ltage

Re f: C ha rle s Eva ns & Asso c . we b p a g e tuto ria l b y Ro n Flle m ing http ://www.c e a .c o m

AES Sensitivity FactorsAES Sensitivity Factors

Peak Height / QuantitationPeak Height / Quantitation

For quantitation the derivativeform of the data is used.

Sensitivity Factors are usedto adjust the peak heights ofall elements present in thesample.

The composition is normalizedto 100% to determine the amountof each element.

Identify surface contaminants and Identify surface contaminants and composition.composition.

Study composition as a function of Study composition as a function of depth.depth.

Analyze sample features as small as Analyze sample features as small as 80nm. Using an electron gun for the 80nm. Using an electron gun for the primary beam allows small analysis primary beam allows small analysis spot sizes.spot sizes.

Additional Capabilities of AugerAdditional Capabilities of Auger

Remove adsorbed gases from Remove adsorbed gases from the sample.the sample.

Eliminate adsorption of Eliminate adsorption of contaminants on the sample. contaminants on the sample.

Prevent arcing and high voltage Prevent arcing and high voltage breakdown.breakdown.

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

Degree of VacuumDegree of Vacuum1010

1010

1010

1010

1010

22

-1-1

-4-4

-8-8

-11-11

Low VacuumLow Vacuum

Medium VacuumMedium Vacuum

High VacuumHigh Vacuum

Ultra-High VacuumUltra-High Vacuum

PressurePressureTorrTorr

Why UHV for Surface Analysis?Why UHV for Surface Analysis?

AES Instrument ConfigurationAES Instrument Configuration

Elements of Typical Auger System: Electron Gun Analyzer Secondary Electron Detector Ion Gun Sample Stage Introduction System

Significance of Primary Beam Significance of Primary Beam

The Electron Beam is functioning The Electron Beam is functioning both as the imaging beam and the both as the imaging beam and the primary beam for analysis. This meansprimary beam for analysis. This meansthat the area of interest on the samplethat the area of interest on the samplecan be directly aligned for analysis.can be directly aligned for analysis.

MRL InstrumentationMRL Instrumentation

PHI Model 660 Scanning Auger Microprobe

Sputtering SamplesSputtering Samples

Al/Pd/GaN Thin Film ExampleAl/Pd/GaN Thin Film Example

(cross section)

Al/Pd/GaN Profile DataAl/Pd/GaN Profile Data

Al/Pd/GaN Atomic Concentration DataAl/Pd/GaN Atomic Concentration Data

Area Specific Depth Profile ExampleArea Specific Depth Profile Example

SP UTTER T IM E (M IN .)

PE

AK

-TO

-PE

AK

Fracture surface of Carbon fibers in BN matrix - analysis area outlined in black

Depth profile on fiber to determ ine point of fracture. Variations in fracture surfaceinterface for d ifferent sam ple treatments w ill be reflected in depth profile.

From research by C . C ofer/J. Econom y, M aterials Science D ept.

Summary of Surface TechniquesSummary of Surface Techniques