Complementary Techniques:Co p e e ta y ec ques:An Introduction to XPS, AES and

ToF-SIMS for Surface Analysis

John F WattsThe Surface Analysis Laboratory

Surrey Materials Institute & School of Engineering

Ion Beam Centre Training Course for Young Researchers

26 – 30 March 2007

Analytical Techniquesy q

Surface AnalysisSurface Analysis

The Principal MethodsThe Principal Methods

• X-Ray Photoelectron Spectroscopy

XPS• XPS

• Auger Electron Spectroscopyg p py

• AES/SAM

S d I M S• Secondary Ion Mass Spectrometry

• SIMS

XPS ChecklistXPS Checklist

• Depth of analysis 5nm

• All elements except hydrogen• All elements except hydrogen

• Readily quantified

• All materials (vacuum compatible)

• Depth profiling by ARXPS or sputtering

• Analysis area mm2 to 10 micrometres

XPS BasicsXPS - Basics

C1s

N1sO1s

EB = hν - EK - ω

XPS – Relationship to XPS – Relationship to Electronic Structure

XPS Survey SpectrumXPS Survey Spectrum

5

5

5

survey O1s

Ge2pGeLMM

Note:

C1s spectrum

5

5

OKLL

p p

XPS and Auger peaks

5

5 OKLLCKLL

peaks

Background –stepwise

5

5

Ge3dC1s stepwise

Valence band0

01002003004005006007008009001000110012001300

Binding Energy (eV)

Chemical shift

XPS SpectrometersXPS Spectrometers

Depth of AnalysisDepth of Analysis

XPS Survey SpectrumXPS Survey Spectrum

5

5

5

survey O1s

Ge2pGeLMM

Note:

C1s spectrum

5

5

OKLL

p p

XPS and Auger peaks

5

5 OKLLCKLL

peaks

Background –stepwise

5

5

Ge3dC1s stepwise

Valence band0

01002003004005006007008009001000110012001300

Binding Energy (eV)

Chemical shift

Germanium XPS and X-AESGermanium XPS and X AES

Ge3d Ge(0)GeLMMGe(IV) Ge3dGeLMM

Ge(IV)

Ge(0)

Ge(IV)

Ge(IV)Ge(0)

8.0 eV

Ge(0)

4 0 V

Ge(IV)

8.2 eV4 0 V

30

Binding Energy (eV)

4.0 eV

1140 1150 1160 1170 1180

Kinetic Energy (eV)

1220

Binding Energy (eV)

4.0 eV

Ge3d: EK = 1453 eV

λ = 2.8 nm

GeLMM: EK = 1140 -1180 eVGe2p: EK = 264eV

λ =0.8 nm

Valence Band SpectraValence Band Spectra

Polyolefines such as poly(ethylene) and Polyolefines such as poly(ethylene) and poly(propylene) have identical C1s spectra but

very characteristic valence bandsvery characteristic valence bands

Failure AnalysisFailure Analysis

Canned beer is id d i h d provided with a dense

head by carbon dioxide contained in plastic “widget”plastic widget

Polymer to Metal InterfacePolymer-to-Metal Interface

C1s

O1s400 μm XPS

Epoxy Lacquer Epoxy Lacquer

μ

2 mm

N1s

2 mm

Nylon Nylon

C1s Spectrum of EpoxyC1s Spectrum of EpoxyCH3 OH CH3

2HC

O

CH CH2 O C

CH3

O CH2 CH CH2 O C

CH3

O CH2 CH

O

CH2

n

Carom.Caliph.

C OC O C-Oarom.C-Oaliph.

CCepoxy

XPS Information DepthXPS Information Depth

“Surface Angle”

Depends Upon Take-Off Angle

“Bulk Angle” g

Minor Additive in Organic CoatingMinor Additive in Organic Coating

Elemental depth profile concentration of CC+FA1

90

100 The addition of poly(acrylic)

60

70

80

atio

n (A

t. %

)

Carbon

of poly(acrylic) flow agent in the formulation

30

40

50

omic

con

cent

ra

Oxygen

Nitrogen

induces a displacement

f th

0

10

20Ato of the urea

component deeperin the coating

0 1 2 3 4 5 6Depth (nm)

in the coating

Boeing Wedge Test Failure SurfacesBoeing Wedge Test Failure Surfaces

Epoxy Adhesive + 1% GPS: XPS Images

Opticalmirror images

C1s Al2p Si2p

Epoxy Adhesive + 1% GPS: XPS Images

mirror images

XPS SpectrometersXPS SpectrometersAxis Ultra

A l i lKratos Analytical

K-Alpha

Quantum 2000Physical Electronics

K AlphaThermo

ESCALAB 250Thermo

Theta ProbeThermo

AES ChecklistAES Checklist

• Smallest volume of any analytical techniquey y q• 10 nm ultimate spatial resolution• Metals and semiconductors• Chemical information (CCC transitions)• Quantification (not as easy as XPS)y• Depth profiling with sputtering

AES ChecklistAES ChecklistImportant considerations

S i l l iSpatial resolutionSEMSAMSmall feature analysis (at low beam

energy)SensitivitySensitivity

Minimise acquisition timMaximise signal to noise ratio

Spectral ResolutionResolve interferencesChemical state analysisMap dopants

Depth ProfilesDepth ProfilesDepth resolution

Auger Electron SpectroscopyAuger Electron Spectroscopy

EKL2,3L2,3(Z) = EK(Z) – [EL2,3(Z) + EL2,3(Z + 1)]

AES/SAM System GeometryAES/SAM System Geometry

Field EmissionElectron Source

Electron Optical

Ion Gun Energy Analyser

Column

LensSpecimen

Scanning Auger MicroscopeScanning Auger Microscope

Auger Microprobe for chemical imaging g p g gSpatial Resolution

<7 nm (SEM)<12 (SAM)<12 nm (SAM)

High Energy ResolutionExcellent Performance even at Excellent Performance even at low beam energyDepth Profiling with precision and sensitivityMultitechnique capability

i h i l XPS EDX with optional XPS, EDX or backscattered electron detector

AES Spectral ResolutionAES Spectral Resolution

AlKLL Auger spectra from thin Al2O3 layer on Al

Scanning Auger Microscopy: Scanning Auger Microscopy: Resolution

Depth ProfilingDepth Profiling

U f i t d th Use of an ion gun to erode the sample surface and re-analyse

E bl l d b Enables layered structures to be investigated

I i i f i fInvestigations of interfaces

Depth resolution improved by:

Low beam energies

Small ion beam sizesSmall ion beam sizes

Sample rotation

Depth ProfilingDepth Profiling

Superb Depth Resolution from metal multilayer structure (layer thickness only 5nm), achieved by:–Low ion beam energy–Azimuthal rotation of specimen during sputtering cyclep g p g y–Almost grazing incidence analysis by use of specimen tilt

AES Chemical State Depth ProfileAES Chemical State Depth Profile

AES Ball CrateringAES Ball Cratering

Depth of crater, d, relative to diameter of crater and radius of ball is given by:o ba s g e by:

d = D2/8R

If x is the radial distance from If x is the radial distance from the edge of the crater to the revealed buried layer then the d th f th l b depth of the layer, z, can be shown to be:

( )x

Taper Sectioning

( )xDRxz −=

2Taper Sectioning

Ball Cratering MachineBall Cratering Machine

S h i di f b ll Schematic diagram of ball cratering machine. Ball is usually ca 30 mm diameter usually ca. 30 mm diameter, fine diamond paste is abrasive.

Once crater is eroded sample is Once crater is eroded sample is lightly sputtered in Auger system prior to analysis to system prior to analysis to remove carbonaceous contamination. AES is carried out along crater walls which is then converted to a compositional depth profilecompositional depth profile.

Depth Profile Zn Coated SteelDepth Profile Zn Coated Steel

D h fil f 30 i f i l Depth profile of a 30 mm coating of zinc on steel, treated with a chromate conversion coating.

Combined AES/EDXCombined AES/EDX

This option on a SAMThis option on a SAM enables bulk analyticalanalytical information (by EDX) to be obtainedEDX) to be obtained in exact register with the surface (AES)the surface (AES) data. Repositioning of the sample is notof the sample is not necessary

Grain Boundary EmbrittlementGrain Boundary Embrittlement

Failure of rotor of turbine at Hinkley Point ypower station during routine overspeed test.p

This is a classic example f th t t hi of the catastrophic

nature of intergranular f tfracture.

FractographyFractography

F il l Failure occurs along the prior Austenite

i b d i grain boundaries, complete absence of

l i d f i plastic deformation or other energy b bi absorbing process.

Brittle FailureBrittle Failure

In Situ Fracture StageIn Situ Fracture Stage

F th t d f For the study of grain boundary

ti segregation phenomena in

t l th l metals the sample must be fractured, i i t l in an intergranular manner, within the UHV f th A UHV of the Auger microscope

Hot Cracking of Steel WeldmentHot Cracking of Steel Weldment

AES S EDX CAES: S, EDX: Cr

Hot Cracking AES/EDXHot Cracking AES/EDX

EDX alone would indicate that the enhanced Cr lt f th t f C O i k AES was a result of the present of Cr2O3 in crack. AES

data alone would indicate that sulphur segregation is the cause of ductility-dip cracking.

AES d EDX t th i di t d C i h AES and EDX together indicates a second Cr-rich phase has formed at grain boundaries: Liquation Cracking

Chemical State in AESChemical State in AES

AES D h P fil i h Ch i l S l iAES Depth Profile with Chemical State resolution

AES/SAM of CeramicsAES/SAM of Ceramics

SWithout charge compensation

SEM

Red = NitrogenGreen = Oxygen

With charge compensation (Ar+ 20 eV)

SIMS ChecklistSIMS Checklist

• Surface mass spectrometry – static SIMS• Ultimate detection limit – ppb for B in Si• Ultimate detection limit – ppb for B in Si• Molecular specificity – polymers• Rapid acquisition• Rapid acquisition• Imaging• Quantification needs very similar standards• Quantification needs very similar standards• Depth profiling - DSIMS

The Sputtering ProcessThe Sputtering Process

Primary ion beam (Ar, Ga, Bin+, Cs, nC60) is used to sputter secondary ions and neutrals.

Secondary ions are Secondary ions are analysed in mass spectrometer

Argon ions impacting on copper surface© Roger Webb

spectrometer

© Roger Webb

ToF-SIMSToF-SIMS

ToF-SIMS Operational ModesToF SIMS Operational Modes

Surface Spectroscopy

Surface ImagingSurface Imaging

Depth Profiling

Modern ToF-SIMS SystemModern ToF SIMS System

Modern ToF-SIMS SystemModern ToF-SIMS System

Defect in Paint FilmDefect in Paint Film

Specific Interactions by ToF-SIMSSpecific Interactions by ToF-SIMS

The intense SiOAl+

peak

is indicative of a covalent

b b hbond between the

aluminium oxide and th the

organosilane

dh i adhesion promoter

C60 Depth Profile of PolymersC60 Depth Profile of Polymers

1.00E+05

F

nts

1.00E+04

Cou

n

O

C1.00E+03

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Time / s

Molecular IonsMolecular Ions

1.00E+05

C3HF4-

1.00E+04

Coun

ts

C4H5O+

C3H2F5-

C2H5O+

1.00E+030 1 2 3 4 5 6 7 8 9 10

Time / s

Low Angle Microtome SectionsLow Angle Microtome Sections

Microtome Knife

Sample

P l l Bl kPolypropylene Block

Angle ranges from 2.0 –0.03o by use of sectioning

blocks of different geometriesgeometries

ULAM GeometryULAM Geometry

Small area XPS analysis mode (100 μm)

XPS spot i /

ULAM taper angle/o

0.03 0.33 2.0size/μm 0.03 0.33 2.0

100 60 600 3500Coating

Substrateθ

15 13 100 500

Depth Resolution ULAM/nm

ToF-SIMS Images of ULAM InterfaceToF SIMS Images of ULAM Interface

b)a)

Polyurethane ions

(a) m/z = 149: C8H5O3+

d)c)

2

(b) m./z = 26: CN-

(c) m/z = 59: C3H4F+

(d) / 19 F

3

2 (d) m/z = 19: F-

1

PVdF ions

Negative SIMS Spectra from ImagesNegative SIMS Spectra from Images

35 00a)25

20 00

25 00

30 00

unts 66

Point 2: Bulk Polyurethane

c)

5 00

10 00

15 00

Cou

41-4249

100

121

)

2

00 20 40 6 0 80 10 0 1 20 14 0 160 1 80 20 0

m /z

1 2 0 0 0

1 3 5 0 0

1 5 0 0 0c) 191

3

6 0 0 0

7 5 0 0

9 0 0 0

1 0 5 0 0

Cou

nts

39

Point 1: Bulk PVdF

0

1 5 0 0

3 0 0 0

4 5 0 0

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

49

39

85

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0m /z

Reconstructed ToF-SIMS of InterfaceReconstructed ToF SIMS of Interface

1 4 0 0b)19

Point 3: PU and PVdF at Interface

8 0 0

1 0 0 0

1 2 0 0

ount

s

85

Point 3: PU and PVdF at Interfacec)

2

2 0 0

4 0 0

6 0 0

C

31

55 71

87 121185141

3

00 20 4 0 6 0 8 0 1 0 0 12 0 1 4 0 1 60 1 8 0 20 0

m /z

1

ToF-SIMS of AdditiveS S dd

2400

2700

3000

31

1500

1800

2100

2400

ount

s

71

85

41

600

900

1200

Co

55 x10

0

300

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

m/z

185

A negative ion ToF-SIMS mass spectra of the pure acrylic co-resin component of the PVdF topcoat formulation in the mass range 30-200m/z.

ToF-SIMS of Acrylic Copolymer Component of PVdF Topcoat

Acrylic ImagesAcrylic Imagesa) b)

Negative Ion Mass

Selected Images

d)c)

g

(a) m/z = 31: CH3O-

(b) m/z = 55: C3H3O-(b) m/z 55: C3H3O

(c) m/z = 71: C3H3O2-

(d) m/z = 85: C H O -

e) f)

(d) m/z = 85: C4H5O2

(e) m/z = 87: C4H7O2-

(f) / 141 C H O -(f) m/z = 141: C9H13O4-

SummarySummary• All three have various hierarchies of use ranging All three have various hierarchies of use ranging

from simple elemental analysis to in-depth chemical characterisation at high spatial resolution

• XPS, AES and SIMS are powerful analytical methods for the chemical and elemental characterisation of surfacescharacterisation of surfaces

• For metallurgical studies AES/SAM is perhaps the most useful

• For polymers a combination of XPS and ToF-SIMS is hard to beat

• Surface analysis is expensive!