Applications of XPS, AES and ToF-SIMS for Solving Problems in Materials...

The Surface Analysis Laboratory

Applications of XPS, AES and ToF-SIMS for Solving Problems in Materials Research

John F Watts

Surrey Materials Institute &

Faculty of Engineering and Physical SciencesSI-Ontario

University of Toronto20 March 2008


University of Surrey


Surface AnalysisX-Ray Photoelectron Spectroscopy (XPS)

Auger Electron Spectroscopy (AES)

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)


Handling Contamination

0

20000

40000

60000

80000

020040060080010001200

Cou

nts

/ s

Binding Energy (eV)

C O Al Si

17.0 58.2 24.8 0.0

0

10000

20000

30000

40000

020040060080010001200

Cou

nts

/ s

Binding Energy (eV)

C O Al Si

37.4 40.2 16.1 6.3

Clean aluminium foil (LHS) low adventitious carbon concentration, following handling by operative (hand cream user) concentration of carbon increases and significant concentration of silicon from silicone oils in hand cream (confirmed by ToF-SIMS).


Forensic Analysis

Canned beer is provided with a dense head by carbon dioxide contained in plastic “widget”

Early version were three part precision mouldings, but there was a desire to replace this with a single part “top hat” component heat sealed to the bottom of the container


XPS Survey Spectra

Nylon Nylon

C1s

O1s

N1s

Epoxy Lacquer Epoxy Lacquer

400 μm XPS

2 mm

Internal can surface Widget bonding surface


Photocured Adhesive

• LuxtrakTM photocured resin based on methacrylate type monomers

•Planned use in microelectronics industry

•Surface mounting of components on alumina

•Fails “pressure cooker” test i.e. adhesion in hot water

•Investigate failure surfaces by XPS after aqueous exposure

O O O

Resin Component

Reactive Diluent


C1s Spectra of Failure Surfaces

A M Taylor, C H McLean, M Charlton, J F Watts, Surf Interf Anal, 23, 342, (1995)

d = 1nm


Molecular Dynamics

Computer chemistry visualisation of reactive diluent at interface

XPS shows the overlayer on substrate side of failure to be about 1 nm of reactive diluent


Reformulated Resin

Reformulated resinwithout reactivediluent has betterdurability

Note π → π* on both interfacial failure surfaces


The Problem Faced by the Analyst

ARXPS d ~10nm

X-ray spectroscopies d ~200nm

RBS d ~1μm

d

Interface Region

Substrate

Adhesive or Coating10’s μm - mm

100’s μm - mm


The Buried Interface

Obtaining analytical information from intact interfaces is very difficult.

Carrying out in-situexperiments within the spectrometer can be useful but only rarely is the interphase chemistry exposed in this manner

J F Watts, Surf Interf Anal, 12, 497-503, (1988)


TEM/PEELS Cross-Sections

A J Kinloch, M Little, J F Watts, Acta Materialia, 48, 4543, (2000)

PAA treated joint PAA + primer joint

abrupt interface diffuse interphase


Oxide Stripping + Depth Profiling

Chemical removal of metal substrate, depth profiling of oxide in situ by ion sputtering. Interphase can then be analysed directly

J F Watts, J E Castle, J Mat Sci, 18, 2987, (1983)


Interface Chemistry

Fe(II)Fe(II) satellite

Iron 2p3/2 spectrum showing Fe(II) component at interface. Bulk oxide is entirely Fe(III).


Ultra Low Angle Microtomy

Angle Sectioning Block

12 x 12 x 7 mm3

+ 25 μm = 0.03O

+ 50 μm = 0.07O

+ 100 μm = 0.15O

+ 200 μm = 0.33O

Microtome Knife

Angled Sectioning Block

Polypropylene Block


ULAM Geometry

ULAM taper angle/oXPS spot size/μm 0.03 0.33 2.0

100 60 600 3500

15 13 100 500

Depth Resolution ULAM/nmCoating

Small area XPS analysis mode (100 μm)

Substrateθ

S J Hinder, C Lowe, J T Maxted, J F Watts, J Mater Sci, 40, 285, (2005)

Depth resolution attainable depends on the taper angle and the size of the analytical probe. In small area XPS in the range 15 -500 μm, for ToF-SIMS < 1 μm


XPS Line Scan Along Taper

0

2

4

6

8

10

12

14

16

18

20

0 0.013 0.026 0.039 0.052 0.065 0.078 0.091 0.104 0.117 0.13 0.143 0.156 0.169

Depth / um

Ato

mic

%

0

0.5

1

1.5

2

2.5

3

3.5

4

FluorineNitrogen

PVdF Polyurethane

X-ray Spot = 15μm

Step Size = 18 μm

13nmF: ΔZ = 50 nm

N: ΔZ = 27 nm

PVdF Topcoat on Polyurethane Primer


ToF-SIMS of ULAM Section

d)

b)a)

c)

1

3

2

+ve SIMS -ve SIMS

Polyurethane ions

PVdF ions

(a) m/z = 149: C8H5O3+

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

(c) m/z = 59: C3H4F+

(d) m/z = 19: F-

FoV is 500 μm

500 μm250 nm

S J Hinder, C Lowe, J T Maxted, J F Watts, Surf Interf Anal, 36, 1575, (2005)


ToF-SIMS Anions from Images

0

5 00

10 00

15 00

20 00

25 00

30 00

35 00

0 20 40 6 0 80 10 0 1 20 14 0 160 1 80 20 0m /z

Cou

nts

a)25

41-4249

66

100

121

0

1 5 0 0

3 0 0 0

4 5 0 0

6 0 0 0

7 5 0 0

9 0 0 0

1 0 5 0 0

1 2 0 0 0

1 3 5 0 0

1 5 0 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 0m /z

Cou

nts

c) 19

49

39

85

Point 2: Bulk Polyurethane

Point 1: Bulk PVdF

c)

1

3

2


ToF-SIMS at Interface

0

2 0 0

4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

1 4 0 0

0 2 0 4 0 6 0 80 1 00 1 2 0 1 4 0 1 6 0 1 8 0 20 0m /z

Cou

nts

b)19

31

55 71

87

85

121185141

Point 3: PU and PVdF at Interfacec)

1

3

2

PCA on Positive Spectra from Interfacial Region to Identify Those that are not Characteristic of PVdF or PU

Negative ToF-SIMS


Minor Additive

0

300

600

900

1200

1500

1800

2100

2400

2700

3000

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

m/z

Cou

nts

31

55

71

85

185

41

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.

x10


ToF-SIMS Images of Acrylic Ionsa) b)

e) f)

d)c)

Negative Ion Mass

Selected Images

(a) m/z = 31: CH3O-

(b) m/z = 55: C3H3O-

(c) m/z = 71: C3H3O2-

(d) m/z = 85: C4H5O2-

(e) m/z = 87: C4H7O2-

(f) m/z = 141: C9H13O4-


The Thin Film Approach

d

Interface Region

Substrate

Adhesive or Coating10’s μm - mm

100’s μm - mm

thin (< 2 nm film on substrate)

select sample from the plateau region of the adsorption isotherm


Organosilane Adhesion Promoters

Molecular Dynamics Models of:(a) Epoxy

(b) Amino

(c) Vinyl


Aluminium Pretreatment for Structural Adhesive Bonding

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100 120 140 160 180Exposure time (hrs)

Frac

ture

ene

rgy

(kJm

-2)

1 hr hydration + silaneOptimised silane pre-treatmentGrit-blasted onlyCAA pre-treatmentPAA pre-treatment


High Resolution ToF-SIMS

The intense SiOAl+

peak is indicative of a

covalent bond between

the aluminium oxide

and the organosilane

adhesion promoter


Specific Interactions

SiHO

OH

O

(CH2)3 O CH2 CH CH2

OH

Al

O H

SiHO

OH

O

(CH2)3 O CH2 CH CH2

O

Al


Wedge Test Failure Surfaces

Epoxy Adhesive + 1% GPS: XPS Images

Opticalmirror images

C1s Al2p Si2p


Single Fibre Pull-Out Test: Cradle to Grave ToF-SIMS

• Single fibre mounted in carrier syringe needle• Specially designed cradle used to hold sample• Fibre observed using optical microscope• Fibre presented to spectrometer for ToF-SIMS analysis pre-

embedding into resin system• Fibre embedded and SFPO test conducted• ToF-SIMS analysis of pulled-out fibre

• Optical and SEM images of pulled-out fibre

Mounting cradle ION-TOF sample platen ION-TOF TOF.SIMS 5

A R Wood, P A Smith, J F Watts, Comp Interf, 14, 287, (2007)


Mechanical Testing

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.60 0.80 1.00 1.20 1.40 1.60 1.80Extension (mm)

Forc

e (N

)

Load cell

Swivel links

Fibre carrier needle

Mould cap

Mounting bolt

Crosshead adapter

Material df (μm) L (μm) Fmax (N) τ (MPa)

Glass/Polyester 12.2 849 0.157 4.8


Positive ToF-SIMS Spectra

Mass (u) Formula Characteristic Structure

91 [C7H7]+ Polyester resin

105 [C7H5O]+ Polyester resin

115 [C9H7]+ Polyester resin

149 [C8H5O3]+ Polyester resin

O+

Mass (u) Formula Characteristic Structure

58 [SiC2H6]+ PDMS/Silane/N species [SiC2H6]+

73 [SiC3H9]+ PDMS/Silane

135 [C9H11O]+ Glass fibre size (epoxy)

OH C+

CH3

CH3

CH3 Si CH3

CH3

Pulled-out fibre tip

Si K

Ca

Si C2H6

Si C3H9

C7H7 C7H5OC9H7

C9H11O

Si2C5H1 5O C8O3H5

Si K

Ca

Si C2H6

Si C3H9

C7H7

C7H5O

C9H7C9H11O

Si2C5H15O C8O3H5

m ass / u20 40 60 80 100 120 140 160 180

3x10

1. 0

2. 0

3. 0

4. 0

5. 0

Inte

nsity

4x10

0. 5

1. 0

1. 5

Inte

nsity

Pre-embedded fibre tip

Pulled-out fibre tip

+

O

O

O

H+

•Bi3+

•Bunched mode

•128 μm x 128 μm

•128x128 resolution


In-Situ Controlled Strain RateFracture

Controlled strain rate + load cell + PC control = Load: Extension curve in situ


Correlation of XPS with Electrochemical History


Corrosion Beneath Organic Coating

Anodic Region

Cathodic Region25 μm


SAM Identifies Cathodic Regions

SEM Ca LMM CKLL

OKLL FeLMM NaKLL


NIST SRM Multilayer

• Superb Depth Resolution from metal multilayer structure (layer thickness only 5nm), achieved by:

– Low ion beam energy

– Azimuthal rotation of specimen during sputtering cycle

– Almost grazing incidence analysis by use of specimen tilt


Chemical State Mapping

High energy resolution (0.1%) Cu maps allow

separation of Cu and CuO


AES/EDX of Inclusions in Steel

Field of View ca. 5 μm

SAM Provides Superior Spatial Resolution to EDX

Grain Boundary Embrittlement

This phenomenon renders engineering steels brittle in nature as a result of the presence of sub-monolayer

quantities of impurities at grain boundaries and phase boundaries.

This can be studied by examining such fracture surfaces by AES but if fracture in air the steel will oxidise and obscure

the analytical signal of the segregant.

In Situ Fracture Studies by AES

For the study of grain boundary segregation phenomena in metals the sample must be

fractured, in an intergranular manner, within the UHV of the

Auger microscope

In Situ Fracture of Steels

Although predominantly intergranular failure this

micrograph shows a region of transgranular

failure in the centre of the field of view. This

provides a convenient “standard” spectrum of

the bulk steel

In Situ Fracture 3Cr-0.5Mo Steel

Hot Cracking of Austenitic Steel Weldment: AES and EDX

AES: S, EDX: Cr

Hot Cracking of Austenitic Steel Weldment: AES and EDX

EDX alone would indicate that the enhanced Cr 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 and EDX together indicates a second Cr-rich phase has formed at grain boundaries:

Liquation Cracking


Conclusions

• All three techniques 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 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!• So start with a service lab such as SI-O or University of

Surrey!

Applications of XPS, AES and ToF-SIMS for Solving Problems in Materials...

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