material characterization with tof-simsfy.chalmers.se/gsms/tofsims_051208.pdf · material...

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Material characterization with TOF-SIMS

Part 1: General- secondary ion mass spectrometry- time-of-flight mass spectrometry- instrumentation- general spectral features

Part 2: Applications- spectroscopy of complex

materials- imaging examples

Jukka LausmaaDepartment of Chemistry and Materials Technology, SP Swedish National Testing and Research Institute, Borås, Sweden

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TOF-SIMS is a mass spectrometric technique

Prerequisites for mass spectrometry:(i) free molecules in gas phase(ii) molecules in an charged state (measure m/z)

This can be achieved by, for example:thermal desorption, field emission, laser ablation, electrospray, electron impact, chemical ionization, plasmas, matrix assisted laser desorption/ionization, …

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SIMS: secondary ion mass spectrometry

Primary ions Secondary ions(~1-50 keV)

Solid

Sputtering

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Sputtering process

• Primary ion → collision cascade- primary recoils- secondary recoils

• Primary recoils cause sampledamage thoughout ion track

• PI’s implanted in material• Secondary recoils

→ particle emission from surface(sputtering)

→ surface damage

PISputtered particles- atoms and clusters- molecules and fragments- neutrals and secondary ions- electrons

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Important numbers and consequences

Sputter yield, Ys = removed particles / PI→ typically 1-10 @ 10 keV→ limit for non-destructive analysis

Secondary ion yield, YSI = secondary ions / PI

→ can vary from 1 – 10-6

(depends on ionization energy and matrix effects)→ quantification difficult

Large number of secondaryrecoils with low energy:→ emission depth ≤3 monolayers (high surface sensitivity)→ excited region diam. 0.3-10 nm (dependent on binding energy)→ low energy distribution (influences mass resolution)

- elements (1 - 5 eV, Thompson)- molecules (0.1 - 0.5 eV, M-B)

PISputteredparticles

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Dynamic SIMS

• High PI intensity• Beam damage• Analysis at continuously increasing depth

Main applications:• Bulk analysis (trace elements)• Depth profiles (e.g. surface films, dopant profiles)• Elemental imaging (e.g., grain boundaries, trace

elements in biological samples)

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Static SIMS

Number of particles removed from surface duringmeasurement should be negligible:

Typically 1014 – 1015 atoms cm-2 in one monolayer (ML)→ Primary ion dose density (PIDD) ≤1013 ions cm-2

Examples: Analysis area PI current Time100 x 100 µm2 1 pA ~10-100 s10 x 10 µm2 0.1 pA ~1-10 s

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Detection limits

Typically 1014 – 1015 atoms or molecules cm-2 in monolayer (1 ML)

Assume sputter yield, YSI = 1 and secondary ion yield YSI = 10-4

Analysis area Atoms/ML Secondary ions formed100 x 100 µm2 ~1010 ~106

10 x 10 µm2 ~108 ~104

→ static SIMS with high detection sensitivity requiresmass analyzer with high transmission

→ time-of-flight (TOF) analyzer

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Ion sourcesGa+ liquid metal ion source: High focus and intensityAu+

x liquid metal ion source: Higher sputter yields, similar focusBi+x liquid metal ion source: Present state-of-the-art

Cs+ liquid metal ion guns: enhances negative SI yields, poor focus

Electron impact guns (poor focus):

Ar+: general purposes, ion etching (depth profiling)

O2+: enhances positive SI yields

SF5+: enhanced yield for large molecular ions

shallow depth profiling (less ion mixing)

C60+ : enhanced yield for large molecular ions

shallow depth profiling (less ion mixing)depth profiling of organics

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Time of flight mass spectrometer

Sampleholder

Extractionelectrodes

Flightpath

Ion detector

TriggerSignal

Photodiode

Computer

For details, see for example:R.J. Cotter, Time-of-Flight Mass SpectrometryACS Symp. series, Vol.549 (1994)

Ion detector

Pulsedlaser

Variableattenuator

Mirrors

Lens

Y

Electrostaticreflector

U(>20 kV)

r e f l

V1(20 kV)

V2

mz = a t + b

2

a, b = constants(calibrated by twoknown masses)

Time0

Coun

ts TOF spectrum

Constant kinetic energyfrom acceleration field:

E = = z U

Flight time:

t =

=

k

2

mv2

2

Lv

2

2

mz

2 U tL

2

2

Pulsed ion beam

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Advantages of TOF-analyzer

• Unlimited mass range(in practice limited by ion formation and ion stability)

• High mass resolution; M/∆M (FWHM) > 10 000(single mass resolution at 10 000 amu)

• High accuracy (calibration dependent); - absolute mass error typically 10-3 amu for <100 amu- relative errors in 10 ppm range

• High transmission (parallell detection, no filtering)

Drawback:

Pulsed measurement (low duty cycle)low signal intensities (compared to other MS)

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High resolution mass spectrum (m/z = 30)

29.95 30.00 30.05

3x10

0.5

1.0

1.5

2.0

0

30Si

29SiH

28SiH2

CH2O

CH4N13CCH5

Silicon wafer, as rec.8 keV Ar+

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Pulsedion gun

secondaryions

ion detector

HV (+/-)

~10 nm

primary ions(Ga , Cs ,Ar , In , O , SF )

+ + +

+ + +

5

atomicions

molecularions

~1 nm

A+

C+

ABC+

AB+

B+

mass filter

extractor/ion opticsU

a c

ABC

Vacuum

TOF-SIMSTime-of-flight secondary ion mass spectrometry

Static SIMS: Pulsed primary ion beam, dose <10 cm (surface layer not removed)Dynamic SIMS: Continuous ion beam, analysis at increasing depths (depth profiling)

TOF: Method for mass filtration (measurement of flight time)

1 2 - 2

8t (m/z)1 / 2

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te1. Surface spectroscopy (static SIMS):• High surface sensitivity (information depth 1-3 molecular layers)• All elements, incl. isotopes are detected• High mass resolution gives specific chemical information• Low detection limits (% of monolayer down to ppm-ppb)

2. Microscopy (imaging):• Submicron lateral resolution• Analysis of composites, particles, fibres and microfabricated materials• Imaging of lateral distributions at surface or in cross sections

3. Depth profiling (dynamic SIMS):• Controlled sputter removal combined with spectroscopy or imaging• Depth distribution from surface and into material (depth resolution < 1nm)• Measurement of film thicknesses and diffusion profiles (< 1 µm thick)

4. 1-3 combined: 3D imaging on submicron scale

TOF-SIMS analysis modes

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Silver, positive ions

x 5

x 50

[amu]100 200 300 500 700 900 1200 1500 1900

3x10

1.0

2.0

3.0

4.0

25 keV Ga+

1011 cm-2Na

K

Ag

Ag2

Ag3

Ag5Ag7 Ag9

Ag11 Ag13 Ag15 Ag17

x5

x50

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K

KŽ

KŽO

H

KŽC

l

K�

ClŽ

K�

Cl�

K‘C

l�

K’C

l‘

K“C

l’

x 5x 500

[amu]50 100 150 200 250 300 350 400 450 500 600 700

5x10

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Inte

nsity

KClKCL1C_P

KmCl(m-1)

Potassium chloride

K

K2

K2ClK4Cl3

K3Cl2 K6Cl5

K5Cl4

K7Cl6

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Hydroxyapatite, Ca5(PO4)3OH

Ca+

+

Na

Ca

CaO

H

CaŽ

CaP

O

CaŽ

O

CaP

OŽ

CaŽ

OŽ

CaŽ

HO

ŽC

aPO

Ž

CaŽ

PO

�

CaŽ

PO

�

x 20

20 30 40 50 60 80 100 120 140 170

5x10

1.0

2.0

3.0

4.0

Ca

CaO

H

Ca 2

OCa

CaO

H

Ca 2

Ca 2

HO

2

CaP

O

CaP

O2

Ca 2

PO4

Ca 2

PO3

CaP

O3

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Polymer identificationH

CH C

HŽ

CH

�

CŽH

�C

ŽH‘

C�

H�

C�

H‘

C�

H“

C�

H‘

C�

H“

C�

H•

C‘H

“C

‘H•

5 15 25 35 45 55 65 75 85 95

3x10

1.0

2.0

3.0

4.0

5.0

C1Hx

C2Hx C3Hx

C4Hx

C5Hx

CxH2x±1

Polyethylene

CH

CŽH

�

C�

H�

C�

H‘

C�

H�

C�

H‘

C�

H“

C�

H•

C‘H

�

C‘H

“C

‘H•

C’H

‘

C“H

“

15 25 35 45 55 65 75 85 95

3x10

0.5

1.0

1.5

2.0

2.5

3.0C3H3

CH

C7H7

Polystyrene

Jukka Lausmaa, Nordic Polymer Days, Gothenburg, August 17, 2005

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Teflon (PTFE)

C

CF

CFŽ

CF�

C�

FŽ

C�

F�

CŽF

�

CŽF

‘

C�

F‘

C�

F‘

20 30 40 50 60 70 80 90 100 120 140

5x10

0.5

1.0

1.5

C

CF

CF2

CF3

C3F2

C3F3 C2F4

C3F5

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Polystyrene oligomer distribution

x 5

800 1000 1400 1800 2200 2600

4x10

0.2

0.4

0.6

0.8

1.0

1.2

PS 2200 dissolved in chloroform and deposited as monolayer on silver foil

(Irgafos 168 + Ag)+

(antioxidant)

∆m = 104 (styrene repeat unit)


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Interpretation of oligomer distribution

x 5

800 1000 1400 1800 2200 2600

4x10

0.2

0.4

0.6

0.8

1.0

1.2Analysis of m/z = 1726 peak:1.Assume silver cationized:

Oligomer mass: 1726 – 107 = 16192. How many monomers?

1619 / 104.1 = 15.5615 monomers

3. Mass of endgroups:0.56 * 104.1 = 58 (H + C4H9)


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23.0

5

43.1

7

107.

02

145.

25 369.

60

493.

56

882.

22

Ion Mass [amu]100 200 300 400 500 600 700 800 900 1000

5x10

0.5

1.0

1.5

2.0

Inte

nsity

Cholesterol on Ag

Ag

(M+Ag)–

(2M+Ag)–

1 mg/ml, 5 yl

Molecular spectra: Cholesterol on silver

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Substance identificationEx: Deprotonated molecular ion, (M-H)-, of cholesterol (C27H45O)

Theoretical spectrum(isotope distribution)

Measured spectrum

• Absolute mass (385.35 u)• Isotope pattern due to 13C

MassC27H45O

386 388 390

Isotope Cluster386 388 390 392

1x10

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

x101

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.073.489%

22.612%

3.503%0.365% 0.029% 0.002% 0.000%

385.

35

386.

34

387.

38/ u

386 388 390 392

2x10

1.0

2.0

3.0

4.0

5.0


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Spectral features

Elemental targets (e.g. metals):- monoatomic ions (Me+), clusters (Men

+)

Inorganics (e.g., metal oxides, salts, ceramics):- monoatomic ions (Me+), sometimes clusters (Men

+) - oxidized species (MemOn

±)

Polymeric materials:- predominantly molecular fragments- characteristic fragmentation patterns- characteristic fragments

Adsorbates and surface contaminants:- predominantly fragments, often also intact (M+H)+ or (M-H)-

- cationized molecular ions (M + Me)+

- oligomer distributions (M + Me)n+

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Surface analysis:Challenges and questions

• Which elements and compounds are present on the surface?

• Which impurities/contaminants are present?• How are they distributed over the surface?• How are they distributed from the surface and into the

material?• Major challenges:

- Distinguish the surface from the rest of the material- Minute amounts of materials (typically 1-10 ng/cm2)

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x 10x 100

x 10

x 100

[amu]50 100 150 200 250 300 400 500

5x10

0.5

1.0

1.5

2.0

2.5

y5x10

0.51.01.52.02.53.03.54.0

y

Surface contamination: fingerprint on Al foil

10x

10x

100x

100x

Al foil, as received

Al foil + fingerprint

Mg

Al

C3HyC4Hy

Phthalatefragment

C

CO H+

O

O

Na

AlC2H3

C3Hy

C4Hy

PDM

S (1

47)

PDM

S (2

07)

PDM

S (2

21)

PDM

S (2

81)

∆m=14(CH2)

∆m=14 (fatty acids)

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Identification of surface contamination

x 5

[amu]50 100 150 200 250 300 350 400

5x10

0.5

1.0

1.5

2.0

2.5

3.0 Ti surface handled withPVC gloves

TiO

Ti

Na

phthalatefragment (DEHP+Na)+

(DEHP+H)+

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Examples of common surface contaminants

Type Characteristic peaks

Plasticizers (phthalates) 149, 391 (M+H)+, 413 (M+Na)+

Fatty acids CH3-(CH2)n-COO- 227, 255, 283, ∆m = 28

Synthetic oils ∆m = 140 (C10H20)n

Polydimethyl siloxane 43, 73, 147, 207, 281, ∆m = 74(PDMS)

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Injection moulding of polystyreneCollaboration with Dept Polymeric Materials, Chalmers(Francesco Pisciotti, grad. student)

-Injection moulding widely used processing method-High pressures and high temperatures (<Tm) involved

Objective:Study chemical composition of surfaces and interfaces,especially migration of impurities and additives

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CH

CH

�

CŽH

�

C�

H�

C�

HŽ

C�

H�

C‘H

�

C’H

‘

C“H

“

C”H

“

C•H

“

C�

ŒH

”

C�

�H

•C

�ŽH

” C�

�H

•C

��

H•

C�

�H

�Œ

x 20

[amu]50 100 150 200 250 300 350 400

3x10

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Injection moulded polystyrene: spectrum from cross section (interior of material)

Characteristic PS spectrum(unsaturated CxHy species dominate) No additives or impuritiesdetected

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CH

�

CŽH

�

C�

H‘

C�

H“

C‘H

•

C’H

•

C“H

“

C•H

“

x 20

[amu]50 100 150 200 250 300 350 400

5x10

0.2

0.4

0.6

0.8

Injection moulded polystyrene: spectrum from surface

Not a characteristic PS spectrum- more saturated CxHy species- traces of CxHyO and CxHyN detected

No specific additives or impuritiesdetected

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x 10

x 200

[amu]200 400 600 800 1200 1600 2000 2400

5x10

0.2

0.4

0.6

0.8

1.0

Ag

Ag2

Ag3

(Irga

nox

1010

+A

g)+

x 200

∆m = 14 (CH2)∆m = 74

Injection moulded polystyrene: extract deposited on Ag-foil

Paraffin wax? PDMS


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[amu]50 100 150 200 250 350 450 550 650 750

6x10

0.2

0.4

0.6

0.8

1.0

1.2

1.4

AGPRE1P, 04.26.2001, 18:52

x 15

[amu]700 750 800 850 900 950 1000 1100 1200

5x10

0.5

1.0

1.5

Ag

Ag2 Ag

3

(DO

P+A

g)+

X15∆m=140 140 140 140

Ag9

(C10H20)

Injection moulded polystyrene: spectrum from Ag-foil rubbed against surface

Synthetic oil (-C10H20-)n

(314u+Ag)Irgafos 168


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Separation/purification of biomolecule samplesby liquid chromatography

Mixture ofbiomolecules

Separationcolumn

Y

YY

YY

Y

YY

Surface functionalizedseparation medium

Purifiedsample

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Surface characterization of media for liquid chromatographyCollaboration with Amersham Pharmacia Biotech, Uppsala(Bo-Lennart Andersson and Mikael Andersson)

Background- Function of LC media dependent on morphology and surface

chemistry- Surface modification and ligands chemical specificity- ”Difficult materials”; beads, roughness, non-conducting,

complex chemistry

Objective:- Can ToF-SIMS provide useful information about

surface chemistry?

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Sepharose beads

20 µm

Surface analyst’s nightmare: Insulating + rough and porous + complex chemistry

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Raw materials

O

OHOH

OHO

OO

OHOHHO

*

OO

OHOH

OHO

*n

HOO

OO

OH

OH

O

O

O

HO

D-Galactose 3,6-anhydro-L-Galactose

Dextran (branching exists)Agarose

Alpha-1,6-D-Glucose

Cross-linker

OH

OH

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Comparison of raw materials

Ion Mass [amu]10 20 30 40 50 60 70 80 90 100 110

3x10

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Inte

nsity

4x10

0.2

0.4

0.6

0.8

Inte

nsity

Agarose

Dextran

C4H5O

C3H5O2

C4H5O2

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Diethyl aminoethyl ligands on cross-linked agarose(DEAE Sepharose Fast Flow)

O NCH2

C2H5

H

CH2 C2H5

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Identification of surface ligands

[amu]20 30 40 50 60 70 80 90 110 130 150

4x10

0.51.01.52.02.53.0

5x10

0.2

0.4

0.6

0.8

1.0

Agarose

Sepharose + DEAE

C2H

5C

H3N

C2H

6N

C3H

6N

C5H12N C6H14N

O NCH2

C2H5

H

CH2 C2H5

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Chemical imaging

1. Focused ion beam (Au+) is scanned oversurface; spectra from 128 x 128 points

BC

D

10 µm – 10 mm(128 x 128 pxl)

2. Mass spectrum from total area showswhich substances that are present

/ u400 450 500 550 600 650 750 850 950

410

0.2

0.4

0.6

0.8

1.0

1.2

A

D B C

A

A

Results are stored in raw data file, containing>16 000 mass spectra, with retained spatial information.

3. Images are constructed from raw data file, showing where substances are located

A B C D ”Overlay”

(alt: sample stage scan)

signal

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Drying stain on Si wafer

Na2Cl

Na2OH

Al

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Na (contamination)Si (wafer) Ti, W (evaporated)

Impurities on semiconductor devices

Användningsområden:•Processutveckling och kvalitetskontroll•Skadeanalyser

25 µm

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ToF-SIMS imaging: Grain boundary segregationin polycrystalline silicon

20 µm

Si Al K

Ti Al K Ti

Sample from: Dr J. Walmsley, SINTEF Technology, Trondheim, Norway

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Analysis of fatigue crack

Video

Ion images

Ion sputteredarea

Jukka Lausmaa, SP

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Ion imaging of microstamped CH3- and COOH-terminatedthiols on Au (40 and 60 µm stripes)

Au C2H3OC2H3

100 µm

Sample preparation by Department of Polymer Technology, Chalmers

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Paints

• Often complex formulations, containing different additives (antioxidants, UV absorbers, leveling agents, …)

• Car paints; multilayer systems• Interesting questions:

- How are additives distributed?- How do additives diffuse?- Degradation mechanisms?

Need for analysis methods that combine detailed chemicalinformation with imaging capability TOF-SIMS

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Spectrum from surface of car paint

M205 = BHT (additive) – CH3* = silicone (anti foaming agent)

M662 = Irgafos 168 (phosphate)M647 = Irgafos 168 (phosphite)

mass220 240 260 280 300 320 340 360 380

3x10

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Inte

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1.0

2.0

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6.0

Inte

nsity

mass500 600 700 800 900

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Artificially aged, 5000 h


Unaged

Unaged

205

662647

539

mass10 20 30 40 50 60 70 80 90

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mass110 120 130 140 150 160 170 180 190

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y g



Unaged

Unaged

*

*

*

*

*

**

*

*

** *

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Sample preparation for cross section analysis

PMMA Paint

Adhesive

Paint PMMA

Direction of microtomingDirection of microtome

Plastic PlasticPaint Paint

Epoxi

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Imaging of cross sections

Plastic

Layer 1

Layer 2

Layer 3 (topcoat)

Adhesive

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Oxidation of paint system

200 x 200 µm

Sample aged in 18O-enriched air

Analysis:Imaging TOF-SIMS of 18O- ions

Result:Oxidation localized to pigmented layer

Ref: Physical ElectronicsJukka Lausmaa, Nordic Polymer Days, Gothenburg, August 17, 2005

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Chemical mapping of biological samples

Knowledge about molecularcomposition of cells and tissuesimportant for research on:

• understanding diseases• drug development• diagnostic methods

Need for improved analyticalmethods:

• which molecules?• spatial distributions?• relevant length scales; nm – mm

3 nm

Alberts et al.: Molecular Biology of the Cell

Lipid molecule Protein molecule

Lipidbilayer

© Sinauer Associates Inc. ~10 µm

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te• Transfer sample molecules to silver surface with retained lateral distribution

• Imaging TOF-SIMS of chemical imprint

Advantages:+ less fragmentation (Ag cationization) improves identification+ higher SI yield improves sensitivity

Cell imprinting

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Positive TOF-SIMS spectrum of cell imprint

/ u200 400 600 800

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/ u490 500

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Ag-ch

Ag-ch2

Ag2 Ag3

Ag2Cl

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Spatially resolved chemical analysis of cells

SEM image of human leukocyte on glass

TOF-SIMS images from imprints on silver

CH4N+ (proteins, DNA) m/z = 184 (phosphocholine)

m/z = 493 (cholesterol + Ag molecular ion)

10 µm

20 µm

P. Sjövall et al. Analytical Chemistry (2003)

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Lipid distributions in mouse brain

cholesterol palmitate (255 u) sulfatide (806-908 u)

cholesterol / palmitat / sulfatid261 u 429 u

P. Sjövall, J. Lausmaa and B. Johansson, Analytical Chemistry,76, 4271-4278, 2004

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Depth profiling using ion etching

Ion beam

Sputtertime

Sign

al in

tens

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• Layer thicknesses ~1-100 nm• Sputter time vs depth can be calibrated• Depth resolution a few nm

Ion beamMS

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Depth profiling (dynamic SIMS): 28 nm thermal oxide on HF etched titanium

Time (S)200 400 600

110

210

310

410

Substance Mass Color

F 19.00

CH� 15.02

O 15.99

TiO 63.94

Interface

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Applications of depth profiling

• Oxide layers (thickness and composition)• Thin films (optical, conducting, hard coatings, …)• Diffusion profiles• Dopant profiles• …

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Summary

• TOF-SIMS a versatile analysis technique, which combines:- detailed chemical information via high-res. MS- high detection sensitivity- high surface sensitivity- imaging capability at submicron scale

• Important applications:- polymeric materials (additives, molecular weight distr., …)- thin film characterization- cross section analysis- grain boundary segregation - microfabricated materials (e.g., microelectronics, µCP, …)- biological samples (emerging)

However:- Best used in combination with other characterizationtechniques

material characterization with tof-simsfy.chalmers.se/gsms/tofsims_051208.pdf · material...

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