cutting and sputtering: getting to the buried interface

The Surface Analysis Laboratory

Cutting and Sputtering:

Getting to the Buried Interface

John F Watts


Department of Mechanical Engineering Sciences

2 July 2014


The Problem!


Inorganic Layers

J E Castle et al, Corr Sci, 16, 145-158, (1975)


High Temperature Oxidation

J C Rivière et al, Surf Sci, 117, 629, (1982)R K Wild, Spectrochim Acta, 40B, 827, (1985)


d

Interface Region

Substrate

Adhesive or Coating10’s m - mm

100’s m - mm

ARXPS d ~10nm

X-ray spectroscopies d ~200nm

RBS d ~1μm

Buried Interfaces: The Problem

One solution is mechanical sectioning of the sample

followed by analysis of the exposed interfacial region


The Buried Interface

Obtaining analytical information from intact interfaces is very difficult.

Carrying out in-situ experiments 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)


Oxide Stripping

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)


XPS Spectrum at Interphase

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

Fe(II) satellite

Fe(II)


Model of Interphase


Complementary Dissolution


Energy Filtered TEM

(a) (b) Energy-filtered (PEELS) TEM images of adhesively bonded aluminium showing the interpenetration of organic and oxide phase that is achieved when a primer is used (a). In the absence of a primer (b) the adhesive merely forms a interfacial boundary with the oxide.

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


MICROM 355S


Ultra-Low Angle Microtomy

angled sectioning block

sample

polyethylene

Angle Sectioning Block

12 x 12 x 7 mm3

+ 25 m = 0.03O

+ 50 m = 0.07O

+ 100m = 0.15O

+ 200 m = 0.33O

microtome blade


ULAM Depth Profiling

Coating

Small area XPS analysis mode (100 m)

Substrate

XPS spot size/m

ULAM taper angle/o

0.03 0.33 2.0

100 60 600 3500

15 13 100 500

Depth Resolution ULAM/nm

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


0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140 160

Depth / nm

Co

nc

en

tra

tio

n /

Ato

mic

%

C1s

O1s

N1s x10

F1s

PVdF (topcoat) Polyurethane (primer)

ULAM/Small Area XPS Depth Profile

S J Hinder, J F Watts, Surf Interf Anal, 36, 1032-1036, (2004).


ToF-SIMS of ULAM Interface

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-

500 m

250 nm

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


0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

a)25

41-4249

66

100

121

0

1500

3000

4500

6000

7500

9000

10500

12000

13500

15000

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

c) 19

49

39

85

Point 2: Bulk Polyurethane

Point 1: Bulk PVdF

c)

1

3

2

Negative SIMS Spectra from Images


0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

b)19

31

55 71

87

85

121185141

Point 3: PU and PVdF at Interfacec)

1

3

2

Reconstructed ToF-SIMS of Interphase


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

Co

un

ts

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 30-200u

x10

ToF-SIMS of Acrylic Copolymer Component of PVdF Topcoat


a) 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-

Retrospective Images of Acrylic Ions


Model Specimen for ULAM

Adhesive

Aluminium foil

Adhesive

Line scanused

Interface Adhesive/Aluminium/Adhesive

Adhesive

M-L Abel, unpublished data (2008)


Polyamide Powder Coating + Aminosilane addition

ULAM is carried out on the intact outer surface to provide profile of air/coating interface and delaminated coating interfacial failure surface to provide steel/coating profile

100 mm thick thermoplastic polyamide powder coating with aminosilane added to the powder

stock prior to spray coating

M Guichenuy, J F Watts, M-L Abel, M Audenaert, Surf Interf Anal, 38, 168-171, (2006).


Aminosilane in PA11 Coating

92 94 96 98 1000

0.5

1

1.5

2

2.5

3

0 1 2 3

Depth / m

Ato

mic

%

//

Air/Coating Interface Coating/Steel Interface

0

1

3

4

2

Ato

mic

%

Depth / μm

100 m thick polyamide powder coating with aminosilane added to the powder stock prior to

spray coating


d

Interface Region

Substrate

Adhesive or Coating10’s m - mm

100’s m - mm

Deposit a very thin layer of organic phase

This may be from the plateau region of an adsorption isotherm

Thin Film Solution

Prepare specimen at monolayer coverage (i.e. plateau region) for XPS or ToF-SIMS analysisIt is then possible to probe interface chemistry directly


Organosilane Adhesion Promoters

Molecular Dynamics Models of:

(a) Epoxy (b)Amino(c) Vinyl


ToF-SIMS to Identify Specific Interactions

The intense SiOAl+

peak is indicative of a

covalent bond between

the aluminium oxide

and the organosilane

adhesion promoter


Conclusions A variety of “mechanical” and chemical methods to approach interfaces

ULAM provides an easy way to section samples at very low angles which has the potential to provide chemical depth profiles at very high depth resolution when used in conjunction with a surface analysis method such as XPS or ToF- SIMS

Polymer/polymer systems are straightforward, if the candidate substrate is metal a thin foil must be used

Thermosetting systems can be cut at ambient temperature, thermoplastic systems may need a cold stage

cutting and sputtering: getting to the buried interface

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