Surface Analytical Techniques for Analysis of Coatings

Mary Jane Walzak, Mark Biesinger and Brad Kobe The University of Western Ontario

Surface Science Western

ISO 9001:2008 Registered

Why do Surface Analysis?

Provide timely economical solutions to common manufacturing issues

• Contamination of raw materials• New product development• Understanding corrosion issues• Adhesion failures• Fracture and wear• Cosmetic staining• Surface modifications

• Quality assurance program• Reverse engineering• Reduce down time• Minimize scrap• Diagnose field returns

Common Analytical Techniques

• Optical Microscopy • Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy

(SEM/EDX)• Fourier Transform Infrared Spectroscopy (FTIR)• Laser Raman Spectroscopy• X-ray Photoelectron Spectroscopy (XPS)• Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)• Dynamic Secondary Ion Mass Spectrometry (SIMS)• Scanning Auger Microscopy/Auger Electron Spectroscopy (SAM/AES)• Atomic Force Microscopy (AFM)• Surface Profilometry

Common Analytical Techniques

SEM/EDX• Vacuum technique• High resolution imaging with nanometer resolution• Elemental information from carbon to uranium• Analysis volumes on the order of 1 micron

FTIR and Raman spectroscopy• Optical microscope techniques• Vibrational techniques (functional groups)• Organic and inorganic species• Analysis of micron sized features

Comparison of hydrocarbon speciesfrom reference material (red)

and paint defect (blue)

SEM image of Ag coating

Common Analytical Techniques

X-ray photoelectron spectroscopy (XPS)• Vacuum technique• Elemental and chemical state information• Very surface sensitive (10 nm probing depth)• Sensitivity: 0.5 atomic %

Time of flight secondary ion mass spectroscopy (ToF-SIMS)• Vacuum technique• Mass spectral technique (up to 10,000 amu)• Analysis of outer most monolayers• Sensitivity is ppm to ppb

XPS scan of electrochemicallygrown coating

ToF-SIMS images of chromedefect on stainless steel

Case 1: Pinhole defects in chrome coatings

Analytical approach• Identification of defects using optical microscopy• Initially examined several defects using SEM/EDX

• No obvious contamination detected• Decided to use a surface more surface sensitive

technique (ToF-SIMS)

Problem• A manufacturer suddenly experienced pinhole defects in vacuum deposited

chrome coatings on polymer substrates

Optical image of pinhole

Case 1: Pinhole defects in chrome coatings

SEM image of pinhole defectResults• SEM imaging showed that the chrome

coating was very thin and feathered-out at the edges of the pinholes

• No obvious particles or surface debris was responsible for the defects

• ToF-SIMS is a very sensitive technique • Nitrate species detected: NO2¯and NO3¯• No ammonia, salt or silicone detected

• Nitrate contaminant prevented deposition of the chromium

ToF-SIMS images of pinhole defect

NO2¯ Cr

Case 2: Contamination of extruded material

Analytical approach• Prepared metallographic cross-sections for SEM/EDX• Thin cross-sections analyzed by FTIR in transmitted

light mode using the diamond compression cell• Raman spectroscopy also provided chemical

information about the defects

Problem• A company was experiencing black defects embedded in a clear extruded

polycarbonate part

Optical image of defect

Case 2: Contamination of extruded material

Results• Backscattered electron (BSE) images of the

defects showed a layered structure• Elemental X-ray intensity maps of defect

• Sodium, magnesium, oxygen and silicon• FTIR showed peaks consistent with talc• Polymer portion of the defect appeared to be

degraded polycarbonate (FTIR)• Raman analysis showed the presence of

amorphous carbon in the defect area

SEM Na

O

MgC

Si

BSE image and EDX maps

Case 3: Reverse engineering of packaging

Problem

Analytical approach

• A food packaging manufacturer was interested in reverse engineering a coffee container

• The total thickness of the sample container was approximately 400 microns

• Cross-sections were prepared for SEM/EDX analysis to determine the variation in the elemental composition of the layers

• Thin cross-sections were prepared for examination by optical microscopy, FTIR and Raman analyses

200 µm

Case 3: Reverse engineering of packaging

Results• Optical and BSE images showed the presence

of a layered structure with a number of thin layers at the ID

• EDX mapping showed variations in the carbon, oxygen and titanium in the various layers

• FTIR and Raman identified nine distinct layers in the material

BSE image and EDX overlay

Case 3: Reverse engineering of packaging

Results

HIGH IMPACT POLYSTYRENE

ETHYLENE VINYL ACETATE COPOLYMER

POLY(VINYL ALCOHOL-CO-ETHYLENE)

POLYETHYLENE

10 µm

POLYSTYRENE with TiO2

100 µm

POLYSTYRENE with TiO2

POLYSTYRENE

POLYSTYRENE with TiO2

POLYSTYRENE

POLYETHYLENE (Textured Surface)

Case 4: Adhesion failure of body side molding

Analytical approach• The foam adhesive was first examined using XPS• Next, the painted side panels exhibiting full failure, interment failure and

good reference panels were analyzed by XPS

Problem• During application at an assembly facility it was noted that intermittent

failures of the adhesive on body side moldings was occurring

Case 4: Adhesion failure of body side molding

Results• XPS analysis of the foam adhesive surfaces

did not reveal any significant contamination• XPS analysis showed significant changes in

the silicon levels on the painted side panel• High resolution silicon 2p spectra showed the

silicon to be present as silicone• After testing is was revealed that the excess

silicone was due to a mixing problem in one of the clearcoat totes

XPS survey spectra of clear coat

Case 5: Raman spectroscopy of pigment

Analytical approach• The defects were identified using a stereo microscope

and thin slices were prepared using a scalpel• The sections were examined using SEM/EDX and laser

Raman spectroscopy

Problem• A company was experiencing dark defects in their basecoat and wanted to

know if the formulation was correct

Case 5: Raman spectroscopy of pigment

Results• EDX spectroscopy detected high levels of carbon,

oxygen, nitrogen and iron in the defect• Laser Raman spectroscopy was then performed• The spectrum of the blue defect material

matched that of ferric ferrocyanide, a common blue pigment

• Ferric ferrocyanide was NOT the specified blue pigment for use in this basecoat

• This was an issue with the pigment supplier

Ferric Ferrocyanide

Defect Material

Raman spectra of defect material and reference blue pigment

Case 6: Analysis of crater defects

Analytical approach• Initially assess the crater defects optically• If no obvious residue or contaminant is visible

• typically examine crater using either XPS or ToF-SIMS• If large contaminants are visible

• Use SEM/EDX combined with FTIR spectroscopy • most likely cross-sectioning would be required

Problem• Many automotive companies experience paint crater defects on car panels

Cast 6: Analysis of crater defect

Results• ToF-SIMS imaging showed fluorine associated

with the particle• Silicone was detected at the center of the

crater and a hydrocarbon species was observed at the edges of the crater

• The particle is consistent with Teflon®• The silicone and hydrocarbon species are

possibly from oils and lubricants

ToF-SIMS images of crater defect

Case 7: Cosmetic corrosion of aluminum

Analytical approach• Initially, these samples were examined by SEM with

elemental X-ray mapping• XPS imaging was then used with spot analyses to

check specific corroded regions

Problem• Cosmetic corrosion study of zinc galvannealed aluminum test panels that

were strapped on vehicles and driven around various cities for two years

Case 7: Cosmetic corrosion of aluminum

Results• SEM/EDX analysis revealed the presence of

sulphur and other salts • What form is this sulphur? Need to know to

change testing procedure• XPS imaging with spot analyses was used to

check the form of the sulphur present

BSE image and elemental X-ray maps

Case 7: Cosmetic corrosion of aluminum

Results• S (2p) high resolution spectra collected from

a 220 micron spot• Sulphur 2p peak found at 169.3 eV indicative

of sulphate• Results were used to improve normal

corrosion tests that use salt sprays or salt baths (containing sodium and chlorine)

NameSulphate

Pos.169.27

FWHM2.19

%Area100.0

S 2p

210

220

230

240

250

260

172 170 168 166 164 162Binding Energy (eV)

Zn

Summary of Surface Analysis Techniques

• Common analytical techniques include:

• These techniques can be used to solve manufacturing issues from many sectors including aerospace, automotive, medical and semiconductor

• Fast and accurate methods to diagnose coating and material issues• Contamination• Corrosion issues• Adhesion failures

• Failure analysis• Reduce scrap• Diagnose field returns

SEM/EDX FTIR Raman XPS ToF-SIMS

ISO 9001:2008 Registered