1. Surface and Interface Characterization of Polymers
October 31, 2018

2. Brief Review of the Principles of XPS and TOF-SIMS
Agenda
Introduction
Brief Review of the Principles of XPS and TOF-SIMS
Case Study #1 – Defect Analysis
Case Study #2 – Failure Analysis
Buried Layers and Interfaces
Summary

3. Introduction
Polymeric Films
Impacted by quality of the interface of the layers of the films along with the surface characteristics.
These impact many properties such as adhesion, barrier performance, printability, wettability, strength and appearance.
Metallizing Polymers
The value of the converted polymer product revolves around the surface modification of the polymeric material and the coating(s) utilized.

4. X-Ray Photoelectron Spectroscopy (XPS)
Principle of XPS
X-Ray Photoelectron Spectroscopy (XPS)
Also known as Electron Spectroscopy for Chemical Analysis (ESCA).
A photon ionizes an atom which results in the ejection of a core electron.
The kinetic energy (KE) of these photoelectrons is related to the x-ray source energy (hν) by the photoelectric effect.
KE = hν – BE (BE = binding energy of the core electron)
Each element on the Periodic Table of Elements has a different electronic configuration (does not detect hydrogen).
This is how XPS can be used to identify the elements in a sample.

5. XPS (Continued) Sample Carbon Nitrogen Oxygen Treated 79.0 3.0 18.0
Untreated
99.0
0.0
1.0

6. XPS (Continued)
Four Main Attributes of XPS
Surface sensitivity (1-10nm sampling depth).
Elemental and chemical state identification.
Quantitative without the use of standards.
Ability to examine highly insulating samples.

7. Time of Flight-Secondary Ion Mass Spectroscopy (TOF-SIMS)
Principle of TOF-SIMS
Time of Flight-Secondary Ion Mass Spectroscopy (TOF-SIMS)
Extraction Field
TOF-SIMS Requires
Pulsed Ion Source
Extraction Field
Flight Tube
Detector Capable of Detecting the Individual Ions

8. TOF-SIMS (Continued)
Positive Mass Spectrum of PDMS contaminated PET. PDMS has been shown in blue for clarity: Si+, SiCH3+, SiC3H9+, Si2C5H15O+

9. TOF-SIMS (Continued) Four Main Attributes of TOF-SIMS
Surface sensitivity (<0.5nm sampling depth).
Elemental and molecular identification.
Ability to chemically map elements/molecules on the surface of a material with <1µm image resolution.
TOF-SIMS has the ability to examine highly insulated materials.
Mg distribution on surface
Organic molecule

10. Case Study #1: Identification of Defects on Metallized Polymer-PSA Laminate
Laminate consisting of an acrylic-based pressure sensitive adhesive (PSA) on a polyester film bonded to a metallized PET with a silicone release layer – experienced isolated defects µm in size.
Defects – undesirable transfer of the metallization to the PSA surface.

11. CASE STUDY #1 (Continued)
In adhesion failures, it is desirable to study the mating sides as the contaminant can preferentially transfer one side or the other.
This investigation can also help confirm the locus of failure as it is not always straightforward in multilayer laminates.
Small area XPS was performed on the mating side of the 200µm defect.
Mating Side (i.e. Void Defect Side)
PSA Side of the Failure (i.e. underside of the Al Flake)

12. CASE STUDY #1 (Continued)
Mating Side: CHx, C-O, O-C=O and silicones – consistent with PET covered in 1-2 monolayers of silicone.
Concern silicone had migrated to the defect post surface.
PSA Side: Al, Al2O3, CHx, C-O, O-C=O and silicones.
Mating Side (i.e. Void Defect Side)
PSA Side of the Failure (i.e. underside of the Al Flake)

13. CASE STUDY #1 (Continued)
Quite clear locus of failure was at the polyester-Al interface.
Close examination at the carbon spectrum from the Al flake underside revealed C-O and O-C=O at equal intensities.
This is indicative of an ester – only organic species should have been from CH3 and silicone and any airborne organic materials.
Area
Carbon
Oxygen
Aluminum
R-Si
SiO2
Metal Side of Defect
67.3
27.9
0.0
4.7
PSA Side of Defect
43.2
35.4
17.0
4.5
Release Layer
44.1
30.6
18.7
6.6

14. CASE STUDY #1 (Continued)
PET to metal transfer was also considered. The high resolution XPS image gave subtle indications that the ester was not from an aromatic source (i.e. PET).
Conclusion: Such shifts are consistent with the presence of an aliphatic ester present on the surface of the PET prior to metallization. This was the ultimate cause of film failure.
PET Reference – Top
Defect Spectrum – Bottom.
See shifts in the binding energies of the C-O and O-C=O.
There is no evidence of the weak aromatic band around 292 eV on the defect.

15. Case Study #2: Failed Heat Seal
Sterile package from a medical device that experienced an adhesion failure at the polyethylene-ethylene acrylic acid (co-polymer) heat seal to the polyethylene interface.
EAA (ethylene acrylic acid) – added at 3% to improve adhesion and lower % crystallinity.
Good and bad samples were compared using both XPS and TOF-SIMS.

16. XPS identified only carbon and oxygen on the surface.
Case Study #2
XPS identified only carbon and oxygen on the surface.
Confirmation of the acrylic acid species.

17. Case Study #2 (Continued)
Making the assumption the oxygen detected comes from the EAA, the following conclusions were reached:
Good heat seal contains the expected 3% EAA.
Bad heat seal contains almost 5% EAA.
Sample
Carbon
Oxygen
Good PE-EAA Surface
98.6
1.4
Failed PE-EAA Surface
97.7
2.3
3% EAA-PE, Theoretical
98.8
1.2

18. Case Study #2 (Continued)
Irganox ® 1010
Case Study #2 (Continued)
TOF-SIMS was then run on the surfaces to confirm the EAA concentrations.
Both surfaces contained ions that were indicative of PE (C2H3, C3H5, C4H7, etc.) and EAA (CH3O, C2H5O, etc.).
However, the bad heat seal contained peaks for a hydroxyhydrocinnamate (HHC) compound (aka antioxidants known under the brand name
of Irganox® ).

19. Case Study #2 (Continued)
Weak HHC peaks were observed on the Good heat seal at roughly 1/3 the intensity as seen on the Bad heat seal.
XPS could only identify the alkyl carbon and a weak O-C=O band.
Because both samples contained the HHC component, it was impossible for XPS to identify the contaminant.
XPS did detect the higher level of oxygen in the Bad seal.
TOF-SIMS was able to determine the excess oxygen was not due to EAA but rather from excessive antioxidants levels on the surface.
TOF-SIMS allowed for the determination of the root cause of failure.

20. BURIED LAYERS AND INTERFACES
The ability to access exposed surfaces and directly or through delamination sample them is straightforward with XPS and TOF-SIMS.
There is interest though in looking at layers that may be buried many microns below the top of the surface.
Historically, the main choices for analysis were techniques such as FTIR, Raman, SEM-EDS or TOF-SIMS.
These are generally done on soft materials using a microtome.
This gives lateral resolution of the sample and the technique limits the thickness of the buried layer/interface that can be examined.

21. Buried Layers and Interface (Continued)
Limitations
SEM-EDS, Raman and TOF-SIMS – resolution is ~1µm.
FTIR – resolution is ~15µm.
The poor lateral resolution
of XPS (20-30µm) limits
the use of XPS for these
types of applications.
SEM image of a cross-
sectioned paint sample
(substrate not shown).
Layers of interest are
>5µm , can use TOF-SIMS.
Clearcoat Basecoat Primer

22. Buried Layers and Interface (Continued)
Clearcoat Basecoat Primer
Green = From Primer Corrosion
Red = Al & Ti from Basecoats
Blue = Cl from Clearcoat

23. Buried Layers and Interface (Continued)
What about the layers <1µm?
Gas Cluster Ion Beam (GCIB) – can sputter into organic systems and maintain chemical state information.
Using TOF-SIMS and GCIB, the molecular signal from two different Irganox molecules were obtained as a function of depth.

24. Summary
XPS is a surface sensitive analytical tool for probing chemical phenomenon on polymers.
Standardless quantitation.
Ability to identify not only the elements on the surface, but also the chemical state.
TOF-SIMS offers two complementary attributes to XPS:
Determination of specific organic compounds present on the surface (rather than simply the functional groups).
Chemical mapping with ~1µm resolution.
Combined, these two tools provide the most complete chemical analysis of polymer surfaces and interfaces.
Recent advances open up these techniques and this field of analysis to new characterization opportunities and multilayer polymeric systems.

25. Thank you for your attention. Questions?