The document discusses controlling the wrinkling pattern in thin metal polymer films. It provides background on why wrinkles are important and can be used for applications like surface enhanced Raman spectroscopy and flexible electronics. The document outlines the theory behind why wrinkles form and how their wavelength can be controlled by factors like the elastic properties, polymer thickness, and capping layer thickness. It then describes the experimental methods used, including deposition techniques and microscopy. The results show that increasing the polymer thickness or decreasing the capping layer thickness and thermal treatment time increased the wrinkle wavelength. Future work is proposed to further examine wavelength effects and control functional surfaces.

1. Controlling the wrinkling pattern
in thin metal polymer films
Colin Fair Brennan

2. Overview
• Motivation – Why wrinkles?
• Background theory
• Experimental methods
• Results
• Conclusions and potential work
• Acknowledgments

3. Motivation
• Wrinkles – Why are they important? What can you do with them?
• There’s a number of applications
• SERS / Flexible electronics / Controlled wettability
• And more…

4. Surface Enhanced Raman Spectroscopy
(SERS)
• Extremely sensitive molecular fingerprinting technique – single
molecules
Number of applications through
forensics, healthcare and diagnostics

5. Flexible Electronics

6. Controlled Wettability
• Wettability due to roughness

7. Theory
• Why do wrinkles form? And how can you control them?
• It all comes down to Energy. Patterns are formed to reduce the overall
free energy of the system.

8. Theory
• Controlling the wrinkles – What affects the wavelength?
𝜆 = 2𝜋ℎ
𝐸𝑓
3𝐸𝑠
1
3
𝜆 = 𝜋ℎ 𝑓
2 1 − 2𝑣
3 1 − 𝑣 1 − 𝑣 𝑓
2
𝐸𝑓
𝜇∞
𝐻
𝐻𝑓
1
4
• Elastic properties – Young’s modulus
• Polymer / Capping layer thickness

9. Experimental Methods
• Polymer Solution
• Deposition – Spin coating / Sputtering
• Thermal Treatment
• Microscopy – AFM, White light interferometer, Optical

10. Deposition
Solid Substrate (Si)
Polymer (PMMA)
Thin
metal film
Polymer Deposition Thin Metal Film Deposition
• Spin Coating
• Sputtering

11. Atomic Force Microscopy (AFM)
• To measure polymer thickness

12. Optical Microscopy
• Wrinkle analysis

13. White Light interferometer

14. Results
• Effects of…
• Polymer thickness
• Capping layer thickness
• Thermal treatment time

15. Polymer thickness
• Images A – D increasing the polymer
thickness

16. Capping layer thickness
10.8nm AuPd
λ = 5.153µm
20.9nm AuPd
λ = 1.92µm

17. Thermal treatment time 5.2nm Cr
7.2nm Cr
Wrinkle wavelengths decrease in time though not substantially!
Thermal treatment time was increased by
twenty minutes from A to B for both samples.
A) λ = 3.125 µm
B) λ = 2.14 µm
A) λ = 3.09 µm
B) λ = 3.02 µm

18. Conclusions
• The overall aim of the study was achieved and from the results some
clear trends appeared
• By increasing the polymer thickness, there was an increase in wrinkle
wavelength
• With an increase in the metallic capping layer thickness there was a
decrease in wrinkle wavelength
• Increasing the time for thermal treatment did decrease the wrinkle
wavelength, however not substantially.

19. Future Work
• Examine the effects of wavelength for both reflectivity and contact
angle.
• To examine further the effects of thermal treatment time and also to
examine varying the temperature of thermal treatment.
• To use the wavelengths as a means of measuring the Young’s modulus
of different materials.
• To use the system to create functional surfaces (i.e. controlled
wettability etc.)

20. Acknowledgments
• A very big thank you to my two supervisors Dr. George Amarandei and
Dr. Izabela Naydenova.
• Thank you to the FOCAS institute for facilitating our needs to carry
out these projects.
• Thank you also to the DIT School of Physics.

21. Thank you for listening
Any questions???