1. Deposition of polymer thin films by PVD process
Olivia Lehtimäki

2. Polymer thin films Wet-coating techniques
Microstructure control difficult
Chemical vapor deposition (CVD)
For polymers that are not soluble
Physical vapor deposition (PVD)
Controllable film morphology
Multilayer structures?
Image source:
How to deposit polymer films by PVD?

3. Pulsed laser deposition (PLD)
A high-energy UV-laser ablates the polymer in a plume onto the substrate surface
Polymers can degrade due to high energy laser
Limited to only a few materials (PTFE, PMMA)
[2]

4. Matrix-assisted pulsed laser deposition
Deviation of PLD
Target is in the form of solution
Target is frozen
Lower laser energy
A more gentle mechanism for polymer deposition
[5]

5. MAPLE Direct-write
Patterned polymer films without lithography

6. INFORMATION SLIDES

7. Introduction
Polymer thin films are important for optoelectronics, sensors and photovoltaics
Traditional wet-coating techniques cannot produce films with controlled morphology
These methods include spin-casting, ink-jet printing, drop-casting, spraying, Langmuir-Blodgett deposition
CVD can be used for polymers that are insoluble in common solvents
Specific reaction requirements needed to produce wanted polymers
Methods need to be developed as the applications for organic thin films grow  PVD
[1], [2], [3]

8. Pulsed laser deposition (PLD)
Limited to only a few materials
Polymer decomposition due to high energy
Succesful for depositing addition polymers (PTFE, PMMA)
A high-energy UV-laser ablates the polymer in a plume onto the substrate surface
Target holder is rotated
The film thickness control arises from the pulsed nature of the laser
The theory of PLD reactions for polymers
The UV laser converts the polymer to monomers and oligomers
These recombine on the substrate surface
The final film may not be chemically identical to the target material
[2], [3], [4]

9. Matrix assisted pulsed laser evaporation
A deviation of pulsed laser deposition (PLD)
Same principle, difference in target and laser fluence
The target material is solution which is frozen by liquid nitrogen
Low concentration solution, highly volatile solvent
Target holder is cryogenically cooled to keep the target frozen
The polymer molecules evaporate with the solvent in a plume
A pulsed laser source ablates the target
The energy of the laser can be lower than for PLD as only the solvent needs to be evaporated
The solution absorbs most of the energy and therefore protects the fragile polymer molecules
Volatile solvent does not stick onto the substrate surface  pumped away
[5]

10. Matrix assisted pulsed laser evaporation
The target holder needs to be positioned on the bottom of the chamber
Liquefied polymer solution can cause droplets in the vacuum
Polymer/solvent mix important to be optimized
Solvent volatile enough to be pumped away, and not to be incorporated in the film
Solvent absorption coefficient in respect to the laser
Solvent needs to be frozen by liquid nitrogen
Polymer needs to be soluble in the solvent (concentrations wt.%)
Single target MAPLE deposition chamber
[6]

11. Matrix assisted pulsed laser evaporation
The method is still under investigation and most depositions are executed in a self-built apparatus
The research is focusing on finding suitable deposition parameters (solvent material, laser energy)
There can also be some difficulties in the process itself
 Matrix needs to be carefully selected
A chunk of the frozen target is ejected (1)
The polymer chain is cut (3)
The UV-laser energy can be enough to degrade some of the polymer chains
[3], [4]

12. Variations of MAPLE MAPLE direct-write (MAPLE DW)
Used to generate patterned polymer films without lithography
Polymer is mixed with an UV-absorbent material, and a focused laser beam is directed through this mixture
The laser vaporizes the matrix and releases ink on the substrate surface
[5]

13. References
R. Pate et. al., RIR-MAPLE deposition of conjugated polymers for application to optoelectronic devices, Applied Physics A 105 (2011)
D.B. Chrisey et. al., Laser Deposition of Polymer and Biomaterial Films, Chemical Reviews (2003)
K.B. Shepard, R.D. Priestley, MAPLE Deposition of Macromolecules, Macromolecular Chemistry and Physics 214 (2013)
R. Eason, Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials, Wiley 2006, pp
A. Piqué et. al., Laser processing of polymer thin films for chemical sensor applications, Surface and Coatings Technology (2003)
J.A. Greer, Design challenges for matrix assisted pulsed laser evaporation and infrared laser evaporation equipment, Applied Physics A 105 (2011)