A. Michelmore, D.A. Steele, J.D. Whittle, J.W. Bradley,

R.D. Short

University of South Australia Based upon review article

RSC Advances, 2013, 3, 13540-13557

Tutorial on Plasma Polymerization

Deposition of Functionalized Films

Mawson Institute

Tutorial covers

• Introduction – Technological importance of plasma polymers + examples

• The plasma phase

– Plasma – surface interactions

– Mechanisms of deposition

- examines W/F - early stages of film grow - the role of ions

Introduction to Plasma polymerization

• Plasma ignited in organic vapour

– Pure vapour or a mixture of vapours

– Reduced pressure

• Polymer (organic) deposit formed on all surfaces

• Chemistry of deposit often similar to vapour (monomer)

– Polymerisation not dependent on functional group

– Plasma polymers tailored from organic to “inorganic”

General properties of plasma polymers

• Ultra-thin (< 50nm)

• Soluble/Insoluble

• Trapped free radicals

• Adherent

• Conformal

• Pinhole free

• Internal stress – Will crack and flake if too thick

Mawson Institute

Plasma polymerization is the ultimate enabling technology

Hydrophobic/Hydrophobic

Functionalized films Chemical Gradients

Responsive “intelligent” surfaces

Mawson Institute

Example - Super hydrophobic coatings

• Produced by pulsed plasma polymerization - Highly fluorinated monomers, e.g. TFE • Large amount of conventional PTFE in ‘ribbons’

- Rough surface • In continuous wave mode no ‘ribbons’ on surface

- Ribbons grow in ‘off’ period from activated sites

Mawson Institute

Example - Treatment of Burns

• In myskinTM technology a plasma polymerized coating is applied to a bandage to allow the culture of patient’s own cells

• Cells are delivered “off” pp-coated bandage

- Highly effective way of getting cells to patients rapidly

- Used in treatment of severe burns

• Range of potential applications

Haddow et al., Plasma Processes Polym., 2006, 3, 419

Renaissance in plasma polymerization:

• Traditionally, <1990s, scratch resistance, barrier layer, wetting – E.g. Nature, 1966, 209, 769

• Recent-cited applications: - Coating of tissue engineering scaffolds (Adv. Mater., 2006, 18,1406)

- Functionalization of nanotubes for covalent coupling of quantum dots (Adv. Mater., 2007, 19, 4003)

- Fabrication of a microcantilever fast humidity sensor (Adv. Mater., 2007, 19, 4248)

- Micro- and nano-engineering of surface structures (Adv. Mater., 2006, 18, 1406; Adv. Mater., 2007, 19, 1947; Adv. Mater., 2010, 22, ,

1451)

- Surfaces for high-throughput screening devices (Adv. Mater., 2008, 20, 116; Lab on a Chip, 2011, 11, 541)

Mawson Institute

Making a plasma polymer

What do you need to start?

Mawson Institute

Reactor

• Enclosed chamber

- Means to introduce monomer as vapour

- Reduced pressure ~1Pa – 100Pa

- (~0.75 mTorr- 75mTorr)

• Method of excitation DC or AC (RF→MW), CW or pulsed

Mawson Institute

RF excitation preferred for plasma polymers

• Electric fields heat electrons, generate plasma

–See Tutorial 2 – The Plasma Phase

• Advantages of RF

–Displacement rather than particle currents

–Stability

–Higher electrons temperature

–Process insulating materials without sputtering at electrodes

Mawson Institute

Plasma polymerization:

Plasma Chamber (under vacuum)

Substrate

Gas (Monomer Vapour) Flows into Chamber

Plasma

Radiofrequency Power Applied to System

Mawson Institute

(a) Clark and Dilks reactor design 1977 [ref 18] and three decades of reactor design evolution since, illustrating a variety of electrode configurations, power supplies and diagnostic tools (b) Ward 1989 [19] (c) Lopez et al. 1992 [20] (d) O’Toole et al. 1995 [21] (e) Favia et al., 1996 [22] (f) Candan et al. 1998 [23] (g) Alexander et al. 1998 [24] (h) Voronin et al. 2006 [25]

A. Michelmore et al, RSC Advances, 2013, 3, 13540

Mawson Institute

Reactor design – Historical Perspective

Gas (Monomer)

Ions Photons Fragments

Electrons

Intact Monomer Atoms Radicals

Oligomers

Metastables

Energy transfer Chemical modification (Deposition Adsorption Grafting)

Desorption Etching

Plasma phase interactions:- Excitation, Ionisation, Relaxation, Ion-Molecule, Radical-Neutral, Fragmentation

Plasma polymerization

Substrate

Mawson Institute

Different types of coating

Plasma parameters:

Non-functionalized Functionalized

Mawson Institute

RF Power, Gas Flowrate, Pressure, Ion Density Electron Temperature, Bias Potentials etc