Tutorial on Plasma Polymerization Deposition of Functionalized Films 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 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
Plasma polymerization is the ultimate enabling technology Hydrophobic/Hydrophobic Functionalized films Chemical Gradients Responsive intelligent surfaces
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
Example - Treatment of Burns In myskin TM 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)
Making a plasma polymer What do you need to start?
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
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
Plasma polymerization: Gas (Monomer Vapour) Flows into Chamber Plasma Chamber (under vacuum) Substrate Plasma Radiofrequency Power Applied to System
Reactor design Historical Perspective (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
Gas (Monomer) Plasma polymerization Ions Photons Fragments Electrons Intact Monomer Atoms Radicals Oligomers Metastables Plasma phase interactions:- Excitation, Ionisation, Relaxation, Ion-Molecule, Radical-Neutral, Fragmentation Desorption Etching Energy transfer Chemical modification (Deposition Adsorption Grafting) Substrate
Plasma parameters: RF Power, Gas Flowrate, Pressure, Ion Density Electron Temperature, Bias Potentials etc Different types of coating Non-functionalized Functionalized