F4280 Technologie depozice a povrchových úprav: Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 1/16 Atmospheric Pressure DBD (AP-DBD) Two forms of dielectric barrier discharges (DBDs) with parallel plate electrodes: ► filamentary homogeneous Stabilization of homogeneous DBDs requires suppression of filament formation. Important role of metal foil U.V. vinyl chloride J ■ • t ----1 it silicone film ceramics metal mesh 0 0 35 325» ► structure and material of electrodes e.g. M. Kogoma, S. Okazaki, JPD (1994) 27 1985 ► higher frequencies of power supply T. Nozaki et al., Plasma Process. Polym. (2008) 5 300) ► gas mixture (He, Ne, N2, Ar + NH3 etc.): ► homogeneous DBD in He, Ar/NH3 and N2 F. Massines et al. Surf. Coat. Technol. 174-175, 8 (2003); Plasma Phys. Controlled Fusion 47, B577 (2005). ► PECVD in HMDSO/N2 and HMDSO/N2/synthetic air mixtures D. Trunecetal. J. Phys. D: Appl. Phys. 37 (2004) 2112; J. Phys. D: Appl. Phys. 43 (2010) 225403 ► PECVD in Ar/C2H2 M. Elias etal. J. Appl. Phys. 117(10) (2015) 103301 F4280 Technologie depozice a povrchových úprav: Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 2/16 Homogeneous Dielectric Barrier Discharges Two different forms of homogeneous discharges were classified by Massines et al. Both start with Townsend breakdown initiating a Townsend discharge but ► in He, during the current increase, the discharge transits to a glow discharge (ne « 1011) having a cathode fall and a positive column if gas gap is > 2 mm - atmospheric pressure glow discharge (APGD) ► in N2, the ionization level is too low (ne « 108) to allow formation of cathode fall and the glow regime cannot be achieved - atm. pressure Townsend discharge (APTD). Visualisation of a Townsend Avalanche Electric. field Key O Ionisation even! - fůnisiňů electron path - Liberated electron path Anode y DC Voltage Source Original Ionisation event Cathode 1000 - 800 - tu 600 Ol to 400 Dark Discharge i 11 Glow Discharge, Arc - I b-b ? 5 If f ■ / // V G/ I " aJJ[A i . . i M i . . i 10 -15 -10 10"iU 10" Current (A) 10l ► C: avalanche Townsend discharge ► D: self-sustained Townsend discharges ► F: sub-normal glow discharge ► G: normal glow discharge F4280 Technologie depozice a povrchových úprav: Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 3/16 Homogeneous DBD (APGD) in Ar/acetylene filamentary DBD in Ar filamentary DBD in Ar/CH4 homogeneous DBD in Ar/C2H2 (80 /is (one half-period) exposure time) ► difference caused by possibility of Penning ionization of C2H2 in Ar ► Ar 1 s5 metastable -11.55 eV, ► C2H2 ionization potential 11.40eV butCH4 12.61 eV > > > (a) DBD in pure Ar, (b) DBD in Ar/( (c) APGD in Ar/C2H2 M. Eliáš etal., J. Appl. Phys. 117(10) (2015) 103301 F4280 Technologie depozice a povrchových úprav: Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 4/16 Why to Use Homogeneous DBD for Deposition? .. to eliminate unwanted surface structures and non-uniformities D. Trunec, Z. Navrátil, P. Sťaheletal. J. Phys. D: Appl. Phys. 37(2004)2112: deposition in APTD (HMDSO/N2) and in filamentary discharge 0 iirri 0 urn H. Caquineauet. all Phys. D:Appl. Phys. 42(2009) 125201: a deposition 2 deposition areas Local increased of the deposition rate, "deposition spots", due to non-uniform power dissipation in micro-filaments. F4280 Technologie depozice a povrchových úprav: Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 5/16 Why to Use Homogeneous DBD for Deposition? ... modification of temperature sensitive and porous polymer nanofibers Interesting novel material, polymer nanofibers, can be prepared by electrospinning but it requires further modification of surface properties (as usually with polymers) Classical nozzle electrospinning: Nozzle-less electrospinning by NanospideriM from ELMARCO: a) polycaprolactone electrospun nanofibers b) coated by plasma polymerization in homogeneous DBD F4280 Technologie depozice a povrchovych uprav: Film Uniformity? Gas Dynamics Modelling ka Zajíčková 6/16 roblem of Film Uniformity Amospheric-pressure plasmas are characterized by high collision frequencies of particles (several orders of magnitude higher compared to low pressure) =>- Delivery of active species to the substrate is much more advection than diffusion-driven (opposed to low-pressure). High electron-neutral collision frequency =>- fast monomer conversion Basic gas delivery set-ups Gas flow Gas flo* Gas flow i—^![I^^Q^[p[g aSĚÍ3 J. * 4 <|r T T V T are modified for optimization of flow patterns by gas dynamics simulations P. Cools et ai, Plasma Process. Polym. H. Caquineau et al. J. Phys. D: Appl. 2015, 12, 1153-1163 Phys. 42(2009) 125201 I Hgjrti. Schematic representation of the four different in let set-ups: a) Sideway inlet, b) ring inlet c) porous glass inlet, and d) microplasma-electrode. gas i: i Iii. hü i grounded 4 «Kodes ■.i ili.Ir.IV: F4280 Technologie depozice a povrchových úprav: Film Uniformity? Gas Dynamics Modelling Lenka Zajíčková 7/16 las Dynamics Simulations in Our Set-up Solving the Navier-Stokes equations (laminar flow) in full 3D geometry for pure Ar (results are shown for 1550 seem): Velocity streamlines, color given by speed logarithm Surface: Velocity magnitude (m/s) Arrow Surface: Velocity field y-coordinate [m] ▼ 5.5x10' Surface: Velocity magnitude (m/s) Arrow Surface: Velocity field Surface: Velocity magnitude (m/s) Arrow Surface: Velocity field =>- Complex flow patterns inside the buffer chamber make the flow through the slit relatively even but better designs of the buffer chamber can be found! F4280 Technologie depozice a povrchovych uprav: Film Uniformity? Gas Dynamics Modelling ka Zajíčková 8/16 Variations of four different geometries tested gas inlet plastic tube buffer chamber exit slit bottom ceramics [electrode underneath) C-UfJfJcr electrodes 0.02 -0.05 0.02 f3 0.02 -0.05 V L. Zajíčková et al. Plasma Physics and Controlled Fusion, submitted F4280 Technologie depozice a povrchových úprav: Film Uniformity? Gas Dynamics Modelling Lenka Zajíčková 9/16 Variations of four different geometries tested Velocity magnitude [m/s] and direction Velocity magnitude [m/s] and direction 1.4 1.2 1 0.8 0.6 0.4 0.2 f '////// / / S , t /,',/,///// s . ■///ff/SSSs-. . -■' / / /////Ss^^-,--- ' - ,-- y / / / . ^ S / / / S s~ . - 2 x-coordinate [cm] 0 x-coordinate [cm] I 1 0.8 0.6 0.4 0.2 Velocity magnitude [m/s] and direction Velocity magnitude [m/s] and direction o u \ 1.4 1.2 1 0.8 0.6 0.4 0.2 0 u y 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 x-coordinate [cm] x-coordinate [cm] F4280 Technologie depozice a povrchovych uprav: Film Uniformity? Gas Dynamics Modelling ka Zajíčková 10/16 oes It Work in Real Life (case study for DBD co-polymerization of MA and C2H2 in Ar, no electrode movement) igas inlet plastic tube buffer chamber exit slit bottom ceramics _nr, [electrode underneath) LUJjpcM electrodes xyJ Interference colours are measured by imaging spectroscopy refractometry fitting of optical data provides spatially resolved film thickness 0 mm 5 10 15 20 25 215 nm 200 180 160 140 120 100