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Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface

Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface. Tae-Young Kim * , *** , Bialuch Ingmar **, Klaus Bewilogua **, Kyu Hwan Oh ***and Kwang-Ryeol Lee * * Future Technology Research Division, KIST, KOREA ** New Tribological Coating, Fraunhofer IST, GERMANY

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Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface

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  1. Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface Tae-Young Kim*,*** , Bialuch Ingmar **, Klaus Bewilogua **, Kyu Hwan Oh ***and Kwang-Ryeol Lee * * Future Technology Research Division, KIST, KOREA ** New Tribological Coating, Fraunhofer IST, GERMANY ***Department of Materials Engineering, SNU, KOREA

  2. Lotus Surface • Properties of Lotus leave • Water wetting angle exceeds 150o • Wetting angle hysteresis is below 10o • Water repellent and/or surface self cleaning effect

  3. Lotus Surface 50μm 20μm Planta, 202,(1998) 1 • Surface Material - cuticular wax • Surface morphology – very rough in micrometer scale Control of surface chemical and structure enhances hydrophobic property

  4. Super-hydrophobic Surface • Water repellent surface • Self cleaning of surface • Surface energy induced drop motion • Low resistance coating against liquid flow

  5. Super Hydrophobic What is super-hydrophobic? Super hydrophobic hydrophobic hydrophilic 150o 90o Flat surface chemical control Surface chemical+roughness control 120o

  6. Just Rough Surface?? Which surface is more hydrophobic?

  7. Just Rough Surface? Water droplets behave differently on tilted surfaces because of the contact angle and contact angle hysteresis. Wetting angle hysteresis = advancing wetting angle –receding wetting angle

  8. Purpose of This Work • Super hydrophobic surface generation • Hydrophobic DLC coating • Surface roughness controlled by Si etching process • Goal • Static wetting angle >150o • wetting angle hysteresis < 10o • Optimizing surface roughness structure • Mono roughness • Double roughness

  9. Experimental Process Thin metal(Cu) film deposition Metal dot formation by heat treatment Si wafer Plasma etching conditions CF4+O2etched surface is flat CF4formation of nano post on etched surface

  10. Plasma Si Etching Plasma source gas : CF4 Nano post formation Plasma source gas : CF4+O2 Flat etched surfac

  11. Si wafer Si wafer Si wafer Surface Structure Manipulation CF4+O2 plasma Si wafer CF4+O2 plasma CF4 plasma CF4 plasma Si wafer Hydrophobic a-C:H:Si:O deposition

  12. Wetting Angle Analysis • Static wetting angle (apparent wetting angle) • Water drop volume : 5μL • Gently drop on the surface • Dynamic wetting angle • Water drop size continuously changed (0.053 μL/sec) • Advancing angle (AA): 0 to 5 μL • Receding angle (RA): 5 to 0 μL • Wetting angle hysterisis : AA-RA

  13. DLC coated nano post Static Wetting Angle DLC coated Si(110)

  14. DLC coated big post DLC coated DRS Static Wetting Angle

  15. DLC coated nano post Dynamic Wetting Angle DLC coated Si(110)

  16. DLC coated big post DLC coated DRS Dynamic Wetting Angle

  17. DRS BP Double Rough Structure Effect DRS is more hydrophobic and suitable for moving droplet application than BP. The difference in structure is just bottom nano post in DRS DRS effect

  18. Summary • We fabricated double rough structure by nano structuring of Si. • Double rough structure shows high static wetting angle and low wetting angle hysteresis. • Double rough structure could be effective structure for moving droplet application. But why?

  19. Thermodynamical Calculation • System idealization • Surface structure : circular post type • Variables : post radius(Pr), post height(Ph), solid fractional factor (f), roughness factor (r), water drop radius(R), young contact angle(θy) R Pr Ph

  20. Thermodynamical Calculation R Pr Ph Lamgmuir 2004, 20, 10015 Langmuir 2003, 19, 8343

  21. Calculations System definition: Pr (205nm), Ph(413nm), f (0.5) (93o), R (5*109)

  22. DRS calculation 0<z<h: calculation results same with BP

  23. Parameters

  24. Small Post Structure System definition: Pr (35nm), Ph(131nm), f (0.5) (93o), R (5*109)

  25. Big Post Structure System definition: Pr (2565nm), Ph(393nm), f (0.065) (93o), R (5*109)

  26. Double Rough Structure System definition: Pr (201nm), Ph(436nm), f (0.08) (93o), R (5*109) (134o)

  27. BP DRS Hysteresis and Energy Barrier (WC)

  28. Conclusion • We fabricated double rough structure by nano structuring of Si. • Double rough structure shows high static wetting angle and low wetting angle hysteresis. • Double rough structure could be effective structure for moving droplet application. • Low hysteresis in DRS would caused by decrement of detaching energy barrier.

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