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

***School of Material Science and Engineering, SNU, KOREA

The International Conference OnMetallurgical Coatings And Thin Films

ICMCTF 2006

Lotus Leaf Surface

• Property of lotus leaf– Water droplet is not

spread (static wetting angle reached 150o)

– Water droplet removed by slight tilting of surface (wetting angle hysteresis is very low)

Applications of Super-hydrophobic Surface

Water repellent surfaceSelf cleaning of surfaceLow resistance coating against liquid flow

Applications related with water droplet moving

Microstructure of Lotus Leaf

Surface Material - cuticular wax Surface morphology – very rough in micrometer scale

20μm

Planta, 202,(1998) 1

Previous Works

Langmuir 2004; 20(2); 287-290

Langmuir 2004; 20(2); 10015

Langmuir 2006; 22; 2433

Dual Roughness Effect?

20μm

Planta, 202,(1998) 1

Motivation of This Work

• Does dual roughness surface structure (DRS) affect super- hydrophobic property?

• How much does DRS contribute the hydrophobic property?

Experimental

Surface structure control:Plasma Si etching technique

Nano-meter size metal mask formation

Surface chemical control: hydrophobic a-C:H:Si:O film

deposition

Super-hydrophobic surface

Analysis

Plasma Si Etching

Plasma source gas : CF4

Plasma source gas : CF4+O2

CF4+O2 plasma gasCF4 plasma gas

Si wafer Si wafer

– RF-PECVD– Source gas : Pure CF4 gas and CF4+O2 mixing

gas – Chamber Pressure : 2 and 5 Pa– RF power : 150 and 300 W– RF bias : 300V– Etching time : 10min

Plasma Si Etching

Plasma source gas : CF4

Nano post formation

Plasma source gas : CF4+O2

Flat etched surface

400nm 400nm

Surface Structure Manipulation

Without Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Si wafer

Si wafer

Flat

Small Post

Nano Size Metal Dot Formation

Si wafer

Metal film separation byby heat treatment

Cu sputtering on Si surface

Surface Structure Manipulation

Without Cu mask With Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Si wafer

Si wafer

Flat

Small Post

Si wafer

Si wafer

Surface Structure Manipulation

Without Cu mask With Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Si wafer Si wafer

Si waferSi wafer

Flat Big Post

Small Post Dual Rough

Microstructures

Without Cu mask With Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Big Post

Small Post

Flat

500nm

250nm

500nm

500nm

Dual Rough

Static Wetting Angle

Without Cu mask With Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Water drop volume : 5μLGently drop on the surface

93.2o 103.8o

134.0o 159.6o

Flat Big Post

Small Post Dual Rough

Static Wetting Angle

• Wetting angle hysteresis

RA

Dynamic Wetting Angle

A R

Wetting angle hysteresis

High Low

Dynamic Wetting Angle

Dynamic Wetting Angle

Without Cu mask With Cu mask

CFCF44+O+O2 2

plasma plasma etchingetching

CFCF44 plasma plasma etchingetching

Flat Big Post

Small Post Dual Rough

: o

o

93.2

:15.3

Y

: o

o53.

1 3.8

8

0

:

Y

: o

o48.

1 4.0

7

3

:

Y

: o

o

159.6

4.8 :

Y

Dynamic Wetting Angle

Dual Rough Structure Effect

134.0Static

wetting angle

159.6

48.7Wetting

angle hysteresis

4.8

Conclusions

• We fabricated various structures with mono and dual roughness through nano structuring of Si and studied their wetting behavior.

• Dual rough structure shows higher static wetting angle and lower wetting angle hysteresis than that of mono structures.

• Dual rough structure could be effective structure for moving droplet application.