Wetting characterisation of silicon (1,0,0) surface

Abstract

Water droplets on bare silicon surfaces are studied to examine the wetting behaviour as a function of the surface energy and to parameterise water–silicon interactions in order to recover the hydrophobic behaviour measured by experiments. Two different wetting regimes characterised by a critical interaction strength value are observed. At a threshold value of the water–silicon interaction parameter, water molecules start penetrating into the first layer of silicon surface under thermally vibrating walls, resulting in two distinct wetting behaviours. Fixed (cold) silicon walls do not exhibit the two different wetting characteristics. Size effects are studied for nano-scale droplets, and line tension influence is observed depending on the surface wettability. Decrease in the droplet size increases the contact angle values for the low wetting cases, while contact angles decrease for smaller droplets on the high wetting surfaces. Considering the line tension effects and droplet size, ϵ_Si–O for water–silicon interactions to recover the hydrophobic behaviour of silicon surfaces is estimated to be 12.5% of the value predicted using the Lorentz–Berthelot mixing rule.

Keywords::

• silicon–water interface
• water nanodroplet
• hydrophobic
• hydrophilic
• line tension

Acknowledgements

This work was supported by the National Science Foundation under Grant No: CBET 0931988. The authors would like to thank the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the National Science Foundation grant number OCI 1053575 for computing resources.