Hi Wenlin,
there has been published some literature on this topic, especially by Roya
Maboudian (Univ. of Berkeley) and M. de Boer (www.sandia.gov). In general the
surface has to be exposed to a halogenized alkylsilane like FDTS (supplier:
www.abcr.de), which forms a hydrophobical monolayer on the surface.

Regards,
Thomas