Fabrication of superhydrophobic Si nanowire patterned surfaces using CF4 plasma

Fabrication of superhydrophobic Si nanowire patterned surfaces using CF4 plasma
si nanowire; plasma; nanopattern; biomimetic; superhydrophobic; PACVD; Si nanowire; hierarchical structure
Issue Date
International Symposium on Nature Inspired Technology(ISNIT2010)
To achieve the hierarchy of roughness as observed in lotus leaves, most artificial water-repellent, or superhydrophobic surfaces have nano-asperities on top of micropillars. However, by choosing high aspect ratio of the height over diameter with nano patterns only, the superhydrophobic surface can be obtained. Thus we fabricate surfaces having the Si nanopillars or nanowire on Si wafer plasma-etching with CF4 precursor and subsequent hydrophobic amorphous carbon coating. The Si wafers were etched to create the nanowires using r.f. glow discharge of CF4 plasma etching at 30 mTorr and -600V of bias voltage using plasma assisted chemical vapor deposition (PACVD) method. Aspect ratio of nanowire was controlled by time of CF4 plasma treatment from 10 min to 60 min as well as bias voltage from 400 to 800Vb, which produced the height and diameter of nanowires in the range of 40-300 nm and 60-850 nm, respectively. To enhance a sharpness of nanowire, pre-wetting process is effective. After plasma etching process, partial wetting using D.I. water is induced an electrochemical reaction. For preparing hydrophobic surfaces, HMDSO gas were used for the deposition of a-C:H:Si:O deposited on each surface by PACVD method. It was shown that contact angle and contact angle hysteresis on the nanowire surfaces were drastically changed. The contact angle on the surfaces increased from 120 to 160 degree as increased CF4 plasma treatment time and the contact angle hysteresis was drastically decreased at the 60 min of CF4 plasma treatment from 45 to 15 degree.
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