Water-repellent surfaces have been prepared by exposing Si substrates with a hydroxylated surface oxide to fluoroalkyl silane (FAS) vapor. Since this chemical vapor surface modification (CVSM) is based on the chemical reaction between organosilane molecules and hydroxyl groups at the oxide surface, prior to CVSM, the substrate surface was completely hydroxylated by irradiating in air with a 172-nm ultraviolet light until the water contact angle of the surface became almost 0°. Under atmospheric pressure, the substrate was then exposed to vapor of an FAS precursor, that is, one of three types of FAS having different perfluoroalkyl chain lengths [CF3(CF2) n CH2CH2Si(OCH3)3, where n = 0, 5, or 7, referred to as FAS-3, FAS-13, and FAS-17, respectively]. The FAS molecules chemically reacted with the hydroxyl groups on the substrate surface and adsorbed onto it, forming a thin layer of less than 2 nm in thickness. The water repellency of the substrate surface increased with an increase in perfluoroalkyl chain length. The maximum water-contact angles of the substrates treated with FAS-3, -13, and -17 were ca. 86°, 106°, and 112°, respectively.

Micropatterning of organosilane self-assembled monolayers (SAMs) was demonstrated on the basis of photolithography using an excimer lamp radiating vacuum ultraviolet light of 172 nm. This lithography is generally applicable to micropatterning of organic thin films including alkyl and fluoroalkyl SAMs, since its patterning mechanism involves cleavage of C-C bonds in organic molecules and subsequent decomposition of the molecules. In this study, SAMs were prepared on Si substrates covered with native oxide by chemical vapor deposition in which an alkylsilane, that is, octadecyltrimethoxysilane, and a fluoroalkylsilane, that is, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, were used as precursors. Each of these SAMs was photoirradiated through a photomask placed on its surface. As confirmed by atomic force microscopy and X-ray photoelectron spectroscopy, the SAMs were decomposed and removed in the photoirradiated area while the masked areas remained undecomposed. Furthermore, these patterned SAMs served as masks for wet chemical etching in order to fabricate microstructures on their Si substrates. A micropattern 2 µm in width was successfully transferred on the Si substrate with an edge resolution of 200 nm.

Articles you may be interested inFabrication of quantum dots using multicoated self-assembled monolayer J. Vac. Sci. Technol. A 28, 730 (2010); 10.1116/1.3360923Self-assembled monolayer of alkanephosphoric acid on nanotextured Ti

Graduate School of Eng., Nagoya Univ. Center for Integrated Research in Sci. and Eng., Nagoya Univ. (Furo-cho, Chikusa-ku, Nagoya-shi, Aichi 464-8603) Fig. 1 IR absorption spectra (a and b) and X-ray diffraction patterns (c) of MPS films.

No abstract