title: Ultralow adhesion and friction of fluoro-hydro alkyne-derived self-assembled monolayers on H-terminated Si(111).
abstract: New fluorine-containing terminal alkynes were synthesized and self-assembled onto Si(111) substrates to obtain fluorine-containing organic monolayers. The monolayers were analyzed in detail by ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS), static water contact angle measurements (CA), and atomic force microscopy (AFM). The SAMs exhibit excellent hydrophobicity, with static water contact angles of up to 119° and low critical surface tensions of 5-20 mN/m depending on the number of F atoms per molecule. IRRAS confirmed the formation of highly ordered monolayers, as indicated by the antisymmetric and symmetric stretching vibrations of the CH(2) moieties at 2918-2920 and 2850-2851 cm(-1), respectively. Upon increasing the number of fluorine atoms in the alkyne chains from 0 to 17, the adhesion of bare silica probes to the SAMs in air decreases from 11.6 ± 0.20 mJ/m(2) for fluorine-free (F0) alkyne monolayers to as low as 3.2 ± 0.03 mJ/m(2) for a heptadecafluoro-hexadecyne (F17)-based monolayer. Likewise, the friction coefficient decreases from 5.7 × 10(-2) to 1.2 × 10(-2). The combination of high ordering, excellent hydrophobicity, low adhesion, and low friction makes these fluoro-hydro alkyne-derived monolayers highly promising candidates for use in high-performance microelectronic devices.
authors.affiliation: Laboratory of Organic Chemistry, Wageningen University, Wageningen, The Netherlands.
authors.forename: Sidharam P
authors.initials: SP
authors.lastname: Pujari
authors.forename: Evan
authors.initials: E
authors.lastname: Spruijt
authors.forename: Martien A
authors.initials: MA
authors.lastname: Cohen Stuart
authors.forename: Cees J M
authors.initials: CJ
authors.lastname: van Rijn
authors.forename: Jos M J
authors.initials: JM
authors.lastname: Paulusse
authors.forename: Han
authors.initials: H
authors.lastname: Zuilhof