Functionalization of oxidized silicon surfaces with methyl groups and their characterization

Abstract

Oxidized silicon surfaces were functionalized with chemically bonded methyl end groups and characterized by means of Fourier transform infrared (FTIR) spectroscopy with the attenuated total reflection (ATR) method, contact angle measurements, scanning force microscopy (SFM), and thermal desorption spectroscopy (TDS). Detailed results are presented for trimethylsilyl (TMS) and pentamethyldisilyl (PMDS) terminated surfaces, which were prepared by silanization with suitable chloro compounds. The IR spectra of the TMS-terminated surface exhibit two CH stretching peaks at 2904 and 2963 cm −1. In the thermal desorption experiments desorption of trimethylsilanol and methane was observed at 550 ∘C. The IR spectra of the PMDS-terminated surface show two CH stretching peaks at 2898 and 2955 cm −1. The thermal desorption spectra indicate cleavage of Si–Si bonds and desorption of trimethylsilane at 530 ∘C. The wetting behavior, adhesion, and mechanical properties were studied by contact angle measurements and SFM. The results are compared with the well-defined Si(111)-(1×1):H surface and a self-assembled monolayer (SAM) on a silicon surface with long hydrocarbon chains, prepared with octadecyltrichlorosilane (OTS, H 3C(CH 2) 17SiCl 3). The water contact angle was 82 ∘ for TMS and 85 ∘ for PMDS end groups. The friction forces measured for the TMS- and PMDS-terminated surfaces were comparable and about 3 times higher than that of the H-terminated silicon and the OTS-SAM surface. The corresponding friction coefficients were 0.17, 0.18, 0.34, and 0.45 for Si(111)-(1×1):H, OTS SAM, TMS, and PMDS surfaces, respectively.