Formation of Dense Self-assembled Monolayers of (n-Decyl)trichlorosilanes on Ta/Ta₂O₅
By De Palma, Randy; Laureyn, Wim; Frederix, Filip; Bonroy, Kristien; Pireaux, Jean-Jaques; Borghs, Gustaaf & Maes, Guido
Published in Langmuir
2007
Abstract
Tantalum pentoxide (Ta₂O₅) is a promising material for the realization of biological interfaces because of its high dielectric constant, its high chemical stability, and its excellent passivating properties. Nevertheless, the deposition of highly organized silane SAMs to realize well-defined and tailored Ta₂O₅-based (bio)interfaces, has not been studied in great detail as of yet. In this work, we have investigated the formation of a highly ordered, dense monolayer of trichlorosilanes on Ta₂O₅ surfaces. Specifically, two different cleaning procedures for Ta₂O₅ were compared and (n-decyl)trichlorosilane (DTS) was used to study the effect of both cleaning methods on the silanization of Ta₂O₅. Both types of cleaning allowed the formation of complete and crystalline DTS monolayers on Ta₂O₅, in contrast with the incomplete, disordered silane layer assembled on uncleaned Ta2O5. The deposited self-assembled monolayers were studied by means of contact angle goniometry, Brewster angle FTIR, X-ray photoelectron spectroscopy, cyclic voltammetry, and ellipsometry. Infrared analysis exhibited a highly ordered DTS silane film on Ta₂O₅ and indicated a larger tilt angle of the alkyl chains on this substrate by comparison to DTS on SiO2. Furthermore, with use of ellipsometry and XPS, the silane film thickness on Ta₂O₅ was determined to be substantially smaller than that reported in the literature for DTS on SiO2, supporting the observations of an increased tilt angle (∼45°) on Ta₂O₅ than on SiO₂ (∼10°). By means of cyclic voltammetry, the formation of a dense, essentially pinhole-free, silane film was observed on the cleaned samples. In conclusion, the fully characterized and optimized procedure for the silanization of Ta₂O₅ surfaces with trichlorosilanes will allow the formation of well-defined, reproducible, and controllable chemical interfaces on Ta₂O₅.