Sensors and Actuators B 126 (2007) 120–125 Covalent grafting of ion-exchanging groups on porous silicon for microsystem applications E. M´ ery a,∗ , S.A. Alekseev b , V.N. Zaitsev b , D. Barbier a a Laboratoire de Physique de la Mati` ere, LPM, UMR CNRS-5511, INSA de Lyon, 7 Avenue Jean-Capelle, Bˆ at. Blaise Pascal, 69621 Villeurbanne Cedex, France b Chemistry Department, Kiev National Taras Shevchenko University, 60 Vladimirskaya St., 01033 Kiev, Ukraine Available online 13 December 2006 Abstract We report the chemical functionalization of porous silicon (PS) by trimethylammoniumpropyl bromide (–(CH 2 ) 3 N(CH 3 ) 3 + Br - ) and alkylsulfonic acid (–C x H 2x SO 3 H) groups for microsystem components. PS was prepared by electrochemical etching of a p-type silicon wafer. Samples of PS were first thermally oxidized at 300 ◦ C and densified at 500 or 700 ◦ C under an inert atmosphere. Mercaptopropyl and trimethylammoniumpropyl bromide groups were grafted on the PS surface via a silanization procedure. The oxidation of mercapto groups was used for the synthesis of –C x H 2x SO 3 H groups. The samples were studied by Fourier transform infrared spectroscopy (FT-IR) and temperature-programmed desorption mass spectrometry (TPD-MS). The grafting of –C x H 2x SO 3 H groups was found to be dependent on the densification treatment of the oxide layer formed at the surface of PS crystallites by low temperature oxidation. For PS samples thermally oxidized at 300 ◦ C, –C x H 2x SO 3 H were not grafted, whereas for PS samples oxidized and densified at 500 or 700 ◦ C, they were successfully grafted. In opposite, the densification treatment of PS samples has no significant influence on the grafting of –(CH 2 ) 3 N(CH 3 ) 3 + Br - groups. © 2006 Elsevier B.V. All rights reserved. Keywords: Porous silicon; Sulfonic acid; Quaternary ammonium salt; Ion-exchanging groups; Silanization; Surface functionalization 1. Introduction Over recent years there has been many research works on porous silicon (PS) for optical devices, chemical and biologi- cal sensors [1,2], micro-arrays [3], micro-reactors [4,5], DNA chips [6] or fuel cells [7]. In fact, porous silicon is compati- ble with silicon-based technologies and exhibits many attractive properties such as its large surface area (up to 600 m 2 /cm 3 ) and adjustable nanostructure parameters: porosity up to 90% and pore size between 1 nm and 1 m. Chemical functionalization of the enormous internal surface of porous silicon with organic fragments found various attractive microsystems applications. Two main approaches are usually used for porous silicon chemical modification: (i) hydrosilyla- tion, which consists in the reaction of alkenes with silane groups (SiH x with x = 1, 2 or 3) of as-prepared porous silicon under photochemical or thermal activation [8] and (ii) mild oxidation of porous silicon which results in the formation of a hydrox- ∗ Corresponding author. E-mail address: emeline.mery@insa-lyon.fr (E. M´ ery). ylated SiO 2 layer ready for the silane chemistry modification commonly applied onto the silica-gel surface [9]. Silica gels with grafted ion-exchanging groups were successfully applied for ion-chromatography [10–12], heterogeneous catalysis [13], solid electrolytes [14], and electrochemical sensors [15,16]. To our knowledge, grafting of alkylsulfonic acid and quaternary ammonium salt groups on the surface of the porous silicon was never described in the literature, and should be very interesting for the fabrication of on chip ion-chromatography devices, solid electrolytic membranes and all other above-mentioned appli- cations. In this paper, we demonstrate how these interesting functions can be achieved in microcomponents based on oxi- dized porous silicon layers easily fabricated using standard clean room processing steps. 2. Experimental 2.1. Porous silicon fabrication and oxidation Porous silicon was prepared by anodic etching of p + -doped (ρ = 10 m cm) double sides polished silicon (100) wafers. 0925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2006.11.003