Chemical and electrochemical grafting of polyaniline on aniline‐terminated porous silicon

Abstract

IntroductionSurface modification of materials with functional polymers is an important research area in polymer science because of the wide applications of polymers in various fields including adhesion, biomaterials, protective coatings, friction and wear, composites, microelectronics and thin-film technology. [1 -3] In recent years, a great deal of research is focused on synthesis of polymer films by various means for potential applications such as components in molecular electronics, [4] optical devices, [5] etch resists, [6] biosensors, [7] and as scaffolds for tissue engineering and fundamental studies in cell biology. [8] Among the available polymers, conducting polymers show much promise in electronics and sensing applications because of their distinguishable electrical properties, mechanical flexibility and relative ease of processing. [9 -11] Polyaniline (PANI) has been extensively studied in different fields of science [12] because of exigent demands for highperformance materials in advanced technologies including active electrodes, [13] microelectronic materials, electrochemical devices, [14] rechargeable batteries, [15] energy storage and transfer, redox miocrotemplates, [16] sensors [17] and actuators. [18] While porous silicon (PSi) displays excellent bulk physical and chemical properties, it does not possess suitable surface properties required for specific applications. Freshly prepared PSi is hydrogen terminated and exhibits good optical and electronic properties. However, the hydrogen-terminated PSi surface (Si-H x termination) is very reactive upon exposure to ambient air, and thus, does not fully protect the optical and electronic properties of the material. For this reason, surface-modification techniques can transform this material into valuable finished products. [19 -23] In this paper, we report on the covalent modification of PSi substrates with PANi films using chemical or electrochemical strategies. The resulting PANi/PSi hybrid interfaces showed a high chemical stability and good electrical properties. The chemical composition of the resulting hybrid structure was characterized by Fourier transform infrared spectroscopy (FTIR), XPS and SIMS, while the morphology of the substrates was studied using SEM. Experimental Section MaterialsSilicon wafers were purchased from Siltronics. All cleaning and etching reagents were clean room grade. Sulfuric acid (H 2 SO 4 ) 96%, hydrogen peroxide (H 2 O 2 ) 30% and hydrofluoric acid (HF) 50% were supplied by Amplex. All other chemicals were reagent grade or higher, and were used as received unless otherwise specified. Milli-Q water (18 M ) was used for all experiments. * Correspondence to: Nawel Chiboub, UDTS, 02, Bd. Frantz Fanon, B. P. 140 Alger Preparation of PSi substratesDouble-side polished Si(100)-oriented p-type silicon wafers (boron-doped, 5-10 -cm resistivity) were first cleaned in 3 : 1 concentrated H 2 SO 4 /30% H 2 O 2 for 20 min at 80• C and then sonicated in Milli-Q water for 10 min. The clean wafers were immersed in 50% HF aq...

Functionalization of Oxide-Free Silicon Surfaces with Redox-Active Assemblies

“…A pyrrole derivative was first covalently anchored to SiO 2 /Si via a silanization reaction, and the bound monomer rings were further used as nucleation sites for the electrochemical growth of a polypyrrole film. Such a procedure was then extended to the deposition of other conducting polymers, such as polythiophene − and polyaniline, − onto monomer-modified oxidized silicon surfaces. Due to the presence of a covalent linkage, the organic polymer films were found to be strongly adherent to the electrode surface and much more adherent than conducting polymer films directly deposited on the semiconductor surface without an organic link. , Another advantage of the method is that the coverage of polymer and thus its thickness could be finely controlled from the electrical charge consumed during the electropolymerization reaction.…”

Mechanisms of polyaniline film formation via solution casting: Intra-chain contraction versus inter-chain association

“…For example, it is well-known that an expanded-coil conformation of doped PANI molecules leads to increased infrared absorption in the electronic spectrum, it also improves mechanical properties and increases electrical conductivity of the film as compared with the film where the molecules are in the compact-coil conformation [1]. In order to provide a required structural organization of a polymer film, various deposition techniques can be employed, such as chemical and electrochemical deposition onto specific substrates [2], spin-and drop-casting [3,4], Langmuir-Blodgett [5][6][7], self-assembly [8][9][10], grafting to the surface [11,12], and molecular imprinting [13]. While many techniques provide more or less controlled structure of PANI films, casting from a solution still leads to ambiguous results in respect to the film structure, since the nature of a cast film depends critically on the relative rate of solvent evaporation in respect to the rate at which changes in molecular interaction occur.…”

Electropolymerization of Poly(para-phenylene)vinylene Films onto and Inside Porous Si layers of Different Types and Morphologies

“…Recently, the deposition of polyaniline in PSi was studied. [13][14][15] Moreover, the application of gas sensing was considered using poly͑3-hexylthiophene͒ grafted on PSi. 16 Of particular interest, poly͑para-phenylene͒vinylene ͑PPV͒ exhibits strong green luminescence.…”