A Detailed Description of the Chemistry of Thiol Supporting Plasma Polymer Films Damien Thiry,* Remy Francq, Damien Cossement, Maxime Guillaume, J er^ ome Cornil, Rony Snyders In this work, the plasma polymerization of propanethiol is investigated with the aim to control the thiol density [SH] in the coatings. The results reveal a nearly constant evolution of [SH] regarding the mean power dissipated in the discharge. This peculiar behavior is explained considering (i) mass spectrometry data revealing a similar relative concentration of condensable SH-bearing species in the plasma and (ii) similar energetic conditions at the growing film/plasma interface. Finally, it is observed that the low hPi synthesized films are not chemically stable in solution likely due to the release of H 2 S molecules trapped in the material network. The whole set of our data allows to provide a deeper understanding of the growth mechanism of propanethiol plasma polymer, essential for future development. 1. Introduction Nowadays, the generation of thiol (–SH) supporting organic surfaces (TSOS) draws more and more interest owing to their potential in a wide range of applications from biotechnology to catalysis. As an example, the –SH functions can serve as anchoring sites for the immobiliza- tion of biomolecules which represents an important task for disease diagnosis or for the conception of biosensors. [1–3] In such applications, the strategy is based on the use of modified target biomolecules holding a chemical group (e.g maleimide or another –SH function) which can react selectively with the supported –SH function. [4] Due to the strong affinity between the thiol functionalities and gold, TSOS can also be employed as: (i) an interlayer for promoting gold adhesion [5] or (ii) as a support for the stabilization of gold nanoparticles. [6,7] The latter is particu- larly important in the area of low temperature catalysis where the stabilization of the gold nanoparticles by the support is crucial for the preservation of the catalytic activity with time. [8–10] The common approach to generate TSOS is by immersion of the substrate in a solution containing molecules bearing a –SH function. [4,11–13] However, this method suffers of several drawbacks. For instance, this wet chemistry route strongly depends on the substrate surface properties which could therefore reduce its applicability to some specific materials. [3] Moreover, most of the time, the desired surface is obtained after surface preparation treatments requiring important use of solvents and long reaction time which could be detrimental from the environmental point of view. [4,12] In this context, the plasma polymerization of a thiol- based precursor appears to be a promising alternative for the generation of TSOS. Indeed, this solvent-free process presents significant advantages over the wet traditional method: one-step process, low reaction time, D. Thiry, R. Francq, R. Snyders Chimie des Interactions Plasma Surface (ChIPS), CIRMAP, Universit e de Mons, 23 Place du Parc, B-7000 Mons, Belgium E-mail: damien.thiry@umons.ac.be R. Francq, D. Cossement, R. Snyders Materia Nova Research Center, Parc Initialis, B-7000 Mons, Belgium M. Guillaume, J. Cornil Service de Chimie des Mat eriaux Nouveaux (CMN), CIRMAP, Universit e de Mons, 23 Place du Parc B-7000 Mons, Belgium Full Paper Plasma Process. Polym. 2014, DOI: 10.1002/ppap.201400015 ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 DOI: 10.1002/ppap.201400015 wileyonlinelibrary.com Early View Publication; these are NOT the final page numbers, use DOI for citation !! R