Mechanical properties of a-C:H/Si-containing a-C:H multilayered coatings grown by LF-PECVD C. Chouquet a,b, ⁎, C. Ducros b , S. Barrat a , A. Billard c , F. Sanchette b a Laboratoire de Science et Génie des Surfaces, Ecole des Mines, Parc de Saurupt, CS 14234, 54042 Nancy, France b CEA Grenoble DRT/LITEN/DTNM/LTS, 17 rue des Martyrs, 38054 Grenoble, France c Laboratoire d'Etudes et de Recherches sur les Matériaux, les Procédés et les Surfaces — UTBM, 90010 Belfort, France abstract article info Available online 15 August 2008 Keywords: LF-PECVD a-C:H/Si-containing a-C:H multilayered films Hardness Young modulus Residual stress Friction Amorphous hydrogenated carbon (a-C:H), Si-containing a-C:H and a-C:H/Si-containing a-C:H multilayered films have been deposited by low frequency plasma enhanced chemical vapour deposition (LF-PECVD) from cyclohexane and/or tetramethylsilane gas mixtures. Structural and mechanical properties of single layers have been first studied in relation with the working pressure, the gas mixture and especially the plasma power. By optimising these parameters, a-C:H films reveal very interesting mechanical and tribological properties (hardness of 23 GPa, friction coefficient of about 0.04 and wear rate of 1.50 10 - 7 mm 3 N - 1 m - 1 (under air, against Al 2 O 3 , with Hertz pressure of 0.65 GPa)) with compressive residual stress values about - 1 GPa. Inversely, Si-containing a-C:H films offer a wider range of mechanical behaviour (7–20 GPa for the hardness and 50–170 GPa for the Young modulus) while preserving lower residual stress values (- 0.5 GPa). Then, previous results have been exploited to study a-C:H/Si-containing a-C:H multilayered coatings. Transmission Electron Microscopy, nanoindentation, stress measurements and ball-on-disk tribometer were used to characterize these multilayered films. First results show the possibility to obtain from precursor gas inlet modulation thick multilayered coatings (∼ 10 μm) with period thicknesses down to 15 nm. Period thickness has no influence on hardness, Young modulus and residual stress within the investigated domain. However, friction coefficient and wear resistance are improved by decreasing the period or by optimising the properties of the Si-containing layer. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Diamond-like Carbon (DLC) is a metastable form of amorphous carbon containing both sp 2 (graphite) and sp 3 (diamond) bonding sites and which can incorporate hydrogen depending on the precursor and the deposition method used [1,2]. Because of their unique combination of properties such as optical transparency (infrared region), high electrical resistivity, good biocom- patibility, extreme hardness, very low friction coefficient and high wear resistance, DLC films have attracted considerable technological interests. Potential applications of these films include protective coatings in areas such as optical windows, magnetic storage disks, car engine parts, biomedical coatings and micro-electromechanical devices (MEMS) [3–5]. However, three main drawbacks often limit their use. The first is their high internal compressive stress, usually several GPa, which prevents good adhesion. The second is their relatively low thermal stability, limiting their working temperature to about 250 °C and the third is a pronounced increase of friction coefficient in humid conditions [6]. Solutions, such as doping these films with different elements (Si, F, B, O, N or metals) in order to stabilize or to improve their resistance against humidity and temperature have already been found [7,8]. Multilayered structures are also elaborated in order to reduce residual stress [9]. The aim of this work was to elaborate and characterize coatings consisting in a stack of hydrogenated Diamond-like Carbon (a-C:H) and Si-containing a-C:H layers. The main goal was to study the influence of period thickness and Si-containing a-C:H layer properties on residual stress, hardness, Young modulus and tribological properties. After a brief presentation of the elementary layers (a-C:H, Si- containing a-C:H), first results concerning the deposition and the mechanical properties of the multilayered coatings are reported. 2. Experimental 2.1. Coatings elaboration Deposition was carried out in an industrial size Low Frequencies PECVD reactor with a capacitively coupled electrode configuration. The lower electrode serving as substrate holder is powered via a 40 kHz LF transmitter. The distance between the two electrodes was Surface & Coatings Technology 203 (2008) 745–749 ⁎ Corresponding author. CEA Grenoble DRT/LITEN/DTNM/LTS, 17 rue des Martyrs, 38054 Grenoble, France. E-mail address: caroline.chouquet@cea.fr (C. Chouquet). 0257-8972/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2008.08.008 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat