Surface analysis and bioreactions of F and Si containing a-C:H R. Hauert a, *, U. Mu ¨ller a , G. Francz a , F. Birchler b , A. Schroeder b , J. Mayer b , E. Wintermantel b a Swiss Federal Laboratories for Materials Testing and Research (EMPA), CH-8600 Du ¨bendorf, Switzerland b Institute for Biocompatible Materials Science and Engineering, ETHZ, CH-8952 Schlieren, Switzerland Abstract Amorphous hydrogenated carbon films containing different amounts of fluorine and silicon have been deposited by plasma activated chemical vapor deposition in a stainless steel high vacuum system, using different mixtures of acetylene and either trifluoromethane or tetramethylsilane. Film composition and the different chemical states present have been characterized by X-ray photoelectron spectroscopy. Cell culture tests with fibroblasts revealed a good surface biocompatibility by means of morphological behavior, but no dependence on the Si or F content in the a-C:H films could be seen. All cells showed good spreading on the surface. Within 2 days confluent cell layers were observed.  1997 Elsevier Science S.A. Keywords: Amorphous carbon; Bioreaction; XPS; a-C:H:F; Si-a-C:H 1. Introduction Thin films of hard amorphous hydrogenated carbon (a- C:H), also known as diamond-like carbon (DLC), are used in many applications due to their outstanding properties, such as high hardness (up to HV 5000), chemical inertness (corrosion resistance), low friction and wear, high thermal conductivity and biocompatibility [1–4]. Specific properties of a-C:H can be modified by introducing additional ele- ments into the a-C:H film. Adding different amounts of F or Si into the a-C:H allows film properties, such as internal stress, hardness, electrical conductivity and surface energy, to be tuned. We have shown before by Raman investiga- tions, that the addition of Si to a a-C:H film increases the thermal stability of the amorphous structure [5] whereas the addition of fluorine decreases it [6]. As with the change in physical properties we expected that the elements added would also influence bioreactions on the a-C:H coatings. Since the toxicity of SiC for macro- phages, fibroblasts and osteoblast cells has been shown [7], one might expect some poisoning effect in the case of Si containing a-C:H (Si-a-C:H), due to SiC at the surface. In the case of the F-containing films (a-C:H:F), the addition of C–F groups at the surface may reduce the cell/surface inter- actions since the C–F bonds are not very reactive (Teflon- like). As a first screening to evaluate a biological influence of F and Si in the films, preliminary cytocompatibility test have been performed by cell culturing with mouse fibro- blasts and analysis of the cell morphology 2 days after incu- bation by scanning electron microscopy (SEM). 2. Experimental 2.1. Film production Silicon containing a-C:H films (Si-a-C:H) films were pro- duced by rf plasma (13.56 MHz) deposition from different mixtures of acetylene (C 2 H 2 ) and tetramethylsilane (TMS, Si(CH 3 ) 4 ). For the fluorine containing a-C:H:F coatings a mixture of acetylene and trifluoromethane (CHF 3 ) was used. Deposition was performed in an all stainless steel high vacuum system with a base pressure better than 2 × 10 -6 Pa. The films were deposited onto 1 inch diameter silicon (100)-wafers. After argon plasma cleaning for 1 min, the deposition was performed at a total pressure of 2.0 Pa with a self-bias of -400 V for the Si-a-C:H films and -300 V for the a-C:H:F films. Samples with a Si content between 0 and 22.5 at% and samples with a F content between 0 and 17.5 at% were obtained (at% determined by in situ X-ray photo- electron spectroscopy, XPS). During deposition the sample temperature increased to approximately 150°C due to Thin Solid Films 308–309 (1997) 191–194 0040-6090/97/$17.00  1997 Elsevier Science S.A. All rights reserved PII S0040-6090(97)00422-7 * Corresponding author.