Fundamental investigations of interlayer processes occurring during DLC coating of selected plastics

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Nowadays plastic material can be found in many fields of application due to their advantageous properties (elasticity and low weight). However, some of their disadvantageous characters (low hardness and abrasion strength, microbial adhesion) limit their use considerably in some fields of application (e.g. medicine). Properties can be improved and consequently applications of conventional plastic material can be extended by coating them with diamond-like carbon (DLC). Generally DLC layers are considered to be robust, anti-bacterial and bio-compatible protective layers. Although DLC layers can be coated on a high number of materials, DLC-coated plastics are yet sparsely investigated. Especially the changes of the chemical and physical properties of the original surface during the initial coating process are yet thoroughly unclear.The purpose of this research project is to elucidate and define the processes that take place during the plasma-assisted deposition of DLC layers on the surface of chosen plastics (polyethylene, polyoxymethylene). Research work will especially focus on the detailed explanation of the initial process during the growing of the layers and the accompanying modifications on the boundary layer between soft plastic material and hard DLC. The prevalent reaction processes will be assigned to the possible process types like deposition, interlayer formation and erosion.Only very few atomic layers are deposited in order to analyze the emerging boundary layer. The composition of the components in the reaction chamber is being observed continuously during the coating process with the help of high-resolution mass spectroscopy. This serves to clarify which plasma interaction takes place with the substrate and how far this can be influenced by varying the process parameters.We expect to obtain relevant information concerning the binding properties on the boundary layer between the DLC layer and the substrate using various x-ray spectroscopy methods (XPS, NEXAFS). Furthermore it is assumed that apart from the coating parameters also chemical composition and the surface of the substrate as well as the amount of deposited DLC have influence on the resulting bonding (boundary layer) and the resulting morphology of the coated plastic material.The purpose of this project is to achieve a basic understanding of the bonding between hard (DLC) and soft (plastic) materials. The used plastic materials serve as typical model substrates. The results will be transferred to other polymer materials thus enabling the production of alternative materials with changed surface characteristics such as low abrasive behavior and at the same time flexible as well as biocompatible surfaces in the future.