NUCLEATION AND GROWTH OF PLASMA-POLYMERIZED HEXAMETHYLDISILAZANE ON IRON-SUBSTRATES

Plasma polymer films of hexamethyldisilazane (HMDSN) were deposited on iron substrates by an audio frequency discharge. The investigations focus on the activation of the iron surface by an oxygen plasma, the adsorption of the monomer and the initial states of polymer formation. Surface compositions were examined by means of in-situ Infrared-Reflection-Absorption-Spectroscopy (IRRAS) and Quartz-Crystal-Nanoweighting (QCN). It turned out that during the oxygen plasma treatment an additional layer of iron oxihydroxide is formed. The resulting high density of surface hydroxyls leads to the hydrolysis of the adsorbed silazane. Plasma-polymerised HMDSN is characterised by a reduced carbon and nitrogen content and the incorporation of siloxane units. In the range of about 4 nanometer the polymer structure changes significantly with the film thickness. With increasing film thickness the concentrations of siloxane and N-H units decrease. The interface between the oxide and the polymer is characterised by strong polar interactions between surface hydroxyls and the siloxane group and additionally by directed bonds via silanolate units.