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Complimentary spectroscopic, microscopic and electrochemical studies were performed to characterise the barrier properties as well as the interface structure of model iron substrates covered with thin plasma polymer films. Cathodic plasma polymers were deposited which show high barrier properties. The metal surface was pre-treated by a reducing or oxidising plasma. This allowed the adjustment of the oxidation state of the interface layer. The interface structure was characterised by means of X-ray photoelectron sputter profiles, infrared spectroscopy and the application of a Kelvin probe. The investigations show that the measured Voltapotential on the plasma polymer surface can be correlated with the oxidation state of the interface. Reducing plasmas lead to an almost oxide free surface. After deposition of the plasma polymer, this reduced state of the oxide is sensitive to re-oxidation of the interface by oxygen that diffuses through the plasma polymer. It could be shown that the increase in the plasma polymer thickness leads to an improved barrier effect as indicated by the more negative Voltapotential. The barrier properties of the organosilicon plasma polymer layers on iron were further quantified by means of electrochemical impedance spectroscopy (EIS). The morphology of the plasma polymer surface was studied using atomic force microscopy (AFM) to support the evaluation of the impedance data. A water diffusion coefficient of 4×10−14 cm2/s was found for the plasma polymer. Moreover, the water uptake of the film was measured to be 0.13%. These values illustrate the high barrier properties of these thin films.

Oxidized silicon is a promising candidate for the adhesion promotion of polymeric coatings on iron and steel. Therefore, the surface of iron must be covered by silicon and silicon oxide. This can be done by the chemical vapor deposition (CVD) of silane gas, a process which might be applied in industry easily. Because of these reasons the CVD of Si on the Fe(100) surface was studied at the deposition temperature of 770°C. The silane partial pressure ranged from 0.02 to 0.2 mbar while the total pressure was constant 990 mbar. It was found that the morphology of the surface changes from a very thin two-dimensional (2D)- to a complex and thick three-dimensional (3D)-structure with increasing deposition time. This is connected with a change of the chemical structure and a change in the reaction mechanism. Different processes like passivation of the surface by oxidation and surface diffusion influence the deposition. Models are proposed to describe the mechanism of growth of the surface layer.

The paper reveals structural changes of the iron surface during the plasma oxidation in an oxygen glow discharge. For this purpose, an in-situ set-up which combines IR-spectroscopy under grazing incidence and quartz crystal micro weighing was used. A Scanning Kelvin Probe was used to measure the influence of the glow discharge on the electronic properties of the iron oxide surface. The glow discharge was initiated by a low power audio frequency voltage source. The results show that an oxygen plasma on iron which is already covered by a natural oxide layer leads to an effective removal of organic contaminations and an increased thickness of the oxide of about 5 to 6 nm. In agreement with the spectroscopic data, the Voltapotential measurements show that the oxide surface is depleted in Fe 2+ states. The structure of the additionally grown oxide is most likely to be γ-Fe 2 O 3 . This means that the n-semiconducting properties of the oxide are changed. Within an subsequent argon discharge, the Fe 3+ in the oxide surface is again reduced to Fe 2+ . The paper illustrates the importance of the consideration of the electronic properties while structuring oxide covered metals and the usefulness of the Scanning Kelvin Probe measurement to reveal electronic properties of semiconducting oxide layers.

Silicon and iron silicides are promising candidates as adhesion promoters on iron. The formation of silicon and iron silicides films on polycrystalline iron is studied in a CVD process with monosilane. The process is performed between 475°C and 800°C with a silane partial pressure of 0.2 to 10 mbar to a total pressure of the silane–hydrogen mixture of 100 to 990 mbar. A model of the reaction mechanism is presented which includes the transport of the gases, the adsorption on the surface, the chemical decomposition of the silane and the interdiffusion between Si and Fe.

In order to increase the chemical and electrochemical stability of metal/polymer composite materials the first monolayer of the organic coating should be bonded by chemical bonds to the substrate. In this study, the bond formation between iron and n-decanethiol has been studied by surface sensitive techniques (XPS, AES) and the stability of the modified surface by cyclic voltammetry in different aqueous electrolytes. Chemisorptive bonds between the substrate and the thiol could be formed probably by cleavage of the S-H bond -only, if the metal surface is free of any oxide layer. Cyclovoltammetry in nitrogen purged acqueous electrolytes enhances the package density of the adsorbed molecules and leads to a more perpendicular orientation of the thiol molecules with respect to the substrate surface. The very stable bond between iron and the thiol supresses an oxidation of both the iron surface and the SH group in air and in electrolytes of different pH within a large potential range.

Monomolecular Langmuir-Blodgett films of silanes have been prepared on water by using a computer-controlled Langmuir balance. The LB films were transferred from the fluid to solid substrates like Fe, Cr and Ni/Cr alloy. By using scanning electron microscopy (SEM) and scanning Auger microscopy (SAM) it was shown that both methods allowed very easy identification of covered and uncovered areas of the solid substrate. Most probably a separation of the LB film occurs during transfer from the fluid to the solid substrate leading to the observed island structure of the LB films on the solids.