PLASMA-POLYMERIZED FILMS OF TRIMETHYLSILANE DEPOSITED ON COLD-ROLLED STEEL SUBSTRATES .1. CHARACTERIZATION BY XPS, AES AND TOF-SIMS

Plasma-polymerized coatings on metal substrates have been suggested as corrosion protection layers, but not much is known about the properties of these films and how these properties relate to the corrosion performance of coated metals. In this study, trimethylsilane plasma films were deposited on cold-rolled steel (CRS) under different deposition conditions. Angular-dependent XPS, AES and time-of-flight (TOF)-SIMS were used to characterize the films. These three techniques were highly complementary in nature. All films were silicon-based and the hydrocarbon content was a function of the deposition conditions. The AES depth profiles indicated that pretreatment of the substrate with oxygen had a significant effect on the type of film produced. Both TOF-SIMS and XPS revealed that the surface of the film was different from the bulk. The surface was oxygen-rich and was apparently modified upon exposure of the plasma film to the atmosphere. Both silicon and carbon were highly oxidized in the surface layers. Thus, these plasma films consist of at least three distinctly different regions: an interfacial region where the film is intimately mixed with the metal oxide; a bulk region with approximately the same elemental composition as the monomer; and a highly oxidized surface region. A correlation between the type of plasma film produced and the deposition conditions is discussed briefly.