Stability in Aqueous Media of 316L Stainless Steel Films Deposited on Internal Reflection Elements

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Abstract
Thin films of 316L stainless steel were sputter-deposited on cylindrical internal reflection elements (IREs) made of germanium. These films are intended for use in Fourier transform infrared (FT-IR) spectroscopy studies on the stability of stainless steel in aqueous media. In these deposits the films tend to peel off the substrate when immersed in water, probably due to galvanic corrosion at the metal/substrate interface. Deposition of a 2-nm-thick layer of chromium oxide on the substrate prior to the deposition of the steel was beneficial on three counts. It provided an electrically insulating layer, it enhanced adhesion, and it solved the steel/germanium incompatibility problem. It was also found that annealing the substrate prior to deposition remarkably enhances the film adhesion and improves the optical properties of the substrate. The microstructure, the topography, and the chemical composition of the films were characterized by scanning and transmission electron microscopy, Auger electron spectroscopy, and atomic force microscopy. The only significant difference between the austenitic stainless steel target material and the film is that the crystalline structure of the film is body-centered cubic. The optical properties of the system germanium/metallic film/water were studied and calculated with the help of a computer program. The absorbance of the water bands in the IR range was measured in coated Ge-IRE.

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