Analysis of corrosion processes at the surface of diamond-like carbon protected zinc selenide waveguides

A detailed surface analytical study on the corrosion behavior of unprotected and diamond-like carbon (DLC)-coated mid-infrared (MIR) waveguides used in remote sensing applications at strongly oxidizing conditions is presented. High-quality DLC films, with a thickness of 100 nm serving as MIR-transparent corrosion barrier, have been produced at the surface of zinc selenide (ZnSe) attenuated total reflection waveguides via pulsed laser deposition techniques. IR microscopy and atomic force microscopy are applied to investigate the chemical inertness of DLC-based membranes against aqueous solutions of hydrogen peroxide. These stability studies show that uncoated ZnSe waveguides are subject to severe chemical surface modifications, while DLC-protected waveguides maintain their optical properties and chemical integrity. In situ studies on the corrosion behavior by a recently developed approach combining scanning electrochemical microscopy (SECM) with Au/Hg amalgam ultramicroelectrodes in a scanning stripping voltammetry experiment provides additional insight into the mechanisms of the corrosion process. It is demonstrated that the combination of surface analytical techniques and, in particular, the innovative application of SECM with amalgam electrodes provides superior information on corrosion processes at the surface of optical waveguides. This detailed study confirms the efficiency of protective DLC coatings deposited onto IR-transparent optical waveguides, rendering this novel concept ideal for sensing applications in harsh environments.