Analysis of Corrosion Processes at the Surface of Diamond-Like Carbon Protected Zinc Selenide Waveguides

Abstract

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.

Elektrochemische Rastermikroskopie zur direkten Abbildung von Reaktionsgeschwindigkeiten

“…Durch Cyclovoltammogramme an der UME oder durch Verwendung ionensensitiver potentiometrischer Mikroelektroden lassen sich die beim Korrosionsprozess lokal freigesetzten Teilchen identifizieren. Untersuchte Materialien umfassen neben Stahl [64,223,224] auch Zahnfüllungen aus Amalgamen und metallischen Implantaten, [225,226] Titan, [227] Legierungen, [63,[228][229][230][231][232][233] organische Beschichtungen auf metallischen Substraten, [234][235][236] potentiometrische Sensoren aus AgI in Cyanidlösungen, [237] Silicium in ¾tzbädern, [238] ungeschützte und kohlenstoffbeschichtete ZnSe-Wellenleiter [239] und amperometrische Biosensoren für NADH-abhängige Dehydrogenasen aus einem Komposit, das als Reservoir für die kontrollierte Abgabe eines Redoxmediators wirkte. [240] SECM kann auch vorteilhaft eingesetzt werden, um simulierte Korrosionsprozesse bei der Fertigung von integrierten Schaltkreisen zu verfolgen.…”

Investigation of Localized Catalytic and Electrocatalytic Processes and Corrosion Reactions with Scanning Electrochemical Microscopy (SECM)

“…It complements other scanning probe techniques such as the scanning reference electrode technique (SRET) [178,179], conductive scanning force microcopy (CSFM), electrochemical scanning tunneling microscopy (ECSTM), and scanning Kelvin probe techniques which are popular methods for the investigation of functional materials [180]. Basic experimental approaches include the imaging of the permeability of applied protective coatings [181][182][183][184][185][186][187][188][189][190][191][192][193], the imaging of regions with distinctly higher electron transfer rates which may be precursor sites for pitting corrosion [29,57,[194][195][196][197][198][199][200][201][202][203][204][205][206][207], the initiation of pitting corrosion by local generation of aggressive species at the UME [208,209] and the detection of active corrosion by collecting released species [55,58,60,104,[210][211][212][213][214]…”

“…In a similar approach, Janotta et al [191] investigated the corrosion properties of uncoated ZnSe waveguides and those covered with a 100 nm thin film of diamond-like carbon (DLC) in a 30% (v.v) aqueous H 2 O 2 solution. In particular, SECM experiments were performed with an Au.Hg amalgam UME allowing scanning stripping voltammetry in an SECM setup.…”

Multidimensional electrochemical imaging in materials science

“…Monitoring of active corrosion by SECM has been realized on a range of materials by identification of locally released species by cyclic voltammetry at the UME or by use of ion-selective potentiometric microelectrodes. The materials investigated include steel [100][101][102], dental fillings [103,104], Si [105], Ti [106,107], alloys [76,[108][109][110][111][112][113], ZnSe wave-guides [114], organic coatings on metallic substrates [115][116][117], AgI-based ion-selective membranes [118], and composite-based amperometric biosensors [119]. Simões et al [120] studied the corrosion behavior of an iron/zinc galvanic couple immersed in aqueous sodium chloride solution.…”