Optical properties and formation kinetics of corrosion inhibitor films at the Cu/[formula omitted]/[formula omitted] interface

Abstract

Optical properties in the wavelength range of visible light and the growth kinetics of films composed of cuprous oxide (Cu2O) and benzotriazole, 2-mercaptobenzothiazole, 2-mercapto-1-methylimidazole, 2-methylimidazole and 4-methylimidazole, on a polished copper surface in the presence of the neutral 3wt% NaCl solution open to air, are studied by the in-situ spectroscopic ellipsometry, and compared with the secondary ion mass spectrometry profiles, as well as their corrosion protectiveness established from cyclic voltammetry. The optical properties of the growing films are determined by the dielectric function (DF), which is fitted from the ellipsometric spectra by employing an optical model based on Bruggemans effective medium approximation. This enables distinguishing the organic from the Cu2O component as well as the surface roughness or porosity, naturally occurring at the polished Cu surfaces. As the main result, the film thickness increase and the variation of the volume fractions of the optical components are driven into relationship with the chemical composition, providing a detailed picture of the material structuring upon film growth. The DFs are discussed in the light of optoelectronic parameters (absorption coefficient and electronic band gap energy) as well as corrosion protectiveness of the studied films, whereupon a clear correlation among these properties is established.