In-Situ Ellipsometric Study of the Optical Properties of LTL-Doped Thin Film Sensors for Copper(II) Ion Detection

Abstract

Optical sensors fabricated in zeolite nanoparticle composite films rely on changes in their optical properties (refractive index, n, and thickness, d) to produce a measurable response in the presence of a target analyte. Here, ellipsometry is used to characterize the changes in optical properties of Linde Type L (LTL) zeolite thin films in the presence of Cu2+ ions in solution, with a view to improving the design of optical sensors that involve the change of n and/or d due to the adsorption of Cu2+ ions. The suitability of two different ellipsometry techniques (single wavelength and spectroscopic) for the evaluation of changes in n and d of both undoped and zeolite-doped films during exposure to water and Cu2+-containing solutions was investigated. The influence of pre-immersion thermal treatment conditions on sensor response was also studied. Due to the high temporal resolution, single wavelength ellipsometry facilitated the identification of a Cu2+ concentration response immediately after Cu2+ introduction, indicating that the single wavelength technique is suitable for dynamic studies of sensor–analyte interactions over short time scales. In comparison, spectroscopic ellipsometry produced a robust analysis of absolute changes in film n and d, as well as yielding insight into the net influence of competing and simultaneous changes in n and d inside the zeolite-doped films arising due to water adsorption and the ion exchange of potassium (K+) cations by copper (Cu2+).

Simplifying Molecular Transport in Polyelectrolyte Multilayer Thin Films

“…[ 88,141 ] Apart from these optical methods, ellipsometry can also be used for measuring thickness of the wide range of thin films. [ 142–146 ] Using ellipsometry variation in the PEM, thickness can be analyzed for studying salt induced molecular exchange or changes with respect to polymer concentration, pH, temperature, etc. [ 113,147–149 ] But, ellipsometry require specialized substrates and complex modelling for data interpretation.…”

Special Issue: “Optical Thin Films and Structures: Design and Advanced Applications”

“…The effects of the annealing temperature on the structural properties, surface roughness, electrical properties, and optical transmittance of the thin films are then systematically explored. Cody et al [6] demonstrated a possibility of optical sensing of copper ions in water using Linde Type L (LTL) zeolite thin films. Both single wavelength and spectroscopic ellipsometry were used for characterization of the changes in optical constants and thickness of films in the presence of heavy metal ions.…”

Structurally designed porous polymer monoliths as probe-anchoring templates as benign and fast responsive solid-state optical sensors for the sensing and recovery of copper ions

“…Among all these techniques, adsorption is one of the most favorable techniques owing to its fast kinetic response even with a very low detection limit, in addition to its simple operating procedure [22]. In this category, adsorbents in the form of resins, goethite, activated carbons, zeolite nanoparticles and holographic-based sensors have been attempted in the past, but with limited success [23][24][25]. In addition to this, liquid-based colorimetric and fluorescent chemosensors have been reported with numerous probe molecules that are mostly soluble in organic solvent, thus making the sensing process more complicated and less sensitive [26].…”