Environmental pollution with cadmium (Cd) is a major concern worldwide, with prolonged exposure to this toxic heavy metal causing serious health problems, such as kidney damage, cancer, or cardiovascular diseases, only to mention a few. Herein, a gold-coated reflection-type fiber optic–-surface plasmon resonance (Au-coated FO-SPR) sensor is manufactured and functionalized with (i) bovine serum albumin (BSA), (ii) chitosan, and (iii) polyaniline (PANI), respectively, for the sensitive detection of cadmium ions (Cd${}^{2+}$) in water. Then, the three sensor functionalization strategies are evaluated and compared one at a time. Out of these strategies, the BSA-functionalized FO-SPR sensor is found to be highly sensitive, exhibiting a limit of detection (LOD) for Cd${}^{2+}$ detection at nM level. Moreover, the presence of Cd${}^{2+}$ on the FO-SPR sensor surface was confirmed by the X-ray photoelectron spectroscopy (XPS) technique and also quantified consecutively for all the above-mentioned functionalization strategies. Hence, the BSA-functionalized FO-SPR sensor is sensitive, provides a rapid detection time, and is cheap and portable, with potential applicability for monitoring trace-level amounts of Cd within environmental or potable water.

In this work, we report results on the fabrication and characterization of a surface plasmon resonance (SPR) pH sensor using platinum (Pt) and polyaniline (PANI) layers successively coated over an unclad core of an optical fiber (FO). The plasmonic thin Pt layer was deposited using a magnetron sputtering technique, while the pH-sensitive PANI layer was synthesized using an electroless polymerization method. Moreover, the formation of PANI film was confirmed by X-ray photoelectron spectroscopy (XPS) technique and its surface morphology was investigated using scanning electron microscopy (SEM). It was found that the PANI/Pt-coated FO-SPR pH sensor exhibits a fast and linear response in either acid or alkali solutions (pH operational range: 1 to 14). The proposed FO-SPR sensor could be used for biomedical applications, environmental monitoring or any remote, real-time on-site measurements.

Zinc selenide (ZnSe) thin films were deposited by RF magnetron sputtering in specific conditions, onto optical glass substrates, at different RF plasma power. The prepared ZnSe layers were afterwards subjected to a series of structural, morphological, optical and electrical characterizations. The obtained results pointed out the optimal sputtering conditions to obtain ZnSe films of excellent quality, especially in terms of better optical properties, lower superficial roughness, reduced micro-strain and a band gap value closer to the one reported for the ZnSe bulk semiconducting material. Electrical characterization were afterwards carried out by measuring the current–voltage (I-V) characteristics at room temperature, of prepared “sandwich”-like Au/ZnSe/Au structures. The analysis of I-V characteristics have shown that at low injection levels there is an Ohmic conduction, followed at high injection levels, after a well-defined transition voltage, by a Space Charge Limited Current (SCLC) in the presence of an exponential trap distribution in the band gap of the ZnSe thin films. The results obtained from all the characterization techniques presented, demonstrated thus the potential of ZnSe thin films sputtered under optimized RF plasma conditions, to be used as alternative environmentally-friendly Cd-free window layers within photovoltaic cells manufacturing.

Zinc telluride thin films with different thicknesses were grown onto glass substrates by the rf magnetron sputtering technique, using time as a variable growth parameter. All other deposition process parameters were kept constant. The deposited thin films with thickness from 75 to 460 nm were characterized using X-ray diffraction, electron microscopy, atomic force microscopy, ellipsometry, and UV-Vis spectroscopy, to evaluate their structures, surface morphology, topology, and optical properties. It was found out that the deposition time increase leads to a larger growth rate. This determines significant changes on the ZnTe thin film structures and their surface morphology. Characteristic surface metrology parameter values varied, and the surface texture evolved with the thickness increase. Optical bandgap energy values slightly decreased as the thickness increased, while the mean grains radius remained almost constant at ~9 nm, and the surface to volume ratio of the films decreased by two orders of magnitude. This study is the first (to our knowledge) that thoroughly considered the correlation of film thickness with ZnTe structuring and surface morphology characteristic parameters. It adds value to the existing knowledge regarding ZnTe thin film fabrication, for various applications in electronic and optoelectronic devices, including photovoltaics.