ABSTRACT
Near-infrared (NIR) waveguides are a key component of planar photonic devices such as optical communication couplers, image sensors, and spectroscopes for chemical or biological molecules. Conventional NIR waveguides used for signal transmission include silicon-on-insulator (SOI) waveguides and channel/ridge-type metal micro-strips. However, these waveguides usually have limitations of either signal delay or signal loss in optically integrated devices. In this study, a novel NIR waveguide composed of a semi-disordered array of metal nanoparticles (sDAMNPs) on Si substrate was proposed, fabricated, and tested. The disordered metallic nanoparticles array is geometrically localized in the form of 1D metal strips, thus replacing sDAMNPs with less lossy micro strip channel waveguides. From the measurements supported by various computational models, the fabricated waveguides operate effectively in the broadband NIR region (1100 to 1700 nm). The waveguide does not support signal transmission in the ultra violet-visible spectrum due to strong signal absorption, scattering, and localization effects inside the metal nanoparticles. Instead, it is capable of transmitting NIR over a distance longer than 100 µm (signal loss â¼3.85 dB per 100 µm for NIR from 1200 to 1600 nm), which is also sufficiently longer than the conventional surface plasmon polariton propagation distance at the metal-Si interface. Compared to a waveguide-free reference, the waveguide exhibited greatly improved signal transmission efficiency up to a factor of 7.42 × 104 at 1367 nm. It also exhibits a high deflection angle sensitivity of 1.89 dB per 0.01 rad, thus efficiently and straightly guiding the broadband NIR signal over a long distance.
ABSTRACT
The higher oxidation state of iron, i.e. Fe(VI), was employed for the oxidation of the important toxic ion cyanide in aqueous/waste waters. Cyanide was oxidized to cyanate, which is 1,000 times less toxic than cyanide, and can often be accepted for its ultimate disposal. It was noted that Fe(VI) is a very powerful oxidizing agent, and can oxidize most of the cyanide within a few minutes, ca 5 minutes, of contact. The extent of the reduction of Fe(VI) was obtained using the UV-Visible measurements. Further, the UV-Visible data was used to explain the reaction kinetics involved in the redox reaction between ferrate(VI) and cyanide. The pseudo-first-order rate constant was calculated by maintaining the cyanide concentration in excess, with the overall second order rate constant values obtained for initial Fe(VI) concentrations of 1.0 and 0.1 mmol/L. The oxidation of cyanide was again confirmed using a cyanide probe. Fe(VI) was further employed for its possible application in the treatment of industrial wastewaters containing cyanide, along with some heavy metals, such as those obtained from electroplating industries.