Sensors play a critical role in improving overall human quality of life. They have been employed in most aspects of our lives. A recently emerging sensing platform is based on plasmonic resonance at the boundary of metals and dielectrics. Localized surface plasmon resonances–based sensors offer miniaturization, a simple setup, and relatively high sensitivity for real-time measurements. The reported figure of merit (FOM) of the LSPR-based sensor is generally limited, primarily due to its broad resonance peak. Nanorings composed of metal nanoparticles are known for their broad-range resonance tunability, high field localization, and large sensing area. Asymmetry of the nanoring with the introduction of core offset relaxes the selection rule for mode mixing, thus resulting in a narrower resonance peak. This may overcome broad resonance peak restriction. Concentric and non-concentric nanorings were simulated using the boundary element method implemented with the MNPBEM toolbox. We map the performance of nanoring sensors over a wide range of geometrical variations, namely, diameter, ring shell thickness, and the offset of the inner ring to the center of the outer ring wall (core offset). Sensitivity and FOM were found to rely substantially on the nanoring size parameters. The sensing performance map helps to obtain optimized nanoring parameters for the intended spectral range region. The obtained high sensitivity and FOM are much higher than the data available in the literature over visible and NIR ranges. The findings demonstrate the potential of nanorings for biosensing applications. Doi: 10.28991/ESJ-2023-07-04-04 Full Text: PDF

The angular behavior of light transmission through opal films over a broad range of wavelengths and angles was investigated. The opal films were prepared using the capillary deposition method (CDM). Many well-defined diffraction peaks were detected and indicate that the CDM results in opal films with high quality. Peaks coinciding at normal incidence split when samples are rotated. The angular shift of these peaks was found to satisfy the kinematical diffraction theory very well. Furthermore, the variation of intensity with incident angle can be interpreted in terms of a simplified dynamical diffraction theory. Moreover, the presence of two differently oriented domains in CDM-made opal films is essential in discussing the measured spectra.

Bio chemical detection using metal nanoparticles has been intensively investigated due to availability of robust nanoparticle synthesis methods whether chemically or using lithographic approach. SPR based sensor employs the shift of plasmonic resonance wavelength when local surrounding medium of metal nanoparticles change even slightly. The shift of the resonance wavelength depends sensitively on geometry and size of nanoparticle. The resonance wavelength and its shift were calculated numerically using boundary element method. Here, we compare the sensitivity of gold and silver nanoparticles to sense small change in refractive index of medium. Four different geometries (spherical, ellipsoidal, cylindrical, and donut-like nanoparticles) of different size were investigated to find the highest sensor sensitivity.

Self-assembled opals that are considered as a promising candidate for three-dimensional photonic crystals often suffer from the existence of internal defects. Defects influence optical properties and limit the applicability of opal films. Directed assembly using external fields may offer a certain degree of tunability in the opal formation process. We investigate the effect of an out-of-plane electric field on the formation and optical properties of opal films deposited using the capillary deposition method. The application of an electric field of intermediate strength (20–30 V/cm) can improve opal quality. The quality of opal films was found to depend on the polarity of the bottom substrate resulting from the beneficial influence of an asymmetry between the growths and the interplay with gravity. The negatively charged bottom substrate results in slightly better opal quality. This finding shows the potential of electric fields to tune opal formation in order to reduce the defect content.

Low solar energy conversion efficiency prevents the widespread of organic solar cells; hence, metal nanoparticles have been used to overcome this problem without increasing cell thickness. We investigated light absorption enhancement in view of the embedment of Ag:SiO2 core-shell nanoparticles of different shell thicknesses, core offsets, offset orientation angles, and vertical mismatches between neighboring particles. The simulations were carried out using the finite element method. This is the first investigation in the use of asymmetric nanoparticles. At optimized conditions, absorption enhancement up to 345% compared to the one without the nanoparticles could be achieved. The enhancement was found much higher than that of the published values. The enhancement results were mainly from the increase of near-field localization and scattering in the active layer of solar cells due to the excitation of Fano resonances. The resonance occurred due to the non-symmetric nature of the core-shell nanoparticles.