arXiv subjects

Masoud Shabaninezhad

Publications and source records attributed to Masoud Shabaninezhad.

4 recordsLinked to original sources

arXiv2024

Plasmonic Electro-Optic Modulators based on Epsilon-Near-Zero Materials: Comparing the Classical Drift-Diffusion and Schr\"odinger-Poisson Coupling Models

We present the design, modeling, and optimization of high-performance plasmonic electro-optic modulators leveraging voltage-gated carrier density in indium tin oxide (ITO) where the gated carrier density is modeled using both the Classical Drift-Diffusion (CDD) and Schr\"odinger-Poisson Coupling (SPC) methods. The latter ensures a more detailed and precise description of carrier distributions under various gate voltages which gains particular significance when applied to an epsilon-near-zero (ENZ) medium such as ITO. Combining the nanoscale confinement and field enhancement enabled by surface plasmon polaritons with the ENZ effect in ITO, modulator designs integrated with silicon waveguides and optimized for operation at {\lambda}0 = 1550 nm achieve a 3-dB bandwidth of 210 GHz, an insertion loss of 3 dB, and an extinction ratio of 5 dB for an overall length of < 4 {\mu}m as predicted by the SPC model. Our results illustrate trade-offs between high-speed modulator operation and low insertion loss, vs. extinction ratio, and the need for precise modelling of carrier distributions in ENZ materials.

physics.optics↗

arXiv2024

Electrically tunable plasmonic metasurface as a matrix of nanoantennas

We report the fabrication and characterization of a plasmonic metasurface comprising electrically contacted sub-wavelength gold dipole nanoantennas, conformally coated by a thin hafnia film, an indium tin oxide layer and a backside mirror, forming metal-oxide-semiconductor (MOS) capacitors, for use as an electrically-tunable reflectarray or metasurface. By voltage biasing the nanoantennas through metallic connectors and leveraging the carrier refraction effect in the MOS capacitors, our measurements demonstrate phase control in reflection over a range of about 30 degrees, with a constant magnitude of reflection coefficient of 0.5, and the absence of secondary lobes. Comprehensive electromagnetic and quantum carrier models of the structure are developed and are in excellent agreement with the measurements. The metasurface holds promise for use as an optical phased array.

physics.optics↗

arXiv2019

Ultrafast Electron Dynamics in Thiolate-Protected Plasmonic Gold Clusters: Size and Ligand Effect

The influence of passivating ligand on electron-phonon relaxation dynamics of the smallest sized gold clusters was studied using ultrafast transient absorption spectroscopy and theoretical modeling. The electron dynamics in Au279, Au329, and Au329 passivated with TBBT, SC2Ph and SC6, respectively, were investigated. Ultrafast transient absorption measurements were also carried out on Au~1400 (SC6) and Au~2000 (SC6) to understand the influence of the size on electron-phonon relaxation with the same passivating ligand. The study has revealed interesting aspects on the role of ligand on electron-phonon relaxation dynamics wherein the aromatic passivating ligands, SC2Ph and TBBT, have shown smaller power dependence and higher plasmon bleach indicating dampened plasmon resonance while the cluster with aliphatic passivating ligand has behaved similarly to regular plasmonic gold nanoparticles. To model the effect of the ligand on the plasmonic properties of the investigated samples , free electron density correction factor of each one was calculated using three-layered Mie theory, and the results show that SC6 inter-acts least with core-gold while TBBT and SC2Ph have a greater effect on the surface electronic conductivity that is attributed to pi-interaction of the ligand with gold. The results also shed light on unusual electron-phonon relaxation and smaller slope observed for Au329 (SC2Ph) that is ascribed to surface gold-pi interaction creating a hybrid state. In contrast, extended pi-interaction is probably the reason for plasmonic nature observed in Au279 (TBBT) even though its size is smaller when compared to Au329. In addition, the results also have shown that the electron-phonon coupling has increased with an increase in the size of the cluster and theoretical modeling has shown higher electron conductivity for larger plasmonic gold clusters.

cond-mat.mes-hall↗

arXiv2019

Theoretical Investigation of Size, Shape and Aspect Ratio Effect on the LSPR Sensitivity of Hollow-Gold Nanoshells

The change in refractive index around plasmonic nanoparticles upon binding to biomolecules is routinely used in localized surface plasmon resonance (LSPR) based biosensors and in bio-sensing platforms. In this study, the plasmon sensitivity of hollow gold (Au) nanoshells is studied using theoretical modeling where the influence of shape, size, shell thickness and aspect ratio are addressed. Different shapes of hollow Au nanoshells are studied that include: sphere, disk, triangular prism, rod, ellipsoid, and rectangular block. Multi-layered Mie theory and discrete dipole approximation (DDA) were used to determine the LSPR peak position, and LSPR sensitivity as a function of size, shell thickness, shape, and aspect ratio. The change in LSPR peak wavelength per unit refractive index is defined as the sensitivity, and interesting results were obtained from the analysis. The rectangular block and rod-shaped Au nanoshells have shown maximum LSPR sensitivity when compared to other shaped Au nanoshells. In addition, increased sensitivity was observed for higher aspect ratio as well as for smaller shell thicknesses. The results are rationalized based on the inner and outer surface plasmonic coupling.

physics.chem-ph↗