We propose and report on the design of a 1-D metallo-dielectric nano-grating on a GaAs substrate. We numerically study the impact of grating period, slit and wire widths, and irradiating angle of incidence on the optical response. The optimal wire width, w = 160 nm, was chosen based on previous results from investigations into the influence of wire width and nano-slit dimensions on optical and electrical enhancements in metal-semiconductor-metal photodetectors. In this present project, resonant absorption and reflection modes were observed while varying the wire and nano-slit widths to study the unique optical modes generated by Rayleigh-Wood anomalies and surface plasmon polaritons. We observed sharp and diffuse changes in optical response to these anomalies, which may potentially be useful in applications such as photo-sensing and photodetectors. Additionally, we found that varying the slit width produced sharper, more intense anomalies in the optical spectrum than varying the wire width.

We report on the tunable edge-plasmon-enhanced absorption of phosphorene nanoribbons supported on a dielectric substrate. Monolayer anisotropic black phosphorous (phosphorene) nanoribbons are explored for light trapping and absorption enhancement on different dielectric substrates. We show that these phosphorene ribbons support infrared surface plasmons with high spatial confinement. The peak position and bandwidth of the calculated phosphorene absorption spectra are tunable with low loss over a wide wavelength range via the surrounding dielectric environment of the periodic nanoribbons. Simulation results show strong edge plasmon modes and enhanced absorption as well as a red-shift of the peak resonance wavelength. The periodic Fabry-Perot grating model was used to analytically evaluate the absorption resonance arising from the edge of the ribbons for comparison with the simulation. The results show promise for the promotion of phosphorene plasmons for both fundamental studies and potential applications in the infrared spectral range.

The adhesion layer used in nanofabrication process of metallic nanostructures affects the surface plasmon modes. We characterize the localized surface plasmon resonances (SPRs) of gold nanodisks of various diameters and heights while varying the thickness of the Ti adhesion layers. Scattering, absorption, and extinction coefficient calculations show a significant dependence of the SPR on the size of nanostructures and the adhesion layer thickness. Comparisons of peak resonance wavelengths of different Ti adhesion layer thicknesses indicate a significant red shift and a reduction in amplitude as the Ti thickness increases. A comparison of spectral broadening of the plasmon mode indicates a linear increase with Ti thickness and percentage. In addition, the decay time of the plasmon mode decreased significantly as the adhesion layer size increases. These observations aid in understanding size dependent adhesion layer effects and optimized fabrication of single nanoplasmonic structures.

Metallic, especially gold, nanostructures exhibit plasmonic behavior in the visible to near-infrared light range. In this study, we investigate optical enhancement and absorption of gold nanobars with different thicknesses for transverse and longitudinal polarizations using finite element method simulations. This study also reports on the discrepancy in the resonance wavelengths and optical enhancement of the sharp-corner and round-corner nanobars of constant length 100 nm and width 60 nm. The result shows that resonance amplitude and wavelength have strong dependences on the thickness of the nanostructure as well as the sharpness of the corners, which is significant since actual fabricated structure often have rounded corners. Primary resonance mode blue-shifts and broadens as the thickess increases due to decoupling of charge dipoles at the surface for both polarizations. The broadening effect is characterized by measuring the full width at half maximum of the spectra. We also present the surface charge distribution showing dipole mode oscillations at resonance frequency and multimode resonance indicating different oscillation directions of the surface charge based on the polarization direction of the field. Results of this work give insight for precisely tuning nanobar structures for sensing and other enhanced optical applications.

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This work studies the effect of a plasmonic array structure coupled with thin film oxide substrate layers on optical surface enhancement using a finite element method. Previous results have shown that as the nanowire spacing increases in the sub-100 nm range, enhancement decreases; however, this work improves upon previous results by extending the range above 100 nm. It also averages optical enhancement across the entire device surface rather than localized regions, which gives a more practical estimate of the sensor response. A significant finding is that in higher ranges, optical enhancement does not always decrease but instead has additional plasmonic modes at greater nanowire and spacing dimensions resonant with the period of the structure and the incident light wavelength, making it possible to optimize enhancement in more accessibly fabricated nanowire array structures. This work also studies surface enhancement to optimize the geometries of plasmonic wires and oxide substrate thickness. Periodic oscillations of surface enhancement are observed at specific oxide thicknesses. These results will help improve future research by providing optimized geometries for SERS molecular sensors.

This work presents a new substrate platform, which provides tunability of the group velocity and spontaneous emission of a dipolar scatterer graphene-ferroelectric slab hybrid system in the terahertz ranges. We use analytical models to determine the hybridization of graphene surface plasmon and ferroelectric LiNbO 3 type I and type II reststrahlen hyperbolic phonon-polariton. The variation of the chemical potential of graphene and the thickness of the ferroelectric layer results in several distinct features. Flipping the group velocity, strongly coupled hybrid hyperbolic surface plasmon-polaritons, and surface plasmon-polariton mode exists for the same momentum at different frequencies. The group velocity sign reversal for both a single-graphene-and doublegraphene-integrated system depends on the thickness of the hyperbolic layer and the chemical potential of graphene. Comparative analysis of Purcell radiation is presented for a quantum emitter positioned at different locations between ferroelectric and graphene-integrated ferroelectric layers, revealing that this system can support strong spontaneous emission that can be modulated with the graphene chemical potential. Changing the chemical potential through selective voltage biasing demonstrates a substantial increase or decrease in the decay rate for spontaneous emission. Further analysis of the emission phenomenon shows a dependence on factors, such as the relative radiating source position and the thickness of the ferroelectric film. These characteristics make graphene-ferroelectric materials promising candidates to modify the light-matter interaction at the low terahertz ranges.

Interaction between metallic nanoparticles has been widely investigated due to the rise of the enhanced local electric field inside the gap. We numerically present the broadband near- and far-field spectra from the near-ultraviolet (UV) through the visible wavelength range using plasmonic heterodimers. Both near- and far-field resonances can be manipulated by the composition of heterodimers. They show strong dependencies on gap width and particle size. Compared with Al-Au and Al-Ag heterodimers, the dipole-mode resonant peak has a redshift for the Au-Ag heterodimer. In the near-UV range, the Al-Ag heterodimer gains the strongest optical enhancement. This is due to the robust optical resonance of Al and Ag particles in the near-UV range. On the other hand, the heterodimers with Au particles exhibit a better field enhancement at longer wavelengths. The physical origin of plasmonic resonances of the bonding dipole modes and higher-order modes are revealed by the simulated mappings of local electric fields and 3D surface charge distributions. Moreover, our simulations also reveal the suitability of the plasmon ruler equation and the power law enhancement equation to quantify the optical response of heterodimers.