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1. Perspective on functional metal-oxide plasmonic metastructures

   https://doi.org/10.1063/5.0134141  

   Sadeghi, Seyed M.; Wing, Waylin J.; Gutha, Rithvik R. (February 2023, Journal of Applied Physics)

   Plasmonic nanostructures and metasurfaces are appealing hosts for investigation of novel optical devices and exploration of new frontiers in physical/optical processes and materials research. Recent studies have shown that these structures hold the promise of greater control over the optical and electronic properties of quantum emitters, offering a unique horizon for ultra-fast spin-controlled optical devices, quantum computation, laser systems, and sensitive photodetectors. In this Perspective, we discuss how heterostructures consisting of metal oxides, metallic nanoantennas, and dielectrics can offer a material platform wherein one can use the decay of plasmons and their near fields to passivate the defect sites of semiconductor quantum dots while enhancing their radiative decay rates. Such a platform, called functional metal-oxide plasmonic metasubstrates (FMOPs), relies on formation of two junctions at very close vicinity of each other. These include an Au/Si Schottky junction and an Si/Al oxide charge barrier. Such a double junction allows one to use hot electrons to generate a field-passivation effect, preventing migration of photo-excited electrons from quantum dots to the defect sites. Prospects of FMOP, including impact of enhancement exciton–plasmon coupling, collective transport of excitation energy, and suppression of quantum dot fluorescence blinking, are discussed. 

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2. Hot Electrons Control of Quantum Dot Emission Using Plasmonic Supercells

   https://doi.org/10.1021/acs.jpcc.6c03809  

   Sadeghi, Seyed M; Gutha, Rithvik; Sharp, Christina; Goul, Ryan W; Wu, Judy (July 2026, The Journal of Physical Chemistry C)

   In hybrid systems composed of metallic nanoantennas and semiconductor quantum dots (QDs), exciton–plasmon coupling plays a central role in controlling the emission intensity and dynamics of the QDs. Here, we investigate how plasmon decay into hot electrons modulates this coupling through electronic modification of the QD environment. The plasmonic platform consists of closely packed periodic arrays of elongated Au nanoantennas that support plasmonic supercells. Owing to their periodicity, these supercells, formed via near-field coupling along the long axes or through hybrid plasmonic–photonic edge coupling, support plasmonic hot-spots and surface lattice resonances (SLRs), supporting enhanced hot-electron generation. The arrays are coated with a thin Si interlayer followed by an ultrathin InP/ZnS QD film, providing both dielectric coupling and electronic pathways for charge transfer. We show that hot electrons injected across the Au/Si interface can charge the environment of QDs, resulting in a polarization-dependent blue shift of the emission of QDs, accompanied by enhancement of their emission lifetime. These results highlight the key roles of SLRs and plasmonic hot spots in enabling hot-electron-mediated control of QD emission. 

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3. Plasmonic metasurface superscatters driven by infrared surface lattice resonances

   https://doi.org/10.1063/5.0159295  

   Sadeghi, Seyed M.; Roberts, Dustin T.; Knox, Harrison; Gutha, Rithvik R. (July 2023, Applied Physics Letters)

   We have demonstrated that plasmonic metasurfaces composed of arrays of Au bowtie nanoantennas can support an infrared bidirectional superscattering state. This state arises when the nanoantennas are coherently coupled together, forming a surface lattice resonance that efficiently guides the infrared range (1–1.6 μm) of incident broadband white light along the plane of the arrays. This process exhibits strong polarization dependence, offering an “OFF” state where a 90° rotation of the incident light polarization effectively suppresses in-plane scattering from all sides. Stokes parameters analysis is used to study the states of polarization of the scattering, demonstrating transformation into a complete depolarized state. The results emphasize the significant influence of the multipolar modes of these nanoantennas on the interference processes associated with such scattering phenomena, and their potential applications in polarization optical switching and unique beamsplitting. 

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4. Quantum Dot Energy Circuits Based on Energy Transfer Driven by Plasmonic Metal Oxide Metasurfaces

   https://doi.org/10.1021/acsaelm.5c01521  

   Sadeghi, Seyed M; Gutha, Rithvik Reddy; Sharp, Christina (September 2025, ACS Applied Electronic Materials)

   Semiconductor heterostructures composed of multiple layers of different colloidal quantum dots (QDs) are key components for various devices, ranging from solar cells to light-emitting diodes. We investigate the control of energy transfer within a heterostructure comprising CdSe/ZnS and InP/ZnS core–shell QDs in interaction with a plasmonic metal oxide metasurface (PMOM). Such a metasurface is engineered with arrays of gold nanoantennas embedded in a thin Si layer and coated with an ultrathin film of Al oxide. We show that the bottom CdSe/ZnS QD layer, which is in direct contact with the metasurface, is driven into a state of directed energy transfer funneling. This behavior is attributed to localized surface plasmon resonances and hot-electron-induced defect passivation. In contrast, the top InP/ZnS QD layer is primarily influenced by surface lattice resonances, which enhance its receptivity and efficiency in capturing energy. The results suggest the formation of an energy circuit, wherein energy flows from the smallest CdSe/ZnS QDs to larger ones and is then routed to the upper layer, forming an energy gate toward the InP/ZnS QDs. The results offer a promising path toward making energy (excitons) transfer more efficient in complicated QD structures. 

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5. Broadband control of flow of light using plasmonic metasurfaces consisting of arrays of metallic split ring nanoantennas

   https://doi.org/10.1063/5.0155031  

   Sadeghi, Seyed M.; Roberts, Dustin T.; Knox, Harrison; Gutha, Rithvik R. (June 2023, Journal of Applied Physics)

   When a metallic U-shaped nanoantenna (split ring resonator) is observed from its sides, variations in the viewing angle can lead to significantly different size and shape projections. In this study, we demonstrate that plasmonic metasurfaces consisting of arrays of such nanoantennas can support unique side (in-plane) scattering switching and routing processes. These processes encompass a polarization switching centered at 1.6 μm, which is driven by the coherent excitation of the nanoantennas’ multipolar modes. They also include spectrally broadband (0.5–1.6 μm) directional control of the flow of in-plane light scattering. Such a process includes a total prohibition of light emerging from one side of the metasurface for a given polarization of the incident light. However, when such polarization is rotated by 90°, the flow of the in-plane scattering opens with high efficiency. We further discuss the impact of the formation of surface lattice resonance on the coherent amplification of infrared scattering around 1.6 μm and its switching process. The results underscore the influence of variations in asymmetry, associated with the sizes and shape projections, on interference processes. They also showcase how in-plane scattering has the capacity to transfer distinct characteristics of plasmonic near-field asymmetries induced by optical fields into far-field scattering. 

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