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1. Harmonic-induced plasmonic resonant energy transfer between metal and semiconductor nanoparticles

   https://doi.org/10.1126/sciadv.adv1822  

   Yan, Yueming; Spear, Nathan J; Cummings, Adam J; Khusainova, Karina; Macdonald, Janet E; Haglund, Richard F (June 2025, Science Advances)

   Heterostructures combining two or more metal and/or semiconductor nanoparticles exhibit enhanced upconversion arising from localized nanoparticle resonances. However, plasmon-exciton coupling in semiconductor-metal nanostructures exhibits nanosecond relaxation times, and multi-plasmon metallic heterostructures are not broadly tunable. Here, we develop a biplasmonic heterostructure in which CuS and Au nanoparticle layers, separated by an alumina spacer of variable thickness, exhibit enhanced second- and third-harmonic generation due to dipole-dipole coupling between Au and CuS plasmons, as seen in the characteristic inverse sixth-power dependence of their separation in the measured harmonic enhancement and confirmed by numerical simulations of near-field CuS-Au nanoparticle coupling. Transient-absorption spectroscopy shows faster relaxation in Au/CuS (690 femtoseconds) compared to CuS heterostructures (929 femtoseconds). Moreover, nonlinear absorption measurements provide evidence for harmonic-induced plasmonic resonant energy transfer between the narrow Au and broad, tunable CuS plasmon resonances. This prototype for ultrafast upconversion showcases a strategy for high-efficiency, tunable plasmonic nonlinear devices with promising applications in photocatalysis, parametric down-conversion, and biomedical imaging. 

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2. Plasmonic metagrating-interlayer semiconductor (PMIS) structure for enhancing photodetection via hot-electron injection

   https://doi.org/10.1364/OE.527826  

   Vu, Nga; Heidarzadeh, Parham; Chen, Pai-Yen (January 2024, Optics Express)

   Internal photoemission or hot-electron injection (HEJ) occurring at the metal-semiconductor (MS) Schottky interface has shown great promise in sub-bandgap photodetection and photovoltaics. In this paper, we put forward a plasmonic metagrating-interlayer-semiconductor (PMIS) structure that can significantly enhance the photon-to-electron conversion efficiency of HEJ-based optoelectronic devices. Thanks to the effect of image force-induced barrier lowering, a metal-interlayer-semiconductor (MIS) heterojunction with an ultrathin 2D material interlayer can considerably facilitate the hot electron transport across the Schottky barrier, resulting in a high internal quantum efficiency (IQE). Meanwhile, nanopatterning the MIS heterojunction into the plasmonic metagrating enables high optical absorption such that the device’s external quantum efficiency (EQE) can be nearly equal to its IQE. In addition, this device can be wavelength- and polarization-selective by tailoring the geometry and dimensions of plasmonic metagrating, thereby paving a promising path toward bandgap-independent photodetection, energy harvesting, and photocatalysis. 

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3. 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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4. Laser-controlled projection of quantum dot dipoles using metal-oxide plasmonic metastructures: maintaining spin polarization memory

   https://doi.org/10.1039/d1tc02532e  

   Sadeghi, Seyed M.; Wing, Waylin; Gutha, Rithvik R.; Sharp, Christina; Roberts, Dustin; Mao, Chuanbin (October 2021, Journal of Materials Chemistry C)

   It is known that the spontaneous emission of semiconductor quantum dots is mostly unpolarized when they are excited off-resonantly. The complete loss of polarization memory is associated with the ultrafast carrier scattering, leading to complete spin polarization relaxation. We study the application of metal-oxide plasmonic double-junction structures to transfer the excitation polarization memory of quantum dots to their spontaneous emission. These structures consist of arrays of metallic nanoantennas in the presence of heterostructures consisting of Au/Si Schottky junctions and Si/Al-oxide charge barriers. Our results show that by using such double-junction structures, one can control the states of polarization and intensity of the emission of quantum dots using the state of polarization of an off-resonant laser field. For achieving this, we explore the optical control of exciton–plasmon coupling using optical lattice modes caused by the arrays of metallic nanoantennas, and the application of the electrostatic field generated by the hot electrons captured at the Au/Si Schottky junction. 

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5. (Invited) Hybrid Plasmonic Nanocatalysts for Solar-Chemical Energy Conversion Systems

   https://doi.org/10.1149/MA2025-02643039mtgabs  

   Nazemi, Reza (November 2025, ECS Meeting Abstracts)

   Utilizing solar energy for chemical transformations has attracted a growing interest in promoting the clean and modular chemical synthesis approach and addressing conventional thermocatalytic systems’ limitations. Noble metal nanoparticles are known to support coherent oscillatory modes of their conduction band electrons when photoexcited with a resonant frequency, producing localized surface plasmon resonances (LSPR). Under light irradiation, noble metal nanoparticles, particularly those characterized by LSPR, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. The LSPR can be excited by UV, visible, or near-infrared (NIR) light, which depends on the nanoparticle’s size, shape, composition, structure (hollow or solid), and the dielectric function of the surrounding medium. By placing various plasmonic nanoparticles in their proximity (< 10 nm), a strong electromagnetic field is generated at a certain distance due to the coupling of the electromagnetic field of individual plasmonic nanoparticles. After plasmonic excitation of plasmonic nanoparticles with incident light, the plasmon can quickly dephase through electron-surface scattering on a few femtoseconds (fs) time scales, generating non-thermal hot electrons. After a few hundred fs, electron-electron scattering produces a distribution of electrons with temperature on the order of hundreds of degrees above the surrounding medium. Within a few picoseconds (ps) of the initial excitation, the absorbed energy is transferred to the nanoparticle’s lattice via electron-phonon coupling (τ_e-ph). The final stage of heat dissipation to the surrounding medium by thermal conduction occurs on a longer timescale ranging from several tens of ps to 10 nanoseconds (ns) through phonon-phonon coupling (τ_ph-ph). At this stage, the heated nanoparticle lattice transfers heat to the surrounding medium, resulting in increasing the medium’s temperature until the nanoparticle lattice and its surrounding medium reach an equilibrium temperature, which is higher than the temperature of the bulk medium. Both non-thermal hot electrons and the local heating could excite electronic or vibrational transitions in adsorbed molecules on the nanoparticle’s surface, thus enabling catalytic reactions. Understanding the electronic and thermal properties of plasmonic nanoparticles and their interactions at the nanoscale in a local catalytic environment with adsorbed molecules is imperative to improving photocatalytic efficiency. We aim to design and develop a plasmonic photothermal reactor to synthesize ammonia from dinitrogen and hydrogen under concentrated sunlight using plasmonic nanoparticles that absorb light in the visible and near-infrared regions (Figure 1). Despite various design strategies for enhancing the catalytic activity of plasmonic nanocatalysts, including controlling nanocatalysts’ size and shape, they have exhibited moderate activity for driving chemical reactions. We incorporate a co-catalyst made of transition metal nanoparticles that could improve the catalytic activity in the hybrid plasmonic-catalytic nanoparticles. In this hybrid system, a plasmonic nanoparticle is mainly responsible for absorbing light, generating hot carriers, and local heat, while transition metal catalytic reactors handle the chemical reactions. Figure 1 

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