More Like this

1. Determining plasmonic hot-carrier energy distributions via single-molecule transport measurements

   https://doi.org/10.1126/science.abb3457  

   Reddy, Harsha; Wang, Kun; Kudyshev, Zhaxylyk; Zhu, Linxiao; Yan, Shen; Vezzoli, Andrea; Higgins, Simon J.; Gavini, Vikram; Boltasseva, Alexandra; Reddy, Pramod; et al (July 2020, Science)

   null (Ed.)

   Hot-carriers in plasmonic nanostructures, generated via plasmon decay, play key roles in applications like photocatalysis and in photodetectors that circumvent band-gap limitations. However, direct experimental quantification of steady-state energy distributions of hot-carriers in nanostructures has so far been lacking. We present transport measurements from single-molecule junctions, created by trapping suitably chosen single molecules between an ultra-thin gold film supporting surface plasmon polaritons and a scanning probe tip, that can provide quantification of plasmonic hot-carrier distributions. Our results show that Landau damping is the dominant physical mechanism of hot-carrier generation in nanoscale systems with strong confinement. The technique developed in this work will enable quantification of plasmonic hot-carrier distributions in nanophotonic and plasmonic devices. 

   more » « less
2. Charge carrier concentration dependence of ultrafast plasmonic relaxation in conducting metal oxide nanocrystals

   https://doi.org/10.1039/C7TC00600D  

   Johns, Robert W.; Blemker, Michelle A.; Azzaro, Michael S.; Heo, Sungyeon; Runnerstrom, Evan L.; Milliron, Delia J.; Roberts, Sean T. (January 2017, Journal of Materials Chemistry C)

   Electronically doped metal oxide nanocrystals exhibit tunable infrared localized surface plasmon resonances (LSPRs). Despite the many benefits of IR resonant LSPRs in solution processable nanocrystals, the ways in which the electronic structure of the host semiconductor material impact metal oxide LSPRs are still being investigated. Semiconductors provide an alternative dielectric environment than metallically bonded solids, such as noble metals, which can impact how these materials undergo electronic relaxation following photoexcitation. Understanding these differences is key to developing applications that take advantage of the unique optical and electronic properties offered by plasmonic metal oxide NCs. Here, we use the two-temperature model in conjunction with femtosecond transient absorption experiments to describe how the internal temperature of two representative metal oxide nanocrystal systems, cubic WO 3−x and bixbyite Sn-doped In 2 O 3 , change following LSPR excitation. We find that the low free carrier concentrations of metal oxide NCs lead to less efficient heat generation as compared to metallic nanocrystals such as Ag. This suggests that metal oxide NCs may be ideal for applications wherein untoward heat generation may disrupt the application's overall performance, such as solar energy conversion and photonic gating. 

   more » « less
3. Ultrafast Microscopy of Plasmonic Vortex Fields

   Zhou, Zhikang (April 2025, University of Pittsburgh)

   Surface Plasmon Polariton (SPP), as a novel information carrier, offers unprecedented opportunity for confining electromagnetic fields that carry orbital angular momentum (OAM) to subwavelength dimensions. In this thesis, I focus experimentally on the generation, manipulation, and spatio-temporal evolution—and theoretically on the analytical modeling—of plasmonic phase singularities, known as plasmonic vortices, at the silver (Ag)/vacuum interface. I image and study the dynamics of plasmonic vortices by interferometric time-resolved multi-photon photoemission electron microscopy (ITR-mP-PEEM). Firstly, I report on the generation, evolution, and topological properties of plasmonic vortices carrying pure geometrically induced orbital angular momentum (OAM), generated by illuminating Archimedean spiral coupling structures with normally incident, linearly polarized light. Next, I present an analytical model describing the generation and evolution of these plasmonic vortices, and based on this model, I further analyze their spatial structure and dynamics. I also derived the spin angular momentum (SAM) of plasmonic vortices, whose textures reveal transient plasmonic spin-Skyrmion topological quasiparticles. In parallel, I also record images of plasmonic vectoral vortex field evolution on the nanometer spatial and femtosecond temporal scale, from which I derive the plasmonic spin Skyrmion boundary and topological charge. The excellent agreement between analytical model and experimental results confirms the topological spin texture at surface plasmon polariton vortex core. To extend the understanding of ITR-PEEM imaging, I perform a simple experiment withv double line coupling structure at the silver/vacuum interface, which reveals an asymmetric cross term between the different components of the SPP field that also appear in the ITR-PEEM imaging. Finally, I approach a novel method to manipulate momentum transport between two plasmonic vortices analytically and experimentally. By tuning the relative distance between two vortex generator structures with same sign and sign of the geometric charge, a conveyor belt-like field could be observed at the center of the device, which can be applied to transport the field, momentum, and energy between two plasmonic vortices. 

   more » « less
4. Plasmon-Induced Electron Transfer between Gold Nanorods and a Carbon Thin Film

   https://doi.org/10.1021/acs.jpcc.3c07754  

   Vo, Tamie; Chang, Wei-Shun (January 2024, The Journal of Physical Chemistry C)

   Plasmonic nanostructures have been demonstrated as emergent photocatalysts because of their efficient photon absorption and their ability to produce hot carriers. However, the plasmon-generated hot carriers decay through ultrafast relaxation pathways, resulting in a short lifetime that impedes the exploitation of hot carriers for chemical reactions. Charge separation at the heterojunction of the hybrid nanostructures can counteract the ultrafast decay to extend the carrier lifetime. Here, we fabricate hybrid nanostructures composed of gold nanorods and a carbon thin film and demonstrate efficient charge transfer between these two materials. Using single-particle dark-field scattering spectroscopy, we observe a broadening of the longitudinal plasmon for gold nanorods on a carbon film compared to those on a glass substrate. We attribute this plasmon damping to the electron transfer from gold nanorods to the carbon film and exclude the contribution from plasmon-induced resonance energy transfer. The electron transfer efficiencies are calculated as 52.8 ± 4.8 and 57.4 ± 4.0% for carbon films with thicknesses of 10 and 25 nm, respectively. This work demonstrates efficient charge separation at the gold–carbon film interface, which can extend the lifetime of hot carriers to promote plasmonic photocatalysts. 

   more » « less
5. Photovoltages and hot electrons in plasmonic nanogaps

   https://doi.org/10.1117/12.2289114  

   Natelson, Douglas; Zolotavin, Pavlo; Evans, Charlotte I. (January 2018, Quantum Sensing and Nano Electronics and Photonics XV;)

   In metal nanostructures under illumination, multiple different processes can drive current flow, and in an opencircuit configuration some of these processes lead to the production of open-circuit photovoltages. Structures that have plasmonic resonances at the illumination wavelength can have enhanced photovoltage response, due to both increased interactions with the incident radiation field, and processes made possible through the dynamics of the plasmon excitations themselves. Here we review photovoltage response driven by thermoelectric effects in continuous metal nanowires and photovoltage response driven by hot electron production and tunneling. We discuss the prospects for enhancing and quantifying hot electron generation and response via the combination of local plasmonic resonances and propagating surface plasmon polaritons. 

   more » « less