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. Epitaxial mid-IR nanophotonic optoelectronics

   https://doi.org/10.1063/5.0086774  

   Nordin, L.; Wasserman, D. (May 2022, Applied Physics Letters)

   There are a range of fundamental challenges associated with scaling optoelectronic devices down to the nano-scale, and the past decades have seen significant research dedicated to the development of sub-diffraction-limit optical devices, often relying on the plasmonic response of metal structures. At the longer wavelengths associated with the mid-infrared, dramatic changes in the optical response of traditional nanophotonic materials, reduced efficiency optoelectronic active regions, and a host of deleterious and/or parasitic effects makes nano-scale optoelectronics at micro-scale wavelengths particularly challenging. In this Perspective, we describe recent work leveraging a class of infrared plasmonic materials, highly doped semiconductors, which not only support sub-diffraction-limit plasmonic modes at long wavelengths, but which can also be integrated into a range of optoelectronic device architectures. We discuss how the wavelength-dependent optical response of these materials can serve a number of different photonic device designs, including dielectric waveguides, epsilon-near-zero dynamic optical devices, cavity-based optoelectronics, and plasmonic device architectures. We present recent results demonstrating that the highly doped semiconductor class of materials offers the opportunity for monolithic, all-epitaxial, device architectures out-performing current state of the art commercial devices, and discuss the perspectives and promise of these materials for infrared nanophotonic optoelectronics. 

   more » « less
3. Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

   https://doi.org/10.1073/pnas.2002284117  

   Evans, Charlotte I.; Yang, Rui; Gan, Lucia T.; Abbasi, Mahdiyeh; Wang, Xifan; Traylor, Rachel; Fan, Jonathan A.; Natelson, Douglas (September 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   The electronic Seebeck response in a conductor involves the energy-dependent mean free path of the charge carriers and is affected by crystal structure, scattering from boundaries and defects, and strain. Previous photothermoelectric (PTE) studies have suggested that the thermoelectric properties of polycrystalline metal nanowires are related to grain structure, although direct evidence linking crystal microstructure to the PTE response is difficult to elucidate. Here, we show that room temperature scanning PTE measurements are sensitive probes that can detect subtle changes in the local Seebeck coefficient of gold tied to the underlying defects and strain that mediate crystal deformation. This connection is revealed through a combination of scanning PTE and electron microscopy measurements of single-crystal and bicrystal gold microscale devices. Unexpectedly, the photovoltage maps strongly correlate with gradually varying crystallographic misorientations detected by electron backscatter diffraction. The effects of individual grain boundaries and differing grain orientations on the PTE signal are minimal. This scanning PTE technique shows promise for identifying minor structural distortions in nanoscale materials and devices. 

   more » « less
4. Tailored Dispersion of Spectro‐Temporal Dynamics in Hot‐Carrier Plasmonics

   https://doi.org/10.1002/advs.202205434  

   Kim, Andrew S.; Taghinejad, Mohammad; Goswami, Anjan; Raju, Lakshmi; Lee, Kyu‐Tae; Cai, Wenshan (March 2023, Advanced Science)

   Abstract Ultrafast optical switching in plasmonic platforms relies on the third‐order Kerr nonlinearity, which is tightly linked to the dynamics of hot carriers in nanostructured metals. Although extensively utilized, a fundamental understanding on the dependence of the switching dynamics upon optical resonances has often been overlooked. Here, all‐optical control of resonance bands in a hybrid photonic‐plasmonic crystal is employed as an empowering technique for probing the resonance‐dependent switching dynamics upon hot carrier formation. Differential optical transmission measurements reveal an enhanced switching performance near the anti‐crossing point arising from strong coupling between local and nonlocal resonance modes. Furthermore, entangled with hot‐carrier dynamics, the nonlinear correspondence between optical resonances and refractive index change results in tailorable dispersion of recovery speeds which can notably deviate from the characteristic lifetime of hot carriers. The comprehensive understanding provides new protocols for optically characterizing hot‐carrier dynamics and optimizing resonance‐based all‐optical switches for operations across the visible spectrum. 

   more » « less
5. Molecular scale nanophotonics: hot carriers, strong coupling, and electrically driven plasmonic processes

   https://doi.org/10.1515/nanoph-2023-0710  

   Zhu, Yunxuan; Raschke, Markus B.; Natelson, Douglas; Cui, Longji (March 2024, Nanophotonics)

   Plasmonic modes confined to metallic nanostructures at the atomic and molecular scale push the boundaries of light–matter interactions. Within these extreme plasmonic structures of ultrathin nanogaps, coupled nanoparticles, and tunnelling junctions, new physical phenomena arise when plasmon resonances couple to electronic, exitonic, or vibrational excitations, as well as the efficient generation of non-radiative hot carriers. This review surveys the latest experimental and theoretical advances in the regime of extreme nano-plasmonics, with an emphasis on plasmon-induced hot carriers, strong coupling effects, and electrically driven processes at the molecular scale. We will also highlight related nanophotonic and optoelectronic applications including plasmon-enhanced molecular light sources, photocatalysis, photodetection, and strong coupling with low dimensional materials. 

   more » « less