Jun Yi

High throughput, wide-field hyperspectral imaging of the dynamic and spatially inhomogeneous electrochemical interface is vital for understanding and controlling electrochemical processes. However, acquiring three-dimensional data cubes with spatial and spectral information is typically time-consuming due to the limited speed of raster scanning or wavelength tuning, which impedes fast tracking of dynamic and inhomogeneous electrochemical reactions. Here, we develop Fourier transform wide-field electrochemical hyperspectral imaging (FT-WEHI) and showcase its application to in situ monitor the electrodeposition of Pt on hundreds of single Au nanospheres and nanorods with detailed scattering spectra. This provides an optical analog of voltammetry for all nanoparticles simultaneously, yielding statistically meaningful results that are difficult to obtain from conventional, time-consuming single-particle studies. Statistical analysis shows that even though structural heterogeneity exists for each nanoparticle, the preferential deposition at the tips of nanorods, having relatively "homogenous" morphology and thus nucleation energy, leads to a narrower distribution of onset deposition potential compared to nanospheres. Spectral evolution reveals distinct deposition processes on nanospheres and nanorods as rationalized by simulations. Our method provides large data sets with high throughput, holding potential for accelerating the study of various energy and biological processes with data-driven strategies.

Exciton-plasmon polaritons, leveraging the coherent nature of their photonic component, can overcome the localization of excitations in disordered molecular solids and enable long-range transport. However, a clear understanding of how the optical cavity properties govern polariton transport is lacking. Furthermore, most studies demonstrated unidirectional propagation of polaritons. An active directional control of polariton propagation, crucial for expanding its optoelectronic functionality, remains much less explored. Here, we show enhanced and anisotropic long-range energy transport in molecular aggregates strongly coupled with surface plasmons on two-dimensional plasmonic nanoarrays. The nanoarrays exhibit in-plane angle-dependent, anisotropic, and periodically modulated plasmonic resonant properties (diffraction order, resonance energy and line width) stemming from the anisotropic dispersion of the plasmonic hexagonal lattice, leading to an anisotropic periodic modulation of the cavity-molecule coupling strength. Wavelength-resolved, momentum-selected real-space photoluminescence study reveals enhanced coherent propagation of upper and lower polaritons with ∼10 μm and large group velocities on the order of the speed of light. Crucially, an anisotropic propagation distance contrast of 90% has been achieved by tuning the dispersion and quality factor of plasmonic modes. The results provide valuable guidance for developing coherent, directional energy transport devices for photovoltaics, photocatalysis, optical routing, and organic optoelectronics applications.

The tight‐binding (TB) model offers a versatile framework for exploring novel photonic phenomena. Its faithful implementation in photonic crystals (PCs), however, requires not only suppressed long‐range couplings but also systematic and scalable control over both the magnitude and the sign of inter‐site couplings. Here, it is demonstrated periodic defect arrays embedded in a photonic band‐gap host as a PCs platform for programmable engineering of TB couplings. The localized defect modes provide an accurate TB description, and by adjusting either the number or the detuning of spacer sites, it is achieved flexible control of the coupling strength together with a robust, parity‐protected reversal of its sign without modifying the defect sites themselves. Numerical simulations confirm that this strategy reproduces the target TB Hamiltonian with high fidelity and greatly expands the accessible design space beyond that of conventional PCs. As proof of concept, a 2D Su–Schrieffer–Heeger lattice that undergoes the predicted topological transition and a nonsymmorphic structure supporting Möbius edge states are implemented. This work provides a versatile and scalable route to TB‐inspired phenomena in PCs.

Interfacial coupling governs the emergent functionality of two-dimensional (2D) organic–inorganic heterostructures, underpinning advances in linear optoelectronics such as photovoltaics. However, extending this control to the nonlinear optical regime remains elusive, as it requires driving the coherent nonlinear polarization of the inorganic lattice using molecular states, which is distinct from the incoherent charge transfer exploited in linear devices. Here we report a giant second-harmonic generation (SHG) response driven purely by long-range interfacial dipolar interactions in an α-perylene organic crystal (α-Pe)/WS2 heterostructure. We show that the specific crystalline anisotropy of the organic layer creates a polarization-tunable antenna, where anisotropic dipole–dipole coupling efficiently channels excitation energy into the WS2 layer to drive the nonlinear process. This mechanism yields a spatially uniform, giant effective second-order susceptibility χ _eff ⁽²⁾ approaching ~20 nm V ^-1 in monolayers and, notably, induces interfacial symmetry breaking to activate robust SHG in nominally centrosymmetric bilayer WS2. Our results establish organic–inorganic interfacial coupling as a generalizable lever for engineering nonlinear optical responses; given the vast abundance of molecular crystals with distinct dipolar symmetries, this strategy offers a scalable route to compact, chemically designable on-chip nonlinear photonic systems.

Phonon-assisted upconversion (UC) for anti-Stokes photoluminescence stands as a fundamental and widely studied process, central to both ultrafast electron-phonon coupling physics and diverse photonic applications. However, the ultrafast dynamics limit of UC has yet to be addressed, preventing its integration into the nonlinear optical regime. Here, we find a giant single-step UC of ~200 milli–electron volts via sub–35-femtosecond phonon dynamics in two-dimensional hybrid organic-inorganic perovskites in the nonlinear regime. The single-step UC approaches the phonon dynamics limit of ~23 femtoseconds and gains energy about eight times the room-temperature thermal energy (~25 milli–electron volts), enabling its synergistic integration into the nonlinear regime. Benefiting from the unique electron-phonon coupling between organic vibrations and excitons in inorganic lattices, the UC demonstrates distinctive signatures of Raman anisotropy and strong nonlinearity. This work opens new avenues for studying uncharted phonon dynamics and nonlinear optical mechanisms, offering substantial advantages in optical refrigeration, upconverting energy harvesting and optical microscopy.

The photonic flat band, defined by minimal dispersion and near-zero group velocity, has facilitated significant advances in optical technologies. The practical applications of flat bands, such as enhanced light-matter interactions, require efficient coupling to far-field radiation. However, achieving controlled coupling between flat bands and their corresponding localized modes with far-field radiation remains challenging and elusive. Here, we achieve the tunable far-field excitation of a flat band in the near-infrared spectral range by coupling it to a photonic anapole mode. Distinct from conventional multipolar resonances in both its physical nature and unique radiation dynamics, the anapole mode offers highly localized field distributions and tunable emission characteristics, enabling the realization of a photonic flat band and precise control over its transition from a nonradiative to a radiative state. We directly observed the flat band within ±25° experimentally by angle-resolved far-field transmissivity spectroscopy. Simulation results extending to 90° confirm the persistence of the band's flatness across all incident angles, validating the inherent flatness of the band. Our findings not only provide a viable approach to accessing photonic flat bands but also significantly advance the field of nanoscale photonic manipulation, offering broad potential applications in optical technologies.

The behaviors of solid-liquid interfacial electron spillovers under negative potentials are crucial for understanding heterogeneous reactions and catalysts. The missing experimental details at the angstrom scale leave the current understanding of interfacial electron spillovers largely conceptual. Herein, we demonstrated interfacial electron spillover at electrode-electrolyte interfaces by combining in situ electrochemical plasmon-enhanced Raman spectroscopy (PERS) with a plasmonic molecular ruler strategy. Using a series of molecules adsorbed on or proximate to metallic electrodes (Pt, Pd, Au, and Ag) as molecular rulers, the electron spillover from electrodes to electrolytes was experimentally and theoretically correlated to the PERS bands of the functional groups of rulers, which provided a spatial resolution down to the angstrom scale. The electron spillover length was highly dependent on the potentials, metals, and electrolytes. An electron spillover with a length of up to 4 Å was observed at the Ag electrode-organic electrolyte interface. These results provide quantitative measurements of the fundamental details of electronic behaviors in metal-liquid interfaces, which may guide efforts to tailor the physical and chemical properties of metals under electrochemical polarization and prospectively enable active control of quantum plasmonics for angstrom-scale interfacial sensing.

Control of light-driven current at the nanoscale is essential for optoelectronics, energy transfer, and information processing, and the single-atom junctions preserving electron coherence serves as a model system with ultimate size to investigate and manipulate light-driven transport. However, the light-driven coherent transport through the single-atom junctions remains elusive due to the challenge of controlling their atomic topography at room temperature. Here, we demonstrate a photocurrent oscillation from photon-assisted coherent transport in single-atom junctions by controlling the atomic structure using the mechanically controllable break junction technique at ambient condition. Such an oscillation results in a giant suppression ratio of up to ~ 50% of the collective photocurrent, which disentangle the coherent interplay between two opposite transport pathways of photon-induced absorption and emission from the plasmon-induced hot-electron transport. Our findings offer an atomically precise strategy to control light-driven transport and open a new route toward atomic-scale high-frequency optoelectronics.