Plasmon Dynamics Research Articles

Unveiling Spatial and Temporal Dynamics of Plasmon-Enhanced Localized Fields in Metallic Nanoframes through Ultrafast Electron Microscopy.

Plasmonic nanomaterials, particularly noble metal nanoframes (NFs), are important for applications such as catalysis, biosensing, and energy harvesting due to their ability to enhance localized electric fields and atomic efficiency via localized surface plasmon resonance (LSPR). Yet the fundamental structure-function relationships and plasmonic dynamics of the NFS are difficult to study experimentally and thus far rely predominately on computational methodologies, limiting their utilization. This study leverages the capabilities of ultrafast electron microscopy (UEM), specifically photon-induced near-field electron microscopy (PINEM), to probe the light-matter interactions within plasmonic NF structures. The effects of shape, size, and plasmonic coupling of Pt@Au core-shell NFs on spatial and temporal characteristics of plasmon-enhanced localized electric fields are explored. Importantly, time-resolved PINEM analysis reveals that the plasmonic fields around hexagonal NF prisms exhibit a spatially dependent excitation and decay rate, indicating a nuanced interplay between the spatial geometry of the NF and the temporal evolution of the localized electric field. These results and observations uncover nanophotonic energy transfer dynamics in NFs and highlight their potential for applications in biosensing and photocatalysis.

Plasmon dephasing time and optical field enhancement in a plasmonic nanobowl substrate studied by scanning near-field optical microscopy.

Plasmonic substrates have been extensively investigated due to their potential applications in fluorescence microscopy, chemical sensing, and photochemical reactions. The optical properties of the substrate depend on the spatial and temporal features of the plasmon excited. Hence, the ability to directly visualize plasmon dynamics is crucial. In this study, we investigated the spatial and temporal properties of plasmon excitation in a plasmonic nanobowl substrate consisting of a periodic hexagonal array of nanoscale bowl-like structures developed with self-assembly. Near-field transmission imaging revealed that multiple plasmon resonance bands are observed from visible to near-infrared spectral region, and the optical contrast of the image is dependent on the observed band. Near-field two-photon photoluminescence microscopy revealed that the probability of excitation inside each nanoscale bowl-like structure is greater than that in the surrounding area. Near-field time-resolved imaging revealed that the nanobowl substrate exhibited a substantially long plasmon dephasing time, exceeding 12fs. Based on the spectral features of the near-field and far-field spectra, we found that optically dark plasmon mode is excited by the near-field illumination and only partly contributes to the long dephasing time observed. This fact indicates that the dephasing time is extended by some other mechanism in the periodic substrate. We revealed from this study that the enhanced optical fields induced in the nanobowl structure originate from the photosynergetic effect of the cavity mode and plasmon mode excited.

Nanoscale terahertz conductivity and ultrafast dynamics of terahertz plasmons in periodic arrays of epitaxial graphene nanoribbons

The dynamics of plasmons in nanoribbons of (hydrogen intercalated) quasi-freestanding single-layer graphene is studied by terahertz spectroscopy both in the steady state and upon photoexcitation by an ultrashort near infrared laser pulse. The use of two-dimensional frequency-domain analysis of the optical pump–terahertz (THz) probe signals allows us to determine the evolution of carrier temperature and plasmon characteristics with ∼100 fs time resolution. Namely, we find that the carrier temperature decreases from more than 5000 K to the lattice temperature within about 7 ps and that during this evolution the carrier mobility remains practically constant. The time-resolved THz conductivity spectra suggest that graphene nanoribbons contain defects which act as low potential barriers causing a weak localization of charges; the potential barriers are overcome upon photoexcitation. Furthermore, the edges of graphene nanoribbons are found to slightly enhance the scattering of carriers. The results are supported by complementary measurements using THz scanning near-field microscopy, which confirm a high uniformity of the THz conductivity across the sample and demonstrate high enough sensitivity to resolve even the impact of nanometric terrace steps on SiC substrate under the graphene monolayer. Published by the American Physical Society 2024

Plasmon Dynamics in Electron‐Doped Graphene and AA‐ versus AB‐Stacked Bilayer Graphene

This study investigates low‐frequency plasmons and single‐particle excitations (SPEs) in monolayer and bilayer graphene with various stacking configurations. The dynamics of wave propagation under different time‐dependent perturbation scenarios are elucidated using the random‐phase approximation dielectric function and tight‐binding Hamiltonian. The modulation of coherent excitations, particularly affecting plasmon waves, provides insights into the spatial and temporal dynamics on graphene sheets. A 2D acoustic plasmon mode is observed in monolayer graphene under extrinsic doping effects, while in bilayer graphene, it is accompanied by higher frequency optical plasmons. The predicted dynamic behavior, indicative of plasmon resonance, SPEs, and Landau damping with respect to stacking and doping effects, can be detected through ultrafast coherent dynamics observed via nanoimaging and nanospectroscopy techniques.

Wighteone, a prenylated flavonoid from licorice, inhibits growth of SW480 colorectal cancer cells by allosteric inhibition of Akt

Ethnopharmacological relevanceLicorice is a frequently used herbal medicine worldwide, and is used to treat cough, hepatitis, cancer and influenza in clinical practice of traditional Chinese medicine. Modern pharmacological studies indicate that prenylated flavonoids play an important role in the anti-tumor activity of licorice, especially the tumors in stomach, lung, colon and liver. Wighteone is one of the main prenylated flavonoids in licorice, and its possible effect and target against colorectal cancer have not been investigated. Aim of the studyThis study aimed to investigate the anti-colorectal cancer effect and underlying mechanism of wighteone. Materials and methodsSW480 human colorectal cancer cells were used to evaluate the in vitro anti-colorectal cancer activity and Akt regulation effect of wighteone by flow cytometry, phosphoproteomic and Western blot analysis. Surface plasmon resonance (SPR) assay, molecular docking and dynamics simulation, and kinase activity assay were used to investigate the direct interaction between wighteone and Akt. A nude mouse xenograft model with SW480 cells was used to verify the in vivo anti-colorectal cancer activity of wighteone. ResultsWighteone inhibited phosphorylation of Akt and its downstream kinases in SW480 cells, which led to a reduction in cell viability. Wighteone had direct interaction with both PH and kinase domains of Akt, which locked Akt in a “closed” conformation with allosteric inhibition, and Gln79, Tyr272, Arg273 and Lys297 played the most critical role due to their hydrogen bond and hydrophobic interactions with wighteone. Based on Akt overexpression or activation in SW480 cells, further mechanistic studies suggested that wighteone-induced Akt inhibition led to cycle arrest, apoptosis and autophagic death of SW480 cells. Moreover, wighteone exerted in vivo anti-colorectal cancer effect and Akt inhibition activity in the nude mouse xenograft model. ConclusionWighteone could inhibit growth of SW480 cells through allosteric inhibition of Akt, which led to cell cycle arrest, apoptosis and autophagic death. The results contributed to understanding of the anti-tumor mechanism of licorice, and also provided a rationale to design novel Akt allosteric inhibitors for the treatment of colorectal cancer.

Nonclassical near-field dynamics of surface plasmons

Nonclassical near-field dynamics of surface plasmons

Coherent and Incoherent Ultrafast Dynamics in Colloidal Gold Nanorods.

The study of the mechanisms that control the ultrafast dynamics in gold nanoparticles is gaining more attention, as these nanomaterials can be used to create nanoarchitectures with outstanding optical properties. Here pump-probe and two-dimensional electronic spectroscopy have been synergistically employed to investigate the early ultrafast femtosecond processes following photoexcitation in colloidal gold nanorods with low aspect ratio. Complementary insights into the coherent plasmonic dynamics at the femtosecond time scale and incoherent hot electron dynamics over picosecond time scales have been obtained, including important information on the different sensitivity to the pump fluence of the longitudinal and transverse plasmons and their different contributions to the photoinduced broadening and shift.

Ultrafast Plasmonics for All-Optical Switching and Pulsed Lasers

Surface plasmon resonances (SPRs) are often regarded as the collective oscillations of charge carriers localized at the dielectric–metal interface that display an ultrafast response upon light excitation. The recent developments in the fabrication and characterization of plasmonic nanostructures have stimulated continuous effects in the search for their potential applications in the photonic fields. Concentrating on the role of plasmonics in photonics, this review covers recent advances in ultrafast plasmonic materials with a prime focus on all-optical switching. Fundamental phenomena of plasmonic light–matter interaction and plasmon dynamics are discussed by elaborating on the ultrafast processes unraveled by both experimental and theoretical methods, along with a comprehensive illustration of leveraging ultrafast plasmonics for all-optical switching and pulse laser generation with a focus on device design and performance. This review is concluded with a brief highlight of the current progress and the potential future directions in ultrafast plasmonics.

Numerical investigation of sequential phase-locked optical gating of free electrons

Recent progress in coherent quantum interactions between free-electron pulses and laser-induced near-field light have revolutionized electron wavepacket shaping. Building on these advancements, we numerically explore the potential of sequential interactions between slow electrons and localized dipolar plasmons in a sequential phase-locked interaction scheme. Taking advantage of the prolonged interaction time between slow electrons and optical near-fields, we aim to explore the effect of plasmon dynamics on the free-electron wavepacket modulation. Our results demonstrate that the initial optical phase of the localized dipolar plasmon at the starting point of the interaction, along with the phase offset between the interaction zones, can serve as control parameters in manipulating the transverse and longitudinal recoil of the electron wavefunction. Moreover, it is shown that the incident angle of the laser light is an additional control knop for tailoring the longitudinal and transverse recoils. We show that a sequential phase-locking method can be employed to precisely manipulate the longitudinal and transverse recoil of the electron wavepacket, leading to selective acceleration or deceleration of the electron energy along specific diffraction angles. These findings have important implications for developing novel techniques for ultrafast electron-light interferometry, shaping the electron wavepacket, and quantum information processing.

Determining hot-carrier transport dynamics from terahertz emission.

Understanding the ultrafast excitation and transport dynamics of plasmon-driven hot carriers is critical to the development of optoelectronics, photochemistry, and solar-energy harvesting. However, the ultrashort time and length scales associated with the behavior of these highly out-of-equilibrium carriers have impaired experimental verification of ab initio quantum theories. Here, we present an approach to studying plasmonic hot-carrier dynamics that analyzes the temporal waveform of coherent terahertz bursts radiated by photo-ejected hot carriers from designer nano-antennas with a broken symmetry. For ballistic carriers ejected from gold antennas, we find an ~11-femtosecond timescale composed of the plasmon lifetime and ballistic transport time. Polarization- and phase-sensitive detection of terahertz fields further grant direct access to their ballistic transport trajectory. Our approach opens explorations of ultrafast carrier dynamics in optically excited nanostructures.

Ultrafast Plasmonic Hot Hole Transfer and Plasmon Dynamics in a Dual Plasmonic Au@p‐Cu2−xSe Heterostructure

AbstractMetal‐semiconductor heterostructures have significant potential in harvesting plasmon induced hot charge carriers for photocatalytic and photovoltaic devices. Despite numerous studies, the field of hot hole transfer in heterostructures remains unexplored. In this work, the plasmon dynamics of a dual plasmonic core–shell Au@p‐Cu2−xSe heterostructure are investigated with the aid of femtosecond broadband pump probe spectroscopy. Ultrafast studies reveal that hot holes generated within the d and sp band after 400 and 800 nm excitations are injected from Au to copper selenide. Hot hole transfer substantially reduces the transient signal intensity and electron phonon relaxation time for Au plasmon. Increment in the transient signal intensity and slower kinetics for the semiconducting plasmon of Au@Cu2−xSe validate the hot hole transfer in the valence band of copper selenide. Fluence dependent studies reveal that d band hot holes extraction is more efficient than that of sp band hot holes.

Recent Advances in Real-Time Time-Dependent Density Functional Theory Simulations of Plasmonic Nanostructures and Plasmonic Photocatalysis.

Plasmonic catalysis provides a possible means for driving chemical reactions under relatively mild conditions. Rational design of these systems is impeded by the difficulty in understanding the electron dynamics and their interplay with reactions. Real-time, time-dependent density functional theory (RT-TDDFT) can provide dynamic information on excited states in plasmonic systems, including those relevant to plasmonic catalysis, at time scales and length scales that are otherwise out of reach of many experimental techniques. Here, we discuss previous RT-TDDFT studies of plasmonic systems, focusing on recent work that gains insight into plasmonic catalysis. These studies provide insight into plasmon dynamics, including size effects and the role of specific electronic states. Further, these studies provide significant insight into mechanisms underlying plasmonic catalysis, showing the importance of charge transfer between metal and adsorbate states, as well as local field enhancement, in different systems.

Dynamics of surface-plasmon lasing in planar metal gratings on semiconductor.

We investigate the dynamics of surface plasmon (SP) lasing in Au gratings fabricated on InGaAs with a period of around 400 nm, which locates the SP resonance near the semiconductor energy gap and facilitates efficient energy transfer. By optically pumping the InGaAs to reach the population inversion required for the amplification and the lasing, we observe SP lasing at specific wavelengths that satisfy the SPR condition depending on the grating period. The carrier dynamics in semiconductor and the photon density in the SP cavity was investigated from the time-resolved pump-probe measurement and the time resolved photoluminescence spectroscopy, respectively. Our results reveal that the photon dynamics is strongly correlated with the carrier dynamics and the lasing build-up is accelerated as the initial gain proportional to the pumping power increases, and this trend is satisfactorily explained using the rate equation model.

Machine Learning Models Capture Plasmon Dynamics in Ag Nanoparticles.

Highly energetic electron-hole pairs (hot carriers) formed from plasmon decay in metallic nanostructures promise sustainable pathways for energy-harvesting devices. However, efficient collection before thermalization remains an obstacle for realization of their full energy generating potential. Addressing this challenge requires detailed understanding of physical processes from plasmon excitation in the metal to their collection in a molecule or a semiconductor, where atomistic theoretical investigation may be particularly beneficial. Unfortunately, first-principles theoretical modeling of these processes is extremely costly, preventing a detailed analysis over a large number of potential nanostructures and limiting the analysis to systems with a few 100s of atoms. Recent advances in machine learned interatomic potentials suggest that dynamics can be accelerated with surrogate models which replace the full solution of the Schrödinger Equation. Here, we modify an existing neural network, Hierarchically Interacting Particle Neural Network (HIP-NN), to predict plasmon dynamics in Ag nanoparticles. The model takes as a minimum as three time steps of the reference real-time time-dependent density functional theory (rt-TDDFT) calculated charges as history and predicts trajectories for 5 fs in great agreement with the reference simulation. Further, we show that a multistep training approach in which the loss function includes errors from future time-step predictions can stabilize the model predictions for the entire simulated trajectory (∼25 fs). This extends the model's capability to accurately predict plasmon dynamics in large nanoparticles of up to 561 atoms, not present in the training data set. More importantly, with machine learning models on GPUs, we gain a speed-up factor of ∼103 as compared with the rt-TDDFT calculations when predicting important physical quantities such as dynamic dipole moments in Ag55 and a factor of ∼104 for extended nanoparticles that are 10 times larger. This underscores the promise of future machine learning accelerated electron/nuclear dynamics simulations for understanding fundamental properties of plasmon-driven hot carrier devices.

Optically Tunable Transient Plasmons in InSb Nanowires.

Optical carrier incubation can effectively alter the electron transport properties of semiconductors; thus, optical switching of the plasmonic response of the semiconductor enables the ultrafast manipulation of the light at the nanoscale. Semiconductor nanostructures are promising platforms in on-chip high-speed plasmonic devices, owing to their high photoinduced electron injection efficiency at sub-picosecond and compatibility with contemporary semiconductor technologies. The pure single crystalline InSb nanowires are promising plasmonic materials in the mid-infrared region due to their high electron mobility and small electron effective mass. Here, the pump-probe nanoscopy is utilized to investigate the pump fluence dependency and the dynamics of the non-equilibrium plasmons in the InSb nanowires. The InSb plasmon is successfully switched by injecting the photoinduced electrons and the practical tuning of the plasmon frequency to one octave is shown by increasing the pump fluence from 0 to 90µJcm-2 . The density of the photoinduced electrons in InSb nanowires is 18.8×1018 cm-3 with pump fluence as low as 90µJcm-2 . The high electron mobility of the InSb supports the low-loss plasmon with a damping rate of ≈200cm-1 . The InSb nanowires' excellent plasmonic properties ensure that they are a promising platform for upcoming high-speed mid-infrared plasmonic materials for informatic devices.

Research progress of ultra-high spatiotemporally resolved microscopy

High-resolution microscopy has opened the door to the exploration of the micro-world, while femtosecond laser has provided a measurement method for detecting ultrafast physical/chemical phenomena. Combination of these two techniques can produce new microscopic techniques with both ultra-high spatial resolution and ultra-fast temporal resolution, and thus has great importance in exploring new scientific phenomena and mechanisms on an extremely small spatial scale and temporal scale. This paper reviews the basic principles and properties of main microscopic techniques with ultra-high temporal resolution and spatial resolution, and introduces the latest research progress of their applications in various fields such as characterizing optoelectronic materials and devices, monitoring femtosecond laser micromachining, and detecting surface plasmon excitation dynamics. In order to conduct these researches systematically, we group these techniques based on time dimension and space dimension, including the near-field multi-pulse imaging techniques, the far-field multi-pulse imaging techniques, and the far-field single-pulse imaging techniques. In Section 2, we introduce the principles and characteristics of the ultra-high spatiotemporally resolved microscopic techniques. The near-field multi-pulse spatiotemporally microscopic techniques based on nano-probe are described in Subsection 2.1, in which is shown the combination of common near-field imaging techniques such as atomic force microscopy (AFM), near-field scanning optical microscopy (NSOM), scanning tunneling microscope (STM), and the ultra-fast temporal detection of pump-probe technique. In Subsection 2.2, we introduce the far-field multi-pulse spatiotemporal microscopic techniques. In contrast to near-field cases, the far-field spatiotemporal microscopic techniques have lower spatial resolution but possess more advantages of being non-invasive and non-contact, wider field of view, and faster imaging speed. In Subsection 2.3 we introduce the far-field single-pulse spatiotemporal microscopic techniques, in which is used a single ultrafast light pulse to capture dynamic processes at different moments in time, thereby enabling real-time imaging of ultrafast phenomena. In Section 3 , the advances in the application of the ultra-high spatiotemporal resolved microscopic techniques are introduced in many frontier areas, including the monitoring of femtosecond laser micromachining in Subsection 3.1, the detection of optoelectronic materials/devices in Subsection 3.2, and the characterization of surface plasmon dynamics in Subsection 3.3. Finally, in Section 4, we summarize the features of all above-mentioned spatiotemporal microscopic techniques in a table, including the spatial resolution and temporal resolution, advantages and disadvantages of each technique, and we also provide an outlook on future development trend in this research field. Looking forward to the future, ultra-high spatiotemporally resolved microscopy will develop rapidly toward the goal of "smaller, faster, smarter and more extensive". Its development not only promotes the research of the microscopy technology, but also provides a powerful tool for various practical applications such as precision machining, two-dimensional material dynamics, optoelectronic device design and characterization.

Optical Properties and Ultrafast Near‐Infrared Localized Surface Plasmon Dynamics in Naturally p‐Type Digenite Films

AbstractCopper chalcogenides are materials characterized by intrinsic doping properties, allowing them to display high carrier concentrations due to their defect‐heavy structures, independent of the preparation method. Such high doping enables these materials to display plasmonic resonances, tunable by varying their stoichiometry. Here, plasmonic dynamics is studied in drop‐cast Cu9S5 (digenite) nanocrystals (NCs) film using ultrafast pump–probe spectroscopy. The NCs are synthesized by thermal annealing of copper foil using chemical vapor deposition (CVD), followed by sonication and drop‐casting of the isolated few‐layered flakes on different substrates. The samples display a broad localized surface plasmon resonance (LSPR) in the near‐infrared (NIR), peaking at 2100 nm. The free carrier response is further confirmed by fitting the linear absorption with a Drude–Lorentz effective medium approximation model. The high temporal resolution allows to measure the relaxation dynamics of the photo‐excited holes, which are dominated by a fast decay (τ1 = 360 ± 20 fs) and correspond to hole–phonon scattering processes, followed by a long‐lived (τ2 > 1 ns) signal associated with phonon–phonon scattering relaxation. These results confirm the possibility of fabricating Cu9S5 films retaining the plasmonic properties of individual NCs, anticipating integrating these films into heterojunctions with suitable hole acceptor materials to build hot‐hole‐transfer‐based optoelectronic devices.

Optical Properties and Ultrafast Near-Infrared Localized Surface Plasmon Dynamics in Naturally p-Type Digenite Films

Optical Properties and Ultrafast Near-Infrared Localized Surface Plasmon Dynamics in Naturally p-Type Digenite Films

Modulation of plasmonic relaxation damping by surface phonons

We experimentally study the effect of amplitude-varying surface acoustic waves on a localized surface plasmon (LSP), which unveils exceptional properties of plasmon-phonon interaction with promising applications in future tunable photonic devices. Gold nanoparticles are deposited on X-cut LiNbO 3 to generate plasmonic oscillation, and an interdigital transducer is fabricated to create surface acoustic wave pulses. The interaction between an amplitude-varying mechanical wave and a plasmonic oscillation affects different plasmon dynamics and relaxation gradients, leading to a systematic change in LSP absorption. We also demonstrated the effect of polarized light on the device, providing a unique characteristic to explore the manipulation process effectively.

Dynamics of broadband photoinduced species and enabled photodetection in MXenes

Abstract Dynamics of photoinduced species, as a key parameter for nanomaterials plays a significantly role in the performance of optoelectronic devices. In this work, the origin of broadband optical response for the emerging Ti3C2T x MXene is revealed by transient spectroscopic analysis. From ultraviolet to infrared, the steady-state and transient optical responses present wavelength-related features. The carrier lifetime is found to change from femtosecond to nanosecond time scale dominated by various photoinduced species, i.e., carrier and surface plasmon. The unique optoelectronic character enables photodetection. This fundamental study on carrier, plasmon dynamics, and application in photodetection is helpful for exploring MXene-based optoelectronic devices.