Hot Electron Generation Research Articles

Plasmonic Metal Mediated Charge Transfer in Stacked Core-Shell Semiconductor Heterojunction for Significantly Enhanced CO2 Photoreduction.

Construction of core-shell semiconductor heterojunctions and plasmonic metal/semiconductor heterostructures represents two promising routes to improved light harvesting and promoted charge separation, but their photocatalytic activities are respectively limited by sluggish consumption of charge carriers confined in the cores, and contradictory migration directions of plasmon-induced hot electrons and semiconductor-generated electrons. Herein, a semiconductor/metal/semiconductor stacked core-shell design is demonstrated to overcome these limitations and significantly boost the photoactivity in CO2 reduction. In this smart design, sandwiched Au serves as a "stone", which "kills two birds" by inducing localized surface plasmon resonance for hot electron generation and mediating unidirectional transmission of conduction band electrons and hot electrons from TiO2 core to MoS2 shell. Meanwhile, upward band bending of TiO2 drives core-to-shell migration of holes through TiO2 -MoS2 interface. The co-existence of TiO2 →Au→MoS2 electron flow and TiO2 →MoS2 hole flow contributes to spatial charge separation on different locations of MoS2 outer layer for overall redox reactions. Additionally, reduction potential of photoelectrons participating in the CO2 reduction is elaborately adjusted by tuning the thickness of MoS2 shell, and thus the product selectivity is delicately regulated. This work provides fresh hints for rationally controlling the charge transfer pathways toward high-efficiency CO2 photoreduction.

Full-spectrum nonmetallic plasmonic carriers for efficient isopropanol dehydration

Plasmonic hot carriers have the advantage of focusing, amplifying, and manipulating optical signals via electron oscillations which offers a feasible pathway to influence catalytic reactions. However, the contribution of nonmetallic hot carriers and thermal effects on the overall reactions are still unclear, and developing methods to enhance the efficiency of the catalysis is critical. Herein, we proposed a new strategy for flexibly modulating the hot electrons using a nonmetallic plasmonic heterostructure (named W18O49-nanowires/reduced-graphene-oxides) for isopropanol dehydration where the reaction rate was 180-fold greater than the corresponding thermocatalytic pathway. The key detail to this strategy lies in the synergetic utilization of ultraviolet light and visible-near-infrared light to enhance the hot electron generation and promote electron transfer for C-O bond cleavage during isopropanol dehydration reaction. This, in turn, results in a reduced reaction activation barrier down to 0.37 eV (compared to 1.0 eV of thermocatalysis) and a significantly improved conversion efficiency of 100% propylene from isopropanol. This work provides an additional strategy to modulate hot carrier of plasmonic semiconductors and helps guide the design of better catalytic materials and chemistries.

Colloidal titanium nitride nanobars for broadband inexpensive plasmonics and photochemistry from visible to mid-IR wavelengths

Developing colloidal plasmonic nanomaterials with high carrier density that show optical resonances and photochemical activity extending from the visible to the mid-infrared (MIR) ranges remains a challenging pursuit. Here, we report the fabrication of titanium nitride (TiN) nanobars obtained using a two–step procedure based on a wet chemical route synthesis of TiO2 nanowires and their subsequent high temperature annealing in ammonia flow. Electromagnetic simulations of the resulting TiN nanobars reveal a rich set of optical resonances featuring transverse, longitudinal and mixed transverse–longitudinal plasmonic modes that cover energies from the visible to MIR region. TiN nanobars decorated with Pt co-catalyst nanocrystals show enhanced photocatalytic hydrogen evolution activity in comparison to both isotropic TiN nanospheres of similar size and TiN nanocubes under near infrared excitation at 940 nm due to the enhanced hot electron generation. We also demonstrate that plasmonic TiN nanobars can be used for the detection of furfural molecular vibrations by providing a strong surface enhanced infrared absorption (SEIRA) effect in the MIR region.

Investigation on the AgPt and AgPd hybrid alloy nanoparticles (HANPs) for the hybrid MoS2/ZnO/HANP UV photodetector application

Hybrid photodetectors made of two or more nanomaterial components can offer the high potential for advanced photodetection applications with enhanced light absorption, improved efficiency and structural tunability. A hybrid UV photodetector (PD) configuration incorporating the plasmonic hybrid alloy nanoparticles (HANP), ZnO quantum dots (QDs) and MoS2 nanoflakes, namely MoS2/ZnO/HANP PD, is demonstrated. The optimized MoS2/ZnO/HANP PD exhibits a high photocurrent of 5.66 mA at 0.34 mW/mm2 under 385 nm illumination with two orders of improvement from the bare ZnO, which is one of the highest photocurrents by the ZnO-based PDs. It also demonstrates high figure-of-merits with the responsivity of 14,523 mA/W, detectivity of 8.13 × 1011 jones, and external quantum efficiency (EQE) of 4,680 %, outperforming most of the ZnO-based hybrid architectures. The enhanced photoresponse is primarily attributed to the significantly enhanced hot electron generation by the AgPd HANPs and photocarrier collection through the ZnO QD layer. MoS2 nanoflakes also provide additional photon absorption sites and boost the photo-carrier transfer process. HANPs are grown by adapting a dual-step solid-state dewetting process (SSD) approach and the superiority of AgPd HANPs is confirmed by systematic investigation, FDTD simulation and comparison of AgPt and AgPd HANPs.

Shock-Augmented Ignition Approach to Laser Inertial Fusion

Shock ignition enables high gain at low implosion velocity, reducing ablative Rayleigh-Taylor instability growth, which can degrade conventional direct drive. With this method, driving a strong shock requires high laser power and intensity, resulting in inefficiencies in the drive and the generation of hot electrons that can preheat the fuel. A new "shock-augmented ignition" pulse shape is described that, by preconditioning the ablation plasma before launching a strong shock, enables the shock ignition of thermonuclear fuel, but importantly, with substantially reduced laser power and intensity requirements. The reduced intensity requirement with respect to shock ignition limits laser-plasma instabilities, such as stimulated Raman and Brillouin scatter, reducing the risk of hot-electron preheat and restoring the laser coupling advantages of conventional direct drive. Simulations indicate that, due to the reduced power requirements, high gain (∼100) ignition of large-scale direct drive implosions (outer radius ∼1750 μm, deuterium-tritium ice thickness ∼165 μm) may be possible within the power and energy limits of existing facilities such as the National Ignition Facility. Moreover, this concept extends to indirect drive implosions, which exhibit substantial yield increases at reduced implosion velocity. Shock-augmented ignition expands the viable design space of laser inertial fusion.

(Invited) Hot Electron Generation and Photocatalysis with Plasmonic Nanocrystals and Metastructures

The generation of energetic (hot) electrons and the photoheating are intrinsic properties of any optically excited plasmonic nanocrystal [1,2]. In addition, high-energy hot electrons and phototemperature contribute to the kinetic processes observed in plasmonic photodetectors, colloidal nanocrystals, and metastructures [1,2]. In this talk, we will focus on the theory of hot electron generation and present related applications for plasmonic photochemistry and plasmonic photocatalysis [3,4,5,6]. [1] L. Chang, L. V. Besteiro, J. Sun, E. Y. Santiago, S. K. Gray, Z. Wang, A. O. Govorov, ACS Energy Lett., 4, 10, 2552-2568 (2019).[2] L. V. Besteiro, P. Yu, Z. Wang, A. W. Holleitner, G. V. Hartland, A. O. Govorov, Nano Today, 27, 120-145 (2019).[3] T. Liu, L.V. Besteiro, T. Liedl, M.A. Correa-Duarte, Z. Wang, A. Govorov, Nano Letters, 19, 1395–1407 (2019).[4] L. Khosravi Khorashad, L. V. Besteiro, M. A. Correa-Duarte, S. Burger, Z. M. Wang, A.O. Govorov, J. Am. Chem. Soc., 142, 9, 4193–4205 (2020).[5] O. Ávalos-Ovando, L.V. Besteiro, A. Movsesyan, G. Markovich, T. Liedl, K. Martens, Zh. Wang, M.A.Correa-Duarte, and A.O. Govorov, Nano Letters (2021); DOI: 10.1021/acs.nanolett.1c02479.[6] A. Movsesyan, E. Y. Santiago, S. Burger, M. A. Correa-Duarte, L. V. Besteiro, Zh. Wang,andA.O.Govorov, Advanced Optical Materials (2022); https://doi.org/10.1002/adom.202102663.

Size effect of gold nanoparticles on optical and electrical properties of plasmonic silicon solar cell

One of important tasks of the day is increasing the efficiency and decreasing the cost of the silicon solar cells. There is method of introducing of metal nanoparticles into solar cells to improve its absorption and reduce transmission as well as reflection coefficients. When metal nanoparticles are introduced into silicon solar cell, nanoplasmonic effect will occur. Nanoplasmonic effect lead to modification of light spectrum and generation of extra hot electrons. Nano-plasmonic effect strongly depends on size of nanoparticles. Therefore, in this paper, effect of gold nanoparticles size on properties of silicon solar cell has been studied by using simulation. Gold nanoparticles with sizes of 4 nm, 6 nm, 9 nm, 11 nm and 21 nm have been input into emitter region of silicon solar cell in order to use both of nanoplasmonic-electric and nanoplasmonic-optic effects for enhancing efficiency of silicon solar cell. Open circuit voltage didn't change when size of nanoparticles has been changed from 4 nm to 11 nm. It dropped by 0.017 V when size of nanoparticles was 21 nm. Short circuit current has been maximum 6.7 mA/cm2 at nanoparticle size of 11 nm and minimum 3.1 mA/cm2 at nanoparticle size of 21 nm. It has been found from obtained results that gold nanoparticle with size of 11 nm affected significantly on properties of silicon solar cell. Besides, thickness of silicon solar cell can be decreased without dropping of efficiency by introducing gold nanoparticles. Because, main part of photons is absorbed near to metal nanoparticles inputted region.

Plasmon-Mediated Peroxidase-like Activity on an Asymmetric Nanotube Architecture for Rapid Visual Detection of Bacteria.

Rapid and sensitive detection of bacteria from a complex real media remains a challenge. Herein, we report a visual bacterial sensing assay with excellent specificity, anti-interference ability, and sensitivity based on a surface plasmon resonance (SPR)-enhanced peroxidase (POD) mimetic. The POD mimetic based on Pt nanoparticles (NPs) asymmetrically decorated on Au/TiO2 magnetic nanotubes (Au/Pt/MTNTs) is designed by combining the intrinsic photocatalytic activity of TiO2 and the limited transport depth of light. It is revealed that the localized surface plasmon resonance (LSPR) effect of the asymmetric nanotubes is more effective in facilitating the generation of hot electrons, which are subsequently transferred to Pt and MTNTs, thus greatly promoting the catalytic performance. Using Staphylococcus aureus (S.aureus) as a model of Gram-positive bacteria, the dependence of the colorimetric reaction on the active sites of the POD mimetic is used for the sensing of target bacteria. Owing to the specific recognition between S.aureus and peptide, the fluorescein isothiocyanate (FITC) labeled peptide probes are captured by S.aureus and removed from the Au/Pt/MTNTs, leading to the recovery of POD-like activity and fluorescence emission of S.aureus. Particularly, benefiting from the Au-SPR effect and the magnetic feature of the Au/Pt/MTNTs, the recovery of catalytic activity induced an improved colorimetric assay with a wider linear response for S.aureus qualification and a detection limit of four cells, as well as satisfactory selectivity and feasibility for application in real samples. The plasmon-enhanced POD activity would provide a simple-yet-effective approach to achieve a colorimetric bioassay with high efficiency and sensitivity. This asymmetric design can also be utilized to engineer nanozymes in colorimetric assays for the specific detection of biotoxins, biomarkers, and cancer cells.

Ultrathin Niobate Nanosheet Assembly with Au NPs and CdS QDs as a Highly Efficient Photocatalyst.

Niobate nanosheets have aroused widespread interest in recent years for their prospects in catalysis. The exploration of 2D niobate catalysis with stable and efficient properties is still the focus in chemistry and materials science. Herein, the successful fabrication of 2D CdS/Au/HNb3 O8 catalyst is demonstrated which revealed efficient photocatalytic properties in H2 evolution, oxidative self-coupling of amines to imines, and degradation of dyes. Especially the assembled architecture can give a rate of 5.85 mmol ⋅ g-1 ⋅ h-1 of photocatalytic H2 evolution, an ∼254-fold enhancement, compared with bare HNb3 O8 nanosheets under identical conditions. In accordance with density functional theory (DFT) and X-ray adsorption fine structure (XAFS) analyses, the vast improvements are benefited from efficient migration and separation of charge carriers. Besides, the surface plasma resonance (SPR) effect of Au NPs enhances the light harvesting capacity and boosts the generation of hot electrons, efficiently improving the visible-light absorption.

Hot electron and x-ray generation by sub-ns kJ-class laser-produced tantalum plasma

This paper presents experimental investigation of temperature scaling and threshold of instability in hot electron and bremsstrahlung radiation from the interaction of sub-nanosecond and kilo-joule class laser pulses with a tantalum foil target at Prague Asterix Laser System. The laser intensity was varied between and W · cm−2 at the target focus. The energy distribution functions of electrons were measured by an angular array of magnetic spectrometers indicating the electron temperature in the range between 30 keV and 70 keV. The bremsstrahlung spectrum was characterized using a scintillator-based calorimeter. In particular, we show the laser-energy scaling of the total flux of hot electrons in the forward and backward directions with respect to the laser vector, the conversion efficiency of the laser energy to the energy carried by hot electrons, and the temperature of hot electrons as well as the unfolded bremsstrahlung temperature using a Monte Carlo code consistent with signals of the scintillator detector. The scaling shows that the electron flux increases discontinuously with increasing laser intensity from W · cm−2 with consequent instability in the production of hot electrons and bremsstrahlung radiation.

Circularly polarized light-sensitive, hot electron transistor with chiral plasmonic nanoparticles

The quantitative detection of circularly polarized light (CPL) is necessary in next-generation optical communication carrying high-density information and in phase-controlled displays exhibiting volumetric imaging. In the current technology, multiple pixels of different wavelengths and polarizers are required, inevitably resulting in high loss and low detection efficiency. Here, we demonstrate a highly efficient CPL-detecting transistor composed of chiral plasmonic nanoparticles with a high Khun’s dissymmetry (g-factor) of 0.2 and a high mobility conducting oxide of InGaZnO. The device successfully distinguished the circular polarization state and displayed an unprecedented photoresponsivity of over 1 A/W under visible CPL excitation. This observation is mainly attributed to the hot electron generation in chiral plasmonic nanoparticles and to the effective collection of hot electrons in the oxide semiconducting transistor. Such characteristics further contribute to opto-neuromorphic operation and the artificial nervous system based on the device successfully performs image classification work. We anticipate that our strategy will aid in the rational design and fabrication of a high-performance CPL detector and opto-neuromorphic operation with a chiral plasmonic structure depending on the wavelength and circular polarization state.

Electrochemical Generation of Hot Electrons in Fully Aqueous Solutions at Tetrahedral Amorphous Carbon Thin Film Electrodes and Electrochemiluminescence Immunoassay of Serum Amyloid A

AbstractElectrochemistry of hot electrons in fully aqueous solutions at tetrahedral amorphous carbon thin film electrodes is discussed. The generation of these highly reducing chemical species was confirmed by normal pulse voltammetry and several electrochemiluminescent systems. Electron transfer into pre‐existing solvent cavities was observed at approximately −2.65 V vs. Ag/AgCl (sat.). Electrogenerated hot electrons were utilized as chemiluminescent mediators in heterogeneous sandwich immunoassay of Serum Amyloid A. The calibration curve was linear over four orders of magnitude and the detection limit was 85 ng L−1 that demonstrates the efficiency of hot electron generation at this electrode material.

Strain engineering for enhanced hot-carrier photodetection

Hot-carrier devices in metal–semiconductor junctions have attracted considerable attention but still with quantum efficiencies far from expectations. Introducing the lattice strain to the material can effectively modulate the electronic structure, providing a way to control the hot-carrier dynamics. Here, we study how this strain affects the generation, transport, and injection of hot carriers in gold (Au) by using first-principles calculations and evaluate the overall responses of Au-based hot-carrier devices by Monte Carlo simulation. We find that the compressive strain can significantly increase the hot-electron generation from direct transition at E > 1.1 eV for Au. The compressive strain delocalizes the band structure and decreases the electron density of state, which, in turn, reduce electron–electron and electron–phonon scatterings to improve the transport of hot carriers. Taking the Au/TiO2 device as an example, we find that the compressive strain (−6%) can enable a 1.5- to 3-fold enhancement of quantum efficiency and responsivity at a photon energy between 1.2 and 3 eV.

Shining at the Tips: Anisotropic Deposition of Pt Nanoparticles Boosting Hot Carrier Utilization for Plasmon-Driven Photocatalysis.

Bimetallic nanostructures are a promising candidate for plasmon-driven photocatalysis. However, knowledge on the generation and utilization of hot carriers in bimetallic nanostructures is still limited. In this work, we explored Pt position-dependent photocatalytic properties of bimetallic Au nanobipyramids (Au NBPs) with single-molecule fluorescence imaging. Compared with all-deposited core-shell nanostructures (aPt-Au NBPs), single-molecule imaging and simulation results show that the end-deposited bimetallic nanostructures (ePt-Au NBPs) can maintain a strong electromagnetic (EM) field and further promote the generation and transfer of energetic hot electrons for photocatalysis. Even though the Pt lattice is more stable than Au, the strong EM field at the sharp tips can boost lattice vibration, where enhanced spontaneous surface restructuring for active reaction site generation takes place. Significantly enhanced catalytic efficiency from ePt-Au NBPs is observed in contrast to that of Au NBPs and aPt-Au NBPs. These microscopic evidences offer valuable guidelines to design plasmon-based photocatalysts, particularly for bimetallic nanostructures.

Two plasmon decay instability stimulated by large-incidence-angle laser in inertial confinement fusion

The two-plasmon-decay instability (TPD) in the large-incidence-angle regime is studied via fluid and particle-in-cell (PIC) simulations. It is found that the TPD threshold in this regime within a narrow incidence angle range close to 60∘ can be orders of magnitude lower than the normal-incidence threshold. A threshold formula is proposed for this regime and is verified by fluid and PIC simulations. PIC simulations show significant laser absorption and energetic electron generation once TPD is excited. The incident angle and the laser spot size have a significant influence on the TPD in the large-incidence-angle regime. The low threshold and significant hot electron generation in this regime pose potentially unexpected preheating risks to inertial confinement fusion.

Demonstration of SWIR Silicon-Based Photodetection by Using Thin ITO/Au/Au Nanoparticles/n-Si Structure.

Plasmonic photodetection based on the hot-electron generation in nanostructures is a promising strategy for sub-band detection due to the high conversion efficiencies; however, it is plagued with the high dark current. In this paper, we have demonstrated the plasmonic photodetection with dark current suppression to create a Si-based broadband photodetector with enhanced performance in the short-wavelength infrared (SWIR) region. By hybridizing a 3 nm Au layer with the spherical Au nanoparticles (NPs) formed by rapid thermal annealing (RTA) on Si substrate, a well-behaved ITO/Au/Au NPs/n-Si Schottky photodetector with suppressed dark current and enhanced absorption in the SWIR region is obtained. This optimized detector shows a broad detection beyond 1200 nm and a high responsivity of 22.82 mA/W at 1310 nm at −1 V, as well as a low dark current density on the order of 10−5 A/cm2. Such a Si-based plasmon-enhanced detector with desirable performance in dark current will be a promising strategy for realization of the high SNR detector while keeping fabrication costs low.

Size effects in plasmonic gold nanorod based Pd-rGO hybrid catalyst for promoting visible-light-driven Suzuki-Miyaura coupling reaction

The studies on the phenomenon of surface plasmon resonance effect by noble metal-based nanoparticles (NPs) have largely been focused on the quantitative enhancement of reaction rates and investigating the mechanistic pathway of the reaction. However, the detailed analysis of the structure-property relation of plasmonic NPs and catalytic performance along with the contribution of absorption vs scattering remains limited. This report focuses on the comparison of the catalytic performance of different aspect ratio of gold nanorods (Au NRs) coupled with Pd-rGO nanocomposite for boosting the product yield of Suzuki-Miyaura coupling reaction under visible light irradiation. The confirmation of the successful synthesis of the Pd/Au NRs@rGO catalyst was done by multiple characterization techniques such as XRD, UV–vis, TEM, XAS, XPS and ICP. Amongst the three different aspect ratios of Au NRs, the superior catalytic performance of medium-sized NRs (length: 56 nm; diameter: 18 nm) with a TON of 50 was achieved under visible light irradiation conditions. A drastic enhancement by a factor of 4.1 was shown by the medium-sized NRs when the reaction results were compared in dark reaction conditions. The obtained enhancement has been ascribed to the higher efficiency of hot electron generation by the SPR effect of Au NRs.

Enhancement of Hot Electron Generation in Colloidal Plasmonic Nanocrystals by Adsorption of Pt Clusters

AbstractSurface scattering of electrons is used to be recognized as a detrimental damping process of the plasmonic oscillation, whereas such electron‐surface scattering generates hot electrons (HEs) inside the metal nanocrystals, being of great significance in practical applications, i.e., photodetection or photocatalytic reactions. However, utilizing surface scattering in colloidal plasmonic nanocrystals in realistic catalytic reactions remains challenging. This work presents a systematic study on the HE rates of colloidal Au nanocrystals, including nanospheres, nanocubes, and nanorods, and their enhancement from the adsorption of Pt clusters. Au nanocubes exhibit the highest single particle‐averaged incident photon‐to‐electron conversion efficiency among the three types of the nanocrystals. The Au nanocrystals are further adsorbed with Pt clusters, and the highest photocurrent enhancement by nearly one order of magnitude is observed. To explain the experimental observations, the contribution of the Pt adsorption to the plasmon damping is characterized by single‐particle dark‐field spectroscopy, and the HE rates are calculated by employing the finite‐element method. The overall significant enhancement of the photocurrent due to the Pt adsorption is finally explained by both electromagnetic and catalytic effects of the Pt clusters.

Plasmon-induced super-semiconductor at room temperature in nanostructured bimetallic arrays

Solid-state electrical conducting materials can be roughly categorized as superconductors, conductors, and semiconductors, depending on their conducting carriers, resistance, and band structures. This research reports the discovery of super-semiconductors, whose resistivity is 3–10 orders of magnitude lower than conventional semiconductors at room temperature. In addition, there is a transition from a metal state to a super-semiconducting state at near room temperatures, which is accompanied by an increase in hole carrier density and the mobility increase in electrons. For the first time, a hole-dominated carrier metal is observed in nanostructured bimetallic arrays near room temperature, and no other special conditions are required. Such a behavior is due to the generation of hot electrons and holes induced by metal plasmon resonance in the infrared range in the nanostructured bimetallic arrays. Our research empowers metals with semiconductor features and paves the way to realize ultra-low-power metal-based semiconductor devices.

Enhanced hot electron generation via laser interference

The interaction of two interfered picosecond laser pulses with overdense plasma and the resulting hot electron generation are studied by particle-in-cell simulation. We find that the yield and temperature of forward hot electrons can be significantly increased when laser interference fringes have a period around 3–9 μm and the angle between the two pulses is about 6°–16°. The enhancements result from local intensity increase at laser interference fringes and the plasma surface structure formed by laser pulses. The optimal angle and fringe period are analyzed, and the dependence between the optimal period and plasma density scale length is discussed. This work could be applied in hot electron generation and the resulting ion acceleration, fast ignition of laser fusion, etc.