Hot Electrons Research Articles

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles’ surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

Sunlight-boosted recovery of precious metal ions from E-waste using tannin-grafted mesoporous silica

The escalating demand and dwindling reserves of precious metals request efficient recycling techniques from electron waste. Addressing this need, we introduce a new method utilizing tannin-grafted mesoporous silica for the sunlight-boosted recovery of precious metals. Our strategy leverages the inherent photoreactivity of tannins, enabling metal–ligand complexation and plasmonic enhancement of chemical reduction. The result is a marked increase in the adsorption capacity and the high selectivity towards precious metal ions in electronic waste. Our robust covalent bonding approach concentrated tannic acids onto silica at a high density (500,000 per square micrometer), which significantly boosted the adsorption of gold ions up to an 11-fold increase, even amidst a mixture of nine other metal species. Impressively, we achieved a maximum adsorption capacity of 68.4 mmol per gram, equivalent to 13.4 g of gold per gram of adsorbent. Also, the adsorption rates for platinum and palladium ions were enhanced by 2.6 and 3.0 times, respectively. The underlying mechanism includes the visible-light-driven plasmonic hot electron transfer that affords nearly perfect selectivity for gold ions (approximately 99%). These findings not only advance the field of metal recovery from electronic waste but also offer an environmentally benign and cost-effective solution that harnesses renewable solar energy.

Phototransformation of achiral metasurfaces into handedness-selectable transient chiral media

Chirality is a geometric property describing the lack of mirror symmetry. This unique feature enables photonic spin-selectivity in light-matter interaction, which is of great significance in stereochemistry, drug development, quantum optics, and optical polarization control. The versatile control of optical geometry renders optical metamaterials as an effective platform for engineered chiral properties at prescribed spectral regimes. Unfortunately, geometry-imposed restrictions only allow one circular polarization state of photons to effectively interact with chiral meta-structures. This limitation motivates the idea of discovering alternative techniques for dynamically reconfiguring the chiroptical responses of metamaterials in a fast and facile manner. Here, we demonstrate an approach that enables optical, sub-picosecond conversion of achiral meta-structures to transient chiral media in the visible regime with desired handedness upon the inhomogeneous generation of plasmonic hot electrons. As a proof of concept, we utilize linearly polarized laser pulse to demonstrate near-complete conversion of spin sensitivity in an achiral meta-platform-a functionality yet achieved in a non-mechanical fashion. Owing to the generation, diffusion, and relaxation dynamics of hot electrons, the demonstrated technique for all-optical creation of chirality is inherently fast, opening new avenues for ultrafast spectro-temporal construction of chiral platforms with on-demand spin-selectivity.

Determining Quasi-Equilibrium Electron and Hole Distributions of Plasmonic Photocatalysts Using Photomodulated X-ray Absorption Spectroscopy.

Most photocatalytic and photovoltaic devices operate under broadband, constant illumination. Electron and hole dynamics in these devices, however, are usually measured by using ultrafast pulsed lasers in a narrow wavelength range. In this work, we use excited-state X-ray theory originally developed for transient X-ray experiments to study steady-state photomodulated X-ray spectra. We use this method to attempt to extract electron and hole distributions from spectra collected at a nontime-resolved synchrotron beamline. A set of plasmonic metal core-shell nanoparticles is designed as the control experiment because they can systematically isolate photothermal, hot electron, and thermalized electron-hole pairs in a TiO2 shell. Steady-state changes in the Ti L2,3 edge are measured with and without continuous-wave illumination of the nanoparticle's localized surface plasmon resonance. The results suggest that within error the quasi-equilibrium carrier distribution can be determined even from relatively noisy data with mixed excited-state phenomena. Just as importantly, the theoretical analysis of noisy data is used to provide guidelines for the beamline development of photomodulated steady-state spectroscopy.

Revolutionizing Technology with Spintronics: Devices and Their Transformative Applications

The scaling of metal oxide semiconductor field effect transistors (MOSFETs) for data storing and logic circuit operation has reached a critical point, beyond which further scaling poses various secondary issues. These problems include short channel effects, hot carrier effects (HCEs), and reliability concerns. However, a promising alternative called spintronics has recently emerged as a highly exciting technology. Spintronics considers both the charge and spin of electrons in device operations and offers superior properties compared to MOSFETs.Researchers have reported numerous spintronics devices that exhibit significant potential in memory and logic circuits when integrated with complementary metal oxide semiconductor (CMOS) technology. These devices not only possess excellent scalability but also consume less power than MOSFETs at the nano-scale level. This article aims to provide a comprehensive review of the current state, future prospects, and challenges associated with spintronics devices.

Time-Dependent Ultrafast Quadratic Nonlinearity in an Epsilon-Near-Zero Platform.

Ultrafast nonlinearity, which results in modulation of the linear optical response, is a basis for the development of time-varying media, in particular those operating in the epsilon-near-zero (ENZ) regime. Here, we demonstrate that the intraband excitation of hot electrons in the ENZ film results in a second-harmonic resonance shift of ∼10 THz (40 nm) and second-harmonic generation (SHG) intensity changes of >100% with only minor (<1%) changes in linear transmission. The modulation is 10-fold enhanced by a plasmonic metasurface coupled to a film, allowing for ultrafast modulation of circularly polarized SHG. The effect is described by the plasma frequency renormalization in the ENZ material and the modification of the electron damping, with a possible influence of the hot-electron dynamics on the quadratic susceptibility. The results elucidate the nature of the second-order nonlinearity in ENZ materials and pave the way to the rational engineering of active nonlinear metamaterials and metasurfaces for time-varying applications.

Bound States in the Continuum for Hot Electron Generation in Integrated-Resonant Metasurfaces

Bound States in the Continuum for Hot Electron Generation in Integrated-Resonant Metasurfaces

Understanding the Behaviors of Plasmon-Induced Hot Carriers and Their Applications in Photocatalysis.

Photocatalysis driven by plasmon-induced hot carriers has been gaining increasing attention. Recent studies have demonstrated that plasmon-induced hot carriers can directly participate in photocatalytic reactions, leading to great enhancement in solar energy conversion efficiency, by improving the catalytic activity or changing selectivity. Nevertheless, the utilization efficiency of hot carriers remains unsatisfactory. Therefore, how to correctly understand the generation and transfer process of hot carriers, as well as accurately differentiate between the possible mechanisms, have become a key point of attention. In this review, we overview the fundamental processes and mechanisms underlying hot carrier generation and transport, followed by highlighting the importance of hot carrier monitoring methods and related photocatalytic reactions. Furthermore, possible strategies for the further characterization of plasmon-induced hot carriers and boosting their utilization efficiency have been proposed. We hope that a comprehensive understanding of the fundamental behaviors of hot carriers can aid in designing more efficient photocatalysts for plasmon-induced photocatalytic reactions.

Model of self-generated magnetic field generation from relativistic laser interaction with solid targets

Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations. The spatial strength distribution of magnetic fields can be accurately predicted by calculating the net flow caused by the superposition of source flow and return flow of hot electrons. The theoretical model established shows good agreement with the simulation results, indicating that the magnetic-field strength scales positively to the temperature of hot electrons. This provides us a way to improve the magnetic-field generation by using a micro-structured plasma grating in front of the solid target. Compared with that for a common flat target, hot electrons can be effectively heated with the well-designed grating size, leading to a stronger magnetic field. The spatial distribution of magnetic fields can be modulated by optimizing the grating period and height as well as the incident angle of the laser pulse.

Revealing the Loss Mechanism of Chemically-Induced Hot Electron Transport.

Hot electrons are crucial for unraveling the intrinsic relationship between chemical reactions and charge transfer in heterogeneous catalysis. Significant research focused on real-time detection of reaction-driven hot electron flow (chemicurrent) to elucidate the energy conversion mechanisms, but it remains elusive because carrier generation contributes to only part of the entire process. Here, a theoretical model for quantifying the chemicurrent yield is presented by clarifying the contributions of hot carrier losses from the internal emission and multiple reflections. The experimental chemicurrent yield verifies our model with a reliable mean free path of hot electrons, emphasizing the importance of comprehensive consideration of the transport process besides hot electron generation. Moreover, Pt nanoparticles (NPs)-decorated Au/TiO2 is examined, showing the role of NPs-induced carrier losses in the performance of catalytic nanodiodes. These findings are expected to contribute to understanding the hot electron detection efficiency and designing nanodiodes with enhanced hot carrier flow and catalytic activity.

Shaped liquid drops generate MeV temperature electron beams with millijoule class laser

MeV temperature electrons are typically generated at laser intensities of 1018 W cm−2. Their generation at non-relativistic intensities (~1016 W cm−2) with high repetition rate lasers is cardinal for the realization of compact, ultra-fast electron sources. Here we report a technique of dynamic target structuring of micro-droplets using a 1 kHz, 25 fs, millijoule class laser, that uses two collinear laser pulses; the first to create a concave surface in the liquid drop and the second, to dynamically-drive electrostatic plasma waves that accelerate electrons to MeV energies. The acceleration mechanism, identified as two plasmon decay instability, is shown to generate two beams of electrons with hot electron temperature components of 200 keV and 1 MeV, respectively, at an intensity of 4 × 1016 Wcm−2, only. The electron beams are demonstrated to be ideal for single shot high resolution (tens of μm) electron radiography.

Construction of Gold/Rhodium Freestanding Superstructures as Antenna-Reactor Photocatalysts for Plasmon-Driven Nitrogen Fixation.

Precisely controlling the architecture and spatial arrangement of plasmonic heterostructures offers unique opportunities to tailor the catalytic property, whereas the lack of a wet-chemistry synthetic approach to fabricating nanostructures with high-index facets limits their practical applications. Herein, we describe a universal synthetic strategy to construct Au/Rh freestanding superstructures (SSs) through the selective growth of ordered Rh nanoarrays on high-index-faceted Au nanobipyramids (NBPs). This synthetic strategy works on various metal nanocrystal substrates and can yield diverse Au/Rh and Pd/Rh SSs. Especially, the obtained Au NBP/Rh SSs exhibit high photocatalytic activity toward N2 fixation as a result of the spatially separated architecture, local electric field enhancement, and the antenna-reactor mechanism. Both theoretical and experimental results reveal that the Au NBPs can function as nanoantennas for light-harvesting to generate hot charge carriers for driving N2 fixation, while the Rh nanoarrays can serve as the active sites for N2 adsorption and activation to synergistically promote the overall catalytic activity in the Au NBP/Rh SSs. This work offers new avenues to rationally designing and constructing spatially separated plasmonic photocatalysts for high-efficiency catalytic applications.

Exploring the photoelectrochemical process through surface states of plasmonic Ag-loaded NiFe-LDH-modified CuWO4 photoanode

Optimizing the interfacial action of photoanode for photoelectrochemical (PEC) behavior to facilitate charge transport is essential for enhancing solar-to-fuel efficiency. Herein, a typical CuWO4/NiFe-LDH/Ag photoanode was reported and an alternative pathway for charge transfer in the PEC process through surface states mechanism was elucidated. In particular, the layer double hydroxides (NiFe-LDH) acted as charge-transfer agents to facilitate the transfer of photogenerated carriers; while the surface plasmon resonance (SPR) effect of the Ag provided hot electrons, which increased the carrier concentration and promoted the charge separation. The influence of presence of surface states on the PEC process was systematically illustrated. Experimental results indicated that the optimized CuWO4/NiFe-LDH/Ag photoanode displayed a photocurrent that was more than an order of magnitude larger than that of the pure CuWO4 (increasing from 0.30 mA cm−2 to 1.45 mA cm−2 at 1.23 V vs. RHE), accompanied by favorable electrochemical impedance and stability (maintaining 92.4%). Importantly, increasing the available filled surface states could be beneficial in enhancing the PEC behavior. This work provided additional insights into photoanode charge transport in PEC processes.

On the propagation of dust-acoustic dressed solitons (DADS) influenced by dust concentration and hot isothermal electrons in an inhomogeneous plasma

On the propagation of dust-acoustic dressed solitons (DADS) influenced by dust concentration and hot isothermal electrons in an inhomogeneous plasma

Design of Wireless Multiple Gases Complementary Architecture Sensors Based on SnSe2 and PtSe2 Layered Films and Oscillating Circuits

AbstractOwing to the increasing demand for monitoring harmful toxic gases using small‐sized low‐power‐consumption gas sensors, a room‐temperature wireless complimentary gas sensor incorporating layered materials is proposed and demonstrated. The compact design allows the sensing module to be installed under all conditions and facilitates multiple detections of toxic gas. Highly chemical‐resistance‐sensitive materials based on n‐type SnSe2 and p‐type PtSe2 layered materials prepared by the plasma‐assisted chemical vapor reaction (PACVR) method at low temperatures are integrated with an oscillation circuit and antenna fabricated by a 28‐nm CMOS high‐k metal gate logic process to achieve dense, low‐powered, and wireless characteristics. By pairing n‐ and p‐type layered semiconductors, the gas sensors feature less influence from the surroundings, such as temperature and humidity, and enhance sensitivity to the target gas simultaneously. The wireless sensing detection method enables a sensor to make signal reception more convenient. Furthermore, a wireless gas sensor with self‐converging calibration using the advantage of a floating‐gate (FG) transistor to control the charge quantity by shifting the threshold voltage (Vth) of each transistor via the channel hot electron injection effect, which helps to reduce the impact of process variations, minimizing readout errors, is proposed.

Au/Ti3C2/g-C3N4 Ternary Composites Boost H2 Evolution Efficiently with Remarkable Long-Term Stability by Synergistic Strategies.

The use of novel two-dimensional MXene materials and conventional g-C3N4 photocatalysts to fabricate the composites for hydrogen evolution reaction (HER) has attracted much attention, for which there is plenty of room for the enhancement of hydrogen evolution rates particularly under visible light and photostability. Herein, g-C3N4 was modified by copolymerization of malonamide and melamine and used to fabricate the ternary composites of Au particles and Ti3C2 MXene, and based on the synergistic effect, the composites enhanced the hydrogen evolution rates by 2.1, 99.8, and ∞ times compared with the unmodified g-C3N4 under UV, simulated sunlight, and visible light illumination, respectively. Moreover, the composite exhibited a sustained hydrogen evolution capacity in the cycle test for up to 120 h. Theoretical calculations and experimental results indicated that the hot electrons of Au are injected into the modified g-C3N4 and transferred to Ti3C2 simultaneously along with the photogenerated electrons of the modified g-C3N4 and then further transferred to Au, forming a photogenerated electron transfer channel of Au and modified g-C3N4 → Ti3C2 → Au within the composite. Ti3C2 acts as a bridge for fast separation of photogenerated electrons and holes on Au and modified g-C3N4, playing a key role in the enhanced photocatalytic performance. In addition, the visible light absorption ability of Au also positively contributed to the enhancement of visible light photocatalytic performance by providing hot electrons. Therefore, the selection of suitable cocatalysts for the design of composites is a crucial research direction to improve the photocatalytic performance and photostability of photocatalysts.

Collimated hot electron generation from sub-wavelength grating target irradiated by a femtosecond laser pulse of relativistic intensity

We investigate the production of hot electrons from the interaction of relativistically intense (I&amp;gt;1018 W/cm2) ultrashort (25 fs) laser pulses with sub-wavelength grating target. We measure the hot electron angular distribution and energy spectra for grating target and compare them with those from a planar mirror target. We observe that hot electrons are emitted in a collimated beam along the specular direction of the grating target. From the measurements, we see fast electron temperature and flux for grating are higher than those for mirror due to a stronger coupling with the laser. We performed numerical simulations, which are in good agreement with experimental results, and offer insights into the acceleration mechanism by resulting electric and magnetic fields. Such collimated fast electron beams have a wide range of applications in applied and fundamental science.

Characterization of larger-single-Lorentzian noise deviated from 1/f characteristics detected by a power-spectral-density-integration method

Larger-single-Lorentzian noise that deviates significantly from a 1/f characteristic generated by MOSFET is quantitatively analyzed using a unique evaluation method, which integrates power spectral density over a predetermined frequency band. As a result, the appearance of larger-single-Lorentzian noise is stochastically present and for low gate voltage. According to drain voltage dependence, it is suggested that the origin of larger-single-Lorentzian noise is in a pinch-off region and results from border traps in a gate oxide film by which hot carriers are trapped/de-trapped.

Characterization and Modeling of Hot Carrier Degradation Under Dynamic Operation Voltage

Characterization and Modeling of Hot Carrier Degradation Under Dynamic Operation Voltage

Gate Electrode Work Function Engineered Nanowire FET with High Performance and Improved Process Sensitivity

MOSFETs have been used in integrated circuits for a long time. These were replaced by FinFET’s in 2011. But for short-channel devices, FinFET’s have low performance due to various effects like velocity saturation, hot carrier effect, drain-induced barrier lowering, channel length modulation, fringing field effect, sub-threshold conduction, threshold voltage roll-off, etc. Gate All Around FET (GAA FET) is the best device that will replace the FinFET’s. Therefore, during the fabrication process, it is crucial to investigate the effects of process variations caused by changes in device dimensions. This research discusses the performance of the proposed device due to process variations. The effect of changes in radius, gate oxide thickness, gate length, and channel doping on GAA FET has been discussed in detail.