Emission Phenomena Research Articles

Recent advances of aggregation‐induced emission in body surface organs

AbstractThe surface organs mainly comprise the superficial layers of various parts of the mammalian body, including the skin, eyes, and ears, which provide solid protection against various threats to the entire body. Damage to surface organs could lead to many serious diseases or even death. Currently, despite significant advancements in this field, there remain numerous enigmas that necessitate expeditious resolution, particularly pertaining to diagnostic and therapeutic objectives. The advancements in nanomedicine have provided a significant impetus for the development of novel approaches in the diagnosis, bioimaging, and therapy of superficial organs. The aggregation‐induced emission (AIE) phenomenon, initially observed by Prof. Ben Zhong Tang, stands out due to its contrasting behavior to the aggregation‐caused quenching effect. This discovery has significantly revolutionized the field of nanomedicine for surface organs owing to its remarkable advantages. In this review of literature, we aim to provide a comprehensive summary of recent advances of AIE lumenogen (AIEgen)‐based nanoplatforms in the fields of detection, diagnosis, imaging, and therapeutics of surface organ‐related diseases and discuss their prospects in the domain. It is hoped that this review will help attract researchers’ attention toward the utilization of this field for the exploration of a wider range of biomedical and clinical applications.

Design, synthesis, crystal structure and DFT analysis of (E)-N-(tert-butyl)-11H-benzo[4,5]imidazo[2,1-a]isoindol-11-imines with dual-state emission property

Benzoimidazoisoindoles are key structural motifs, widely found in pharmaceutical drugs and functional materials. However, very few strategies have been developed for the synthesis of benzoimidazoisoindoles, which greatly limited their applications. Herein we report an efficient approach for synthesizing benzoimidazoisoindole derivatives via palladium-catalyzed tandem cyclization of 2-(2-bromophenyl)-1H-benzo[d]imidazoles and isocyanides. Various benzoimidazoisoindoles were prepared in 63–86 % yields under air atmosphere at 100°C. The benzoimidazoisoindoles were characterized by UV–vis, photo-fluorescence, 1H and 13C NMR and HMRS. Furthermore, the single crystal structure of compound 3aa was determined to be of monoclinic system, space group I2/a, with α = 17.0080(4), b = 5.89820(10), c = 29.3286(7) Å, β = 102.948(2)°, V = 2867.34(11) Å3, Dc = 1.276 g/cm3, Z = 8, F(000) = 1168.0, μ(Cu Kα) = 0.599 mm−1, R = 0.0373 and wR = 0.0961. Photophysical property tests demonstrated that the designed benzoimidazoisoindoles exhibited typical dual-state emission (DSE) phenomenon. Density functional theory (DFT) calculation was also conducted to help understand the relationship between electronic structures and photophysical properties. Modified skeleton, the fused system includes benzoimidazoisoindole ring based on the structure–property relationship helps to design new, more effective types of dual-state emission materials.

Physical mechanism of secondary-electron emission in Si wafers

CMOS-compatible RF/microwave devices, such as filters and amplifiers, have been widely used in wireless communication systems. However, secondary-electron emission phenomena often occur in RF/microwave devices based on silicon (Si) wafers, especially in the high-frequency range. In this paper, we have studied the major factors that influence the secondary-electron yield (SEY) in commercial Si wafers with different doping concentrations. We show that the SEY is suppressed as the doping concentration increases, corresponding to a relatively short effective escape depth λ. Meanwhile, the reduced narrow band gap is beneficial in suppressing the SEY, in which the absence of a shallow energy band below the conduction band will easily capture electrons, as revealed by first-principles calculations. Thus, the new physical mechanism combined with the effective escape depth and band gap can provide useful guidance for the design of integrated RF/microwave devices based on Si wafers.

A novel approach to supramolecular Aggregation-Induced emission using tetracationic tetraphenylethylene and sulfated β-Cyclodextrin

The combination of aggregation-induced emission-based luminogens (AIEgens) with supramolecular chemistry has gained significant attention due to its ability to produce intense emission even at low concentrations. In this study, we report a supramolecular arrangement characterized by aggregation-induced emission through the integration of tetracationic tetraphenylethylene with a macrocyclic polyanionic derivative of β-cyclodextrin. Despite the exploration of ionic derivatives of cyclodextrins in pharmaceutical and host–guest supramolecular chemistry, the phenomenon of supramolecular aggregation-induced emission based on non-covalent interactions between the ionic derivative of β-cyclodextrin and derivatives of tetraphenylethyelene, a class of AIEgens, has received limited investigation. Our work explores AIE shown by the allylimidazolium derivative of tetracationic tetraphenylethyelene (ALITPE) induced by complexation with polyanionic sulfated β-cyclodextrin (SCD). The effectiveness of the emission intensity of this supramolecular assembly based on AIE is confirmed by steady-state and time-resolved fluorescence measurements, which are supported by ground-state absorption measurements. We also investigate the effect of changes in external environment, such as temperature, pH, and ionic strength, on the supramolecular assembly. Moreover, the aggregation behavior of ALITPE with SCD is comparatively studied with neutral native β-cyclodextrin, highlighting the contribution of high negative charge density on the surface of SCD for efficient aggregation with ALITPE molecules. Additionally, Molecular Docking calculations are employed to provide insights into the aggregation behavior of ALITPE molecules induced by SCD. Overall, our findings demonstrate the potential applicability of the ALITPE/SCD supramolecular assembly as a potential fluorescent sensing probe for various biological applications.

Investigating the multidrifting behaviour of subpulses in PSR J2007 + 0910 with the FAST

ABSTRACT The multidrifting subpulse behaviours in PSR J2007 + 0910 have been studied carefully with the high sensitivity observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. We found that there are at least six different single emission modes in PSR J2007 + 0910 are observed, four of which show significant subpulse drifting behaviours (modes A, B, C, and D), and the remaining two (modes E1 and E2) show stationary subpulse structures. The subpulse drifting periods of modes A, B, C, and D are P3,A = 8.7 ± 1.6P, P3,B = 15.8 ± 1.2P, P3,C = 21.6 ± 1.3P, and P3,D = 32.3 ± 0.9P, respectively, where P represents the pulse period of this pulsar. The subpulse separation is almost the same for all modes P2 = 6.01 ± 0.18°. Deep analysis suggests that the appearance and significant changes in the drifting period of multidrifting subpulse emission modes for a pulsar may originate from the aliasing effect. The observed non-drifting modes may be caused by the spark point move with a period ∼P2. Our statistical analysis shows that the drift mode of this pulsar almost always switches from slower to faster drifts in the mode change. The interesting subpulse emission phenomenon of PSR J2007 + 0910 provides a unique opportunity to understand the switching mechanism of multidrift mode.

Heat transfer rate and thermal energy analysis of MHD powell-eyring fluid in a permeable medium

This study is of significant importance as it focuses on exploring the intricate dynamics of viscous dissipation over a layered stretching surface in the context of MHD free and forced convective flow influenced by Powell-Eyring fluid. The primary aim of this research is to analyze the impact of heat emission and immersion phenomena on the flow, and to achieve this, conformable transformations of similarity have been pragmatic to adapt the governing equations from a set of non-linear PDE's into ODE's. The research methodology employed in this study involves numerical analysis using a 4th order Runge-Kutta formulation, implemented through MATLAB. The study precisely examines the stimulus of different flow constraints on velocity and temperature profiles. The outcomes of this investigation are presented through graphical representations, providing a comprehensive view of the flow characteristics. Furthermore, this study goes beyond the basic analysis by presenting important engineering metrics, the Nusselt number and skin-friction coefficient, explicitly across dissimilar variables. In conclusion, the findings of this research reveal as the Eyring-Powell fluid velocity profile rises, the temperature profile decreases, while the temperature profile rises with rising radiation.

Broadband Emission Origin in Metal Halide Perovskites: Are Self-Trapped Excitons or Ions?

It has always been a goal to realize high efficiency and broadband emission in single-component materials. The appearance of metal halide perovskites makes it possible. Their soft lattice characteristics and significant electron-phonon coupling synergistically generate self-trapped excitons (STEs), contributing to a broadband emission with a large Stokes shift. Meanwhile, their structural/compositional diversity provides suitable active sites and coordination environments for doping of ns2 ions, allowing 3 Pn ( n =0,1,2) →1 S0 transitions toward broadband emission. The ns2 ions emission is phenomenologically similar to that of STE emission, hindering in-depth understanding of their emission origin, and leading to failure to meet the design requirements for practical applications. In this scenario, herein, the fundamentals and development of such two emission mechanisms are summarized to establish a clear and comprehensive understanding of the broadband emission phenomenon, which may pave the way to an ideal customization of broadband-emission metal halide perovskites.

Dual-Emissive Rectangular Supramolecular Pt(II)-p-Biphenyl with 4,4'-Bipyridine Derivative Metallacycles: Stepwise Synthesis and Photophysical Properties.

Mixed-ligand tetranuclear supramolecular coordination complexes (SCCs) of Pt(II)-p-biphenyl and bridging ligands derivatives of 4,4'-bypiridine (8)-(10), were synthesized and characterized. The SCCs were synthesized stepwise, starting from the Pt-p-biphenyl -Pt core. The crystal structure of complex {[Pt(2,2'-bpy)]4(μ-bph)2(μ-(4,4'-bpy)2}{PF6}4 (2,2'-bpy = 2,2'-bipyridine, bph = p-biphenyl and 4,4'-bpy = 4,4' bipyridine), was determined using single-crystal diffraction methods. The emission profile of the tetranuclear complexes (8)-(10) was influenced by the length of the bridging ligands and was found to depend on solvent polarity. Dual-emission patterns in methanol-water mixtures were observed only in the cases of complexes (9) and (10), attributed to aggregation-induced emission phenomena.

Suppression of Secondary Electron Emissions on the Graphene-Coated Polyimide Materials Prepared by Chemical Vapor Deposition

Polyimide thin-film materials are widely used in aerospace and particle gas pedals, etc., but the phenomenon of secondary electron emission occurred under vacuum conditions. The graphene-coated polyimide materials were prepared for this phenomenon to suppress secondary electron emissions. The graphene coating was prepared on the polyimide surface through chemical vapor deposition (CVD). Scanning electron microscope images (SEM), X-ray photoelectron spectrometer images (XPS), Raman spectroscopy, atomic force microscopy (AFM), and other analytical methods were used to characterize the properties of the prepared materials. The C1s XPS fine spectra and Raman curve analyses showed that the material has an abundant sp2 hybridized structure, and the sp2 structure can reduce secondary electron emissions. The C, O, and N contents in the tested samples were 65.85, 20.47, and 13.68 at.%, respectively. It was examined that the graphene coating had an inhibitory effect on the secondary electron emissions of polyimide materials, and the secondary electron emission yield (SEY) was significantly reduced. The results of secondary electron tests showed that the maximum SEY (δmax) of the polyimide material decreased from 1.72 to 1.52 after the preparation of the graphene coating. The mechanism of using a graphene coating to reduce the SEY of polyimide was analyzed from experimental and theoretical perspectives. The results of this study can provide research ideas for polyimide thin film materials in aerospace, particle gas pedals, and other applications.

Monomer and Excimer Emission in Electrogenerated Chemiluminescence of Pyrene and 2,7-Di-tert-butylpyrene Associated with Electron Transfer Distance.

Electrogenerated chemiluminescence (ECL) is a light emission phenomenon caused by electrochemically generated radical anions (R•-) and cations (R•+), in which the ion annihilation results in the formation of a pair of excited (R*) and ground state (R) of a luminescent molecule. Here, the ECL properties of pyrene (Py) and 2,7-di-tert-butylpyrene (di-t-BuPy) are reported. It was found that at a commonly employed concentration (1 mM), the ECL spectra were time-dependent because of increasing the oligomer emission and increasing the concentration of R near R*, leading to an enhancement of the excimer emission. At a low concentration range (20-30 μM), the shape of the ECL spectra containing the monomer and excimer emission was determined by isolated pairs of R* and R, which were generated through ion annihilation of R•- and R•+. It was found that in the ECL of Py and di-t-BuPy originated from the isolated pairs of R•- and R•+, 58 and 48% of the excited states were the excimer states, respectively. Diffusion equation analysis indicates that the lower excimer formation in the case of di-t-BuPy is because of a farther initial separation distance between R* and R, i.e., a longer electron transfer distance between the radical ions. The Marcus model for the electron transfer kinetics suggests that the farther electron transfer distance is mainly caused by the larger molecular size, which resulted in a smaller reorganization energy of the solvent acetonitrile molecule. Taking advantage of the photophysical and electrochemical properties of Py and di-t-Bu Py, the monomer and excimer emission in ECL is discussed.

Ball Pivoting Algorithm and discrete gaussian curvature: A direct way to curved nanographene circularly polarized luminescence spectral simulation

Theoretical innovations for constructing robust computational protocols are of fundamental significance for a variety of advanced chiroptical spectroscopies. The new generation of chiral curved nanographenes offered us the opportunity to study the chiral emission phenomena in the nanometers scale. Herein we reported a distinctive method that combines topological aspects and the density functional theory in order to reach a coherent description of calculated circularly polarized luminescence spectra of negatively curved nanographenes. Our computational plan was defined as a multi-sequence strategy, paying the attention on the relationship between the molecular curvature and the relative spectroscopic properties: 1) the Ball Pivoting Algorithm for the nanographene surface reconstruction; 2) the atom by atom discrete gaussian curvature analysis to establish which DFT functional better approximates the shape of nanographenes backbones; 3) molecular dynamics in the first excited state for accounting the thermal effect; 4) TDDFT benchmark to scrutinize which functional provides the most reliable excitation energies and rotatory strengths for an accurate CPL spectral simulation. The direct merging of the previous steps celebrated the B3LYP (coupled with the 6-311G(d,p) basis set) as the most precise exchange–correlation functional in duplicating exquisitely the CPL profiles of a heterogeneous set of functionalized nanographene.

Photoactivable AIEgen-based Lipid-Droplet-Specific Drug Delivery Model for Live Cell Imaging and Two-Photon Light-Triggered Anticancer Drug Delivery.

Lipid droplets (LDs) are dynamic complex organelles involved in various physiological processes, and their number and activity are linked to multiple diseases, including cancer. In this study, we have developed LD-specific near-infrared (NIR) light-responsive nano-drug delivery systems (DDSs) based on chalcone derivatives for cancer treatment. The reported nano-DDSs localized inside the cancer microenvironment of LDs, and upon exposure to light, they delivered the anticancer drug valproic acid in a spatiotemporally controlled manner. The developed systems, namely, 2'-hydroxyacetophenone-dimethylaminobenzaldehyde-valproic (HA-DAB-VPA) and 2'-hydroxyacetophenone-diphenylaminobenzaldehyde-valproic (HA-DPB-VPA) ester conjugates, required only two simple synthetic steps. Our reported DDSs exhibited interesting properties such as excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) phenomena, which provided advantages such as AIE-initiated photorelease and ESIPT-enhanced rate of photorelease upon exposure to one- or two-photon light. Further, colocalization studies of the nano-DDSs by employing two cancerous cell lines (MCF-7 cell line and CT-26 cell line) and one normal cell line (HEK cell line) revealed LD concentration-dependent enhanced fluorescence intensity. Furthermore, systematic investigations of both the nano-DDSs in the presence and absence of oleic acid inside the cells revealed that nano-DDS HA-DPB-VPA accumulated more selectively in the LDs. This unique selectivity by the nano-DDS HA-DPB-VPA toward the LDs is due to the hydrophobic nature of the diphenylaminobenzaldehyde (mimicking the LD core), which significantly leads to the aggregation and ESIPT (at 90% volume of fw, ΦF = 20.4% and in oleic acid ΦF = 24.6%), respectively. Significantly, we used this as a light-triggered anticancer drug delivery model to take advantage of the high selectivity and accumulation of the nano-DDS HA-DPB-VPA inside the LDs. Hence, these findings give a prototype for designing drug delivery models for monitoring LD-related intracellular activities and significantly triggering the release of LD-specific drugs in the biological field.

Influence of specimen size on granite fracture characteristics and acoustic emission phenomena under mode I loading conditions

The rock mode I fracture characteristics and the size effect are of great significance in understanding the crack initiation, nucleation, propagation, and characterizing the fracture toughness of rocks which is essential for predicting the behavior of rock masses and designing underground structures. In this paper, three-point bending fracture experiments were carried out using single-edge notched beam specimens of different sizes. The fracture characteristics of the entire loading stage, including the post peak stage, were analyzed using digital image correlation (DIC) technology and acoustic emission (AE) technology. Specifically, the calculation of the b value uses the Fisher optimal split and global search algorithm (FGS) method. The results show that both the Fracture process zone (FPZ) length and fracture toughness of granite are size-dependent parameters, and the FPZ length growth rate increases with increasing load level. The failure mode of the source during fracture is mainly tensile failure, and the proportion of tensile failure tends to increase with the increase of specimen size. The temporal b value, average AF value and RA value show corresponding stage changes with time, and the minimum b value, minimum AF value and maximum RA value can characterize the maximum of macroscopic growth rate.

Non-chemical signalling between mitochondria.

A wide variety of studies have reported some form of non-chemical or non-aqueous communication between physically isolated organisms, eliciting changes in cellular proliferation, morphology, and/or metabolism. The sources and mechanisms of such signalling pathways are still unknown, but have been postulated to involve vibration, volatile transmission, or light through the phenomenon of ultraweak photon emission. Here, we report non-chemical communication between isolated mitochondria from MCF7 (cancer) and MCF10A (non-cancer) cell lines. We found that mitochondria in one cuvette stressed by an electron transport chain inhibitor, antimycin, alters the respiration of mitochondria in an adjacent, but chemically and physically separate cuvette, significantly decreasing the rate of oxygen consumption compared to a control (p = <0.0001 in MCF7 and MCF10A mitochondria). Moreover, the changes in O2-consumption were dependent on the origin of mitochondria (cancer vs. non-cancer) as well as the presence of "ambient" light. Our results support the existence of non-chemical signalling between isolated mitochondria. The experimental design suggests that the non-chemical communication is light-based, although further work is needed to fully elucidate its nature.

Dangling Water Molecules Bridge for ESIPT in Aggregated TMP: A Theoretical Study.

We present a theoretical study on the occurrence of excited-state proton transfer in an aggregated structure of 2-(benzo[d]thiazol-2-yl)-6-methoxyphenol (TMP) exclusively in water among polar solvents, as reported in a recent experiment (Bhattacharyya, A. New J. Chem. 2019, 43, 15087). Our extensive investigation of the TMP monomer and dimer implementing density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, in three different solvents, namely, water, methanol, and dimethyl sulfoxide (DMSO), with explicit inclusion of solvent molecules demonstrated the existence of both enol and keto forms of the TMP dimer in the excited state, but only in water; this confirmed the experimental emission spectra completely and simultaneously validated the aggregation-induced emission phenomenon. Further analysis of various parameters such as potential energy scan (PES) of the hydroxyl (O-H) bond involved in hydrogen bonding, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and infrared (IR) stretching frequencies of both the monomer and dimer forms of TMP in different solvents clearly indicated the geometry of the dimer, with the arrangement of the solvent molecules to be the sole reason for the excited-state charge transfer. The bridging alignment of water molecules in between the stacked units of the TMP dimer results in intermolecular interactions, ultimately leading to intermolecular proton transfer in the excited state.

On luminescence and sonochemical reactions in liquid ammonia induced by ultrasound

Light emission phenomena in the single- and multibubble sonolysis of liquid ammonia and solutions of salts (NaCl, AgNO3, EuCl3, and SmCl3) in liquid ammonia at −70 оС were considered for the first time. It was found that the key mechanisms of glow excitation found for other liquids with known sonoluminescence are also implemented in this case. Under the action of ultrasound, light flashes arise in liquid NH3, caused by the formation of nonequilibrium plasma in the cavitation bubbles due to their periodic compression and strong heating and emission of photons by the plasma, characterized of a spectrally broad, structureless continuum in the 240–800 nm range. In addition, especially in solutions containing additives, there is sonoluminescence of these additives, solvent molecules, or the products of sonochemical reactions of these molecules and additives, after they get into bubbles to give individual emitters during collisional excitation in the bubble plasma. For example, sodium atoms, undergo such collisional excitation, as follows from the presence of 589 nm line in the sonoluminescence spectrum of an NaCl solution in NH3. Apart from the bubble sonoluminescence, plasma generation may give rise to glow outside the bubbles, caused by chemiluminescent reactions of the primary sonolysis products that arise in the plasma and get into the liquid. In the case of moving single-bubble sonolysis of NH3 solutions, solvated electron (es–) was shown to be present among these primary products. In particular, it can reduce trivalent lanthanide ions in solution, thus generating light-emitting electronically excited divalent ions, as was found, for example, for europium (450 nm) and samarium (755 nm). In the presence of Ag+ ions, acting as es– acceptors, this sonochemiluminescence is quenched.

Quantum-Chemical Study of Aggregation of 5-(4'-Dimethylaminobenzylidene)Barbituric Acid

Decreasing fluorescence efficiency in the solid-state is general and is mainly attributed to the intermolecular vibronic interactions, which induce the nonradiative deactivation process. Whereas the isolated dye molecules are virtually non-luminescent in dilute solutions, they become highly emissive upon solution thickening or aggregation in poor solvents or in the solid-state show an increase of luminescence intensity, the phenomenon of the aggregation-induced emission (AIE phenomenon). The development of efficient luminescent materials is a topic of great current interest. Theoretical calculation shows that the dye molecules' aggregation-induced emission characteristics result from intermolecular interactions. Utilizing such features, the molecules can be employed as fluorescent probes for the detection of the ethanol content in aqueous solutions. Quantum-chemical calculations using the method of density functional theory the computations of structure and electronic spectra of aggregated forms of 5-(4’-dimethylaminobenzylidene)barbituric acid and the Gaussian 98 program packages have been performed. The unusual spectral behavior of 5-(4’-dimethylamino-benzylidene)barbituric acid was investigated theoretically by the DFT method and its time-dependent variant TDDFT. Carried out calculations using Zindo, as well as ab initio calculations, confirm the appearance of a new band during aggregation and its shift to the red region when the number of molecules increases.

Analysis of multilayer OLED for improvement in drive current and luminescent power

This research paper discusses the performance enhancement techniques of multi-layered OLED structures. OLED’s electrical behaviour is evaluated using an analytical model using benchmarked industry-standard Atlas 2-D numerical device simulator. It highlights the extraction of emission and charge transport phenomena and charges injection role. Multilayer OLED device has been investigated by extracting the key performance parameters, including the current density and luminescent power as a function of anode voltage. There is an improvement of 15% in the current density. Furthermore, this work has proceeded with internal analysis and using a mathematical model, where the electric field, total current density, electron and hole concentration, and internal device parameters have been extracted to understand the performance of OLED devices better. Additionally, the internal physics and behaviour of the device have been studied in terms of Langevin recombination. Internal analysis is performed by making cutlines in a vertical fashion so that device physics and the process occurring in the internal part can be clearly understood. The OLED device behaviour analysis is performed using the industry standard state of art device simulation tool.

Experimental and numerical analysis of unburned ammonia and nitrous oxide emission characteristics in ammonia/diesel dual-fuel engine

Ammonia (NH3) combustion has been investigated as a carbon-free fuel for internal combustion engines. The marine sector attempts to use NH3 as fuel for diesel engines. However, NH3 combustion in diesel engines can emit unburned NH3 and nitrous oxide (N2O) via the greenhouse effect, and the mechanisms of emission production remain unclear. In this study, the combustion of a premixed NH3–diesel dual-fuel initiated by a pilot fuel is investigated experimentally and numerically. The experiments reveal a change in combustion phasing and emission characteristics for up to 80% of the energy fraction of NH3. As the energy fraction of NH3 increases, the onset of combustion is delayed, the center of combustion is slightly advanced and then retracted, and the end of combustion is slightly advanced. NO and unburned NH3 emissions increased, whereas CO emission decreased as the energy fraction of NH3 increased; by contrast, N2O emissions increased. However, the increase in N2O diminished when the energy fraction of NH3 increased by 40% or more. Computation fluid dynamics simulations based on n-heptane and ammonia reaction kinetics qualitatively reproduced the experimental results. The numerical analysis facilitates the understanding of the underlying phenomena of emission via ammonia–diesel dual-fuel combustion. N2O formation can be categorized into two stages: a steep formation of N2O with main heat release and CO2 production, followed by a relatively low formation rate of N2O with a decreasing rate of NH3 decomposition and reduction in CO2 production. The early injection of pilot fuel allowed the pilot fuel to distribute to the wide area of the combustion chamber and NH3 to rapidly combust without remaining N2O. The rapid combustion eliminates the second stage of relatively slow combustion, which generated N2O. The low NH3 and N2O emissions observed experimentally with the early pilot fuel injection may be due to this mechanism

Ultrahigh‐Q Resonance in Bound States in the Continuum–Enabled Plasmonic Terahertz Metasurface

The study of optical resonators is of significant importance in terms of their ability to confine light in optical devices. A major drawback of optical resonators is the phenomenon of light emission due to their limited capacity for light confinement. Bound states in the continuum are gaining significant attention in the realization of optical devices due to their unique ability for reducing light scattering via interference mechanisms. This process can potentially suppress scattering, leading to improved optical performance. Using this concept, a metasurface having two elliptical silicon (Si) resonators nonidentically angled to create an out‐of‐plane asymmetry is studied. Various parameters are optimized by employing a genetic algorithm (GA) to subsequently achieve a high‐Q factor at terahertz frequencies. Herein, the device is fabricated using a novel method, and a thick high‐index resonator is achieved. Terahertz measurements are carried out to validate the results. It is indicated in the experimental results that plasmons appear at the top surface of the metasurface and create strong sharp resonances that are sensitive to the external environment. Owing to strong field confinement ability, and high‐Q factor, the metasurface is sensitive to its surrounding environment and can be essentially employed in terahertz sensing applications.