Electron Photon Research Articles

Effects of simulation dimensionality on laser-driven electron acceleration and photon emission in hollow microchannel targets.

Using two-dimensional (2D) and three-dimensional (3D) kinetic simulations, we examine the impact of simulation dimensionality on the laser-driven electron acceleration and the emission of collimated γ-ray beams from hollow microchannel targets. We demonstrate that the dimensionality of the simulations considerably influences the results of electron acceleration and photon generation owing to the variation of laser phase velocity in different geometries. In a 3D simulation with a cylindrical geometry, the acceleration process of electrons terminates early due to the higher phase velocity of the propagating laser fields; in contrast, 2D simulations with planar geometry tend to have prolonged electron acceleration and thus produce much more energetic electrons. The photon beam generated in the 3D setup is found to be more diverged accompanied with a lower conversion efficiency. Our paper concludes that the 2D simulation can qualitatively reproduce the features in 3D simulation, but for quantitative evaluations and reliable predictions to facilitate experiment designs 3D modeling is strongly recommended.

Engineering attractive interaction in ZIF-based phase change materials for boosting electro- and photo- driven thermal energy storage

Metal organic frameworks contain abundant empty space for selectively absorbing phase change materials (PCM) molecules and sometimes chemically transformed. However, the strong attractive interaction between metal organic frameworks and PCM severely blocks sufficient crystalline-amorphous state transition of PCM. Herein, we proposed an attractive interaction engineering strategy on hierarchical zeolitic imidazolate frameworks (ZIF) based phase change materials (polyethylene glycol/carbon cloth@ZIF, PEG/CC@ZIF) for boosting crystalline-amorphous state transition behavior and electro-/photo- driven thermal performance. Carboxyl-modified CC scaffold regulates attractive interaction between ZIF and PEG, which enhances energy storage capacity of the phase change composite. Moreover, ZIF nanoflakes deposited on the surface of CC reduce the convective heat loss at the solid–gas interface, and CC scaffold facilitates electron transportation and photon penetration, thus significantly enhancing electro- and photo- driven thermal energy storage. Furthermore, ZIF-induced chain effect between PEG and CC enhances the mechanical properties of PEG/CC@ZIF. Notably, commercially available transition metal oxide photocatalyst can be uniformly sprayed on the surface of PEG/CC@ZIF through coordination chemical engineering for multi-functional phase change composite.

Prospects in x-ray science emerging from quantum optics and nanomaterials

The science of x-rays is by now over 125 years old, starting with Wilhelm Röntgen's discovery of x-rays in 1895, for which Röntgen was awarded the first Nobel Prize in Physics. X-rays have fundamentally changed the world in areas, including medical imaging, security scanners, industrial inspection, materials development, and drugs spectroscopy. X-ray science has been so far responsible for over 25 Nobel Prizes in Physics, Chemistry, and Medicine/Physiology. With x-ray generation being a highly commercialized, widely adopted technology, it may appear that there is little left to discover regarding the fundamentals of x-ray science. Contrary to this notion, recent years have shown renewed interest in the research and development of innovative x-ray concepts. We highlight, in this Perspective, promising directions for future research in x-ray science that result from advances in quantum science and in nanomaterials. Specifically, we describe three key opportunities for advancing x-ray science in the near future: (1) emerging material platforms for x-ray generation, especially 2D materials and their heterostructures; (2) free-electron-driven emission of entangled photon–photon and electron–photon pairs for x-ray quantum optics; and (3) shaping free-electron wavepackets for controllable x-ray emission. These research directions could lead to improvements in x-ray resonance fluoroscopy, high-contrast x-ray imaging, stimulated coherent x rays, x-ray superradiance, and other prospects for x-ray quantum optics.

Simultaneous Excitation of Helium by Means of an Electron and a Photon: A Joined Experimental and Theoretical Study

We report on a joined experimental and theoretical study of differential cross-sections resulting from inelastic scattering of a monoenergetic electron by helium atoms in the presence of an intense carbon dioxide laser. In particular, we measured the signals of the scattered electrons during the simultaneous electron–photon excitation of He 21P state for the first three microseconds of the laser pulse. The signals were measured for an incident electron energy of 45 eV and showed a structure that emerged at small scattering angles. The latter was found to be sensitive to the nature of the transferred photons, as well as the intensity of the laser field. The experimental findings were supported by quantum calculations based on the second-order Born approximation in which the correlated electron–electron interactions were taken into account.

Organic Chiral Spin‐Optics: The Interaction between Spin and Photon in Organic Chiral Materials

AbstractRecently, the spin‐dependent effects in chiral materials are being intensively explored due to requirements of fundamental research and technological applications. In organic chiral materials, there is a strong electron−phonon coupling, which will affect the magnitude of spin polarization. Moreover, the chirality‐generated orbital angular momentum can also affect spin polarization. Thus, the coupling among the electron spin, orbit, lattice, and photon can be effectively enhanced in organic chiral materials, which allows the existence of magneto‐chiral dichroism, chirality‐induced spin selection effects, magnetic field dependence of circularly polarized light emission and transmission. Recent studies on the electron spin and photon interaction in organic chiral materials are presented and understood here, which provides guidance for the future development and application in organic chiral spin‐optics.

Synthesis of nanocubic shape controlled Gold-Prussian blue nanocomposite for enhanced electrocatalytic hydrazine oxidation

• A facile wet chemical method used for the synthesis of nano cubic shape controlled Au-PB-NCs. • Au-PB-NC/GCE shows 13 times higher catalytic current density of hydrazine than pristine PB-NCs. • The sensitivity of Au-PB-NCs/GCE is 111 μA.cm −2 μM −1 with LOD of 0.709 µM for sensing of hydrazine. Herein, we report for the first time, facile chemical synthesis of gold nanoparticles embedded in nano-cubic shaped prussian blue (Au-PB-NCs). To understand the role of gold nanoparticles (AuNPs) present in the Au-PB-NCs, the same chemical method is used without involving gold precursor solution for pristine prussian blue nanocubes (PB-NCs). For the proof-of-concept experiment, both Au-PB-NCs and PB-NCs are modified on glassy carbon electrodes (it is called as Au-PB-NCs/GCE and PB-NCs/GCE respectively) to study the electrocatalytic activity of hydrazine molecules as a model system. The exact size of the PB-NCs and the nature of the distribution of AuNPs into the Au-PB-NCs matrix are confirmed by high-resolution transmission electron microscopy (HR-TEM) and high-angle annular dark-field scanning transmission electron microscopic (HAADF-STEM) analysis. X-ray diffraction (XRD) and X-ray photon electron microscopy (XPS) results reveal that the PB-NCs has high crystalline and the oxidation state of Au is Au 0 and Au + in Au-PB-NCs. Compared with PB-NCs/GCE, the Au-PB-NCs/GCE showed higher redox current density and improved charge transfer kinetics in electrochemical measurements. Remarkably, it exhibits higher electrocatalytic oxidation current and excellent amperometric response with the linear range of 0–40 µM for hydrazine molecule when compared with PB-NCs/GCE. The calculated low detection limit and sensitivity value of Au-PB-NCs/GCE is 0.709 µM and 111 µA. cm −2 . µM −1 , respectively, which are comparable with reported literature. The selectivity and stability of electrooxidation of hydrazine molecule on fabricated Au-PB-NCs/GCE platform is investigated by amperometric method. The obtained results clearly indicate that Au-PB-NCs/GCE has excellent stability and selectivity towards hydrazine sensing without the impact of other interference. Also, the developed Au-PB-NCs/GCE sensor platform is applied to the real water samples analysis and showed the results of good recovery, reproducibility and repeatability, which implies its feasibility for realistic application in hydrazine estimation.

Electron and photon responses of CWO scintillation crystal

The electron response and photon response of cadmium tungstate crystal (CWO) scintillation crystal have been investigated. For the photon response measurement, the 133Ba, 22Na, 137Cs and 60Co were used as radioactive sources in the energy range of 356–1332 keV. For the electron response measurement, the 137Cs source with gamma energy at 662 keV was used for the measurement of the coincidence electron energy spectra at seven scattering angles from 30° to 120°. The seven consistent electron energies were found in the range of 101.27–443.27 keV. The light yield results for both techniques showed a slight increase when gamma energy increased. Besides, for the energy resolutions and electron energy resolutions, the graph showed the relationship between the electron energy resolution and the inverse of the square root of the electron energy.

Design and Testing of the Front-End Electronics of WCDA in LHAASO

Water Cherenkov detector array (WCDA) is one of the key parts of the Large High Altitude Air Shower Observatory (LHAASO), the construction of which was completed by the end of 2020. The WCDA covers a 78 000-m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area and there exist 3120 large size photomultiplier tubes (PMTs) in three ponds: 8-in PMTs are used in WCDA pond No. 1 and 20-in PMTs are used in ponds No. 2 and No. 3. The front-end electronics (FEE) system based on multigain measurement technique is designed to achieve both high-precision time and charge measurements over a large dynamic range from single photon electron (S.P.E.) to 4000 P.E. (for water pond No. 1)/1800 P.E. (for water ponds No. 2 and No. 3). To achieve a high-quality clock distribution and phase alignment as well as mixed transmission of data, clock, and commands in one fiber over a long distance, an enhanced white rabbit (WR) technique is used. Testing of all the 350 FEE modules for the WCDA is presented in this article. Test results indicate that the charge resolution is better than 20% at S.P.E. and 1% at 1800/4000 P.E. and the time resolution is better than 300 ps root mean square (rms), which successfully meets the application requirement. All the FEE modules have been fabricated and installed for the LHAASO WCDA from 2018 to 2020, and the initial commissioning operation indicates that the FEEs function well.

Structure, small polaron hopping conduction and relaxor behavior of Gd2NiMnO6 double perovskite

In this study, double perovskite Gd2NiMnO6 is prepared via auto–ignition method. Rietveld refinement of the XRD profile confirms the single phase monoclinic structure with space group P21/n. The cation Ni exhibits mixed valence state (+2/+4) and Mn exhibits +4 valence state. Grain, grain boundary and dc conductivity increase with temperature indicating the semi–conductive nature of the material. The grain conductivity is much higher and activation energy for grain conductivity is much lower than the grain boundary. The activation energy for dc conduction and hopping energy are almost identical at different temperature regions. The charge conduction mechanism follows non–overlapping small polaron tunnelling (NSPT) model. Different Mott's parameters confirm small polaron hopping. The polaron hopping mechanism is non–adiabatic in nature. Time–temperature superposition principle confirms the temperature independent nature of hopping mechanism. The value of electron photon coupling constant is 8.27 which confirms the strong electron–phonon coupling in this material. The dielectric relaxor behavior is found to follow modified Curie–Weiss law which becomes more conform with frequency. The value of co–efficient of diffuseness lies in the range 1.69–1.96 which confirms the diffuse behavior of the material.

Facilely Solution‐Processed Lithium Carbonate for Tailoring Electron Injection in High‐Performance Inverted Near‐UV Organic Light‐Emitting Diodes

Electron injection plays a key role in electron–photon conversion properties of inverted UV–visible organic light‐emitting diodes (OLEDs). Herein, facilely prepared solution‐processed lithium carbonate (Li2CO3) formic acid and boric acid solutions for tailoring electron injection in inverted near‐UV (NUV) OLEDs are studied. Superior film morphology and exceptional electronic properties of spin‐coated Li2CO3 films are examined by atomic force microscopy, X‐ray/ultraviolet photoelectron spectroscopy, current–voltage curves, and impedance spectroscopy. Efficient inverted NUV OLEDs are assembled using wide‐bandgap molecule of 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole as emissive layer, showing maximum radiance of 5.24 mW cm−2 (2.28 mW cm−2) and external quantum efficiency of 2.47% (2.17%) with an optimal Li2CO3 formic acid of 3 mg ml−1 (Li2CO3 boric acid of 7 mg ml−1) as electron injection tailoring. The NUV emission shows electroluminescence peaks of 404–406 nm and full width at half maximum of 52–56 nm. The results provide some feasible approaches for enhancing the performance of organic electronic devices, which require strong electron injection/extraction and accelerate industrialization.

Dynamic structure of highly disordered manganese oxide catalysts for low-temperature CO oxidation

The dynamic structures of a highly disordered manganese oxide catalyst (HDMO) and intermediates were thoroughly studied from precursor to working catalyst. Excellent CO oxidation activity at low temperatures (T50 = 83 °C) was performed over a HDMO in the presence of H2O and CO2. The specific reaction rate of 4.56 μmolCO·gcat−1·s−1 at 90 °C was approximately 25 times and 15 times higher than those of bixbyite-type α-Mn2O3 and cryptomelane-type α-MnO2, respectively. With X-ray photon electron spectroscopy (XPS), we reveal that more surface oxygen vacancies (Ov) and adsorbed oxygen species from the highly disordered structure could promote the redox property and oxygen release capability. In situ Raman and DRIFTS spectroscopy were used to identify a dynamic surface phase transformation during CO adsorption and oxidation. In combination with kinetic studies of CO oxidation, we conclude that there are two mixed mechanisms for CO oxidation over HDMO: the Langmuir-Hinshelwood (L-H) mechanism and the Mars-van Krevelen (MvK) mechanism.

A PIPS + SrI2(Eu) detector for atmospheric radioxenon monitoring

The PIPS–SrI2(Eu) is a prototype atmospheric radioxenon detection system designed at Oregon State University in support of international efforts towards monitoring clandestine nuclear weapon testing activities. This detector aims to address some shortcomings found in currently deployed beta–gamma atmospheric radioxenon detection systems, such as lackluster energy resolution and memory effect, by employing modern detection materials and readout. The system uses a PIPSBox, a silicon-based gas cell, for electron detection, and a pair of ultrabright, D-shaped SrI2(Eu) scintillators coupled to silicon photomultipliers for photon detection. A custom eight-channel digital pulse processor equipped with a field programmable gate-array (FPGA) identifies electron–photon coincidences between the volumes in near real-time. Gas samples of the four radioxenon isotopes of interest were independently measured with the PIPS–SrI2(Eu) detection system to determine energy resolution and efficiency. Application of FPGA-based coincidence discrimination in near real-time reduced the ambient background count rate by 95.85 ± 0.04%. Using parameters from the Xenon International gas processing unit and assuming a blank sample and zero memory effect the minimum detectable concentrations (MDCs) for the isotopes were calculated to be 0.12 ± 0.03, 0.27 ± 0.05, 0.15 ± 0.02, and 1.00 ± 0.08 mBq/m3 air for 131mXe, 133Xe, 133mXe, and 135Xe, respectively. These MDC estimates compare well with other radioxenon detection systems employed in the International Monitoring System (IMS) and indicate that the PIPS–SrI2(Eu) is in compliance with the Comprehensive Nuclear Test-Ban-Treaty Organization (CTBTO) sensitivity requirement of ≤1 mBq/m3 for 133Xe.

Genome-Wide Characterization of B-Box Gene Family and Its Roles in Responses to Light Quality and Cold Stress in Tomato.

Perceiving incoming environmental information is critical for optimizing plant growth and development. Multiple B-box proteins (BBXs) play essential roles in light-dependent developmental processes in plants. However, whether BBXs function as a signal integrator between light and temperature in tomato plants remains elusive. In this study, 31 SlBBX genes were identified from the newly released tomato (Solanum lycopersicum) genome sequences and were clustered into five subgroups. Gene structure and protein motif analyses showed relatively high conservation of closely clustered SlBBX genes within each subgroup; however, genome mapping analysis indicated the uneven distribution of the SlBBX genes on tomato chromosomes. Promoter cis-regulatory elements prediction and gene expression indicated that SlBBX genes were highly responsive to light, hormones, and stress conditions. Reverse genetic approaches revealed that disruption of SlBBX7, SlBBX9, and SlBBX20 largely suppressed the cold tolerance of tomato plants. Furthermore, the impairment of SlBBX7, SlBBX9, and SlBBX20 suppressed the photosynthetic response immediately after cold stress. Due to the impairment of non-photochemical quenching (NPQ), the excess photon energy and electron flow excited by low temperature were not consumed in SlBBX7-, SlBBX9-, and SlBBX20- silenced plants, leading to the over reduction of electron carriers and damage of the photosystem. Our study emphasized the positive roles of light signaling transcription factors SlBBXs in cold tolerance in tomato plants, which may improve the current understanding of how plants integrate light and temperature signals to adapt to adverse environments.

Molecularly Imprinted Scaffold Based on poly (3-aminobenzoic acid) for Electrochemical Sensing of Vitamin B6

Inadequate or excess consumption of Vitamin B6 (Vit B6) can have ill effects on the overall well-being of humans, thereby making it necessary to control their content and composition in the food we consume. A simple sensor is fabricated in this work for Vit B6 detection based on employing an electropolymerized molecularly imprinted polymer (MIP) of 3-amino benzoic acid. The poly (3- aminobenzoic acid) (P-(3ABA)) film was electrodeposited by potentiodynamic cycling of potential with and without Vit B6 (template) on carbon fiber paper electrode (CFP). The modified working electrodes were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Field emission scanning microscopy, Energy dispersive X-ray spectrometry, Fourier Transform Infrared spectroscopy, Optical profilometry and X-ray photon electron spectroscopy were used for characterization. Nyquist plots revealed least charge transfer resistance at MIP/CFP than other control electrodes due to the molecularly imprinted sites. Under the optimized experimental conditions the developed MIP sensor showed a linear range 0.6 μM to 700 μM, with a detection limit of 0.010 μM. Also a value of the imprinting factor (β = 3.50) indicates very good selectivity of the prepared sensor towards Vit B6 detection over its structurally similar analogues in the analysis of real sample matrices.

Spin dynamics in GaN/Al0.1Ga0.9N quantum well with complex band edge structure

Spectrally distinguished spin relaxation dynamics in a single GaN/Al0.1Ga0.9N quantum well was investigated by a time-resolved Kerr rotation spectrum at room temperature. Three spin relaxation processes were well distinguished by a photon energy upon the excitation energy being resonated with the bandgap of various layers. It is observed that the electron spin relaxation time of 7 ps in a GaN quantum well is much shorter than that of 140 ps in an Al0.1Ga0.9N barrier layer due to the considerable polarization electric field at a GaN/Al0.1Ga0.9N heterointerface. For electrons in bulk GaN and Al0.1Ga0.9N, the dominant role of electron–photon scattering and alloy disorder scattering in the anisotropic D'yakonov–Perel’ (DP) relaxation was revealed by the photoexcited electron density and magnetic field dependence of the spin relaxation time.

Red-emission analysis, Judd–Ofelt intensity parameters and laser properties of CdMgZnO:xEu3+ nanocrystals: the effects of Eu3+ concentration

In this paper, we discuss a strong red Eu3+-concentration-dependent emission line associated with an electric dipole transition (5D0 → 7F2) at 616 nm in CdMgZnO:xEu3+ nanocrystals made via a sol–gel synthesis route. Oxygen interstitial defects created by the presence of a mixed-valence state of Eu 3+ and Eu2+ ions as rare-earth cations lead to a structural distortion which is confirmed by x-ray photon electron spectroscopy. The Judd–Ofelt intensity parameters, Ω2 and Ω4, obtained from the emission spectra, show a trend for Ω2 > Ω4 that translates to stronger covalence and a stable local structure surrounding the Eu3+ ions in CdMgZnO nanocrystals. The asymmetry ratio (R o), radiative lifetime (), branching ratio , stimulated emission cross-section, and the gain bandwidth (δ e× Δλ eff) for 5D0 are computed and analysed. A radiative lifetime ranging from 789 to 984 µs points to a suitable material for orange-red fluorescent phosphors for lighting and display technologies. The gain bandwidth (δ e× Δλ eff), which is dependent on the Eu3+ concentration, suggests the use of the CdMgZnO:xEu3+ nanocrystal material in fibre amplifiers, while the sample with x = 1.5%, which yields the largest emission cross-section (15.79 × 10−22 cm2), the highest gain bandwidth (28.8 × 10−28 cm3), and a high branching ratio (71%), is the best candidate for red laser applications.

Photon-recycling effect in perovskites for photovoltaic applications: a Monte Carlo study.

Photon recycling has been shown to play an important role in the optoelectronic properties and device performance of perovskite solar cells recently. However, there lacks an analytical method to accurately predict the dynamics of charge carriers and photons and the device performance with photon recycling due to the complexity of multiple electron-photon conversion processes involved in photon recycling. We propose a model based on the Monte Carlo simulation method that combines charge carrier diffusion and photon radiation transport to analyze the effects of photon recycling on electron-photon dynamics and device performance of perovskite solar cells. We show that the carrier lifetime can be significantly boosted by photon recycling in the radiative limit, which yields a 37 meV increase in the open-circuit voltage for a 500 nm thick perovskite solar cell. Our results provide insights for the working mechanisms of perovskite solar cells, and the new model can be further applied to other types of solar cells with photon recycling.

Ultrafast Pump‐Probe Spectroscopy—A Powerful Tool for Tracking Spin‐Quantum Dynamics in Metal Halide Perovskites

AbstractUltrafast pump‐probe spectroscopy provides a powerful tool for deep insight into sophisticated electron–hole dynamics for materials development and devices optimization, particularly for emerging metal halide perovskites (hereafter, termed perovskites), due to their great potentials for optoelectronic and photonic applications in solar cells, light‐emitting diodes, photodetectors, and lasers. Recently, flourishing spin‐related photophysical phenomena (such as, Rashba effect, optical Stark effect, and magneto­optical effect) in perovskites and their relevant devices have experimentally been observed, attributed to huge spin‐orbital coupling effect and strong interaction of electron–photon in perovskites. However, fundamental understanding of spin‐dependent photophysics in perovskites is still at its nascent stage. In recent few years, circularly‐polarized ultrafast pump‐probe technique has pushed burgeoning development of spin‐selective photophysics in perovskites for spintronic device applications. Nevertheless, few review papers summarize this emerging field systematically, completely, and insightfully. Herein, to evoke broader attraction and research interest, recent advances in spin‐quantum dynamics in perovskites revealed by circularly‐polarized pump‐probe technique are reviewed: from the fundamentals and theories of circularly‐polarized ultrafast pump‐probe transient absorption and time‐resolved Faraday rotation spectroscopy; to the recent enlightening works on spin relaxation dynamics, spin‐selective exciton optical Stark effect, magnetic spin effect, and spin polarization dynamics. Finally, current challenges and perspectives are given.

Beyond Fermi’s golden rule in free-electron quantum electrodynamics: acceleration/radiation correspondence

In this article, we present a unified reciprocal quantum electrodynamics (QED) formulation of free-electron and quantum–light interaction. For electron–light interactions, we bridge the underlying theories of photon-induced near-field electron microscopy, laser-induced particle accelerators, and radiation sources, such as quantum free electron laser, transition radiation and Smith-Purcell effect. We demonstrate an electron–photon spectral reciprocity relation between the electron energy loss/gain and the radiation spectra. This ‘acceleration/radiation correspondence’ (ARC) conserves the electron energy, and photon number exchanged, that is, ΔE/ℏω + Δν q = 0, and in the representation of a quantum electron wavepacket, displays explicit dependence on the history-dependent phase and shape of the wavepacket configuration. It originates from an interaction-induced quantum interference term that is usually ignored in Fermi’s golden rule analyses, but is kept in our combined quantum free electron–photon state formulation. We apply this formulation to both stimulated interaction and spontaneous emission of classical and quantum light by the quantum-featured electrons. The ‘spontaneous’ emissions of coherent states (‘classical’ light) are remarked and squeezed states of quantum light is shown to be enhanced with squeezing. This reciprocal QED formulation has promise for extensions to other fundamental research issues in quantum light and quantum matter interactions.

Driven electronic bridge processes via defect states in Th229 -doped crystals

The electronic defect states resulting from doping $^{229}$Th in CaF$_2$ offer a unique opportunity to excite the nuclear isomeric state $^{229m}$Th at approximately 8 eV via electronic bridge mechanisms. We consider bridge schemes involving stimulated emission and absorption using an optical laser. The role of different multipole contributions, both for the emitted or absorbed photon and nuclear transition, to the total bridge rates are investigated theoretically. We show that the electric dipole component is dominant for the electronic bridge photon. In contradistinction, the electric quadrupole channel of the $^{229}$Th isomeric transition plays the dominant role for the bridge processes presented. The driven bridge rates are discussed in the context of background signals in the crystal environment and of implementation methods. We show that inverse electronic bridge processes quenching the isomeric state population can improve the performance of a solid-state nuclear clock based on $^{229m}$Th.