Electron Decay Research Articles

Transient Absorption Spectrum Analysis for Photothermal Catalysis Perovskite Materials

To gain insight into photocatalytic behavior, transient absorption spectroscopy (TAS) was used to study LaCoxMn1−xO3, LaMnxNi1−xO3 and LaNixCo1−xO3 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) on a microsecond time scale. The results show that the electron lifetime is key to determining the photocatalytic reduction of CO2. This is the first time that the photogenerated electron lifetime in perovskite has been proposed to express the performance of the photocatalytic reduction of CO2 with H2O into CH4. In all cases, the decay curve can be well explained by two consecutive first-order kinetics, indicating that the electron exists within two major populations: one with a short lifetime and the other one with a long lifetime. The long-lived electrons are the rate-limiting species for the photocatalytic reaction and are related to the activity of the photocatalytic reduction of CO2 with H2O to produce CH4. For different photocatalysts, we find that the longer the electron decay lifetime is, the stronger the electron de-trapping ability is, and the electrons perform more activity. In this paper, TAS can not only detect the micro-dynamics process of carriers, but it is also demonstrated to be an easy and effective method for screening the most active catalyst in various catalysts for the photocatalytic reduction of CO2 with H2O accurately and quickly.

Direct time-resolved plasma characterization with broadband terahertz light pulses.

We report here the results of comprehensive plasma characterization and diagnostics by analyzing time-resolved absorption spectra of short ultrabroadband (0.1-50 THz) pulses propagated through the test plasma. Spectral analysis of plasma-induced absorption of such THz pulses provides very direct, in situ, high dynamical range, potentially single-shot access to the plasma density, plasma decay time, electron temperature, and ballistic dynamics of the plasma expansion. We have demonstrated a proof-of-principle measurement of plasma created by an intense laser beam. In particular, we showed a reliable measurement of plasma densities from around 10^{16} to 10^{20}cm^{-3}. Apart from the plasma parameters, this method allowed us to reconstruct peak intensity inside the plasma spot and to observe a very early stage of plasma evolution after its excitation.

Micro drilling of PMMA with double-pulse femtosecond laser

Micro holes drilling in polymers have a variety of applications in industry and research. Especially, the fabrication of micro hole with high aspect ratio is a key technology for advanced applications. In this work, we report an improvement in drilling on poly-methyl methacrylate (PMMA) by using double-pulse femtosecond laser. Compared to single pulse, the achievable depth by double pulses can be increased by 50% when the pulse delay is 100 fs and gradually decreases with delay increasing. The depth evolution with the increasing of pulse number is investigated. When the micro hole depth reaches a certain value, the processing speed of double pulse is less restricted than single pulse. Furthermore, the relationship between the depth improvement and electrons decay together with absorption increase is studied.

Revisiting molecularly conformation-planarized organic dyes for NIR-II fluorescence imaging.

Fluorescence imaging in the second window (NIR-II, 1000-1700 nm) provides deeper penetration depth and higher resolution, but there is still a dilemma for designing NIR-II dyes for simultaneously enhancing fluorescence efficiency and prolonging excitation wavelength. Herein, a molecular conformation planarization strategy has been revisited to guide the synthesis of two donor-acceptor-donor dyes (named T-BBT and BT-BBT). On the one hand, conformational planarization can extend the absorption peaks of T-BBT and BT-BBT to the NIR region with high molar extinction coefficients of 30.5 × 103 and 16.4 × 103 L (mol-1 cm-1) at 1064 nm, respectively. On the other hand, structural rigidity can weaken electronic vibration coupling-related non-radiative decay pathways, whereby both T-BBT and BT-BBT display rather high fluorescence efficiencies of 3.6% and 13.5% in solution. Furthermore, a molecular doping strategy is adopted to alleviate fluorescence quenching in the aggregated state by suppressing long-distance energy migration, and 2.5 wt% doped BT-BBT nanoparticles show a high fluorescence efficiency of 2.0%, which enables the application of in vivo deep NIR-II fluorescence imaging for vessels and tumors with high resolution under 980 nm excitation. This work demonstrates that organic dyes with structural planarization can bridge the gap between NIR-II absorption and fluorescence efficiency.

Low-temperature vibronic spectroscopy of condensed chromophore exhibiting inhomogeneous distribution of vibrational frequencies in a mixed quantum-classical environment.

This work has been motivated by the recent paper by the author [M. Toutounji, Phys. Chem. Chem. Phys., 2021, 23, 21981] whereby a mixed quantum-classical Liouville equation was used to probe the spectroscopy and dynamics of a spin-boson system. A mixed quantum-classical Liouville equation treats the system of interest quantum mechanically, the bath classically, and the coupling term mixed quantum-classical mechanically. This paper offers a two-fold advantage: correcting the treatment of the electronic transition decay (width in frequency domain) and assessing the local heterogeneous vibrational structure. The homogeneous linear absorption spectrum of a chromophore embedded in a mixed quantum-classical environment at low temperature is composed of a sharp peak called a zero-phonon line (ZPL) and a broad phonon sideband (PSB), whereby the ZPL and the PSB are assimilated by a Lorentzian function and Voigt profiles, respectively. The PSB, in this case, is characterized by a local heterogeneous structure due to a dispersive medium of vibrations, modeled by vibrational Gaussian distributions to represent the arising inhomogeneous broadening and Lorentzians to model the homogeneous vibrations. This description seems to model proteins and amorphous solids exhibiting a local heterogeneous structure as both electronic and vibrational inhomogeneous broadening seems to be large in these media. This work provides a derivation of linear absorption lineshape and vibronic transition dipole moment time correlation functions, both of which account for pure electronic dephasing (ZPL width) the Voigt profile description of the phonon profiles (PSB) in dispersive media.

Interatomic Coulombic decay in small helium clusters.

Interatomic Coulombic decay (ICD) is an ultrafast non-radiative electronic decay process wherein an excited atom transfers its excess energy to a neighboring species leading to the ionization of the latter. In helium clusters, ICD can take place, for example, after simultaneous ionization and excitation of one helium atom within the cluster. After ICD, two helium ions are created and the system undergoes a Coulomb explosion. In this work, we investigate theoretically ICD in small helium clusters containing between two and seven atoms and compare our findings to two sets of coincidence measurements on clusters of different mean sizes. We provide a prediction on the lifetime of the excited dimer and show that ICD is faster for larger clusters. This is due to (i) the increased number of neighboring atoms (and therefore the number of decay channels) and (ii) the substantial decrease of the interatomic distances. In order to provide more details on the decay dynamics, we report on the kinetic-energy distributions of the helium ions. These distributions clearly show that the ions may undergo charge exchange with the neutral atoms within the cluster, such process is known as frustrated Coulomb explosion. The probability for these charge-exchange processes increases with the size of the clusters and is reflected in our calculated and measured kinetic-energy distributions. These distributions are therefore characteristics of the size distribution of small helium clusters.

Sodium ion doped graphitic carbon nitride with high crystallinity for superior photocatalytic hydrogen evolution efficiency

Photogenerated electron decay kinetics studies unravel the correlation between high crystallinity of Na+-doped and NH4Cl-assisted Na+-doped graphitic carbon nitride and their superior photocatalytic water splitting hydrogen evolution activities.

Electroweak-boson production from small to large systems with ALICE at the LHC

Results on the recent measurements of the electroweak-boson production performed by the ALICE Collaboration are reported. The W±-boson production was measured at midrapidity in pp collisions at √S = 13 TeV, via the electronic decay of the boson. It was also measured in association with a hadron emitted back-to-back with respect to the electron. In heavy-ion collisions, the W±- and Z0-boson production was measured at forward rapidity in p–Pb collisions at √SNN = 8.16 TeV and Pb–Pb collisions at √SNN = 5.02 TeV, in their muonic decay channel. Measurements in pp collisions shed light on multiple parton interactions and colour reconnection mechanisms. In heavy-ion collisions the measurements of electroweak bosons allow to probe the initial state of the collision.

Enhanced thermal assisted photocatalysis reduction of carbon dioxide over a Fe2−xGaxO3 solid solution

The CO evolution rate of Fe1.96Ga0.04O3 is about 2.4 times that of pure Fe2O3. The introduction of Ga changes the electron spin state in CB, from spin up for Fe2O3 to spin down for Fe2−xGaxO3, resulting in the suppression of electron decay in VB.

Nanoplasmon‐Nanoplasma Transition in Cu Nanoparticle: Distinction of Electron Emission

AbstractThe electron response of nanoplasmon and nanoplasma in the laser field is greatly important for improving the functionality and efficiency of many potential applications. However, how and under what conditions the nanoplasmon‐nanoplasma transition works remains poorly understood due to radiation damage and charge buildup. Utilizing the combined aerodynamic lens and velocity map imaging spectrometer, this transition mediated by different mechanisms are demonstrated, as verified by the distinct photoelectron momentum distributions from Cu nanoparticles. Initially the polarization‐dependent distributions emphasize the domination of surface emission driven by the plasmonic field. Subsequently the transition starts and the competition of volume‐multiphoton and thermionic emission plays the intermediate state dominating the transition process. Finally, a complete plasma is generated with the leading role of thermionic emission, which is confirmed by first observing the correlated electronic decay in metal nanoparticles. These findings bridge the gap between electron emission in nanoplasmonic and nanoplasma states and identify the mechanism‐specific contributions, which will offer general principles for designing nanostructure and laser fields to control electron excitation and emission in practice.

Three-Electron Dynamics of the Interparticle Coulombic Decay in Doubly Excited Clusters with One-Dimensional Continuum Confinement.

A detailed analysis of the electronic structure and decay dynamics in a symmetric system with three electrons in three linearly aligned binding sites representing quantum dots (QDs) is given. The two outer A QDs are two-level potentials and can act as (virtual) photon emitters, whereas the central B QD can be ionized from its one level into a continuum confined on the QD axis upon absorbing virtual photons in the inter-Coulombic decay (ICD) process. Two scenarios in such an ABA array are explored. One ICD process is from a singly excited resonance state, whose decay releasing one virtual photon we find superimposed with resonance energy transfer among both A QDs. Moreover, the decay-process manifold for a doubly excited (DE) resonance is explored, in which collective ICD among all three sites and excited ICD among the outer QDs engage. Rates for all processes are found to be extremely low, although ICD rates with two neighbors are predicted to double compared to ICD among two sites only. The slowing is caused by Coulomb barriers imposed from ground or excited state electrons in the A sites. Outliers occur on the one hand at short distances, where the charge transfer among QDs mixes the possible decay pathways. On the other hand, we discovered a shape resonance-enhanced DE-ICD pathway, in which an excited and localized B* shape resonance state forms, which is able to decay quickly into the final ICD continuum.

Structural and visible fluorescence traits of Dy3+ ion activated Lu1.5Y1.5Al5O12 phosphors

In the current work, a series of Lu1.5Y1.5Al5O12 (LuYAG) phosphors doped with different Dy3+ ion concentrations (0.5, 1, 2, 3, 4, and 5 at% in nominal) have been synthesized by high-temperature solid-phase approach and characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, transmission electron microscopy, optical absorption, emission, and decay lifetimes. The shape and position of Dy3+ ion absorption peaks were consistent in all samples, and the absorption peak intensity increased with enhancing Dy3+ concentration. Under λexci. = 448 nm, 4F9/2 → 6H15/2, 13/2, 11/2, 9/2 emission transitions have been identified in which the 4F9/2 → 6H13/2 transition possesses the highest intensity. Luminescence decay times were evaluated for Dy3+: 4F9/2 level. Relying on the absorption and luminescence spectra, along with fluorescence decay patterns, the optimal doping concentration of 1 at% was identified. The energy transfer process between Dy–Dy ions was discussed and utilized to explain the concentration quenching phenomenon. Notably, 1 at% Dy: LuYAG could be used as a potential candidate for commercial yellow phosphors.

Studying Same-Sign Top Pair Production through Top-Higgs FCNC Interactions at the HL-LHC

We investigate the potential of the HL-LHC for discovering new physics effects via the same-sign top pair signatures. We focus on the semileptonic (electron and muon) decay of the top quarks and study the reach for a simplified model approach where top quark flavor changing could occur through a neutral scalar exchange. A relatively smaller background contribution and clean signature are the advantages of the leptonic decay mode of the same-sign W bosons in the same-sign production processes of top quark pairs. Assuming the FCNC between top quark, up-type quark, and scalar boson from the new physics interactions, the branchings could be excluded of the order O 1 0 − 4 . We use angular observables of the same-sign lepton pairs and the top quark kinematics in the process which provide the possibility of separation of new physics signal from the SM backgrounds using machine-learning techniques. We find that the same-sign top quark pair production is quite capable of testing the top-Higgs FCNCs at the HL-LHC.

Electron-Impact Excitation of the λ190.8 nm and λ179.9 nm Intercombination Lines in the Tl+ Ion

The results of experimental and theoretical studies on electron-impact excitation of the 6s6p P1° 3→6s2 S0 1 (λ190.8 nm) and 6s7s S0 1→6s6p P1° 3 (λ179.9 nm) intercombination transitions in the single-charged thallium ion are presented. The crossed-beams technique was used in combination with a spectroscopic method in the experiment. A distinct structure revealed in the cross-sections of both lines results from electron decay of atomic autoionizing states and radiative transitions from upper ionic levels. The dominant mechanism of the structure formation was the Coster–Kronig process. Relativistic distorted wave calculations were performed to obtain emission cross-sections for the above transitions. The absolute values of the cross-sections were found to be (0.25 ± 0.08) × 10−16 cm2 (λ190.8 nm) and (0.10 ± 0.04) × 10−16 cm2 (λ179.9 nm) at the electron energy of 100 eV.

Joint photon-electron Lorentz violation parameter plane from LHAASO data

The Large High Altitude Air Shower Observatory (LHAASO) is one of the most sensitive gamma-ray detector arrays, whose ultrahigh-energy (UHE) work bands not only help to study the origin and acceleration mechanism of UHE cosmic rays, but also provide the opportunity to test fundamental physics concepts such as Lorentz symmetry. LHAASO directly observes the 1.42PeV highest-energy photon. By adopting the synchrotion self-Compton model, LHAASO also suggests that the 1.12PeV high-energy photon from Crab Nebula corresponds to a 2.3PeV high-energy electron. We study the 1.42PeV photon decay and the 2.3PeV electron decay to perform a joint analysis on photon and electron two-dimensional Lorentz violation (LV) parameter plane. Our analysis is systematic and comprehensive, and we naturally get the strictest constraints from merely considering photon LV effect in photon decay and electron LV effect in electron decay. Our result also permits the parameter space for new physics beyond relativity.

The LiNA experiment: Development of multi-layered time projection chamber

The neutron lifetime is an important parameter for particle physics and cosmology. There are two types of measurement methods carried out so far, but their results are in disagreement with 4.6σ. In the beam method carried out at J-PARC, a neutron bunch passes through a gaseous detector Time Projection Chamber (TPC). The TPC counts a beta decay electron and a neutron flux by 3He(n,p)3H reaction. However, the result of this experiment still has large uncertainty. The largest two contributions to the uncertainty are background contamination and signal cut inefficiency. A new experiment, the LiNA experiment, was proposed to overcome the problems. This system suppresses background events that come from the detector wall and improves signal cut efficiency by applying a uniform magnetic field in parallel to the beam axis. The detector system which has three drift layers was developed at Kyushu University. The detector and magnet integration tests were carried out at KEK. The β-ray source was installed in the center of the detector to imitate the neutron beta decay electron. The γ-ray source was installed on the side of the detector to evaluate background suppression with the field. It was confirmed that β-ray is confined while γ-ray background is suppressed to 3% in the signal region. This system can measure the neutron lifetime with an accuracy of 0.2% by 30 days measurement at J-PARC.

Quantifying Radiation Belt Electron Loss Processes at L

We present a comprehensive analysis of the processes that lead to quasilinear pitch-angle-scattering loss of electrons from the L<4 region of the Earth's inner magnetosphere during geomagnetically quiet times. We consider scattering via Coulomb collisions, hiss waves, lightning-generated whistler (LGW) waves, waves from ground-based very-low-frequency (VLF) transmitters, and electromagnetic ion cyclotron (EMIC) waves. The amplitude, frequency, and wave normal angle spectra of these waves are parameterized with empirical wave models, which are then used to compute pitch-angle diffusion coefficients. From these coefficients, we estimate the decay timescales, or lifetimes, of 30keV to 4MeV electrons and compare the results with timescales obtained from in-situ observations. We demonstrate good quantitative agreement between the two over most of the L and energy range under investigation. Our analysis suggests that the electron decay timescales are very sensitive to the choice of plasmaspheric density model. At L<2, where our theoretical lifetimes do not agree well with the observations, we show that including Coulomb energy drag (ionization energy loss) in our calculations significantly improves the quantitative agreement with the observed decay timescales. We also use an accurate model of the geomagnetic field to provide an estimate of the effect that the drift-loss cone has on the theoretically calculated electron lifetimes, which are usually obtained using an axisymmetric dipole field.

The Importance of Ion Composition for Radiation Belt Modeling

AbstractThe banded structure of electromagnetic ion cyclotron (EMIC) wave spectra and their resonant interactions with radiation belt electrons depend on the cold ion composition. However, there is a great deal of uncertainty in the composition in the inner magnetosphere due to difficulties in direct flux measurements. Here, we show that the hydrogen and helium band wave spectra are most consistent with a helium and oxygen composition of a few percent. Less than 10% of hydrogen band wave intensity is consistent with a high helium fraction of ∼20%. Similarly, only ∼20% helium band wave intensity is consistent with an oxygen torus ion composition. Furthermore, we find that the decay of the ultra‐relativistic electrons in the radiation belts by EMIC waves depends on the ion composition. The decay is most sensitive to the helium fraction, and the strongest agreement with Van Allen Probes data is found when the helium fraction is a few percent. We suggest that more observations of the cold ion composition would significantly help understand and set constraints on the decay of ultrarelativistic electrons in the radiation belts.

Complete collision data set for electrons scattering on molecular hydrogen and its isotopologues: III. Vibrational excitation via electronic excitation and radiative decay

We present state-resolved cross sections for vibrational excitation via electronic excitation followed by radiative decay (ERD), for electrons scattering on all bound vibrational levels of the ground electronic state (X1Σg+) of molecular hydrogen and its isotopologues (H2, HD, HT, D2, DT and T2). We consider excitation of the singlet n=2–3 states (where n refers to the united-atoms-limit principle quantum number) and account for all possible decay pathways back to the bound vibrational levels of the ground electronic state (X1Σg+) to produce an estimate for the ERD cross sections. A selection of the results are presented in graphical form and a full data set is provided as both numerical values and analytic fit functions in supplementary data files. The uncertainty in the cross sections is estimated to be 11%, except for scattering on the highest bound vibrational level of HD, HT, D2, and DT, where the uncertainty is 21%. The data can be downloaded from the MCCC database at mccc-db.org.

Ultrafast Dynamics of Photoinduced Electron Transfer in Bay-Aryl-Substituted Perylene Diimide Derivatives.

Blends of donors and acceptors have been widely used in bulk-heterojunction solar cells to have exciton formation and charge separation by photoinduced electron transfer (PET). In this work, we have synthesized perylene diimide (PDI)-based materials having different aryl substituents at the bay positions (4-Anisyl-PDI, CBZ-N-Ph-PDI, and 4-Pyridyl-PDI) to understand the excited-state dynamics of electron transfer. The detailed photophysics was studied using steady-state as well as ultrafast dynamics of the excited states in different solvents. CBZ-N-Ph-PDI showed tremendous effects of the solvent on the electronic properties compared with the other two derivatives. The emission quantum yield of CBZ-N-Ph-PDI decreases drastically in dichloromethane and other polar solvents, indicating strong electron transfer. DFT calculations showed that in CBZ-N-Ph-PDI the HOMO is centered mostly on the N-phenylcarbazole and the LUMO is on the electron-poor PDI moieties. In addition, the energy levels of the HOMO and HOMO-1 in CBZ-N-Ph-PDI are estimated to be identical. The free energy change for charge separation (ΔGCS) was calculated using electrochemical and photophysical data and found to be negative for CBZ-N-Ph-PDI. The ground- and excited-state dipole moment ratios suggest that the excited state of 4-Pyridyl-PDI (1.90) is less polar than that of 4-Anisyl-PDI (3.67), which provides an idea of the lower possibility of charge separation in 4-Anisyl-PDI and 4-Pyridyl-PDI. Ultrafast photodynamics studies of 4-Anisyl-PDI, CBZ-N-Ph-PDI, and 4-Pyridyl-PDI showed fast electron transfer only in CBZ-N-Ph-PDI and not in the other PDI derivatives. It was also observed that electron transfer is faster in DCM and THF than in toluene. Ultrafast dynamics studies showed the presence of an equilibrium between electron transfer and decay from the singlet excited state. Ultrafast studies also showed the features of the N-phenylcarbazole cation and PDI anion, further confirming the intramolecular electron transfer in CBZ-N-Ph-PDI.