Electron Lifetime Research Articles

Tailoring band gaps of KBiO3-NaBiO3 heterostructures by the interface actions for enhancing visible light photoelectric response

Heterostructures with wide and narrow band gap semiconductors may harvest short and long wavelength light for enhancing photoelectric response. Here we adopt narrower-band-gap KBiO 3 to combine with wider-band-gap NaBiO 3 for KBiO 3 /NaBiO 3 heterostructures by adding KOH into NaBiO 3 . The band gaps of the heterostructures change with the ratios of KOH:NaBiO 3 in raw materials and are abnormally narrower than that of KBiO 3 . The interfaces between KBiO 3 and NaBiO 3 change with their ratios and then their interactions vary. The width and intensity of surface photovoltage spectra of the heterostructures increase notably in the visible light region, which results from prolonged lifetime of photogenerated electrons transferring from KBiO 3 to NaBiO 3 . • KBiO 3 /NaBiO 3 heterostructures are constructed with different ratios. • The band gaps of KBiO 3 /NaBiO 3 heterostructures are tailored by their interactions. • The SPV range of NaBiO 3 is expanded from 475 to 600 nm by the heterostructures.

Effect of diffusion on the peak value of energy loss observed in a LArTPC

Liquid Argon Time Projection Chamber (LArTPC) detectors observe ionization electrons to measure charged particle trajectories and energy. In a LArTPC, the long time (∼ms) between when the ionization is produced and when it is collected means that diffusion can smear the charge by an amount comparable to the spatial resolution of the detector, given by the spacing between charge sensing channels (∼mm). This smearing has an impact on the distribution of energy losses measured by each channel. In particular, the smearing increases the length of the charged particle trajectory observed by each channel, and therefore the most-probable-value (MPV) of particle energy loss recorded by that channel. We find, for example, that this effect shifts the MPV dE/dx of a muon with an energy of 1 GeV by ∼4% for a 2 ms drift time and 4.7 mm wire spacing, as in the DUNE-FD LArTPC. This has implications for the energy-scale calibration and electron lifetime measurements in a LArTPC, which both use the MPV of the muon energy loss distribution as a “standard candle”. The impact of diffusion on these calibrations is assessed.

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.

Edge modification facilitated heterogenization and exfoliation of two-dimensional nanomaterials for cancer catalytic therapy.

The rapid recombination of electron-hole pairs and limited substrates are the most critical factors astricting the effect of catalytic therapy. Thus, two-dimensional interplanar heterojunction (BiOCl/Bi2O3) that prolongs the lifetime of excited electrons and holes and extends the selectivity of substrates under ultrasound irradiation is prepared to facilitate high-performance cancer therapy. An edge modification displacing marginal BiOCl to Bi2O3 is proposed to construct the interplanar heterojunction, promoting ultrathin nanosheets exfoliation due to the enhanced edge affinity with H2O. The spontaneously aligning Fermi levels mediate a built-in electric field–guided Z-scheme interplanar heterojunction, retard electron-hole pairs recombination, and improve redox potentials. Hence, these high-powered electrons and holes are capable of catalyzing diverse and stable substrates, such as the reduction reactions, O2 → ·O2− and CO2 → CO, and oxidation reactions, GSH → GSSG and H2O → ·OH. The Z-scheme interplanar heterojunction with the extending substrates selectivity completely breaks the tumor microenvironment limitation, exhibiting high anticancer activity.

Highly Efficient CuInSe2 Sensitized TiO2 Nanotube Films for Photocathodic Protection of 316 Stainless Steel

CuInSe2 nanoparticles were successfully deposited on the surface of TiO2 nanotube arrays (NTAs) by a solvothermal method for the photocathodic protection (PCP) of metals. Compared with TiO2 NTAs, the CuInSe2/TiO2 composites exhibited stronger visible light absorption and higher photoelectric conversion efficiency. After 316 Stainless Steel (SS) was coupled with CuInSe2/TiO2, the potential of 316 SS could drop to −0.90 V. The photocurrent density of CuInSe2/TiO2 connected to 316 SS reached 140 μA cm−2, which was four times that of TiO2 NTAs. The composites exhibited a protective effect in the dark state for more than 8 h after 4 h of visible light illumination. The above could be attributed to increased visible light absorption, the extended lifetime of photogenerated electrons, and generation of oxygen vacancies.

On-Surface Synthesis and Spectroscopy of Aluminum Phthalocyanine on Superconducting Lead.

Large ordered islands of aluminum phthalocyanine (AlPc) molecules, which are unstable in air, are synthesized from ClAlPc on Pb(100) via dechlorination. Low-temperature scanning tunneling microscopy reveals that isolated AlPc molecules lose their spin moment on superconducting Pb(100). Molecular magnetism, which is detected via Yu-Shiba-Rusinov (YSR) resonances, may be restored by surrounding a molecule with an array of neighbor molecules in artificial arrays or in a self-assembled monolayer. Unlike phthalocyanine (H2Pc) or lead phthalocyanine (PbPc) monolayers, where the YSR energy was found to depend strongly on the detailed configuration of the neighboring molecules, we find a similar magnetic moment on every second molecule for AlPc. In addition, YSR resonances lead to unusually high conductance peaks that are due to vibrational excitations. Twelve vibrational modes are resolved and discussed with respect to similar results from PbPc. The enhancement of the inelastic transitions is tentatively attributed to the large amplitude of the YSR resonances and the long lifetime of electrons in the molecular bound state. By assembling neighboring molecules into configurations that differ from those of the monolayer, the YSR energy may be fine-tuned, and a simple spin-state switching device is constructed.

Numerical study on all-optical modulation characteristics of quantum cascade lasers.

To explain the phenomenon of all-optical modulation of quantum cascade laser (QCL), and explore the physics in QCL’s gain medium which consists of multiple of dielectric nanostructures with high refractive index under light injection, we modified the 1½-period model to calculate values of electron population and lifetime in each subband which is separated by the nanostructures, optical gain, current and number of photons in the cavity of a mid-infrared QCL modulated with near-infrared optical injection. The results were consistent with an experiment, where the injected light increases the electron population and lifetime, but does not affect the optical gain obviously. Our study can be helpful for optimizing its use and dielectric nanostructure design.

Stimuli-responsive heterojunctions based photo-electrocatalytic membrane reactors for reactive filtration of persistent organic pollutants

The design of semiconducting metal oxide heterojunctions is promising to overcome conventional limitations associated to photocatalysis or electrocatalysis, such as fast recombination of electron-hole pairs and poor long-term stability leading to low catalytic performance. A route to tackle this issue is to design catalysts at the atomic levels by arranging order and controlling nanoscale interfaces to yield catalytic materials with greater response rates and stability to dissolution or corrosion. The present study focuses on the formation of such nanoscale heterojunctions between TiO2 and ZnO via atomic layer deposition across conductive and porous stainless-steel substrates to develop enhanced photo-electro-responsive catalytic membrane reactors. The heterojunction nano-sheet based structures produced higher density of electron and hole pairs and offered efficient separation of charges, longer lifetime of photo-generated electrons compared to single metal oxides, resulting in enhanced photocurrent efficiency. The tailoring of both the nanoscale dimensions of the metal oxide layers and the stacking of these inorganic nano-sheets led to the development of multi-heterojunctions, of a few tens of nanometres, deposited across conductive porous substrates. The high electron mobility across the heterojunction nano-sheets increased the oxygen evolution potential from 1.4 to 1.7 eV, leading to enhanced electrochemical reactions, as well as offered photocurrent densities 2–3 times higher than pristine single metal oxide membranes. The formation of type II heterojunction structures between TiO2 and ZnO leads to band alignment at the interface, yielding an efficient charge separation mechanism and high catalytic performance. A prototype of novel cross-flow filtration module was designed in this study to support the coupling of photo-electrocatalysis on the membrane surface and simultaneous pressure driven membrane processes. The designed 3D printed modules demonstrated highly enhanced degradation of several persistent organic pollutants, leading to reactivity up to 75 × 10−3 min−1 up to 500 % greater compared to single metal oxides generated with the same conditions. The intimate and synergistic interactions across the stacked metal oxide nano-sheets enabled high catalytic efficiency and stability, opening new avenues stimuli-responsive membranes scale up and implementation in wastewater remediation and compact reactors design, where sieving and reactivity are of prime importance.

A Solid‐State Carrier Transport‐Prompted Z‐Scheme BiVO4 Quantum Dots‐Based Photocatalyst for Boosted Photocatalytic Degradation of Antibiotics

Monoclinic BiVO4 is extensively exploited in organic oxidation because of its appropriate valence band and remarkable catalytic activity. BiVO4 quantum dots not only have a high specific surface area and active sites for photocatalytic reactions, but can address the short carrier diffusion path problem. Herein, a Z‐scheme BiVO4 quantum dots/reduced graphene oxide/g‐C3N4 photocatalyst is constructed. Benefiting from the distinct BiVO4 quantum dots and layered g‐C3N4 sheets, the photocatalytic compound possesses a considerable light capture capability and surface area. The established Z‐scheme photocatalytic compound with a suitable electronic band structure and redox potential is integrated with a “synthesis and assembly” method. The sodium oleate surfactant plays an important role in the preparation of uniform BiVO4 quantum dots with a diameter of 3–6 nm. The optimized photocatalytic degradation experiments show that the ciprofloxacin and amoxicillin photocatalytic efficiencies are up to 92.2% and 70.7% in 1 h, respectively. It is shown that the improved photocatalytic activities involve in the prolonged lifetime of photogenerated electrons and fast carrier migration in the compound upon simulated sunlight exposure. Herein, a prospective stage for developing more Z‐scheme heterojunctions with excellent photocatalytic properties for antibiotic wastewater treatment and reproducible solar capture in photochemical energy conversion is offered.

Synergistic Effect of Charge Separation and Multiple Reactive Oxygen Species Generation on Boosting Photocatalytic Degradation of Fluvastatin by ZnIn2S4/Bi2WO6 Z-Scheme Heterostructured Photocatalytst.

The application of semiconductor photocatalysts with narrow band gaps is hindered by the rapid recombination of electron–hole pairs and limitation of multiple reactive oxygen species (ROS) synchronous generation. A n–n-type direct Z-scheme heterostructured photocatalyst was constructed based on the staggered band alignment of bismuth tungstate (Bi2WO6) and indium zinc sulfide (ZnIn2S4) to reveal the synergistic effect of charge separation and multiple ROS synchronous generation on boosting photocatalytic performance. Under irradiation, electrons in the conduction band (CB) of Bi2WO6 and holes in the valence band (VB) of ZnIn2S4 recombined at interface to prolong the lifetime of electrons in the CB of ZnIn2S4 and holes in the VB of Bi2WO6. Meanwhile, the multiple ROS synchronously generated to oxidize pollutant due to the strong redox ability of electrons of ZnIn2S4 and holes of Bi2WO6, which was determined by the CB potential of ZnIn2S4 and VB potential of Bi2WO6. The results provided valuable insights for the application of photocatalysts with a narrow band gap in the field of water pollution control.

Investigation on the effect of neodymium ion doping in TiO2 on the photovoltaic performance of dye-sensitized solar cells

Titanium dioxide (TiO2), neodymium (Nd3+) doped TiO2 with the doping levels of 0.3% and 0.5% were synthesised by hydrothermal method and were characterized by powder X-ray diffraction (XRD), UV–vis diffused reflectance spectroscopy (DRS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Ultraviolet X-ray photoelectron spectroscopy (UPS) and high resolution transmission electron microscopy (HRTEM). Doping of Nd3+ ions have been created new surface energy states below the conduction band of TiO2 which mediate the photoinjected electrons through TiO2 network to external load without any impediment. The Fermilevel (Ef) of TiO2 was shifted to downward direction upon Nd3+ ion doping confirmed from UPS analysis. An enhanced photoconversion efficiency (PCE) of 10.7% was achieved for the device fabricated using 0.3% Nd3+ ion doped TiO2 which is higher than that of the device with undoped TiO2 (10.1%). The noticeable increment in the PCE was due to the reduced charge recombination, longer electron lifetime and improved charge injection form LUMO of the N719 dye to the CB of TiO2.

Tailored Plasmonic Ru/OV-MoO2 on TiO2 Catalysts via Solid-Phase Interface Engineering: Toward Highly Efficient Photoassisted Li-O2 Batteries with Enhanced Cycling Reliability.

The photoassisted electrochemical reactions are considered an effective method to reduce the overpotential of Li-O2 batteries. However, achieving long-term cell cycling stability remains a challenge. Here, we report a solid-phase interfacial reaction (SPIR) strategy that introduces both oxygen vacancies (OV) and metal centers (Ru) into the MoO2 to synthesize the surface plasmon (i.e., Ru/OV-MoO2). Then, Ru/OV-MoO2 can be uniformly loaded on the TiO2 nanowires by the hydrothermal method. The plasma effect of Ru/OV-MoO2 demonstrates the effective reduction of the photoexcited electron and hole recombination to improve visible light-harvesting ability. The lifetime of electrons and holes can be extended by Ru nanoparticles, which is beneficial for promoting the formation and decomposition of Li2O2. In addition, the generated OV further enhanced the migration of electrons and Li+, thus improving the ORR performance. The Ru/OV-MT/CC cathode corroborates excellent stability and catalytic performance in the photoassisted Li-O2 battery, with an overpotential value of 0.47 V, achieving the highest energy efficiency of 93.94%, retaining at 89.13% after 800 h. This work offers a platform for preparing a stable, bifunctional catalyst with the high total activity of a photoassisted Li-O2 battery.

Development and validation of an improved model for Dye-sensitized solar cell and estimation of the optimum design parameters for maximum performance

ObjectiveThe performance of a Dye-Sensitized Solar Cell (DSSC) mainly depends on specific surface area, dye loading, pore-volume, thickness of the semiconductor layer, and electron lifetime. The optimization of these set of parameters is crucial in obtaining the best performance. The experimental optimization of the above parameters is often expensive and time consuming, therefore the present study aims for validation of an improved mathematical model and extraction of these set of parameters using the mathematical model. MethodThe current work proposes an improved mathematical model and an optimal design for Degussa P25 (DP25) based DSSC after optimizing the mathematical model formulated using continuity and transport equations. The proposed model describes the charge transport and recombination process of a DSSC. A metaheuristic-based optimization algorithm is used to extract the optimal design parameters for the DP25 based DSSC. ResultsThe J-V characteristics produced by the proposed model are qualitatively analyzed against the different reported experimental results using TiO2 (DP25), SnO2, and ZnO as photoanodes. The model results are in well agreement with the published experimental results and can be used to further optimize the performance of the DSSC. The proposed model using the extracted parameters reveals that the performance of the DSSC can be further enhanced by using optimal design variables during the development. AdvancementThis study opens a new era of research for fabricating efficient DSSCs at low cost through the combined approach of theoretical modeling and experimentation.

Unveiling the underlying interactions in Ta2NiSe5 from photoinduced lifetime change

We present a generic procedure for quantifying the interplay of electronic and lattice degrees of freedom in photo-doped insulators through a comparative analysis of theoretical many-body simulations and time- and angle-resolved photoemission spectroscopy (TR-ARPES) of the transient response of the candidate excitonic insulator Ta2NiSe5. Our analysis demonstrates that the electron-electron interactions dominate the electron-phonon ones. In particular, a detailed analysis of the TRARPES spectrum enables a clear separation of the dominant broadening (electronic lifetime) effects from the much smaller bandgap renormalization. Theoretical calculations show that the observed strong spectral broadening arises from the electronic scattering of the photo-excited particle-hole pairs and cannot be accounted for in a model in which electron-phonon interactions are dominant. We demonstrate that the magnitude of the weaker subdominant bandgap renormalization sensitively depends on the distance from the semiconductor/semimetal transition in the high-temperature state, which could explain apparent contradictions between various TR-ARPES experiments. The analysis presented here indicates that electron-electron interactions play a vital role (although not necessarily the sole one) in stabilizing the insulating state.

On the effective temperature of large sunspot umbra using AlH molecular lines

In this work, the radiative transition parameters including Franck–Condon (FC) factors, r-centroids, electronic transition moment, Einstein coefficients, band strength, oscillator strength, lifetime and effective vibrational temperature have been computed for A1Π−X1Σ+ and C1Σ+−A1Π systems of aluminium monohydride (AlH) molecule by the numerical integration method for the experimentally known vibrational levels using Rydberg – Klein – Rees (RKR) potential. The computed radiative transition parameters are tabulated. A significant number of well resolved AlH molecular rotational lines of A1Π−X1Σ+ (0,0), (1,1) and (0,1) bands are identified in the sunspot umbral spectrum and the estimated effective rotational temperature has been determined as 2315 K, 2155 K and 1838 K respectively. The effective vibrational temperatures of the A1Π−X1Σ+ and C1Σ+−A1Π systems are found to be 5682 K and 3472 K respectively. Hence, the radiative transition parameters and the effective temperatures confirm the presence of AlH molecule in sunspot spectra.

Effects of Ag doping on LaMnO3 photocatalysts for photoelectrochemical water splitting

As a redox material, perovskite is considered one of the most efficient photovoltaic materials for producing hydrogen via water splitting reactions. This study used a wet chemical method to synthesize La1−xAgxMnO3 nanoparticles (0.00 ≤ x ≤ 0.09). The formation, chemical composition, and morphology of samples were examined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HR-TEM). The optical properties were examined by ultraviolet visible (UV) diffuse reflectance spectroscopy. XRD demonstrated that the samples had a rhombohedral hexagonal structure with a space group R overline{3 } c. The pore volume, pore size, and surface area were calculated and examined. The prepared samples were used as a photoanode in alkaline media for water splitting, and the photocurrent was measured. The photocurrent density recorded (14.01, 12.02, 11.67, and 10.28 μA/cm2) for x = (0.09, 0.06, 0.03, and 0.00) at 1 V vs. Ag/AgCl, respectively. The smaller impedance of the sample (x = 0.09) photoanodes than the sample (x = 0.00), which displayed a considerable decrease in charge transfer resistance. The electron lifetime (τ) increased with increasing Ag concentration, where x = 0.09 has the largest electron lifetime (τ) = 10.04 ms. Therefore, the electron–hole recombination rate of La0.91Ag0.09MnO3 is lower than LaMnO3. The samples demonstrated long-term stability for 1 h and enhanced photoelectrochemical performance.

First application of benzotriazole as a dye additive to dye-sensitized solar cells: electrochemical device characterization

Dye-sensitized solar cell, known as an emergent technology, has been attracted attention around the world. It has been easily produced by a mesoporous semiconductor oxide (SO), with a dye. On the other hand, some unexpected reactions as the back-electron recombination, reducing the solar cell efficiency. The presence of some molecules to act as an oxide passivation might rise up the collection reaction rate, and enhance the photoelectrochemical solar system parameters. The molecule used as a dye additive, must effortlessly adsorb in SO and potentiate the dye deaggregation. This work aims to study the benzotriazole (BTAH) insertion in DSSC with TiO2, evaluating its capability as a passivator molecule in such PV technology. The electrochemical results showed better electrochemical energy conversion efficiency with lower resistance with BTAH at 2.0 mg mL−1, achieving a jsc = 9.92 ± 0.26, Voc = 0.770 ± 0.022, FF = 0.557 ± 0.014, ɳ = 4.26 ± 0.13 with superior electron lifetime and amazing recombination prevention.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13738-022-02645-1.

Enhanced photovoltaic performance of D-π-A organic sensitizers by simple fluorination of acceptor unit

A simple and facile molecular modification method is presented to enhance the photovoltaic and photoelectrochemical properties of D- π -A organic sensitizers. This modification is obtained by incorporating fluorine as an additional acceptor unit. By the electron-withdrawing ability of fluorine, the electron transfer to the anchoring group is promoted, which ultimately leads to a decrease in the HOMO-LUMO energy gap. In addition, the incorporated fluorine also induces prominent J -aggregation, resulting in an increase in the dye loading amount on the photoanode. Because of these positive effects, the additional fluorine acceptor enhances both the photocurrent and photovoltage of dye-sensitized solar cells (DSSCs). In particular, electrochemical impedance study reveals that the electron lifetime in the dye-sensitized photoanode also increases by the incorporation of fluorine in the dye molecules, mostly because of enhanced dye loading. • Simple fluorination leads to enhanced photovoltaic property of organic sensitizer. • Electron-withdrawing ability of fluorine extends light absorption range. • Fluorine also induces prominent J -aggregation, resulting in an increased dye loading. • Fluorine greatly enhances the conversion efficiency of DSSCs by about 29%.

Cover picture: Production of mesoporous carbon nitrides and their photocatalytic properties for degradation of organic pollutants (BKCS 09/2022)

AbstractMesoporous C3N4 materials were produced through the self‐assembly of melamine and cyanuric acid. The materials showed excellent performance for degrading organic pollutants, rhodamine B, under the irradiation of visible light. Various study revealed that high surface areas, good adsorption ability of visible light, and long lifetimes of the photoexcited electrons would be origins for the photocatalytic superiority. More information can be found in the article by S. Park et al. image

Low Frequency Plasmaspheric Hiss Wave Activity Parameterized by Plasmapause Location: Models and Simulations

AbstractPlasmaspheric hiss waves are a dominant source of scattering for keV‐MeV radiation belt electrons within the plasmasphere. Previous simulation and modeling work concerning hiss waves has often incorporated them via particle‐based parameterizations (e.g., L‐shell). However, recent work has shown that not only is hiss wave power loosely dependent on L‐shell, but that proximity to the plasmapause may yield more accurate wave power distributions as it pertains to the modeling and scattering of electrons. This work serves to expand upon those previous studies by creating a low frequency (20–150 Hz) hiss wave model and incorporating a previously crafted high frequency (&gt;150 Hz) hiss wave model based on plasmapause location, proximity to the plasmapause, and Kp activity level. Diffusion coefficients created using this method produced shorter lifetimes for electrons between ∼300 keV and 4 MeV than their L‐sorted counterparts. Furthermore, 3D‐simulations using and comparing the different hiss wave models (plasmapause sorting vs. L‐sorting) find that the plasmapause‐based approach yields more accurate results when compared to Van Allen Probe‐A observations.