Continuous Electron Research Articles

On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks.

Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 Å), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.

Low and Stable Secondary Electron Yields of Alodine-Treated Aluminum Alloys Under Continuous Electron Bombardment

High secondary electron yields of aluminum (Al) alloys limit the performances of high-power microwave devices and even extremely degrade their lifetimes. In this work, a strategy of alodine treatment for Al alloys was proposed to achieve a goal of the secondary electron emission suppression under continuous electron bombardment. It was found that a porous chromate conversion film including the mixture of basic chromium chromate and alumina with a mean pore size of 69.1 nm was formed on the surface of the Al alloy treated by alodine solution. On the basis of the secondary electron yield (SEY) measurement results, this alodine treatment brings about a reduction of maximal SEY of the Al alloy from 1.67 to 1.33 with a ratio of 20.4% and has just a remarkably tiny SEY change within 0.01~0.03 under 240-min continuous electron bombardment.

Efficient ternary all small molecule organic photovoltaics with NC70BA as third component materials

Inverted small molecule organic photovoltaics (SMPVs) were fabricated with BTR as a donor, the narrow band gap material Y11 as an acceptor and NC70BA fullerene derivatives with a broad band gap as the third component materials. When 20 wt% Y11 was replaced by NC70BA, a higher PCE of 13.92% was achieved, which is attributed to simultaneous enhancement of the JSC of 22.16 mA cm−2, the VOC of 0.905 V and the FF of 69.4%. The hollow spherical structure of NC70BA may lead to the connection of Y11 and BTR molecules to form more continuous electron transport channels. Shallow lowest unoccupied molecular orbital (LUMO) energy levels form a cascade of LUMO energy levels among the used materials. In addition, the molecular arrangement and crystallinity in the photoactive layer can be markedly adjusted by incorporating NC70BA into BTR:Y11 binary films. The well-optimized phase separation and molecular arrangement in ternary photoactive layers can well support an enhanced JSC and FF for ternary SMPVs. Thus, the photovoltaic performance of SMPVs can be well improved by employing a ternary strategy with NC70BA as the third component materials.

Engineering heterostructured Ni@Ni(OH)2 core-shell nanomaterials for synergistically enhanced water electrolysis

Heterostructure engineering of electrocatalysts provides a fascinating platform to reasonably manipulate the physicochemical properties of nanomaterials and further improve their catalytic efficiency for water electrolysis. However, it still remains a huge challenge to construct well-designed core-shell heterostructured catalysts and identify the key role of components for synergistic catalysis. Herein, a melted polymeric salt tactics was innovatively developed to synthesize heterostructured Ni@Ni(OH)2 core-shell nanomaterials supported on porous carbon (named Ni@Ni(OH)2/PC), wherein well-defined Ni(OH)2-Ni heterostructure plays a pivotal role in improving electrocatalytic activity for water reduction and oxidation. Besides, the stable porous carbon support functions as a highway for continuous electron transfer between Ni and Ni(OH)2, and simultaneously enables the full exposure of accessible active sites. The fabricated Ni@Ni(OH)2/PC exhibits outstanding bifunctional electrocatalytic performance for overall water splitting (ƞ10 = 1.55 V) with a good long-time stability. This work sheds new light on the design of engineering heterostructure of active bifunctional electrocatalysts for efficient energy conversion system.

Atomic-Resolution Imaging of Fast Nanoscale Dynamics with Bright Microsecond Electron Pulses.

Atomic-resolution electron microscopy is a crucial tool to elucidate the structure of matter. Recently, fast electron cameras have added the time domain to high-resolution imaging, allowing static images to be acquired as movies from which sample drift can later be removed computationally and enabling real-time observations of atomic-scale dynamics on the millisecond time scale. Even higher time resolution can be achieved with short electron pulses, yet their potential for atomic-resolution imaging remains unexplored. Here, we generate high-brightness microsecond electron pulses from a Schottky emitter whose current we briefly drive to near its limit. We demonstrate that drift-corrected imaging with such pulses can achieve atomic resolution in the presence of much larger amounts of drift than with a continuous electron beam. Moreover, such pulses enable atomic-resolution observations on the microsecond time scale, which we employ to elucidate the crystallization pathways of individual metal nanoparticles as well as the high-temperature transformation of perovskite nanocrystals.

Conformational Differences Are Observed for the Active and Inactive Forms of Pinholin S21 Using DEER Spectroscopy.

Bacteriophages have evolved with an efficient host cell lysis mechanism to terminate the infection cycle and release the new progeny virions at the optimum time, allowing adaptation with the changing host and environment. Among the lytic proteins, holin controls the first and rate-limiting step of host cell lysis by permeabilizing the inner membrane at an allele-specific time known as "holin triggering". Pinholin S21 is a prototype holin of phage Φ21 which makes many nanoscale holes and destroys the proton motive force, which in turn activates the signal anchor release (SAR) endolysin system to degrade the peptidoglycan layer of the host cell and destruction of the outer membrane by the spanin complex. Like many others, phage Φ21 has two holin proteins: active pinholin and antipinholin. The antipinholin form differs only by three extra amino acids at the N-terminus; however, it has a different structural topology and conformation with respect to the membrane. Predefined combinations of active pinholin and antipinholin fine-tune the lysis timing through structural dynamics and conformational changes. Previously, the dynamics and topology of active pinholin and antipinholin were investigated (Ahammad et al. JPCB 2019, 2020) using continuous wave electron paramagnetic resonance (CW-EPR) spectroscopy. However, detailed structural studies and direct comparison of these two forms of pinholin S21 are absent in the literature. In this study, the structural topology and conformations of active pinholin (S2168) and inactive antipinholin (S2168IRS) in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) proteoliposomes were investigated using the four-pulse double electron-electron resonance (DEER) EPR spectroscopic technique to measure distances between transmembrane domains 1 and 2 (TMD1 and TMD2). Five sets of interlabel distances were measured via DEER spectroscopy for both the active and inactive forms of pinholin S21. Structural models of the active pinholin and inactive antipinholin forms in DMPC proteoliposomes were obtained using the experimental DEER distances coupled with the simulated annealing software package Xplor-NIH. TMD2 of S2168 remains in the lipid bilayer, and TMD1 is partially externalized from the bilayer with some residues located on the surface. However, both TMDs remain incorporated in the lipid bilayer for the inactive S2168IRS form. This study demonstrates, for the first time, clear structural topology and conformational differences between the two forms of pinholin S21. This work will pave the way for further studies of other holin systems using the DEER spectroscopic technique and will give structural insight into these biological clocks in molecular detail.

Manipulation of Molecular Qubits by Isotope Effect on Spin Dynamics

Controlling spin behavior via external stimuli is a key route to develop molecular spintronics devices. Photons, temperature, pressure, chemicals, and electric field are the possible stimuli. Herei...

Copper–Calcium Poly(Acrylic Acid) Composite Hydrogels as Studied by Electron Paramagnetic Resonance (EPR) Spectroscopy

Front Cover: In article number 2000262 by Haleh H. Haeri, Dariush Hinderberger, and co-workers, incorporating copper ions into synthetic poly acrylic acid polymer hydrogels results in toughening of these hydrogels. Continuous wave and pulsed electron paramagnetic resonance spectroscopic techniques reveal that the origin of the observed boost in mechanical properties stems from parts of the hydrogel network that interact with and through hydrated copper ions.

Photoproduction of the Λ(1520) hyperon with a 9 GeV photon beam at GlueX

The GlueX experiment is located at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, VA, USA. It features a hermetic 4π detector with excellent tracking and calorimetry capabilities. Its 9 GeV linearly polarized photon beam is produced from the 12 GeV electron beam, delivered by JLab’s Continuous Electron Beam Accelerator Facility (CEBAF), via bremsstrahlung on a thin diamond and is incident on a LH2 target. GlueX recently finished its first data taking period and published first results.The main goal of GlueX is to measure gluonic excitations of mesons. These so-called hybrid or exotic mesons are predicted by Quantum Chromodynamics (QCD) but haven’t been experimentally confirmed yet. They can have quantum numbers not accessible by ordinary quark-antiquark pairs which helps in identifying them using partial wave analysis techniques. The search for exotic mesons requires a very good understanding of photoproduction processes in a wide range of final states, one of them being pK + K − which contains many meson and baryon reactions. The Λ(1520) is a prominent hyperon resonance in this final state and is the subject of this presentation.This talk will give an introduction to the GlueX experiment and show preliminary results for the photoproduction of the Λ(1520) hyperon. The measurement of important observables like the photon beam asymmetry and spin-density matrix elements will be discussed and an outlook to possible measurements of further hyperon states in the pK + K − final state will be given.

Effect of passivation on the n-InP optical and electronic properties

The effect of sulphur surface passivation on the optical and electronic properties of InP was investigated. In the work, the approach of simultaneous measurement of the dynamics of the absorbed current and cathodoluminescence under continuous electron beam irradiation is used. This approach allows us to study the trapping of charge by traps and their influence on the luminescent properties. It was shown that hole traps are observed in the samples; moreover, the localization of a positive charge leads to an increase in the luminescence intensity. Passivation was found to significantly reduce the number of hole traps.

Superconducting radio-frequency cavity fault classification using machine learning at Jefferson Laboratory

We report on the development of machine learning models for classifying C100 superconducting radio-frequency (SRF) cavity faults in the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. CEBAF is a continuous-wave recirculating linac utilizing 418 SRF cavities to accelerate electrons up to 12 GeV through 5-passes. Of these, 96 cavities (12 cryomodules) are designed with a digital low-level RF system configured such that a cavity fault triggers waveform recordings of 17 RF signals for each of the 8 cavities in the cryomodule. Subject matter experts (SME) are able to analyze the collected time-series data and identify which of the eight cavities faulted first and classify the type of fault. This information is used to find trends and strategically deploy mitigations to problematic cryomodules. However manually labeling the data is laborious and time-consuming. By leveraging machine learning, near real-time (rather than post-mortem) identification of the offending cavity and classification of the fault type has been implemented. We discuss performance of the ML models during a recent physics run. Results show the cavity identification and fault classification models have accuracies of 84.9% and 78.2%, respectively.

High Photocurrent Density and Continuous Electron Emission Characterization of a Multi-Alkali Antimonide Photocathode

High photocurrent density cathodes that enable small cross-section electron beams are required for high-power terahertz vacuum devices. Multi-alkali antimonide photocathodes may be well suited for generating sub-mm electron beam sources. This paper involves the repeatability, stability, uniformity, and linearity experiments of the multi-alkali antimonide photocathodes electron emission operations under a continuous-wave 450 nm laser with a bias voltage of 5000 V. The effect of heat, electric contact, and cathode surface roughness to emission characterizations is analyzed. The methods to maintain the high-current-density emission and avoid the fatigue of the photocathode are verified. The emission can be repeated with increased optical power. The stable photocurrent density of near 1 A/cm2 and maximum current density of near 1.43 A/cm2 is recorded. The continuous photocurrent density is significantly improved compared to the current density reported in traditional applications. It is found that the current curves measuring at different areas of the photocathode differ greatly after the laser power of 800 mW. The increase in current for some areas may be attributed to the conductive current caused by built-in electric fields between the emission rough area and its adjacent areas.

Electron-transfer-dominated non-radical activation of peroxydisulfate for efficient removal of chlorophenol contaminants by one-pot synthesized nitrogen and sulfur codoped mesoporous carbon

Synergistic adsorption and oxidative degradation (via persulfate activation) on metal-free carbonaceous materials are expected to be environmentally friendly and highly efficient approach toward contaminants removal. Herein, nitrogen and sulfur codoped mesoporous carbon (NSDMC) were firstly synthesized via co-carbonization of calcium citrate and thiourea without any templates. NSDMC samples exhibit remarkably enhanced adsorption capacity and oxidative degradation (by activating PDS) for chlorophenols elimination. Increased SBET and introduced N-containing functional groups are beneficial for chlorophenols adsorption, PDS accessibility and successive activation. Doped sulfur species (especially for thiophenic S) can enhance the electron-transport performance of NSDMC, further promoting PDS activation and chlorophenols degradation. It can be ascribed to the synergistic effect of N and S codoping. NSDMC-30 (containing 5.83 at.% nitrogen and 2.15 at.% sulfur, and possessing SBET of 1935.9 m2 g−1) exhibits the optimal adsorption and catalytic oxidation capability for 4-CP removal. Degradation rate constant of NSDMC-30 is 0.125 min−1, which is 3.0 times and 7.8 times higher than nitrogen-doped MC and pristine MC, respectively. Radicals quenching experiments and EPR tests demonstrate that non-radical pathways play dominant role for PDS activation and chlorophenols degradation. Based on the influences of catalyst loading, initial 4-CP concentration, and PDS dosage on degradation kinetics of 4-CP, the pre-adsorption is unveiled to be the critical step determining oxidation rate of chlorophenols. More importantly, the results of in-situ Raman and electrochemical tests show that the surface-confined and activated PDS complex (carbon-PDS*) and continuous electron transfer from co-adsorbed 4-CP are mainly responsible for the oxidative degradation of chlorophenols. The intermediate products and TOC removal indicate that chlorophenols can be efficiently degraded and mineralized by as-synthesized NSDMC via activating PDS. Besides, the present NSDMC/PDS system is also applicable for purification of actual polluted water samples. This work provides in-depth knowledge of carbon-driven nonradical process for PDS activation and contaminants remediation.

Modulating Effect of Ligand Charge on the Electronic Properties of 2Ni-2S Structures and Implications for Biological 2M-2S Sites.

Sulfur-bridged bimetallic 2M-2S type structures are essential cofactors that participate in biological long-range electron transport and metabolism. Metal-sulfur bond covalency is a decisive property for inner sphere (through-bond) type electron transfer that dominates in buried or hydrophobic protein environments. This work reports on a combined experimental and computational study of the effect of ligand charge on the electronic structure of a 2Ni-2S model site that adopts the biologically relevant S = 1/2 redox state. Starting out from an isostructural dinickel(1.5+)-dithiophenolate platform with sulfur-bridged tetrahedral Ni sites, η2:η2-μ-coordination of the S = 1/2 [2Ni-2S]+ core to either a neutral π-system or strongly σ-donating cyclohexadienido renders its electronic structure substantially different. Density functional theory analysis corroborates pulse and continuous wave electron paramagnetic resonance data that associate co-ligand charge with the significant change in the mechanism and size of electron-31P nuclear spin hyperfine coupling to a phosphine reporter ligand at each nickel center. An increasing level of charge donation attenuates direct and through-bridge electronic coupling of the metal sites, resulting in a stronger electronic coupling of the 2Ni-2S core to its terminal phosphine donors. Drawing a connection to biological 2M-2S sites, our 2Ni-2S system indicates that a fine balance of intracore and core-protein electronic coupling is key to biological function for which the degree of charge donation by peripheral donors appears to be a significant parameter.

EPR Spectral Studies of Manganese(I) Based Molecular Squares

Manganese(I) based molecular squares of type [Mn(CO)3Br(μ-L)]4 where L = pyrazine, 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethylene were synthesized and studied in detail by EPR spectroscopy. The continuous wave electron paramagnetic resonance (CW EPR) spectrum of these compounds consists of a broad transition at g = 2.006 and 4.16 that corresponds to an interacting low spin Mn(II) center and a narrow transition at g = 2.004 that corresponds to a nitrogen center radical. These results are discussed in detail and the observation of these characteristic EPR spectral signals is attributed to a partial transfer of an electron from Mn(I) center to the nitrogenous ligand through MLCT.

Continuous wave electron paramagnetic resonance L-band spectrometer with direct digitalization using time-locked subsampling

This article describes a novel digital L-band EPR spectrometer. The spectrometer uses direct digital detection with time-locked subsampling (TLSS). The device consists of a microwave bridge equipped with a microwave source based on direct digital synthesis (DDS) and a digital receiver.DDS technology combined with an ultra-low noise 1 GHz master clock allowed the development of a digitally controlled microwave source with exceptionally good phase noise characteristics. The obtained level of phase noise is as low as −140 dBc/Hz at 30.5 kHz from the carrier frequency of 1.15 GHz, which is important when registering the EPR dispersion signal.The receiver is equipped with a high-speed A/D converter that enables direct digitalization of the L-band microwave signal. The obtained discrete data are then buffered and averaged in a programmable logic FPGA device. Data packets from FPGA are transferred to a DSP microcontroller that correlates them with the appropriate reference signals. This detection algorithm requires time locking of the generator and the receiver, which is ensured by clocking both devices from the same reference source. This procedure allows the simultaneous detection of the absorption and dispersion signals at the magnetic field modulation frequency and at any of its harmonics.The software to control the spectrometer was designed in the LabView programming environment. The program also allows further data processing. To the best of our knowledge, the described spectrometer is one of the first full implementation of the direct digital detection technique which could replace conventional analog CW spectrometers that utilize magnetic field modulation. For an 11 µm aqueous TEMPOL solution, the new spectrometer obtained a S/N ratio greater than 160 for an EPR spectrum registered in 69 s.

Efficient electrochemical dehalogenation of florfenicol without discharging toxic intermediates via direct electron transfer over electrochromic WO3

Complete dehalogenation of florfenicol (FLO) was realized on a self-supporting, electrochromic WO3 nanocluster electrocatalyst prepared by anodization, effectively inhibiting the generation of toxic intermediates that can pose harmful influence on the ecosystem. Three dimensional, omnidirectional WO3 clusters made up of WO3 nanoflakes are grown from a W mesh substrate, which can work as catalyst and electrode enable the complete dehalogenation via a direct electron transfer because of the inherent electron-storage and self-supporting nature. Assisted by bias potential, continuous electron streams are generated and reserved in the porous WO3 interface, building an electron-rich circumstance for activating the C–Cl and C–F bonds to detach the halogen groups. The best electrocatalytic dehalogenation performance, 99.7% in 120 min was acquired using the optimal WO3/W anodized at 25 V. The possible sites attacked by electrons is predicted by Fukui index, that is evidenced by the MS of intermediates originated from FLO decomposition. ECOSAR simulation and E. coli surviving evaluation verifies that there is no hazard on ecosystem of the chemicals without –F and –Cl. Particularly, the self-supporting WO3 nanocluster electrocatalyst exhibits a superior durability with no decay in activity after 20 h running, indicating a promising prospect in establishing a feasible, cost-effective, and durable electrochemical strategy for antibiotic dehalogenation.

The Non-innocent Role of Spin Traps in Monitoring Radical Formation in Copper-Catalyzed Reactions

Spin traps, like 5,5-dimethyl-1-pyrroline N-oxide (DMPO), are commonly used to identify radicals formed in numerous chemical and biological systems, many of which contain metal-ion complexes. In this study, continuous wave electron paramagnetic resonance and hyperfine spectroscopy are used to prove the equatorial ligation of DMPO(-derived) molecules to Cu(II), even in the presence of competing nitrogen bases. The experimental data are corroborated with density functional theory calculations. It is shown that 14N HYSCORE can be used as a fingerprint method to reveal the coordination of DMPO(-derived) molecules to Cu(II), an interaction that might influence the outcome of spin-trapping experiments and consequently the conclusion drawn on the mechanism under study.

In-situ growth of TiO2 film on carbonized eggshell membrane as 3D electrode for high-performance lithium storage

3D electrodes have shown extraordinary promise for electrochemical energy storage devices in wearable electronics. However, it is still a significant challenge to rationally design 3D electrode that has the characteristics of lightweight, flexibility, low cost, high performance and miniaturization. In this work, we present a novel design of 3D electrode by directly growing the nanocrystalline TiO2 film on carbonized eggshell membrane. The unique architecture can supply not only a continuous electron transport pathway through an interconnected carbon fibrous network but also an efficient electrolyte flux via an interpenetrating porous network. Besides, nanocrystalline TiO2 film on carbonized eggshell membrane offers a short ion diffusion path in the solid-phase, leading to a rapid kinetic of electrochemical reaction. When tested as an anode for Li-ion battery, TiO2 film in 3D electrode demonstrated excellent electrochemical performance with a large reversible capacity, excellent rate capacity and long life cycling property.

In-situ formation of mesoporous SnO2@C nanocomposite electrode for supercapacitors

In this work, we report a supercapacitor based on SnO2@C composite electrode with better electrochemical performance. SnO2@C composite is synthesized from porous polymer beads by the impregnation method. The resultant composite is porous and retains uniform spherical morphology of polymer beads. The composite exhibits the bimodal distribution of pores with a specific surface area of 286 m2g−1. SnO2@C composite electrode show specific capacitance of 432 F g−1 at 1 A g−1 in 1M KOH electrolyte with capacitance retention of 95.5% for 2000 cycles. Besides, the composite electrode shows an energy density of 29.4 Wh kg−1 at a power density of 418 W kg−1 at 1 A g−1 current density. The optimize electrode design improves cyclic stability due to reducing crystal growth of SnO2 as well as diffusion kinetics because of the presence of bimodal pores which provides continuous electron path. The bimodal micropores and mesopores in carbon matrix have the accessibility of electrolyte to SnO2, improving overall electrochemical performance and therefore SnO2@C composite is suitable as electrode material for supercapacitors.