Free Electron Research Articles

Modelling for Temperature Distribution Calculation using Surface Scattering of Free Electrons in Finite Metal Solid

This study generalizes the temperature distribution equation for finite metal solid, unifying previous separate models for thick and thin plates. Effects of surface scattering of free electrons on heat conduction is taken account. As plate thickness decreases, these scattering events increase, leading to elevated temperatures due to reduction in mean free paths. We propose a prediction model for temperature distribution incorporating these effects onto the existing Rosenthal solution. It exhibits excellent agreement with finite element analysis results across all thicknesses. Furthermore, from an engineering standpoint, two examples of how heat concentration occurs in material with geometry that promotes multiple surface scattering are presented.

Dynamics of the Davydov’s soliton in external oscillating magnetic field

The influence of an external oscillating in time magnetic field on the dynamics of the Davydov’s soliton is studied. It is shown that soliton parameters depend on the amplitude and frequency of the magnetic field, as well as on the field orientation with respect to the molecular chain axis. Electron dynamics in the parallel magnetic field is a composition of the “free” soliton coherent propagation along the molecular chain and oscillatory movement in the transverse direction. The latter is described by the functions of the harmonic oscillator with the cyclotron frequency depending on the field frequency. In a perpendicular field the soliton dynamics is a superposition of (i) the free electron plane wave in the plane perpendicular to the molecular chain, and (ii) propagation along the chain which is described by the modified Nonlinear Schrödinger equation with an extra term depending on the field. This equation is solved using the nonlinear perturbation theory. It is shown that the soliton velocity and phase are given by expressions which include the terms oscillating in time with the frequency of the main harmonic, given by the external field frequency, and higher multiple harmonics. Such complex effects of external time-depending magnetic fields on the dynamics of solitons modify the charge transport in low-dimensional molecular systems, which in its turn, can affect the functioning of the devices based on such compounds. These results suggest also the physical mechanism of therapeutic effects of oscillating magnetic fields, based on the field influence on the dynamics of solitons which provide charge transport through biological macromolecules in the redox processes.

Releasing Au Electrons to Mo Site for Weakened Mo─H Bond of Mo2C MXene Cocatalyst Toward Improved Photocatalytic H2 Production.

Mo2C MXene (Mo2CTx) is one of the most promising noble-metal-free cocatalysts for photocatalytic H2 production because of its excellent electron transport capacity and abundant Mo sites. However, Mo2CTx typically exhibits a strong Mo─Hads bond, resulting in that the produced H2 difficultly desorbs from the Mo surface for the limited activity. To effectively weaken the Mo─Hads bond, in this paper, a regulation strategy of electron donor Au releasing electrons to the d-orbitals of Mo sites in Mo2CTx is proposed. Herein, the Mo2CTx-Au/CdS photocatalysts are prepared through a two-step process, including the initial loading of Au nanoparticles on the Mo2CTx surface and the subsequent in situ growth of CdS onto the Mo2CTx-Au surface. Photocatalytic measurements indicate that the maximal H2-production rate of Mo2CTx-Au/CdS reaches up to 2799.44µmol g-1h-1, which is 30.99 and 3.60 times higher than that of CdS and Mo2CTx/CdS, respectively. Experimental and theoretical data corroborate that metallic Au can transfer free electrons to Mo2CTx to generate electron-enriched Moδ- sites, thus causing the increased antibonding-orbital occupancy state and the weakened Mo─Hads bond for the boosted H2-production efficiency. This research provides a promising approach for designing Mo2CTx-based cocatalysts by regulating the antibonding-orbital occupancy of Mo sites for improved photocatalytic performance.

Protocols for x-ray transient grating pump/optical probe experiments at x-ray free electron lasers

Protocols for x-ray transient grating pump/optical probe experiments at x-ray free electron lasers

Synergistic enhancement of singlet oxygen generation in Au and oxygen vacancy co-modified Bi2MoO6 ultrathin nanosheets for efficient ciprofloxacin degradation

Solar-driven molecular oxygen activation (MOA) is crucial for generating reactive oxygen species (ROS) for pollutant degradation, while the low activation efficiency greatly weakens the degradation efficiency. Herein, oxygen vacancies (OVs) and Au nanoparticles are co-introduced into Bi2MoO6 (ABMOH) to enhance the photocatalytic activity of Bi2MoO6 (BMO), thereby promoting MOA efficiency. Density functional theory demonstrates that the introduction of OVs not only improves the molecular oxygen adsorption on BMO, and but also strengthens the O-O bond dissociation of molecular oxygen, which is beneficial to MOA. Meanwhile, the unique localized surface plasmon resonance effect of Au nanoparticles immensely increases the photo-absorption capacity. Crucially, both OVs and Au nanoparticles work as “electron traps” to capture photogenerated electrons, thereby accelerating charge transfer. Based on the advantage of OVs and Au nanoparticles, ABMOH displays excellent MOA efficiency, and the degradation rate constant of ciprofloxacin (CIPF) by ABMOH-4 is 3.62-fold higher than BMO. Free radical trapping experiment and electron spin resonance suggest that singlet oxygen (1O2) can be selectively formed in the ABMOH system for CIPF degradation, and superoxide radical (•O2–) conversion and energy transfer are two pathways for 1O2 formation. This investigation serves as a beacon for the strategic design of high-performance and stable photocatalysts for MOA activation, paving the way for advancements in environmental remediation.

To 200,000 m/z and Beyond: Native Electron Capture Charge Reduction Mass Spectrometry Deconvolves Heterogeneous Signals in Large Biopharmaceutical Analytes.

Great progress has been made in the detection of large biomolecular analytes by native mass spectrometry; however, characterizing highly heterogeneous samples remains challenging due to the presence of many overlapping signals from complex ion distributions. Electron-capture charge reduction (ECCR), in which a protein cation captures free electrons without apparent dissociation, can separate overlapping signals by shifting the ions to lower charge states. The concomitant shift to higher m/z also facilitates the exploration of instrument upper m/z limits if large complexes are used. Here we perform native ECCR on the bacterial chaperonin GroEL and megadalton scale adeno-associated virus (AAV) capsid assemblies on a Q Exactive UHMR mass spectrometer. Charge reduction of AAV8 capsids by up to 90% pushes signals well above 100,000 m/z and enables charge state resolution and mean mass determination of these highly heterogeneous samples, even for capsids loaded with genetic cargo. With minor instrument modifications, the UHMR instrument can detect charge-reduced ion signals beyond 200,000 m/z. This work demonstrates the utility of ECCR for deconvolving heterogeneous signals in native mass spectrometry and presents the highest m/z signals ever recorded on an Orbitrap instrument, opening up the use of Orbitrap native mass spectrometry for heavier analytes than ever before.

Formation of nonclassical and non-Gaussian states of a strong electromagnetic field due to its interaction with free electrons produced by ionization of a target gas

Formation of nonclassical and non-Gaussian states of a strong electromagnetic field due to its interaction with free electrons produced by ionization of a target gas

All-Calixarene-Protected Silver Nanocluster with All Silver Atoms in a Face-Centered Cubic Arrangement.

Tailoring the surface ligands of metal nanoclusters is important for engineering unique configurations of metal nanoclusters. Thiacalix[4]arene has found extensive applications in the construction of metal nanoclusters. In this investigation, we present the synthesis and characterization of the first all-calixarene-protected silver nanoclusters, [Ag(CH3CN)4]2[Ag44(BTCA)6] (Ag44, H4BTCA = p-tert-butylthiacalix[4]arene). Single-crystal X-ray structural analysis reveals that all silver atoms are in a face-centered cubic (fcc) arrangement. The formation of such an fcc structure is attributed to the selectively passivation on {100} facets by BTCA4-. Thiacalixarene substantially facilitates the stability of Ag44 due to its multiple coordination sites and bulkiness. Mass spectrometry and theoretical calculations reveal that Ag44 is a superatomic silver nanocluster with 22 free electrons in the following configuration: 1S21P61D61F22S21D4. This work not only elucidates the impact of macrocyclic ligands on the stabilization of silver clusters but also furnishes an approach for assembling atomically precise fcc nanoclusters.

Direct Operando Identification of Reactive Electron Species Driving Photocatalytic Hydrogen Evolution on Metal-Loaded Oxides.

Performing operando spectroscopy under practical reaction conditions and extracting spectral components correlating with reaction activity are crucial in elucidating the reactive species in photocatalysis. However, the observation of weak signals corresponding to reactive photogenerated species is frequently hampered under reaction conditions owing to intense background signals originating from thermally induced species unrelated to the photoinduced reactions. Herein, by synchronizing the millisecond periodic excitations of photocatalysts with a Michelson interferometer used for FT-IR spectroscopy, we succeeded in significantly suppressing the signals derived from thermally excited electrons and observing the reactive photogenerated electrons contributing to the photocatalytic hydrogen evolution. This demonstration was achieved for metal-loaded oxide photocatalysts under steam methane reforming and water splitting conditions. Although it has long been conventionally believed that loaded metal cocatalysts function as sinks for reactive photogenerated electrons and active sites for reduction reactions, we found that the free electrons in the metal cocatalysts were not directly involved in the reduction reaction. Alternatively, the electrons shallowly trapped in the in-gap states of oxides contributed to enhancing the hydrogen evolution rate upon the loading of metal cocatalysts. We verified that the electron abundance in the in-gap states was clearly correlated to the reaction activity, suggesting that metal-induced semiconductor surface states formed in the periphery of the metal cocatalyst play key roles in the photocatalytic hydrogen evolution. Our microscopic insights shift a paradigm on the traditionally believed role of metal cocatalysts in photocatalysis and provide a fundamental basis for rational design of the metal/oxide interfaces as promising platforms for nonthermal hydrogen evolution.

Optical design of the time-resolved ARPES beamline of the new material spectroscopy experimental station for the update of CAEP THz-FEL facility

Abstract The Chinese Academy of Engineering Physics Terahertz Free Electron Laser Facility (CAEP THz FEL, CTFEL) is the only high-average power free electron laser terahertz source based on superconducting accelerators in China. The update of the CTFEL is now undergoing and will expand the frequency range from 0.1-4.2 THz to 0.1-125 THz. Two experimental stations for material spectroscopy and biomedicine will be built. A high harmonic generation (HHG) lightsource based beamline at the material spectroscopy experimental station for time-resolved angle-resolved photoemission spectroscopy (ARPES) research will be constructed and the optical design is presented. The HHG lightsource covers the extreme ultraviolet (XUV) photon energy range of 20-50 eV. A Czerny-Turner monochromator with two plane gratings worked in conical diffraction configuration is employed for maintaining the transmission efficiency and preserving the pulse time duration. The calculated beamline transmission efficiency is better than 5% in the whole photon energy range. To our knowledge, this is the first time in China to combine THz-infrared FEL with HHG light source, and this experimental station will be a powerful and effective instrument and give new research opportunities in the future for users doing research on dynamic evolution of excited electron band structure of material surface.

NiSe2 crystals integrated with nickel cobalt hydroxide for high-performance aqueous supercapacitors

The integration of NiSe2 crystals onto the surface of NiCo-LDHs was successfully achieved by electrostatic self-assembly, thereby enhancing exposure to electrochemical active sites and synergistically improving capacitance performance. First-principles calculations suggest that this integration enhances the proportion of free electrons in NiSe2/NiCo-LDHs, facilitating improved charge transport behavior during electrochemical reactions. As a result of these excellent properties, NiSe2/NiCo-LDHs-4 electrodes exhibit a remarkable specific capacitance of 1252.3 F g−1 at a current density of 1 A g−1 and a capacitance retention of 79.58 % after 4000 cycles at a high current density of 20 A g−1. ASC devices based on NiSe2/NiCo-LDHs-4 exhibit energy densities as high as 36.43 Wh kg−1 at a power density of 1521.73 W kg−1 and capacitance retention as high as 125.88 % after 10,000 cycles at a high current density of 10 A g−1, highlighting the tremendous potential of NiSe2/NiCo-LDHs-4 materials for advanced energy storage applications.

TiO2/Ti3C2Tx gel microsphere for efficient photocatalytic degradation of organic pollutant with excellent recycling stability

Enhancing the recycling stability of photocatalysts is crucial for practical applications. The significant loss of powder catalyst materials during the recycling process hampers its degradation rate and results in a low reuse rate. Herein, the in-situ prepared TiO2/Ti3C2Tx (TOTC) heterojunction is embedded in gel microsphere (GMS) as a recyclable photocatalyst TOTC@GMS for efficient photocatalytic degradation of Congo red (CR). The experimental results show that the removal rate can reach 99 % in 120 min without any co-catalysts or sacrificial reagents. The GMS can be recycled after rinsing in deionized water for only 2 min, and the removal rate still maintains over 90 % after 25 cycles. Additionally, under natural sunlight exposure, TOTC@GMS achieves a removal rate of 90 % for CR in real water samples. The degradation mechanism is elucidated through hydroxyl radicals (OH) and superoxide radicals (O2−) as the main reactive species, as confirmed by free radical scavenging and electron paramagnetic resonance (EPR) experiments. The degradation products are further analyzed using high-performance liquid chromatography-mass spectrometry (LC-MS), allowing for the deduction of degradation pathways of CR. Furthermore, a phytotoxicity test confirms the non-toxicity of the organic micromolecules generated after degradation. This study presents a practical strategy to improve the recycling stability of photocatalysts, thereby effectively reducing the cost of wastewater treatment.

Molecular Hydrogen Formation via Vibrational Excitation of Partially Superhydrogenated Pyrenes

While polycyclic aromatic hydrocarbons (PAHs) are now accepted to be abundant in interstellar space, the abundance and influence of superhydrogenated PAHs (HPAHs) in the interstellar medium (ISM) are still under investigation. HPAHs may act as catalysts for or reactants in small-molecule formation via hydrogen abstraction reactions, H2 evaporation, and carbon skeleton fragmentation. Here, we present a gas-phase infrared (IR) action spectroscopy study of the HPAH 4, 5, 9, 10-tetrahydropyrene (THP; C16H14), performed at the Free Electron Lasers for Infrared eXperiments facility. IR action spectroscopy was performed on the THP cation, protonated THP, and their fragments produced by collision-induced dissociation in the range from 600 to 1800 cm−1. Calculated IR spectra, at the density functional theory level, agree with experimental IR spectra to a high degree and were utilized to determine molecular structures of the HPAH fragments. Molecular dynamics simulations compared with experimental mass spectra reveal favorable HPAH fragmentation pathways. Molecular hydrogen (H2) is observed to be a primary fragment of [THP+H]+ with superhydrogenated duo groups. This contrasts the notion that HPAHs typically undergo carbon skeleton fragmentation leading to C x H y formation. These observations show that lowered symmetry and duo or trio aliphatic groups on HPAHs uniquely change their IR spectra, stability, and fragmentation patterns. As a result, these species may contribute to H2 formation in the ISM.

Unlocking the secrets of colored glass: Structural-optical behaviors and non-linear optical properties of [formula omitted] and [formula omitted] ions-doped borates

Investigations of structural-optical properties were performed for La3+-doped borate glass host based on a fixed ratio of Fe3+ ions, and within a lanthanum oxide concentration range of (0–8 mol%). The density was measured and confirmed the increase in bond density of the network, with increasing its volume. While infrared spectroscopy was carried out to investigate the dominant role of lanthanum on structural variations of glass, for example, the BO3 to BO4 conversion and the conspicuous decrease in NBO content. Optically, the d-d visible transitions of Fe3+ ions were suppressed by La3+ quenchers, preventing their peaking within the optical absorption spectra of glass samples. Further, in good coalescence with density and infrared spectroscopy results, Tauc gap energy increased with lanthanum oxide addition owing to the band structure modulations. Additionally, the metallization criterion changed from 0.262 (eV)0.5 to 0.325 (eV)0.5, owing to the Tauc gap energy increment, indicating that the lanthanum addition causes a shift toward the semiconducting nature of the prepared samples. On the other hand, Urbach energy decreased with increasing lanthanum oxide content, manifesting the glass structure's propensity toward less disorder and high polymerization. Besides, the increase in electron-phonon interaction energy indicates a high possibility of phonon consumption to bind free electrons as pairs, mitigating the network disorder. Surprisingly, the non-linear optical properties of the glass matrix were enhanced through lanthanum oxide addition. For the current glass host activated by La3+ ions, including Fe3+ color centers, the correlation between these above-mentioned structural modifications, and optical findings provide a decent paradigm for the optics realm.

Effects of NOx and NH3 on the secondary organic aerosol formation from α-pinene photooxidation

Understanding the effects of mixed anthropogenic pollutants on the photooxidation of volatile organic compounds (VOCs) is essential for unraveling the formation pathways of secondary organic aerosols (SOA). Yet, it remains a highly challenging experimental target owing to the complexities in the precise measurement of molecular compositions of products and number/mass concentrations of particles as a function of pollutant concentration in the ambient atmosphere. Here, a series of well-defined chamber experiments were performed to explore the effects of NOx and NH3 on the SOA formation from photooxidation of the most abundant monoterpene, α-pinene. The results indicate that the suppression effect of NO and NO2 on the α-pinene photooxidation shows monotonous and parabolic trends, respectively. The presence of NH3 enhances particle number concentrations during the α-pinene + NOx photooxidation by participating in reactions with organic acids. New compounds, including organic peroxides, esters, organic nitrates, and peroxyacyl nitrates, are observed at molecular weight (MW) = 166, 173, 217, 231, 280, 282, 304, and 410 through threshold photoionization making use of a recently constructed vacuum ultraviolet free electron laser in positive ion mode. The molecular structures and formation paths of these species are speculated, which advance the category of VOC oxidation products. Our study provides significant understanding of the influence of NOx and NH3 on the VOC photooxidation, which can be utilized to establish predictive SOA formation networks and to improve atmospheric models.

Relationship between Structural Defects and Free Electrons in Icosahedral Nanoclusters.

According to the classic superatom model, metal nanoclusters with a "magic number" of free valence electrons display high stability, manifesting as the closed-shell-dependent electronic robustness. The icosahedral nanobuilding blocks containing eight free electrons were the most common in constructing metal nanoclusters; however, the structure defect-dependent variations of the free electron count in icosahedral configurations are still far from thorough research. Here, we reported a hydride-containing [Pt2Ag15(SAdm)4(DPPOE)4H]2+ nanocluster with two largely defective Pt1Ag8 icosahedral cores. Together with previously reported complete or slightly defective icosahedra in metal nanoclusters, the largely defective Pt1Ag8 core provided important clues to reveal the evolutionary mode of structural defects and free electrons in icosahedral nanoclusters; the free electron count of icosahedron was reduced two-by-two (i.e., from 8e to 6e and then to 4e) accompanied by the structure defection. Overall, the work presented a novel Pt2Ag15 nanocluster with a largely defective core structure that enables an atomic-level understanding of the relationship between structural defects and free electrons in icosahedral nanoclusters.

Effects of B2O3 Dopants on the Electrical Properties of Ta‐Doped SnO2 Varistors

As a new core component of surge arresters, it is crucial for manganese dioxide varistors to solve the challenges of reducing the leakage current and lowering the residual voltage ratio. In this study, the electrical characteristics of tin dioxide varistors using B2O3 as the acceptor dopant and Ta2O5 as the donor dopant are investigated. Several tin dioxide based varistors doped with different amounts of B2O3 are prepared and characterized by the researchers. X ray diffraction (XRD) is used to analyze the structural features of the samples and to observe the phases involved. It is found that the B2O3 dopant provides oxygen vacancies, reduces the grain size, increases the barrier height, and decreases the residual pressure ratio. The Ta2O5 dopant provides donor defects and free electrons needed to form the barrier. When balancing the concentrations of B2O3 and Ta2O5, the optimum dopant concentrations is found to be 0.1 mol% of B and 0.05 mol% of Ta; these concentrations result in a leakage current of 0.25 μA cm−2, a residual pressure ratio of 1.95, a nonlinear coefficient of 25, and a voltage gradient of 394 V mm−1 for the varistor.

Boosting visible-light photocatalytic performance of graphitic carbon nitride by regulating its donor-acceptor structure via maleamide

Graphitic carbon nitride (GCN) has attracted much attention due to its many advantages as a kind of photocatalyst, including low cost, easy to prepare, eco-friendly and so on. However, GCN suffers from limited light-absorption capacity and rapid recombination of photogenerated charge carriers. Herein, a new kind of photocatalyst based on GCN has been synthesized by introducing a small molecule compound (maleamide) through a facile thermal polycondensation method (550 ℃ for 180 min) and applied it to photocatalytic removal of bisphenol A (BPA). The optimized GCN-20 (20 mg maleamide in 10 g urea) exhibits the best BPA degradation performance and good stability. The UV–vis test shows that the introduction of maleamide broadens the optical response threshold of GCN from 435 nm to 460 nm. The promoted photocatalytic performance is mainly attributed to enhanced donor-acceptor structure by electron-withdrawing group, which accelerates charge separation and inhibits recombination of free holes and electrons. The active species including superoxide radicals (⋅O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (⋅OH), play dominant roles in the photocatalytic degradation process.

Solvation structure and electron isolation synergy of piperidine ionic liquid additives inspires high performance lithium metal batteries

The safety concerns associated with lithium metal stand as the foremost barrier preventing widespread application of lithium metal batteries, especially due to lithium dendrite growth and gas evolution from electrolyte decomposition. This study employed N‑butyl‑N-methyl-piperidinium bis(trifluoro-methyl-sulfonyl) imide (PP14TFSI) as an additive in the electrolyte, aimed at improving the safety attributes of lithium metal batteries. The assessment conducted on the protective mechanism of the PP14TFSI additive unveiled its capability to control create robust and rapidly ion-conductive SEI by adjusting the solvation structure. Simultaneously, PP14+ intercepts free electrons, inhibiting the decomposition of DME and subsequent gas generation. Due to the synergistic effects of these two mechanisms, the rate of gas generation was reduced by half. A comprehensive investigation of lithium metal-based cells exhibited promising performance, maintaining stable cycling for 2160 h at 25 °C, 0.5 mA cm−2, displaying consistently high CE > 98.5 % in a Li||Cu cell. Moreover, at 60 °C, 2 mA cm−2, the cells maintaining stability for 240 cycles while still exhibiting relatively high CE > 98.5 %. In addition, at a low N/P ratio of 4:1, the Li-S battery maintains a high capacity of 673.4 mA h g−1 after 200 cycles, while the Li-LFP battery maintains a capacity of 131.16 mA h g−1 and capacity retention of 91.02 % after 300 cycles at 1 C. This research lays groundwork for the exploration of ionic liquids as additives in lithium metal battery electrolytes to further enhance battery safety performance.

Dielectric Sphere Oligomers as Optical Nanoantenna for Circularly Polarized Light.

Control of circularly polarized light (CPL) is important for next-generation optical communications as well as for investigating the optical properties of materials. In this study, we explore dielectric-sphere oligomers for chiral nanoantenna applications, leveraging the cathodoluminescence (CL) technique, which employs accelerated free electrons for excitation and allows mapping the optical response on the nanoscale. For a certain particle-dimers configuration, one of the spheres becomes responsible for the left-handed circular polarization of the emitted light, while right-handed circular polarization is selectively yielded when the other sphere is excited by the electron beam. Similar patterns are also observed in trimers. These phenomena are understood in terms of optical coupling between the electric and magnetic modes hosted by the dielectric spheres. Our research not only expands the understanding of CPL generation mechanisms in dielectric-sphere oligomer antennas but also underscores the potential of such structures in optical applications. We further highlight the utility of CL as a powerful analytical tool for investigating the optical properties of nanoscale structures as well as the potential of electron beams for light generation with switchable CPL parities.