Electron Motion Research Articles

Structurally-controllable electron-momentum filter based on hybrid ferromagnet, Schottky-metal and semiconductor nanostructure

Half-infinitely-wide ferromagnetic stripe and nanosized Schottky-metal stripe can be experimentally assembled on surface of GaAs/AlxGa1-xAs heterostructure, fabricating a hybrid semiconductor nanostructure, which was recently proven to act as an electron-momentum filter (a type of emerging nanoelectronics device). With the help of atomic-layer doping technique, a tunable δ-potential can be intentionally embedded inside the device. Because the inclusion of δ-doping does not clear two-dimensional characteristic of electron motion, an obvious wave vector filtering (WVF) effect still appears. Moreover, the effective potential experienced by electron in the semiconductor nanostructure is closely related to the δ-doping, therefore, a structurally-controllable electron-momentum filter with a tunable WVF efficiency by weight or position of the δ-doping can be obtained for nanoelectronics device applications.

Electronic energy levels and wave-functions evolution from 3-D to 2-D of a hydrogen atom confined by two parallel planes

The compression of an atom produced by two planes induces a change in its electronic structure that evolves from a free atom in 3-D to a 2-D atom. This behavior is of importance in low-dimensional materials and high compression produced by an anvil cell. In this work, we study the evolution of the energy levels and electronic wave-functions of a hydrogen atom placed between two impenetrable planes as a function of the inter-plane separation through a numerical approach. As the inter-plane separation is reduced, the electron motion is restricted along the direction normal to the planes, similar to a particle in a box, while leaving the electron to move unrestricted along the planes, thus, breaking the spherical geometry of the H atom caused by the planes’ compression. The energy levels evolve from 3-D, described by nlm quantum numbers to a 2-D described by n′ml′ , where l′ is the quantum number for a particle in a box along the z direction and n′ is the principal quantum number of the 2-D atom radial direction. We evaluate the energy levels from 3-D to 2-D and the radial average distance 〈ρ〉 in cylindrical coordinates, as a function of the inter-plane separation D along the z-direction. We find that as the inter-plane separation is reduced, the angular momentum quantum number l merges to the z-component of the angular momentum and it produces two branches, a symmetric for l-even and one anti-symmetric for l-odd, connected to a particle in a box quantum number l′ along the z-axis with implications in the atom photo-luminescence, resulting from the symmetry of the system. Furthermore, states with l-odd merge with states with l-even, as they have the same energy and average distance when D → 0. We provide an Aufbau principle for it. Our results agree to the analytical solutions at the 3-D and 2-D limiting cases.

Impact ionization double peaks analyzed in high temporal resolution on Solar Orbiter

Abstract. Solar Orbiter is equipped with electrical antennas performing fast measurements of the surrounding electric field. The antennas register high-velocity dust impacts through the electrical signatures of impact ionization. Although the basic principle of the detection has been known for decades, the understanding of the underlying process is not complete, due to the unique mechanical and electrical design of each spacecraft and the variability of the process. We present a study of electrical signatures of dust impacts on Solar Orbiter's body, as measured with the Radio and Plasma Waves electrical suite. A large proportion of the signatures present double-peak electrical waveforms in addition to the fast pre-spike due to electron motion, which are systematically observed for the first time. We believe this is due to Solar Orbiter's unique antenna design and a high temporal resolution of the measurements. The double peaks are explained as being due to two distinct processes. Qualitative and quantitative features of both peaks are described. The process for producing the primary peak has been studied extensively before, and the process for producing the secondary peak has been proposed before (Pantellini et al., 2012a) for Solar Terrestrial Relations Observatory (STEREO), although the corresponding delay of 100–300 µs between the primary and the secondary peak has not been observed until now. Based on this study, we conclude that the primary peak's amplitude is the better measure of the impact-produced charge, for which we find a typical value of around 8 pC. Therefore, the primary peak should be used to derive the impact-generated charge rather than the maximum. The observed asymmetry between the primary peaks measured with individual antennas is quantitatively explained as electrostatic induction. A relationship between the amplitude of the primary and the secondary peak is found to be non-linear, and the relation is partially explained with a model for electrical interaction through the antennas' photoelectron sheath.

Femtosecond Drift Photocurrents Generated by an Inversely Designed Plasmonic Antenna.

Photocurrents play a crucial role in various applications, including light detection, photovoltaics, and THz radiation generation. Despite the abundance of methods and materials for converting light into electrical signals, the use of metals in this context has been relatively limited. Nanostructures supporting surface plasmons in metals offer precise light manipulation and induce light-driven electron motion. Through the inverse design optimization of a gold nanostructure, we demonstrate enhanced volumetric, unidirectional, intense, and ultrafast photocurrents via a magneto-optical process derived from the inverse Faraday effect. This is achieved through fine-tuning the amplitude, polarization, and gradients in the local light field. The virtually instantaneous process allows dynamic photocurrent modulation by varying optical pulse duration, potentially yielding nanosources of intense, ultrafast, planar magnetic fields and frequency-tunable THz emission. These findings open avenues for ultrafast magnetic material manipulation and hold promise for nanoscale THz spectroscopy.

Epoxy/Graphene Nanoplatelet (GNP) Nanocomposites: An Experimental Study on Tensile, Compressive, and Thermal Properties.

This paper presents an experimental investigation of nanocomposites composed of three ratios of epoxy/graphene nanoplatelets (GNPs) by weight. The 0.1, 0.2, and 0.3 wt.% specimens were carefully manufactured, and their mechanical and thermal conductivity properties were examined. The tensile strength and modulus of epoxy/GNPs were enhanced by the large surface area of graphene nanoplatelets, causing crack deflection that created new fracture fronts and friction because of the rough fracture surface. However, the compressive strength was gradually reduced as GNP loading percentages increased. This was probably due to severe plastic yielding on the epoxy, leading to catastrophic axial splitting caused by premature fractures. Furthermore, the highest thermal conductivity was 0.1283 W/m-K, representing a 20.92% improvement over neat epoxy (0.1061 W/m-K) when 0.3 wt.% GNPs were added to the epoxy. This was because of efficient heat propagation in the GNPs due to electron movement through percolative paths. The tensile failure mode in epoxy/GNP nanocomposites showed a few deflected and bifurcated rough cracks and brittle, dimple-like fractures. Contrarily, compressive failure mode in GNP-added epoxy showed plastic flexural buckling and brittle large-axial splitting. The epoxy/GNP nanocomposites were considered a damage-tolerant material.

Capturing electron-driven chiral dynamics in UV-excited molecules

Chiral molecules, used in applications such as enantioselective photocatalysis1, circularly polarized light detection2 and emission3 and molecular switches4,5, exist in two geometrical configurations that are non-superimposable mirror images of each other. These so-called (R) and (S) enantiomers exhibit different physical and chemical properties when interacting with other chiral entities. Attosecond technology might enable influence over such interactions, given that it can probe and even direct electron motion within molecules on the intrinsic electronic timescale6 and thereby control reactivity7–9. Electron currents in photoexcited chiral molecules have indeed been predicted to enable enantiosensitive molecular orientation10, but electron-driven chiral dynamics in neutral molecules have not yet been demonstrated owing to the lack of ultrashort, non-ionizing and perturbative light pulses. Here we use time-resolved photoelectron circular dichroism (TR-PECD)11–15 with an unprecedented temporal resolution of 2.9 fs to map the coherent electronic motion initiated by ultraviolet (UV) excitation of neutral chiral molecules. We find that electronic beatings between Rydberg states lead to periodic modulations of the chiroptical response on the few-femtosecond timescale, showing a sign inversion in less than 10 fs. Calculations validate this and also confirm that the combination of the photoinduced chiral current with a circularly polarized probe pulse realizes an enantioselective filter of molecular orientations following photoionization. We anticipate that our approach will enable further investigations of ultrafast electron dynamics in chiral systems and reveal a route towards enantiosensitive charge-directed reactivity.

Extreme magnetoresistance at high-mobility oxide heterointerfaces with dynamic defect tunability

Magnetic field-induced changes in the electrical resistance of materials reveal insights into the fundamental properties governing their electronic and magnetic behavior. Various classes of magnetoresistance have been realized, including giant, colossal, and extraordinary magnetoresistance, each with distinct physical origins. In recent years, extreme magnetoresistance (XMR) has been observed in topological and non-topological materials displaying a non-saturating magnetoresistance reaching 103−108% in magnetic fields up to 60 T. XMR is often intimately linked to a gapless band structure with steep bands and charge compensation. Here, we show that a linear XMR of 80,000% at 15 T and 2 K emerges at the high-mobility interface between the large band-gap oxides γ-Al2O3 and SrTiO3. Despite the chemically and electronically very dissimilar environment, the temperature/field phase diagrams of γ-Al2O3/SrTiO3 bear a striking resemblance to XMR semimetals. By comparing magnetotransport, microscopic current imaging, and momentum-resolved band structures, we conclude that the XMR in γ-Al2O3/SrTiO3 is not strongly linked to the band structure, but arises from weak disorder enforcing a squeezed guiding center motion of electrons. We also present a dynamic XMR self-enhancement through an autonomous redistribution of quasi-mobile oxygen vacancies. Our findings shed new light on XMR and introduce tunability using dynamic defect engineering.

Directional movement of electron induced by interfacial coupling in CuS@NiCo-LDHs for efficient alkaline oxygen evolution reaction

Heterojunction has the characteristics of adjusting catalyst structure, improving oxygen evolution kinetics and breaking the elevated reaction barrier of oxygen evolution process. In this paper, a heterostructure catalyst of NiCo-LDHs nanosheets encapsulated CuS hollow nano-octahedrals has been reported, which has better stability and higher mass transfer efficiency compared with two-dimensional nanosheets. Density functional theory (DFT) calculations indicate that the heterostructure strengthens the orbital hybridization of metal 3d and O 2p, at the same time, the heterointerface coupling induces the directional movement of electrons from NiCo-LDHs to CuS, which together provide abundant high-valence Ni and Co active sites, promote the conversion of *OH to *O species, thus reducing the energy required for the reaction. Hence, CuS@NiCo-LDHs exhibits excellent OER performance and good stability in 1 M KOH. When the current density is 10 mA/cm2, the overpotential and Tafel slope of this catalyst is only 253 mV and 56 mV/dec, respectively. This study furnishes the construction of heterogeneous structures and the catalyst exploitation with serviceable insights.

Fabrication of highly flexible, wearable, free-standing symmetric supercapacitors with high voltage operation enabled by hierarchical graphene/cerium oxide/polypyrrole hybrid films

Flexible, free-standing supercapacitors play a significant role in the development of future wearable energy storage devices. Herein, we successfully fabricated the highly flexible and free-standing graphene/cerium oxide/polypyrrole hybrid films by thermal reduction of graphene oxide (GO) followed by the sol–gel synthesis of CeO2 and then the addition of PPy. By regulating oxygen functional groups in GO, the electronic conductivity and electroactive sites of the hybrid films are significantly controlled, leading to enhanced energy storage capability. Finally, a symmetric flexible supercapacitor (FSC) device was developed using the prepared films as electrodes. Resulting, the integrated symmetric GO-400/CeO2/PPy FSC manifests excellent areal capacitance of 49.0 mF cm−2 at 1 mA cm−2, with a durability of 83.1 % over 10,000 cycles. Specifically, the FSC exhibited capacitance retention of 77.2 % after 10,000 cycles under bending state with exceptional rate ability. Meanwhile, an impressive energy density of 19.69 µW h cm−2 was attained at a power density of 0.85 mW cm−2. Evidently, the synergistic interactions between GO and PPy nanosheets, along with CeO2 favour the rapid electron movement of electrode material for next-generation wearable, portable electronics.

Phase control of nonlinear Breit-Wheeler pair creation

Electron-positron pair creation occurs throughout the universe in the environments of extreme astrophysical objects, such as pulsar magnetospheres and black hole accretion disks. The difficulty of emulating these environments in the laboratory has motivated the use of ultrahigh-intensity laser pulses for pair creation. Here we show that the phase offset between a laser pulse and its second harmonic can be used to control the relative transverse motion of electrons and positrons created in the nonlinear Breit-Wheeler process. Analytic theory and particle-in-cell simulations of a head-on collision between a two-color laser pulse and electron beam predict that with an appropriate phase offset, the electrons will drift in one direction and the positrons in the other. The resulting current may provide a collective signature of nonlinear Breit-Wheeler, while the spatial separation resulting from the relative motion may facilitate isolation of positrons for subsequent applications or detection. Published by the American Physical Society 2024

Deciphering Charge Transfer Processes in Transition Metal Complexes from the Perspective of Ultrafast Electronic and Nuclear Motions.

Chemical transformations in charge transfer states result from the interplay between electronic dynamics and nuclear reorganization along excited-state trajectories. Here, we investigate the ultrafast structural dynamics following photoinduced electron transfer from the metal-metal-to-ligand charge transfer state of an electron donor, a Pt dimer complex, to a covalently linked electron acceptor group using ultrafast time-resolved wide-angle X-ray scattering and optical transient absorption spectroscopy methods to disentangle the interdependence of the excited-state electronic and nuclear dynamics. Following photoexcitation, Pt-Pt bond formation and contraction takes up to 1 ps, much slower than the corresponding process in analogous complexes without electron acceptor groups. Because the Pt-Pt distance change is slow with respect to excited-state electron transfer, it can affect the rate of electron transfer. These results have potential impacts on controlling electron transfer rates via structural alterations to the electron donor group, tuning the charge transfer driving force.

Analysis of undergraduate chemistry students’ responses to substitution reaction mechanisms: a road to mastery

Abstract This study analyzed third-year undergraduate Chemistry major students’ drawings and written explanations of substitution reactions. Seventy (70) students were purposively selected for this study. The main data collection instrument was a diagnostic test and students’ responses were analyzed using deductive coding. The study aimed to unearth students’ conceptual understanding and difficulties on substitution reactions to provide significant insights into improving teaching strategies and learning outcomes. The findings revealed that: 1. Students were more familiar with SN2 reaction mechanisms and could answer questions on SN2 reaction mechanisms better than SN1 reaction mechanisms; 2. Students’ use of ‘chemical vocabulary’ did not translate into an understanding of electron movement and causal mechanistic explanation; 3. About 97 % of the students who gave a correct/partially correct description provided a description of what was happening in the reaction without any further explanation of why the reaction occurred; 4. Students had a slightly better understanding of drawing the correct mechanisms than providing accurate explanations. This study recommends that, in teaching organic reaction mechanisms, instructors should emphasize on electron-pushing formalisms and explain how and why reactions occur to encourage mechanistic thinking in students. Also, students should be given ample practice in organic reaction mechanisms to improve mastery.

Photo-Fenton-like degradation of tetracycline through peroxymonosulfate activation over 2D BiOBr/FeOOH nanosheets and membrane application

The selection of photosensitizer substrates with high photocatalytic efficiency is crucial for leveraging the advantages of metal-based materials in photo-Fenton-like process. Herein, we report a novel 2D layered BiOBr/FeOOH nanosheets equipped with a built-in electric field (BIEF) to activate peroxymonosulfate (PMS) for the degradation of tetracycline (TC). The photocatalytic efficiency of BiOBr is enhanced by fine-tuning the Br source quantity. Both experimental and theoretical analyses confirm that BIEF at the BiOBr/FeOOH heterointerface expedites the movement of photogenerated electrons, significantly boosting both photocatalytic and photo-Fenton-like activities. The BiOBr/FeOOH + PMS + Vis system exhibits a high TC removal rate of 96 % with only 0.24 mM of PMS and nearly 100 % of PMS utilization. Moreover, affixing BiOBr/FeOOH nanosheets onto a PVDF microfiltration membrane, we establish a continuous flow reactor system for antibiotic wastewater treatment. This system demonstrates a remarkable TC removal efficiency consistently above 97.5 % for 6 h of continuous injection, underscoring its practicality and potential for real-world applications.

Statistical Properties of Exohiss Waves and Associated Scattering Losses of Radiation Belt Electrons

AbstractExohiss waves are a type of structureless whistler‐mode waves that exist in the low density plasmatrough outside the plasmapause and may potentially perturb the motions of electrons in the radiation belt and ring current. Using data from Van Allen Probe A, we analyze the distribution of magnetic power spectral density (PSD) of exohiss waves in different magnetic local time (MLT) and L‐shell regions near the geomagnetic equator. The results reveal that the peak magnetic PSD of exohiss waves is the weakest at MLT = 0–6 and the strongest at MLT = 12–18. The magnetic PSDs of exohiss waves are much lower than those of chorus and hiss waves except for the MLT = 12–18 sector. In addition, we calculated the quasi‐linear bounce‐averaged pitch angle and momentum diffusion coefficients (〈Dαα〉 and 〈Dpp〉) of electrons caused by exohiss waves. The diffusion coefficients are then compared with those caused by chorus and hiss waves. The peak 〈Dαα〉 of electrons driven by exohiss waves becomes stronger as L‐shell increases at all MLTs and is the greatest on the dayside, especially in the sector of MLT = 12–18. Exohiss waves have more significant effect on the loss of radiation belt electrons with specific energy levels related to MLT and L‐shell region compared to chorus and hiss waves. On the other hand, 〈Dpp〉 of electrons caused by exohiss waves is very small, which illustrates that exohiss waves have almost no acceleration effect on electrons.

Unraveling charge transfer dynamics in AgBr/Bi4Ti3O12/Bi2Sn2O7 ternary S-scheme heterojunction photocatalyst

In this study, AgBr/Bi4Ti3O12/Bi2Sn2O7 (ABr/BTO/BSO) composites were successfully synthesized to facilitate multi-channel fast charge transfer. This directs the charge carriers to travel along multichannel pathways and suppresses carrier recombination. The mechanisms underlying charge transfer in the dual S-scheme heterojunction composites were elucidated using density functional theory (DFT) and in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS). Furthermore, electron spin resonance (ESR) and burst experiments verified h+, ·O2 -, and ·OH as the primary active species in the catalytic process. The ABr/BTO/BSO composites demonstrated exceptional photocatalytic redox capabilities, completely degrading rhodamine B (RhB) and achieving degradation rates of 77.21% for tetracycline (TC) and 81.04% for Cr (VI). Both experimental and theoretical analyses confirmed the intrinsic efficacy of photo-induced electron movement within the composites. This research introduces innovative design concepts and strategies for the advanced exploration of electron channel transfer in ABr/BTO/BSO ternary composites and the development of novel composite photocatalytic systems.

Particle traps constructed on the insulator of conductive slip rings for surface flashover mitigation under particle adhesion

The generation of abrasive particles is an unavoidable consequence of sliding electrical contact wear in conductive slip rings (SRs). The adhesion of abrasive particles to the insulators may lead to a decrease in flashover voltage, posing a risk to satellite power transmission. In this paper, the effect of abrasive particles on flashover is first studied. Surface abrasive particles can distort the surface electric field of the dielectric, absorb scattered electrons, and then re-emit them, thereby accelerating the development and formation of secondary electron avalanches. Flashover test results indicate that surface abrasive particles lead to a significant reduction in flashover voltage. To mitigate the impact of particle adhesion on flashover, a method of constructing particle traps on the surface of insulators is proposed. The location and structural parameters of the particle trap are further optimized and determined. The flashover test results using planar dielectric samples and SR insulator samples both demonstrate that the optimized particle trap can significantly improve the flashover voltage. The dielectric maintains high electrical strength even when particles are trapped in particle traps. The physical details of the impact of particles on flashover and the effect of particle traps are analyzed utilizing an electron movement simulation, corroborating the experiment from a microscopic aspect.

Metal–organic framework–derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc–air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe–NC@p–NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M–N–C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08–NC@p–NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm−2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm−2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm−2.

Integration of Sn(IV)porphyrin on mesoporous alumina support and visible light catalytic photodegradation of methylene blue

Two composite catalysts, designated as SnTTP/SA@Al2O3 and SnTTP@Al2O3, were synthesized by the reaction of Al2O3 and trans-dihydroxo-[5,10,15,20-tetrakis(p-tolyl)porphyrinato]tin(IV) (SnTTP) with and without succinic acid (SA) pretreatment, respectively. Chemically, SnTTP was more tightly incorporated onto the surface of Al2O3 through the anchoring group SA in SnTTP/SA@Al2O3 than that in SnTTP@Al2O3. The SA bridging anchoring groups hindered the dissociation of SnTTP from SnTTP@Al2O3 during photodegradation. Therefore, the strong association between Al2O3 and SnTTP via SA connections not only intensified the quantity of tin porphyrin on the surface of Al2O3 but also accelerated electron movement from the excited SnTTP molecules to the conduction band of Al2O3. The aforementioned mechanism demonstrates a significant improvement in the catalytic photodegradation of methylene blue (MB) dye for SnTTP/SA@Al2O3 compared to SnTTP, Al2O3, and SnTTP@Al2O3 under visible-light irradiation. Within 90 min of using SnTTP/SA@Al2O3 at a rate of 0.0406 min−1, the photodegradation capacity of MB was found to be 98 %. The synergistic effect between Al2O3 and SnTTP improved the catalytic efficiency of SnTTP/SA@Al2O3 compared to that of both SnTTP and Al2O3. This study provides a new direction for the construction of highly efficient porphyrin-based photocatalysts and has significant value for extending their applications in water treatment.

Theoretical triple differential cross sections for ionization of N 2 and CH 4 molecules by electron impact

We present the angular distribution of electron emission by calculating the triple differential cross sections for (e, 2e) process on N 2 and CH 4 by using the three-body formalism of molecular first Born approximation (MFBA), two-Coulomb wave (M2CW), and three-Coulomb wave (M3CW) models, respectively. In these models, a Coulomb distorted wave is considered for the motion of the incident electron. We have considered the continuum-continuum correlation effect by choosing the final state as the three-Coulomb and two-Coulomb wave functions in M3CW and M2CW models, whereas the ejected electron is affected by a single centre field of the target in the MFBA model. In the M2CW model, the interaction between scattered electron-residual target ion has been described as a plane wave. The distinguishing feature among the three models has been noted in the TDCS as a strong binary peak with and without a recoil peak for several electron emission energies at fixed scattering angle. In the case of N 2 molecule, the TDCS shows oscillatory behaviour with the variation of the electron emission angle. The positions of the binary peak obtained by our theoretical models are well established by the experimental findings, but a large deviation is found in the region of the recoil peak. The contributions of TDCS for different molecular orbitals of the molecules to the spectrum of angular distributions at different electron emission energies have also been analyzed. Finally, a comparison is made with the measurement in coplanar asymmetry geometry. Overall, good agreement was found between experiments and M3CW theory.

Controlling electron motion with attosecond precision by a shaped femtosecond intense laser pulse

Controlling electron motion with attosecond precision by a shaped femtosecond intense laser pulse