Electron Motion Research Articles

Development of an electron track-structure mode for arbitrary semiconductor materials in PHITS

Abstract Optimizing the design of semiconductor detector requires an electron track-structure code that can trace an incident electron motion with energies down to a few eV and simulate the production process of excited electrons in semiconductors. We therefore developed an Electron Track Structure mode applicable to ARbitrary Targets (ETSART) and implemented it into Particle and Heavy Ion Transport code System (PHITS). ETSART can simulate the electrons’ motion in arbitrary semiconductor materials using their bandgap energies. The accuracy of ETSART was validated by comparing the calculated electron path lengths in semiconductor materials with the corresponding data in the ICRU Report 37. Using ETSART, we also computed the mean energy required to produce an electron–hole pair (epsilon value) in various semiconductors and found that the epsilon value varies nonlinearly with the bandgap energy. Thus, ETSART can be useful for initial and mechanistic evaluations of electron–hole pair formation in new materials.

Spin Atomic Model: Role of Electron Spin in forming Atoms and Molecules

This paper recounts the history of atomic models and their limitations in brief. The role of spin motion of paired electrons in building the atoms is a subject of the discussion. The opposite spin velocity of paired electrons in an atom should reduce the repulsion between them. Hence, by adjusting their opposite spin velocity, the force of repulsion between the paired electrons and the force of attraction between the nucleus and the individual electrons in that pair can be balanced without revolving the electrons in orbits. In this way a pair of electrons can maintain their particular distance from the nucleus in atom with adjusting their spin motions. This arrangement easily supports the atoms to build the different molecules, compounds and solid materials. This atomic model may be referred as spin atomic model which should be the fact.

Initial kinetics of electrons, ions and electric field in planar vacuum diode with plasma cathode

The paper presents the results of a 1D1V theoretical study of the initial stage of plasma expansion into a planar vacuum gap 1 cm long with an applied voltage of 500–5000 V. Based on the collisionless kinetic and Maxwell equations, the motion of a two-component electron–ion plasma in a self-consistent electric field is described. The fundamental mechanism of ‘superthermal’ velocities of the emission edge of the plasma and anode-directed velocities of positive ions is demonstrated in detail. The general regularities of this process are established for variations in the number density of the initial plasma and the applied voltage.

Azimuthal ion movement in HiPIMS plasmas—part I: velocity distribution function

Magnetron sputtering discharges feature complex magnetic field configurations to confine the electrons close to the cathode surface. This magnetic field configuration gives rise to a strong electron drift in azimuthal direction, with typical drift velocities on the order of 100 km s−1. In high power impulse magnetron sputtering plasmas, the ions have also been observed to follow the movement of electrons with velocities of a few km s−1, despite being not magnetized. In this work, we report on measurements of the azimuthal ion velocity using spatially resolved optical emission spectroscopy, allowing for a more direct measurement compared to experiments performed using mass spectrometry. The azimuthal ion velocities increase with target distance, peaking at about 1.55 km s−1 for argon ions and 1.25 km s−1 for titanium ions. Titanium neutrals are also found to follow the azimuthal ion movement which is explained with resonant charge exchange collisions. The experiments are then compared to a simple test-particle simulation of the titanium ion movement, yielding good agreement to the experiments when only considering the momentum transfer from electrons to ions via Coulomb collisions as the only source of acceleration in azimuthal direction. Based on these results, we propose this momentum transfer as the primary source for ion acceleration in azimuthal direction.

Ballistic transport spectroscopy of spin-orbit-coupled bands in monolayer graphene on WSe2

Van der Waals interactions with transition metal dichalcogenides were shown to induce strong spin-orbit coupling (SOC) in graphene, offering great promises to combine large experimental flexibility of graphene with unique tuning capabilities of the SOC. Here, we probe SOC-driven band splitting and electron dynamics in graphene on WSe2 by measuring ballistic transverse magnetic focusing. We found a clear splitting in the first focusing peak whose evolution in charge density and magnetic field is well reproduced by calculations using the SOC strength of ~ 13 meV, and no splitting in the second peak that indicates stronger Rashba SOC. Possible suppression of electron-electron scatterings was found in temperature dependence measurement. Further, we found that Shubnikov-de Haas oscillations exhibit a weaker band splitting, suggesting that it probes different electron dynamics, calling for a new theory. Our study demonstrates an interesting possibility to exploit ballistic electron motion pronounced in graphene for emerging spin-orbitronics.

Optoelectronic Manifestation of Orbital Angular Momentum Driven by Chiral Hopping in Helical Se Chains.

Chiral materials have garnered significant attention in the field of condensed matter physics. Nevertheless, the magnetic moment induced by the chiral spatial motion of electrons in helical materials, such as elemental Te and Se, remains inadequately understood. In this work, we investigate the development of quantum angular momentum enforced by chirality by using static and time-dependent density functional theory calculations for an elemental Se chain. Our findings reveal the emergence of an unconventional orbital texture driven by the chiral geometry, giving rise to a nonvanishing current-induced orbital moment. By incorporating spin-orbit coupling, we demonstrate that current-induced spin accumulation arises in the chiral chain, which fundamentally differs from the conventional Edelstein effect. Furthermore, we demonstrate optoelectronic detection of the orbital angular momentum in the chiral Se chain, providing an alternative to the interband Berry curvature, which is ill-defined in low dimensions.

The zitterbewegung electron puzzle

This work is an updated revision of semiclassical descriptions for the electron, including the fully relativistic QED-P model from H. J. Wilson based on the original Dirac equation (DE). The models presented hereafter go beyond the depiction of the electron as a structureless nondimensional point like charge with momentum and position determined by a probabilistic interpretation of the wavefunction described in terms of an electronic density cloud. These models share features in common that provide useful insights concerning the nature of the electron; for instance, they all consider zitterbewegung, a light speed “trembling-along-the-way” electron motion, to be a real oscillatory motion of the electron. The last model presented in this review is the electron mass model from Val Baker et al. [Phys. Essays 32, 255 (2019)], where the electron mass is defined in terms of a holographic surface-to-volume ratio Φ and the relationship of the electric charge at the Planck scale to that at the electron scale, obtaining a value in agreement with the latest CODATA value. We discuss the relationship between these models. The large number of correspondences between the models should not be taken lightly and indicate, in our view, that something very fundamental about the nature of the electron is being put forward by this study.

Influence of cerium and yttrium addition on strength and electrical conductivity of pure aluminum alloys

To develop pure aluminum alloys with high conductivity and strength, Al-0.2Ce and Al-0.2Ce-0.1Y alloys were prepared by rolling and annealing processes in this study. The effects of trace rare earth elements on the strength and electrical conductivity of the pure aluminum alloys were investigated. It is revealed that the addition of Ce and Y to pure aluminum can effectively enhance the strength and electrical conductivity of the alloys. In Al-0.2Ce, the addition of Ce can effectively refine the grain size of α-Al, with an average grain size of 90.68 μm in the as-cast state. The grain size of the alloy is further reduced to 87.55 μm by the simultaneous addition of Y. The synergistic addition of Ce and Y changes the properties of the alloy. The addition of Ce and Y also produces the Al11Ce3 and Al3Y second phases, which have coherent relationship with α-Al. The two-dimensional mismatch degree was calculated to be only 4.43% and 0.85%, respectively, which can provide a certain amount of nucleation substrate for α-Al in the incubation stage. The interfacial match between the L12 structure of Al3Y and α-Al was calculated using first-principles simulations. The results indicate that Al3Y has a strong bonding effect with α-Al. Nanoscale second phases at grain boundaries can be effective in reducing resistivity due to dislocation motion. Nanoscale second phases with better matching interfaces to the substrate have no positive effect on the scattering motion of electrons.

Principle of CoS2/ZnIn2S4 heterostructure effect and its mechanism of action in a visible light-catalyzed antibacterial process

The development of visible-light-driven catalytic antimicrobial technology is a significant challenge. In this study, heterojunctions were constructed for the appropriate modification of semiconductor-based photocatalysts. A simple hydrothermal method was used for material reconstruction, and smaller CoS2 nanoparticles were deposited and in situ grown on two-dimensional nanoflower-like ZnIn2S4 carriers to form CoS2/ZnIn2S4 (CS/ZIS) Schottky heterojunctions. Systematic study via characterization techniques and density functional theory calculations indicated that the excellent photocatalytic activity of CS/ZIS stemmed from the solid interfacial coupling between the two solid-phase materials. These materials acted as co-catalysts to increase the number of active reaction sites, enhance charge transfer, drive unidirectional electron movement, and improve charge separation efficiency, which effectively facilitated the production of reactive oxygen species (ROS). The optimized CS/ZIS heterojunction exhibited excellent performance for the efficient photocatalytic degradation of organic matter and inactivation of Escherichia coli (E. coli) compared with the ZnIn2S4 photocatalyst. Moreover, the antibacterial mechanism of the heterojunction photocatalyst and the extent of damage to the cell membrane and internal cytoplasm were explored by performing various assays. It was demonstrated that superoxide radicals are the predominant active species and multiple ROS act together to cause oxidative stress damage and cell inactivation.

Numerical Simulations of Space Charge Waves Amplification Using Negative Differential Conductance in Strained Si/SiGe at 4.2 K

This paper introduces a two-dimensional (2D) numerical simulation of the amplification of space charge waves using negative differential conductance in a typical MOS silicon–germanium (SiGe)-based field-effect transistors (FET) and complementary metal oxide semiconductor (CMOS) technology at 4.2 K. The hydrodynamic model of electron transport was applied to describe the amplification of space charge waves in this nonlinear medium (i.e., the negative differential conductance). This phenomenon shows up in GaAs thin films at room temperature. However, this can be also observed in a strained Si/SiGe heterostructure at very low temperatures (T < 77 K) and at high electric fields (E > 10 KV/cm). The results show the amplification and non-linear interaction of space charge waves in a strained Si/SiGe heterostructure occurs for frequencies up to approximately 60 GHz at T = 1.3 K, 47 GHz at T = 4.2 K, and 40 GHz at T = 77 K. The variation of concentration and electric field in the Z and Y directions are calculated at 4.2 K. The electric field in the Z direction is greater than in the Y direction. This is due to the fact that this is the direction of electron motion. In addition to deep space applications, these types of devices have potential uses in terrestrial applications which include magnetic levitation transportation systems, medical diagnostics, cryogenic instrumentation, and superconducting magnetic energy storage systems.

A Numerical Simulation Study on DC Positive Corona Discharge Characteristics at the Conductor’s Tip Defect

For investigating the relationship between the surface corona discharge of a DC wire and other influencing factors, a hybrid numerical model based on a fluid-chemical reaction was proposed to simulate the discharge process at the tip defect of the wire. Under different defect geometries and gas pressures achieved via simulation, the microscopic process of the reaction and movement of electrons and heavy particles during a positive corona discharge was studied, and characteristic parameters such as corona inception voltage and discharge current were analyzed. Furthermore, through the corona cage test, for a specific electrode configuration, corona inception voltages under different pressures were compared and verified, which showed that the model was reasonable. The results showed that the maximum electron density of the streamer head was about 1 × 1020 m−3, the rise time of the pulse current was about 10 ns, and the decay time was about 300–500 ns. The corona inception voltage decreased with an increase in the tip height and decreases in the tip curvature radius, conductor radius, and background air pressure; the amplitude of the pulse current increased with increases in the wire radius and curvature radius of the defect tip and decreases in tip height and background air pressure. The experimental results are consistent with the simulation results, which verifies the reasonability of the model.

High-order harmonic generation of ZnO crystals in chirped and static electric fields

High harmonic generation in ZnO crystals under chirped single-color field and static electric field are investigated by solving the semiconductor Bloch equation (SBE). It is found that when the chirp pulse is introduced, the interference structure becomes obvious while the harmonic cutoff is not extended. Furthermore, the harmonic efficiency is improved when the static electric field is included. These phenomena are demonstrated by the classical recollision model in real space affected by the waveform of laser field and inversion symmetry. Specifically, the electron motion in k-space shows that the change of waveform and the destruction of the symmetry of the laser field lead to the incomplete X-structure of the crystal-momentum-resolved (k-resolved) inter-band harmonic spectrum. Furthermore, a pre-acceleration process in the solid four-step model is confirmed.

Tailoring surface plasmon wave based on natural hyperbolic dispersion of black phosphorus

The unique transport behavior of surface plasmons confined in the xy-plane is explored using different transition frequencies for different crystallographic axes of black phosphorus (BP). Electromagnetic simulations reveal that the proportion of intraband and interband electron motion within the two-dimensional (2D) BP governs the propagation state of surface plasmons. We illustrate the topological transformation in the dispersion curve of 2D BP that can lead to changes in the surface plasmon propagation state. Moreover, the different dispersion relations have been tuned by changing the electron doping concentration of 2D BP that can be applied to manipulate the propagation direction of surface plasmons. Our design offers a promising platform for plasma control applications in the field of optics.

Hybrid neuroelectronics: towards a solution-centric way of thinking about complex problems in neurostimulation tools

Responsive neuromodulation is increasingly being used to treat patients with neuropsychiatric diseases. Yet, inefficient bridges between traditional and new materials and technological innovations impede advancements in neurostimulation tools. Signaling in the brain is accomplished predominantly by ion flux rather than the movement of electrons. However, the status quo for the acquisition of neural signals is using materials, such as noble metals, that can only interact with electrons. As a result, ions accumulate at the biotic/abiotic interface, creating a double-layer capacitance that increases impedance and negatively impacts the efficiency of neural interrogation. Alternative materials, such as conducting polymers, allow ion penetration in the matrix, creating a volumetric capacitor (two orders of magnitude larger than an area-dependent capacitor) that lowers the impedance and increases the spatiotemporal resolution of the recording/stimulation. On the other hand, the increased development and integration capabilities of CMOS-based back-end electronics have enabled the creation of increasingly powerful and energy-efficient microchips. These include stimulation and recording systems-on-a-chip (SoCs) with up to tens of thousands of channels, fully integrated circuitry for stimulation, signal conditioning, digitation, wireless power and data telemetry, and on-chip signal processing. Here, we aim to compile information on the best component for each building block and try to strengthen the vision that bridges the gap among various materials and technologies in an effort to advance neurostimulation tools and promote a solution-centric way of considering their complex problems.

Enhancing photocatalytic performance of Co-TiO2 and Mo-TiO2-based catalysts through defect engineering and doping: A study on the degradation of organic pollutants under UV light

Nanostructured photocatalysts based on cobalt and molybdenum-doped TiO2 composite materials were developed to enhance photocatalytic performance. The creation of defects through partial carbothermal reduction resulted in materials with lower band gaps, improving efficiency. The carbon lattice facilitated electron movement and inhibited electron-hole recombination, while the large surface area of the nanosheets enhanced catalyst effectiveness. The materials were characterized using XRD, FTIR, Raman spectroscopy, FESEM, and UV–Vis spectroscopy. The degradation of arsenazo 3 dye was used to evaluate the catalysts, with all three showing efficient degradation. The TiO2-Mo-C catalyst exhibited the highest degradation rate (99.8%). Kinetic data indicated that the photodegradation followed pseudo-first-order and Langmuir-Hinshelwood kinetics. Remarkably, the reaction rate constant (kC = 41.61 mg L-1 min−1) and adsorption equilibrium constant (KLH = 1.26 × 10-3 L mg−1) of the TiO2-Mo-C catalyst were significantly superior to other catalysts. These photocatalysts demonstrated excellent stability and reusability over six cycles.

Pump and ionizing-probe dynamics in a simultaneous treatment of electronic and nuclear motion in LiH

Pump and ionizing-probe dynamics in a simultaneous treatment of electronic and nuclear motion in LiH

Interdisciplinary Fundamental Concepts in STEM: Solid State Physics and COVID-19 Pandemic Evolution

The rapid development of computer-aided design tools, such as MATLAB or Octave, or Mathematica enabled students to solve many complicated problems focusing less on underlying STEM-related concepts that are interdisciplinary. Therefore, it is important to demonstrate how it could be done using specific examples that could be linked to different subjects or even to their everyday life experience. This paper reports on using the COVID-19 pandemic evolution model (Shur, 2022) in my class on the physics of advanced semiconductors devices. I use this model to show how the concepts, such as the Born-Oppenheimer approximation and Fermi-Dirac distribution function could be used in a completely different STEM field. In solid-state physics, the Born-Oppenheimer approximation is used to separate rapid electronic motion, relevant to the electronic states and much slower nuclei motion (since nuclei are thousands of times heavier than electrons). Likewise, the COVID-19 model uses a relatively fast pandemic evolution growth or decay constant, a slow function of time itself. In solid-state physics, the Fermi-Dirac distribution function describes the transition from the occupied electronic states to empty electron states with the temperature determining the transition interval. The COVID-19 model uses the generalized Fermi-distribution function to describe the mitigation measures that determine the transition from a high to a lower infection rate. A more accurate COVID-19 evolution model requires a generalized Fermi-Dirac function that accounts for a slow variation of the effect of the mitigation measures with time. In turn, this generalization could be used in solid-state physics to describe the electron temperature increase in the electric field.

The effect of thermomechanical processing on the piezoelectric and electrical conductivity of PLA/2.5%MWCNT composite

The electrical properties of polymer materials, such as electrical conductivity and piezoelectricity, are significantly influenced by the ratio of amorphous to crystalline regions. Additionally, the alignment of added particles and formed crystallites is another factor that affects these properties. Conversely, a well-designed thermomechanical process can significantly impact the rate of change. This study investigates nanocomposite production with an optimal percentage of modified nanoparticles using a revamped electrospinning process and fully effective post-processing. Piezoelectric constant d33 of PLLA-2.5%CNT discussion was pioneered in this article. It was proved that the crystallinity percentage of nanocomposites can be improved by up to 70% by applying a suitable thermomechanical process and adding a suitable percentage of particles. The formation of the ordered phase, the creation of a special pattern for the movement of electrons, and the change in the conformation of the carbonyl group are the reasons for increasing the piezoelectric constant from 0.2 to 3 and increasing the electrical conductivity by 1000 orders of magnitude. Among other reasons, we can mention the alignment increment of polymer particles and crystallites and their way of texturizing in order to apply thermomechanical processing.

Relationship between fluorescence characteristics of coal macerals and excitation time

The fluorescence characteristics of coal macerals can be used as one of the indexes to evaluate the properties of coking coal. In this work, a single-wavelength laser with a wavelength of 360 nm was used as the excitation source to excite the surface of particulate block under a polarizing microscope. Effect of excitation time on fluorescence characteristics of the macerals was studied. The relationship between spontaneous fluorescence intensity and the excitation time of each maceral of six kinds of coking coals show that the fluorescence characteristics of coal macerals are related to the type and metamorphism of coal. The excitation time has a certain effect on the fluorescence parameters of the macerals. By comparing the relative fluorescence intensity values under different excitation times, it is found that the mean relative fluorescence intensity within 15 s can be used as an optical parameter to characterize the structure and metamorphic grade of different macerals. The essence of this method is to express movement of electrons in outer layer of nucleus by macroscopic fluorescence spectrum and relative fluorescence intensity of the initial state value and simplify microscopic complexity into macroscopic and numerical form generally accepted.

Nonadiabatic dynamics near metal surfaces under Floquet engineering: Floquet electronic friction vs Floquet surface hopping.

In the previous study Wang and Dou [J. Chem. Phys. 158, 224109 (2023)], we have derived a Floquet classical master equation (FCME) to treat nonadiabatic dynamics near metal surfaces under Floquet engineering. We have also proposed a trajectory surface hopping algorithm to solve the FCME. In this study, we map the FCME into a Floquet Fokker-Planck equation in the limit of fast Floquet driving and fast electron motion as compared to nuclear motion. The Fokker-Planck equation is then being solved using Langevin dynamics with explicit friction and random force from the nonadiabatic effects of hybridized electrons and Floquet states. We benchmark the Floquet electronic friction dynamics against Floquet quantum master equation and Floquet surface hopping. We find that Floquet driving results in a violation of the second fluctuation-dissipation theorem, which further gives rise to heating effects.