Low Beam Research Articles

Stabilizing Metal Halide Perovskite Films via Chemical Vapor Deposition and Cryogenic Electron Beam Patterning.

Halide perovskites are hailed as semiconductors of the 21st century. Chemical vapor deposition (CVD), a solvent-free method, allows versatility in the growth of thin films of 3- and 2D organic-inorganic halide perovskites. Using CVD grown methylammonium lead iodide (MAPbI3) films as a prototype, the impact of electron beam dosage under cryogenic conditions is evaluated. With 5 kV accelerating voltage, the dosage is varied between 50 and 50000 µC cm-2. An optimum dosage of 35 000 µC cm-2 results in a significant blue shift and enhancement of the photoluminescence peak. Concomitantly, a strong increase in the photocurrent is observed. A similar electron beam treatment on chlorine incorporated MAPbI3, where chlorine is known to passivate defects, shows a blue shift in the photoluminescence without improving the photocurrent properties. Low electron beam dosage under cryogenic conditions is found to damage CVD grown 2D phenylethlyammoinum lead iodide films. Monte Carlo simulations reveal differences in electron beam interaction with 3- and 2D halide perovskite films.

Lebt of the Heavy Ion Linear Accelerator

At the NRC “Kurchatov Institute” (Kurchatov Complex for Theoretical and Experimental Physics), the pulsed linear resonant heavy ion accelerator is being developed. The Low Energy Beam Transport (LEBT) channel transports the beam from a laser-plasma source of multi-charged ions with an A/Z ratio from 4 to 8 (up to Bi27+) to the RFQ. This paper shares the results of the beam dynamics simulation of the LEBT, which ensures the separation of the working fraction of the ion beam and its matching with the RFQ.

Enhancement of reactive oxygen species production by ultra-short electron pulses.

The development of laser-driven accelerators-on-chip has provided an opportunity to miniaturize devices for electron radiotherapy delivery. Laser-driven accelerators produce highly time-compressed electron pulses, on the 100 fs to 1 ps scale. This delivers electrons at high peak power yet low average beam current compared with conventional delivery devices, which generate pulses of approximately 3 µs. The biophysical effects of this time structure, however, are unclear. Here, we use a Monte Carlo simulation approach to explore the effects of the electron beam time structure on the production of reactive oxygen species (ROS) in water. Our results show a power law increase in the generation of hydroxyl ions per deposited electron with decreasing pulse length over the pulse length range of 10 µs to 100 fs. Similar trends were observed for hydrogen peroxide, superoxide, hydroperoxyl, hydronium and solvated electrons. In practical terms, this indicates a fourfold increase in the efficiency of free radical production for sub-picosecond pulses, relative to that of conventional microsecond pulses, for the same number of deposited electrons.

Monte Carlo Simulation of Electron Beam Induced Current in Au/Si Schottky Diodes: effects of metal layer thickness and minority carrier diffusion length

The Electron Beam Induced Current (EBIC) technique, when combined with scanning electron microscopy (SEM), offers valuable insights into the electronic properties of semiconductor materials at the nanoscale. This study leverages EBIC and Monte Carlo simulations to investigate the behavior of Schottky diodes, particularly focusing on the influence of gold layer thickness on current gain and backscatter electron (BSE) yield. The simulation results reveal the significant effects of depletion depth and minority carrier diffusion length on the diode’s performance. A key finding is that the EBIC current decreases with increased gold layer thickness, due to a higher BSE fraction. Additionally, at low beam energies, the current is negligible when the interaction volume is confined within the metal layer, while at higher energies, some penetration into the semiconductor occurs, generating a measurable EBIC current. These findings provide a better understanding of the interplay between metal layer thickness and semiconductor performance, which is crucial for optimizing semiconductor devices.

A single-feed circularly polarized antenna with a low vertical profile and hemispherical axial-ratio beam coverage

ABSTRACT A novel wide axial-ratio beamwidth (ARBW) circularly polarized (CP) antenna with a single layer substrate fed by a single probe is proposed. It consists of an inner annular slotted radiator containing eight outer sector units with arc branches, a ground plane, and eight grounded vias. The antenna has an ARBW covering the upper hemisphere and has a low vertical profile. The ultra-hemispherical ARBW is formed by ingeniously merging the endfire omnidirectional CP radiation pattern with the boresight CP radiation pattern. The two radiation patterns can be excited by a central coaxial probe without an additional feeding network. An antenna prototype of dimensions 1.15 × 1.15 × 0.02 (λ 0 3) is fabricated and measured to validate the design concept. Measured results show that the impedance bandwidth of the proposed antenna is 2.0% (3.328–3.394 GHz) and the 3 dB axial ratio (AR) bandwidth is 1.3% (3.332–3.374 GHz). The 3 dB AR beamwidth can cover more than 217° and the maximum gain is 0.79 dBic at 3.35 GHz. A good agreement between the simulated and measured results is obtained.

Experimental Investigation of Energy Harvesting by Employing Piezoelectric Element and Metallic Cantilever Beam

In this paper, in response to the worldwide energy crisis, a piezoelectric element (0.2*35*50) mounted on a host metallic cantilever beam (0.8*37*220) will be presented as a unique contribution to power generation via the micro-electrical mechanical system. It's made out of aluminium and low carbon steel, both of which have a Young modulus of elasticity of 6.8 and 196 GPa, respectively. In order to take advantage of the engine's vibration as an exciting external force to collect energy in the aforementioned piezoelectric device, the whole rig has been coupled to a diesel engine 5kw 3000 rpm (50 Hz). The average power generated by the aluminium beam was 943 microWatts, while the power generated by the low carbon steel beam was 335 microWatts, an increase of 256%. In addition, for both scenarios, (45) mm from the cantilever beam's fixed point was where the engaged piezoelectric element performed best. The used two metals have different stiffnesses, and this accounts for the obtained difference between the induced powers; increasing the stiffness will result in relatively more power created, and vice versa.

An optimal penalty method for the joint stiffening in beam models of additively manufactured lattice structures

Additive manufacturing is revolutionizing structural design, with lattice structures becoming increasingly prominent due to their superior mechanical properties. However, simulating these structures quickly and accurately using the finite element method (FEM) remains challenging. Recent research has highlighted beam element simulation within FEM as a more efficient alternative to traditional solid FE simulations, achieving similar accuracy with reduced computational resources. However, a significant challenge is managing the lack of rigidity at nodes and the prevalence of low aspect ratio beams. While various methodologies have been proposed to address these issues, there is still a gap in the comprehensive evaluation of their limitations. An optimal node penalization methodology is required to expand the limited range of accurately represented lattice behavior. A preliminary study investigates lattice geometries through comparative analysis of solid and beam FE simulations. Built on this, we developed a methodology suitable to linear, dynamics and nonlinear beam FE simulations, contributing to enhanced computational speed and accuracy. Several lattice structures were printed using material jetting and quasi-static compressive tests were conducted to validate the methodology’s accuracy. The numerical results reveal a good accuracy between the proposed beam FE methodology and the experimental data, offering a better alternative to conventional FEM for energy absorption in terms of computing time.

On the possibility of domain structure formation in lithium niobate by low energy (< 5 keV) electron beam

The authors' assumption about the possibility of nanodomain generation in the ferroelectric LiNbO3 by relatively low energy (< 5 keV) electron beams has been experimentally confirmed. The calculated electron-induced electric fields and changes in the polarization state of the near-surface layer in the -Z cut of LiNbO3 agree with the experimental results at the energies of the primary electrons Eb = 1 and 3 keV. In the proposed four-layer model of surface charging by low-energy electrons, electron-stimulated desorption of compensating atoms and molecules from the contaminated absorbing film into a vacuum plays an important role. The presented new results confirming the formation of domains in the near-surface layer at low electron beam energy can expand the possibilities of domain engineering using electron beam technologies, especially in the field of photonics.

Testing the accuracy of low-beam-energy electron-excited X-ray microanalysis with energy-dispersive spectrometry

The accuracy of electron-excited X-ray microanalysis with energy-dispersive spectrometry (EDS) has been tested in the low beam energy range, specifically at an incident beam energy of 5 keV, which is the lowest beam energy for which a useful characteristic X-ray peak can be excited for all elements of the periodic table, excepting H and He. Elemental analysis results are reported for certified reference materials (CRM), stoichiometric compounds, minerals, and metal alloys of independently known or measured composition which had microscopic homogeneity suitable for microanalysis. Two-hundred sixty-three concentration measurements for 39 elements in 113 materials were determined following the k-ratio protocol and using the EDS analytical software NIST DTSA-II. The accuracy of the results, as characterized by the relative deviation from expected value (RDEV) metric, was such that more than 98% of the results were found to be captured within a range of ±5% RDEV, while 82% of the results fell in the range -2% to 2% RDEV.

Development of a low energy loss micro-channel plate based position-sensitive detector for the Rare Radio-Isotope Ring

A position-sensitive micro-channel plate type detector has been developed for use in the Rare Radio-Isotope Ring at RIKEN, Japan. It uses secondary electrons emitted from a conversion foil and deflected at 90° to create a position signal. Design constraints included operation in a high-vacuum, a large area to cover the ring acceptance and low beam interaction to reduce energy loss. It must achieve a precision sufficient to measure the in-ring dispersion and perform position diagnostics for tuning the injection. Reducing the time-of-flight of secondary electrons was principal in improving resolution as it reduces their final gaussian spread. This was implemented by compacting the geometry of the detector and raising the acceleration potential. Electric field homogeneity was also improved by decreasing the electrostatic grid wire pitch from 2 mm to 1 mm. Offline tests with alpha sources and online tests with a 200 MeV/u 84Kr beam were conducted, reaching a final average position resolution of σ=1.3 mm. This is sufficient for conducting beam diagnostics in the storage ring.

Contactless thermal diffusivity characterization of second order magnetocaloric materials under magnetic field using modulated photo-thermal radiometry method with very low power probe beam

The thermal diffusivity of magnetocaloric materials has a transition point at a given temperature that depends on the intensity of the applied magnetic field. Consequently, a fine temperature resolution on the material sample is needed to obtain an accurate determination of the thermal diffusivity variation with temperature. The coupling between the external and the internal fields has to be carefully mastered since the pertinent operating condition is fixed by the actual internal field which is not directly measurable and may be heavily affected by any element in contact with the sample. Therefore, contactless methods such as Photo-Thermal Radiometry (PTR) are privileged. The latter is based on a radiative excitation of the front face of a thin sample and the detection of the thermal effect on the opposite face. However, the powerful radiative source may significantly increase the sample temperature which is not suitable for caloric materials. In this work, a low power modulated PTR method is proposed to characterize second order magnetocaloric materials under magnetic field. It was compared to high energy thermo-flash PTR and validated on common materials such as steel and stainless steel, and then applied to gadolinium which is the reference magnetocaloric material for magnetic refrigeration and heat pumping study. The thermal diffusivity of gadolinium samples is measured in the 285.1 K to 305.1 K temperature range, including the magnetic transition temperature without and under an external magnetic flux density of 0.5 T in the 13 mm air gap of the permanent magnet magnetic circuit. The low power probe beam ensures a temperature stability with a negligible sample temperature fluctuation less than 0.05 K on the incident sample surface and less than 0.03 K on the measurement surface. The experimental results without magnetic field align with those using other methods including the magnetic transition temperatures determination. This low-power optical method proved its efficiency to characterize highly temperature dependent materials such as magnetocaloric materials sensitive to magnetic field. The data obtained partly fills the lack of information in the literature on excited gadolinium.

Dynamic low earth orbit multi satellite hopping beam resource allocation considering load and dynamic coverage balance (LDCB-MSHBRA)

A dynamic low earth orbit multi satellite hopping beam resource allocation method based on time slicing is proposed to address the issue of changing coverage and beam interference caused by satellite mobility in multi satellite and multi beam communication scenarios. The method involves six processes: (1) Establishing a low earth orbit satellite system with three identical configuration parameters and motion speed parameters; (2)Assign a value to the time slicing weight coefficient and use the principle of load balancing to minimize the difference in demand for dual star services as the optimization objective; (3) Obtain initial power resource allocation with maximum system capacity as the optimization objective; (4) Considering the mobility of low earth orbit satellites, updating weight coefficients and dynamically allocating power resources, a time resource dynamic allocation matrix and the optimal service cell set are obtained; (5) Update the independent coverage cell set of the third low earth orbit satellite, use the Lagrange equation of the weighted fair objective function to obtain the time resource allocation optimization matrix, and use one-way search to determine the optimal service cell set; (6) With the goal of maximizing system capacity, the optimal solution of the power resource allocation matrix for the third low earth orbit satellite is obtained. The system throughput is introduced to intuitively measure system performance, and adjustments are made based on the overlap of Samsung coverage. The resource allocation method is based on a fairness model, considering load balancing and dynamic coverage range changes. On the basis of improving the overall system throughput, it ensures the fairness of resource allocation and allocates time, frequency, and power resources to multiple satellites with overlapping coverage, which helps to improve the throughput and resource utilization of satellite systems.

Effect of As4 beam equivalent pressure on the growth dynamics of InAs films grown at low temperature on graphene layers

The present study investigates the growth of InAs films at low temperature on graphene synthesized via molecular beam epitaxy, emphasizing the effect of As4 beam equivalent pressure (5.0 × 10⁻6 Torr (low) and 4.5 × 10⁻⁵ (high)) on the growth dynamics. X-ray diffraction, scanning electron microscopy, and atomic force microscopy, along with correlation functions, revealed that monitoring the As4 beam equivalent pressure affects the structural properties of polycrystalline InAs films grown on the graphene/Si layer. The film thickness (particle size) was found to be 172 ± 10 nm and 216 ± 10 nm (40 ± 2 nm and 42 ± 2 nm) for the InAs layers grown at low and high As4 beam equivalent pressure. The increase in the film thickness and particle size with increasing the As4 beam equivalent pressure is attributed to improved material availability and surface kinetics due to the large migration energy of As compared to In and hence the larger diffusion length of In. Conversely, decreasing As4 beam equivalent pressure raises the roughness scaling exponent and enlarges interface width (0.17 µm and 0.31 µm for films grown at high and low As4 beam equivalent pressure) and lateral correlation length, implying smoother surfaces due to larger particles. These insights are pivotal for fabricating advanced semiconductors, underscoring As4 beam equivalent pressure's role in optimizing InAs films for electronic and optoelectronic applications.

Modifying of surface properties and structural characteristics of low energy argon beam irradiated methylcellulose/TiO2 nanocomposite films

Flexible polymeric nanocomposites MC/TiO2 films, which consisting of titanium dioxide (TiO2) and methyl cellulose (MC) were fabricated in this research for applied in coating devices. The successful manufacturing of MC/TiO2 sheets were verified by FTIR, SEM and XRD methods, which demonstrated a uniform distribution of TiO2 in MC. Additionally, the chemical bonds of MC and TiO2 contribute for the broadening and decreasing of MC in the peaks intensity of XRD and FTIR with increasing TiO2, indicating the successful incorporation of TiO2 in MC. The impacts of argon beam bombardment on MC/TiO2 composites using cold cathode source with fluencies (2.5×1015, 5×1015 and 7.5×1015 ions/cm2 ). The contact angle, work of adhesion and surface free energy of MC/TiO2 were determined as a function of ion irradiation. The water contact angle is decreased from 70.32o to 43.34o by increasing ion fluence from 2.5×1015 ions/cm2 to 7.5×1015 ions/cm2 , while the surface free energy is enhanced from 38.83 mJ/m2 to 64.17 mJ/m2 . The collected data confirmed that the surface wettability of the irradiated MC/TiO2 films were improved to be can usage in coating and printing applications

Structural analysis of selective laser melted copper-tin alloy

Additively manufactured complex geometries from copper alloys with high thermal and mechanical properties have drawn the attention of researchers. The present contribution explores the additive manufacturing (AM) of copper-based alloys from powder particles intended for heat sink and heat exchange applications. Selective laser melting (SLM) parameters featuring low laser beam power (160 W), moderate scanning speed (320 mm/s), and high energy density (200 J/mm³) were employed to fabricate dense components from CuSn10 particles. The present work deal with structural analysis and precision investigation of microfabrication, particularly in Struts, Tubes, and Fins. Mechanical properties (compression and hardness) for Strut structure, differential pressure evaluations for Tube structure, and analyses of thermal and electrical conductivities for Fin structure were investigated. The results showed an improvement in strength compared to those of pure copper, facilitating ease of AM. The obtained results affirm the feasibility of AM, demonstrating the successful creation of complex and combined solid-porous structures using SLM process from Cu alloys. A comprehensive structural investigation and characterization of the Cu–Sn alloy is presented here, aiming to establish a standardized approach for analysing Cu alloys. The results indicate that small-scaled structures fabricated via CuSn10 alloy exhibits a thermal conductivity of 34.3 W·m⁻¹·K⁻¹, an electrical conductivity of 4.72×10⁶ S/m, a hardness of 119 HV-50, a uniform surface roughness of 6 µm, and can withstand a force loading of 1 kN.

Analysis of hydrogen peroxide production in pure water: Ultrahigh versus conventional dose-rate irradiation and mechanistic insights.

Ultrahigh dose-rate radiation (UHDR) produces less hydrogen peroxide (H2O2) in pure water, as suggested by some experimental studies, and is used as an argument for the validity of the theory that FLASH spares the normal tissue due to less reactive oxygen species (ROS) production. In contrast, most Monte Carlo simulation studies suggest the opposite. We aim to unveil the effect of UHDR on H2O2 production in pure water and its underlying mechanism, to serve as a benchmark for Monte Carlo simulation. We hypothesized that the reaction of solvated electrons ( ) removing hydroxyl radicals (•OH), the precursor of H2O2, is the reason why UHDR leads to a lower G-value (molecules/100eV) for H2O2 (G[H2O2]), because: 1, the third-order reaction between and •OH is more sensitive to increased instantaneous ROS concentration by UHDR than a two-order reaction of •OH self-reaction producing H2O2; 2, has two times higher diffusion coefficient and higher reaction rate constant than that of •OH, which means would dominate the competition for •OH and benefit more from the inter-track effect of UHDR. Meanwhile, we also experimentally verify the theory of long-lived radicals causing lower G(H2O2) in conventional irradiation, which is mentioned in some simulation studies. H2O2 was measured by Amplex UltraRed assay. 430.1MeV/u carbon ions (50 and 0.1Gy/s), 9MeV electrons (600 and 0.62Gy/s), and 200kV x-ray tube (10 and 0.1Gy/s) were employed. For three kinds of water (real hypoxic: 1% O2; hypoxic: 1% O2 and 5% CO2; and normoxic: 21% O2), unbubbled and bubbled samples with N2O, the scavenger of , were irradiated by carbon ions and electrons with conventional and UHDR at different absolute dose levels. Normoxic water dissolved with sodium nitrate (NaNO3), another scavenger of , and bubbled with N2O was irradiated by x-ray to verify the results of low-LET electron beam. UHDR leads to a lower G(H2O2) than conventional irradiation. O2 and CO2 can both increase G(H2O2). N2O increases G(H2O2) of both UHDR and conventional irradiation and eliminates the difference between them for carbon ions. However, N2O decreases G(H2O2) in electron conventional irradiation but increases G(H2O2) in the case of UHDR, ending up with no dose-rate dependency of G(H2O2). Three-spilled carbon UHDR does not have a lower G(H2O2) than one-spilled UHDR. However, the electron beam shows a lower G(H2O2) for three-spilled UHDR than for one-spilled UHDR. Normoxic water with N2O or NaNO3 can both eliminate the dose rate dependency of H2O2 production for x-ray. UHDR has a lower G(H2O2) than the conventional irradiation for both high LET carbon and low LET electron and x-ray beams. Both scavengers for , N2O and NaNO3, eliminate the dose-rate dependency of G(H2O2), which suggests is the reason for decreased G(H2O2) for UHDR. Three-spilled UHDR versus one-spilled UHDR indicates that the assumption of residual radicals reducing G(H2O2) of conventional irradiation may only be valid for low LET electron beam.

Characterization of the LEBT based neutron source

Neutron generation by implantation and subsequent beam interaction of 40 keV deuterons at Soreq Applied Research Accelerator Facility (SARAF) low energy beam transport (LEBT) section was measured and characterized. The generation of 2.45 MeV neutrons by a deuteron beam of several mA was verified by a neutron spectrometer. Relative neutron yields were studied as a function of beam energy and beam spot size using two types of available implantation surfaces. The buildup of neutron yield was studied at long and short time scales. Absolute neutron yield was measured via activation at several conditions. The maximum neutron yield that could be obtained at the SARAF LEBT is of the order of 107 n/s, which presents a convenient source for testing neutron instrumentation in DC or pulsed mode.

Phase space reconstruction technique for beam optimization in the Low Energy High Intensity Proton Accelerator (LEHIPA)

The Low Energy High Intensity Proton Accelerator (LEHIPA) has been commissioned to the design energy of 20 MeV at BARC, India. The low energy beam transport (LEBT) channel of LEHIPA consists of two solenoids and drift spaces for matching the 50 keV proton beam from the ECR ion source (ECR-IS) to the RFQ. The ion beam extracted from the ECR-IS also contains molecular species like H2 + and H3 +. Proton fraction in the beam is found to degrade slowly with time due to surface contamination of the plasma chamber and this reduction in proton beam current has implications for longitudinal and transverse beam dynamics. Hence, it becomes important to characterise the beam at different proton fraction levels to understand the end-to-end beam dynamics of LEHIPA. Computed Tomography (CT) technique has been used for the beam phase-space reconstruction in LEHIPA, using a Python program, incorporating the feature of filtering secondary species from the beam profiles measured using slit scanners in the LEBT. Simultaneous Algebraic Reconstruction Technique (SART) is used in the reconstruction since it is identified to be a better technique for a limited number of projections. The reconstruction program is benchmarked with the TraceWin beam dynamics code and implemented on the measured beam profiles to recreate the phase space distribution at the beginning of LEBT. Further, the tomographic reconstruction method is compared with the solenoid scan method and the rms emittance values are found to be in good agreement. The measured tomographic phase space distribution has then been used as TraceWin input for LEHIPA end-end beam dynamics simulations and the LEHIPA beam line parameters are re-optimized for minimum beam emittance growth. This paper presents the simulations of CT technique, benchmarking simulations with TraceWin, phase space reconstruction with measured beam profiles and beam dynamics studies of LEHIPA using the reconstructed beam distributions.

The Reliability of Field-Based Static and Dynamic Balance Tests in Primary School-Aged Autistic Children.

Previous research has proven that the balance of autistic children is poor. However, the reliability of assessing balance in this cohort has been inadequately researched. This study therefore aimed to examine if field-based static and dynamic balance tests can be reliably assessed in autistic children, to determine the number of familiarisation sessions required and whether autistic severity impacts on the reliability of these balance tests. The balance of eighteen primary school-aged autistic children was assessed three times a week over five weeks, using the flamingo balance test, a modified version of the balance error scoring system (BESS), the low beam walking test, and the heel to toe walking test. Reliability criteria included an intraclass correlation coefficient (ICC) level of ≥0.75 and a coefficient of variance (CV%) of ≤46% for the low beam walking test, the heel to toe walking test, and the BESS, and a CV% of ≤82% or the flamingo balance test. Inter-session reliability was achieved and required the least number of familiarisation sessions for the flamingo balance test, compared to the low beam walking test, which required a greater number of familiarisation sessions to achieve inter-session reliability. The heel to toe walking test and the BESS achieved inter-session reliability and familiarisation in an acceptable time frame. Due to the large CV% values reported in the current study, practitioners need to be aware that balance interventions need to achieve improvements greater than the CV% in this cohort.

Design and performance of a low-emittance electron gun for electron beam probe

An Electron Beam Probe (EBP) is preferable to provide a non-interceptive measurement of the transverse distribution of a dense bunched ion beam. During EBP operation, it was observed that the electron beam spot subjects to expansion when scanned across the ion beam due to the strong space charge field of the ion bunch, leading to significant degradation of spatial resolution. To mitigate this effect, a small electron beam spot is beneficial as demonstrated in previous research. This paper presents design details of a low-emittance, small-spot, and long-work-distance electron gun. Geometry optimization of the gun and focus lens is conducted using a multiobjective genetic algorithm (MOGA) interfaced with space charge simulation codes to maintain normalized thermal emittance within an acceptable increase and achieve a small spot at a long work distance. The emittance is measured using a slit-screen technique, resulting in a norm. rms emittance of 0.046(+-0.005) um*rad under low beam current conditions (50 nA). In high-resolution mode, a beam spot size of 0.6 mm (rms) is achieved at a work distance of 1.2 m with the combination of Einzel lens and solenoid. The gun has been successfully operated as part of EBP experiments for accurate and high-resolution measurement of ion beam width, demonstrating excellent agreement with wire scanner measurements with relative deviation not exceeding 1%.