Single-layer Geometry Research Articles

Development of a High-Efficiency Device for Thermal Neutron Detection Using a Sandwich of Two High-Purity 10B Enriched Layers.

The shortage of 3He, a crucial element widely used as a neutron converter in neutron detection applications, has sparked significant research efforts aimed at finding alternative materials, developing appropriate deposition methods, and exploring new detector architectures. This issue has required the exploration of novel approaches to address the challenges faced in neutron detection. Among the available conversion materials, 10B has emerged as one of the most promising choices due to its high neutron-capture cross-section and relatively high Q value. In our previous papers, we delved into the possibility of depositing neutron conversion layers based on 10B using Pulsed Laser Deposition (PLD). We investigated and evaluated the performance of these layers based on various factors, including deposition conditions, substrate properties, and film thickness. Moreover, we successfully developed and tested a device that employed a single conversion layer coupled with a silicon particle detector. In this current study, we present the development of a new device that showcases improved performance in terms of efficiency, sensitivity, and discrimination against γ background signals. The background signals can arise from the environment or be associated with the neutron field. To achieve these advancements, we considered a new detection geometry that incorporates the simultaneous use of two 10B conversion layers, each with a thickness of 1.5 μm, along with two solid-state silicon detectors. The primary objective of this design was to enhance the overall detection efficiency when compared to the single-layer geometry. By employing this novel setup, our results demonstrate a significant enhancement in the device's performance when exposed to a neutron flux from an Am-Be neutron source, emitting a flux of approximately 2.2 × 106 neutrons per second. Furthermore, we established a noteworthy agreement between the experimental data obtained and the simulation results.

Broadband and Short-Length Polarization Splitter on Dual Hollow-Core Antiresonant Fiber

We present a compact polarization splitter on a dual hollow-core antiresonant fiber with broad bandwidth covering two well-known communication wavelengths of <inline-formula> <tex-math notation="LaTeX">$1.31~\mu \text{m}$ </tex-math></inline-formula> and 1.55 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>. It can achieve excellent polarization splitting performances in a simpler optimized single-layer geometry compared to the related splitters and for the first time, simultaneously offers a very short splitter length of 21.52 mm and a broad bandwidth of 340 nm by maintaining an extinction ratio higher than 20 dB. It also achieves the highest extinction ratio of 140 dB at <inline-formula> <tex-math notation="LaTeX">$1.55~\mu \text{m}$ </tex-math></inline-formula> and maintains a standard single mode performance. Therefore, the proposed splitter has the potentiality to be a promising candidate for the integrated optical devices in communication systems.

A Compact Single-Layer Four-Port Orthogonally Polarized Yagi-Like MIMO Antenna System

A wideband compact Yagi-like directional multiple-input- multiple-output (MIMO) antenna system is presented based on a slot loop excitation. Four orthogonally polarized beams are generated by orthogonally feeding the slot loop elements using microstrip lines. The proposed design is based on a single-layer geometry with an overall size of 35 × 90 × 0.76 mm3, which is suitable for compact wireless handheld devices. The conventional vertically polarized omnidirectional beams from each slot loop element are made directional and horizontally polarized by using two passive complementary slot reflector (CSR) elements. The antenna system has a wide measured bandwidth of 620 MHz (3.26-3.88 GHz) targeting the 3.6 GHz WiMAX band. It has a maximum realized gain of 4 dBi and front to back ratio (FBR) of more than 7 dB within the band of operation. The proposed antenna system shows good MIMO performance with a minimum measured isolation of 10 dB between the adjacent ports and more than 20 dB between other ports. The orthogonal beams of the antenna system help in achieving low envelope correlation coefficient (ECC) values of less than 0.1. The measured total efficiency of the antenna system is more than 75% for all the ports of the antenna system.

Analysis of the effect of dielectric losses on the bandwidth of microstrip patch antenna in stacked geometry and modelling

This paper presents a detailed analysis involving dielectric materials, by giving rigorous formulations including losses within nonmagnetic dielectric materials. The choice of these latter has shown a thorough attention in designing microstrip patch antenna (MPA), since they have significant correlation with the MPA performance. This study aims to analyze dielectric losses effect on MPA bandwidth in stacked patch geometry, including two rectangular patches etched on two layers, rather than single-layer geometry. The paper provides detailed formulations of rigorous analysis method, in which transfer matrices at boundaries are given regarding the studied case. Numerical results are presented and agreed with previous findings, where the dielectric losses show positive effect on both lower and upper bandwidths of the stacked patch geometry. The present study therefore provides additional evidence to the losses within low cost dielectric materials.

Frequency reconfigurable Yagi‐like MIMO antenna system with a wideband reflector

A compact single layer frequency reconfigurable Yagi-like multiple-input multiple-output (MIMO) antenna system is presented based on a half-ring closed loop slot excitation. The traditional omnidirectional pattern of a slot antenna is made directional by using a single slot-based complementary wideband reflector (CWBR) element. The proposed CWBR is compact in size, simple in construction, and is based on a single-layer geometry unlike complex multi-layer reflectors used in the literature. It improves the front-to-back ratio between 5 and 17 dB in the entire frequency range covering 2.5–4.5 GHz. The proposed reconfigurable MIMO antenna system covers the LTE and WiMAX bands with a minimum measured bandwidth of 200 MHz per covered bands. The frequency reconfigurability is achieved by reactively loading the slot loop with varactor diodes. The overall size of the proposed antenna system is 40 × 100 × 0.76 mm 3 , making it suitable for tablet handheld devices and access points. It has a maximum measured peak gain of 5 dBi and total measured radiation efficiency of 78%. The proposed MIMO antenna system has port isolation of > 10 dB within the entire band of operation. The radiation patterns are isolated in space from each other and ensure very low envelope correlation coefficient.

Porous surfaces with structural gradient: Enhancing boiling heat transfer and its application in phase-change devices

Surface micro/nano processing is an important method and research hotspot for enhancing the boiling heat transfer process. However, the effects of a structural gradient on a boiling surface have not been systematically studied. In this paper, we review researches that focus on porous surfaces with a structural gradient and their effects on the enhancement of boiling heat transfer and performance of phase-change devices from two main aspects: Geometric gradient and wettability gradient. Porous surfaces with a geometric (structural) gradient were divided into four series: single-layer geometric gradient structure, multi-layer geometric gradient structure, surface covered with a micro/nanolayer, and surface with a radial gradient. In addition, the surface with a wettability gradient also has a considerable improvement in boiling heat transfer. Especially, we present some of the work related to the improvement in boiling heat transfer for porous surfaces with structural gradient, which has been carried out by our research group. Honeycomb-like and forest-like porous copper surfaces are typical single-layer geometric gradient porous surfaces with excellent boiling heat transfer performance. They have abundant microstructures and sub-microstructures/nanostructures, which are favorable for vapor escaping and liquid rewetting, respectively. For all the mentioned single-layer geometry gradient porous surfaces, the critical heat flux increases as the sample thickness increases. Furthermore, we fabricated a two-layer composite porous surface (TLCS) with a honeycomb-like porous copper surface on top of a forest-like porous copper surface. This TLCS is a multilayer geometric gradient structure porous surface that can further enhance the boiling heat transfer process. The heat transfer coefficient (HTC) of TLCS is 1.5 and 1.2 times larger than those of the biomimetic copper forest and honeycomb structures, respectively. When a small current is applied to the honeycomb-like porous copper surface, the dendrites on the pore wall transferred to micro balls and a surface with a structural gradient is obtained. The modified surface is a microstructural porous surface covered by a nanolayer that further enhances the HTC (1.7 times). The diameter of the honeycomb-like porous copper surface can be controlled with a radial diameter gradient. A sample in which the diameter around the center is much smaller than that around the edge enhances the HTC 1.4 times compared with a sample with uniform diameter. When the TLCS was modified with polytetrafluoroethylene (PTFE), it became a hybrid wetting surface. The experimental results show that the wall superheat temperature at the same heat flux during the heat flux decreasing can repeat that during the heat flux increasing well within 0.5°C, demonstrating that the boiling hysteresis was successfully eliminated. As the porous surface with a structural gradient has excellent performance in boiling heat transfer, it has been widely used in phase-change devices, such as loop and flat heat pipes, to improve their functioning. An ultra-thin flat heat pipe (UTHP), which is only 0.6 mm thick, can significantly reduce the evaporator temperature by 10°C under a 6 W heat load compared with a copper plate. This paper summarizes the most relevant features related to boiling heat transfer enhancement when using structural-gradient porous surfaces and the improvements in phase-change devices that use such surfaces. Despite the advances in this aspect, the porous surfaces can be further optimized to achieve a better heat transfer performance.

Design of multiband multipolarised single feed patch antenna

A new low profile, multiband, multipolarised single feed antenna is designed. A corner truncated patch loaded with slots and a complementary split ring resonator is used to achieve three frequency bands with different polarisations. The antenna exhibits right-hand circular, linear, and left-hand circular polarisation at three different bands, respectively. To obtain circular polarisation, orthogonal modes are excited by truncating corners of the patch and etching slits. Single feed, single layer geometry with Y-shaped feed structure is employed. The antenna is fabricated on a low-cost FR4 substrate with an overall size of $70\, {\rm mm} \times 70\, {\rm mm}$70 mm×70 mm, and the proposed design has been verified experimentally. The selected frequency bands are centred at 2.313, 2.396, and 2.478 GHz, and they have -10 dB impedance bandwidths of 2.14, 2.50, and 2.42%, respectively. The first frequency band exhibits right-hand circular polarisation with a 3 dB axial ratio bandwidth of 0.85%. The second frequency band exhibits linear polarisation, whereas the third frequency band exhibits left-hand circular polarisation with a 3 dB axial ratio bandwidth of 0.81%.

Estimating the NEMA characteristics of the J-PET tomograph using the GATE package

A novel whole-body positron emission tomography (PET) system based on plastic scintillators is developed by the J-PET Collaboration. It consists of plastic scintillator strips arranged axially in the form of a cylinder, allowing the cost-effective construction of the total-body PET system. In order to determine the properties of the scanner prototype and optimize its geometry, advanced computer simulations were performed using the GATE (Geant4 application for tomographic emission) software.The spatial resolution, sensitivity, scatter fraction and noise equivalent count rate were estimated according to the National Electrical Manufacturers Association norm, as a function of the length of the tomograph, the number of detection layers, the diameter of the tomographic chamber and for various types of applied readout. For the single-layer geometry with a diameter of 85 cm, a strip length of 100 cm, a cross-section of 4 mm × 20 mm and silicon photomultipliers with an additional layer of wavelength shifter as the readout, the spatial resolution (full width at half maximum) in the centre of the scanner is equal to 3 mm (radial, tangential) and 6 mm (axial). For the analogous double-layer geometry with the same readout, diameter and scintillator length, with a strip cross-section of 7 mm × 20 mm, a noise equivalent count rate peak of 300 kcps was reached at 40 kBq cc−1 activity concentration, the scatter fraction is estimated to be about 35% and the sensitivity at the centre amounts to 14.9 cps kBq−1. Sensitivity profiles were also determined.

Improvements in simulation of multiple scattering effects in ATLAS fast simulation

Fast ATLAS Tracking Simulation (Fatras) package was verified on single layer geometry with respect to full simulation with GEANT4. Fatras hadronic interactions and multiple scattering simulation were studied in comparison with GEANT4. Disagreement was found in multiple scattering distributions of primary charged particles (μ, π, e). A new model for multiple scattering simulation was implemented in Fatras. The model was based on R. Fruhwirth’s mixture models. New model was tested on single layer geometry and a good agreement with GEANT4 was achieved. Also a comparison of reconstructed tracks’ parameters was performed for Inner Detector geometry, and Fatras with new multiple scattering model proved to have better agreement with GEANT4. New model of multiple scattering was added as a part of Fatras package in the development release of ATLAS software—ATHENA.

Low-current, narrow-linewidth microwave signal generation in NiMnSb based single-layer nanocontact spin-torque oscillators

We report on the fabrication of nano-contact spin-torque oscillators based on single layers of the epitaxially grown half-metal NiMnSb with ultralow spin wave damping. We demonstrate magnetization auto-oscillations at microwave frequencies in the 1–3 GHz range in out-of-plane magnetic fields. Threshold current densities as low as 3 × 1011 A m−2 are observed as well as minimum oscillation linewidths of 200 kHz, both of which are much lower than the values achieved in conventional metallic spin-valve-based devices of comparable dimensions. These results enable the fabrication of spin transfer torque driven magnonic devices with low current density requirements, improved signal linewidths, and in a simplified single-layer geometry.

Modification of Electronic and Vibrational Properties of Doped Black-P Films

ABSTRACTBlack phosphorus (black-P) research has been the most absent for 100 years since its date of first synthesis in 1914 among all the polymorphs of phosphorus. However, recently it has been re-examined due to its specific puckered single layer geometry. Few or single atomic layer forms of black-P can be isolated using techniques such as micromechanical or liquid exfoliation. However, the exfoliation techniques limit the use of black-P, hence a method of black-P layer deposition onto a substrate is needed. Few or atomic layer deposition of black-P leads to substrate-material interactions and a possible appearance of a band gap opening at the K point. Hence, a series of experiments were conducted in order to grow black-P on different substrates. With the incorporation of doping elements, there was substantial modification in the vibrational and electrical properties. It was observed that sulfur and boron doped films exhibit improved electrical and electronic properties as compared to pristine black-P. Density functional theory predicts significant changes in the band structure and density of states as a consequence of doping. The effects of doping was also reflected in Raman A1g mode. The shift in peak position was also found to be consistent with molar mass of dopants.

The renaissance of black phosphorus

One hundred years after its first successful synthesis in the bulk form in 1914, black phosphorus (black P) was recently rediscovered from the perspective of a 2D layered material, attracting tremendous interest from condensed matter physicists, chemists, semiconductor device engineers, and material scientists. Similar to graphite and transition metal dichalcogenides (TMDs), black P has a layered structure but with a unique puckered single-layer geometry. Because the direct electronic band gap of thin film black P can be varied from 0.3 eV to around 2 eV, depending on its film thickness, and because of its high carrier mobility and anisotropic in-plane properties, black P is promising for novel applications in nanoelectronics and nanophotonics different from graphene and TMDs. Black P as a nanomaterial has already attracted much attention from researchers within the past year. Here, we offer our opinions on this emerging material with the goal of motivating and inspiring fellow researchers in the 2D materials community and the broad readership of PNAS to discuss and contribute to this exciting new field. We also give our perspectives on future 2D and thin film black P research directions, aiming to assist researchers coming from a variety of disciplines who are desirous of working in this exciting research field.

The dielectric functions and optical band gaps of thin films of amorphous and cubic crystalline Mg~ 2NiH~ 4

Magnesium nickel hydride films have earlier been suggested for several optoelectronic applications, but the optical properties and band gap have not been firmly established. In this work, the dielectric functions and the optical band gaps of thin films of Mg2NiH4 have been determined experimentally from optical modeling using spectroscopic ellipsometry and spectrophotometry in the photon energy range between 0.7 and 4.2eV. Samples were prepared by reactive sputtering, resulting in a single-layer geometry that could easily be studied by ellipsometry. Crystalline samples were prepared by annealing the as-deposited amorphous films ex-situ. The resulting films remained in the high temperature cubic Mg2NiH4 structure even after cooling to room temperature. Tauc analysis of the dielectric functions shows that Mg2NiH4 films exhibit a band gap of 1.6eV for the amorphous structure and 2.1eV for the cubic crystalline structure.

Fork-Coupled Resonators for High-Frequency Characterization of Dielectric Substrate Materials

Efficient coupling of energy in and out of a resonator can significantly enhance its performance, particularly when used for dielectric characterization of materials. In this paper, a new microstrip resonator is introduced, which uses fork-shaped feed elements for improving the coupling efficiency. The proposed resonator is studied both experimentally and theoretically with field simulation software. An important advantage of the fork microstrip resonator is attributed to its single-layer geometry and easier manufacturing processes. This resonator is used to characterize three different dielectric materials. Comparison of measurement results from the fork resonator with those obtained with a stripline resonator suggests that the proposed resonator offers a superior performance

Depth dependence of ion implantation damage in AlxGa1−xAs/GaAs heterostructures

To determine the influence of interface type on the accumulation of damage and ion mixing in GaAs/AlxGa1−xAs heterostructures, the damage produced by ion implantation at 77 K in single-layer (GaAs/AlxGa1−xAs/GaAs) and double-layer (GaAs/AlxGa1−xAs/GaAs/ AlxGa1−xAs/GaAs) heterostructures has been investigated by using a combination of Rutherford backscattering spectrometry and transmission electron microscopy. In the single-layer geometry, the degree of disorder increases with depth and the mixing is greater at the AlxGa1−xAs on GaAs interface than at the GaAs on AlxGa1−xAs one. The damage distribution in the sample with the double-layer geometry was different in the two layers, but overall it was similar to that in the single-layer geometry. These trends were observed in samples with x=0.6 and 0.2. These results indicate that migration of charged defects due to the presence of an implantation-induced electric field is not responsible for the asymmetry in the damage accumulation across the layer, the interface disorder and ion mixing, and the initiation of amorphization at interfaces. Instead, these effects can be better understood in terms of the depth dependence of the density of cascade events.