Spatial Uniformity Research Articles

Timepix3 detector for measuring radon decay products

The present work is focused on the characterization of a Timepix3 (TPX3) based test system for the identification of particles produced by the complex decay chain of 222Rn. The detector used is composed of a pixelated Cadmium Telluride (CdTe) semiconductor (500 μm thick) bump-bonded on an ASIC TPX3 chip. Measurements were carried out at the NIXT Laboratory (ENEA Frascati) using radioactive sources and exploiting the presence of natural radon gas by collecting its decay products on the sensor surface. Estimation of the radon gas risk is one of the most important problems in radiation protection and has stimulated further development of new advanced methods suitable for detecting this gas in confined environments. A study of the spatial uniformity and high energy calibration is also presented and an improved cluster analysis is introduced. The performance highlighted in this study will allow a detailed and faster analysis of the radon products and may have an important impact on the environmental radioprotection applications. This paper describes the application and use of this test system to identify the different decay signatures and follow the temporal evolution of the Radon decay chain.

The Influence of Inter-Element Phase Difference on the Beamforming and Spatial Electromagnetic Field Distribution of a Quad Microstrip Patch Antenna Array in the X Band

Abstract A simple model of 1x4 linear array of microstrip antennas was used to analyse the influence of phase difference between antenna elements on the performance of beamforming at 8.9 GHz. Simulations with full wave CST Studio were performed over a number of phase sets. Among them we identified the most constructive and the most destructive cases based on the maximum gain, the total efficiency and the polarization. It resulted that [0;0;0;0] phase case provided 10.6 dB higher gain, 46.5% higher efficiency and much more spatial uniformity of polarization along the propagation path than the [0;180;0;180] case. Field strength computations and vector representations proved the complexity of beamforming when one also takes into account the mutual coupling of the elements.

3D ultrasound imaging by synthetic transmit aperture beamforming using a spherically curved array transducer

Visualization of dermal circulation is important in the field of skin healthcare. We have developed a three-dimensional (3D) photoacoustic (PA) imaging system using a spherically curved array transducer that can visualize the microscale circulation in the skin layers, but limited anatomical information was available around the microvasculature. To provide such anatomical information, this study was aimed at devising a high-quality and high-speed ultrasound (US) imaging framework, particularly, for the spherical array transducer. We tested three synthetic transmit aperture (STA) methods, all-elements, outer-track, and inner-track, for transmission by evaluating the spatial resolution and uniformity of 3D images of point and copper-wire targets. The results demonstrated that the all-elements and outer-track STA methods could provide uniform and clear 3D images. In addition, the outer-track STA could be performed with fewer transmissions than the all-elements STA, and it will be useful for realizing real-time, high-resolution 3D PA/US imaging.

Scale up of polyamide reverse osmosis membranes surface modification with tethered poly(acrylic acid) for fabrication of low fouling spiral-wound elements

Scale up of atmospheric pressure plasma-induced graft polymerization (APPIGP) was demonstrated for surface nano-structuring (SNS) of a base polyamide (PA) reverse osmosis (RO) membrane with tethered poly(acrylic acid) (PAA) chains. Large SNS-PAA-PA membrane sheets, measuring 76.2 cm × 60.9 cm, were synthesized and used to fabricate small spiral-wound low fouling seawater RO elements (2.5 in. × 21 in.). The SNS-PAA-PA membrane sheets were of high spatial uniformity with respect to both water permeability and salt rejection. Lower SNS-PAA-PA membrane fouling propensity, relative to commercial membranes, was demonstrated in BSA and sodium alginate fouling tests of both membrane coupon and spiral-wound elements. Permeability recovery, upon water flushing of the fouled SNS-PAA-PA spiral-wound membrane elements was complete. Complete permeability recovery was also achieved for the sodium alginate fouled Dow SW30 element upon water flushing; however, permeability recovery was lower (91.6%) for the BSA fouled element, thus suggesting the need for added chemical cleaning. The study results suggest that APPIGP process scale up is feasible for fabrication of commercial-scale low fouling spiral-wound RO elements. However, further scale up toward continuous APPIGP will be required for larger size elements and automated element fabrication should be employed to minimize membrane and element construction imperfections.

Effect of the air humidity on the chlorine treatment for CdTe thin films solar cells

Chlorine treatment is considered one of the most important processes to obtain high-efficiency CdTe solar cells. Such treatments are usually performed by exposing the devices to CdCl2 or other chlorine compounds and annealing them at high temperatures. Annealing processes were carried out in vacuum, inert atmosphere, reactive atmosphere, or air. The usage of ambient air has several advantages either technical or economical. However, the presence of moisture in the atmosphere may affect the treatment results or their reproducibility, especially in countries where the relative humidity (RH%) of the air could be an issue. However, despite many reports on CdTe Cl-treatments, the RH% effect on the finished solar-cell performance was not extensively reported. In this work, RH% was varied from 0% to 60%, comparing two different Cl treatments: CHClF2 (gas) and CdCl2 (in MeOH solution). It was observed that the RH% negatively affects the electrical properties of CHClF2-treated solar cells, while it could reduce the spatial uniformity using CdCl2. We conclude that relative air humidity is a parameter that should be controlled for producing high-quality CdTe-based PV devices.

Corn emergence uniformity estimation and mapping using UAV imagery and deep learning

Assessment of corn (Zea Mays L.) emergence uniformity is important to evaluate crop yield potential. Previous studies have shown the potential of unmanned aerial vehicle (UAV) imagery and deep learning (DL) models in estimating early stand count and plant spacing uniformity, but few have extended further to field-scale mapping. Additionally, estimation of plant emergence date using UAV imagery in field-scale studies has not been achieved. This study aimed to estimate and map corn emergence uniformity using UAV imagery and DL modeling. Corn emergence uniformity was quantified with plant density, plant spacing standard deviation (PSstd), and mean days to imaging after emergence (DAEmean). Corn was planted at four depths (3.8, 5.1, 6.4, and 7.6 cm). A UAV imaging system equipped with a red, green, and blue (RGB) camera was used to acquire images at 10 m above ground level at 32 days after planting (20 days after emergence at V2-V4 growth stage). A pre-trained convolutional neural network, ResNet18, was used to estimate the three emergence parameters. Results showed the estimation accuracies in the testing dataset for plant density, PSstd, and DAEmean were 0.97, 0.73, and 0.95, respectively. The developed method had higher accuracy and lower root-mean-square-error for plant density and DAEmean, indicating better performance than previous studies. A case study was conducted to assess the emergence uniformity of corn at different planting depths using the developed estimation models at the field scale. From this, field maps were produced. Results showed that the average plant density and DAEmean decreased and the average PSstd increased with increasing depths, indicating deeper planting depths caused less and later emergence and less spatial uniformity in this field. These emergence uniformity field maps could be used for future field-scale agronomic studies on temporal and spatial crop emergence uniformity and for making planting decisions in commercial production.

Modeling and Optimizing the Impact of Process and Equipment Parameters in Sputtering Deposition Systems Using a Gaussian Process Machine Learning Framework

We present a method for empirically modeling and optimizing variations in sputtering deposition processes using Gaussian Process (GP) machine learning methods. Our predictive models can be trained with limited training data to enable rapid sputtering process tuning. As a first case, we model the effect of process recipe parameters such as chamber pressure and power on sputtered film thickness uniformity. A second more challenging case is also demonstrated: modeling film thickness spatial uniformity as a function of equipment configuration parameters. The effects of the chamber configuration variables are complex, motivating incorporation of prior process knowledge into the GP framework by utilizing a physics-based solver. Because adjusting equipment configuration parameters and obtaining corresponding wafer fabrication data is costly, a key metric is the expected number of tunes required until process constraints are met. Using past experimental data, we show that tunes using the GP-based predictive model are expected to converge in significantly fewer iterations compared to tunes using polynomial, gradient boosted regression tree, multivariate spline, and deep learning based modeling methods.

Characterisation of the performance of p-type Si detectors for hard X-ray spectroscopy

High-density compound semiconductors with sufficiently-high photon attenuations, such as CdZnTe, are required for the detection of the high-energy X-rays (>20 keV), typical to applications of the HEXITEC ASIC. However, in low-energy applications (2–20 keV), the lower electron-hole-pair generation energy of Si offers the potential of improved spectroscopic resolution. Si-based pixelated X-ray sensors are typically based on n-type material where holes are the carrier that form the signal measured on the pixels. However, the incorporation of p-type dopants into the material enables these sensors to be operated effectively in electron readout. This is similar to CdZnTe sensors, where electrons are measured by the pixels. Critically, this allows a single electron-sensitive chip to be utilised for low- and high-energy measurements. Presented in this paper are the results of the spectroscopic characterisation of four p-type-Si sensors (two 300 μm and two 500 μm thick), manufactured by Micron Semiconductors Ltd., and flip-chip bonded to the HEXITEC ASIC. At 13.94 keV all tested devices displayed average FWHM of <540 eV and the average ASIC-limited FWHM of 489 ± 75 eV measured for a single 300 μm module represents the highest resolution measured with the HEXITEC ASIC. Results also show very low pixel-to-pixel variations in the measured FWHM demonstrating the excellent spatial uniformity of these devices, and a study into the temporal stability of a single detector over a ∼30 h period demonstrated negligible changes in spectroscopic performance.

Two‐dimensional analysis for the transition from nonlocal to local electron kinetics and its effect on the spatial uniformity of a capacitively coupled plasma

AbstractIn capacitively coupled plasmas (CCPs) operated under various pressure conditions in semiconductor manufacturing processes, the transition in discharge characteristics is observed depending on local or nonlocal electron kinetics. A two‐dimensional (2D) particle‐in‐cell (PIC) simulation is required because the one‐dimensional PIC method cannot capture the effect of device structures and because fluid models cannot treat the self‐consistent change in the energy distributions. Using a 2D PIC simulation parallelized with a graphics processing unit, we investigated the transition of electron kinetics for the variation of the driving voltage, gas pressure, the gap distance between upper and lower electrodes, and the sidewall condition. Moreover, the mechanism for electron energy relaxation in a CCP is elucidated to develop a method to improve the process uniformity.

Loop-gap microwave resonator for millimeter-scale diamond quantum sensor

The diamond quantum sensors based on NV (Nitrogen-Vacancy) center is one of the promising candidates for magnetoencephalography, which requires sub-pT/√Hz magnetic field sensitivity. To achieve high sensitivity, it is necessary to excite millimeter volume scale in diamond crystal by light and microwaves, and to collect fluorescence efficiently emitted from NV centers in the volume. We proposed and fabricated a printed circuit board-based loop-gap microwave resonator to improve the spatial uniformity of the microwave field to the millimeter volume scale. Moreover, our resonator can incorporate features such as efficient optical excitation and collection, and heat dissipation. Using this resonator, we demonstrated that the NV ensemble, formed by CVD process, were driven within an area of 5 mm square. The average strength of the microwave magnetic field was 0.53 G at 46 dBm input power, which is sufficient to drive the NV centers for our sensor. The uniformity of the microwave field strength was within 0.27G of the peak-to-peak amplitude for 1 mm3 volume. Differential input of microwaves into a loop-gap resonator with two gaps improves the peak-to-peak amplitude for 1 mm3 to 0.093 G in the simulation.

Effects of InGaN quantum disk thickness on the optical properties of GaN nanowires

The impact of InGaN quantum disk (Qdisk) thickness on the optical emission properties of axial InGaN/GaN nanowires is experimentally studied. The luminescence of InGaN/GaN nanowire heterostructures grown by plasma assisted molecular beam epitaxy were measured using a combination of photoluminescence and cathodoluminescence spectroscopy. The variation of peak emission wavelength, spectral lineshape, width, and maximum intensity with the change of Qdisk thickness over the range of 4–12 nm was systematically analyzed. Both the spectroscopic measurements from the average InGaN Qdisk-related emissions reveal the presence of built-in piezoelectric strain as evidenced by the luminescence blueshift with increasing pump signal. To determine the material compositions and their spatial uniformity across the stacked InGaN Qdisks separated by GaN barriers, transmission electron microscopy with energy-dispersive x-ray spectroscopy were also performed. This provides further insights into the structural properties of the InGaN Qdisks within GaN nanowires. Thus, our experimental study serves to advance the understanding of, in general, III-nitride nanostructures for the implementation of classical and non-classical optoelectronic devices.

Large-Scale Fatigue Testing Based on the Rotating Beam Method

A large-scale fatigue testing machine based on the rotating beam method in a four-point bending configuration was designed and built. With the device, high-strength metal specimens with a 32-mm gauge diameter and a 100-mm gauge length can be tested at a cyclic frequency of up to 48 Hz. In this work, particular attention was paid to evaluating the spatial and temporal uniformity of the loading within the large specimen; methods for quantitative evaluation of these effects were developed. The developed test methodology allows for the fatigue testing of specimens with size, microstructure, and surface conditions that are similar to actual machine parts.

Semisolid Pharmaceutical Product Characterization Using Non-invasive X-ray Microscopy and AI-Based Image Analytics.

This work reports the use of X-ray microscopy (XRM) imaging to characterize the microstructure of semisolid formulations containing multiple immiscible phases. For emulsion-based semisolid formulations, the disperse phase globule size and its distribution can be critical quality attributes of the product. Optical microscopy and light diffraction techniques are traditionally used to characterize globule size distribution. These techniques are subjected to sample preparation bias and present challenges from matrix interference and data processing. XRM imaging is an emergent technique that when combined with intelligent data processing has been used to characterize microstructures of pharmaceutical dosage forms including oral solid formulations, controlled release microspheres, and lyophilized products. This work described our first attempt to use XRM imaging to characterize two complex emulsion-based semisolid formulations, a petrolatum-based ointment with a dispersed phase comprising a hydrophilic liquid, and an oil-in-water cream. This initial assessment of technology showed that microstructure details such as globule size distribution, volume fraction, spatial distribution uniformity, inter-globule spacing, and globule sphericity could be obtained and parameterized. It was concluded that XRM imaging, combined with artificial intelligence-based image processing is feasible to generate advanced characterization of semisolid formulation microstructure through 3D visualization and parameterization of globule attributes. This technique holds promise to provide significantly richer microstructure details of semisolid formulations. When fully developed and validated, it is potentially useful for quantitative comparison of microstructure equivalence of semisolid formulations.

Physically Detachable and Operationally Stable Cs2SnI6 Photodetector Arrays Integrated with µ‐LEDs for Broadband Flexible Optical Systems

AbstractWith the surge in perovskite research, practical features for future applications are desired to be secured, but the reliability of the materials and the use of hazardous Pb are longstanding problems. Here, an air‐stable Cs2SnI6 (CSI) is prepared via diluted hydriodic acid solvent‐based precursor optimization during scalable hydrothermal growth. Materials characterization is performed using various elemental peak analyses and crystallographic identification. The resulting CSI exhibits long‐term operating stability over 6 months, i) at elevated temperatures, ii) in ambient air, and iii) under light illumination from UV to near‐infrared. More importantly, to demonstrate an intriguing class of applications up to system level, physically detachable CSI photodetector arrays (PD‐arrays), integrated with micro‐light‐emitting‐diodes (μ‐LEDs) arrays, are successfully fabricated. In addition, 3 × 3 flexible CSI PDs are fully operational, even in air, and their spatial uniformity in pixels is quantitatively evaluated. The charge‐transport mechanisms of the CSI PDs under light and elevated temperature are assessed via temperature‐dependent characterization from 148 to 373 K, implying the involvement of 3D variable‐range hopping. Multicycle evaluation of the CSI PD‐arrays confirms their operational stability in AC and DC modes, demonstrating this platform's potential benefit for wireless optical interconnection in advanced Si technology.

An experimental method for efficiently evaluating the size-resolved sampling efficiency of liquid-absorption aerosol samplers

Aerosol samplers are critical tools for studying indoor and outdoor aerosols. Development and evaluation of samplers is often labor-intensive and time-consuming due to the need to use monodisperse aerosols spanning a range of sizes. This study develops a rapid experimental methodology using polydisperse solid aerosols to evaluate size-resolved aerosol-to-aerosol (AtoA) and aerosol-to-hydrosol (AtoH) sampling efficiencies. Arizona Test Dust (diameter 0.5–20 µm) was generated and dispersed into an aerosol test chamber and two candidate samplers were tested. For the AtoA test, aerosols upstream and downstream of a sampler were measured using an online aerodynamic particle sizer. For the AtoH test, aerosols collected in sampling medium were mixed with a reference sample and then measured by the laser diffraction method. The experimental methodology were validated as an impressive time-saving procedure, with reasonable spatial uniformity and time stability of aerosols in the test chamber and an acceptable accuracy of absolute mass quantification of collected particles. Evaluation results showed that the AGI-30 and the BioSampler sampler had similar size-resolved sampling efficiencies and that efficiencies decreased with decreasing sampling flow rate. The combined evaluation of AtoA and AtoH efficiency provided more comprehensive performance indicators than either test alone. The experimental methodology presented here can facilitate the design and choice of aerosol sampler.

Does weed suppression by high crop density depend on crop spatial pattern and soil water availability?

Size-asymmetric competition, in which larger plants obtain a disproportionally larger share of contested resources, can be applied in agriculture to suppress weeds by increasing crop density and spatial uniformity, as these practices enhance the initial size-asymmetric competitive advantages of crop seedlings over weed seedlings early in the growing season. We do not yet know how agronomic factors influence weed suppression at high crop density. We performed a field experiment to ask how crop density, spatial pattern and irrigation interact to influence weed suppression and grain yield in semi-arid croplands. The experimental was a factorial design with 4 factors: wheat cultivar (Ningchun4, Xihan2), irrigation level (control, irrigated), sowing density (low, 196 seeds m−2; moderate, 400 seeds m-2; high, 625 seeds m−2), and spatial sowing pattern (rows, uniform). Weed growth was effectively suppressed by increased crop density and spatial uniformity. Effects of crop density on weed suppression and grain yield were more pronounced in the uniform pattern than in crop rows. Weed biomass was 55.7% lower and grain yield increased 29.7% higher in the high density uniform pattern compared to the low density and row pattern. Crop density interacted with cultivar in determining both weed biomass and grain yield, potentially reflecting different traits regulating crop competitive ability. Irrigation and crop density had additive effects on weed biomass but interacted to influence grain yield. Our findings support the idea that increased crop density and spatial uniformity can make a valuable and environmentally friendly contribution to weed control in wheat, reducing the need for chemical or mechanical weed control. We need a better understanding of the interactions among climate, agricultural management and crop genotype to improve our ability to effectively suppress weeds with high crop density and spatial uniformity.

Optimization of spatial lighting uniformity using non-planar arrays and photosynthetic photon flux density modulation

Optimization of spatial lighting uniformity using non-planar arrays and photosynthetic photon flux density modulation

Numerical investigation on the role of a mixer on spray impingement and mixing in channel cross-stream airflow

The present study numerically investigates the influence of introducing a spin-type mixer and different angular orientations of the mixer blades on the spray-wall interaction and mixing, following cross-stream injection of a pulsed spray into airflow in a circular duct. This is relevant to the Selective Catalytic Reduction system in diesel engines for exhaust gas after-treatment. The spin-type static mixer is located downstream of the injector and generates a swirling airflow in the duct. All simulations were carried out using ANSYS Fluent V18.0. The standard k–ω model is used to simulate the turbulent continuous phase flow, while the discrete phase model is employed to track the spray droplets. The Taylor Analogy Breakup and Kuhnke wall film models are adopted to model droplet breakup and wall-film formation, respectively. First, the swirling airflow characteristics without spray injection are validated against in-house particle image velocimetry measurements. Second, the spray computations are compared with the experiment. Overall, good agreement between simulation and experiment is achieved. Furthermore, the choice of water and urea water solution injection liquid on the in-channel spray characteristics is also studied. The main focus of the present work is on the study of the influence of spin mixer clocking on the post-impingement spray evolution, droplet redistribution and mixing, and wall-film characteristics. The results show that the choice of the angular orientation of the mixer governs the extent of droplet deposition and splashing on the mixer blades and, as a result, strongly influences the spatial uniformity of droplets and ammonia species at the channel exit.

Application of Digital Image Correlation in Space and Frequency Domains to Deformation Analysis of Polymer Film.

Using speckle patterns formed by an expanded and collimated He-Ne laser beam, we apply DIC (Digital Image Correlation) methods to estimate the deformation of LLDPE (linear low-density polyethylene) film. The laser beam was transmitted through the film specimen while a tensile machine applied a load to the specimen vertically. The transmitted laser light was projected on a screen, and the resultant image was captured by a digital camera. The captured image was analyzed both in space and frequency domains. For the space-domain analysis, the random speckle pattern was used to register the local displacement due to the deformation. For the frequency-domain analysis, the diffraction-like pattern, due to the horizontally-running, periodic groove-like structure of the film was used to characterize the overall deformation along vertical columns of analysis. It has been found that when the deformation is small and uniform, the conventional space domain analysis is applicable to the entire film specimen. However, once the deformation loses the spatial uniformity, the space-domain analysis falls short if applied to the entire specimen. The application of DIC to local (windowed) regions is still useful but time consuming. In the non-uniform situation, the frequency-domain analysis is found capable of revealing average deformation along each column of analysis.

이중 안테나 제어에 따른 유도결합 N₂/NH₃/SiH₄ 플라스마의 전자 및 라디칼 밀도 분포

Low temperature N₂/NH₃/SiH₄ plasma is used to deposit hydrogenated silicon nitride(SiN<SUB>x</SUB>:H). In this process, the main factor influencing the quality of the deposited film is the active species, such as SiH<SUB>x</SUB> and NH<SUB>x</SUB> radicals. In the conventional methods, it was insufficient to explain the correlation between generation of active species and the process parameters. So, a fluid model of 2D axis-symmetry based on dual antenna inductively coupled plasma (ICP) source using N₂/NH₃/SiH₄ gas mixture has been developed for SiN<SUB>x</SUB>:H film deposition. The gas mixture model was comprised of 57 species, 195 chemical reactions and 16 surface reactions. The ratio of input power between independent antenna system affects the electron and SiH<SUB>x</SUB>, NH<SUB>x</SUB> radical generation. And it was observed that the spatial uniformity of electron and radical density increases when the independent input power of dual antenna system is set to 500:500W.