Sample Plane Research Articles

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

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

Lithography‐Free Method to Synthesize Quasiperiodic Silicon Inverted‐Pyramid Arrays: A Broadband Light Trapper for High‐Efficiency Thin Silicon Solar Cells

Thin silicon solar cells can be a low‐cost effective photo‐conversion device, if the device can efficiently absorb the solar spectrum. Herein, a new lithography‐free technique is developed for the fabrication of quasiperiodic silicon inverted‐pyramids arrays (SiIPAs), which show a high‐light‐trapping phenomenon in the ultraviolet–visible—near‐infrared (300–2000 nm). Fabricated SiIPA samples show a significant reduction of reflectance (3%) in the silicon absorption band (300–1000 nm). A unique additional absorption of 33–44% compared to the planar silicon is observed in the sub‐bandgap region of silicon (1100–2000 nm) for these samples. Photocurrent response measurement confirms the generation of additional electron–hole pairs in the sub‐bandgap region of silicon for the SiIPA samples in comparison with planar sample. In these results, the effect of field confinement and the creation of optical resonance modes within these structures, qualitatively supported by numerical simulation, are signified. The estimated short‐circuit current density using the experimental absorption spectrum of SiIPAs is 55.46 mA cm−2, which is far higher than the Lambertian limit of ≈43 mA cm−2. The theoretical efficiency of the solar cell can be achieved up to 35.22%, which surpasses the Shockley–Queisser limit of 33.7%.

Asymmetric and anisotropic quench sensitivity of ZA81M magnesium alloy

The quench sensitivity of the ZA81M magnesium alloy is studied by combining experiment and crystal plasticity finite element simulation. The quench sensitivity is high in tension and low in compression making the single-valued quench sensitivity calculated from hardness insufficient. So, there is different loss rate of strength, along different test directions of the alloy, due to slow quenching, i.e., the quench sensitivity is asymmetric and anisotropic. The coarsening of the precipitate and widening of the precipitate-free zone are the origin of the quench sensitivity. Crystal plasticity finite element simulation is proposed to calculate the quench sensitivity. The phenomenological constitutive model is used to explicitly consider the strengthening effect of precipitates on different slip and twinning systems. So, the precipitate characteristics of the water-quenched and air-cooled alloy are easily captured. The anisotropy and asymmetry of the quench sensitivity in two perpendicular sample planes are determined by simulation. Such a method can be useful for determining the quench sensitivity of precipitation-hardening alloys with low crystal symmetry and with precipitates having different strengthening efficiencies on different slip or twinning systems.

Automated Structure Discovery for Scanning Tunneling Microscopy.

Scanning tunneling microscopy (STM) with a functionalized tip apex reveals the geometric and electronic structures of a sample within the same experiment. However, the complex nature of the signal makes images difficult to interpret and has so far limited most research to planar samples with a known chemical composition. Here, we present automated structure discovery for STM (ASD-STM), a machine learning tool for predicting the atomic structure directly from an STM image, by building upon successful methods for structure discovery in noncontact atomic force microscopy (nc-AFM). We apply the method on various organic molecules and achieve good accuracy on structure predictions and chemical identification on a qualitative level while highlighting future development requirements for ASD-STM. This method is directly applicable to experimental STM images of organic molecules, making structure discovery available for a wider scanning probe microscopy audience outside of nc-AFM. This work also allows more advanced machine learning methods to be developed for STM structure discovery.

Mueller-Gabor holographic microscopy

Despite the emergence of various methods for Mueller matrix recovery, achieving complete volumetric Mueller matrix retrieval remains a challenge. An alternative approach that leverages in-line Gabor holography to comprehensively extract polarization information from volumetric samples is introduced in this context. The proposed polarization-sensitive in-line Gabor holographic setup enables the recovery of the complete Mueller matrix of three-dimensional (3D) samples after the numerical repropagation of the holographically rendered complex field to various sample planes. This proposal is validated using a calibrated birefringent polarization test target, a sample of Calcium Oxalate crystals, and a volumetric sample containing microplastics, providing the 3D measurement of polarimetric parameters such as diattenuation, polarizance, depolarization, and retardance. The results agree with those obtained through reference methods based on image-plane brightfield polarimetry. The in-line Gabor holographic system proposed is sensitive to the axial variations in polarimetric information within volumetric samples without any mechanical movement nor optical adjustments— an accomplishment that remains elusive to conventional image-plane reference methods and non-holographic/interferometric systems. These findings emphasize the versatility and potential of this alternative approach in recovering the intricate polarization characteristics of 3D specimens, offering the first in-line holographic Mueller imaging to the best of the authors' knowledge.

Performance measurements for indoor photovoltaic devices: Classification of a novel light source

There is an increasing interest in using indoor photovoltaic (IPV) devices to power Internet of Things applications, low power communications, and indoor environmental sensing. For the commercialization of IPV technologies, device performance measurements need to conform to the relevant standardized specifications. We present a novel IPV device measurement system that incorporates digital light processing (DLP) to deliver a spectrally invariant light source at all required illuminance levels, as specified by the indoor standard testing conditions in IEC TS 62607-7-2:2023. We evaluated the DLP system according to requirements for spectral coincidence, temporal stability, and non-uniformity at the sample plane. We demonstrate the measurements to define the classification status of the system and the unique benefits of the DLP system that allow a stable spectral profile and high levels of uniformity across all illuminance levels. This is the first reported measurement system for IPV device testing based on DLP technology, and the classification methodology of this work can be used as an example for the classification of indoor light simulators in laboratory environments based on the latest IEC TS 62607-7-2:2023.

Structural and magnetic properties of Ni cluster embedded (111)NiO layers grown on (0001)GaN films

(111) NiO epitaxial layers embedded with crystallographically oriented Ni-clusters are grown on c-GaN/Sapphire templates using the pulsed laser deposition technique. Structural and magnetic properties of the films are examined by a variety of techniques including high-resolution x-ray diffraction, precession-electron diffraction, and superconducting quantum interference device magnetometry. It has been found that Ni-clusters are formed in the NiO matrix only at sufficiently low oxygen pressures during the growth. The study further reveals that the orientation, shape, size, density, and magnetic properties of these clusters depend strongly on the growth temperature (TG). Although most of the Ni-clusters are found to be obtained crystallographically aligned with the NiO matrix with Ni(111) ∥NiO(111), clusters with other orientations also exist, especially in samples grown at lower temperatures. The average size and density of the clusters increase with TG. The proportion of the Ni(111) ∥ NiO(111)-oriented clusters also improves as TG is increased. All cluster embedded films show ferromagnetic behavior even at room temperature. Easy-axis is found to be oriented in the layer plane in samples grown at relatively lower temperatures. However, it turns perpendicular to the layer plane for samples grown at sufficiently high temperatures. This reversal of easy-axis has been attributed to the size dependent competition between the shape and magnetoelastic and the surface anisotropies of the clusters. This composite material thus has great potential to serve as a spin-injector and spin-storage medium in GaN-based spintronics of the future.

Unraveling the surface heat flux heterogeneity in cone calorimetry of cylindrical charring material: Insights from experiments and 2D modeling

Although originally designed for planar samples, cone calorimeter is frequently used for the flammability assessment and pyrolysis modeling of non-planar objects, like electrical cables. Prescribing the boundary conditions for the numerical models of such objects requires knowledge about the radiative and convective heat fluxes along the sample circumference. In this work, we performed gasification and flaming experiments and 2D numerical simulations on birch cylinders. During the gasification of a single-rod, the char front propagated faster vertically than horizontally, while similar rates were observed in the flaming condition. With five rods, ∪- and ∩-shaped char fronts were observed in gasification and flaming conditions, respectively. From the simulations, we extracted detailed heat flux distributions, with main deviation from flat samples being the steep reduction in incident radiation between the top and sides of the cylinders. Moreover, in five-rod configurations, radiative flux to the sides of the central rod increases up to 10 (gasification) and 20 kW m−2 (flaming). On the outermost rod, the descending flame induces downward-moving waves of heat fluxes with amplitudes 20 kW m−2 for convection and 15 kW m−2 for radiation. Simplified expressions for the heat transfer boundary conditions were tabulated for practical engineering applications.

S-polarized light-sheets improve resolution and light-efficiency in oblique plane microscopy

Oblique plane microscopy (OPM) offers 3D optically sectioned imaging with high spatial- and temporal-resolution while enabling conventional sample mounting. The technique uses a concatenation of three microscopes, two for remote focusing and a tilted tertiary microscope, often including an immersion objective, to image an oblique sample plane. This design induces Fresnel reflections and a reduced effective aperture, thus impacting the resolution and light efficiency of the system. Using vectorial diffraction simulations, the system performance was characterized based on illumination angle and polarization, signal to noise ratio, and refractive index of the tertiary objective immersion. We show that for samples with high fluorescent anisotropy, s-polarized light-sheets yield higher average resolution for all system configurations, as well as higher light-efficiency. We also provide a tool for performance characterization of arbitrary light-sheet imaging systems.

An automated slide scanning system for membrane filter imaging in diagnosis of urogenital schistosomiasis.

Traditionally, automated slide scanning involves capturing a rectangular grid of field-of-view (FoV) images which can be stitched together to create whole slide images, while the autofocusing algorithm captures a focal stack of images to determine the best in-focus image. However, these methods can be time-consuming due to the need for X-, Y- and Z-axis movements of the digital microscope while capturing multiple FoV images. In this paper, we propose a solution to minimise these redundancies by presenting an optimal procedure for automated slide scanning of circular membrane filters on a glass slide. We achieve this by following an optimal path in the sample plane, ensuring that only FoVs overlapping the filter membrane are captured. To capture the best in-focus FoV image, we utilise a hill-climbing approach that tracks the peak of the mean of Gaussian gradient of the captured FoVs images along the Z-axis. We implemented this procedure to optimise the efficiency of the Schistoscope, an automated digital microscope developed to diagnose urogenital schistosomiasis by imaging Schistosoma haematobium eggs on 13 or 25 mm membrane filters. Our improved method reduces the automated slide scanning time by 63.18% and 72.52% for the respective filter sizes. This advancement greatly supports the practicality of the Schistoscope in large-scale schistosomiasis monitoring and evaluation programs in endemic regions. This will save time, resources and also accelerate generation of data that is critical in achieving the targets for schistosomiasiselimination.

Scan-less microscopy based on acousto-optic encoded illumination.

Several optical microscopy methods are now available for characterizing scientific and industrial processes at sub-micron resolution. However, they are often ill-suited for imaging rapid events. Limited by the trade-off between camera frame-rate and sensitivity, or the need for mechanical scanning, current microscopes are optimized for imaging at hundreds of frames-per-second (fps), well-below what is needed in processes such as neuronal signaling or moving parts in manufacturing lines. Here, we present a scan-less technology that allows sub-micrometric imaging at thousands of fps. It is based on combining a single-pixel camera with parallelized encoded illumination. We use two acousto-optic deflectors (AODs) placed in a Mach-Zehnder interferometer and drive them simultaneously with multiple and unique acoustic frequencies. As a result, orthogonal light stripes are obtained that interfere with the sample plane, forming a two-dimensional array of flickering spots - each with its modulation frequency. The light from the sample is collected with a single photodiode that, after spectrum analysis, allows for image reconstruction at speeds only limited by the AOD's bandwidth and laser power. We describe the working principle of our approach, characterize its imaging performance as a function of the number of pixels - up to 400 × 400 - and characterize dynamic events at 5000 fps.

Thermal and electric field effects on the nonlinear optical response of a cyanobiphenyl liquid crystal doped with carbon dots

The present study is devoted to the investigation of the nonlinear optical response of a cyanobiphenyl liquid crystal (8CB) doped with carbon dots derived from dansyl chloride (CD-DsCl). Using the time-resolved z-scan technique, it is investigated how the CD-DsCl addition affects the nonlinear refractive coefficient of planar liquid crystal samples. The temperature dependence of nonlinear optical responses of pristine and doped samples are analyzed close to smectic-A - nematic and nematic - isotropic phase transitions. Furthermore, the effects of an external electric field are analyzed. Our results show that doped 8CB samples may exhibit an enhanced nonlinear optical response, which depends on the strength of the external field.

Metal–Insulator Transition and Other Electronic Properties of AB-Stacked Bilayer Graphene Deposited on a Ferromagnetic Substrate

Using a simple theoretical model, AB-stacked bilayer graphene deposited on a ferromagnetic insulating substrate is studied. In addition to the exchange Zeeman field induced by the substrate, the model allows one to take into account the effective external electric field perpendicular to the graphene sample plane (such field arises due to the contact with the substrate and can also be induced by applying a gate voltage). It has been demonstrated that AB-stacked graphene in zero electric field is in a metallic state. As the field increases, a transition to the insulating phase occurs. The spectrum of electron states, the band gap, and other characteristics of the phases on both sides of the metal−insulator transition have been calculated. Our results are consistent with density functional theory calculations and can be useful for spintronics.

High temperature AlN thin film ultrasonic transducers with dual mode wave excitation

AlN thin film ultrasonic transducers with dual mode wave (transverse and longitudinal) excitation were deposited by reactive RF magnetron sputtering technique. The transducers deposited at radial distances of 0 and 50 mm in the sample plane exhibited well-developed straight and inclined columnar structures with dominating (002) and (103) X-ray diffraction peaks, respectively. The transducers deposited at radial distances of 0, 30, and 50 mm demonstrated excitation of longitudinal, transverse, and longitudinal-transverse waves, respectively. Short term heat treatment was conducted in air within a temperature range of 20–900 °C to investigate the high temperature ultrasonic response. Temperature dependencies of the time-of-flight and pulse-echo amplitude were analyzed. Long term heat treatment in air at 700 °C for 192 h revealed a degradation of ultrasonic response due to the oxidation of the AlN layer.

Tandem aberration correction optics (TACO) in wide-field structured illumination microscopy.

Structured illumination microscopy (SIM) is a powerful super-resolution imaging technique that uses patterned illumination to down-modulate high spatial-frequency information of samples. However, the presence of spatially-dependent aberrations can severely disrupt the illumination pattern, limiting the quality of SIM imaging. Conventional adaptive optics (AO) techniques that employ wavefront correctors at the pupil plane are not capable of effectively correcting these spatially-dependent aberrations. We introduce the Tandem Aberration Correction Optics (TACO) approach that combines both pupil AO and conjugate AO for aberration correction in SIM. TACO incorporates a deformable mirror (DM) for pupil AO in the detection path to correct for global aberrations, while a spatial light modulator (SLM) is placed at the plane conjugate to the aberration source near the sample plane, termed conjugate AO, to compensate spatially-varying aberrations in the illumination path. Our numerical simulations and experimental results show that the TACO approach can recover the illumination pattern close to an ideal condition, even when severely misshaped by aberrations, resulting in high-quality super-resolution SIM reconstruction. The TACO approach resolves a critical traditional shortcoming of aberration correction for structured illumination. This advance significantly expands the application of SIM imaging in the study of complex, particularly biological, samples and should be effective in other wide-field microscopies.

Strong exciton-photon coupling in self-hybridized organic–inorganic lead halide perovskite microcavities

Abstract Controlling coherent light–matter interactions in semiconductor microcavities is at the heart of the next-generation solid-state polaritonic devices. Organic–inorganic hybrid perovskites are potential materials for room-temperature polaritonics owing to their high exciton oscillator strengths and large exciton binding energies. Herein, we report on strong exciton-photon coupling in the micro-platelet and micro-ribbon shaped methylammonium lead bromide single crystals. Owing to high crystallinity and large refractive index, the as-grown perovskite microcrystals serve as self-hybridized optical microcavities along different orientations due to their distinct physical dimensionalities. In this regard, the perovskite micro-platelet forms a simple Fabry–Perot microcavity in out-of-plane orientation, while the micro-ribbon functions as a Fabry–Perot type waveguide microcavity within the plane of the perovskite sample. Consequently, excitons in these microcavities strongly interact with their corresponding uncoupled cavity modes, yielding multimode exciton-polaritons with Rabi splitting energies ∼205 and 235 meV for micro-platelet and micro-ribbon geometry, respectively. Furthermore, micro-ribbon geometry displays Young’s double-slit-like interference patterns, which together with the numerical simulation readily reveals the parity and the mode order of the uncoupled cavity modes. Thus, our results not only shed light on strong exciton-photon coupling in various morphologies of methylammonium lead bromide microcrystals but also open an avenue for advanced polaritonic devices.

Effects of incorporating manganese in CdS thin films elaborated by CBD and the performance of Schottky diodes TCO/CdS:Mn/C

This study focuses on manganese doped CdS thin films by chemical bath deposition (CBD). Thin films and Schottky diodes of CdS and CdS:Mn are synthesized by a simple chemical route. The influence of the incorporation of Mn2+ cations in the crystalline structure of CdS has been characterized by techniques such as XRD, SEM, XPS, UV–Vis spectroscopy, and I–V curves. Doped thin films have a uniform hexagonal structure and preferentially grow along the (100) and (002) planes. The higher the amount of Mn2+ cations, the preferential orientation of the (100) plane gradually disappears, while the undoped sample shows a preferential orientation in the (002) plane. In addition, the morphology, when incorporating manganese, exhibits a drastic change, generating scale-like and needle-like structures, and the average size of the particles varies from 67 nm to 107 nm, in contrast to virgin CdS particles that show a mean size of 23 nm and spherical structures. The variation of the bandgap is 0.067 eV due to the presence of the preferential orientation in the (100) crystal plane in the Mn-doped samples and the doping increase in crystallite size. Doped Schottky diodes exhibit a saturation current of 2 nA and a potential barrier of 0.66 eV, compared to undoped diodes that exhibit a saturation current of 0.93 nA and a potential barrier of 0.823 eV. In addition, it was possible to modify the rectification speed of the diodes by almost 70 % by incorporating manganese. Overall, our study reveals that there is great potential in the design of affordable high-speed optoelectronic devices, although we are aware that we are still at an early stage in achieving these goals.

The fabrication of GaN/InGaN nano-pyramids photoanode and its enhanced water splitting performance

In this paper, we have successfully fabricated a GaN/InGaN nano-pyramids photoanode utilizing the selective area growth (SAG) method. This method has demonstrated a notable improvement in water splitting performance, with a photocurrent enhancement of approximately 1.5 times when compared to the planar GaN/InGaN sample. The remarkable enhancement in water splitting performance can be chiefly attributed to the presence of In-rich InGaN grown on the (10−11) plane and nano-pyramids morphology. The In-content in the pyramid GaN/InGaN structure is approximately 2.25 times higher than that of the planar sample, resulting in increased photon absorption due to a narrower bandgap. Moreover, the nano-pyramids morphology possesses a larger specific surface area, further enhancing its light absorption capacity. These combined advantages significantly contribute to the outstanding improvement in water splitting performance observed in the pyramid GaN/InGaN structure. Our work introduces a novel approach to harnessing GaN materials for highly efficient water splitting applications.

GH3536 superalloy prepared by selective laser melting: microstructure and properties

In this paper, GH3536 superalloy was prepared by selective laser melting (SLM) using plasma rotating electrode powder as raw material. The effects of forming and heat treatment processes on the microstructure and mechanical properties of GH3536 superalloy were studied. The results show that there were obvious micro-cracks on the laser scanning plane of SLM samples, and the length of micro-cracks was between 10-100μm. The micro-cracks originated from the inside of the molten pools and penetrated the melting channels, and the heat treatment could not eliminate the cracks. With the increase of volume energy density (VED), the tensile strength and yield strength of SLM samples increased first and then decreased. The maximum values of tensile strength and yield strength reached 772.3MPa and 613.3MPa, respectively. However, with the increase of VED, the elongation of SLM samples decreased to 27.3%. After heat treatment, the tensile strength and yield strength of the material increased (up to 789MPa and 410MPa), but the elongation decreased.

Metal–Insulator Transition and Other Electronic Properties of AB-Stacked Bilayer Graphene Deposited on a Ferromagnetic Substrate

Using a simple theoretical model, AB-stacked bilayer graphene deposited on a ferromagnetic insulating substrate is studied. In addition to the exchange Zeeman field induced by the substrate, the model allows one to take into account the effective external electric field perpendicular to the graphene sample plane (such field arises due to the contact with the substrate and can also be induced by applying a gate voltage). It has been demonstrated that AB-stacked graphene in zero electric field is in a metallic state. As the field increases, a transition to the insulating phase occurs. The spectrum of electron states, the band gap, and other characteristics of the phases on both sides of the metal−insulator transition have been calculated. Our results are consistent with density functional theory calculations and can be useful for spintronics.