Pyramidal Array Research Articles

Purcell enhancement using spatially distributed random cavities enabled by silicon pyramid arrays

Purcell enhancement using spatially distributed random cavities enabled by silicon pyramid arrays

Research on the influence of different pyramid array structures on plane blackbody emissivity

The plane blackbody radiation source is pivotal to the infrared remote sensing detection system, with emissivity serving as a critical metric for its performance evaluation. This metric is predominantly influenced by the surface structure and coating properties. To improve emissivity, existing works have utilized pyramid structures to expand the contact area between the radiation surface and light, thereby augmenting light absorption. Nonetheless, there is relatively little research exploring the impact of pyramid structure on emissivity, leading to a scarcity of related emissivity data for plane blackbody. In this paper, we explored the impact on the blackbody emissivity induced by different pyramid structures, including the triangular pyramid array (TPA), the quadrangular pyramid array (QPA), the pentagonal pyramid array (PPA), and the hexagonal pyramid array (HPA). Also, the effects involving coating properties, the base-height ratio of the pyramid, and reflection characteristics on emissivity were investigated based on the Monte Carlo Method. Then, the specimens with diffuse reflection (DR) and near-specular reflection (NSR) were fabricated and tested experimentally. The uncertainties of simulation and experiment were maintained below 0.21 % and 0.50 %, respectively. Experimental results are well aligned with the corresponding simulation results, indicating that the normal emissivity of the TPA blackbody is 0.12 % higher than the QPA blackbody, and the directional emissivity uniform of the TPA blackbody is superior to that of the QPA blackbody for the DR model in the 8–14 μm waveband. Furthermore, the temperature field distributions of radiation surface for TPA and QPA blackbody were analysed, noting a maximum temperature difference of 50 mK and 30 mK, respectively. This paper provides experimental support and design references for further improving the emissivity of plane blackbodies.

Geometrically Controlled Microscale Patterning and Epitaxial Lateral Overgrowth of Nitrogen-Polar GaN.

In this Letter, we report on a novel two-step epitaxial growth technique that enables a significant improvement of the crystal quality of nitrogen-polar GaN. The starting material is grown on 4° vicinal sapphire substrates by metal-organic vapor-phase epitaxy, with an initial high-temperature sapphire nitridation to control polarity. The material is then converted to a regular array of hexagonal pyramids by wet-etching in a KOH solution and subsequently regrown to coalesce the pyramids back into a smooth layer of improved crystal quality. The key points that enable this technique are the control of the array geometry, obtained by exploiting the anisotropic behavior of the wet-etch step, and the use of regrowth conditions that preserve the orientation of the pyramids' sidewalls. In contrast, growth conditions that cause an excessive expansion of the residual (0001̅) facets on the pyramids' tops cause the onset of a very rough surface morphology upon full coalescence. An X-ray diffraction study confirms the reduction of the threading dislocation density as the regrowth step develops. The analysis of the relative position of the 0002̅ GaN peak, with respect to the 0006 sapphire peak, reveals a macroscopic tilt of the pyramids, probably induced by the large off-axis substrate orientation. This tilt correlates very well with an anomalous broadening of the 0002̅ diffraction peaks at the beginning of the regrowth step.

Absorption dominated broadband terahertz electromagnetic shielding properties of ultrathin rGO paper

The demand for absorption-dominated terahertz (THz) electromagnetic shielding materials is critical in THz devices or components for electromagnetic compatibility and protection. However, it is challenging to find out an ultrathin, absorption-dominated shielding material with high absorptivity in a broad range. Herein, we demonstrate the hydrogen iodine (HI) acid reduced graphene oxide (rGO) ultrathin paper as a promising candidate for absorption-dominated electromagnetic interference (EMI) shielding. By optimizing the conductivity and layered structures, rGO paper with thickness of only 13 μm exhibited an absorption-dominated EMI shielding effectiveness (SE) of 21.09 dB in a broad band from 0.2 to 1.2 THz. Simple stacking of the rGO papers further improved the EMI SE up to 42.53 dB with a total thickness of 40 μm. rGO papers can also be integrated into structured substrates for applications in different scenarios. Covering a single rGO paper onto the wedge structure array, a broadband THz absorption over 99 % can be achieved. Similarly, combining rGO papers and arrays of zinc pyramids, and the average SE and the max THz absorption were enhanced to 54.83 dB and 99.986 %, respectively. We believe this absorption-dominated THz shielding rGO paper paves an efficient avenue towards high performance THz shielding/absorption devices for diverse applications.

Epitaxial Growth of the Large-Scale, Highly-Ordered 3D GaN-Truncated Pyramid Array Toward an Ultrahigh Rejection Ratio and Responsivity Visible-Blind Ultraviolet Photodetection.

The micro- and nanostructures of III-nitride semiconductors captivate strong interest owing to their distinctive properties and myriad potential applications. Nevertheless, challenges endure in managing the damage inflicted on crystals through top-down processes or achieving extensive control over the large-area growth of these microstructures via bottom-up methods, thereby impacting their optical and electronic properties. Here, we present novel epitaxially grown 3D GaN truncated pyramid arrays (TPAs) on patterned Si substrates, devoid of any catalyst. These GaN TPAs feature highly ordered, large-scale structures, attributed to the utilization of 3D Si substrates and thin AlN interlayers to alleviate epitaxial strains and limit dislocation formation. Comprehensive characterization via scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and cathodoluminescence attests to the superior structural and optical attributes of these crystals. Furthermore, photoluminescence and ultraviolet (UV)-visible diffuse reflectance spectroscopy reveal sharp band-edge emission and significant light trapping in the UV bands. Employing these GaN TPAs, we constructed metal-semiconductor-metal visible-blind UV photodetectors (PDs) incorporating Ti3C2 MXene as Schottky electrodes. These PDs display exceptional responsivity, achieving 5.32 × 103 mA/W at 255 nm and an ultrahigh UV/visible rejection ratio (R255nm/R450nm) approaching 106, which are 1-2 orders of magnitude higher than most recently reported works. This exploration showcases novel GaN-based microstructures characterized by uniformity, ordered geometry, and exemplary crystalline integrity, paving the way for developing optoelectronic applications.

Covalently Linking Reduced Graphene Oxide Facilitated Electrodeposition of MoS2 on Silicon Pyramidal Photocathode To Enhance Hydrogen Evolution.

In recent years, increasing attention has been paid to photoelectrochemical (PEC) hydrogen production owing to the utilization of sustainable solar energy and its promising performance. Silicon-based composites are generally considered ideal materials for PEC hydrogen production. However, slow reaction kinetics and poor stability are still key factors hindering the development of silicon-based photoelectrocatalysts. Herein, we present an n+-p Si pyramidal photocathode assembly method to load reduced graphene oxide (rGO) onto the surface of the n+-p Si pyramid by covalently linking (Si/rGO). rGO is utilized as a conductive layer to reduce the interfacial charge-transfer resistance. Then, MoS2 can be successfully electrodeposited on the surface of Si/rGO to form the Si/rGO/MoS2 composite, which possesses excellent PEC hydrogen evolution performance with a high and stable photocurrent of -41.6 mA cm-2 and a hydrogen evolution rate of about 18.1 μmol min-1 cm-2 under 0 V (vs RHE). The covalently linking rGO layer effectively enhances the transfer of photogenerated carriers between the Si substrate and MoS2. MoS2 provides abundant hydrogen evolution active sites, which accelerate the surface reaction kinetics, as well as a protective layer for the Si pyramidal array structure. This work provides a low-cost, convenient, and efficient way of preparing silicon-based photocathodes.

Fly-Cutting Processing of Micro-Triangular Pyramid Arrays and Synchronous Micro-Scrap Removal.

Many micro-scraps are generated when a micro-triangular pyramid array (MTPA) is machined by the fly-cutting method. Micro-scraps are generally not removed quickly enough; therefore, these residual micro-scraps participate in the cutting process again, scratching the workpiece surface and accelerating diamond tool wear. To remove micro-scraps rapidly, a fly-cutting method to produce MTPAs on vertically oriented working surfaces was developed during this study. The results show that an MTPA produced by fly cutting on a vertical workpiece had a clearly outlined structure, high dimensional accuracy, and a low surface roughness. There was no micro-scrap residue on the workpiece surface and the diamond tool wear was small. The cutting inlet edges had no burrs, and the cutting outlet edges had only a small number of burrs. This method of fly cutting MTPAs on vertically oriented working surfaces provides a foundation for the development of high-precision micro-triangular pyramid optical elements.

Controlled fabrication of upright and inverted pyramid arrays of silicon via the interaction of copper ions and oxidants in hydrofluoric acid

Recent advances in chemical etching of silicon have allowed its widespread use in the fabrication of microelectronic devices and energy converters, in which shaped silicon exhibits outstanding properties and functions. The texturing process used to fabricate light-trapping structures on silicon surfaces is an indispensable step in preparing solar cells. Here, this manuscript describes the use of a one-step wet chemical etching method with copper as a catalyst to manufacture different structures, including inverted pyramid structures and upright pyramid structures, on silicon surfaces, which can be easily controlled by varying the solution composition and etching time. Moreover, this manuscript demonstrates an exciting method for fabricating random inverted pyramid and random upright pyramid arrays of silicon. The findings provide important contributions that can help improve the fabrication methods for silicon-based solar cell devices and optimize the light trapping structure on the cell surface.

Multi-color emission based on InGaN/GaN micro-truncated pyramid arrays

3D micro-nano devices are expected to become the mainstay of multi-color solid-state lighting in the future because of their broad-band characteristic and the advantage of integrating the monolithic light-emitting diode on a single chip. In this work, InGaN/GaN micro-truncated pyramid arrays with six equivalent (101̄1) semi-polar facets and one (0001) polar facet were successfully prepared by the metal-organic chemical vapor deposition technology. The average diameter of the obtained uniform micro-truncated pyramids was 6.8 µm with a height of 2.4 µm. According to the results of micro-photoluminescence performed, the InGaN/GaN micro-truncated pyramid arrays can achieve multi-color emission from blue to red. The luminescent positions corresponding to different wavelengths were detected by the cathode luminescence spectrum. The multi-color emission was related to the quantum hybrid structures apart from the discrepancy of In composition in different positions. The developed microstructure can create multi-color emission by combining distinct luminescence modes, which can aid in the design of future optoelectronic devices.

Coordinated multi-band stealth based on phase change materials

With the integrated application of multiple detection technologies, multi-band compatible stealth is crucial to improve the counter-detection capability of targets. However, there are still significant challenges in achieving stealth that is compatible with different bands. This paper presents a wavelength-selective emitter with a structure consisting of a layer composed of a high-temperature-resistant material and a phase change material Ge2Sb2Te5 (GST), and an upper truncated pyramid array composed of TiO2. The structure can transition between “stealthy” and “non-stealthy” states by controlling the phase transition process of the GST. The structure in stealth mode has low reflectivity in the visible (VIS) region, low emissivity in the mid-wave infrared and long-wave infrared region. In addition, it has laser stealth at 1.06 μm and 1.54 μm, and provides radiative cooling in the non-atmospheric window (5–8 μm). The dipole resonance formed by TiO2 on the side gives the structure lower reflectivity in the VIS band and at two laser wavelengths. The high emission in the non-atmospheric window is mainly attributed to the Fabry-Perot resonance supported in the structure. In addition, the effects of incidence angle and temperature on the stealth performance of the structure are investigated. This research has promising applications in the field of multi-band compatible stealth.

Bioinspired Polymer Films with Surface Ordered Pyramid Arrays and 3D Hierarchical Pores for Enhanced Passive Radiative Cooling.

Passive radiative cooling (PRC) has been acknowledged to be an environmentally friendly cooling technique, and especially artificial photonic materials with manipulating light-matter interaction ability are more favorable for PRC. However, scalable production of radiative cooling materials with advanced biologically inspired structures, fascinating properties, and high throughput is still challenging. Herein, we reported a bioinspired design combining surface ordered pyramid arrays and internal three-dimensional hierarchical pores for highly efficient PRC based on mimicking natural photonic structures of the white beetle Cyphochilus' wings. The biological photonic film consisting of surface ordered pyramid arrays with a bottom side length of 4 μm together with amounts of internal nano- and micropores was fabricated by using scalable phase separation and a quick hot-pressing process. Optimization of pore structures and surface-enhanced photonic arrays enables the bioinspired film to possess an average solar reflectance of ∼98% and a high infrared emissivity of ∼96%. A temperature drop of ∼8.8 °C below the ambient temperature is recorded in the daytime. Besides the notable PRC capability, the bioinspired film exhibits excellent flexibility, strong mechanical strength, and hydrophobicity; therefore, it can be applied in many complex outdoor scenarios. This work provides a highly efficient and mold replication-like route to develop highly efficient passive cooling devices.

Real-Time Embedded Simulation Platform for Hippocampal Traveling Waves of Electric Field Conduction

The investigation of hippocampal traveling waves has gained significant importance in comprehending and treating neural disorders such as epilepsy, as well as unraveling the neural mechanisms underlying memory and cognition. Recently, it has been discovered through both in vivo and in vitro experiments that hippocampal traveling waves are typically characterized by the coexistence of fast and slow waves. However, electrophysiological experiments face limitations in terms of cost, reproducibility, and ethical considerations, which hinder the exploration of the mechanisms behind these traveling waves. Model-based real-time virtual simulations can serve as a reliable alternative to pre-experiments on hippocampal preparations. In this paper, we propose a real-time simulation method for traveling waves of electric field conduction on a 2D plane by implementing a hippocampal network model on a multi-core parallel embedded computing platform (MPEP). A numerical model, reproducing both NMDA-dependent fast waves and Ca-dependent slow waves, is optimized for deployment on this platform. A multi-core parallel scheduling policy is employed to address the conflict between model complexity and limited physical resources. With the support of a graphical user interface (GUI), users can rapidly construct large-scale models and monitor the progress of real simulations. Experimental results using MPEP with four computing boards and one routing board demonstrate that a hippocampal network with a 200 × 16 pyramidal neuron array can execute real-time generation of both fast and slow traveling waves with total power consumption below 500 mW. This study presents a real-time virtual simulation strategy as an efficient alternative to electrophysiological experiments for future research on hippocampal traveling waves.

Modulating Electronic Structure of Iridium Single-Atom Anchored on 3D Fe-Doped β-Ni(OH)2 Catalyst with Nanopyramid Array Structure for Enhanced Oxygen Evolution Reaction.

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) is crucial in the pursuit of clean and sustainable hydrogen energy, yet still challenging. Herein, a spontaneous redox strategy is reported to achieve iridium single-atoms anchored on hierarchical nanosheet-based porous Fe doped β-Ni(OH)2 pyramid array electrodes (SAs Ir/Fe-β-Ni(OH)2), which exhibits high OER performance with a low overpotential of 175mV at 10mAcm-2 and a remarkable OER current density in alkaline electrolyte, surpassing Fe-β-Ni(OH)2/NF and IrO2 by 31 and 38 times at 1.43V versus RHE, respectively. OER catalytic mechanism demonstrates that the conversion of *OH→*O and the active lattice O content can be significantly improved due to the modulation effect of the Ir single atoms on the local electronic structure and the redox behavior of FeNi (oxy) hydroxide true active species. This work provides a promising insight into understanding the OER enhancement mechanism for Ir single-atoms modified FeNi-hydroxide systems.

Rapid and low temperature micro inverted pyramid texturing of silicon via copper catalyzed chemical etching for high efficiency PEDOT:PSS/silicon hybrid solar cells

Here, a rapid, low-temperature yet effective micro-inverted structuring of silicon (Si) via a low thermal budget copper catalyzed chemical etching (CuCCE) has been demonstrated for efficient hybrid heterojunction solar cells (HSCs) based on poly (3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS)/Si in the basic device design ‘Ag/PEDOT:PSS/n-Si/In:Ga’. The inverted pyramidal (IP) arrays have been obtained on a large area of the partially polished (PP) Si surface by the CuCCE in etch bath consisting of Cu(NO3)2/HF/ H2O2 in 100 mM:4.5 M:1.5 M at room temperature (30 °C). The IP-Si shows significantly reduced total surface reflectance (<7 %) than the PP-Si (>30 %) for broad spectral range. The high efficiency device on the interconnected IP-Si surface shows power conversion efficiency (PCE) >10.75 % which is direct enhancement of ∼4 folds (absolute) when compared with the HSCs made on the PP-Si surface. Such high efficiency HSCs employing the CuCCE based inverted structured solar grade Si surface and detailed analyses of PEDOT:PSS/Si interface have rarely been addressed. The junction property has been studied with the help of Nyquist plots and Mott-Schottky (C-V) analyses of impedance sepctroscopy. A direct 2.9 fold enhancement in the recombination resistance along with high barrier potential found for the optimized IP-Si structured HSCs facilitated the improved junction and minimum recombination at the PEDOT:PSS/n-Si interface. The enhanced PCE is primarily attributed to improved light harvesting ability of the IP-Si surface, junction and passivation properties with conformal coverage of the PEDOT:PSS layer. The study will help to explore the high potential of the CuCCE based IP-Si surfaces for future high efficiency devices.

An Improved 3-D Sound Source Localization of Varied Sources Using Oblique Square Pyramid Array

An Improved 3-D Sound Source Localization of Varied Sources Using Oblique Square Pyramid Array

One-step Cu-assisted chemical etching at room temperature of inverted pyramid array for high-performance crystalline silicon solar cells

Previous studies on the one-step Cu-assisted texturization of silicon wafers have predominantly focused on etching conditions at relatively high temperatures, which are unsuitable for the mass production of solar cells in industrial settings. In this study, we introduced the one-step Cu-assisted chemical etching (Cu-ACE) technique at room temperature to obtain large-area silicon inverted pyramid (IP) array structures. Based on this structure, diamond wire saw (DWS) mc-Si solar cells can achieve a balance between enhanced light trapping and lower carrier recombination by optimizing the concentration of the component Cu(NO3)2/HF/H2O2 in the etchant solution and the etching time during the Cu-ACE process. As a result, these solar cells deliver a power conversion efficiency (PCE) of 18.20 %, which is 1.99 % absolute higher than solar cells using traditional etching techniques. This work paves a new pathway toward the mass production of high-efficiency crystalline Si solar cells, offering a cost-effective and simple texturization approach.

Generation of Multiple Concentration Gradients Using a Two-Dimensional Pyramid Array.

Concentration heterogeneity of diffusible reactants is a prevalent phenomenon in biochemical processes, requiring the generation of concentration gradients for the relevant experiments. In this study, we present a high-density pyramid array microfluidic network for the effective and precise generation of multiple concentration gradients. The complex gradient distribution in the 2D array can be adaptively adjusted by modulating the reactant velocities and concentrations at the inlets. In addition, the unique design of each reaction chamber and mixing block in the array ensures uniform concentrations within each chamber during dynamic changes, enabling large-scale reactions with low reactant volumes. Through detailed numerical simulation of mass transport within the complex microchannel networks, the proposed method allows researchers to determine the desired number of reaction chambers within a given concentration range based on experimental requirements and to quickly obtain the operating conditions with the help of machine learning-based prediction. The effectiveness in generating a multiple concentration gradient environment was further demonstrated by concentration-dependent calcium carbonate crystallization experiments. This device provides a highly efficient mixing and adaptable concentration platform that is well suited for high-throughput and multiplexed reactions.

3D Cu Pyramid Array Grown on Planar Cu Foil for Stable and Dendrite-free Lithium Deposition

Lithium metal is recognized as the anticipated anode for rechargeable batteries because of its inherent physicochemical properties. Unfortunately, the industrialization of Li metal anodes (LMAs) has been entangled in some intractable problems stemming from the uncontrollable growth of Li dendrites, which could result in the issue of short-circuit, thereby leading to cell failure. Here, a three-dimensional structured Cu pyramid array (CPA@CF) is constructed on planar Cu foil (CF) by the simple electrodeposition method. Owing to the features of large surface area and 3D porous structure, the proposed CPA@CF not only can promote Li-ion diffusion and charge transfer, but also effectively slow down the volume change of Li. Consequently, an even and steady Li plating/stripping process up to 360 h is realized using such a CPA@CF current collector. The Li@CPA@CF|LiFePO4 full cell achieves an excellent Coulombic efficiency (CE) of 99.3 % for 160 cycles at 0.3 C with a superior capacity retention of 84.2 %.

Microwave absorption and compression performance design of continuous carbon fiber reinforced 3D printing pyramidal array sandwich structure

In this study, continuous carbon fiber reinforced 3D printing technology was used to create a novel pyramidal array sandwich structure (PASS), which contains microwave absorption and enhanced compression performances. By utilizing the electromagnetic and mechanical properties of continuous carbon fiber (CF), a spoof surface plasmon polaritons (SSPPs) microwave absorbing core was formed by winding continuous carbon fiber into a pyramidal array. Simulated and experimental results demonstrated that the proposed PASS efficiently absorbs a wide band (4–18 GHz) microwaves at large incident angles (0–60°), with an average absorptivity exceeding 90 %. Additionally, compression tests revealed that present continuous carbon fiber reinforced PASS has a compressive strength of 9.60 MPa and a modulus of 123 MPa, respectively. Furthermore, it exhibits 34.3 % and 24.8 % higher energy absorption per unit volume and mass compared to the pure polylactic acid (PLA) PASS. The advantages of microwave absorption, compression, and economical manufacturing performances make it highly promising for the engineering applications.

Intersatellite and Downlink Agile Attitude Maneuvers

This research is focused on the problem of agile attitude maneuvering, aimed at the precise pointing of a satellite forming a typical constellation in low Earth orbit. We consider two different operational scenarios: (a) pointing toward a specific ground station, located on the Earth surface (for downlink data routing), and (b) pointing toward a companion satellite (for establishing an intersatellite connection). The two preceding operational requirements can both be formulated as attitude tracking problems. In this study, we use an inertia-free nonlinear attitude control algorithm based on rotation matrices and possessing remarkable stability properties, in conjunction with a pyramidal array of single-gimbal control momentum gyroscopes. Numerical simulations, in both nominal and nonnominal flight conditions, demonstrate that the attitude control architecture proposed in this work is effective for the purpose of performing agile attitude maneuvering, aimed at precise pointing during downlink and intersat data routing.