Pyramidal Array Research Articles

PCM-based ceiling panels for passive cooling in buildings: A CFD modelling

To relieve the upsurge of the energy demand associated to building indoor cooling, passive cooling employing phase change materials (PCMs) has been proposed as a promising technique to stabilise indoor air temperature fluctuation and reduce building energy demand. PCMs can exchange a large amount of latent heat during the melting and solidification processes, which can be utilised in line with the discharging and charging processes of a cooling system. The use of encapsulated PCM ceiling panels in buildings has immense application potential for passive cooling, which has attracted investigations in recent years. The geometry selection of the PCM ceiling panel is vital as it determines the exposed surface area to the surrounding air and the natural convection, and therefore the heat transfer rate to/from the PCM, which generally suffers from low thermal conductivity. This paper builds on the geometric optimisation of enclosed PCM capsules driven by natural convection, aiming to investigate the phase change behaviour and thermal performance of encapsulated PCM ceiling panels of different geometries. Here, the presented study focuses on the conjugate heat transfer phenomena through the surrounding air, panel shell, and PCM. A mixture of lauric, capric, and oleic acids was selected as PCM encapsulated in a thin-shell enclosure made of acrylonitrile butadiene styrene plastic, which forms the aesthetic panels attached to the ceiling. A computational fluid dynamics model was validated using full-scale experimental data and further employed to analyse the discharging process and design considerations of the PCM ceiling panels. The effects of various influencing factors were explored, such as panel volume, the initial temperature difference between PCMs and surrounding air, shell thickness, and geometrical features. The results indicate that the panel comprised of a pyramid array is more advantageous than the tetrahedral-based panel in terms of thermal performance, where the average melting rate is 20.8 % higher when the panel volume is 250 mL. In addition, tweaking the geometric features of the panel will largely impact its thermal performance as the effective heat transfer area and natural convection conditions are varied. Finally, it was found that hanging the panel to the ceiling will effectively enhance the heat transfer compared to directly attaching it to the ceiling. The results complement the knowledge body of macro-encapsulated PCM ceiling panels in terms of thermal performance and geometric optimisation. The effects of geometric features on the thermal performance of the PCM ceiling panels are studied in a more holistic manner.

Highly Uniform Array of Hexagonally Symmetric Micro‐Pyramid Structures for Scalable and Single Quantum Dot Emitters

AbstractControlling the site, size, and shape of group III‐nitride quantum dots (QDs) is critical for the development of mass‐producible single‐photon sources for scalable quantum technologies operable at room temperature. Herein, a methodology is proposed for fabricating high‐purity single QD emitters by controlling site‐controlled GaN micro‐pyramid structures with a high degree of uniformity and symmetry. To achieve a uniformly grown, hexagonally symmetric micro‐pyramid array, the H2/N2 carrier gas ratio, growth temperature, and V/III ratio are controlled to attain self‐limited growth regime and self‐limited width at the GaN pyramid apex. A thin InGaN layer is consecutively grown on a pyramid array under the growth condition for enhancing the growth rate anisotropy to hinder the growth of InGaN quantum wells (QWs) at semi‐polar facets. As a result, single‐photon emission is observed from apex QD with suppressed background side QW emission while maintaining more than 90% high hexagonal QD symmetry over the large area of the wafer.

Hierarchical Colloidal Self-Assembly on Lattice-Mismatched Moiré Patterns.

Extending atomic epitaxy concepts to colloidal systems for realizing functional surface structures has recently piqued scientific interest. Akin to the growth of ordered metal clusters on graphene moiré, spatially ordered colloidal crystals have been realized on soft lithographically fabricated moiré patterns. In addition to moiré periodicity, lattice misfit strain can bring about a further level of hierarchy in colloidal self-assembly, although its role in self-organization remains unexplored. Here, we demonstrate the self-organized growth of micrometer-sized colloidal pyramid arrays with lateral order extending over millimeter length scales on lattice-mismatched moiré patterns. By probing the film growth dynamics with single-particle resolution, we uncovered the interplay between lattice misfit strain and topographically varying surface potential within the moiré unit cell, which significantly alters the nucleation process. We also show that the structural organization of colloids within moiré regions primarily depends on the moiré angle, and by tuning it, multiple levels of hierarchy can be achieved.

Carbon nanotubes field-effect transistor pressure sensor based on three-dimensional conformal force-sensitive gate modulation

Pressure sensors based on field-effect transistor mechanism has received a lot of attention from researchers, which can effectively suppress low contrast and crosstalk effects. In this paper, we demonstrate a pressure sensor based on carbon nanotube field-effect transistor (CNTs-FET) and three-dimensional conformal force-sensitive top electrode with high sensitivity and easy integration. The high mobility field-effect transistor sensors were prepared using CNTs films with 99.9999% semiconductor concentration as the channel material. Conformal graphene nanowalls (GNWs) film on pyramidal micro-structure arrays worked as force-sensitive top electrode, the field-effect transistor sensor shows a sensitivity of 946.23 kPa−1 and 43.79 kPa−1 in the linear range of 0–30 Pa and 0.03–10 kPa, much higher than piezoresistive sensor (the sensitivity of about 377.73 kPa−1) and capacitive sensor (the sensitivity of 115.78 kPa−1). And the sensitivity and range of the sensor can be adjusted by the force-sensitive layer orientation design. Additionally, the sensor's response time is less than 30 ms, the recovery time is about 30 ms. The field-effect pressure sensor could detect ultra-low pressure (about 1.3 mg) of the chrysanthemum petals, and also could record the dynamic crawling process of the insect.

Evaluation of Candy Retroreflector Using 50μm Triangular Pyramidal Array Structure Mold Fabricated by 3D Lithography

Evaluation of Candy Retroreflector Using 50μm Triangular Pyramidal Array Structure Mold Fabricated by 3D Lithography

3D printed smart glove with pyramidal MXene/Ecoflex composite-based toroidal triboelectric nanogenerators for wearable human-machine interaction applications

Self-powered sensors based on triboelectric nanogenerators (TENGs) have shown great advantages in human-machine interactions. However, the complex preparation process and high cost of conventional electrodes hinder their practical implementation. In this study, we develop a wearable self-powered toroidal triboelectric sensor (STTS) with a pyramidal structure for self-powered human-machine interactions based on an extremely simplified design strategy. 3D printing technology is employed to fabricate pyramidal arrays on MXene/Ecoflex nanocomposites, thus providing a comfortable space between the finger skin and the negatively charged layer to overcome the space requirements in traditional triboelectric-based sensors. Furthermore, the developed pyramidal structure of the nanocomposite and flexible conductive fabric electrodes assembled with 3D-printed gloves based on the flexible TPU material maintained the wearability of the sensing system. The flexible and simplified single-electrode design strategy of the STTS can be easily worn on the human hand for comfortable and natural interaction with machines and devices. The high peak-to-peak voltage (19.91 V), high sensitivity (0.088 VkPa−1), and wide pressure detection range (0–120 kPa) enable the generation of high-quality output signals for the accurate detection of various finger movements exhibiting great potential for use in human-machine interaction applications in next-generation artificial intelligence and interactive devices.

A simulation approach for optimization of optical absorption in amorphous silicon solar cell

One of the major drawbacks of thin-film silicon solar cells is their limited optical absorptance due to the thin absorber layer and the minimal absorption coefficient. The mechanism of using surface textured interface in layered structure is widely accepted to scatter light and enhance the optical path length, which in turn enhances the optical absorption and improves the solar cell efficiency. A textured amorphous silicon solar cell is designed in order to observe the impact of scattering layers on optical absorption and efficiency. A pyramid, cylindrical and micro lenses array structure has been simulated using simulation tool used to obtain the optimum absorption at a particular wave length. A max Power conversion efficiency of 0.0992 is obtained at Voc of 0.9218 V. In this regard, the impact of scattering layers and different geometrical structure on V-I characteristics solar cell were observed. The maximum value obtained for refractive index is 2.0 for optimized a-Si solar cell.

Maximizing the Light Extraction Efficiency for AlGaN-Based DUV-LEDs with Two Optimally Designed Surface Structures under the Guidance of PSO

A novel method of utilizing an intelligent algorithm to guide the light extraction surface structure designing process for deep-ultraviolet light emitting diodes (DUV-LEDs) is proposed and investigated. Two kinds of surface structures based on the truncated pyramid array (TPA) and truncated cone array (TCA) are applied, which are expected to suppress the total internal reflection (TIR) effect and increase the light extraction efficiency (LEE). By addressing particle swarm optimization (PSO), the TPA and TCA microstructures constructed on the sapphire layer of the flip-chip DUV-LEDs are optimized. Compared to the conventional structure design method of parameter sweeping, this algorithm has much higher design efficiency and better optical properties. At the DUV wavelength of 280 nm, as a result, significant increases of 221% and 257% on the LEE are realized over the two forms of optimized surface structures. This approach provides another design path for DUV-LED light extraction structures.

A Universal Cl‐PEDOT Coating Strategy Based on Oxidative Chemical Vapor Deposition toward Solar‐Driven Multifunctional Energy Management

AbstractConverting renewable solar energy into manageable thermal energy is significant for diverse applications. Nevertheless, integrating multifunctional solar‐to‐heat coating on various substrates and achieving large‐scale manufacture remains a challenge. Herein, Cl− doped poly(3,4‐ethylenedioxythiophene) (Cl‐PEDOT) coating on multiple substrates is successfully created using oxidative chemical vapor deposition (oCVD) without to be restricted to the changeable substrate surface chemistry (e.g., wettability), sizes as well as dimensions (2D–3D). Partial Cl− doping and spontaneously formed microstructures can remarkably enhance near‐infrared absorption and hydrophilicity of coating. The Cl‐PEDOT coating manifests many advantages: universality, scalability, low‐cost, high efficiency, and stability. When used for solar steam generation, all Cl‐PEDOT coated substrates represent reinforced evaporation performance. The universality makes it possible to optimize the evaporator performance by structural design. Structural design as optimized energy flow enables the pyramid array wood‐based evaporator to set an evaporation record (≈1.19 kg m−2 h−1, ≈91%) under the weak‐light (0.5 sun). Moreover, a greenhouse and a crude‐oil cleaner are designed to achieve eco‐friendly, energy‐saving solar‐driven heating/dehumidification, and crude‐oil recovery without additional energy input. This study reveals that well‐designed oCVD is a simple and straightforward way to engineer lightweight and thermally insulating polymers into multifunctional solar‐to‐thermal composites toward diverse solar‐driven applications.

On the electron pairing mechanism of copper-oxide high temperature superconductivity

The elementary CuO2 plane sustaining cuprate high-temperature superconductivity occurs typically at the base of a periodic array of edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent planar Cu and O atoms, occurring at a rate t/ℏ and across the charge-transfer energy gap [Formula: see text], generate "superexchange" spin-spin interactions of energy [Formula: see text] in an antiferromagnetic correlated-insulator state. However, hole doping this CuO2 plane converts this into a very-high-temperature superconducting state whose electron pairing is exceptional. A leading proposal for the mechanism of this intense electron pairing is that, while hole doping destroys magnetic order, it preserves pair-forming superexchange interactions governed by the charge-transfer energy scale [Formula: see text]. To explore this hypothesis directly at atomic scale, we combine single-electron and electron-pair (Josephson) scanning tunneling microscopy to visualize the interplay of [Formula: see text] and the electron-pair density nP in Bi2Sr2CaCu2O8+x. The responses of both [Formula: see text] and nP to alterations in the distance δ between planar Cu and apical O atoms are then determined. These data reveal the empirical crux of strongly correlated superconductivity in CuO2, the response of the electron-pair condensate to varying the charge-transfer energy. Concurrence of predictions from strong-correlation theory for hole-doped charge-transfer insulators with these observations indicates that charge-transfer superexchange is the electron-pairing mechanism of superconductive Bi2Sr2CaCu2O8+x.

Fabrication of P(100) silicon macro-pore and pillar array by wet electrochemical etching

In this paper, pyramidal notch array was pre-etched on P(100) silicon wafer using anisotropic wet chemical etching, then macro-pore/pillar array were successfully processed in the pyramidal notch array by an anodic electrochemical etching. The formation mechanism of macro-pore and pillar in pyramidal notch were investigated, it indicates that the silicon dissolution rate is proportional to electric field, while electric field is mainly concentrated on the tip, edges and corners of the pyramidal notch. Therefore, there is an etching rate difference between the notch corner and planar regions in the pyramid notch. The notch corners are preferentially etched at first, then a pore is formed in the notch. If the shape of the open window is truncated and the bottom size is large enough, four pores would initiate at the notch angels due to etching rate difference between the truncated pyramidal notch corner and notch center, consequently, a pillar is formed in the notch center.

Towards high-efficiency Al-BSF c-Si solar cell with both superior omnidirectional and electrical performance by modulating the tilt angle of quasi-periodic inverted pyramid arrays

Seeking efficient light trapping structures with both superior omnidirectional and electrical performance is always on the way for increasing electrical energy output of c -Si solar cell over a wide range of light incident angle (θ). Here, tile angle (δ) of quasi-periodic structure arrays is systematically modulated from 35.9° to 72.8° on diamond-wire-sawn (DWS) c -Si by a simple and cost-effective Cu and Ni co-assisted chemical etching way followed by a post treatment. Interestingly, compared with the conventional micro pyramid (MP), the optimized inverted pyramid (IP) like arrays with a δ of 64° possess both lower light reflectance and carrier recombination, leading to a corresponding solar cell with a higher efficiency (∼19.67%) than that of MP based counterpart (∼19.31%). Moreover, during the increase of θ, the external quantum efficiency (EQE) of 64° IP based cell drops much more slowly than that of MP based one by properly adjusting the relative position of the structure arrays and incident light, indicating its omnidirectional property. Simultaneously, a maximum relative enhancement of electrical output power approaching ∼5.8% in the θ range of −90°–90° is achieved on 64° IP based cell compared to the MP based one, the mechanism behind which is further explained by optical simulation. The above finds pave a new way to increase the electrical energy output in a simple and cost-effective way. • Tilt angle control of quasi-periodic IP was achieved by varying Cu and Ni ratio. • 0.36% absolute increase in solar cell efficiency was made based on 64° IP. • ∼5.8% relative increase of output power was achieved on 64° IP based cell. • Mechanism behind omnidirectional performance was explained by optical simulation.

Numerical investigation on performance of ultra-thin GaAs solar cells enabled with frontal surface pyramid array

In this paper, the optical and electrical characteristics of ultra-thin GaAs solar cell with front-surface pyramid array are investigated systematically. The results show that the cell with pyramid array could significantly improve the photon absorption efficiency due to synergistic effects of antireflection and diffraction compared with reference solar cells with single and double anti-reflective coating (ARC), and the maximal integrated quantum efficiency of 0.88 is obtained for pyramid cells, much higher than that of 0.75 and 0.71 for double and single ARC solar cells, respectively. Electric simulation demonstrates the total recombination rate of solar cell with pyramid array is higher than that of reference solar cells due to higher carrier concentration. The radiative recombination dominated in the base and emitter region, while the Shockely-Read-Hall recombination becomes the primary recombination mechanism in the space charge region, both which are much higher than Auger recombination. Surface recombination has little impact on the photovoltaic performance due to the presence of wide bandgap window layer. For pyramid cell, the of 22.65 mA cm−2, 1.120 V and 21.84% are obtained when considering photon recycling effect, respectively, are higher than those of 19.52 mA cm−2, 1.106 V and 18.72% for double ARC solar cell, and those of 18.32 mA cm−2, 1.106 V and 17.60% for single ARC solar cell.

Design and modeling of a graphene-based composite structure optical pressure sensor.

In this paper, a novel graphene-based composite structure optical pressure sensor is designed and built with the aid of modeling. A PDMS force-sensitive structural mechanics model is established to optimize the size of the pyramid array distributed on the PDMS layer so that to support high levels of sensitivity and stability. Meanwhile, a graphene waveguide optical model is established to obtain the optimized interference length (L), arm spacing (H) and core width (W), with the objectives of advanced sensitivity, low propagation loss, high resolution. The experimental results show that the pressure sensitivity of the proposed sensor is 17.86 nm/kPa and the maximum pressure that can be detected is 3.40 kPa, which is consistent with the theoretical analysis and verifies the feasibility of the design, also the modeling methods of the graphene-based composite structure optical pressure sensor.

Runout and deflection of granular flow past an array of obstacles on a slope

The interaction between granular flow and an array of obstacles is an important research subject in geological disaster prevention. We used a numerical model for the depth-integrated equations formulated in a bed-fitted coordinate system to simulate the runout and deflection of granular flow past an array of simple obstacles. Numerical simulations of granular flow encountering arrays of square columns and tetrahedral pyramids gave a lot of interesting and fascinating deposits. We then proposed a new dimensionless index called deflection efficiency (DE), together with the runout efficiency (RE) to quantify the comprehensive effects of the obstacle system on the runout and deflection behavior. There are three physical effects, a dissipation effect through bow shock, a deflection effect by splitting the granular flow, and a retention effect via trapping some granular mass, the combinations of which determine the mobility and deposit of granular flow. We found that RE decreases as either the height or number of rows of obstacles increases because of the dissipation effect, while DE increases as height increases due to the deflection effect for both tetrahedral and square column obstacles. However, if the retention effect was as important as the deflection effect, the DE could be reduced when the row numbers increase further. These findings provide some constructive help for the design of obstacle arrays and complement the understanding of subsequent flow after interaction between granular flow and obstacle arrays.

Wideband Radomes for Millimeter-Wave Automotive Radars

We demonstrate the efficacy of periodic corrugations, fabricated as part of the radar cover to serve the dual purpose of protecting the radar circuitry and maximizing transmission in millimeter-wave automotive radars. A 2-dimensional array of square-base pyramids engraved on the plastic radar cover was optimized to achieve minimum reflection for a wide range of incident angles, ± 40° and across the operating frequency band of 76 to 81 GHz. More importantly, we present an alternative radome texture, namely the inverse-pyramid corrugations that results in improved structural integrity as compared to the pyramidal corrugations. This novel inverse-pyramid radome structure is also much easier to manufacture and achieves similar performance as the more conventional pyramid structure. Both designs are shown to significantly reduce radar cover reflections, which is perhaps the most significant bottleneck in modern millimeter-wave automotive radar sensor performance.

Instant Intracellular Delivery of miRNA via Photothermal Effect Induced on Plasmonic Pyramid Arrays (Adv. Funct. Mater. 9/2022)

Intracellular miRNA Delivery In article number 2107999, Zhen Fan, Xiaobin Xu, and co-workers report using scanning laser stimulation to generate instantaneous high temperature on plasmonic pyramid arrays to disrupt the cell membranes to facilitate intracellular delivery of biocargos like miRNA. Intracellular delivery of miRNA-185 to Taxol-resistance esophageal cancer cells is achieved within minutes.

Biomimetic sapphire windows enabled by inside-out femtosecond laser deep-scribing

Femtosecond laser machining of biomimetic micro/nanostructures with high aspect ratio (larger than 10) on ultrahard materials, such as sapphire, is a challenging task, because the uncontrollable surface damage usually results in poor surface structures, especially for deep scribing. Here, we report an inside-out femtosecond laser deep scribing technology in combination with etching process for fabricating bio-inspired micro/nanostructures with high-aspect-ratio on sapphire. To effectively avoid the uncontrollable damage at the solid/air interface, a sacrificial layer of silicon oxide was employed for surface protection. High-quality microstructures with an aspect ratio as high as 80:1 have been fabricated on sapphire surface. As a proof-of-concept application, we produced a moth-eye inspired antireflective window with sub-wavelength pyramid arrays on sapphire surface, by which broadband (3–5 μm) and high transmittance (98% at 4 μm, the best results reported so far) have been achieved. The sacrificial layer assisted inside-out femtosecond laser deep scribing technology is effective and universal, holding great promise for producing micro/nanostructured optical devices.

Enhanced Efficiency of Graphene-Silicon Schottky Junction Solar Cell through Pyramid Arrays Texturation

Graphene/silicon (Gr/Si) Schottky junction solar cells have attracted extensive research interest due to their simple structure and potential low-cost. Surface texturing is an important part of high-efficiency solar cells. In this paper, the effects of TMAH concentration, IPA concentration and etching time on the structure and anti-reflection ability of silicon pyramid array (SiPa) were systematically studied to obtain uniform and reliable pyramid array. Under the optimized conditions, a large scale SiPa with uniform size distribution was obtained and applied to Gr/Si solar cells. The results show that the TMAH etched SiPa has a better Schottky junction contact between graphene and the SiPa surface, and the SiPa can further improves the ability of collecting photogenerated carriers. Compared with Gr/Si solar cells, the power conversion efficiency (PCE) of Gr/SiPa device is 1.66 times higher than that of Gr/Si solar cells. Finally, Gr/SiPa devices with PCE of 5.67% is successfully obtained by HNO3 doping. This work proposes a new strategy for TMAH etching SiPa to improve the performance of Gr/Si solar cells.

3D-printed NiFe-layered double hydroxide pyramid electrodes for enhanced electrocatalytic oxygen evolution reaction

Electrochemical water splitting has been considered one of the most promising methods of hydrogen production, which does not cause environmental pollution or greenhouse gas emissions. Oxygen evolution reaction (OER) is a significant step for highly efficient water splitting because OER involves the four electron transfer, overcoming the associated energy barrier that demands a potential greater than that required by hydrogen evolution reaction. Therefore, an OER electrocatalyst with large surface area and high conductivity is needed to increase the OER activity. In this work, we demonstrated an effective strategy to produce a highly active three-dimensional (3D)-printed NiFe-layered double hydroxide (LDH) pyramid electrode for OER using a three-step method, which involves direct-ink-writing of a graphene pyramid array and electrodeposition of a copper conducive layer and NiFe-LDH electrocatalyst layer on printed pyramids. The 3D pyramid structures with NiFe-LDH electrocatalyst layers increased the surface area and the active sites of the electrode and improved the OER activity. The overpotential (η) and exchange current density (i0) of the NiFe-LDH pyramid electrode were further improved compared to that of the NiFe-LDH deposited Cu (NiFe-LDH/Cu) foil electrode with the same base area. The 3D-printed NiFe-LDH electrode also exhibited excellent durability without potential decay for 60 h. Our 3D printing strategy provides an effective approach for the fabrication of highly active, stable, and low-cost OER electrocatalyst electrodes.