Periodic Surface Research Articles

Liquid‐Assisted Laser Nanotexturing of Silicon: Onset of Hydrodynamic Processes Regulated by Laser‐Induced Periodic Surface Structures

AbstractUpon systematic studies of femtosecond‐laser processing of monocrystalline Si in oxidation‐preventing methanol, it is shown that the electromagnetic processes dominating at initial steps of the progressive morphology evolution define the onset of the hydrodynamic processes and morphology upon subsequent multi‐pulse exposure. Under promoted exposure quasi‐regular subwavelength laser‐induced periodic surface structures (LIPSSs) are justified to evolve through the template‐assisted development of the Rayleigh‐Plateau hydrodynamic instability in the molten ridges forming quasi‐regular patterns with a supra‐wavelength periodicity and preferential alignment along polarization direction of the incident light. Subsequent exposure promotes fusion‐assisted morphology rearrangement resulting in a spiky surface with random orientation, yet constant inter‐structure distance correlated with initial LIPSS periodicity. Along with the insight onto the physical picture driving the morphology evolution and supra‐wavelength nanostructure formation, this experiments also demonstrated that resulting quasi‐regular and random spiky morphology can be tailored by the intensity/polarization distribution of incident laser beam allowing on‐demand surface nanotexturing with diverse hierarchical surface morphologies exhibiting reduced reflectivity at visible and shortwave‐IR wavelengths. Finally, the practical attractiveness of the suggested approach for improving near‐IR photoresponse and expanding operation spectral range of vertical p‐n junction Si photodetector operating under room temperature and zero‐bias conditions via single‐step annealing‐free nanopatterning is highlighted.

Impact of Hybrid Electromagnetic Surface Modes on the Formation of Low Spatial Frequency LIPSS: A Universal Approach

AbstractIn this article, the impact of the excited electromagnetic surface modes in a comprehensive investigation of the formation of laser‐induced periodic surface structures (LIPSS) is analyzed. It is demonstrated that the electromagnetic origin of low spatial‐frequency LIPSS (LSFL) is the frequency detuning between propagating and localized modes due to their coupling/hybridization. The influence of the pattern profile, inhomogeneity, and material type on the coupling strength, electric‐field spatial distribution, and associated near‐field scattering are highlighted. Exploiting the potential of the approach, evidence of a universal manifestation of LSFLs is provided irrespective of the material and the authors are able to predict and validate the experimentally‐proven lower limit of LSFL periodicity (i.e., λL/2, where λL stands for the laser wavelength). Furthermore, the analysis of the electromagnetic modes predicts that the periodicity of LSFL is practically unaffected by the laser fluence, while a suppression of LSFL at high excitation levels or large number of pulses is also predicted. It is also shown that plasmonic‐active materials are not necessary for LSFL formation perpendicular to polarization. Toward these directions, an important generic metric, namely the resonance quality factor, is additionally inserted. The approach can, thus, serve as a guide for controlling laser‐induced surface topography.

Hybrid manufacturing and mechanical properties of architected interpenetrating phase metal-ceramic and metal-metal composites

A hybrid manufacturing process for the fabrication of architected metal-ceramic and metal-metal interpenetrating phase composites (IPCs) is elaborated and employed to assess the mechanical performance of novel, advanced composite materials. In particular, aluminum-based co-continuous composites, reinforced with triply periodic minimal surface (TPMS) steel and ceramic (zirconia) phases are engineered, combining 3D-printing and investment casting techniques. The hybrid process results in excellent wettability between the ceramic-Al and steel-Al phases, characterized through Scanning Electron Microscopy (SEM) and micro-CT scanning analysis. The arising IPCs yield mechanical properties that utterly differ from the performance of the base ceramic or steel TPMS reinforcement topologies, with the ceramic-Al composites to furnish a highly ductile response and steel-Al IPCs a remarkable post-elastic stiffening performance. Ceramic-based IPCs yield a specific energy absorption (SEA) that is more than 400 times higher than the one of single-phase ceramic metamaterials, while steel-based IPCs allow for SEA values in the order of 50 J/g, values which rank among the highest ever reported for architected IPCs. A broader Ashby-type classification is provided, while the efficiency of the IPC plastification process is associated with the obtained SEA values. Moreover, experimental results are complemented by finite element analysis insights in the effect of the interpenetrating phase design on the inner stresses developed. The hybrid manufacturing process and the co-continuous composites investigated open novel pathways in the engineering of next-generation multifunctional architected IPCs for base material combinations beyond the ones here considered.

Modified strain gradient analysis of the functionally graded triply periodic minimal surface microplate using isogeometric approach

Modified strain gradient analysis of the functionally graded triply periodic minimal surface microplate using isogeometric approach

Finite element modeling of the free boundary effect on gyroid additively manufactured samples

There is a significant need for models that can capture the mechanical behavior of complex porous lattice architectures produced by 3D printing. The free boundary effect is an experimentally observed behavior of lattice architectures including the gyroid triply periodic minimal surface where the number of unit cell repeats has been shown to influence the mechanical performance of the lattice. The purpose of this study is to use finite element modeling to investigate how architecture porosity, unit cell size, and sample size dictate mechanical behavior. Samples with varying porosity and increasing number of unit cells (relative to sample size) were modeled under an axial compressive load to determine the effective modulus. The finite element model captured the free boundary effect and captured experimental trends in the structure’s modulus. The findings of this study show that samples with higher porosity are more susceptible to the impact of the free boundary effect and in some samples, the modulus can be 20% smaller in samples with smaller numbers of unit cell repeats within a given sample boundary. The outcomes from this study provide a deeper understanding of the gyroid structure and the implications of design choices including porosity, unit cell size, and overall sample size.

Triply Periodic Minimal Surface Structures: Design, Fabrication, 3D Printing Techniques, State‐of‐the‐Art Studies, and Prospective Thermal Applications for Efficient Energy Utilization

This review highlights the latest developments of triply periodic minimal surface (TPMS) structures with the aim of the system's energy utilization. TPMS structures have gained widespread recognition due to their significant heat transfer (e.g., enhanced surface area) and diverse mechanical properties (e.g., structural stability), making them highly valuable in numerous thermal applications. A comprehensive survey of the design approaches, software tools, commercial materials, and 3D printing techniques of TPMS‐based structures is provided. Research gaps and future perspectives for the commercialization of TMPS structures are identified. Moreover, the potential applications of TPMS‐based structures for heat transfer augmentation and thermal management are discussed. TPMS‐based structures are promising topologies for heat exchangers on account of their intrinsically outstanding specific surface area. In this context, TPMS‐based structures have received considerable attention for various applications, including heat exchangers, latent heat storage, hydrogen storage, battery cooling/thermal management, and membrane distillation. Besides, distinct potential applications of TPMS‐based structures are proposed for heat transfer intensification and thermal management of photovoltaic/thermal collectors and fuel cells. Meanwhile, new proposals for using TPMS‐based structures for different sorption‐based applications, notably adsorption cooling/desalination systems, adsorption atmospheric water harvesting, thermochemical energy storage, and desiccant air conditioning, are nominated for forward‐looking perspectives.

Experimental and numerical assessments of thermal transport in phase change material embedding additively manufactured triply periodic minimal surfaces: A comparative evaluation

Phase change materials (PCMs), due to their inherent low conductivity, are presently restricted in their potential applications for thermal energy storage (TES) systems. Extensive effort has been made over the past few years to investigate the potential of porous materials, such as metal foams, as effective thermal conductivity enhancers (TCEs) for PCMs. Porous materials have superior specific surface area over conventional honeycomb structures and fins, providing great potential in thermal storage systems. In this study, taking advantage of the implicit function of triply periodic minimal surface (TPMS), new varieties of lattices with continuous surface structures were developed and then manufactured by using AlSi10Mg powder via selective laser melting (SLM). A three-dimensional transient phase-change heat storage model of TPMS (Primitive and I-WP) structure-paraffin composite PCMs was adopted to study both the phase-change heat transfer performance and heat storage capability of TPMS-PCMs during the phase transition. Meanwhile, the evolution of the solid–liquid interface and temperature–time history were investigated by utilizing the visualized thermal storage experiments. The findings revealed that embedding TPMS lattice decreased the natural convection effect, resulting in a maximum flow velocity of liquid paraffin wax (PX) within TPMS-PCMs that was only 0.1 times that of pure PX. The melting onset time of TPMS-PCMs was advanced by 82.2 %-91.1 %, and the duration of phase change was shortened by 68.3 %-75.9 %, respectively. In addition, the total heat storage of TPMS-PCMs fell from 4464.0 J to 4217.2 J compared to pure PX, but their average heat storage rate rose from 1.04 to 4.58 J/s. Primitive rod (PS)-type TPMS-PCM was the most potential among the three types of TPMS lattices as the TCE for PCM because it achieved the highest heat storage rate with the most negligible overall heat storage loss.

Sound absorption properties of additively manufactured porous materials with minimal surface pore geometries

This study explores the use of additive manufacturing, specifically stereolithography (SLA), to create porous acoustical materials with precise pore geometries for aircraft engine noise reduction. Unlike traditional methods like foaming and fiber-spinning, SLA allows for exact control over pore shapes. Three triply periodic minimal surface (TPMS) pore designs were investigated: split-P, lidinoid, and diamond. These structures were designed through implicit modeling and made from polymeric resin. Their sound absorption capabilities were tested under normal incidence in a two-microphone impedance tube to examine how porosity influences their acoustic performance. Findings revealed unique sound absorption profiles for each geometry, which can be modified by adjusting porosity. Additionally, the static flow resistivity was measured using a raylometer, where results showed that flow resistance is a key factor in their absorption efficiency. Among the three samples, the split-P geometry shows superior sound absorption. This preliminary research highlights the potential of using tailored TPMS geometries in acoustic liners for effective noise control in aerospace applications.

Deformation and Energy Absorption Performance of Functionally Graded TPMS Structures Fabricated by Selective Laser Melting

Triply periodic minimal surface (TPMS) structures have unique geometries and excellent mechanical properties, which have attracted much attention in many fields. However, the relationship between different filling forms and different directions of functionally graded TPMS structures on energy absorption has not been fully studied. In this study, a functionally graded strategy was proposed to investigate the effect of filling form and direction gradient on the energy absorption of TPMS structures. The design of functionally graded Gyroid and Diamond TPMS cellular structures with multiple forms was characterized, and the structures were fabricated using additive manufacturing technology. The effects of uniformity and different directional gradients on the deformation and energy absorption properties of the structures were studied experimentally and numerically. According to the compression test results, it was found that different filling forms of the TPMS structure behave differently in terms of yield plateau and deformation pattern, and the sheet structures can develop a better deformation pattern to enhance energy absorption capacity. Functionally graded sheet Diamond TPMS cellular structures along the compression direction exhibit a 32% reduction in initial peak force, providing more advantages in structural deformation and energy absorption. More closely, it is possible to further reduce the initial peak force, delay the densification point, and thus increase the energy absorption capacity by designing functionally graded sheet Diamond TPMS based cellular structures. The results of this study provide valuable guidance for the design of high-performance impact-protection components.

Sound absorption performance of a micro-perforated plate sandwich structure based on selective laser melting

ABSTRACT This study proposes a sandwich structure of triply periodic minimal surface (TPMS) based on the theory of micro-perforated plates. This structure was processed using laser selective melting (SLM) with the acoustic-vibration theoretical model established through the acoustic-electrical analogy method. The theoretical model was verified by comparison with the experimental results, showing that the micro-perforated plate TPMS sandwich structure exhibited good sound absorption performance with the maximum sound absorption coefficients being higher than 0.8. The micro-perforated plate TPMS sandwich resonated when excited by sound waves. The change in the volume fraction affected the size of the cavity volume behind the micro-perforated plate, thereby affecting the resonance frequency. The increase in volume fraction decreased the volume of the cavity behind the structural plate, the sound absorption performance to increase, the resonance frequency to move towards high frequencies, and the sound absorption bandwidth to decrease. The resonance frequency was negatively correlated with the panel thickness. The increase in the panel thickness increased the maximum sound absorption coefficient and decreased the sound absorption bandwidth when the structure resonated. Also, high-order resonance frequencies appeared when the number of cell layers increased to a certain level.

Functionally graded triply periodic minimal surface scaffold of HA-Al2O3 via Vat photopolymerization 3D printing

Hydroxyapatite (HA) is widely used in scaffolds due to its high similarity in the composition to natural bone. However, the weak and fragile characteristics of synthetic HA limit its application. The strength of HA can be increased by the incorporation of alumina (Al2O3) to obtain composites with extraordinary compressive strength and biocompatibility. HA-Al2O3 composites with different ratios were prepared by Vat photopolymerization 3D printing, and their shrinkage, porosity, phase composition and biocompatibility were systematically investigated. In addition, the Diamond structure of the scaffold was chosen to achieve the trade-off relationship between compressive strength and porosity. The results suggest that the HA-Al2O3 composite with 20 vol% HA possesses the maximum compressive strength and 60 vol% HA has optimal biocompatibility. A compositional gradient scaffold from 60 vol% HA and 20 vol% HA was proposed to satisfy different needs of the different parts in scaffold for biocompatibility and compressive strength. The HA-Al2O3 gradient scaffold achieves a preferable compressive strength of 13.7 MPa while possessing gradient biocompatibility.

Gyroid Liquid Crystals as Quasi-Solid-State Electrolytes Toward Ultrastable Zinc Batteries.

The potential for optimizing ion transport through triply periodic minimal surface (TPMS) structures renders promising electrochemical applications. In this study, as a proof-of-concept, we extend the inherent efficiency and mathematical beauty of TPMS structures to fabricate liquid-crystalline electrolytes with high ionic conductivity and superior structural stability for aqueous rechargeable zinc-ion batteries. The specific topological configuration of the liquid-crystalline electrolytes, featuring a Gyroid geometry, enables the formation of a continuous ion conduction pathway enriched with confined water. This, in turn, promotes the smooth transport of charge carriers and contributes to high ionic conductivity. Meanwhile, the quasi-solid hydrophobic phase assembled by hydrophobic alkyl chains exhibits notable rigidity and toughness, enabling uniform and compact dendrite-free Zn deposition. These merits synergistically enhance the overall performance of the corresponding full batteries. This work highlights the distinctive role of TPMS structures in developing high-performance, liquid-crystalline electrolytes, which can provide a viable route for the rational design of next-generation quasi-solid-state electrolytes.

Energy absorption of gradient triply periodic minimal surface structure manufactured by stereolithography

Abstract Triply periodic minimal surface (TPMS) metamaterials possess exceptional properties not commonly found in natural materials. TPMS metamaterials are used in lightweight structures and impact energy absorption structures due to their surface geometry and mechanical properties. The quasi-static mechanic properties of resin-based homogeneous and gradient TPMS structures manufactured by stereolithography are investigated in this study. The results of both experimental and numerical simulations reveal that the gradient TPMS structures have superior energy absorption abilities compared to the homogeneous TPMS structures. Furthermore, the benefits of gradient TPMS structures can be further enhanced by changing the gradient variation interval of the relative density and cell thickness of TPMS. If the slope and intercept of the C value function of the TPMS structures remain constant, selecting a design where the gradient direction of the cell aligns with the direction of the load on the material can enhance the energy absorption capability of the TPMS structures.

Moiré effect enables versatile design of topological defects in nematic liquid crystals

Recent advances in surface-patterning techniques of liquid crystals have enabled the precise creation of topological defects, which promise a variety of emergent applications. However, the manipulation and application of these defects remain limited. Here, we harness the moiré effect to engineer topological defects in patterned nematic liquid crystal cells. Specifically, we combine simulation and experiment to examine a nematic cell confined between two substrates of periodic surface anchoring patterns; by rotating one surface against the other, we observe a rich variety of highly tunable, novel topological defects. These defects are shown to guide the three-dimensional self-assembly of colloids, which can conversely impact defects by preventing the self-annihilation of loop-defects through jamming. Finally, we demonstrate that certain nematic moiré cells can engender arbitrary shapes represented by defect regions. As such, the proposed simple twist method enables the design and tuning of mesoscopic structures in liquid crystals, facilitating applications including defect-directed self-assembly, material transport, micro-reactors, photonic devices, and anti-counterfeiting materials.

Bulk ceramics of lanthanum hexaboride with enhanced spectral selectivity and photothermal efficiency for novel hybrid thermal-thermionic solar absorbers

Lanthanum hexaboride (LaB6) single-crystals are known from a long time for their excellent thermionic and field-assisted electron-emitting properties. Recently, multi-crystalline ceramics, which offer several technological advantages over single-crystals, have been studied as well, proving a low work function and Richardson constant, in addition to favorable optical properties for high-temperature solar radiation absorbers. However, to fully disclose to LaB6 ceramics the novel application of a double-function bulk thermionic emitter, enabled by the direct absorption of solar radiation, and, at the same time, thermodynamic solar absorber for Concentrating Solar Power (CSP), their optical properties should be further optimized. The ideal result, consisting in the selective increase of the solar absorptance and decrease of the thermal emittance, thus increasing both the spectral selectivity and the photothermal efficiency of the absorber, has been obtained in this work by realizing Laser-Induced Periodic Surface Structures (LIPSS) on the ceramic surface by means of femtosecond-laser treatments. LIPPS formation has been investigated as a function of the accumulated laser fluence.

Small-dependent nonlinear analysis of functionally graded triply periodic minimal surface nanoplates

This paper introduces an effective and simple approach to analyze functionally graded triply periodic minimal surface (FG-TPMS) nanoplates, taking advantage of a novel nonlocal strain gradient nonlinear analysis. TPMS has recently gained attention as an extraordinary solution for constructing structures, drawing inspiration from natural architectures. It offers remarkable features, including high interconnectivity porous architectures, smooth surfaces, and the ability to achieve mathematically controllable geometry features. However, the extensive potential and benefits of TPMS structures have not been fully explored in current research. Hence, this study aims to address this limitation and unlock new possibilities for FG-TPMS nanoplates. Three patterns of FG-TPMS nanoplates, namely Primitive (P), Gyroid (G), and I-gragh and Wrapped Package-graph (IWP), are utilized in this investigation. The proposed model effectively incorporates the nonlocal,strain gradient and nonlinear effects into nanoplate structures. It enables a comprehensive understanding of the mechanisms responsible for both reducing and enhancing stiffness in the nanoplate by fine-tuning the nonlocal and strain gradient parameters. This research offers promising prospects for future design and optimization, providing a robust approach to address the intricate nonlinear behavior observed in FG-TPMS nanoplates.

On the mechanical properties of dual-scale microlattice of starfish ossicles: A computational study

While engineering cellular solids, either stochastic foams or architected lattices, are usually made of polycrystalline or amorphous materials, echinoderms (e.g., sea urchins, starfish, and brittle stars) build their microporous skeletal elements with single-crystalline calcite. This class of biomineralized cellular solid, known as stereom, also exhibits a vast diversity in pore morphology, ranging from random open-cell foams to fully periodic lattices. In particular, the skeletal elements (also known as ossicles) of some starfish species are composed of a diamond-triply periodic minimal surface (diamond-TPMS) microlattice. In addition, the crystallographic symmetries at both atomic (calcite) and lattice (diamond-TPMS) levels are precisely aligned. Here we investigate the mechanical performance of this unique dual-scale microlattice and discuss the synergistic effects of atomic- and lattice-scale crystallographic coalignment. Our computational and theoretical analysis suggests that the mechanical isotropy of ossicles is enhanced due to the property compensation between the atomic-level and lattice-level architectures. Moreover, the observed 50 vol% relative density in the diamond-TPMS microlattice of ossicles may be a result of achieving overall mechanical isotropy, minimal surface curvature, and maximized surface area. We believe the methodology introduced here will be useful for understanding the mechanical behavior of natural crystalline cellular solids such as echinoderms’ stereom and designing dual-scale lattice materials.

Direct slicing of microcellular structures for digital light processing (DLP) additive manufacturing

PurposeAdditive Manufacturing (AM) conventionally necessitates an intermediary slicing procedure using the standard tessellation language (STL) data, which can be computationally burdensome, especially for intricate microcellular architectures. This study aims to propose a direct slicing method tailored for digital light processing-type AM processes for the efficient generation of slicing data for microcellular structures.Design/methodology/approachThe authors proposed a direct slicing method designed for microcellular structures, encompassing micro-lattice and triply periodic minimal surface (TPMS) structures. The sliced data of these structures were represented mathematically and then convert into 2D monochromatic images, bypassing the time-consuming slicing procedures required by 3D STL data. The efficiency of the proposed method was validated through data preparations for lattice-based nasopharyngeal swabs and TPMS-based ellipsoid components. Furthermore, its adaptability was highlighted by incorporating 2D images of additional features, eliminating the requirement for complex 3D Boolean operations.FindingsThe direct slicing method offered significant benefits upon implementation for microcellular structures. For lattice-based nasopharyngeal swabs, it reduced data size by a factor of 1/300 and data preparation time by a factor of 1/8. Similarly, for TPMS-based ellipsoid components, it reduced data size by a factor of 1/60 and preparation time by a factor of 1/16.Originality/valueThe direct slicing method allows for bypasses the computational burdens associated with traditional indirect slicing from 3D STL data, by directly translating complex cellular structures into 2D sliced images. This method not only reduces data volume and processing time significantly but also demonstrates the versatility of sliced data preparation by integrating supplementary features using 2D operations.

Revealing damage evolution and ablation behavior of SiC/SiC ceramic matrix composites by picosecond laser high-efficiency ablation

The picosecond laser was utilized to fabricate the slanting microholes efficiently on SiC/SiC ceramic matrix composites. The machining damage, material oxidation, and temperature field were mainly analyzed through static and in-situ detections. The damage evolution and ablation behavior of SiC/SiC composites were qualitatively and quantitatively revealed. The results showed that the lowest peak temperature of the slanting microhole was 282.6 °C. The heat accumulation effect and thermal stress that was tensile stress in nature present caused recasts, microcracks, fiber fracture, fiber debonding, and fiber stripping. Fibers and matrix underwent slight oxidation, forming SiO2 recasts through the phase transition. The pulse energy, frequency, and inclination angle regularly affected the quantity, size, and distribution of microcracks, material removal rate (MRR), and hole wall roughness. The maximum MRR was about 2.5 mm3/s, corresponding to the minimum time was 0.9 s. The circularly polarized picosecond laser could process parallel striped laser-induced periodic surface structures (LIPSS) on the hole wall.

Effect of aspect ratio on mechanical anisotropy of lattice structures

Triply periodic minimal surface (TPMS) lattice structures with controllable mechanical properties and porous architecture are promising candidates for lightweight and energy-absorbing applications. In parametric structural design, the research on structural geometric characteristics, such as aspect ratio (R) and surface curvature, has mainly focused on fluid and heat transfer considerations. However, their impact on multi-directional mechanical properties has yet to be thoroughly investigated. This study, combining representative volume elements (RVE) based on periodic boundary conditions and theoretical surface morphological characteristics, investigates the mechanical properties and deformation behavior of lattice structures with different aspect ratios in multiple directions. The results indicate that the aspect ratio highly influences the deformation behavior of the lattice structure in different directions. The local curvature and force state of the lattice structure can be adjusted by aspect ratio to reduce local stresses and deformations in different loading directions. Compared with the simulation results of representative volume elements, the structural stress concentration and failure position can be predicted by the Gaussian curvature distribution. In addition, the elastic modulus of the structures in the [100] and [001] directions can also be adjusted by aspect ratio. Through experimental verification in the [001] direction, the structure with an aspect ratio of 2 can greatly enhance the elastic modulus (121%∼440%), maximum stress (10%∼183%), and energy absorption (33%∼85%). The significance of this work is to improve the understanding of the influence of geometric features on the mechanical properties and deformation behavior of lattice structures, which provides a new design approach for triply periodic minimal surface lattice structures in applications of impact protection and bone scaffold.