Periodic Structures Research Articles

Improvement of ferroelectric and dielectric properties in BaTiO3/LaNiO3 superlattices by regulating the ferroelectric layer thickness

Ferroelectric superlattices exhibit rich functional characteristics. Yet, the ferroelectric properties are always unsatisfactory due to the presence of depolarization field resulting from the polarization discontinuities between the component materials, which has become a bottleneck problem hindering the improvement of ferroelectric properties and further industrial applications. Here, the BTO/LNO superlattices composed of ferroelectric (BaTiO3, BTO) and metallic (LaNiO3, LNO) materials were prepared by pulsed laser deposition (PLD). The periodic thickness of the LNO layers was fixed to 2 unit cells, while the periodic thickness of the BTO layers was changed. We demonstrate experimentally that by regulating the BTO periodic thickness, BTO/LNO superlattices exhibit excellent and adjustable ferroelectric and dielectric properties. The enhancement of electrical properties is closely related to the increase of tetragonality (c/a) combined with the effect of the ultra-thin LNO layers and the accumulation of oxygen vacancies at superlattice interfaces on reducing the depolarization field. We hope this work will provide an effective strategy for optimizing the ferroelectric properties of ferroelectric superlattices based on the component material and periodic structure regulation.

Nanopatterning and nanostructure formation with femtosecond laser: Revolutionizing surface engineering on soda-lime glass

Glass, due to its high transparency and chemical stability, has found extensive use in electrical, electronic, and optoelectronic devices. This study presents a novel approach to modify the morphological features of laser-generated tracks and produced nanoparticles in soda-lime glass using the accuracy of micro processing by femtosecond laser pulses. The investigation has meticulously examined how variations in the incident laser pulse energy and scanning velocity dictate the formation of distinct morphological characteristics on the glass surface. FESEM has revealed three distinct morphological formations, including particulate, self-ordered periodic surface structures, and a combination of the two. Additionally, TEM analysis has shown the generation of both spherical and irregular-shaped nanoparticles with diameters ranging from 10 nm to less than 2 μm, and an amorphous structure confirmed by SAED patterns. The periodicity of the LIPSS was found to be 550±25 nm, and they were oriented perpendicular to the laser polarization vector.

Analysis of the Polarization Distribution and Spin Angular Momentum of the Interference Field Obtained by Co-Planar Beams with Linear and Circular Polarization

Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation of light fields with 1D and 2D periodic structure of both intensity and polarization is demonstrated. We can control the periodic structure both by changing the polarization state of the interfering beams and by changing the numerical aperture of focusing. We consider examples with a basic configuration, as well as those with a certain symmetry in the polarization state of the interfering beams. In some cases, increasing the numerical aperture of the focusing system significantly affects the generated distributions of both intensity and polarization. Experimental results, obtained using a polarization video camera, are in good agreement with the simulation results. The considered light fields can be used in laser processing of thin films of photosensitive (as well as polarization-sensitive) materials in order to create arrays of various ordered nano- and microstructures.

Deep-subwavelength single grooves prepared by femtosecond laser direct writing on Si

Abstract It is well known that, femtosecond-laser pulses are easy to spontaneously induce deep-subwavelength periodic surface structures on transparent dielectrics, but not on non-transparent semiconductors. Nevertheless, in the study we demonstrate that by high-NA 800-nm femtosecond-laser direct writing with controlling the pulse energy and scanning speed in the near-damage-threshold regime, polarization-dependent deep-subwavelength single grooves with linewidths of ~180 nm can be controllably prepared on Si. Generally, the single-groove linewidth increases slightly with the increase of pulse energy and the decrease of scanning speed, whereas the single-groove depth significantly increases from ~300 to ~600 nm with the decrease of scanning speed, or even over 1 μm with the multi-processing, indicating the characteristics of transversal clamping and longitudinal growing of such deep-subwavelength single grooves. Then, EDS composition analysis of the near-groove region confirms that the single-groove formation tends to be an ultrafast, non-thermal ablation process, and the oxidized deposits nearby the grooves are easy to clean up. Furthermore, the results showing the strong dependence of groove orientation on laser polarization, and the occurrence of double-groove structures due to the interference of pre-formed orthogonal grooves, both indicate that the extraordinary field enhancement of strong polarization sensitiveness in the deep-subwavelength groove plays an important role for single-groove growth with high stability and collimation.

Period measurement of a periodic structure by using a heterodyne grating interferometer

This paper proposes an alternative method for grating period measurement based on heterodyne grating interferometry. The optical configurations for measuring the period of reflection/transmission gratings were demonstrated, and four commercially available gratings were used to evaluate the effectiveness of the proposed method. Based on the phase-lock technique, the grating period could be obtained immediately through the phase wrapped/unwrapped process. Under precise measurement conditions, the grating period measurement error of the proposed method was better than 1 nm, and the grating period difference between product specifications was less than 1%. In addition, the measurement results of the proposed method also exhibited high similarity with optical microscopy measurements.

Periodic Stratification of Colloids in a Liquid Phase Produced by a Precipitation Reaction and Gel Swelling.

Pattern formation is a frequent phenomenon occurring in animate and inanimate systems. The interplay between the mass transport of the chemical species and the underlying chemical reaction networks generates most patterns in chemical systems. Periodic precipitation is an emblematic example of reaction-diffusion patterns, in which the process generates a spatial periodic structure in porous media. Here, we use the dormant reagent method to produce colloidal particles of Prussian blue (PB) and PB analogues at the liquid-gel interface. The generated particles produced a stable periodic stratification pattern in time in the liquid phase placed on top of the solid hydrogel. The phenomenon is governed by periodic swelling of the gel driven by the osmotic stress and stability of the formed particles. To illustrate the phenomenon, we developed an extended reaction-diffusion model, which incorporated the gel swelling and sedimentation effect of the formed colloids and could qualitatively reproduce the pattern formation in the liquid phase.

Miniaturized Vivaldi antenna with multiband and high-gain for millimeter-wave applications

ABSTRACT A novel miniaturised quad-band printed Vivaldi antenna is proposed for millimetre-wave applications. It can be seen as a two-arm antenna where the antenna arms bound the tapered Vivaldi slot. The antenna arms are printed on the opposite sides of a flexible millimetre-wave substrate. Three periodic structures are added to the antenna geometry and printed in the area surrounding the radiating slot structure to improve the impedance matching over the antenna’s four operational frequency bands and enhance the gain. These periodic structures are parasitic ring array loaded to the antenna arms, ring-array reflector inserted between the antenna arms and the ground plane, and metamaterial director printed in front of the antenna arms. A prototype of the proposed antenna is fabricated for experimental assessment of the antenna performance. The experimental measurements show good agreement with the simulation results. The proposed antenna impedance is matched over the four frequency bands centred at 25 , 35 , 45 , and 55 GHz . The bandwidth of each operational band is about 5 GHz with percent bandwidths of 20 % , 15 % , 11 % , and 9 % , respectively. The corresponding values of the maximum gain are 7.5 , 10.5 , 12 , and 13 dBi , respectively. The radiation efficiency is maintained above 93 % over the entire frequency band (20–60 GHz).

Homoclinic Bifurcations and Chaotic Dynamics in a Bistable Vibro-Impact SD Oscillator Subject to Gaussian White Noise

This paper studies the effect of Gaussian white noise on homoclinic bifurcations and chaotic dynamics of a bistable, vibro-impact Smooth-and-Discontinuous (SD) oscillator. First, the SD oscillator is reproduced and generalized by installing a slider on a fixed rod, so the slider is connected by a pair of linear springs initially pre-compressed in the vertical direction to achieve bistable vibration characteristics, and two screw nuts are installed on the rod as two adjustable bilateral rigid constraints to generate the vibro-impact. A discontinuous dynamical equation with a map defined on switching boundaries to represent velocity loss during each collision is derived to describe the vibration pattern of the bistable, vibro-impact SD oscillator through studying the persistence of the unique, unperturbed, nonsmooth, homoclinic structure. Second, the general framework of random Melnikov process for a class of bistable, vibro-impact systems contaminated with Gaussian white noise is derived and employed through the corresponding Melnikov function to obtain the necessary parameter thresholds for homoclinic tangency and possible chaos of the bistable, vibro-impact SD oscillator. Third, the effectiveness of a semi-analytical prediction by the Melnikov function is verified using the largest Lyapunov exponent, bifurcation series, and 0–1 test. Finally, the sensitivity to the initial values of chaos is verified by the fractal attractor basins, and the influence of the Gaussian white noise on periodic and chaotic structures is studied through Poincaré mapping to show the rich dynamical geometric structures.

Multiplying vortex beams by diffraction from almost periodic structures: Theory and experiment

We advance theoretically and verify experimentally a protocol for generating arrays of self-similar light beams with the aid of almost periodic structures (APSs), which we refer to as pure amplitude 2N-gonal APSs. We illustrate our general results by realizing a circular array of exact replicas of a Laguerre–Gaussian source beam and registering good agreement between the theory and experiment. Our work carries promise for optical communications, optical tweezing, multi-particle trapping, screening, and micro-manipulation.

Fabrication of Gradient Periodic Surface Structures on Stainless Steel Using Direct Laser Interference Patterning

In this work, the fabrication of gradient periodic line‐like structures with continuously changing spatial period on stainless steel by means of two‐beam direct laser interference patterning (DLIP) is studied. A 70 ps (picosecond [ps]) pulsed laser operating at 532 nm wavelength and 0.64 J cm−2 laser fluence is used to produce the gradient microstructures. By continuously changing the overlapping angle between the sub‐beams, the spatial period of gradient structures smoothly increases from 2.01 ± 0.09 to 3.99 ± 0.12 μm within a 500 μm long processed area. Different pulse‐to‐pulse overlaps are applied to study the influence of cumulated fluence on the topography of gradient structures. The surface topography is analyzed by optical confocal microscopy and is characterized by the roughness parameters Ra and Rz. Fourier transformations of the confocal images allows the verification of the variations of the spatial periods. In the experiments performed in this work, design rules are provided for fabricating complex microstructures in the future using DLIP‐based technology to achieve advanced surface function like anisotropic wetting or cell growth.

Mechanical evaluation of elastomeric thermoplastic polyurethane additively manufactured triply periodic minimal surface area lattice structures for adjustable cushioning properties

Purpose Cushioning is a useful material property applicable for a range of applications from medical devices to personal protective equipment. The current ability to apply cushioning in a product context is limited by the appropriateness of available materials, with polyurethane foams being the current gold standard material. The purpose of this study is to investigate additively manufactured flexible printing of scaffold structures as an alternative. Design/methodology/approach In this study, this study investigates triply periodic minimal surface (TPMS) structures, including Gyroid, Diamond and Schwarz P formed in thermoplastic polyurethane (TPU), as a possible alternative. Each TPMS structure was fabricated using material extrusion additive manufacturing and evaluated to ASTM mechanical testing standard for polymers. This study focuses attention to TPMS structures fabricated for a fixed unit cell size of 10 mm and examine the compressive properties for changes in the scaffold porosity for samples fabricated in TPU with a shore hardness of 63A and 90A. Findings It was discovered that for increased porosity there was a measured reduction in the load required to deform the scaffold. Additionally, a complex relationship between the shore hardness and the stiffness of a structure. It was highlighted that through the adjustment of porosity, the compressive strength required to deform the scaffolds to a point of densification could be controlled and predicted with high repeatability. Originality/value The results indicate the ability to tailor the scaffold design parameters using both 63A and 90A TPU material, to mimic the loading properties of common polyurethane foams. The use of these structures indicates a next generation of tailored cushioning using additive manufacturing techniques by tailoring both geometry and porosity to loading and compressive strengths.

Identification method on the vibration properties of a periodic core sandwich: Thermal impact on the band gap

This paper focuses on the thermal impact of filtering properties on sandwich structures with periodic core. The evolution of the bandgap is carefully studied as a function of temperature. Sandwich structure allows to shear the viscoelastic core layer and increases passive damping. Two polymers are selected for their viscoelastic properties and their adhesion properties with metal surfaces. The mechanical properties, shear modulus G(ω) and loss factor η(ω) of these polymers, are determined at temperature by an inverse method. The periodicity of the sandwich structure is achieved by alternating two materials with specific viscoelastic properties in the core, allowing resonant frequencies to be located in beams creating frequency ranges without resonant peaks. Temperature has a strong influence on the mechanical properties of polymer materials. This is why we felt it was important to be able to carry out a temperature investigation. Numerical finite element modelling is developed considering periodicity and temperature. Periodic sandwich fabricated in our laboratory are tested under thermal conditioned. The results show the importance of considering the effect of temperature. It has a direct impact on the filtering properties obtained by periodic structures.

Development of Micro/Nano Pattern Arrays with Grating-Based Periodic Structures using the Direct Laser Lithography System

Introduction: This research delves into utilizing the Direct Laser Lithography System to produce micro/nanopattern arrays with grating-based periodic structures. Initially, refining the variation in periodic structures within these arrays becomes a pivotal pursuit. This demands a deep comprehension of how structural variation aligns with specific applications, particularly in photonics and material science. Method: Advancements in hardware, software, or process optimization techniques hold potential for reaching this objective. Using an optical beam, this system enables the engraving of moderate periodic and quasi-periodic structures, enhancing pattern formation in a three-dimensional environment. Through cost-effective direct-beam interferometry systems utilizing 405 nm GaN and 290 to 780 nm AlInGaN semiconductor laser diodes, patterns ranging from in period were created, employing 300 nm gratings. Result: The system's cost-efficiency and ability to achieve high-resolution permit the creation of both regular and irregular grating designs. By employing an optical head assembly from a bluray disc recorder, housing a semiconductor laser diode and an objective lens with an NA of 0.85, this system displays promising potential in progressing the fabrication of micro/nanopattern arrays. Conclusion: Assessing their optical, mechanical, and electrical properties and exploring potential applications across varied fields like optoelectronics, photovoltaics, sensors, and biomedical devices represent critical strides for further exploration and advancement.

Phase Transition in a Periodic Tubular Structure

Phase Transition in a Periodic Tubular Structure

Size matters: how periodicity and depth of LIPSS influences E. coli adhesion on ferritic stainless steel

Bacterial adhesion is a serious problem in the healthcare and food industries, causing health problems and economic losses. This study evaluates the generation of Laser-Induced Periodic Surface Structures (LIPSS) with different periodicities to reduce bacterial adhesion on ferritic stainless steels. LIPSS nanostructuring evolves from hydrophilic to hydrophobic with air exposure. Fresh samples with 870 nm LIPSS show nearly 50 % reduced E. coli adhesion, but this effect diminishes in stabilized samples. This effect on bacterial adhesion can be attributed to LIPSS periodicity being like bacterial size, which would allow bacteria to accommodate and provide a suitable environment for their adhesion. Our results show that, in stable samples when the LIPSS periodicity is around 400 nm, reductions by almost 30 % are achieved and this reduction reaches 35 % when periodicity is close to 270 nm. These results indicate that smaller spatial periods prevent bacteria from fitting into valleys, so they remain on the peaks, hindering bacterial adhesion. Additionally, deeper LIPSS produced by a higher Surface Density of Applied Energy (SDAE), enhance bacteria-material interaction and, thus, increases adhesion.

Excitation of symmetry-protected vertical modes through arrays of coaxial sub-λ apertures for THz applications

Abstract We numerically study the excitation of a Symmetry-Protected Vertical Mode (SPVM) within a specific periodic structure of coaxial apertures made in gold. The geometrical parameters are chosen to operate in the THz domain. Contrarily to classical SP modes that correspond to a mode propagating in the direction of periodicity of the structure, here the SP mode consists on the Transverse Electro Magnetic (TEM) guided mode that propagates vertically inside the coaxial aperture along the metal thickness. This feature makes the spectral properties of the excited mode less-sensitive to the spatial extension of the grating allowing thus the design of less-cumbersome devices. We demonstrate that the spectrally localized resonance corresponding to this mode is particularly sensitive to mechanical perturbation (acoustic wave for instance) of the geometry, enabling the design of highly efficient THz modulators operating at λ ≈ 300 μm with a sensitivity as great as 12.4 μm/◦ of the tilt angle of its metal core.

Electromagnetic Transverse Modes in Periodic Structures: Mathematical Analysis and Engineering Applications

This study explores the electromagnetic transverse modes in periodic structures, combining mathematical analysis with practical engineering applications. We showcase how the deliberate arrangement of materials, using Maxwell's equations and Bloch's theorem, may control and guide electromagnetic waves for novel applications in devices. We emphasize the progress made in photonic crystals and metamaterials, which have resulted in significant developments in fields such as optical computing and stealth technologies. The debate encompasses the potential of computational methods to further improve the functions of materials and devices. This paper highlights the important interaction between theoretical physics and applied engineering, which lays the foundation for future technical advancements in wave manipulation.

Impact behavior of periodic, stochastic, and anisotropic minimal surface-lattice sandwich structures

Recent advancements in 3D printing technologies have made it possible to fabricate intricate lattice architectures with high precision. These lattices can now be utilized to design lightweight sandwich structures that serve multiple functions. To enhance the impact loading performance of these structures, it is crucial to understand how the lattice's topological properties, particularly those with minimal surface attributes like periodic or stochastic Primitive and Gyroid triply periodic minimal surfaces (TPMS) and spinodal-like stochastic cellular materials, associate with the mechanical properties of sandwich structures while keeping the skin thickness fixed. Thus, this paper explores the low-velocity impact behavior of various sheet/shell-based minimal surface-latticed cores of sandwich structures with woven composite skins. The elasto-plastic-damage numerical simulations consider lattice core periodicity, randomness, and anisotropy while keeping the relative density constant. Core lattice randomness and anisotropy are designed using the Gaussian Random Field (GRF) method for spinodal-based stochastic cellular materials and stochastic TPMS. The simulation results showed that the periodic Primitive-lattice core exhibits high out-of-plane shearing strength, enabling the sandwich structure to demonstrate the highest perforation limit. GRF spinodal-based core achieved the highest peak load due to its anisotropic mechanical properties. However, the post-yielding bending of the lattice sheet limited its ability to resist perforation, and absorb and dissipated energy. Interestingly, the stochastic Gyroid TPMS topology, with its inherent densely-distributed microstructure, showed high sensitivity to loading rate, resulting in enhanced energy absorption and dissipation of the sandwich structure. These findings offer valuable insights for optimizing multifunctional sandwich structures with superior impact performance and their design for additive manufacturing.

Facile and rapid synthesis method of dielectric nanocomposite for simultaneous enhancement of electromagnetic wave absorbing/shielding characteristics

The present study involves the fabrication of poly[4-(2-thiophene)aniline] (PTA) nanocomposite for absorption-dependent shielding applications, demonstrating enhanced absorption and small reflection properties. The Microwave absorption characteristics of the fabricated polymer were studied at different loading ratios, resulting in a minimum reflection loss (RLmini) of − 44 dB for the 8 wt % loading ratio. The macromolecular architecture of the PTA material offers higher dielectric loss resulting from higher conduction and interfacial loss. Additionally, the shielding performance is also evaluated, and the sample containing 8 wt % filler demonstrates an impressive − 36.5 dB shielding efficacy. The performance of polymers is significantly impacted by their unit periodic order arrangement. Conducting polymers with linear structure and special π-orbitals angles possess unique characteristics in comparison to their branched and the random copolymer, making them highly sought after as efficient organic conductors, magnetic substances, electrochromic materials, and high dielectric agents. Monomer units contained two periodical cyclic structures and the creation of the inductive effects of heteroatoms elongates the conjugation and reduces the energy bandgap difference between the HOMO and LUMO levels, enabling smoother electron flow and enhancing absorption capacity. The findings indicate that PTA nanocomposite is a promising radar-absorbing coating material due to its superior absorption ability and outstanding shielding performance.

Sub-bandgap photo-response of black silicon fabricated by femtosecond laser irradiation under water

Here we propose a method to fabricate black Si without the need for any chalcogenide doping, accomplished by femtosecond (fs) laser irradiation in a liquid environment, aiming to fabricate the infrared detector and investigating their optoelectronic performance. Multi-scale laser-induced periodical surface structures (LIPSSs), containing micron sized grooves decorated with low spatial frequency ripples on the surface, can be clearly observed by SEM and 3D confocal microscope. The generated black Si demonstrates superior absorption capabilities across a broad wavelength range of 200-2500 nm, achieving an average absorptance of up to 71%. This represents a notable enhancement in comparison to untreated Si, which exhibits an average absorption rate of no more than 20% across the entire detectable spectrum. A metal-semiconductor-metal (MSM) type photodetector was fabricated based on this black Si, demonstrating remarkable optoelectronic properties, specifically, it attains a responsivity of 50.2 mA/W@10 V and an external quantum efficiency (EQE) of 4.02% at a wavelength of 1550 nm, significantly outperforming the unprocessed Si by more than five orders of magnitude. The great enhancement in infrared absorption as well as the optoelectronic performance can be ascribed to the synergistic effect of the multi-scale LIPSSs and the generated intermediate energy levels. On one hand, the multi-scale structures contribute to an anti-reflection and light trapping property; on the other hand, the defects levels generated through fs laser ablation process under water may narrow the band gap of the Si. The results therefore underscore the remarkable potential of black Si processed by fs laser under water for the application of photodetection, especially in the near-infrared band.