Fine Periodic Structure Research Articles

Mechanical properties of single-sided-loop 2D woven laminated composites

Carbon fiber laminated composites are widely used in aerospace and high speed railways industries due to their high specific strength and stiffness, but the poor interlaminar properties affect their further applications. In order to solve the problem of poor interlayer performance of woven laminated composites, this paper proposes a new type of laminated composite, called single-sided-loop two-dimensional (2D) woven laminated composites (SWLC). By introducing loop warp yarns to the thickness of general 2D woven laminated composites (GWLC), the loop between its preform and resin can improve the way of the fibers attached to the substrate and increase the volume content of the fibers between the layers. The mechanical behavior of SWLC is investigated experimentally and numerically. For numerical simulations, a unit cell is established based on the fine periodic structure. A progressive damage model is established using the 3D Hashin and the von-Mises criteria. Numerical results are in good agreement with the experimental data. Results show that the looped fabric can improve interlayer properties at the expense of slight reduction of some in-plane properties.

Control of Metal/Polymer Adhesion Strength by Metal Surface Structure for Sustainable Society

The relationship between the shear strength of the metal-resin and the periodic structure of the metal surface was investigated. Femtosecond laser processing was applied to the Cr-plated carbon tool steel surface to form irregularities with a pitch of about 20 μm and a depth of about 10 μm, and a nano-scale fine periodic structure (so-called LIPSS) was formed on the top of the peaks. The epoxy resin was then placed in a mold and pressed by a heat press onto a metal plate. Then, the molded epoxy resin was pressed from the side with an indenter to measure the shear force, and the shear strength define as the maximum shear force. As a result, a positive correlation was observed between the shear strength and the opening valley angle of the micro-periodic structure, and a negative correlation was observed between the shear strength and the aspect ratio, which is the depth of the micro-periodic structure divided by the pitch.

Application of lung substitute material as ripple filter for multi-ion therapy with helium-, carbon-, oxygen-, and neon-ion beams

A development project for hypo-fractionated multi-ion therapy has been initiated at the National Institute of Radiological Sciences in Japan. In the treatment, helium, carbon, oxygen, and neon ions will be used as primary beams with pencil beam scanning. A ripple filter (RiFi), consisting of a thin plastic or aluminum plate with a fine periodic ridge and groove structure, has been used to broaden the Bragg peak of heavy-ion beams in the beam direction. To sufficiently broaden the Bragg peak of helium-, carbon-, oxygen-, and neon-ion beams with suppressed lateral scattering and surface dose inhomogeneity, in this study, we tested a plate made of a lung substitute material, Gammex LN300, as the RiFi. The planar integrated dose distribution of a 183.5 MeV u−1 neon-ion beam was measured behind a 3 cm thick LN300 plate in water. The Bragg peak of the pristine beam was broadened following the normal distribution with the standard deviation σ value of 1.29 mm, while the range of the beam was reduced by 8.8 mm by the plate. To verify the LN300 performance as the RiFi in multi-ion therapy, we measured the pencil beam data of helium-, carbon-, oxygen- and neon-ion beams penetrating the 3 cm thick LN300 plate. The data were then modeled and used in a treatment planning system to achieve a uniform 10% survival of human undifferentiated carcinoma cells within a cuboid target by the beam for each of the different ion species. The measured survival fractions were reasonably reproduced by the planned ones for all the ion species. No surface dose inhomogeneity was observed for any ion species even when the plate was placed close to the phantom surface. The plate made of lung substitute material, Gammex LN300, is applicable as the RiFi in multi-ion therapy with helium-, carbon-, oxygen- and neon-ion beams.

Fine Structure of the Photoluminescence Spectrum of Diamond under the Multiple Emission of an Optical Phonon during the Autolocalization of Photoexcited Electrons

The autolocalization of electrons photoexcited by laser pulses with a wavelength of 525 nm in the visible range and with a duration of 150 fs in an electron-hole plasma (density ∼1021 cm−3) in natural diamond at room temperature occurs unsteadily through step-by-step multiple (up to nine acts) emission of an optical phonon at subpicosecond times. This process is manifested for the probe photoluminescence signal in its fine periodic structure in the band gap beginning from the interband absorption edge. The intensity of multiphonon photoluminescence peaks reaches a maximum after four to six emission acts, where the energy of an electron-softened optical phonon is recovered and the broadening of peaks increases monotonically. Attributing the broadening of peaks to the kinetics of the emission of a successive phonon, one can compare their widths to the time dynamic scale of the electron-hole plasma and multiphonon emission during autolocalization. Then, the initial increase in the intensity of the peaks demonstrates the emission of phonons during autolocalization, whereas saturation and subsequent decrease are due to the subpicosecond Auger recombination of the plasma, which significantly suppresses photoluminescence because of the sharp decrease in the hole density (to 1019 cm−3), but not the process of autolocalization itself.

Study on the Creation of Fine Periodic Structure on V-Shaped Groove with Short-Pulsed Laser

Functional surface creation technologies have garnered increasing attention over the years. These technologies can provide various functions to a material by establishing a fine structure on the material surface and responding to the needs of industrial products with distinguished functions or high values. In addition, by creating a “composite fine structure,” which is composed of two kinds of structures with different scales, the enhancement of functions and emergence of new functionalities can be expected. Hence, our study combined a micrometer-scale V-shaped groove structure using an ultra-precision cutting and nanometer-scale ultra-fine periodic structure (LIPSS) using a short-pulsed laser. Then, we clarified the creation principle and studied the functionality of the structure, specifically, its wettability. As a result, it was found that optical behavior inside the V-shaped groove changed; therefore, the composite structure changed depending on the groove angle, laser polarization direction, and number of times of irradiation. In addition, it was found that the water wettability changed depending on the type of formed micro-nano composite structures. Moreover, the wettability could be controlled by depending on how the structure is used.

Analysis of hierarchical wrinkle structure generated in thin film on winkler spring substrate

The buckling deformation of a structure consisting of a soft substrate and a hard thin film induces autonomous formation of a fine periodic structure represented by wrinkles. In recent years, a hierarchical wrinkle structure in which wrinkles with different periods are superimposed has attracted attention, and its engineering application is expected. However, no methodology has been established for structural control. In this study, we investigate the mechanism of autonomous formation of hierarchical wrinkle structure using thin film-winkle spring substrate system.

Amplification of Sensor Signals from Metal Mesh Device with Fine Periodic Structure.

Two types of metal mesh devices with hole diameters of 1.7 and 0.3 μm were prepared by an electroforming method. The metal mesh devices with hole diameters of 1.7 and 0.3 μm transmitted electromagnetic waves with frequencies of approximately 100 and 285 THz, respectively. These spectral frequencies shifted depending on the adsorption amount of protein. The slope in the linear relationship between the adsorption amount and spectral shift (i.e. sensitivity) of the metal mesh device with a hole diameter of 0.3 μm was seven times as great as that of the device with a hole diameter of 1.7 μm. These results agreed with the theoretical concept of the sensitivity for the metal mesh device sensor being proportional to the square of the transmittance frequency. As biosensors, the structurally refined metal mesh devices amplified the output signals.

Effect of Crystal Structure on Fabrication of Fine Periodic Surface Structures with Short Pulsed Laser

In recent years, nanostructures have been required for industry and medical services, to perform functions such as reduction in friction, control of wettability, and enhancement in biological affinity. Ultrashort pulsed lasers have been applied to meet these demands, and have been actively studied both experimentally and theoretically in terms of phenomena and principles. In this study, to clarify the phenomenon of the fabrication of laser-induced periodic surface structures (LIPSS), and its application to industry, experiments were conducted on SUS304, titanium, and nickel-phosphorus by a short pulsed laser that has a longer pulse duration, higher cost-effectiveness, and higher stability than ultrashort pulsed lasers. The results confirmed that while LIPSS were fabricated on Ti and Ni-P workpieces, a uniform fine periodic structure was not fabricated on the whole irradiated surface of SUS304, and crystal grain boundaries appeared with low energy density and irradiation number because SUS304 is an alloy composed of Fe, Cr, and Ni. Further, the short pulsed laser has a low power and long pulse duration, inducing the thermal effect. We clarified the effect of crystal structure on fabricating fine periodic surface structures with short pulsed laser.

Super-resolution x-ray imaging using interaction between periodic structure of object and standing wave generated with total-reflection-mirror interferometer

A super-resolution method in projection-type x-ray imaging is proposed. In this method, interference fringes generated with a two-beam interferometer are used for detecting the fine periodic structure of the object. When the sample has a fine periodic structure, the structure can be detected as interaction between the periodic structure of object and the standing wave formed by the two-beam interferometer. Feasibility studies have been carried out using wavefront-division interferometer with total-reflection-mirror optics and a resolution test chart as a model sample. The fine structures with a period up to 100 nm were detected as modulation of transmitting x-ray intensity at 11.5 keV.

The asymptotic homogenization elasticity tensor properties for composites with material discontinuities

The classical asymptotic homogenization approach for linear elastic composites with discontinuous material properties is considered as a starting point. The sharp length scale separation between the fine periodic structure and the whole material formally leads to anisotropic elastic-type balance equations on the coarse scale, where the arising fourth rank operator is to be computed solving single periodic cell problems on the fine scale. After revisiting the derivation of the problem, which here explicitly points out how the discontinuity in the individual constituents’ elastic coefficients translates into stress jump interface conditions for the cell problems, we prove that the gradient of the cell problem solution is minor symmetric and that its cell average is zero. This property holds for perfect interfaces only (i.e., when the elastic displacement is continuous across the composite’s interface) and can be used to assess the accuracy of the computed numerical solutions. These facts are further exploited, together with the individual constituents’ elastic coefficients and the specific form of the cell problems, to prove a theorem that characterizes the fourth rank operator appearing in the coarse-scale elastic-type balance equations as a composite material effective elasticity tensor. We both recover known facts, such as minor and major symmetries and positive definiteness, and establish new facts concerning the Voigt and Reuss bounds. The latter are shown for the first time without assuming any equivalence between coarse and fine-scale energies (Hill’s condition), which, in contrast to the case of representative volume elements, does not identically hold in the context of asymptotic homogenization. We conclude with instructive three-dimensional numerical simulations of a soft elastic matrix with an embedded cubic stiffer inclusion to show the profile of the physically relevant elastic moduli (Young’s and shear moduli) and Poisson’s ratio at increasing (up to 100 %) inclusion’s volume fraction, thus providing a proxy for the design of artificial elastic composites.

Laser marking on soda-lime glass by laser-induced backside wet etching with two-beam interference

For crack-free marking of glass materials, a beam-scanning laser-induced backside wet etching (LIBWE) process by a beam spot with a fine periodic structure was examined. The fine periodic structure was produced within a beam spot by means of a Mach–Zehnder interferometer incorporated to the optical setup for the beam-scanning LIBWE. A fine structure with a period of 9 µm was observed within the microstructures with a diameter of ca. 40 µm fabricated by a laser shot under double-beam irradiation, and they could be homogeneously fabricated within an area of 800 × 800 µm. The area filled with the microstructures, including fine periodic structures, could be observed in high contrast under a diffuse, on-axis illumination that was used in commercial QR code readers.

Photochemical technology of the formation of polymer materials’ nanomarkers

A new photochemical technology for forming latent markers, i.e., protective identifiers of different polymer products and other materials, is developed. This technique allows one to encode identifiers of both individual products and lots of different kinds of products. Designed markers can be nanostructured and do not violate the appearance of products. The possibility of forming resistant latent identifiers in a variety of materials is shown that can be performed with fine periodic structure, including nanotechnology. The use of these markers realizes the possibility of developing new design elements of the product with multilevel coding. The proposed technology in combination with the development of ways of reading latent and multilevel information can serve as the basis for the development of a new method of identifying and protecting against the falsification of products, documents, data carriers, and valuable objects.

Periodic microstructures of Cr–O–N coatings deposited by arc ion plating

Coatings of chromium nitride (CrN) and Cr–O–N with varying O contents were prepared in a gaseous mixture of nitrogen and oxygen by arc ion plating, and their mechanical properties and microstructures were investigated. The oxygen content in the Cr–O–N coatings increased with the oxygen flow rate. When the substrate table was rotated during deposition, all Cr–O–N coatings exhibited a NaCl-type cubic CrN phase, up to an oxygen flow rate of 30%. Other phases such as chromium oxide (Cr2O3) were not detected. Field emission scanning electron microscopy observations revealed a columnar structure of the CrN coatings, whereas the Cr–O–N coatings have a very fine microstructure and develop nanometer-scale striped patterns, regardless of oxygen content. The period of the stripes depends on the rotation speed of the substrate table in the physical vapor deposition equipment. Transmission electron microscopy (TEM) clearly revealed the very fine periodic structure of the Cr–O–N coating. Moreover, scanning transmission electron microscopy and energy dispersive spectroscopy analyses revealed higher oxygen concentration in the striped patterns than in other areas. From TEM observations, the striped patterns were inferred to be amorphous Cr2O3. We determined that Cr2O3 formed when the substrate was largely separated from the vapor source, whereas cubic oxynitride formed when the substrate moved close to the vapor source.

Homogenization and Geometric Linearization for Multi‐Well Energies

AbstractThe concept of linear elasticity is to assume that the stored energy has one‐well structure and to consider small displacements. The energy function is then expanded around the equilibrium state and higher‐order terms are neglected. It was proved in [3] that this concept really gives results that provide a good approximation for the actual problem. On the other hand, for materials with fine periodic structure we accomplish a simplification of the problem in an analogous manner by homogenizing the energy. It was recently shown by Müller and Neukamm in [8] that both processes, homogenization and linearization, are interchangeable for such elastic energies. If we consider an energy with multiple wells then, under some reasonable conditions, it is also possible to (geometrically) linearize the problem. The second author proved that quasiconvexification of the limit function yields the desired result. We present that in this case both processes still commute. This is not a priori clear since the proof by Müller and Neukamm significantly rests upon the one‐well structure and properties of quadratic forms. They also provide an example when the statement does not hold. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of five-layered Si/Si xGe 1− x nano-films by RF helicon magnetron sputtering

Five-layered Si/Si x Ge 1− x films on Si(1 0 0) substrate with single-layer thickness of 30 nm, 10 nm and 5 nm, respectively were prepared by RF helicon magnetron sputtering with dual targets of Si and Ge to investigate the feasibility of an industrial fabrication method on multi-stacked superlattice structure for thin-film thermoelectric applications. The fine periodic structure is confirmed in the samples except for the case of 5 nm in single-layer thickness. Fine crystalline Si x Ge 1− x layer is obtained from 700 °C in substrate temperature, while higher than 700 °C is required for Si good layer. The composition ratio ( x) in Si x Ge 1− x is varied depending on the applied power to Si and Ge targets. Typical power ratio to obtain x = 0.83 was 7:3, Hall coefficient, p-type carrier concentration, sheet carrier concentration and mobility measured for the sample composed of five layers of Si (10 nm)/Si 0.82Ge 0.18 (10 nm) are 2.55 × 10 6 /°C, 2.56 × 10 12 cm −3, 1.28 × 10 7 cm −2, and 15.8 cm −2/(V s), respectively.

Towards fabrication of In‐polar InN films and InN/GaN MQWs

AbstractIn‐polarity InN films were grown by radio frequency plasma‐assisted molecular‐beam epitaxy and their structural properties as a function of III/V beam‐flux ratio were investigated. It was found that the window for the surface stoichiometry to achieve high quality InN films was very narrow; only 11% change in In beam‐equivalent pressure drastically affected surface morphology and structural property. This is because the upper‐limited growth temperature of the In‐polarity growth is as low as about 500 °C. Under the growth condition around the unity stoichiometry, a step‐flow‐like surface with a 2 mono‐layer step height was obtained in the In‐polarity growth. Best values for the measurements of structural and electrical properties were as follows; full width at half maximum of X‐ray rocking curves were 645 arcsec and 1425 arcsec for (0002) and (10‐12) reflections, respectively and the electron concentration and mobility were 1.3×1018 cm–3 and 1650 cm2/V s, respectively. Furthermore, we tried to fabricate In‐polarity InN/GaN multi‐quantum wells with a 1 mono‐layer InN well thickness. A result of X‐ray 2θ–ω scan showed clearly satellite peaks up to 2nd order and fringe peaks, which indicates that a fine periodic structure is achieved in the In‐polarity MQWs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of stress on the microstructure of the corner defect in As +-implanted, two-dimensional amorphized Si

The effect of stress induced by a chemical vapor deposited SiO 2 film on the microstructure of the corner defects in As +-implanted, two-dimensional amorphized Si has been studied by transmission electron microscopy. A fine periodic trench structure was used to form two-dimensional amorphous layers and to induce the stress in the Si substrate. As implantation with an energy of 80 keV and a dose of 3×10 15/cm 2 amorphized a 100-nm-thick silicon surface under the trench bottom and produced a sharply curved amorphous/crystalline interface under the bottom corner of the trench. The trench filled with a high-tensile stressed chemical vapor deposited SiO 2 film induced a high stress field in the Si substrate. The microstructure of the corner defects was closely related to the stress induced by the trench. In the case of the absence of the stress vacancy-type dislocation half loops were generated on {1 1 1} planes after annealing at 650°C or 800°C at the corner of the regrowth regions. While, in the case of the presence of the stress induced by the trench, microtwins were formed on {1 1 1} planes after annealing. It was found that the microstructure of the corner defects was determined by the SPE regrowth behavior at intermediate stages of the regrowth process.

25 nm pitch GaInAs/InP buried structure: Improvement by calixarene as an electron beam resist and tertiarybutylphosphine as a P source in organometallic vapor phase epitaxy regrowth

To achieve a fine periodic semiconductor structure by electron beam (EB) lithography, calixarene was used as an EB resist. A 25 nm pitch InP pattern was formed successfully and 40 nm pitch InP structures were achieved with good reproducibility. A shorter developing time, precise stage motion, accurate control of the widths of lines and spaces, and slight O2 ashing were important to obtain a fine InP pattern by a two-step wet chemical etching process. Furthermore, the fabricated periodic InP pattern was buried in a GaInAs structure by organometallic vapor phase epitaxy. The introduction of tertiarybutylphosphine as the phosphorus source prevented the fine structure from deforming when the temperature was raised and a 25 nm pitch periodic structure was buried successfully.

Propagating fronts, chaos and multistability in a cell replication model.

Numerical solutions to a model equation that describes cell population dynamics are presented and analyzed. A distinctive feature of the model equation (a hyperbolic partial differential equation) is the presence of delayed arguments in the time (t) and maturation (x) variables due to the nonzero length of the cell cycle. This transport like equation balances a linear convection with a nonlinear, nonlocal, and delayed reaction term. The linear convection term acts to impress the value of u(t,x=0) on the entire population while the death term acts to drive the population to extinction. The rich phenomenology of solution behaviour presented here arises from the nonlinear, nonlocal birth term. The existence of this kinetic nonlinearity accounts for the existence and propagation of soliton-like or front solutions, while the increasing effect of nonlocality and temporal delays acts to produce a fine periodic structure on the trailing part of the front. This nonlinear, nonlocal, and delayed kinetic term is also shown to be responsible for the existence of a Hopf bifurcation and subsequent period doublings to apparent "chaos" along the characteristics of this hyperbolic partial differential equation. In the time maturation plane, the combined effects of nonlinearity, nonlocality, and delays leads to solution behaviour exhibiting spatial chaos for certain parameter values. Although analytic results are not available for the system we have studied, consistency and validation of the numerical results was achieved by using different numerical methods. A general conclusion of this work, of interest for the understanding of any biological system modeled by a hyperbolic delayed partial differential equation, is that increasing the spatio-temporal delays will often lead to spatial complexity and irregular wave propagation. (c) 1996 American Institute of Physics.

Transient statistics in stabilizing periodic orbits

The statistics of chaotic and periodic transient time intervals preceding the stabilization of a given periodic orbit have been experimentally studied in a ${\mathrm{CO}}_{2}$ laser with modulated losses, subjected to a small subharmonic perturbation. As predicted by the theory, an exponential tail has been found in the probability distribution of chaotic transients. Furthermore, a fine periodic structure in the distributions of the periodic transients, resulting from the interaction of the control signal and the local structure of the chaotic attractor, has been revealed.