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Materials, Volume 5, Issue 5 (May 2012), Pages 741-1004

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Research

Jump to: Review

Open AccessArticle Kinetics of Holographic Recording and Spontaneous Erasure Processes in Light-Sensitive Liquid Crystal Elastomers
Materials 2012, 5(5), 741-753; doi:10.3390/ma5050741
Received: 20 February 2012 / Revised: 16 March 2012 / Accepted: 22 March 2012 / Published: 25 April 2012
Cited by 7 | PDF Full-text (650 KB) | HTML Full-text | XML Full-text
Abstract
The optical mechanism for imprinting one-dimensional grating structures into thin films of a light-sensitive monodomain liquid crystal elastomer is investigated by analyzing the time dependence of optical diffraction properties. The recording kinetics shows an irregular oscillatory behavior, which is most expressed at [...] Read more.
The optical mechanism for imprinting one-dimensional grating structures into thin films of a light-sensitive monodomain liquid crystal elastomer is investigated by analyzing the time dependence of optical diffraction properties. The recording kinetics shows an irregular oscillatory behavior, which is most expressed at small grating spacings and at temperatures close to the nematic-isotropic phase transition. The oscillations are attributed to the opto-mechanical response of the film, i.e., to contraction of the film during the recording process. At temperatures far below the nematic-isotropic phase transition, the spontaneous erasure kinetics exhibits exponential relaxation with relaxation time following the Arrhenius activation law. However, at temperatures close to the nematic-isotropic phase transition, the erasure process shows an interesting nonmonotonic behavior that we attribute to the non-linear relation between the concentration of the photo-transformed chemical groups and the nematic order parameter. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
Open AccessArticle Biophotopol: A Sustainable Photopolymer for Holographic Data Storage Applications
Materials 2012, 5(5), 772-783; doi:10.3390/ma5050772
Received: 28 March 2012 / Revised: 26 April 2012 / Accepted: 28 April 2012 / Published: 2 May 2012
Cited by 6 | PDF Full-text (379 KB) | HTML Full-text | XML Full-text
Abstract
Photopolymers have proved to be useful for different holographic applications such as holographic data storage or holographic optical elements. However, most photopolymers have certain undesirable features, such as the toxicity of some of their components or their low environmental compatibility. For this [...] Read more.
Photopolymers have proved to be useful for different holographic applications such as holographic data storage or holographic optical elements. However, most photopolymers have certain undesirable features, such as the toxicity of some of their components or their low environmental compatibility. For this reason, the Holography and Optical Processing Group at the University of Alicante developed a new dry photopolymer with low toxicity and high thickness called biophotopol, which is very adequate for holographic data storage applications. In this paper we describe our recent studies on biophotopol and the main characteristics of this material. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
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Open AccessCommunication Diamond-Structured Photonic Crystals with Graded Air Spheres Radii
Materials 2012, 5(5), 851-856; doi:10.3390/ma5050851
Received: 5 March 2012 / Revised: 24 April 2012 / Accepted: 2 May 2012 / Published: 11 May 2012
Cited by 1 | PDF Full-text (388 KB) | HTML Full-text | XML Full-text
Abstract
A diamond-structured photonic crystal (PC) with graded air spheres radii was fabricated successfully by stereolithography (SL) and gel-casting process. The graded radii in photonic crystal were formed by uniting different radii in photonic crystals with a uniform radius together along the Г‑Х [...] Read more.
A diamond-structured photonic crystal (PC) with graded air spheres radii was fabricated successfully by stereolithography (SL) and gel-casting process. The graded radii in photonic crystal were formed by uniting different radii in photonic crystals with a uniform radius together along the Г‑Х direction. The stop band was observed between 26.1 GHz and 34.3 GHz by reflection and transmission measurements in the direction. The result agreed well with the simulation attained by the Finite Integration Technique (FIT). The stop band width was 8.2 GHz and the resulting gap/midgap ratio was 27.2%, which became respectively 141.4% and 161.9% of the perfect PC. The results indicate that the stop band width of the diamond-structured PC can be expanded by graded air spheres radii along the Г‑Х direction, which is beneficial to develop a multi bandpass filter. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
Open AccessArticle Optical Isolator Utilizing Surface Plasmons
Materials 2012, 5(5), 857-871; doi:10.3390/ma5050857
Received: 30 March 2012 / Revised: 9 May 2012 / Accepted: 9 May 2012 / Published: 16 May 2012
Cited by 13 | PDF Full-text (150 KB) | HTML Full-text | XML Full-text
Abstract
Feasibility of usage of surface plasmons in a new design of an integrated optical isolator has been studied. In the case of surface plasmons propagating at a boundary between a transition metal and a double-layer dielectric, there is a significant difference of [...] Read more.
Feasibility of usage of surface plasmons in a new design of an integrated optical isolator has been studied. In the case of surface plasmons propagating at a boundary between a transition metal and a double-layer dielectric, there is a significant difference of optical loss for surface plasmons propagating in opposite directions. Utilizing this structure, it is feasible to fabricate a competitive plasmonic isolator, which benefits from a broad wavelength operational bandwidth and a good technological compatibility for integration into the Photonic Integrated Circuits (PIC). The linear dispersion relation was derived for plasmons propagating in a multilayer magneto-optical slab. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
Open AccessArticle Alkylation of Benzene with Propylene in a Flow-Through Membrane Reactor and Fixed-Bed Reactor: Preliminary Results
Materials 2012, 5(5), 872-881; doi:10.3390/ma5050872
Received: 4 March 2012 / Revised: 14 April 2012 / Accepted: 24 April 2012 / Published: 18 May 2012
Cited by 3 | PDF Full-text (575 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Benzene alkylation with propylene was studied in the gas phase using a catalytic membrane reactor and a fixed-bed reactor in the temperature range of 200–300 °C and with a weight hourly space velocity (WHSV) of 51 h−1. β-zeolite was [...] Read more.
Benzene alkylation with propylene was studied in the gas phase using a catalytic membrane reactor and a fixed-bed reactor in the temperature range of 200–300 °C and with a weight hourly space velocity (WHSV) of 51 h−1. β-zeolite was prepared by hydrothermal synthesis using silica, aluminum metal and TEAOH as precursors. The membrane’s XRD patterns showed good crystallinity for the β-zeolite film, while scanning electron microscopy SEM results indicated that its random polycrystalline film was approximately 1 μm thick. The powders’ specific area was determined to be 400 m2×g−1 by N2 adsorption/desorption, and the TPD results indicated an overall acidity of 3.4 mmol NH3×g−1. Relative to the powdered catalyst, the catalytic membrane showed good activity and product selectivity for cumene. Full article
(This article belongs to the Special Issue Zeolite Membranes: Novel Synthesis and Innovative Applications)
Open AccessArticle Flux Dynamics in Y358 Superconductors
Materials 2012, 5(5), 882-888; doi:10.3390/ma5050882
Received: 10 March 2012 / Revised: 30 April 2012 / Accepted: 8 May 2012 / Published: 18 May 2012
Cited by 2 | PDF Full-text (645 KB) | Retraction
Abstract
Thermally activated flux motion and specific electric resistance in Y358 were studied under different magnetic fields ranging from 0 to 15 kOe. Through investigating the broadening of normal-superconducting transition, we found that the thermally-activated-flux-motion model can describe the electronic effect near the superconducting transition [...] Read more.
Thermally activated flux motion and specific electric resistance in Y358 were studied under different magnetic fields ranging from 0 to 15 kOe. Through investigating the broadening of normal-superconducting transition, we found that the thermally-activated-flux-motion model can describe the electronic effect near the superconducting transition temperature. By modifying this model, specific electric resistance at different magnetic fields was calculated. Full article
Open AccessArticle Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy
Materials 2012, 5(5), 909-921; doi:10.3390/ma5050909
Received: 14 March 2012 / Revised: 9 May 2012 / Accepted: 11 May 2012 / Published: 22 May 2012
Cited by 3 | PDF Full-text (894 KB) | HTML Full-text | XML Full-text
Abstract
If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection [...] Read more.
If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
Open AccessArticle Surface Fractal Analysis for Estimating the Fracture Energy Absorption of Nanoparticle Reinforced Composites
Materials 2012, 5(5), 922-936; doi:10.3390/ma5050922
Received: 19 March 2012 / Revised: 8 May 2012 / Accepted: 11 May 2012 / Published: 23 May 2012
Cited by 8 | PDF Full-text (222 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the fractal dimensions of failure surfaces of vinyl ester based nanocomposites are estimated using two classical methods, Vertical Section Method (VSM) and Slit Island Method (SIM), based on the processing of 3D digital microscopic images. Self-affine fractal geometry has [...] Read more.
In this study, the fractal dimensions of failure surfaces of vinyl ester based nanocomposites are estimated using two classical methods, Vertical Section Method (VSM) and Slit Island Method (SIM), based on the processing of 3D digital microscopic images. Self-affine fractal geometry has been observed in the experimentally obtained failure surfaces of graphite platelet reinforced nanocomposites subjected to quasi-static uniaxial tensile and low velocity punch-shear loading. Fracture energy and fracture toughness are estimated analytically from the surface fractal dimensionality. Sensitivity studies show an exponential dependency of fracture energy and fracture toughness on the fractal dimensionality. Contribution of fracture energy to the total energy absorption of these nanoparticle reinforced composites is demonstrated. For the graphite platelet reinforced nanocomposites investigated, surface fractal analysis has depicted the probable ductile or brittle fracture propagation mechanism, depending upon the rate of loading. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
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Open AccessArticle “Pore-Like” Effects of Super-Molecular Self-Assembly on Molecular Diffusion of Poly(Ethylene Oxide)-Poly(Propylene Oxide)-Poly(Ethylene Oxide) in Water
Materials 2012, 5(5), 966-984; doi:10.3390/ma5050966
Received: 22 February 2012 / Revised: 25 April 2012 / Accepted: 9 May 2012 / Published: 24 May 2012
Cited by 3 | PDF Full-text (830 KB) | HTML Full-text | XML Full-text
Abstract
Molecular diffusion of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in water was studied with the help of Pulsed Field Gradient NMR in the broad range of polymer weight fractions from 0.09 to 0.8. Owing to amphiphilic nature of the molecules, these block [...] Read more.
Molecular diffusion of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in water was studied with the help of Pulsed Field Gradient NMR in the broad range of polymer weight fractions from 0.09 to 0.8. Owing to amphiphilic nature of the molecules, these block copolymers exhibit rich self-organization properties when mixed with water. In particular, at ambient temperatures they form micelles and three liquid crystalline mesophases: cubic, hexagonal, and lamellar. The corresponding super-molecular structure formations were studied with the same block copolymer and at the same temperature. Self-assembly of molecules was shown to produce “pore-like” effects on their self-diffusion properties by imposing severe constraints on the dimensionality of propagation. Diffusion in the hexagonal phase was shown to be quasi one-dimensional in the direction parallel to the long axis of the ordered molecular rods. In the lamellar phase, diffusion was found to be quasi two-dimensional, in the plane of the lamellar structures. The observed diffusion anisotropy was attributed to the effects of the specific molecular ordering on the mesoscopic length scale. Full article
(This article belongs to the Special Issue Diffusion in Micropores)

Review

Jump to: Research

Open AccessReview Photonic Crystal Structure and Coloration of Wing Scales of Butterflies Exhibiting Selective Wavelength Iridescence
Materials 2012, 5(5), 754-771; doi:10.3390/ma5050754
Received: 21 March 2012 / Revised: 11 April 2012 / Accepted: 12 April 2012 / Published: 30 April 2012
Cited by 2 | PDF Full-text (953 KB) | HTML Full-text | XML Full-text
Abstract
The coloration of butterflies that exhibit human visible iridescence from violet to green has been elucidated. Highly tilted multilayers of cuticle on the ridges, which were found in the scales of male S. charonda and E. mulciber butterflies, produce a limited-view, selective [...] Read more.
The coloration of butterflies that exhibit human visible iridescence from violet to green has been elucidated. Highly tilted multilayers of cuticle on the ridges, which were found in the scales of male S. charonda and E. mulciber butterflies, produce a limited-view, selective wavelength iridescence (ultraviolet (UV)~green) as a result of multiple interference between the cuticle-air layers. The iridescence from C. ataxus originates from multilayers in the groove plates between the ridges and ribs. The interference takes place between the top and bottom surfaces of each layer and incoherently between different layers. Consequently, the male with the layers that are ~270 nm thick reflects light of UV~560 nm (green) and the female with the layers that are ~191 nm thick reflects light of UV~400 nm (violet). T. aeacus does not produce the iridescent sheen which T. magellanus does. No iridescent sheen is ascribed to microrib layers, which are perpendicular to the scale plane, so that they cannot reflect any backscattering. The structures of these butterflies would provide us helpful hints to manipulate light in photoelectric devices, such as blue or UV LEDs. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
Open AccessReview Semiconductor CdF2:Ga and CdF2:In Crystals as Media for Real-Time Holography
Materials 2012, 5(5), 784-817; doi:10.3390/ma5050784
Received: 14 March 2012 / Revised: 24 April 2012 / Accepted: 25 April 2012 / Published: 7 May 2012
PDF Full-text (987 KB) | HTML Full-text | XML Full-text
Abstract
Monocrystalline cadmium fluoride is a dielectric solid that can be converted into a semiconductor by doping with donor impurities and subsequent heating in the reduction atmosphere. For two donor elements, Ga and In, the donor (“shallow”) state is a metastable one separated [...] Read more.
Monocrystalline cadmium fluoride is a dielectric solid that can be converted into a semiconductor by doping with donor impurities and subsequent heating in the reduction atmosphere. For two donor elements, Ga and In, the donor (“shallow”) state is a metastable one separated from the ground (“deep”) state by a barrier. Photoinduced deep-to-shallow state transition underlies the photochromism of CdF2:Ga and CdF2:In. Real-time phase holograms are recorded in these crystals capable of following up optical processes in a wide frequency range. The features of photochromic transformations in CdF2:Ga and CdF2:In crystals as well as holographic characteristics of these media are discussed. Exemplary applications of CdF2-based holographic elements are given. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
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Open AccessReview Investigating the Defect Structures in Transparent Conducting Oxides Using X-ray and Neutron Scattering Techniques
Materials 2012, 5(5), 818-850; doi:10.3390/ma5050818
Received: 31 March 2012 / Accepted: 4 May 2012 / Published: 11 May 2012
Cited by 12 | PDF Full-text (555 KB) | HTML Full-text | XML Full-text
Abstract
Transparent conducting oxide (TCO) materials are implemented into a wide variety of commercial devices because they possess a unique combination of high optical transparency and high electrical conductivity. Created during the processing of the TCOs, defects within the atomic-scale structure are responsible [...] Read more.
Transparent conducting oxide (TCO) materials are implemented into a wide variety of commercial devices because they possess a unique combination of high optical transparency and high electrical conductivity. Created during the processing of the TCOs, defects within the atomic-scale structure are responsible for their desirable optical and electrical properties. Therefore, studying the defect structure is essential to a better understanding of the behavior of transparent conductors. X-ray and neutron scattering techniques are powerful tools to investigate the atomic lattice structural defects in these materials. This review paper presents some of the current developments in the study of structural defects in n-type TCOs using x-ray diffraction (XRD), neutron diffraction, extended x-ray absorption fine structure (EXAFS), pair distribution functions (PDFs), and x-ray fluorescence (XRF). Full article
(This article belongs to the Special Issue Advances in Transparent Conducting Oxides)
Open AccessReview Strained Silicon Photonics
Materials 2012, 5(5), 889-908; doi:10.3390/ma5050889
Received: 22 March 2012 / Revised: 9 May 2012 / Accepted: 9 May 2012 / Published: 22 May 2012
Cited by 11 | PDF Full-text (1622 KB) | HTML Full-text | XML Full-text
Abstract
A review of recent progress in the field of strained silicon photonics is presented. The application of strain to waveguide and photonic crystal structures can be used to alter the linear and nonlinear optical properties of these devices. Here, methods for the [...] Read more.
A review of recent progress in the field of strained silicon photonics is presented. The application of strain to waveguide and photonic crystal structures can be used to alter the linear and nonlinear optical properties of these devices. Here, methods for the fabrication of strained devices are summarized and recent examples of linear and nonlinear optical devices are discussed. Furthermore, the relation between strain and the enhancement of the second order nonlinear susceptibility is investigated, which may enable the construction of optically active photonic devices made of silicon. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
Open AccessReview In-Line Phase-Contrast X-ray Imaging and Tomography for Materials Science
Materials 2012, 5(5), 937-965; doi:10.3390/ma5050937
Received: 1 April 2012 / Revised: 11 May 2012 / Accepted: 16 May 2012 / Published: 24 May 2012
Cited by 35 | PDF Full-text (2087 KB) | HTML Full-text | XML Full-text
Abstract
X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast [...] Read more.
X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X-rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients. Here we review the use of phase-contrast imaging and tomography for a wide variety of materials science characterization problems using both synchrotron and laboratory sources and further demonstrate the particular benefits of phase contrast in the laboratory setting with a series of case studies. Full article
(This article belongs to the Special Issue X-ray Imaging in Materials Science)
Open AccessReview Direct Wafer Bonding and Its Application to Waveguide Optical Isolators
Materials 2012, 5(5), 985-1004; doi:10.3390/ma5050985
Received: 31 March 2012 / Revised: 18 May 2012 / Accepted: 21 May 2012 / Published: 24 May 2012
Cited by 13 | PDF Full-text (389 KB) | HTML Full-text | XML Full-text
Abstract
This paper reviews the direct bonding technique focusing on the waveguide optical isolator application. A surface activated direct bonding technique is a powerful tool to realize a tight contact between dissimilar materials. This technique has the potential advantage that dissimilar materials are [...] Read more.
This paper reviews the direct bonding technique focusing on the waveguide optical isolator application. A surface activated direct bonding technique is a powerful tool to realize a tight contact between dissimilar materials. This technique has the potential advantage that dissimilar materials are bonded at low temperature, which enables one to avoid the issue associated with the difference in thermal expansion. Using this technique, a magneto-optic garnet is successfully bonded on silicon, III-V compound semiconductors and LiNbO3. As an application of this technique, waveguide optical isolators are investigated including an interferometric waveguide optical isolator and a semileaky waveguide optical isolator. The interferometric waveguide optical isolator that uses nonreciprocal phase shift is applicable to a variety of waveguide platforms. The low refractive index of buried oxide layer in a silicon-on-insulator (SOI) waveguide enhances the magneto-optic phase shift, which contributes to the size reduction of the isolator. A semileaky waveguide optical isolator has the advantage of large fabrication-tolerance as well as a wide operation wavelength range. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)

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