Gyroid cuticular structures in butterfly wing scales: biological photonic crystals

We present a systematic study of the cuticular structure in the butterfly wing scales of some papilionids (Parides sesostris and Teinopalpus imperialis) and lycaenids (Callophrys rubi, Cyanophrys remus, Mitoura gryneus and Callophrys dumetorum). Using published scanning and transmission electron microscopy (TEM) images, analytical modelling and computer-generated TEM micrographs, we find that the three-dimensional cuticular structures can be modelled by gyroid structures with various filling fractions and lattice parameters. We give a brief discussion of the formation of cubic gyroid membranes from the smooth endoplasmic reticulum in the scale's cell, which dry and harden to leave the cuticular structure behind when the cell dies. The scales of C. rubi are a potentially attractive biotemplate for producing three-dimensional optical photonic crystals since for these scales the cuticle-filling fraction is nearly optimal for obtaining the largest photonic band gap in a gyroid structure.     

Cryptic iridescence in a fossil weevil generated by single diamond photonic crystals

Nature''s most spectacular colours originate in integumentary tissue architectures that scatter light via nanoscale modulations of the refractive index. The most intricate biophotonic nanostructures are three-dimensional crystals with opal, single diamond or single gyroid lattices. Despite intense interest in their optical and structural properties, the evolution of such nanostructures is poorly understood, due in part to a lack of data from the fossil record. Here, we report preservation of single diamond (Fd-3m) three-dimensional photonic crystals in scales of a 735 000 year old specimen of the brown Nearctic weevil Hypera diversipunctata from Gold Run, Canada, and in extant conspecifics. The preserved red to green structural colours exhibit near-field brilliancy yet are inconspicuous from afar; they most likely had cryptic functions in substrate matching. The discovery of pristine fossil examples indicates that the fossil record is likely to yield further data on the evolution of three-dimensional photonic nanostructures and their biological functions.     

Block copolymer morphologies in dye-sensitized solar cells: probing the photovoltaic structure-function relation

We integrate mesostructured titania arrays into dye-sensitized solar cells by replicating ordered, oriented one-dimensional (1D) columnar and three-dimensional (3D) bicontinuous gyroid block copolymer phases. The solar cell performance, charge transport, and recombination are investigated. We observe faster charge transport in 1D "wires" than through 3D gyroid arrays. However, owing to their structural instability, the surface area of the wire arrays is low, inhibiting the solar cell performance. The gyroid morphology, on the other hand, outperforms the current state-of-the-art mesoporous nanoparticle films.     

Effect of graphene nanoplatelet addition on properties of thermo-responsive shape memory polyurethane-based nanocomposite

Graphene nanoplatelet (GNP) was added as reinforcement to novel blend of polyurethane (PU) and poly(ethylene-co-ethyl acrylate-co-maleic anhydride) (PEEAMA) with an intended application for heat-induced shape recovery. Objective of the study was to explore the effect of GNP addition on morphology, mechanical properties, and heat-induced shape recovery. Physical inter-linking of GNP platelets to blend components directed unique self-assembled pattern. Neat blend revealed gyroid morphology while addition of functional GNP initiated well-defined double gyroid pattern on folds of primary gyroid structure. At a concentration of 5 wt.% GNP, the nanocomposite film showed highest improvement in tensile strength (54%) and Young's modulus (57%) as compared to blend. The nanocomposite samples showed shape recovery phenomenon at T_m (60°C). In 5 wt.% GNP-loaded nanocomposite, the original shape of samples was nearly 96% recovered within 7 s.     

Metasurfaces Atop Metamaterials: Surface Morphology Induces Linear Dichroism in Gyroid Optical Metamaterials

Optical metamaterials offer the tantalizing possibility of creating extraordinary optical properties through the careful design and arrangement of subwavelength structural units. Gyroid‐structured optical metamaterials possess a chiral, cubic, and triply periodic bulk morphology that exhibits a redshifted effective plasma frequency. They also exhibit a strong linear dichroism, the origin of which is not yet understood. Here, the interaction of light with gold gyroid optical metamaterials is studied and a strong correlation between the surface morphology and its linear dichroism is found. The termination of the gyroid surface breaks the cubic symmetry of the bulk lattice and gives rise to the observed wavelength‐ and polarization‐dependent reflection. The results show that light couples into both localized and propagating plasmon modes associated with anisotropic surface protrusions and the gaps between such protrusions. The localized surface modes give rise to the anisotropic optical response, creating the linear dichroism. Simulated reflection spectra are highly sensitive to minute details of these surface terminations, down to the nanometer level, and can be understood with analogy to the optical properties of a 2D anisotropic metasurface atop a 3D isotropic metamaterial. This pronounced sensitivity to the subwavelength surface morphology has significant consequences for both the design and application of optical metamaterials.     

Templated Sub‐100‐nm‐Thick Double‐Gyroid Structure from Si‐Containing Block Copolymer Thin Films

The directed self‐assembly of diblock copolymer chains (poly(1,1‐dimethyl silacyclobutane)‐block‐polystyrene, PDMSB‐b‐PS) into a thin film double gyroid structure is described. A decrease of the kinetics of a typical double‐wave pattern formation is reported within the 3D‐nanostructure when the film thickness on mesas is lower than the gyroid unit cell. However, optimization of the solvent‐vapor annealing process results in very large grains (over 10 µm²) with specific orientation (i.e., parallel to the air substrate) and direction (i.e., along the groove direction) of the characteristic (211) plane, demonstrated by templating sub‐100‐nm‐thick PDMSB‐b‐PS films.     

Band structure symmetry effects in Gd multilayers grown on W(1 1 2)

We present evidence of coverage-dependent band structure symmetry effects in scanning tunneling microscopy. We find that the symmetry of the Gd induced band located at about 2 eV below the Fermi energy, at the surface Brillouin zone center, appears to be strongly dependent on the atomic structure in the bilayer regime for Gd on W(1 1 2). Light polarization dependent photoemission from this band indicates more d_z² symmetry character for rectangular Gd structures and rather more d_xzd_yz character for the quasi hexagonal bilayer structure. Band symmetry changes accompanying the structural phase transition from rectangular to quasi-hexagonal Gd bilayer structures are consistent with arguments used to explain the apparent STM corrugation observed for Gd on W(1 1 2) (Surf Sci 520(2002)43).     

Additively manufactured heterogeneously porous metallic bone with biostructural functions and bone-like mechanical properties

A compatible artificialbone impla nt requires large pores for enhanced nutrients transports,small pores to allow cell seeding and bone-like mechanical properties to avoid stress shielding.Herein,we report novel improved gyroid lattices with millimetre-scaled gyroid wall spacings and micrometre-scaled additional pores on the walls.Designs are successfully fabricated by electron beam melting using Ti-6 Al-4 V to high part qualities while exhibiting bone-like mechanical properties with a range of Young's modulus of 8-15 GPa and strength of 150-250 MPa.The improved design also eliminates brittle failure by allowing the structure to deform more stably.     

Structural and ferroelectric properties of europium doped lead zirconate titanate thin films by a sol-gel method

Using a sol-gel method, rare earth element europium doped lead zirconate titanate thin films with a pure perovskite structure were obtained. The effects of excess lead and pyrolyzing temperature on the crystalline structure of the thin films were investigated using X-ray diffraction. Their ferroelectric and dielectric properties were determined by P-E loop and impedance measurements. The remnant polarization is 23.5 μC/cm² and the coercive electric field strength is 5.5 kV/mm. The dielectric constant and the dissipation factor is approximately 950 and 0.07, respectively.     

Directional reflectance and milli-scale feather morphology of the African Emerald Cuckoo,Chrysococcyx cupreus

Diverse plumages have evolved among birds through complex morphological modifications. We investigate how the interplay of light with surface and subsurface feather morphology determines the direction of light propagation, an understudied aspect of avian visual signalling. We hypothesize that milli-scale modifications of feathers produce anisotropic reflectance, the direction of which may be predicted by the orientation of the milli-scale structure. The subject of this study is the African Emerald Cuckoo, Chrysococcyx cupreus, noted for its shimmering green iridescent appearance. Using a spherical gantry, we measured the change in the directional reflectance across the feather surface and over a hemisphere of incident lighting directions. Using a microCT scanner, we also studied the morphology of the structural branches of the barb. We tracked the changes in the directional reflectance to the orientation of the structural branches as observed in the CT data. We conclude that (i) the far-field signal of the feather consists of multiple specular components, each associated with a different structural branch and (ii) the direction of each specular component is correlated to the orientation of the corresponding structure.     

Current-induced formation of gradient crystals in block copolymer electrolytes

Conventional ordered phases such as crystals and liquid crystals have constant domain spacings. In this Letter, we report on the formation of coherently ordered morphologies wherein the domain spacing changes continuously along a specified direction. We have coined the term "gradient crystal" to refer to this structure, a signature of which is a small-angle X-ray scattering pattern that resembles a sundial. Gradient crystals composed of a gyroid morphology form spontaneously when ionic current is driven through a block copolymer electrolyte. We propose that this structure forms because it allows for a continuous change in domain spacing without requiring the introduction of defects. Previous studies have shown that applied electric fields ranging from 1000 to 40,000 V/mm can induce long-range structural order, alignment, and morphological transitions in block copolymers. Gradient crystals form under applied electric fields as low as 2.5 V/mm due to the presence of direct ionic currents that are absent in the aforementioned studies.     

Effects of Nd substitution on the polarization properties and electronic structures of bismuth titanate single crystals

Single crystals of Nd-substituted Bi₄Ti₃O₁₂ ferroelectrics were grown by a self-flux method, and the effects of Nd substitution on the polarization properties and optical transmission spectra of the crystals have been investigated. Bi_3.52Nd_0.48Ti₃O₁₂ crystals showed a smaller remanent polarization along the a axis of 29 μC/cm² than Bi₄Ti₃O₁₂ crystals (46 μC/cm²), and this result is in good qualitative agreement with the calculation of the spontaneous polarization based on Rietveld analysis of neutron diffraction. Electronic band structure calculations using the structural data suggest that the orbital hybridization between the Nd 5d and O 2p states stabilizes oxide ions in the perovskite layers, which is consistent with the much smaller leakage current observed for Nd-substituted crystals.     

Imaging polarimetry of the rainbow

Using imaging polarimetry, we measured the polarization patterns of a rainbow on the shore of the Finnish town of Oulu in July 2001. We present here high-resolution color-coded maps of the spatial distributions of the degree and angle of linear polarization of the rainbow in the red (650 +/- 30 nm), green (550 +/- 30 nm), and blue (450 +/- 30 nm) ranges of the spectrum. The measured polarization characteristics of the investigated rainbow support earlier theoretical and computational results and are in accordance with previous qualitative observations. To our knowledge, this is the first imaging polarimetric study of rainbow polarization.     

Suppression of polarization dependence in the design of an arrayed-waveguide grating with photodefinable polyimide

We report on an effective means of suppressing polarization dependence in the design of an arrayed waveguide grating (AWG) made of photodefinable polyimide. The polarization dependence of the arrayed-waveguide grating device is excellently suppressed by controlling the grating order (m) for a given refractive index difference between TE- and TM-modes within polyimide. The transmission characteristics of two AWG’s for two grating orders, m=70 and 90, show wavelength shift of 5.04 nm and nearly zero, respectively, strongly supporting and confirming the method that we have identified for the birefringence suppression.     

Multiple Routes to Bicontinuous Cubic Liquid Crystal Phases Discovered by High-Throughput Self-Assembly Screening of Multi-Tail Lipidoids

Bicontinuous cubic phases offer advantageous routes to a broad range of applied materials ranging from drug delivery devices to membranes. However, a priori design of molecules that assemble into these phases remains a technological challenge. In this article, a high-throughput synthesis of lipidoids that undergo protonation-driven self-assembly (PrSA) into liquid crystalline (LC) phases is conducted. With this screening approach, 12 different multi-tail lipidoid structures capable of assembling into the bicontinuous double gyroid phase are discovered. The large volume of small-angle X-ray scattering (SAXS) data uncovers unexpected design criteria that enable phase selection as a function of lipidoid headgroup size and architecture, tail length and architecture, and counterion identity. Surprisingly, combining branched headgroups with bulky tails forces lipidoids to adopt unconventional pseudo-disc conformations that pack into double gyroid networks, entirely distinct from other synthetic or biological amphiphiles within bicontinuous cubic phases. From a multitude of possible applications, two examples of functional materials from lipidoid liquid crystals are demonstrated. First, the fabrication of gyroid nanostructured films by interfacial PrSA, which are rapidly responsive to the external medium. Second, it is shown that colloidally-dispersed lipidoid cubosomes, for example, for drug delivery, are easily assembled using top-down solvent evaporation methods.     

Highly spin-polarized materials and devices for spintronics?

The performance of spintronics depends on the spin polarization of the current. In this study half-metallic Co-based full-Heusler alloys and a spin filtering device (SFD) using a ferromagnetic barrier have been investigated as highly spin-polarized current sources. The multilayers were prepared by magnetron sputtering in an ultrahigh vacuum and microfabricated using photolithography and Ar ion etching. We investigated two systems of Co-based full-Heusler alloys, Co₂Cr_{1 − x}Fe_xAl (CCFA(x)) and Co₂FeSi_{1 − x}Al_x (CFSA(x)) and revealed the structure and magnetic and transport properties. We demonstrated giant tunnel magnetoresistance (TMR) of up to 220% at room temperature and 390% at 5 K for the magnetic tunnel junctions (MTJs) using Co₂FeSi_0.5Al_0.5 (CFSA(0.5)) Heusler alloy electrodes. The 390% TMR corresponds to 0.81 spin polarization for CFSA(0.5) at 5 K. We also investigated the crystalline structure and local structure around Co atoms by x-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses, respectively, for CFSA films sputtered on a Cr-buffered MgO (001) substrate followed by post-annealing at various temperatures in an ultrahigh vacuum. The disordered structures in CFSA films were clarified by NMR measurements and the relationship between TMR and the disordered structure was discussed. We clarified that the TMR of the MTJs with CFSA(0.5) electrodes depends on the structure, and is significantly higher for L2₁ than B2 in the crystalline structure. The second part of this paper is devoted to a SFD using a ferromagnetic barrier. The Co ferrite is investigated as a ferromagnetic barrier because of its high Curie temperature and high resistivity. We demonstrate the strong spin filtering effect through an ultrathin insulating ferrimagnetic Co-ferrite barrier at a low temperature. The barrier was prepared by the surface plasma oxidization of a CoFe₂ film deposited on a MgO (001) single crystal substrate, wherein the spinel structure of CoFe₂O₄ (CFO) and an epitaxial relationship of MgO(001)[100]/CoFe₂ (001)]110]/CFO(001)[100] were induced. A SFD consisting of CoFe₂ /CFO/Ta on a MgO (001) substrate exhibits the inverse TMR of - 124% at 10 K when the configuration of the magnetizations of CFO and CoFe₂ changes from parallel to antiparallel. The inverse TMR suggests the negative spin polarization of CFO, which is consistent with the band structure of CFO obtained by first principle calculation. The - 124% TMR corresponds to the spin filtering efficiency of 77% by the CFO barrier.     

Morphology and Thermodynamic Properties of a Copolymer with an Electronically Conducting Block: Poly(3-ethylhexylthiophene)-block-poly(ethylene oxide)

We report on the synthesis and morphology of a block copolymer, poly(3-(2'-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory-Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the "breaking out" of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization).     

Mechanical properties of the double gyroid phase in oriented thermoplastic elastomers

We investigate the mechanical properties of triblock copolymers with oriented double gyroid (DG) morphology in poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymers by deforming textured samples along both the [111] direction and transverse to this direction. The modulus anisotropy for the two directions of this cubic material is approximately a factor of 5. Deformation along [111] causes the sample to form a distinct neck and draw, while the deformation in the transverse direction proceeds without neck formation. In addition, the mechanical hysteresis of the [111] stretch is 50% higher than that transverse to the [111] direction. Upon unloading and annealing above the polystyrene Tg, the DG structure recovers fully, both macroscopically and microscopically. The mechanical properties of the DG are compared to those of the classical block copolymer morphologies to gain insight into the deformation mechanism.     

Tensile Properties of 3D-Projected 4-Polytopes: A New Class of Mechanical Metamaterial

In this article, we research the tensile behavior mechanical metamaterial based on the 3D projections of 4D geometries (4-polytopes). The specific properties of these mechanical metamaterials can be enhanced by more than fourfold when optimized within a framework powered by an evolutionary algorithm. We show that the best-performing metamaterial structure, the 8-cell (tesseract), has specific yield strength and specific stiffness values in a similar range to those of hexagonal honeycombs tested out-of-plane. The 8-cell structures are also cubically symmetrical and have the same mechanical properties in three orthogonal axes. The effect of structure is quantified by comparing metamaterial tensile strength against the Young's modulus of constituent solid material. We find that the strength-to-modulus value of the 8-cell structures exceeds that of the hexagonal honeycomb by 76%. The 5-cell (pentatope) and 16-cell (orthoplex) metamaterials are shown to be more effective under tensile loading than gyroid structures, while 24-cell (octaplex) structures display the least optimal structure-properties relationships. The findings presented in this paper showcase the importance of macro-scale architecture and highlight the potential of 3D projections of 4-polytopes as the basis for a new class of mechanical metamaterial.     

Precision Neutron Polarimetry for Neutron Beta Decay

The abBA collaboration is developing a new type of field-expansion spectrometer for a measurement of the three correlation coefficients a, A, and B and the shape parameter b. The measurement of A and B requires precision neutron polarimetry. We will polarize a pulsed cold neutron beam from the SNS using a ³He neutron spin filter. The well-known polarizing cross section for n-³He has a 1/v dependence, where v is the neutron velocity, which is used to determine the absolute beam polarization through a time-of-flight (TOF) measurement. We show that by measuring the TOF dependence of A and B, the coefficients and the neutron polarization can be determined with a small loss of the statistical precision and with negligible systematic error. We conclude that it is possible to determine the neutron polarization averaged over a long run in the neutron beta decay experiment with a statistical error less than 10⁻⁴. We discuss various sources of systematic uncertainty in the measurement of A and B and conclude that the fractional systematic errors are less than 2 × 10⁻⁴.