Phase-separated semiconductors containing magnetic nanostructures are relevant systems for the realization of high-density recording media. Here, the controlled strain engineering of GaδFeN layers with FeyN embedded nanocrystals (NCs) via AlxGa1−xN buffers with different Al concentration 0<xAl<41% is presented. Through the addition of Al to the buffer, the formation of predominantly prolate-shaped ε-Fe3N NCs takes place. Already at an Al concentration xAl≈ 5% the structural properties—phase, shape, orientation—as well as the spatial distribution of the embedded NCs are modified in comparison to those grown on a GaN buffer. Although the magnetic easy axis of the cubic γ’-GayFe4−yN nanocrystals in the layer on the xAl=0% buffer lies in-plane, the easy axis of the ε-Fe3N NCs in all samples with AlxGa1−xN buffers coincides with the [0001] growth direction, leading to a sizeable out-of-plane magnetic anisotropy and opening wide perspectives for perpendicular recording based on nitride-based magnetic nanocrystals.
Structural color originates from the interference of light with periodic structures that feature characteristic length scales on the order of the wavelength of visible light. Long‐range order in photonic structures usually causes iridescence, and increasing disorder renders colors angle‐independent. Random disorder distributes scattering intensity over all wavelengths, producing white in the absence of absorption. Various non‐iridescent, vivid color patterns are found in Sternotomini longhorn beetles. Herein, Sternotomis virescens is investigated, where elytral scales produce a green‐blue color pattern on otherwise black elytra. Combining focused ion beam scanning electron microscopy (FIB‐SEM) tomography, ultra‐small‐angle X‐ray scattering (USAXS), structural modeling, and full‐wave optical simulations, it is found that the color originates from amorphous photonic networks based on sub‐units resembling the I‐WP unit cell, a triply‐periodic minimal surface with body‐centered‐cubic symmetry. This work provides insights into how quasi‐order produces stable colors in S. virescens longhorn beetles, highlights the advantages of volumetric imaging using FIB‐SEM tomography of porous nanostructured materials, and raises interesting questions about the formation mechanisms of amorphous structures in vivo.
structure periodicity, thereby enabling a photonic response across the entire visible spectrum. [1][2][3] Among these engineered systems, photonic pigments are of particular interest, as they offer pure and brilliant coloration free from chemical-or photo-bleaching. Hence, such pigments represent a central goal in the future developments of paints, cosmetics, and displays. [4][5][6][7][8] So far, most efforts to develop structurally colored pigments have been based on confining the self-assembly of colloidal particles [9,10] or liquid crystals [11] in specific geometries. However, significant limitations of synthesizing large quantities of photonic pigments based on these amorphous arrays include the lack of control over incoherent and multiple scattering and the difficulty in producing pigments with distinct colors across the entire visible spectrum. [12] A promising alternative is the 3D confined self-assembly of block copolymers (BCPs) in emulsion droplets, which, in principle, represents a user-friendly and scalable procedure to fabricate polymer-based PhCs with vivid coloration spanning the entire visible spectrum. [13,14] BCPs exhibit rapid assembly kinetics in solution, macroscopic ordering into self-assembled morphologies, tolerance to high loading of functional additives, and the possibility to manipulate the produced coloration simply by tuning the polymer chain length and structure. [15,16] Several efforts employing BCPs focused on fabricating planar multilayer structures that show brilliant but iridescent coloration, [17][18][19][20][21] while more recent studies showed that linear symmetric BCPs can form a concentric lamellar structure (i.e., onion-like microspheres) within spherical confinement in emulsion droplets, resulting in photonic multilayered particles. [22][23][24][25][26] These ordered systems comprise two blocks that form lamellar domains, each having a distinct refractive index, and show strong reflection when Bragg reflection conditions are satisfied, thus holding promise as non-iridescent photonic pigments due to their spherical shape. [15,24] Controlling the optical properties of such photonic pigments generally requires the synthesis of long BCPs whose self-assembly kinetic is slowed by their high molecular weight. Domain spacings beyond 100 nm can be achieved, for example, by using bottle-brush BCPs as their non-linear chain architecture with grafted side chains limits chain entanglement thereby accelerating structural reorganization. [27,28] Alternatively, Creation of color through photonic morphologies manufactured by molecular self-assembly is a promising approach, but the complexity and lack of robustness of the fabrication processes have limited their technical exploitation. Here, it is shown that photonic spheres with full-color tuning across the entire visible spectrum can be readily and reliably achieved by the emulsification of solutions containing a block copolymer (BCP) and two swelling additives. Solvent diffusion out of the emulsion droplets gives rise to 20-150 µm-size...
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