Visualizing Magnetic Structure in 3D Nanoscale Ni-Fe Gyroid Networks.

Arrays of interacting 2D nanomagnets display unprecedented electromagnetic properties via collective effects, demonstrated in artificial spin ices and magnonic crystals. Progress toward 3D magnetic metamaterials is hampered by two challenges: fabricating 3D structures near intrinsic magnetic length scales (sub-100 nm) and visualizing their magnetic configurations. Here, we fabricate and measure nanoscale magnetic gyroids, periodic chiral networks comprising nanowire-like struts forming three-connected vertices. Via block copolymer templating, we produce Ni75Fe25 single-gyroid and double-gyroid (an inversion pair of single-gyroids) nanostructures with a 42 nm unit cell and 11 nm diameter struts, comparable to the exchange length in Ni-Fe. We visualize their magnetization distributions via off-axis electron holography with nanometer spatial resolution and interpret the patterns using finite-element micromagnetic simulations. Our results suggest an intricate, frustrated remanent state which is ferromagnetic but without a unique equilibrium configuration, opening new possibilities for collective phenomena in magnetism, including 3D magnonic crystals and unconventional computing.

Visualization of energy: light dose indicator based on electrochromic gyroid nano-materials.

The typical applications of electrochromic devices do not make use of the charge-dependent, gradual optical response due to their slow voltage-sensitive coloration. However, in this paper we present a design for a reusable, self-powered light dose indicator consisting of a solar cell and a gyroid-structured nickel oxide (NiO) electrochromic display that measures the cumulative charge per se, making use of the efficient voltage-sensitive coloration of gyroid materials. To circumvent the stability issues associated with the standard aqueous electrolyte that is typically accompanied by water splitting and gas evolution, we investigate a novel nano-gyroid NiO electrochromic device based on organic solvents of 1,1,1,3,3,3-hexafluoropropan-2-ol, and room temperature ionic liquid (RTIL) triethylsulfonium bis(trifluoromethylsulfonyl) imide ([SET3][TFSI]) containing lithium bis(trifluoromethylsulfonyl) imide. We show that an effective light dose indicator can be enabled by nano-gyroid NiO with RTIL; this proves to be a reliable device since it does not involve solvent degradation or gas generation.

Efficient electrochromic devices made from 3D nanotubular gyroid networks.

Ion intercalation processes into metal oxide porous materials benefit from a high surface-to-volume ratio, while electronic charge transport requires a continuous network morphology. Detailed control over structure formation on the 10 nm length scale is therefore an effective strategy to enhance performance in electrochromic devices, supercapacitors, and batteries. Here we demonstrate the transformation of nickel patterned in a three-dimensional, highly interconnected, periodic nanomorphology into a self-supporting nickel oxide array with hollow struts. The oxidation of nickel gives rise to the nanoscale Kirkendall effect, which substantially increases the surface area of the NiO gyroid framework, without sacrificing its connectivity. Applicable to a vast range of electroplatable metals, this is a versatile route to high surface area metal oxides/chalcogenides which is especially suitable for various thin film applications. Nanostructured NiO electrodes showed substantially enhanced electrochromic performance, combining fast switching speeds with high coloration contrast.

Polymer crystallization as a tool to pattern hybrid nanostructures: growth of 12 nm ZnO arrays in poly(3-hexylthiophene).

Well-ordered hybrid materials with a 10 nm length scale are highly desired. We make use of the natural length scale (typically 10-15 nm) of the alternating crystalline and amorphous layers that are generally found in semicrystalline polymers to direct the growth of a semiconducting metal oxide. This approach is exemplified with the growth of ZnO within a carboxylic acid end-functionalized poly(3-hexylthiophene) (P3HT-COOH). The metal-oxide precursor vapors diffuse into the amorphous parts of the semicrystalline polymer so that sheets of ZnO up to 0.5 µm in size can be grown. This P3HT-ZnO nanostructure further functions as a donor-acceptor photovoltaic system, with length scales appropriate for charge photogeneration.

A nanostructured electrochromic supercapacitor.

We report the first successful application of an ordered bicontinuous double-gyroid vanadium pentoxide network in an electrochromic supercapacitor. The freestanding vanadia network was fabricated by electrodeposition into a voided block copolymer template that had self-assembled into the double-gyroid morphology. The highly ordered structure with 11.0 nm wide struts and a high specific surface to bulk volume ratio of 161.4 µm(-1) is ideal for fast and efficient lithium ion intercalation/extraction and faradaic surface reactions, which are essential for high energy and high power density electrochemical energy storage devices. Supercapacitors made from such gyroid-structured vanadia electrodes exhibit a high specific capacitance of 155 F g(-1) and show a strong electrochromic color change from green/gray to yellow, indicating the capacitor's charge condition. The nanostructuring approach and utilizing an electrode material that has intrinsic electrochemical color-change properties are concepts that can be readily extended to other electrochromic intercalation compounds.

Luminescent Surfaces with Tailored Angular Emission for Compact Dark-Field Imaging Devices.

Dark-field microscopy is a standard imaging technique widely employed in biology that provides high image contrast for a broad range of unstained specimens1. Unlike bright-field microscopy, it accentuates high spatial frequencies and can therefore be used to emphasize and resolve small features. However, the use of dark-field microscopy for reliable analysis of blood cells, bacteria, algae, and other marine organisms often requires specialized, bulky microscope systems, and expensive additional components, such as dark-field-compatible objectives or condensers2,3. Here, we propose to simplify and downsize dark-field microscopy equipment by generating the high-angle illumination cone required for dark field microscopy directly within the sample substrate. We introduce a luminescent photonic substrate with a controlled angular emission profile and demonstrate its ability to generate high-contrast dark-field images of micrometre-sized living organisms using standard optical microscopy equipment. This new type of substrate forms the basis for miniaturized lab-on-chip dark-field imaging devices, compatible with simple and compact light microscopes.

Gyroidal mesoporous multifunctional nanocomposites via atomic layer deposition.

We demonstrate the preparation of rationally designed, multifunctional, monolithic and periodically ordered mesoporous core-shell nanocomposites with tunable structural characteristics. Three-dimensionally (3D) co-continuous gyroidal mesoporous polymer monoliths are fabricated from a solution-based triblock terpolymer-resol co-assembly and used as the functional templates for the fabrication of free-standing core-shell carbon-titania composites using atomic layer deposition (ALD). The deposition depth into the torturous gyroidal nanonetwork is investigated as a function of ALD conditions and the resulting composites are submitted to different thermal treatments. Results suggest that ALD can homogenously coat mesoporous templates with well defined pore sizes below 50 nm and thicknesses above 10 µm. Structural tunability like titania shell thickness and pore size control is demonstrated. The ordered nanocomposites exhibit triple functionality; a 3D continuous conductive carbon core that is coated with a crystalline titania shell that in turn is in contact with a 3D continuous mesopore network in a compact monolithic architecture. This materials design is of interest for applications including energy conversion and storage. Gyroidal mesoporous titania monoliths can be obtained through simultaneous titania crystallization and template removal in air.

Labyrinth-induced faceted electrochemical growth.

A path-length bias of nucleated electrochemical growth in a 3D periodic nano-maze is found to cause facet formation of an intrinsically isotropic material in a porous self-assembled gyroid network. This is the first report of faceted electrochemical growth that is not based on the crystallographic order of the constituent building blocks, but rather reflects the symmetry of the template in which the material is synthesized.

Mechanically strong, fluorescent hydrogels from zwitterionic, fully π-conjugated polymers.

Mechanically strong supramolecular hydrogels (up to 98.9% water content) were obtained by the combination of a rigid, fully π-conjugated polymer backbone and zwitterionic side chains. The gels were characterized by SAXS, SEM and rheology measurements and are fluorescent, stimuli responsive (temperature, salts) and bind DNA.

RYB tri-colour electrochromism based on a molecular cobaloxime.

The three oxidation states of Co in a molecular cobaloxime were used to realise an electrochromic device displaying the red, yellow, blue (RYB) set of subtractive primary colours. A facile method for the lithographic patterning of a several micrometre thick indium tin oxide (ITO) mesoporous layer was developed, which served as the scaffold for cobaloxime adsorption.

Enhanced electrochromism in gyroid-structured vanadium pentoxide.

Manufacturing V(2)O(5) in a 3D periodic highly interconnected gyroid structure on the 10 nm length scale is shown to lead to a significant electrochromic performance enhancement. The structured devices surpass previous inorganic electrochromic materials in all relevant parameters: the switching speed, coloration contrast, and composite coloration efficiency. In particular, the 85 ms switching speed lies within a factor of two of video rate. Enhanced ion intercalation into the gyroid morphology can be extended to other transition-metal oxides and is therefore promising for lithium ion batteries, supercapacitors, and sensors.

Mimicking the colourful wing scale structure of the Papilio blumei butterfly.

The brightest and most vivid colours in nature arise from the interaction of light with surfaces that exhibit periodic structure on the micro- and nanoscale. In the wings of butterflies, for example, a combination of multilayer interference, optical gratings, photonic crystals and other optical structures gives rise to complex colour mixing. Although the physics of structural colours is well understood, it remains a challenge to create artificial replicas of natural photonic structures. Here we use a combination of layer deposition techniques, including colloidal self-assembly, sputtering and atomic layer deposition, to fabricate photonic structures that mimic the colour mixing effect found on the wings of the Indonesian butterfly Papilio blumei. We also show that a conceptual variation to the natural structure leads to enhanced optical properties. Our approach offers improved efficiency, versatility and scalability compared with previous approaches.