Advanced Materials

Template-synthesized V₂O₅ nanostructured electrodes (see Figure and cover) are used as tools for fundamental investigations into the poor low-temperature performance of Li-ion batteries. The electrodes consisted of nanofibers of V₂O₅, and by controlling the dimensions of the nanofibers it has been determined that the rate-limiting factor at low temperatures is the concentration polarization of the Li ion in the electrode material.

A thin-film, organic solid-state laser operating in the ultraviolet wavelength region is fabricated using a novel spiro-linked material as an active organic layer in an optically pumped distributed feedback (DFB) structure. The laser could be tuned between 377.7 nm and 395 nm by varying the grating period of the substrate and was utilized as the excitation source for solutions containing biomarker fluorescent dyes (see Figure and inside cover).

Single-walled carbon nanotubes are now considered chemical reagents in their own right. Understanding the reactivity of carbon nanotubes will lead to manipulation of their unique properties in a predictable manner. In this review, reactions leading to functionalization of carbon nanotubes at their ends, at defect sites, and along their sidewalls are discussed with the goal of creating functional nanomaterials with possible device applications and of generating nanoscale hierarchical architectures and assemblies.

A thin-film, organic solid-state laser operating in the ultraviolet wavelength region is fabricated using a novel spiro-linked material as an active organic layer in an optically pumped distributed feedback (DFB) structure. The laser could be tuned between 377.7 nm and 395 nm by varying the grating period of the substrate and was utilized as the excitation source for solutions containing biomarker fluorescent dyes (see Figure and inside cover).

Bright, balanced white-light electroluminescence has been achieved from a single active oligothiophene compound. White light is created by the superposition of a broad blue–green-light emission originating from the single molecule and a red-shifted narrow peak due to dimer formation. These results open the way to the fabrication of novel, low-cost white-light-emitting devices with a single molecular material as the active compound.

Ruthenium-based metathesis catalysts have been successfully covalently bound to a thermal oxide layer on a Si(100) wafer. Selective inactivation of the catalyst is achieved via exposure to UV light using standard photolithographic techniques. Subsequent exposure of the wafer to a suitable monomer results in the formation of a patterned polymeric film that is covalently attached to the oxide layer (see Figure).

Three-dimensional nanoarchitectures (see Figure) are formed by the oriented aggregation of CuO nanoparticles. One-dimensional orientation in the early stages of aggregation (in the [001] plane) of CuO nanoparticles is followed by formation of single-crystalline nanostructures consisting of hundreds of oriented nanoparticles.

Gyroidal cubic Ia3d silica monoliths (see Figure) with controlled pores of 8–10 nm diameter, thick-walled framework up to 17 nm, and highly uniform mesoporosity have been fabricated using a simple strategy. Such structural features are likely to expand the industrial applications of these monoliths.

Ordered, mesoporous cobalt oxide was synthesized via a nanocasting pathway from organically modified large-pore Ia3d silica. A replica structure could be obtained, which shows weak magnetic ordering at low temperatures due to the small size of the individual Co₃O₄ domains forming the mesostructure.

Silicon nanowire arrays on silicon substrates can be synthesized with precise orientation depending on the crystal orientation of the substrate using a vapor–liquid–solid epitaxial growth mechanism. The projections of the as-grown arrays form rectangular networks on silicon (100) substrates (see Figure), parallel straight lines on silicon (110) substrates, and triangular networks on silicon (111) substrates.

Titania foams (see Figure) can be produced using a non-static air–liquid foaming sol–gel process where nitrogen is bubbled through a mixture of a surfactant and a sol–gel precursor. Either anatase or rutile phase mesoporous titania foams are produced upon thermal treatment. Macroscopic cell morphologies can be tuned by changing the air-to-liquid-foam ratios and the size of the nitrogen bubbles, while wall topologies can be varied by changing surfactant.

An organic hybrid planar-mixed molecular heterojunction photovoltaic cell, whose photoactive region consists of a mixed layer of donor and acceptor molecules sandwiched between homogeneous donor and acceptor layers, is demonstrated. A power conversion efficiency of (5.0 ± 0.3) % under 1 sun AM1.5G solar illumination is achieved. The cell exhibits a low resistance to charge transport and a high exciton-diffusion efficiency.

Metallofullerene-based nanowire and nanotube arrays are fabricated for the first time using a technique that allows the diameter, length, and morphology of the non-crystalline Sc@C₈₂ nanostructures to be controlled by adjusting the experimental conditions. The Figure shows the geometrical structure of Sc@C₈₂.

Ordered wood cellular structures are used for the synthesis of hierarchical SiC via mineralization with silica followed by carbothermal reduction in argon.

Thin graphite nanoplatelets synthesized by an intercalation/exfoliation process are incorporated into a polymer fiber matrix by an electrospinning process, creating ultrafine nanocomposite fibrils (see Figure). Uniform nanofibers of average diameter 300 nm show a modest increase in thermal stability with increasing weight percentage of graphite nanoplatelets. The mechanical properties of the fibrils are examined, and the normalized Young's modulus is found to increase two-fold upon addition of 4 wt.-% graphite nanoplatelets.

Highly selective molecular sieve composite membranes have been prepared using dispersions of porous coordination compounds confined within amorphous glassy polysulfone. This new approach is a promising method for fabricating organic molecular sieve composite membranes with tailor-made structures and pore sizes. The organic molecular sieves exhibit enhanced selectivity for H₂ over CH₄ (approximately 200 at 5 wt.-% loading).

The toughness of the major ampullate silk of spiders is shown to increase at low temperatures, unlike synthetic fibers. This temperature dependence of the mechanical properties of spider silk, together with other remarkable properties, demonstrates the potential usefulness of such a super-fiber in harsh environments. The Figure shows a single fiber of Nephila edulis spider silk fractured in liquid nitrogen.

Introducing carbon nanotubes into zirconia is shown to drastically reduce grain boundary sliding and consequently mechanical loss at high temperatures. The nanotubes are observed at the grain boundaries by high-resolution transmission electron microscopy (see Figure) and are related to the reduction of superplastic flow through the boundaries, which should improve creep resistance.

Strong near-infrared (NIR) electroluminescent emission at wavelengths used in telecommunication optical fibers was produced from rare-earth-doped GaN semiconductors in thin-metal-film/semiconductor/insulator/metal structures (see Figure). Strong near-infrared emission at wavelengths of 800 nm, 1082 nm, and 1550 nm has been demonstrated at room temperature with the trivalent thulium-, neodymium-, or erbium-doped GaN devices, respectively.

A polymer-stabilized liquid-crystal blue phase with a Kerr constant 170 times larger than that of nitrobenzene is shown to be capable of microsecond electro-optical switching over a wide temperature range in flat Kerr cells, without need for additional surface processing to generate alignment. The Figure shows a polarizing optical micrograph, under crossed polarizers, of an in-plane switched Kerr cell containing the polymer-stabilized blue phase.

Mesoporous solid superacid molecular sieve films have been prepared (see Figure) and used as photocatalysts. The new class of superacid possesses large surface area, uniform pore size, and accessible 3D mesoporous architecture. These are attractive properties for catalytic or photocatalytic applications.

Monodisperse amorphous-selenium spherical colloids (see Figure) have been synthesized in large quantities by reducing selenious acid with hydrazine in ethylene glycol. The diameters of these colloids could be controlled in the range of 90–420 nm by adjusting the molar ratio between selenious acid and hydrazine. The as-obtained colloids could be readily crystallized into long-range-ordered three-dimensional lattices with well-defined Bragg-diffraction peaks.

Interlayer surfaces of layered double hydroxide (LDH) have been functionalized with amine moieties by condensation between the hydroxyl groups and (3-aminopropyl)triethoxysilane (APS) molecules via the covalent oxane bonds M-O-Si (M=Zn and Cr) (see Figure). Since the galleries of the modified LDHs have a hydrophobic field, various functional molecules such as enzymes, catalysts, and organic molecules can be incorporated between the LDH layers.

Hierarchical single-crystalline AlN nanocombs were self-assembled through a chemical-vapor transport and condensation process. The wurtzite AlN nanoarchitectures are composed of core stems along the <0001> direction and comb-like nanotips growing perpendicularly out from both sides of the stems along the <01�10> direction (see Figure). Low-threshold field emission could be obtained from the nanostructures, with potential applications in field-emission displays and microvacuum tubes for microwave amplifiers.

The use of nanoporous alumina membranes to control the diameter of silicon nanowires synthesized by vapor–liquid–solid growth is demonstrated. An increase in nanowire diameter was observed when the nanowires grew out from the top surface of the membrane (see Figure). The diameter increase was attributed to a change in the shape of the Au–Si liquid alloy when the nanowires emerged from the membrane surface.

A closed-loop sol–gel–sol transition is reported for aqueous solutions of a multiblock polyoxamer. The combination of ionizable carboxylic acid groups and water-soluble poly(ethylene glycol) units balance each other to form a gel phase between pH 4 and 6 (see Figure).

A novel method for synthesizing ordered macroporous polymers is presented. Simply irradiating an electron beam onto colloidal polymer crystals generates regularly ordered macroporous polymers. No post-treatment is required for the formation of porous polymers. In addition, arbitrarily shaped two- and three-dimensional macroporous polymers of tunable pore sizes are fabricated via the electron-irradiation method.

Template-synthesized V₂O₅ nanostructured electrodes (see Figure and cover) are used as tools for fundamental investigations into the poor low-temperature performance of Li-ion batteries. The electrodes consisted of nanofibers of V₂O₅, and by controlling the dimensions of the nanofibers it has been determined that the rate-limiting factor at low temperatures is the concentration polarization of the Li ion in the electrode material.