Advanced Materials

Modification of the surface chemistry of nanocrystalline VN yields a new class of supercapacitors that deliver an impressive specific capacitance. The creation of surface nanolayers of VO_x (poor electronic conductivity) on the electronically conductive nanocrystalline VN shown in the figure and on the cover gives rise to a series of reversible redox reactions that are thought to be responsible for the high capacitance. Application of the concept to other transition metals is expected to broaden the scope of supercapacitor materials.

Trilayered ceramic–metal–polymer thermally sensitive microcantilevers with the topmost polymer nanocomposite layers reinforced with carbon nanotubes and metal nanoparticles are described (see figure and inside cover). These trilayered microcantilevers show dramatically enhanced thermal sensitivity and could be used in next-generation uncooled IR sensor arrays with thermal and spatial resolution many times higher than currently available sensors.

Enzymes catalyze the growth of metallic nanoparticles (NPs, see figure). The enzyme-mediated growth of metallic NPs provides a general means to follow biocatalyzed transformations and a route to optical sensors for substrates such as glucose, 3,4,dihydroxy-L-phenylalamine, L-DOPA, alcohols, lactate, or nerve-gas analogs. Dip-pen nanolithography can be used to pattern enzymes on Si surfaces that template growth of nanowires consisting of different metals.

The poly(3,4-dioxypyrrole) family of conducting and electroactive polymers may not have received as much attention to date as their poly(3,4-ethylenedioxythiophene) cousins, but that may be about to change. The authors review the synthesis and properties of these versatile systems, demonstrating that these materials may be the final piece in the conjugated polymer puzzle, combining a large bandgap and a low oxidation potential.

Amine-active N-hydroxysuccinimide-terminated alkyl thiol templates are generated using parallel dip-pen nanolithography (DPN) and are used to covalently couple protein A/G. The protein arrays generated (see figure) are used to capture antibodies through affinity binding, while preserving their biological recognition properties. The versatility of the parallel DPN method for making many similar structures in a relatively high-throughput manner (14 000 dots in 10 min) is described.

Ice-segregation-induced self- assembly is a versatile and biocompatible process that facilitates the preparation of hierarchical biohybrid materials exhibiting a very sophisticated structure with up to six levels of space organization: the ternary structure of esterase, the PVA domains surrounding esterase, the silica cages entrapping the PVA domains, and the macroporous structure resulting from ice segregation (see figure). The resulting materials are attractive for biomedical and sensor applications.

Nanodots are produced over large areas with controlled size and density in a new single-step, low-cost process. This process is based on surfactant-made multilamellar vesicles that serve as nanovectors. Copper ions are incorporated inside vesicles by chemical complexation. Vesicles are attracted under a DC electric field towards an electrode, where they are reduced to produce the metal nanodots shown in the figure.

Controlled self-assembly of colloidal nanoparticles onto an electrically nanopatterned electret film is presented (see figure; EFM: electrostatic force microscopy). An unprecedented reolution of 30 nm is achieved for both charge patterning and nanoparticle assembly. Furthermore, only a close-packed monolayer of nanoparticles is assembled, allowing better structural control and the possibility of forming hierarchical nanoparticle structures.

A planar microfluidic system produces monodisperse biphasic droplets that are subsequently polymerized to form bicolored Janus microspheres (see figure). Engineered spheres have a dipolar character and can be electrically actuated for application in a particle-based electronic paper display. A scale-up approach using multiple-channel integration on a chip is also described, which achieves high throughput for practical material production.

Trilayered ceramic–metal–polymer thermally sensitive microcantilevers with the topmost polymer nanocomposite layers reinforced with carbon nanotubes and metal nanoparticles are described (see figure and inside cover). These trilayered microcantilevers show dramatically enhanced thermal sensitivity and could be used in next-generation uncooled IR sensor arrays with thermal and spatial resolution many times higher than currently available sensors.

A new, simple, versatile, and easily scaleable one-step preparation method – an impregnated carbon procedure (ICP) – is proposed to produce highly dispersed active phases on supports of tailored porosity (see scheme; AC: activated carbon). This one-step synthesis unites simplicity of preparation with outstanding properties of the final catalysts and offers an interesting pathway towards industrial-catalyst manufacture.

Absorption spectroscopy of stretch-aligned single-walled carbon nanotube (SWNT)/polymer composite films from the terahertz through the visible region of the electromagnetic spectrum reveal that the peak centered near 100 cm^–1 is highly polarized along the tube axis (see figure). This result provides new information on the morphology-dependent low-energy response of SWNTs, and may predict application of SWNTs in the terahertz region.

The p-type Ag(Pb_1–ySn_y)_mSbTe_2+m materials shown in the figure demonstrate promising thermoelectric properties that are controlled with the parameters y and m. They can reach a maximum figure of merit of ∼ 1.45 at 630 K. This surpasses the figure of merit of the present state-of-the-art p-type materials such as TAGS (1.2) and PbTe (0.8) at comparable temperatures.

Uniform cubic, octahedral, and star-like copper sulfide mesocages with single-crystalline shells (see figure) are synthesized by the sulfidation of various shape-controlled Cu₂O crystals into Cu₂O/Cu_xS core/shell structures, followed by the removal of the inner Cu₂O cores. Potential applications of these materials in solar energy conversion, optics, and sensors are envisaged.

Modification of the surface chemistry of nanocrystalline VN yields a new class of supercapacitors that deliver an impressive specific capacitance. The creation of surface nanolayers of VO_x (poor electronic conductivity) on the electronically conductive nanocrystalline VN shown in the figure and on the cover gives rise to a series of reversible redox reactions that are thought to be responsible for the high capacitance. Application of the concept to other transition metals is expected to broaden the scope of supercapacitor materials.

A new type of 2D defect within artificial opals is presented. Sequential deposition of a colloidal crystal by convective self-assembly and a slab of oxide nanocrystals by spin-coating gives rise to heterostructures (as shown in the figure). The nanocrystalline layer behaves as an optical dopant, opening transmission windows within the forbidden frequency interval of the lattice, as can be seen in the superimposed transmittance spectra.

Transparent ZnS/polymer bulk nanocomposites with high particle contents are prepared via γ-ray irradiation initiated polymerization. This strategy involves the design and tailoring of the surface of the nanoparticles and choice of the monomer as well as the selection of the polymerization route. The figure shows a TEM image of a bulk nanocomposite containing mercaptoethanol-capped ZnS with a particle content of 20 wt %.

Water-soluble single-walled carbon nanotubes are readily prepared by treating oxidatively purified nanotubes with molten urea. Evidence is provided for appended amido and ureido groups in the product (see figure), which can be further modified by condensation reactions if p-anisaldehyde is added during the process.

The most favorable dopants for solid-state hydrogen-storage materials are still considered to be compounds of titanium in spite of intensive research on other catalysts. Here, we show that NaAlH₄ doped with ScCl₃ is a highly efficient dopant, both with respect to storage capacity and kinetics: 2 mol % ScCl₃ exhibits a nearly theoretical hydrogen-storage capacity (4.9 wt %, see graph). Other rare-earth metal trichlorides are also investigated.

A mesoscopic bilayer TiO₂ film used as an electron collector in conjunction with an acetonitrile- or ionic liquid-based electrolyte greatly improves the performance of dye-sensitized solar cells (see figure). The thickness of the nanocrystalline TiO₂ film affects the photovoltaic characteristics, particularly for the ionic-liquid-based electrolyte, owing to a limitation of the photocurrent by the diffusion of I₃^– ions.

Chiral bis-alkoxysilanes are used as building blocks for the synthesis of new periodically ordered mesoporous organosilica materials (see figure). A bis-alkoxysilane molecule with a chiral group as a bridging organic ligand is prepared via enantioselective organometallic catalysis using a ruthenium catalyst with 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene as a ligand. The synergistic co-assembly is then used to prepare a high-surface-area mesoporous material with an average pore size of about 3 nm.

Ultrafine nanocrystalline bulk material of pure rare-earth metals has been prepared using a combination of inert gas condensation and spark plasma sintering (see figure). Some of the bulk properties such as the microhardness and specific heat capacity are remarkably improved compared to the conventional polycrystalline material. This new preparation technique enables the preparation and study of a variety of other nanostructured metal materials.

Blue electrophosphorescence in organic light-emitting diodes (OLEDs) is enhanced by the use of 3,6-bis(triphenylsilyl)carbazole (see figure). This carbazole derivative with sterically bulky and large-gap triphenylsilyl groups is an electrochemically and morphologically stable efficient host material for blue electrophosphorescence. When utilized in OLEDs, high efficiencies of up to 16 %, 30.6 cd A^–1, and 26.7 lm W^–1 are achieved.