Advanced Materials

Isolation, mass production, and characterization in solution and in the solid state of the facial stereoisomer of tris(quinolin-8-olato)aluminum(III) (Alq₃) is reported. A phase- transformation diagram shows how to selectively produce the two blue-emitting polymorphs of the fac isomer (γ- and δ-Alq₃; see Figure) via a solid-to-solid reaction, opening the route to the development of blue-light-emitting Alq₃-based OLEDs.

Exploiting the self-assembling properties of liquid crystals, large-scale spontaneous alignment of single- and multi-walled carbon nanotubes induced by elastic interactions with the nematic LC matrix is demonstrated (see Figure). Collective reorientation processes of the liquid crystal are further used to reversibly manipulate the alignment direction of the dispersed nanotubes, as evidenced by conductivity measurements.

The iron(II) complex [Fe(3C16-L)₂(NCS)₂] (see Figure) exhibits three coexisting physical properties due to its geometric flexibility. It shows liquid-crystal behavior in the temperature range 345–400 K, spin-crossover behavior (T_1/2 = 217 K) between high-spin and low-spin states, and photoinduced spin transition (T(LIESST; light-induced excited spin state trapping) = 61 K) from a low-spin state to a metastable high-spin state.

Highly organized monolayer and multilayer films of titania nanosheets have been fabricated via electrostatic self-assembly of large-sized sheets and subsequent ultrasonic treatment. Overlapped or crumpled portions of the nanosheets in an as-deposited film are effectively trimmed upon ultrasonication in a tetrabutylammonium hydroxide solution, resulting in neat tiling of the nanosheets without gaps and extensive overlaps (see Figure).

The use of organic–organometallic block copolymers as catalyst precursors for templated carbon nanotube (CNT) growth (see Figure) is demonstrated for the first time. A thin film of block copolymer was treated with O₂ plasma to produce ordered iron-containing catalyst nanoparticle arrays, which are efficient catalysts for CNT growth. This approach allows control of catalyst domain size and spacing by tailoring block copolymer composition.

Grain boundaries (GBs) participate in the photovoltaic energy conversion process in polycrystalline solar cells as efficient photocurrent collectors and transporters, as shown by high- resolution characterization of CdTe GBs in CdTe/CdS cells (see Figure). This suggests that structural defects can be advantageous for device performance, if properly designed, even in devices whose operation is based on physics of ideal, perfect solids.

Continuous mesoporous carbon thin films (see Figure) have been synthesized through direct carbonization of sucrose/silica nanocomposite films and subsequent removal of the silica to create a mesoporous carbon network. This method provides a simple and efficient method to synthesize continuous, high surface area and pore volume mesoporous carbon thin films with uniform-sized and interconnected pore channels.

Hollow spheres of well-ordered mesoporous carbon (see Figure) may be obtained via a simple chemical vapor deposition route, which utilizes mesoporous silica SBA-15 as a solid template and suitable organic compounds (e.g., styrene) as the carbon source.

Good quality CaCu₃Ti₄O₁₂ giant dielectric constant films have been prepared by metal–organic chemical vapor deposition on LaAlO₃ (001) substrates, using a multimetal molten precursor source. The growth of the oxide layer by a two-step in-situ process, namely deposition of an amorphous matrix and the consequent in-situ annealing, has resulted in epitaxial (00l) CaCu₃Ti₄O₁₂ thin films.

Single-walled carbon nanotubes have been functionalized with derivatized porphyrins (see Figure). The photoexcited state properties of the nanotube-tethered porphyrin moieties are investigated via steady-state and time-resolved fluorescence methods. Intramolecular energy-transfer quenching of porphyrin fluorescence by the tethered nanotube occurs in the sample with a longer tether, but no fluorescence quenching is observed in the sample with a shorter tether.

A new class of porous oxide interconnects with a regularly perforated SiN support structure is presented here. The method is demonstrated by constructing γ-alumina, MCM-48 silica (see Figure), and amorphous titania interconnects. Ionic transport through the gate is established by externally varying the potential difference across the interconnects, which allows cationic, anionic, or no transport, depending on the magnitude and sign of the applied potential difference.

A soft-template method for the controlled synthesis of hollow beads using laser- assisted growth with ethanol droplets as the soft template is proposed (see Figure). Single-crystalline ZnO polyhedral hollow beads in the range of 200–500 nm have been successfully synthesized.

The synthesis and solution behavior of a series of β-sheet fibril-forming peptide–polymers is described. Several block copolymer architectures are explored, with various lengths and arrangements of the peptide and polymer blocks. One peptide–polymer, an 11-amino acid peptide conjugated to a polydisperse poly(ethylene glycol) chain, has the ability to form uncommonly regular, aligned, and minimally aggregated β-sheet fibrils (see Figure).

A one-step process for the preparation of porous polymer membranes (see Figure) by spreading mixtures of particles and organic liquid onto a water surface, followed by solidification of the liquid, removal of the particles, and transfer to desired supports, is reported (see Figure). The thickness of the porous membranes can be tuned from a single layer to more than ten layers.

The coiled-coil-based assembly of gold nanoparticles (see Figure and cover) is demonstrated. Control over the assembly and disassembly of nanostructures is achieved under mild conditions (near-neutral pH and ambient temperature). The flexibility in design afforded by varying the peptide sequence to produce coiled coils with different stabilities is also highlighted by the generation of more stable binary nanoparticle systems with controlled spacing and architecture.

A cathode material for rechargeable lithium batteries is one possible application for the birnessite-related layered MnO₂ nanobelts (see Figure) reported here. A simple hydrothermal procedure is described that results in high-purity, long (up to several tens of micrometers) nanobelts with narrow size dispersion (width 5–15 nm) that are usually self-assembled into bundles.

Fluorescence is reversibly photoregulated in high-density random copolymers constructed from photochromic phenoxynaphthacenequinones and porphyrins (see Figure) using ring-opening metathesis polymerization. Alternating irradiation of the polymers with ultraviolet and visible light toggles the photochromic components between two isomers differing in their ability to act as electron-acceptors in a photoinduced electron-transfer process.

The most desirable features of PbS nanocrystal (NC) synthesis are demonstrated in a new one-stage route: Aqueous synthesis to enable compatibility with biological assays and polymer–nanocrystal device fabrication; simplicity; non-toxic solvents; and moderate reaction temperatures. The NCs produced (see Figure) have stable, narrow fluorescence peaks that are size-tunable in the near-IR spectral range and a high quantum yield.

Coaxial cubic-aluminum-nitride–boron-nitride composite nanotubes have been synthesized via a template-free and catalyst-free two-stage route. The synthesized nanotubes have a uniform outer diameter of 50 nm and wall thickness of 15 nm, with a 2–3 nm thick BN coating. A vapor–solid (VS) mechanism is proposed for their growth, and insight is provided into the atomistic mechanism of coaxial nanotube growth.

Hollow polymeric nanospheres (see Figure) are directly obtained by polymerization of acrylic acid monomers inside micelles comprised of a biopolymer with amino groups, (chitosan) and an organic monomer with carboxylic group (acrylic acid). In this approach, the nanospheres form in aqueous solution without the aid of surfactant, organic solvent, precursors of block and graft copolymers, templating cores, or emulsion phases.