Advanced Functional Materials

A one step in situ method, developed to generate monodisperse ordered mesoporous silica microspheres with controllable size and surface morphology, is described by I. Lee et al. on page 4014. It combines generation of uniform precursor droplets in a microfluidic device and subsequent self-assembly induced by diffusion of solvent in situ in the microfluidic channel. The cover image shows the very distinctive surface morphology of the microspheres, with hierarchical internal nanostructures.

Bai Yang and co-workers report a novel method to fabricate nanoring structures from a wide variety of materials on page 4036. Large-area arrays of polystyrene (PS), magnetite, Au, Si, Fe₃O₄ nanoparticle/PS, and Au/PS double-layer composite nanorings are successfully prepared. Most of the nanorings fabricated by this method can be lifted off the substrate, resulting in free-standing nanorings, which show interesting and important applications as magnetic scaffolds for tissue engineering, self-assembly building blocks, ultra-sensitive sensors, or as imaging agents.

The deliberate introduction of impurity ions provides a route to altering the physical properties of semiconductor nanostructures. This article describes recent advances in doping one of the most widely studied semiconductor nanostructures, CdSe quantum dots, with one of the most widely studied impurities, Mn²⁺, and summarizes the major new physical properties observed in parallel colloidal and self-assembled materials.

Functional perovskite materials have a wide spectrum of attractive properties. They can be grown as epitaxial films, multilayers, superlattices, and well-ordered arrays of nanoislands, allowing for investigations of preparation-microstructure-property relations and for a wide variation of properties. An overview of the authors' recent work is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites.

Charge trapping in pentacene transistors prepared by vacuum sublimation is studied by scanning Kelvin probe microscopy. It is shown that trapped charges are preferentially located in the thin intergrain regions, where only an incomplete accumulation layer is formed. These charges may reside in pentacene molecules not belonging to well-ordered molecular crystallites but constituting electronic defects situated at the edges of the nucleation sites.

A facile strategy of solvent-evaporation-induced coating and self-assembly for the mass production of ordered mesoporous carbon-silica composite monoliths with macroporous architecture is demonstrated using commercial polyol-based polyurethane foam as a sacrificial scaffold.

Deep-blue light-emitting organic materials are still rare. Here, deep-blue fluorescent emitters based on phenylquinoline–carbazole derivatives are synthesized for organic light-emitting diodes (OLEDs). Multilayered OLEDs are fabricated with these materials as the emitting layer (non-doped OLEDs) or as the host for BCzVBi dopant (doped OLEDs). The devices exhibit deep-blue emission with high efficiencies (see figure).

Dual-functional probes: A new class of water-soluble, fluorescent, magnetic quantum dot–magnetoferritin (QD–MFt) bioconjugates is prepared. The nanostructures are patterned mainly as dimer particles as characterized by high-angle annular dark-field scanning electon microscopy and electron energy loss spectroscopy. Magnetic and fluorescent properties (see figure) of both nanoblocks remain in the final nanostructure.

A new class of superabsorbent polymers that swell and absorb various organic solvents, from low-dielectric media to highly polar solvents, by introduction of dissociable ionic groups and variation of the alkyl groups of the acrylate co-monomers is shown (see figure). By varying polarity of the neutral monomer in these polyelectrolyte gels, gels can be designed that absorb solvents of nearly any polarity.

A superior anode material for lithium-ion batteries is realized by introducing carbon coatings on the surface of iron oxide nanospindles. The carbon coating layers not only enhance the electronic conductivity of the electrode materials, but also lead to stabilized solid electrolyte interphase films. As a result, the as-prepared carbon-coated Fe₃O₄ nanospindles exhibit very high reversible capacity, significantly improved cycling performance, and high rate performance compared with commercial magnetite particles and bare hematite nanospindles.

The electronic transport properties of perylene-substituted polyisocyanopeptides are studied using thin-film transistors. Carrier mobilities of order 10⁻³ cm² V⁻¹ s⁻¹ at 350 K are obtained, as limited by inter-chain transport processes. The influence of π–π interactions on the electronic and the electronic-transport properties of these systems are further investigated using Kelvin probe force microscopy and a theoretical study of electronic coupling.

P3HT/PCBM-based polymer solar cells with surface relief gratings (SRGs) are studied as an efficient light-trapping scheme with a view to increasing the overall performance of the organic solar cell (OSC). Power conversion efficiencies of OSCs with 1D and 2D gratings increase primarily because of the enhancement of short-circuit current density (see figure), indicating that SRGs induce further photon absorption in active layers by increasing the optical path length and light trapping.

Hole-injection in single-layer devices and polymer light-emitting diodes is controlled by modifying the surface of the ITO anode with unique self-assembled monolayers. Increased current density is achieved through careful molecular design.

Novel materials can be synthesized by emulating the self-assembly strategy of nature. Using the principle of biomimicry, a novel strategy for synthesizing de novo cell interactive templates is demonstrated, which can also promote template-driven mineralization of crystalline apatite for hard tissue regeneration.

The aggregation behaviors of amphiphilicr resorcinarene are studied and those structures critical for the self-assembly of resorcinarene into microtubes in aqueous media are revealed. By utilizing the obtained microtubes as templates, a gold/organic microtubular composite is successfully prepared.

A three-dimensional ordered nanoporous SiO₂ film is prepared on a glass slide and functionalized with streptavidin. Based on the recognition of streptavidin to biotin-labeled antibody a novel immunosensor is further constructed for highly efficient chemiluminescent immunosensing, which shows excellent performance such as fast immunoreaction, wide dynamic range, high sensitivity, and good reproducibility and stability.

When using molecular monolayers to modify charge injection into electronic devices, their dielectric constant plays a crucial role. It is shown that the effective dielectric constant needed in the Helmholtz equation (to describe, for example, induced work function changes) and the “true” dielectric constant of a molecular monolayer (reflecting its response to a uniform external electric field) are two clearly distinct quantities; their relationship is investigated by quantum-mechanical calculations and explained on the basis of electrostatic considerations.

Hybrid silica nanotubes with uniform and precise pore sizes are prepared. These hybrid nanotubes show selective functionality in the inner channel and outer surface. They can also be converted into 1D periodic nanohole arrays by calcination.

Monodisperse ordered mesoporous silica microspheres are prepared using a one-step in situ method in a microfluidic device, termed as microfluidic diffusion-induced self-assembly (DISA). The surface morphology and particle size of the silica microspheres (see figure) are systematically controlled by adjusting the fluidic conditions.

Carbosiloxane porous thin films are prepared from methylene-bridged polycarbosilane and triblock copolymer porogen using the sol–gel process. The elastic modulus values measured for these materials substantially exceed those of traditional porous organosilicates of identical dielectric constant. These results confirm that silicates containing carbon bridging groups belong to a different class of materials when considering the mechanical properties of porous low-k dielectrics.

The improved short circuit current of P3HT/PCBM solar cells with annealing is examined using transient absorption spectroscopy. A two-fold increase in the polaron yield is observed, correlated with a decrease in P3HT ionization potential. This agrees with a model in which efficient dissociation of the bound radical pair is dependent upon it being thermally hot, enabling it to overcome its coulombic binding energy.

Fe₃O₄ nanoparticle/polystyrene composite nanorings are prepared based on a colloidal-crystal-template strategy. Height and magnetic/atomic force microscopy images of the composite nanoring arrays corroborate the magnetism of the nanorings. This kind of nanoring array can be released from the supporting substrate, forming free-standing nanoparticle/PS nanoring structures as shown by transmission electron microscopy (see image).