Advanced Materials

Manipulation of molecules with nanoscale accuracy is important in nanotechnology. In the novel process reported here, electrostatic interactions direct the deposition of polycationic Mn₁₂ single-molecule magnets into a predefined region of a 1 cm² silicon chip with 40 nm accuracy (see figure). The process is based on the integration of local oxidation nanolithography with surface functionalization of the Si substrate.

Efficient excimer emission is demonstrated in white organic light-emitting diodes (see figure) based on platinum(II)[2-(4′,6′-difluorophenyl)pyridinato-N, C^2′)](2,4-pentanedionato) utilized in devices incorporating the novel host material 2,6-Bis(N-carbazolyl)pyridine (26mCPy). External quantum (power) efficiencies of 15.9 % (12.6 lm W^–1) are realized at 500 cd m^–2.

Extreme care has to be taken when extrapolating optical properties of conjugated polymers via the oligomer approach and when comparing theoretical and experimental data. This Review introduces conceptual strategies for the correct determination of optical transitions and relevant extrapolation procedures. The impact of conformational, substitution, solvent, and solid-state effects is discussed.

A chalcogenide glass and a polyamideimide polymer are used to fabricate freestanding membranes (see figure). The membranes are less than 3 μm thick but provide a near-unity omnidirectional reflection band in the near infrared. Optomechanical tuning of the filter response and manual construction of microcavities are demonstrated.

Efficient excimer emission is demonstrated in white organic light-emitting diodes (see figure) based on platinum(II)[2-(4′,6′-difluorophenyl)pyridinato-N, C^2′)](2,4-pentanedionato) utilized in devices incorporating the novel host material 2,6-Bis(N-carbazolyl)pyridine (26mCPy). External quantum (power) efficiencies of 15.9 % (12.6 lm W^–1) are realized at 500 cd m^–2.

Control of the morphology of ceria nanocrystals is achieved through a simple, rapid, and green chemistry approach by tuning the reaction of organic ligand molecules with specific crystallographic planes of fluorite cubic ceria crystal during supercritical hydrothermal synthesis, as shown in the figure. It provides a novel self-assembly approach for producing metal oxide nanocrystals with uniform size and well-defined shape.

High-quality polymeric 3D spiral photonic crystals are fabricated via direct laser writing. Polarization stop bands for circularly polarized light are observed, leading to 5 % transmittance for the circular light polarization, which matches the handedness of the helix, and 95 % for the other polarization (see figure). The experimental results are in good agreement with theoretical calculations.

A chiral, nonracemic ester with a bent-core molecular architecture (see figure) has been synthesized and evaluated for mesomorphic behavior and physical properties. The compound has a low melting point, a chiral smectic C phase with a wide temperature range, and it shows an unusually high tilt angle at a very low value of spontaneous polarization. However, the most significant aspect of the compound is the helical structure of the smectic A phase.

The orientation and π-interaction of the frontier layers of regioregular poly(3-hexylthiophene) at both the air and substrate interfaces are directly measured for the first time using near-edge X-ray absorption fine-structure spectroscopy for thin films cast from a series of solvents (see figure). Results suggest the already high hole mobility in this material is still substantially limited by disorder at the interfaces.

Selective etching of multilayered Ge-quantum-dot/Si-spacer has been used to fabricate stacked Ge@SiO₂ nanolenses with the ability to filter and focus 1.5 μm light. These lenses have potential for use as Si-compatible photodetector materials for telecommunications. The left figure is a schematic sketch of the nanolenses and the right figure is a transmission electron microscopy image of the lenses.

A storage material that is suitable for rewritable volume holographic media with a thickness in the millimeter range is presented (see figure). Writing, reading, and deleting are possible by purely optical means, and inscribed multiplexed gratings exhibit good long-term stability. A two-step method of optical deleting allows for more than 1000 erase–rewrite cycles without a measurable change in the material.

PbSe quantum dots (QDs) are conjugated onto the surface of single-walled carbon nanotubes by a novel ligation procedure. The nanotubes are first surface-functionalized with thiol groups, which enable the adhesion of large numbers of colloidally prepared PbSe QDs. Polymeric nanocomposite IR photosensitizers made from these conjugate structures (see figure) generate significantly enhanced (≥ 100 %) IR photocurrents compared to devices using only QDs.

Single-crystalline Pt nanosheets with a nanogroove-network structure (see figure) are reported. A method of loading the nanogrooved Pt nanosheets on a carbon support is also described and the resulting nanogroove-networked Pt on a carbon support (Pt/C) is demonstrated to exhibit fairly high electrocatalytic activity for oxygen reduction, which is of interest for fuel cells.

Self-assembly of metal-complexed lipid nanotubes results from the simple mixing of two aqueous solutions containing a metal cation and an oligoglycine-based lipid under mild conditions. Mn²⁺, Fe³⁺, and Cu²⁺ in octahedral coordinations tend to form tubular structures with the lipids examined. Calcination using the Cu²⁺- or Mn²⁺-complexed lipid nanotubes as templates gives copper or manganese oxide nanotubes in a single step; a schematic illustration of a metal-complexed lipid nanotube is shown in the figure.

Multilayer coatings of colloidal particle substrates (see figure) formed entirely from block copolymer micelles are demonstrated. Such multilayer coatings provide a highly functional organized coating that may have application across a wide range of technology areas, and provide a coating mechanism for controlled loading and release of active materials.

A low-temperature fusion method for preparing polymeric nanostructures based on low-pressure CO₂-enhanced chain mobility at the nanoscale is presented. Characterization of the structures reveals a pressure-tunable rubbery layer on the surface. The successful fusion of polymeric nanostructures (see figure) at temperatures below the bulk glass-transition temperature of the polymer is demonstrated. The technique has potential for the assembly of 3D micro/nanoscale polymeric devices for biomedical applications.

Hierarchically roughened nonwoven fabrics that exhibit superhydrophobic behavior (see figure) are obtained by decorating electrospun fibers (diameter ca. 1 μm) with pores or particles of a diameter of ca. 100 nm, followed by surface hydrophobization. The enhanced hydrophobicity, due to a second level of roughness originating from the introduction of pores or particles, is evidenced by higher contact angles and lower contact-angle hysteresis.

Propionic acid tethering hemicyanine dye molecules preferentially enter the channels of silicalite-1 films with the head part first, in water in the presence of tetrabutylammonium hydroxide (this is shown schematically in the figure), giving rise to high-concentration hemicyanine-incorporating silicalite films with high second-harmonic-generation efficiency.

Metal nitride nanoparticles are synthesized using mesoporous carbon nitride, first as a nanoconfinement matrix and then as a nitrogen source. The reaction-confining matrix is thermally decomposed during synthesis, thus becoming a source of nitrogen donation, and removing the need for further purification and isolation steps. Using this approach, direct copies of silica nanostructures are generated in metal nitride form (see figure).

Thermoresponsive brushes with a tunable structure are grafted in a controlled way to gold substrates, exploiting an initiator–transfer–terminator agent (iniferter)-based photopolymerization (see figure). The chain length of the polymers is controlled by using UV light as a trigger and the end groups exposed are shown to be easily exchangeable following the grafting process. Reversible volume shrinkage/expansion, roughening, and variation of adhesion are observed.

Rhodium nanoclusters show a series of quantized double-layer-charging events in solution-phase voltammetry at room temperature (see figure). The unusual variation in the FWHM for both the cathodic and anodic regions in differential pulse voltammetry experiments can be explained by several complex factors including reorganization and disproportionation of charged clusters coupled with electron-transfer processes pertaining to the Rh–Rh bonds.

Highly efficient, low-voltage OLEDs comprising bis(2-phenylpyridi- nato-N,C^2′)iridium(acetylacetonate) ((ppy)₂Ir(acac)) as the host and tris(1-phenylisoquinolinolato-C²,N)iridium(III) (Ir(piq)₃) as a red phosphorescent guest are fabricated. Reduced driving voltage, increased maximum power efficiency (see figure), and improved durability of the OLEDs are demonstrated.

Transport trough electromigrated molecular junctions that contain an individual thiol end-capped oligophenylenevinylene molecule has been studied. At low temperatures more than fifteen excitations appear in the differential conductance map (see figure). Their energies agree with energies obtained from optical measurements on the same molecule, and are therefore attributed to vibrational modes. Addition energies are consistently an order of magnitude smaller than the optical HOMO–LUMO gap.

Highly localized, selective deprotection chemistry and efficient grafting reactions in microcontacts between elastomeric stamps and reactive polystyrene-block-poly(tert-butyl acrylate) (PS₆₉₀-b-PtBA₁₂₁₀) diblock copolymer films are developed. The procedure yields well-defined protein–poly(ethylene glycol) (PEG) nanopatterns (see figure), which may find applications in, for example, cancer-cell–surface interaction studies.

Manipulation of molecules with nanoscale accuracy is important in nanotechnology. In the novel process reported here, electrostatic interactions direct the deposition of polycationic Mn₁₂ single-molecule magnets into a predefined region of a 1 cm² silicon chip with 40 nm accuracy (see figure). The process is based on the integration of local oxidation nanolithography with surface functionalization of the Si substrate.

Bi₂Te₃/(Bi_0.3Sb_0.7)₂Te₃superlattice thermoelectric nanowires are synthesized by using a template-directed electrodeposition method. Adjustment of the deposition times and potentials enables precise control over the composition and length of each segment of the nanowires. Characterization of the superlattice nanowires by, amongst others, energy dispersive X-ray analysis (see figure) reveals their periodically varying structure.

High-efficiency white polymer light-emitting diodes are demonstrated by using a hole-injection/transport bilayer. The excellent solvent resistance of the fully crosslinked hole-injection layer ensures the subsequent solution processing of the light-emitting layer. High power efficiency can be achieved. The device also emits quite stable white light. The figure shows a schematic of the device and the chemical structure of the VB-TCTA layer.