Advanced Materials

Regular, 2D metallodielectric microstructures (see Figure) have been produced in nanocomposite glass by electric-field assisted dissolution of the embedded silver particles. Any pattern of a structured electrode (in this work, macroporous silicon) can be transferred to the nanocomposite. This technique is potentially useful for production of diffractive optical elements, channel waveguides, and submicrometer optical structures suitable for plasmonic applications.

Capillary-driven microfluidics have evolved from simple microfluidic networks to refined systems that integrate capillary valves and advanced flow control (see Figure). These are used to pattern biomolecules on surfaces with micrometer resolution, effect miniaturized surface immunoassays, and perform reactions in parallel or in a combinatorial manner. The transition from contact to non-contact technology is described.

An ordered and controlled microarray of isolated organic electroluminescent pixels (see Figure) is fabricated by a surface-tension-driven technique. The technique combines the instability of liquids, following dewetting phenomena, with geometrical confinement, induced by a template mesh, to deposit optically active molecules in an ordered fashion. The flexibility, ease of realization, and absence of any damaging lithographic step makes this a promising technique for future OLED fabrication.

A versatile confocal-based laser scanning lithographic method for controlled, high-fidelity two-dimensional and three-dimensional surface patterning of deformable, solvated, photoactive substrates is presented (see Figure; scale bars represent 200 μm). Patterned substrates functionalized with gradients of different cell-adhesive ligands can be fabricated, providing a tool for investigating cell–biomaterial interactions and the structure–function relationships of tissues.

Solution-grown CdSe nanowires (NWs) combine numerous aspects of 1D carrier physics. The effects of disorder on the optical properties of individual, quantum-confined straight/branched NWs (see TEM and fluorescence images) is shown here; in these NWs the optical heterogeneity is apparent through non-uniform intrawire emission intensities. The current study has relevance to applications of NWs as y-branch switches^[17] or as active elements in hybrid photovoltaics given the impact such heterogeneity may have on their transport properties.

Spin-crossover (SCO) complexes based on three-dimensional coordination polymers (see Figure) exhibit unprecedented pressure-tunable thermal and piezochromic bistability at room temperature. The thermal- and piezohysteresis loops of the material can be tuned, providing a step towards reliable pressure-based memory systems or displays.

Nanostructures with tunable size and shapes are produced using a charge-transfer complex, copper tetracyanoquinodimethane (CuTCNQ). Surfaces can be coated with the charge-transfer complex nanoparticles (see Figure). These superhydrophobic coatings may be useful for constructing water/moisture-resistant and contamination-free electronic devices.

Uniform carbon/Co nanorods with unique cross-sections (see Figure), Co/carbon core/shell nanospheres, and multiwalled carbon nanotubes are selectively prepared in high yield by solid-state thermolysis of polyphenylene dendrimer/cobalt complexes under controlled heating procedures. The obtained materials have potential catalytic and magnetic applications.

The effective exciton diffusion length of poly(3-hexylthiophene) (P3HT) can be improved with resonance-energy transfer from P3HT to poly(N-dodecyl-2,5-bis(2'-thienyl)pyrrole-2,1,3-benzothiadiazole) (PTPTB), a low-bandgap polymer, which results in a threefold increase of the photocurrent. Directional resonance energy transfer to the exciton-splitting interface has the potential to overcome a number of limitations associated with exciton transport in polymer photovoltaic cells.

A hydrating–exfoliating–splitting model is proposed to explain the formation of V₂O₄·0.25H₂O nanowires from raw V₂O₄ particles (see Figure). In this synthetic route, only the raw material and water are used to synthesize the crystallized nanowires—no templates or reactants are introduced into the reaction system.

Vanadium oxide macroscopic fibers (see Figure) are obtained by an extrusion process. The fibers consist of nanoscopic ribbons with a preferential orientation and a longitudinal Young's modulus of around 15 GPa. As well as showing high sensitivity, the fibers reversibly cycle between insulating and semiconducting upon exposure to alcohol vapor sources, with signature responses to different alcohols.

A light-emitting polymer with simultaneous blue (λ_max = 445 nm), green (λ_max = 515 nm), and red light (λ_max = 624 nm) emission for bias-independent white electroluminescence is reported (see Figure). The polymer is synthesized by covalently attaching a green-light-emissive and a red-light-emissive chromophore to a macromolecule with blue-light emission. White-light color coordinates of (0.31, 0.34) and a luminance efficiency of 1.59 cd A^–1 are obtained.

The shape of hysteresis loops in exchange-bias systems can be fully tailored from single-shifted to double-shifted loops (with adjustable magnetization amplitudes and horizontal shifts, see Figure) through exploiting the length scales of the exchange bias via carefully engineered heat-treatment processes. This provides a valuable tool to engineer multilayer magnetic properties after multilayer deposition.

Regular, 2D metallodielectric microstructures (see Figure) have been produced in nanocomposite glass by electric-field assisted dissolution of the embedded silver particles. Any pattern of a structured electrode (in this work, macroporous silicon) can be transferred to the nanocomposite. This technique is potentially useful for production of diffractive optical elements, channel waveguides, and submicrometer optical structures suitable for plasmonic applications.

Aligned multiwalled carbon nanotube (MWNT)–polymer composites are synthesized for use in microelectromechanical systems (MEMS) applications. Indentation and bending tests reveal that the elastic modulus of the MWNT–MEMS devices is promoted by a factor of 20. Dynamic bending experiments show that MWNT–MEMS devices can be driven at a lower pull-in voltage compared with classical devices. Complex and delicate MWNT–MEMS devices can also be fabricated (see Figure).

α-Fe₂O₃ nanotubes that can be used as chemical sensors (see Figure) are fabricated by a novel carbon nanotube (CNT) templated synthesis. CNTs are coated with a continuous layer of Fe₂O₃ nanoparticles by the decomposition of Fe(NO₃)₃ in a supercritical CO₂/ethanol solution. Subsequent removal of the CNTs gives α-Fe₂O₃ nanotubes that are highly sensitive to H₂S, which makes them attractive materials for chemiluminescent H₂S sensors.

CdS nanocrystals with cubic, triangular, and hexagonal geometries have been synthesized using simple wet-chemistry techniques. Analysis of the crystal structures revealed that the cubic nanocrystals have a zinc-blende crystal structure whilst the triangular and hexagonal CdS nanocrystals have a wurtzite crystal structure. When dried, these CdS nanocrystals self-assemble to form complex structures such as linear rods (see Figure), nanoarrows and dimers.

Dimerization in a “butterfly” fashion: a soluble pentacene derivative undergoes photoinduced dimerization upon exposure to UV and visible light, both in solution and in the solid state. This pathway of degradation does not involve oxygen or moisture. Strategies to limit the damage require use of highly crystalline thin films or storage as a solution in benzene, which cooperatively interacts with the pentacene core, hampering the dimerization process.

Fluorite-structured CeO₂ nanotubes have been synthesized by controlled annealing of layered Ce(OH)₃ nanotubes. The latter have been fabricated by means of hydrothermal treatment of anhydrate cerium chloride. The Ce(OH)₃ nanotube formation has been attributed to lamellar rolling under appropriate conditions. The non-layered CeO₂ could possess nanotubular morphology only in the presence of structural defects (see Figure; tube diameter: ∼ 18 nm).

Nanoscience is no longer limited to a world of inanimate nanoscale objects. In this article, we explore the emerging field of chemically powered nanomachines that can derive their power from in-situ chemical reactions, move through fluid phases, and, in the not-too-distant future, be directed to perform useful tasks in the fields of biomedicine, analytical chemistry, and environmental conservation.