Advanced Materials

The partial oxidation of an ordered macroporous silicon membrane (see figure and cover) with different pore-wall thicknesses results in a regular compartmentalized structure of SiO₂ domains separated by opaque silicon walls. Experimental conditions ensure the flatness of the partially oxidized macroporous silicon. Fluorescence crossover is minimized within the photonic crystal, enabling its use as microarray support for sensitive bioanalytics, demonstrated with a DNA-hybridization experiment.

Learning from Nature gives us inspiration for constructing functional surfaces with special wettability through the control of surface micro-/nanostructure and chemical composition. In this Review, recent achievements in the construction of surfaces with superhydrophobicity, superhydrophilicity, superoleophobicity, and superoleophilicity, and their combinations, as well as switching properties between these states, are presented (see figure).

Functional protein patterns with lateral dimensions of less than 300 nm (see figure; scale bar is 20 μm) are obtained from scanning probe nanolithography (SPN) on low-fouling plasma polymer multilayer thin films. The advantage of this technique over conventional SPN techniques is that the molecule or protein to be coupled to the patterned surface does not have to be present during the lithography process.

Ultrasound is used as an external trigger for the pulsatile release of the drug ibuprofen. The system is composed of mesoporous silica as the drug reservoir and poly(dimethylsiloxane) (PDMS) as an implantable body. This system could find use for in vivo delivery of drugs in response to changes in physiological conditions.

Oriented NiAl-layered double hydroxide (LDH) films with micro-/nanometer scale binary structures are prepared by in situ crystallization, without using any external aluminum source or shape-directing surfactant, on a porous anodic alumina/aluminum substrate. The NiAl-LDH film structures can be controlled by tuning crystallization temperature and time. Facile hydrophobic modification of the film surface leads to superhydrophobicity, as shown in the figure.

A nonlithographic breath-figure method is used to obtain ordered arrays of pores in polymer films. The pore size depends on the viscosity of the polymer solution, and is readily controlled by varying the composition of the polymer. Microbeads are patterned on the films using the pores as a template (see figure); the size of the microbeads should match that of the pores to obtain a stable array of microbeads.

Epitaxial (Fe,Mn)₃O₄thin films are patterned into nanochannels using molybdenum/poly(methyl methacrylate) (PMMA) nanomasks realized by combining local anodic oxidation of Mo and dry etching of PMMA. Nanostructures on the 100 nm scale can be easily fabricated by subsequent wet chemical etching with H₃PO₄ (see figure). (Fe,Mn)₃O₄ nanochannels open the possibility of fabricating spin-polarized nanocircuits for room-temperature spintronics.

Hierarchical heteronanostructures of W nanothorns on WO₃nanowhiskers, as shown in the figure, was fabricated with a simple two-step thermal-evaporation process. A high density of W nanothorns form a heteronanostructure with thick WO₃ nanowhiskers. A chemical transport–condensation model based on a vapor–solid mechanism is proposed for the formation of the W/WO₃ hierarchical structures.

Polyethylene microtubes are obtained through in situ polymerization catalyzed by Cr active sites anchored on the surface of silica microfibers, followed by removal of the silica core by selective chemical etching (see figure). No cocatalysts or solvents are required for this inverse-templating method, and the obtained microtubes are potentially applicable in several fields of nanotechnology.

A new strategy to achieve antiadhesion surface coatings is introduced. The approach, which uses molds coated in a thin film of poly(dimethylsiloxane) (PDMS, see figure) to achieve the antiadhesive surfaces, is applicable to virtually any type of mold material due to the use of silane chemistry and the low surface energy of PDMS. This allows simple and rapid replication of high complexity, high-aspect-ratio nanostructures with excellent replication fidelity.

A highly ordered polydiacetylene thin film was prepared by vacuum deposition of 10,12-pentacosadiynoic acid, followed by photopolymerization of this layer under UV irradiation. Using an optimum substrate temperature of 50 °C during the monomer deposition, we obtained a high field-effect hole mobility of 0.8 cm² V^–1s^–1 with p-type field-effect transistor characteristics in the top source–drain electrode configuration.

Multiferroic hexagonal TbMnO₃thin films have been epitaxially stabilized on substrates with hexagonal in-plane symmetry by pulsed laser deposition. The hexagonal TbMnO₃ films show ferroelectricity below ca. 60 K with a remnant polarization 20 times larger compared to its orthorhombic bulk phase. In addition, these samples show an electric-field-induced antiferroelectric-to-ferroelectric phase transition.

A p–n junction in an organic emissive polymer is chemically fixed through the use of polymerizable ions. This leads to a permanent configuration of compensating ions, unlike dynamic light-emitting electrochemical cells. The process is demonstrated with red-, green-, and blue-light-emissive polymers; a photovoltaic effect is also demonstrated.

The partial oxidation of an ordered macroporous silicon membrane (see figure and cover) with different pore-wall thicknesses results in a regular compartmentalized structure of SiO₂ domains separated by opaque silicon walls. Experimental conditions ensure the flatness of the partially oxidized macroporous silicon. Fluorescence crossover is minimized within the photonic crystal, enabling its use as microarray support for sensitive bioanalytics, demonstrated with a DNA-hybridization experiment.

Poly(o-toluidine) hollow spheres with controllable size (see figure) are synthesized in aqueous solution by the droplet template formed by the monomer itself. The size of the hollow spheres and the size of the hole in the surface of each sphere are affected by the concentration of o-toluidine and the molar ratio of initiator to monomer, respectively.

Detection of bacteria in human blood within two hours is achieved through the use of vancomycin-functionalized FePt nanoparticles in combination with a vancomycin-conjugated fluorescent probe, as shown in the figure (B: bacteria; Van: vancomycin; FLA: fluorescein amine). This promises to be a sensitive and rapid protocol for detecting bacteria in blood products or other targets in biological samples.

Rapid fabrication of uniform nanopores and nanopore arrays in Si₃N₄membranes (see figure) is achieved using a high-intensity electron beam. Expansion or contraction of the pores under electron-beam irradiation is observed and utilized for the controlled fabrication of highly uniform nanopores in the size range 2–20 nm. Our nanopores exhibit a truncated double-cone structure, as revealed by 3D-TEM tomography.

A modified polyol process for the synthesis of cubic-shaped FeCo particles at 403 K is demonstrated. Control of the particle composition and size was achieved by varying the experimental conditions. The Fe content in the FeCo particles can be varied from 90 to 20 mol %, and the size of the cubes can be controlled to obtain particles with sizes between 300 and 35 nm (see figure). The magnetic properties of the particles closely resemble those of bulk FeCo.

Arrays of well-aligned, ca. 4.7 mm long carbon nanotubes (CNTs) are grown in a simple, safe, and cost-effective manner using an efficient Al₂O₃/Fe catalyst prepared by an ion-beam assisted deposition technique (see figure). Importantly, the as-synthesized CNT arrays with lengths ranging from 500 μm to 1.5 mm are conducive to spinning, and CNT fibers spun from such long CNT arrays show remarkably improved tensile strength.

Micropatterned porous-Si Bragg mirrors (see figure) are created by dry-removal soft lithography. This lift-off technique utilizes a patterned polymer stamp to remove porous-Si layers from the Si substrate. The nanostructure and optical properties of the porous-Si photonic crystal are conserved throughout the micropatterning process. In addition, reversible chemical sensing via optical reflectivity is demonstrated with a porous-Si Bragg mirror.

The zero strain Li_4+xTi₅O₁₂material as a two-phase system is, in contrast to common knowledge, unstable at room temperature (see figure), and it is fast Li insertion that leads to a kinetically induced effective two-phase reaction. The solid-solution-induced disorder, resulting from the mixed 8a/16c occupation, is most likely responsible for the high rate capabilities in Li_4+xTi₅O₁₂.

A thin film of crosslinked poly(acrylic acid) (PAA), patterned within microfluidic channels (see figure) and crosslinked with metal cations, serves as a platform for rapid “on-chip” growth of patterned metallic and semiconductor nanoparticles. The embedded particles serve as catalysts for electroless deposition of metal films.

An organic field-effect transistor (OFET) memory device based on pentacene is fabricated using an additional poly(α-methyl styrene) gate dielectric layer (PαMS, see figure) that has charge-trapping ability (an electret). The device has excellent non-volatile OFET memory characteristics, believed to originate from the stored charges in PαMS layer and transferred from the semiconductor to the polymeric gate electret.