Advanced Materials

Bi-chiral photonic crystals are tailored man-made solids inspired by blue-phase cholesteric liquid crystals. They possess two types of chirality, leading to four different types of bi-chiral structures. In naturally occurring blue-phase liquid crystals, only two of these are thermodynamically stable. On p. 4680, Michael Thiel and co-workers fabricate all four via direct laser writing.

Graphene oxide (GO) is a promising precursor for the mass production of graphene. As an important step in this direction, the electrical conductivity of GO has been enhanced by six orders of magnitude, thus closely approaching that of exfoliated graphene. The novel two-step process reported by Cristina Gómez-Navarro and co-workers on p. 4683 involves hydrogen reduction and healing by a gaseous carbon feedstock. The inside cover shows a snapshot of the crucial second step. The oxidized regions in GO are represented in red, and the blue patches correspond to vacancies.

Current strategies for the bridging peripheral nerve gaps without the use of autografts, critical to nerve regeneration therapy, are explored in this review. The figure shows a dorsal root ganglion cultured on aligned fiber based topography. Schwann cell migration and neurite outgrowth are directed by underlying aligned topography.

Four different types of bi-chiral photonic crystals are experimentally realized and characterized (see figure). In these 3D bi-chiral photonic crystals one type of handedness stems from the motif (the spirals in our case) and the other one from the corner, that is, from the fictitious skeleton onto which the motif is arranged. In nature only two of these types of bi-chiral photonic crystals exist. We realized all four bi-chiral combinations for the first time.

Highly conductive chemically-derived graphene can be synthesized using an efficient two-step method starting from graphene oxide. The key strategy involves the use of a CVD process to heal defects contained within the monolayers, which imparts a two order of magnitude enhancement of electrical conductivity over the merely reduced samples.

Liquid crystals are a successful example of how the control of self-assembly via chemical design leads to novel applications. Massimiliano Cavallini, Fabio Biscari, and co-workers report on p. 4688 that direct patterning of a continuous metal-free mesogenic phthalocyanine film (discotic LCs) is achieved by spatial control of column orientation using unconventional lithography. These patterned films work as time–temperature integrators at the columnar rectangular–hexagonal transition temperature.

Liquid crystals are a successful example of how the control of self-assembly via chemical design leads to novel applications. Direct patterning of a continuous metal-free mesogenic phthalocyanine film (discotick liquid crystals) is shown by the spatial control of columns orientation by unconventional lithography. These patterned films work as time–temperature integrators at a columnar rectangular–hexagonal transition temperature.

Nitrogen-containing carbon nanotube cups are crosslinked with glutaraldehyde to form capsule-shaped nanostructures. Introduction of commercially available gold nanoparticles prior to the crosslinkage process results in their encapsulation within the interior cavity of the linked structures (see image). A similar encapsulation of ZnS:Tb nanoparticles shows the general applicability of the system. Such a facile protocol alludes to drug-delivery and energy-storage applications.

A dual network gel, consisting of a micrometer-scaled network-like structure of a semi-rigid polyion complex nested in a nanometer-scaled polycationic network, has been developed by polymerization of a cationic monomer in the presence of a small amount of semi-rigid polyanion as dopant. Self-assembly and viscoelastic phase separation (see figure) compete with each other during the polymerization and render the micrometer-scaled network structure, which is permanently frozen by the subsequent gelation.

A bottom-imprint method to fabricate high-quality Si [100] nanowire arrays is described (see figure). This new approach combines the functions of a highly ordered anodic aluminum oxide (AAO) template that acts as both a stamp and a template. Vertically aligned, Al-catalyzed Si nanowire (NW) arrays are grown epitaxially on the Si substrate with a narrow size distribution.

Surfaces with steep height or composition gradients at the nanometer scale are synthesized from self-asssembled photoinitiator monolayers. The monolayers are prestructured by interference lithography followed by brush growth. Through step-and-repeat processes, surfaces with nano meter-scale composition gradients are obtained.

A novel multiferroic heterostructure consisting of a FeGaB thin film and a PZN-PT single crystal slab shows giant tunability of the ferromagnetic resonance (FMR) frequency of the heterostructure by electric field (see figure). The overall electric-field-induced FMR frequency change of 5.82 GHz is the largest reported so far. FeGaB/PZN-PT multiferroic heterostructures are promising candidates for wide-band electrostatically tunable microwave devices.

Research on lead-free piezoceramics has dramatically increased over the last years due to stringent legislation demanding to phase out current lead-containing piezoceramics. The use of electrostrictive materials for electric-field induced strain has been largely overlooked. In this paper we demonstrate that electrostrictive materials around a ferroelectric–antiferroelectric transition are capable of providing high strains over a wide temperature regime that was not accessible before.

A method concerning step-edge-induced area-selective growth for the patterning of aromatic organic molecules is proposed. Based on such a growth mechanism, crack-free, organic crystalline films and the growth of different molecules at defined locations can be achieved. The figure shows a schematic representation of the separation of molecules by nucleation-sites recognition.

Boron- and nitrogen-doped graphenes are are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres. Using a combination of experiment and theories based on first principles, systematic changes in the carrier-concentration and electronic structure of the doped graphenes are demonstrated. Stiffening of the G-band mode and intensification of the defect-related D-band in the Raman spectra are also observed.

High-performance antireflective and antifogging surfaces are fabricated on planar silica substrates and planconvex lenses. Such surfaces dramatically suppress reflection over a large range of wavelengths and a large field of view. Additionally, the ARS surfaces exhibit high-quality superhydrophilic properties. For antireflective and antifogging applications, the ARS surfaces exhibit more high-quality mechanical stability and better durability than multilayered films.

p-Phenylenediamine is used to successively generate two aryl radicals that are required to link silicon nanoparticles to graphite flakes by a phenyl bridge and form new silicon/graphite nanocomposites (see image). Such a covalent grafting technique enhances the cycling ability and the gravimetric capacity of the nano composite-based electrode in a lithium-ion battery.

High-quality charge-transfer complex AgTCNQ nanowires have been successfully synthesized by a facile nanoelectrochemical approach utilizing carbon nanotube (CNT) electrodes. These nanowires have diameters of 30–80 nm and lengths of up to several tens of micrometers, and exhibit remarkable electrical switching bistability. The uniform and high aspect ratio nature of nanowires originates from the one-dimensional structural feature and ultrasmall surface area of the CNTs.

Direct infrared spectroscopic evidence has been obtained for photodoping of high mobility regioregular poly(3-alkylthiophene) and poly[2,5-bis(3-alkyllthiophen-2-yl) thieno (3,2-b)thiophene] with the attendant formation of hydroxide counter-ions. This reveals the central role of dissolved water, explains the key features of degradation of the electrical characteristics of organic semiconductors in the ambient (see figure), and points to possible strategies to further improve their stability.

Nanocomposites containing graphite oxide (GO) and metal–organic frameworks (MOFs) are prepared. They have a well-defined structure, in which graphene layers from GO alternate with layers of MOF via linkages between epoxy groups from GO and zinc oxide from the MOF (see image). The enhanced porosity and dispersive forces of the composites compared to the precursors provide views for applications in gas adsorption.