Advanced Materials

Microstructures such as grippers and cubic containers reversibly open and close when exposed to chemicals without the need for any wires, tethers, or batteries, as demonstrated by David Gracias and co-workers on p. 407. The cover shows bidirectional microgrippers with selected digits closing and opening spontaneously in response to surface oxidation and reduction of copper films within thin-film bilayer hinges. Image created by Martin Rietveld and Jatinder Randhawa.

Complex reconfigurable three-dimensional photonic quasicrystals (PQCs) are fabricated in a nonlinear photorefractive material by an optical phase-engineering-based optical induction approach. Cornelia Denz and co-workers report on p. 356 that various scalable 3D PQC structures possessing higher order rotational symmetry with defined diffraction patterns can be realized in real time.

Bias-induced phase transitions in ferroelectric and related materials underpin a range of information and energy storage technologies. The mechanisms of these transitions are controlled by local defects. The synergy of scanning probe microscopy, defect-engineered structures, electron microscopy, focused X-ray microprobes, and neural-network-based data-analysis routines holds the promise of understanding atomistic and mesoscopic mechanisms of these transitions on a single-defect level (see image).

The assembly of species of biological origin with inorganic solids of different topology, structure and physico-chemical properties, represents a topic of increasing interest as the resulting nanostructured biohybrid materials deal with numerous advanced applications covering areas as different as tissue engineering, drug delivery systems, biosensing devices, biocatalysis, green nanocomposites, etc.

Graphenic carbon can be etched into arbitrarily complex and preset channel patterns using cobalt-based catalyst particles for the dioxygen reaction at low temperatures in externally applied magnetic fields. Scanning electron microscopy images demonstrate active steering for particles/channels down to 200 nm (see image).

Pentacene-based thin-film transistors (TFTs) are fabricated, and characterized, on UV-curable polymer gate dielectrics with different photocrosslinking times (hence, different degrees of crosslinking). The results show that pentacene TFT measurements can be an informative probe of polymer film viscoelastic properties, as modified by crosslinking, and relatively mild, contactless polymer dielectric processing can dramatically enhance the OTFT performance.

Nickel cobaltite (NiCo₂O₄) aerogels, synthesized with a chloride-based epoxide-driven sol–gel process, exhibit ultrahigh specific capacitances (1400 F g⁻¹; see figure), excellent reversibility, and outstanding cycle stability, at a relatively high mass loading of 0.4 mg cm⁻².

Desired numbers of proteins can be positioned on surfaces by using dip-pen nanolithography (DPN). Ferritin nanoarrays are fabricated by direct-writing nanodroplets of a ferritin solution on TEM surfaces. After the contact-angle value of these droplets is determined, the concentration of the inking protein solution and the diameter of the dot-like feature can be modulated to position a single ferritin particle on a surface (see figure).

Complex reconfigurable 3D photonic quasicrystals (PQCs) are fabricated in nonlinear photorefractive strontium barium niobate by an optical phase engineering-based single-step optical induction approach (see image). The approach demonstrates the embedded potential to use these structures as a reconfigurable platform for the investigation of advanced nonlinear light-matter interaction, or as templates fabricated in various photosensitive materials for photonic bandgap structures.

Negative Poisson's ratio behavior has been uncovered in cellular solids that comprise a solid matrix with a square array of circular voids. The simplicity of the fabrication implies robust behavior, which is relevant over a range of scales. The behavior results from an elastic instability, which induces a pattern transformation and excellent quantitative agreement is found between calculation and experiment.

Replacing a carbon atom with silicon (see figure) on the main chain of a conjugated polythiophene gives a polysilole with higher crystallinity, improved charge transport, reduced bimolecular recombination, and reduced formation of charge transfer complexes when blended with a fullerene derivative. Optimized bulk heterojunction solar cells using this blend give certified efficiencies of 5.2% under AM1.5 illumination.

A new silole-containing low bandgap polymer is synthesized by replacing the 5-position carbon of PCPDTBT with a silicon atom (PSBTBT). Through experiments and computational calculations, we show that the material properties, particular the packing of polymer chains, can be altered significantly. As a result, the polymer changes from amorphous to highly crystalline with the replacement of the silicon atom.

Superhydrophobic surfaces composed of single-crystalline nanowires of an organic semiconductor are demonstrated by model water striders. Model copper water striders with self-assembled crystalline nanowires on their “legs” can nicely “stand” on the surface of water. 1.0 mg of such nanowires could support a 372 mg model strider, indicating the striking water-repellent ability of the model legs (see image).

Polymer tandem solar cells with a PCE of 5.8% are demonstrated by employing a p–n junction as an interlayer between the two subcells. The role of the interlayer and several important issues of the tandem structure is addressed including optical optimization, interfacial engineering, and accurate efficiency characterization (see image). It is revealed that the interlayer acts as a metal/semiconductor contact as opposed to a traditional tunnel junction in inorganic tandem cells.

Evidence for a band-like, lateral transport of electrons through the cores of HBC-thiolates, forming a highly ordered self-assembled monolayer (SAM) containing a very regular array of HBC-cores, is provided based on a detailed analysis of temperature-dependent scanning tunneling microscopy (STM) data recorded for islands of aromatic SAMs immersed in an insulating matrix.

Enzymatic manipulation of DNA on well-dispersed gold nanoparticles (AuNPs) offers an ideal system for high-throughput screening of G-quadruplex ligands and evaluation of their selectivity with respect to duplex and quadruplex DNA (see figure). This work has implications for the future use of nanoparticle-based technologies in the discovery of potential cancer therapeutic agents.

A new hydrogen storage system of poly(methyl acrylate)-confined ammonia borane, which has been prepared by a solution-blending method, has shown the characteristics of controllable dehydrogenation performance and water resistance.

Single-molecule force spectroscopy experiments demonstrate that hydrogenation and oxidation of polycrystalline diamond effectively control molecular adhesion (see figure). Aging changes these properties and originates from the rapid formation of a thin and resistant contamination layer, as well as degradation of the artificial surface termination on longer time scales. This aging also affects the wettability, morphology, and the electrical properties of the surfaces.

FePt/ZnO core/shell nanoparticles are successfully synthesized by seed-mediated growth. TEM/HRTEM measurements (see figure) show a quasi-epitaxial growth between the FePt core and the ZnO shell nanoparticles. The synthesized FePt/ZnO core/shell nanoparticles can exhibit a wide range of semiconducting, magnetic, and piezoelectric properties that can be used to fine-tune the material's response to magnetic, electrical, optical, and mechanical stimuli, which has potential in data storage, optoelectronic, magneto-electromechanical and biomedical applications.

Reversible curving of chromium/copper bilayers on exposure to oxidative and reductive environments is described. Bilayers are lithographically patterned as hinges within larger microstructures to enable reversible opening and closing, without the need for any tethers or batteries (see image). Demonstrations suggest a new strategy for coupling chemical reactions and surface modification to mechanical motion to enable autonomous, chemically responsive microstructures.

The resistive switching properties of Sr₂TiO₄ thin films with specific defect distribution have been studied. Junctions of Sr₂TiO₄ thin films containing a high density of defects show well-pronounced resistive switching properties while those with well-ordered microstructure exhibited insignificant hysteresis windows. This work clearly demonstrates the crucial role of defects for the microscopic switching mechanisms in oxide thin films.

Simple physical blending of SiO₂and ethyl-capped Ge gels leads to flexible dimensional control of Ge nanoparticles, and an increasing weight fraction of the latter leads to ordered 3D porous nanoparticle assemblies (see figure). The long-range ordering of the 3D porous Ge nanoparticles and their very thin pore wall thicknesses (<20 nm) induce excellent cycling performance, showing only a 2% capacity decrease after 100 cycles.

Photopatterning of graphene oxide films can be achieved by exposing a thin film of graphene oxide to a photographic flash. Absorption of light causes rapid heating of the graphene oxide resulting in deoxygenation to graphitic carbon. Using a transmission electron microscope grid as a mask, the grid pattern can be transferred to a graphene oxide film.

Organic metal-semiconductor transistors, where the gate consists of a low work-function metal directly deposited on the semiconductor, are fabricated on rubrene single crystals (see figure). A careful analysis of the current–voltage characteristics and impedance spectroscopy of the corres ponding diode leads to the conclusion that the current in the transistor is controlled by a modulation of charge injection from the source electrode.