Articles in 2015

A series of twistacene-functionalized dendrimers were successfully synthesized and characterized. They can self-assemble into organic nanoparticles through re-precipitation method and emit blue, cyan, green and red fluorescence in water. These multicolor nanoparticles showed low cytotoxicity and good photostability, which could be used for fluorescence imaging of living cells.

Inspired by multifunctional fish scales with swift stimulus-responsive capabilities, we developed inorganic nanostructured isolated particles and nanostructured coatings with surface morphology that can mimic that of natural fish scales via a facile self-assembly approach. The bio-inspired nanostructures feature tunable light refraction and reflection, tunable surface wettability and damage-tolerant mechanical properties, and provide new insights for developing novel functional materials for ‘smart’ structures and applications.

This study demonstrated that the formation of triazole moieties accompanying with a linker or substituent group(s) having a resonance effect (which can provide a charge stabilization power) by using azide–alkyne click chemistry is a very powerful synthetic route to develop electrical memory polymers with high performances. The memory mode can be further tuned by changing the linker or substituent group(s) in the triazole moiety.

We report a bulk hybrid nanostructured Al alloy with super-high strength at both room and elevated temperatures. The strengthening mechanisms were clearly elucidated, which are mainly attributed to the composite structure and confinement effect between the nano phases. The confining effect can effectively suppress the premature brittle fracture of the nano-intermetallic phases. The microstructural strategy and strengthening mechanisms in this work may be beneficial for the scientific community in understanding and designing high-strength materials.

This paper describes materials and design strategies for wireless, bioresorbable drug delivery devices that allow localized release of drugs in precisely controlled, patient-specific time sequences. The device architecture combines completely bioresorbable wireless electronics and thermally actuated lipid membranes infused with multiple types of drugs, to enable remote time-controlled release profiles with near-zero leakage in the off-state. Complete bioresorption following an engineered operational lifetime eliminates unnecessary patient risk and device load on the body, without the need for surgical extraction. Systematic in vivo and in vitro studies demonstrate the underlying principles and all of the relevant features of operation. The capabilities offered by this platform have potential utility in clinical therapies to improve patient compliance and the efficacy of current procedures.

This review highlights the recent advances in utilizing a combinatorial strategy of mechanistic investigation, theoretical prediction and experimental validation to develop cheap and earth-abundant high-performance electrocatalysts as counter electrode materials for dye-sensitized solar cells. The effectiveness of the combinatorial strategy over the conventional ‘trial-and-error’ tactic is illustrated with plentiful successful examples of earth-abundant materials. Perspectives are given to elucidate the opportunities and challenges.

We report a generic aqueous coating methodology that provides highly biocompatible surfaces. The method is inspired by prebiotic chemistry that involves the polymerization of hydrogen cyanide (HCN). The neutralization of the commercially available HCN trimer aminomalononitrile toluenesulfonate results in spontaneous polymerization that can be used to coat a wide variety of surfaces with a highly nitrogenous polymer. The non-cytotoxic coating provides excellent cell attachment and its chemistry allows the immobilization of other compounds including metals both during coating formation or by subsequent secondary immobilization reactions. This gives access to bioactive coatings including antimicrobial surfaces. Prebiotic chemistry has always been focussed on the understanding of the chemical origin of life and has remained highly fundamental research. To our knowledge this is the first application of prebiotic chemistry to material science.

A one-step and continuous method to produce a spherical Li₄Ti₅O₁₂/graphene composite for the lithium-ion battery anode is reported. The high conductivity and hollow structure of the crumpled graphene sphere greatly enhance the rate capability and cycling performance of the Li₄Ti₅O₁₂ anode. This method provides a new and exciting approach for high-performance anode material design and fabrication.

The synthesis and application of organoboron complexes are a topic with high relevance owing to their unique characteristics. This manuscript introduces the results primarily from recent studies of boron diketonates, ketoiminates and diiminates containing polymers and particularly focuses on their optical properties.

A heterogeneous palladium–silver alloy can catalyze selective methylation of aromatic amines under ambient pressure and without additives. Methylation of amines is used to manufacture chemicals used in fertilizers, fungicides, synthetic leathers and polymers. Formic acid, which is produced from biomass, is an environmentally friendly reagent for producing amines. They achieved complete conversion and high selectivities in the range 90–97% for methylation and dimethylation of various substituted aromatic amines only by formic acid as the source. The catalyst realized yields comparable to those of homogenous catalysts with acid additives for methylation with carbon dioxide and hydrogen under high pressure.

Cd₃As₂, which is known as a topological Dirac semimetal, has been grown on mica substrates by molecular beam epitaxy with high mobility. The temperature-dependent resistance of as-grown Cd₃As₂ thin films showed semiconducting behavior, indicating the band gap opening as opposed to the bulk counterpart. By solid electrolyte gating, the ambipolar effect and gate-tunable quantum oscillations were clearly demonstrated. These features make the Cd₃As₂ thin film system a promising platform to observe various exotic phenomena and realize new electronic applications.

A photovoltaic device based on a high-work-function metal/single-walled carbon nanotube (SWNT)/low-work-function metal hybrid junction was constructed to generate a strong built-in electric field in the SWNT for efficiently separating photogenerated electron-hole pairs. In the dark, the device behaved as a gate-dependent Schottky diode, with a high rectification ratio (I_forward/I_reverse) of >10³ achieved for the device fabricated with an 1.4-nm-diameter SWNT. Under monochromatic illumination, this device exhibited an open-circuit voltage of 0.15 V and a high quantum efficiency of ~75%. It was found that the SWNT diameter had an important effect on the device characteristics.

The polyallylamine functionalization imparted Pd–Pt nanodendrites with extraordinary selectivity for the oxygen reduction reaction because of its steric hindrance effect and ethanol-phobic property.

Recently, a research group from the Center for Nanoscale Science and Technology at the National Institute of Standards and Technology (NIST), and the Massachusetts Institute of Technology in the United States has demonstrated a new type of quantum electro-optic phenomenon, whispering-gallery mode resonators.¹ The resonators are generated by a scanning tunneling microscope (STM) in proximity to graphene devices (Figure 1). On the basis of the quantum effect of electron tunneling, STM is a powerful technique to investigate the local electronic properties of both metallic and semiconducting systems with atomic resolution. Graphene, the most acclaimed material of the last decade, has enabled new horizons for STM research. The graphene surface can be directly probed by the scanning tip, whereas remaining chemically stable and clean even exposure to ambient air for days. Charged carriers in graphene can be readily tuned from holes to electrons using an external gate electrode. Furthermore, the charge carriers in graphene, often called Dirac particles, behave like electromagnetic waves, setting the stage for graphene to realize quantum electro-optic phenomena such as Veselago lensing² and Klein tunneling.³

A facile process to prepare multi-layered nanopatterned photoanodes (MNPs) is presented with well-arrayed mesoporous inorganic oxide layers. The MNPs were prepared by multiple stacking of nanopatterned TiO₂ layers using a sacrificial polystyrene-thin film layer, which not only guided the stacking TiO₂ layer but also was removed completely by calcination without generating cracks. The MNPs were applied to solid-state solar cells, to exhibit an enhancement of 73% and a 65% in J_sc and power conversion efficiency (PCE), respectively.

Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling, suggesting a new passivation strategy by biasing the competition between these phases through the tuning of the carrier density in the dislocation.

Inspired by photosynthesis in nature, an artificial smart system that has similar regulation mechanism is constructed, which is selective to anions after direct reactions with CO₂.

Herein, we reported deformation-free single crystal ZnS microsprings produced by the polar-surface-driven growth process with novel optoelectronic properties for the first time. The entire spring is synthesized by a block-by-block stacking process following a hexagonal screw model, without introducing distortion in crystal lattices. The electrical characteristics of individual ZnS microsprings under electron beam irradiation and their potential applications in UV light sensor and waveguides were thoroughly investigated. The high crystal quality, fast response to UV light and the low propagation loss indicate ZnS microsprings will have important applications in future optoelectronic systems.