Advanced Materials

Fluorescent, DNA-stabilized silver clusters are generating growing interest as selective sensors and biolabels, but the origins for their wideranging, sequence-tuned colors are obscure. On page 2797, Elisabeth Gwinn and co-workers report that compositionally pure complexes with 10–24 silver atoms, formed on a variety of DNA strands, all contain both neutral and cationic silver. Optical properties indicate a nanorod geometry, with color reflecting the length of a silver atom chain in the nanorod core.

Generally, damaged polymeric materials do not return to their original shape and strength. If the damaged materials can recover spontaneously, material consumption can be minimized. Polymeric materials cross-linked with a hostguest interaction successfully showed a selfhealing property, as reported by Akira Harada and co-workers on page 2849. The authors choose cyclodextrin-host and hydrocarbon guest moieties to obtain self-healing materials. When cutting the material, cooperative host–guest complexation on the cut surfaces should effectively adhere to each other and recover the material strength.

Organic/metal nanowire heterostructures are prepared by embedding Ag nanowire branches in organic microwire trunks during the self-assembly in liquid phase. The formation of exciton polaritons in organic wire under the excitation greatly improves the plasmon launch efficiency due to the direct photon-plasmon coupling. The light signals inputted from the organic waveguide can be selectively out-coupled to the predetermined subwavelength Ag nanowires. These organic/metal nanowire heterostructures are potentially applied in integrated photonic circuits as underlying optical multiplexers. Further details can be found in the article by Jiannian Yao, Yong Sheng Zhao, and co-workers on page 2784.

The emerging field of iPSCs evokes a wave of excitement in regenerative medicine. Although iPSCs create numerous opportunities, researchers are faced with several difficult challenges. One of the main obstacles is to avoid insertional mutagenesis during the reprogramming process. This review describes the progress made in iPSC producing techniques since its initial discovery in 2006.

Health-monitoring devices that can be mounted onto the human skin are of great medical interest. On page 2773, John A. Rogers and co-workers present materials and designs for electronics and sensors that can be conformally and robustly integrated onto the surface of the skin. This image shows an epidermal electronic system of serpentine traces that is directly printed onto the skin with conformal lamination.

Materials and designs are presented for electronics and sensors that can be conformally and robustly integrated onto the surface of the skin. A multifunctional device of this type can record various physiological signals relevant to health and wellness. This class of technology offers capabilities in biocompatible, non-invasive measurement that lie beyond those available with conventional, point-contact electrode interfaces to the skin.

A simple and effective way to make DNA patchy particles is reported. A small patch of DNA strands is “stamped” from a gold surface onto colloidal particles of different sizes by streptavidin-biotin bonds. These DNA patchy particles provide direction-selective and thermoreversible interactions, and hence can lead to unique assembly protocols and structures controlled by temperature.

A novel approach to manipulating multiple optical signals at subwavelength scale is proposed in dendritic organic/metal nanowire heterostructures. The heterostructures are prepared by embedding Ag nanowires in fac-tris(2-phenylpyridine) iridium microwires during the self-assembly in liquid phase. Optical signals inputted from the organic waveguide can be selectively transferred to the predetermined subwavelength output ports based on the angular dependence of the photon-plasmon coupling.

Colloidal quantum dot photovoltaics show great promise for future solar energy conversion applications but remain limited by inefficient charge carrier extraction. Ordered arrays of ZnO nanowires, shown here in blue, can decouple light absorption and carrier collection, yielding a significant relative enhancement in the photocurrent and efficiency of quantum dot solar cells. Further details can be found in the article by Vladimir Bulović and co-workers on page 2790.

Vertical arrays of ZnO nanowires can decouple light absorption from carrier collection in PbS quantum dot solar cells and increase power conversion efficiencies by 35%. The resulting ordered bulk heterojunction devices achieve short-circuit current densities in excess of 20 mA cm⁻² and efficiencies of up to 4.9%.

Fluorescent DNA-stabilized silver nanoclusters contain both cationic and neutral silver atoms. The absorbance spectra of compositionally pure solutions follow the trend expected for rod-shaped silver clusters, consistent with the polarized emission measured from individual nanoclusters. The data suggest a rod-like assembly of silver atoms, with silver cations mediating attachment to the bases.

Organic droplet epitaxy is presented as a method for growing nanopatterned crystalline heterostructures, thanks to the transport of molecules of an amorphous first-layer on top of a crystalline second-layer, where they form an epitaxial interface. Such heterostructures may be transferred to any substrates, raising particular interest for applications (e.g., for organic photovoltaics), where crystallinity and nanopatterning constitute well recognized advantages.

Well-separated RGO sheets decorated with MnO₂ nanoparticles facilitate easy access of the electrolyte ions to the high surface area of the paper electrode, enabling the fabrication of a thicker electrode with heavier areal mass and higher areal capacitance (up to 897 mF cm⁻²). The electrochemical performance of the bent asymmetric device with a total active mass of 15 mg remains similar to the one in the flat configuration, demonstrating good mechanical robustness of the device.

A sub-monolayer distribution of isolated molecular Fe₁₄(bta)₆ nanomagnets is deposited intact on a Au(111) surface and investigated by X-ray magnetic circular dichroism spectroscopy. The entropy variation with respect to the applied magnetic field is extracted from the magnetization curves and evidences high magnetocaloric values at the single molecule level.

A simplified encapsulation strategy for metal-oxide based TFTs, using ozone instead of water as an oxygen source in a low-temperature ALD process is demonstrated. Thereby, the threshold voltage remains unaltered and the hysteresis is permanently reduced. Costly energy- and time-consuming post-treatment processes can be avoided. This concept is widely applicable to various encapsulation materials (e.g., Al₂O₃, TiO₂, ZrO₂) and metal-oxide channel semiconductors (e.g., zinc–tin–oxide (ZTO), indium–gallium–zinc–oxide (IGZO)).

An organic semiconductor laser, simply fabricated by UV-nanoimprint lithography (UV-NIL), that is pumped with a pulsed InGaN LED is demonstrated. Molecular weight optimization of the polymer gain medium on a nanoimprinted polymer distributed feedback resonator enables the lowest reported UV-NIL laser threshold density of 770 W cm⁻², establishing the potential for scalable organic laser fabrication compatible with mass-produced LEDs.

Adding ethylene glycol (EG) to a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution improves the crystallinity of the PEDOT and the ordering of the PEDOT nanocrystals in solid films. The carrier-mobility enhancement is confirmed by using ion-gel transistors combined with in situ UV–vis–NIR spectroscopy.

A strategy towards efficient mechanochromic luminogens with high contrast is developed. The twisted propeller-like conformations and effective intermolecular interactions not only endow the luminogens with AIE characteristics and high efficiency in the crystalline state, but also render them to undergo conformational planarization and disruption in intermolecular interactions upon mechanical stimuli, resulting in remarkable changes in emission wavelength and efficiency.

The phase inversion of water-toluene emulsions stabilized with a single thermo- and pH-sensitive copolymer occurs through the formation of multiple emulsions. At low pH and ambient temperature, oil in water emulsions are formed which transform into highly stable multiple emulsions at pHs immediately lower than the inversion border. At higher pHs, the emulsion turns into a water in oil one.

Supramolecular hydrogels formed by a host-guest interaction show self-healing properties. The cube-shaped hydrogels with β-cyclodextrin and adamantane guest molecules mend after being broken. The hydrogels sufficiently heal to form a single gel, and the initial strength is restored. Although contact between a freshly cut and uncut surface does not mend the gels, two freshly cut surfaces selectively mend.

Organic color-graded optical waveguides permit low-power photonic analogies of diode/transistors based on the energy-transferred conversion of exciton species. The donor–acceptor junction can asymmetrically output blue/red colors due to the mono-directional energy transfer during light propagation. The switching function of transistors is achieved with an additional gate input by altering the ground state density of acceptors. These organic heterogeneous waveguides are further cascaded together to steer the guided light flows for potential applications in photonic integrations.

A new organic light-emitting field-effect transistor characterized by a metal oxide layer inserted between the organic layer and the gate insulator is proposed. The metal oxide is indirectly connected with source and drain electrodes through the organic layer. Upon increasing the potential difference between the source and drain electrodes, the emission becomes exceedingly strong and the emission region encompasses the whole channel zone.