Advanced Materials

Natural silk fibers provide the raw material to constitute biocompatible films with favorable properties for nanopatterning and device integration. The image shows a free-standing credit-card sized film constituted entirely by silk and containing a number of diffractive optics (lenses, microlens arrays, gratings, phase masks). Such elements can be obtained either by casting or rapid nanoimprinting of silk films (master courtesy of Tessera Inc.). Further details can be found in the Communication by Fiorenzo Omenetto and co-workers on p. 1746.

Jean-Charles Ribierre and co-workers report on the conversion of the majority carrier type by laser irradiation in solution-processed organic thin films based on a quinoidal oligothiophene derivative (p. 1722). Patterning of p-type and n-type microstructures is achieved by direct laser writing and can be visualized using a Kelvin-probe force microscope. The method is extremely promising for the fabrication of CMOS logic circuits and lateral p-n diodes based on a monolithic solution-processible organic semiconductor.

Carbon nanotube–polymer composites have been developed in recent years as potential alternative materials for various applications, including flexible electrodes in displays (see image), bullet-proof vests, and high-performance composites for aircraft industries. In this article, the most recent progress on the development of carbon nanotube–polymer composites is presented, with particular attention to their mechanical and electrical (conductive) properties.

Single-molecule spectroscopy provides a powerful approach to unraveling intrinsic material properties from the bottom up. Building on the success in life sciences, such techniques are now finding increasing applicability in materials science, effectively enabling the dissection of the bulk down to the level of the individual molecular constituent. This article reviews recent progress in single-molecule spectroscopy of conjugated polymers as used in organic electronics (see figure).

Complementary organic logic circuits and lateral bipolar microstructures with specified p- and n-region profiles can be patterned by direct laser writing in solution- processed thin films faricated from a quinoidal oligothiophene derivative. To demonstrate the versatility of this method, the fabrication of NAND and NOR logic gates as well as a gate-modulated lateral p-n diode is reported (see figure).

A novel conducting polymer/non-conducting polymer composite (PEDOT/PEG), produced by vapor phase polymerization of PEDOT in the presence of PEG, shows stable electrocatalytic reduction of protons to hydrogen with conversion currents and over-potential comparable to platinum. The swelling of the composite by PEG and especially its ability to coordinate protons seems to be essential for the catalytic activity of the composite.

An ITO/TPAPAM-GO/Al memory device (see figure; ITO = indium tin oxide, TPAPAM-GO = graphene oxide covalently grafted with triphenylamine-based polyazomethine) exhibits typical bistable electrical switching and a nonvolatile rewritable memory effect with a turn-on voltage of −1.0 V and an ON/OFF-state current ratio of more than 10³. Both ON and OFF state are stable under a constant voltage stress and survive up to 10⁸ read cycles at a read voltage of −1.0 V.

A stable, biocompatible, free-standing “paperlike” material composed of polyoxyethylene sorbitan laurate (TWEEN) and reduced graphene oxide platelets is presented. The TWEEN paper is highly stable in water (no leakage of TWEEN) and sufficiently robust to be handled by hand without breaking (see image). Furthermore, the material is noncytotoxic to three mammalian cell lines and inhibits nonspecific binding of Gram-positive bacteria.

Multiple NaNbO₃ nanoplates are created within Nb₂O₅ nanotubes forming a unique class of heterostructure nanotubes combining ferroelectric and semiconducting nanomaterials. Local piezoelectric studies on NaNbO₃ nanoplates show clear ferroelectric behavior (see figure), while the semiconductive properties of the host Nb₂O₅ nanotubes allows for switching of electrical conductivity by an external electric field.

With soft micro- and nanopatterned materials becoming increasingly useful for various, optical, mechanical, electronic, microfluidic, and optofluidic devices, the extension of this paradigm to a pure protein-based material substrate provides entirely new options for such devices. Silk fibroin combines the properties of an ideal nanoimprint resist with superior optical quality and biocompatibility making it a new technology platform that seamlessly combines nanophotonics, biopolymeric, and biocompatible materials.

Halogen precursor polymers to poly[(2,3-diphenyl-p-phenylene)vinylene] (DP-PPV) are examined for use as advanced capacitor dielectrics. The polymer is demonstrated to function as a good dielectric until it reaches a set temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a ‘built-in’ safety mechanism for electronic devices. Conducting Polymers.

Selective metal–insulator–metal optical nanoantennas are fabricated with Au deposition on top of anodic aluminum oxide layer (see figure). The complicated nanoantennas are easily analyzed by using an equivalent-circuit system and characterized by surface-enhanced Raman scattering.

A way to achieve a high-efficiency dye-sensitized solar cell is to combine an n-type TiO₂-based photoanode with a p-type photocathode in a tandem configuration. The development of an efficient photocathode is, at present, the key target. We have optimized the NiO, I₃⁻/I⁻ p-DSSC system to obtain record photocurrent, giving 64% incident photon-to-current conversion efficiency (IPCE) and 5.48 mAcm⁻²J_SC.

Appreciable photovoltaic responses to visible light are observed in epitaxial ferroelectric BiFeO₃ thin films by sputtering deposition. The photocurrent direction is opposite to the BiFeO₃ polarization vector and can be switched by poling the films in different directions (see figure). The as-deposited films are strongly self-polarized, exhibiting significant photovoltaic response before any electrical poling process.

For the first time nanocarbon composites with C₇₀ molecules aligned on the sidewall of single-walled carbon nanotubes (SWNTs) are demonstrated. The C₇₀–SWNT photoelectrochemical devices exhibit efficient photocurrent generation properties that result from selective formation of a single composite film consisting of a SWNT network covered with C₇₀ molecules and high electron mobility through the C₇₀–SWNT network.