Advanced Materials

Takhee Lee and co-workers demonstrate on p. 5048 the fabrication of three-dimensionally stacked 8 × 8 cross-bar array organic resistive memory devices. These devices show non-volatile memory switching behavior, and individual memory cells in the different layers are independently controlled and monitored. The demonstrated 3D stacking fabrication will enable high-density integration of organic memory cells and other organic-based electronics devices.

Membrane projection lithography is used to deposit split ring resonator structures (SRRs) on the interior faces of a cubic SU-8 cavity in work reported by Bruce Burckel and co-workers on p. 5053. The arrows in the inset schematic diagram show three of the five evaporation directions, while the SEM image shows the resulting metamaterial layers with SRRs on each of the five interior faces of the 6-μm cubic unit cell.

The ability to provide reproducible, repeated, and safe drug delivery, where the magnitude and period of dosing can be adjusted, could present substantial advantages in the clinic. This review describes devices that could achieve on-demand drug release in response to remote stimuli.

Hexagonally ordered mesoporous LiFePO₄/C nanocomposites can be synthesised with LiFePO₄ nanoparticles embedded in an interconnected carbon framework. Mesoporous LiFePO₄/C nanocomposites exhibit superior electrochemical performance and ultra-high specific power density, which makes this architecture suitable for high power applications such as HEVs and stationary energy storage for smart grids.

Random donor-acceptor conjugated copolymers with broad and even absorption across the visible region exhibit black neutral states and highly transmissive oxidized states. Polymer films show excellent optical contrasts, fast switching times, and long-term redox switching stability. Additionally, the utility of this black-to-transmissive switching polymer in a window-type electrochromic device has been demonstrated.

Antitags are reported. These materials bring together two or more metallic nanoparticles by using a dithiolated organic molecule and contain antibodies on the surface to function as antigen-specific recognition elements. The linker position leads to a behavior characteristic of surface enhanced Raman spectroscopy (SERS). In conjunction with a surface containing capture antibody, antitags can be used to detect antigens with sensitivities approaching those of the widely used enzyme linked immunosorbent assay (ELISA).

A fiber made of carbon nanotubes is shown to resemble a conventional yarn in terms of its structure, composed of discrete fibrillar sub-units, and its properties, such as high flexibility in bending, cutting resistance and 100% knot efficiency. Its combination of yarn-like character and tensile properties in the high-performance range make this CNT fiber an exceptional new material.

Uniaxial magnetic anisotropy has been observed in La_0.7Sr_0.3MnO₃ thin films grown on top of multiferroic BiFeO₃ with ferroelectric stripe domains (see Figure). The magnetic easy axis of La_0.7Sr_0.3MnO₃ correlates with the ferroelectric stripe domains. A possible spin coupling model at the La_0.7Sr_0.3MnO₃/BiFeO₃ interface is established between ferromagnetic and antiferromagnetic orders to explain this phenomenon.

Two complementary lift-off approaches for thin films from MgO, based on standard chemicals, are reported. Accompanied by appropriate annealing treatments they can be employed to synthesize freestanding single crystalline Fe-Pd films in the face centered tetragonal martensitic phase required for miniaturized magnetic shape memory acutation. Generalizations to other materials systems, e.g. epitaxially grown martensitic Ni-Mn-Ga magnetic shape memory alloy films, are also demonstrated.

Quasi-amorphous colloidal structures exhibiting angle-independent tunable photonic colors in response to the electric stimuli. Moderately polydisperse colloidal Fe₃O₄@SiO₂ nanoparticles dispersed in organic solvents exclusively form quasi-amorphous photonic materials at sufficiently high concentrations, and which reversibly reflect incident light in visible region in response to the relatively low bias voltages.

Microbatteries with large area capacity and no power limitation can be obtained by designing 3D structured batteries. 3D electrodes composed of 30 nm-thick films of LiCoO₂ coating free-standing columns of Al current collector were achieved. By comparison with a planar electrode presenting an equivalent nominal capacity, a 3D electrode exhibits improved capacity retention: 68% of the nominal capacity at 8C instead of 11%.

Nanostructured amorphous titanium suboxide electrodes were fabricated to determine the effects of the electrode geometry on the device performance of poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester inverted solar cells. It was found that a combination of electrode geometry and active layer processing influences the open circuit voltage in these devices.

Transient photovoltage and charge extraction analyses are employed to analyzes charge carrier densities and bimolecular recombination dynamics in organic polymer: fullerene solar cells under open circuit operating conditions, employing four different donor polymers. An equation is derived which allows us to calculate the device V_OC from these kinetic measurements. This equation allows us to calculate voltage output of devices within ± 25 meV of directly measured values. This analysis thus allows us to relate device open circuit voltage directly to the kinetics of bimolecular recombination, and thereby the influence of nanomorphology upon device voltage output.

New semiconducting copolymers based on benzobisthiazole show excellent environmental stability in high-humidity air, which is an unusual performance for semiconducting polymers, along with OFET mobilities of as high as 0.26 cm²/Vs, even with disordered thin-film structures. With these unique features, these new copolymers are fascinating materials with high processability, mobility, and stability as active layers for printable electronics.

A method for fabricating microcapsules with gel-immobilized colloidal crystal shells using microfluidics is reported. The diffraction color or photonic wavelength of the gel-immobilized colloidal crystal shells can be adjusted by varying the particle concentration before gelation and tuned by external stimuli after preparation. The gel-immobilized colloidal crystal shell has a higher sensitivity and wider range in the stop band wavelength than that displayed by a bulk gel.

A blue iridium carbene complex realizes high-efficiency blue and white OLEDs (see figure). For a blue OLED, η_p,max is recorded to be 35.9 lm W⁻¹. For a white OLED, η_p,max and η_p,1000 are measured to be 59.9 lm W⁻¹ and 43.3 lm W⁻¹, respectively, without any light-outcoupling enhancement. This white OLED also shows an illumination-acceptable CRI over 80.

By simply applying an electric current across a graphene oxide (GO) film, GO can be easily recovered to produce reduced GO (RGO). The resulting RGO film can be used as efficient gap electrodes in organic photoswitching devices, which display comparable efficiency to those using Au as gap electrodes.

Elastomeric smart windows with switchable optical transparency and wetting properties (see Fig.) are fabricated through the combination of replica molding and surface wrinkling. The resulting smart windows, with a surface topography that is tunable via mechanical strain, exhibit not only significant changes in optical transmittance and wetting properties, but also the additional functions of self-cleaning and antireflection.

A new method for obtaining asymmetric (nano)electrodes through the adsorption and electrochemical desorption of self-assembled monolayers on gold is described. The selective WF modification is demonstrated by Kelvin Probe Force Microscopy and electrical characterization of organic FETs. The proposed method is simple, fast and could allow parallel, large-scale fabrication of asymmetric electrodes for micro- and large-area electronics.

The composition of temperature-responsive copolymer brushes based on oligo(ethylene glycol) methacrylates is tuned to obtain a collapse temperature of ∼35 °C. The chains are grafted by antibacterial magainin I peptide, whose activity is tested at different temperatures against various bacteria. The brushes switch from bactericidal to cell-repellent below and slightly above 35 °C, respectively, due to the progressive vertical collapse of the brush.

In epitaxial heterostructures combining strongly correlated manganese oxides with antiferromagnetic-insulator or half-metallic character, a large interfacial moment is found and used to produce a spin-filter-like behavior in all-manganite tunnel junctions. The results suggest that after playing a key role in exchange-bias for spin-valves, uncompensated moments at engineered antiferromagnetic interfaces represent a novel route for generating highly spin-polarized currents with antiferromagnets.

Black silicon with aspect ratios up to 10 and an average optical reflectance of only 2.5% over the whole absorbing spectral range was covered perfectly conformal with a transparent conductive oxide. The thin film was deposited by thermal ALD and exhibited a resistivity of 1.1 Ohm cm. This concept promises a new design for an efficient heterojunction silicon solar cell.

An indium-assisted ultrafast carbon nanotube (CNT) transfer method with a yield rate over 90% is described. Metal-coated as-transferred CNT structures exhibit excellent electrical performance that is at least one order of magnitude better than the previously published results. Shear test results show that the adhesion between CNTs and the substrate is greatly improved and excellent flexibility is obtained after the transfer process.

Inverse-opal strong polyelectrolyte sensors, achieved by using a colloidal crystal templating method, respond sensitively and universally to various anions, cations, and zwitterions with brilliant structural colors that can even be observed by the naked eye. They are very attractive for a range of applications, such as ion detection, separation, ionic conduction, and catalysts.

Organic memory: Our three-dimensionally (3D) stacked 8 × 8 cross-bar array organic resistive memory devices showed non-volatile memory switching behavior, in which individual memory cells in the different layers can be independently controlled and monitored. The 3D stackable organic memory devices will enable achieving highly integrable organic memory devices and other organic-based electronics with much increased cell density.

Membrane projection lithography is used to create vertically oriented split-ring resonators which show measured electric and magnetic resonances (λ = 22, 11, and 7 μm). We then create composite structures with 5 split ring resonators per unit cell (image). This approach provides a long-sought, manufacturable path toward the realization of 3D optical and infrared metamaterials.

The light output power and wall-plug efficiency of the Si nanocrystal (nc-Si) light-emitting diode (LED) were significantly enhanced by employing the multiple-luminescent structures. This improvement was attributed to a strong confinement of carriers in the SiNx luminescent layers containing the nc-Si due to the band offset between the luminescent layer and barrier layer.

Ambipolar pentacene transistors in bottom contact-bottom gate geometry are fabricated on flexible substrates using parylene as a dielectric and self-assembled monolayer treatment of the source-drain electrodes to improve charge injection. Hole and electron mobilities of 0.07-0.1 cm² V⁻¹ s⁻¹ and 0.01-0.04 cm² V⁻¹ s⁻¹ are achieved. CMOS like inverters are built and gains of up to 110 are reported.