Advanced Functional Materials

Engineering disorder makes it possible to realize materials with advanced optical properties. On page 965, Bertolotti et al. report the recipe for Lévy glasses, strongly inhomogeneous disordered systems displaying superdiffusive light transport. The degree of superdiffusion is fine-tuned by embedding transparent spheres varying in size by orders of magnitude in a scattering medium.

The inside cover image shows a tilted SEMFE image of La_0.7Sr_0.3MnO₃ vertical nanorods. A. Carretero-Genevrier and co-workers have established a new method to generate vertical complex oxides nanostructures based on a sol–gel precursor solution and using track-etched polymers that act to buffer the substrate, which is described on page 892. These vertical nanorods grown at mild temperature undergo a complete structural, morphological, and chemical transformation into single crystalline (LaSr)_xO_y nanopyramids upon thermal activation at 1000°C.

Palladium alkanethiolate acts as a single-source precursor to produce Pd₄S films in a simple, single-step method. The films are robust and have special attributes, such as withstanding harsh chemical environments and conducting like a metal. Due to the ability of the precursor to be patterned via electron beam lithography (EBL) and micromolding (MIMIC), the conducting etch masks of Pd₄S can be patterned. By suitably modifying the synthesis route, films of Pd₁₆S₇ and PdS can also be prepared.

A roll-to-roll process for fabricating flexible and stretchable transparent conducting films (TCFs) using superaligned carbon nanotubes is demonstrated. Practical touch panels are assembled based on these TCFs, which are superior in flexibility and wearability and comparable in linearity to touch panels based on indium tin oxide TCFs. Combined with obtained improvements in the transparency and sheet resistance of such films, this approach has immediate industrial potential.

A novel version of track-etched polymers directly buffering oxide substrate is adopted to prepare vertical La_0.7Sr_0.3MnO₃ polycrystalline nanorods by chemical-solution deposition. The La_0.7Sr_0.3MnO₃ nanorods suffer a heavy transformation into vertical single-crystalline (La,Sr)_xO_y nanopyramids sitting on the LSMO epitaxial wetting layer upon thermal activation. This methodology presented here opens this field to the growth of other functional oxide vertical nanostructures.

Dual-gate transducers are fabricated with buried electrodes to eliminate Faradaic leakage currents. The transducers are potentiometric sensors where the detection relies on measuring a shift in threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. The sensitivity is enhanced over conventional ion-sensitive field-effect transistors by adjusting the ratio of the top and bottom gate capacitances.

An electronegative conjugated compound composed of a newly designed carbonyl-bridged bithiazole is synthesized as a candidate for air-stable n-type OFET materials. The properties of this compound are investigated by photophysical and electrochemical measurements. OFET devices based on this compound show high electron mobilities even under ambient conditions (see figure).

The dewetting of discotic liquid crystals (DLC) in their isotropic phase, on surfaces chemically patterned with stripes, produces isolated droplets in hydrophilic regions. Upon cooling into their columnar phase, a number of DLC materials can be found to be aligned in a planar manner with the columnar director either parallel or perpendicular to the patterning direction.

A fully transparent non-volatile memory thin-film transistor is demonstrated with a hybrid-type gate stack composed of an organic ferroelectric poly(vinylidene fluoride- trifluoroethylene) gate insulator and a semiconducting Al-Zn-Sn-O channel. The transmittance of the device is more than 90% at the wavelength of 550 nm. This embeddable transistor will provide functionalities for various system applications in future transparent electronics.

The performance of organic electronic devices depends heavily on the charge transport property of the organic semiconductor material employed. Fluorenyl hexa-peri-hexabenzocoronene (FHBC) materials have the ability to self-organize into columnar structures which can enhance charge transport. A field-effect mobility of 2.8 × 10⁻³ cm² V⁻¹ s⁻¹ was obtained for the organic field-effect transistor device and a power conversion efficiency of 1.5% was recorded for the bulk heterojunction solar cell.

The coupling of surface-confined polymer-ization techniques for the synthesis of well-defined brush layers and easy post-functionalization methods allows the pre-paration of gel-brush/metal nanoparticle hybrids. This new class of macromolecular platforms shows a multifunctional char-acter and precisely adjustable physical and structural properties. Such hybrid films may find applications as catalytic layers, antibacterial surfaces, sensors, and model platforms for optics and electronics.

Two-dimensional Ag metalized grating structures exhibit significant plasmonic coupling efficiency for enhanced fluorescence observations under a microscope. They have 100 times the enhancement of fluorescence intensity versus a plain glass surface, and an improvement of about three times the enhancement of fluorescence intensity of a 1D grating. This type of substrate has application in biodiagnostics, imaging, sensing, and photovoltaic cells.

A gold-nanocluster-based fluorescent sensor for cyanide is presented, based on cyanide etching-induced fluorescence quenching of Au nanoclusters. This sensing system is proven to be highly sensitive and selective towards cyanide. Importantly, it can be readily used for detecting low-concentrations of cyanide in real water samples.

Highly aligned, ultralong Ag nanowire films can spontaneously form at the three-phase interface of oil–water–air. The ordered films exhibit intrinsic large electromagnetic (EM) fields that are localized in the interstitials between adjacent nanowires. This new three-phase interface approach has been found to be a general route, and can be extended to self-assemble other ultralong nanowires to produce ordered films.

Typical disordered optical materials are known to lead to normal diffusive light transport. This article proposes a novel method to realize disordered dielectric samples in which light propagates superdiffusively. This unique feature is obtained by creating power-law spatial inhomogeneities in the density of light scatterers.

A controllable and convenient hydrothermal synthetic route is developed to synthesize layer-by-layer triplex Au–Ag–C core–shell nanoparticles, which can incorporate the SERS (surface-enhanced Raman spectroscopy) label, 4-mercapto benzoic acid (4-MBA). The colloidal carbon-encapsulated Au_core/Ag_shell spheres have a monodisperse size distribution, and they act as a novel type of SERS tag to detect mouse IgG at concentrations of ∼100–10 ng/mL.

Quantum-dot-tagged bioresponsive hydrogel photonic beads are used as the encoded microcarriers of a suspension array for multiplex label-free DNA detection. In the assay, specific hybridization of the DNA will cause hydrogel shrinking, which can be detected as a corresponding blue-shift in the beads' Bragg diffraction peak that can then be used for quantitatively estimating the amount of target DNA.

Nanocrystalline electroplated Cu_1–xNi_x thin films show an interesting combination of mechanical and magnetic properties. These films exhibit large and tunable values of hardness and Young's modulus, linked to the reduced crystallite sizes. From a magnetic viewpoint, either paramagnetic or ferromagnetic behavior is observed depending on the exact alloy composition.

Efficient cell attachment, detachment, and excellent conductivity are obtained from nanocomposite boronic acid-functionalized multiwalled carbon nanotubes. Using K562 leukemia cells as a model, this nanocomposite is used to construct a reusable impedance biosensor for cell determination. The sensor not only measures the quantity of the cells but it can also determine their proliferation or apoptosis state.

Temperature-dependent hysteresis for conjugated polymers in the operation of a polymer thin film transistor (PTFT) is observed for the first time. This observation is explained by the limited main chain segmental motion that cannot be aligned by polarization in phase with the applied gate voltage. This investigation shows for the first time that chain relaxation in conjugated polymers is the origin of the hysteresis in PTFT.

Semiconducting films of InAs quantum dots targeted for optoelectronic applications are fabricated and investigated in field-effect transistors. A cascade of interface modifications allowed for improved performance following each film treatment, resulting in ON/OFF ratios of around 10⁵ for these transistors.

A simple route is presented to fabricate water-soluble CdSe-nanofibers by the self-assembly of elastin-like polymers (ELPs). Non-toxic CdSe nanoparticles are synthesized and effectively stabilized in situ at room temperature with the ELP shell. The self-assembly into nanofibers is directed by adjusting the pH value of the solution. The nanofibers show a non-toxic response and increased cell viability against B14 hamster fibroblast cells.

6-Methyl-anthra[2,3-b]benzo[d]thiophene (Me-ABT) is synthesized and its high-quality microribbons are grown by a solution process. The solution of Me-ABT demonstrates a moderate fluorescence quantum yield of 0.34 while the microribbons show a glaucous light emission. Phototransistors based on an individual Me-ABT microribbon prepared by a solution-phase self-assembly process show a high mobility of 1.66 cm² V⁻¹ s⁻¹, a large photoresponsivity of 12 000 A W⁻¹, and a photocurrent/dark-current ratio of 6000.