Advanced Materials

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured biohybrid materials, report Joerg Lahann and co-workers on p. 4920. Functional polarity due to two biologically distinct hemispheres has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Combining bottom-up sol–gel assembly with micro- and nanofabrication offers a simple and fast route to develop multifunctional integrated platforms, from microfluidics to microarrays, allowing the chemistry and geometry to be tailored to the application, as reported by Paolo Falcaro, Plinio Innocenzi, and co-workers on p. 4932. The inside cover illustrates different patterns of functionalized surfaces. The background is an example of highly controlled microfluidic interface fabricated combining deep X-rays lithography with sol–gel syntheses.

Intriguing optical properties suitable for a wide range of applications are exhibited by gold nanorods. In this review, the optical properties are discussed in terms of radiative and nonradiative properties. Various synthetic routes are then outlined, followed by a discussion on nanorod assembly. Current biological and biomedical applications are summarized, with an emphasis on cancer diagnosis and photothermal therapy.

Permittivity peaks in single crystal thin film capacitors are strongly suppressed compared to bulk in the case of Pt/SrTiO₃/Pt, but are relatively unaffected in Pt/BaTiO₃/Pt structures. This is consistent with the recent suggestion that subtle variations in interfacial bonding between the dielectric and electrode are critical in determining the presence or absence of inherent dielectric “dead layers”.

The conductivity behavior of MWCNT networks within the volume of polymer nanocomposite samples is analyzed with nanometer resolution in all three dimensions. It is demonstrated that close to but above the percolation threshold for electrical conduction most of the MWCNTs do not contribute to the conductive network within the nanocomposite.

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured bio-hybrid materials. Functional polarity due to two biologically distinct hemispheres (see figure) has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films.

Deep X-ray lithography combined with sol–gel techniques offers facile fabrication of controlled patterned films. Using sol–gel, different functional properties can be induced; deep X-ray lithography alters the functionality in the exposed regions. Miniaturized devices based on local property changes are easily fabricated: this technique requires no resist, enabling direct patterning of films in a one-step lithographic process.

A red shift of the exciton of ZnO nanowires is efficiently produced by bending strain, as demonstrated by a low-temperature (81 K) cathodoluminescence (CL) study of ZnO nanowires bent into L- or S-shapes. The figure shows a nanowire (Fig. a) with the positions of CL measurements marked. The corresponding CL spectra—revealing a peak shift and broadening in the region of the bend—are shown in Figure b.

Exciton–exciton interaction in dot/rod CdSe/CdS nanocrystals has proved to be very sensitive to the shape of nanocrystals, due to the unique band alignment between CdSe and CdS. Repulsive exciton–exciton interaction is demonstrated, which makes CdSe/CdS dot/rods promising gain media for solution-processable lasers, with projected pump threshold densities below 1 kW cm⁻² for continuous wave lasing.

End-modified polymers are promising for the nonviral delivery of genes to cancer cells, immune cells, and human stem cells and point to polymer end-groups as regulators for cell-type specificity. A library of polymers has been synthesized and, although some polymers are strong transfection agents overall, for each cell type, a particular polymer is most effective (see image).

Pt–Co alloyed nanoparticles can be facilely immobilized onto CN_x nanotubes due to the incorporated nitrogen, report Yanwen Ma, Zheng Hu, and co-workers on p. 4953. The as-prepared electrocatalysts exhibit good performance for oxygen reduction reactions in acidic media arising from the high dispersion and alloying effect of Pt–Co nanoparticles, as well as the intrinsic catalytic capacity of CN_x nanotubes, which is significant for the development of fuel cells.

A straight forward method for immobilizing Pt–Co alloyed nanoparticles onto nitrogen-doped CN_x nanotubes is presented (see image). The as-prepared electrocatalysts exhibit good performance for oxygen reduction reaction in acidic medium arising from the high-dispersion and alloying effect of the Pt–Co nanoparticles and the intrinsic catalytic capacity of the CN_x nanotubes.

Phosphorescent light-emitting transistors, in which light emission from singlet and triplet energy levels is harvested using solution-processed materials (see figure), are presented. While a green phosphorescent dendrimer exhibits an external quantum efficiency of 0.45% at 480 cd m⁻², a red polymer/phosphorescent small-molecule blend produces a brightness exceeding 30 cd m⁻² with a relatively high hole mobility of 2.5 × 10⁻² cm² V⁻¹ s⁻¹.

A solution approach to assembling Au(I)-alkanethiolates into nanotube structures at room temperature is presented, in which Au(I) cations and alkanethiolate ligands are coordinated into thin platelet forms that then evolve into an open tubular configuration (see figure). The organic–inorganic hybrid nature of the nanotubes, their ability to be modified, and their high stability make them of interest for practical applications.

Local structure, chemistry, and bonding at interfaces often radically affect the properties of materials. A combination of scanning transmission electron microscopy and density functional theory calculations reveals an atomic layer of carbon at a SiC/Ti₃SiC₂ interface in Ohmic contact to p-type SiC (see image), which results in stronger adhesion, a lowered Schottky barrier, and enhanced transport. This is a key factor to understanding the origin of the Ohmic nature.

Hexagonal-phase single-crystal Gd₂O₃ is deposited on GaN in a molecular beam epitaxy system (see image). The dielectric constant is about twice that of its cubic counterpart when deposited on InGaAs or Si. The capacitive effective thickness of 0.5 nm in hexagonal Gd₂O₃ is perhaps the lowest on GaN-metal-oxide-semiconductor devices. The heterostructure is thermo dynamically stable at high temperatures and exhibits low interfacial densities of states after high-temperature annealing.

A nanowire-based nanosensor for detecting biologically and chemically charged molecules that is probe-free and highly sensitive is demonstrated. The device relies on the nonsymmetrical Schottky contact under reverse bias (see figure), and is much more sensitive than the device based on the symmetric ohmic contact. This approach serves as a guideline for designing more practical chemical and biochemical sensors.

Vertically aligned single-crystalline Co₅Ge₇ nanowire (NW) and nanobelt arrays are grown on a very thin graphite layer as well as a curved graphite layer with a good epitaxial lattice match. Co₅Ge₇ NW arrays, thus grown, show very efficient field emission properties comparable to those of carbon nanotubes and may be used for flexible field emission displays in the future.

A novel class of hosts suitable for solution processing has been developed based on a conjugated dendritic scaffold. By increasing the dendron generation, the highest occupied molecular orbital (HOMO) energy level can be tuned to facilitate hole injection, while the triplet energy remains at a high level, sufficient to host high-energy-triplet emitters. A power-efficient blue-electrophosphorescent device based on H2 (see figure) is presented.

Electrophoretic ink nanoparticles with high mobility are successfully fabricated by dispersion polymerization. The color of test cells can be changed by applying a bias voltage, as shown in the figure: the lower row shows the same cells as the upper row but with an applied voltage. These all-organic, encapsulated-dye, electrophoretic ink particles are expected to reduce the fabrication cost of e-ink in electrophoretic image display cells.

A newly developed SiN microhotplate allows specimens to be studied at temperatures up to 1000 K at a resolution of 100 picometer (see image). Aberration-corrected transmission electron microscopy has become a commonplace tool to investigate stable crystals; however, imaging transient nanocrystals is much more demanding. Morphological transformations in gold nanoparticles and layer-by-layer sublimation of PbSe nanocrystals is imaged with atomic resolution.

Suppression of nucleation around a gold electrode during pentacene growth on a SiO₂ channel is found by photoemission electron microscopy. Mass flow is driven by the difference between the molecular orientations on SiO₂ and gold. The poor connectivity at the channel/electrode boundary causes degradation in the performance of a field-effect transistor, which is found to be improved by self-assembled monolayer treatment on the electrode (see figure; thickness in monolayers (ML)).

A nanocrystalline (NC) NiFe alloy is presented, in which both highly improved plasticity and strength are achieved by the dynamic-loading-induced deformation mechanisms of de-twinning (that is, reduction of twin density) and significant grain coarsening (see figure). This work highlights potential ingenious avenues to exploit the superior behavior of NC materials under extreme conditions.

Step-growth, radically mediated thiol-norbornene photopolymerization is used to create versatile, stimuli-responsive poly(ethylene glycol)-co-peptide hydrogels (see image) The reaction is cytocompatible and allows for the encapsulation of human mesenchymal stem cells with a viability greater than 95%. Cellular spreading is dictated via three-dimensional biochemical photopatterning.

Repair of physically separated thermoplastic polymers containing γ-Fe₂O₃ nanoparticles without sacrificing their mechanical properties is achieved by applying an oscillating magnetic field. As γ-Fe₂O₃ nanoparticles oscillate at the frequency of the magnetic field, localized amorphous flow occur, and a permanent repair of physically separated polymeric films is achieved.

Single-crystalline zinc selenide (ZnSe) nanobelts were fabricated via the ethylenediamine (en)-assisted ternary solution technique and subsequent thermal treatment. Individual ZnSe nanobelts were assembled into nanoscale devices (see figure), showing a high spectral selectivity and photocurrent/immediate-decay ratio and a fast time response, justifying effective utilization of the ZnSe nanobelts as blue/UV-light-sensitive photodetectors.

Quantum dot/conducting polymer hybrid films are used to prepare light-emitting diodes (LEDs). The hybrid films (CdSe@ZnS quantum dots excellently dispersed in a conducting polymer matrix, see figure) are readily prepared by various solution-based processes and are also easily micropatterned. The LEDs exhibit a turn-on voltage of 4 V, an external quantum efficiency greater than 1.5%, and almost pure-green quantum-dot electroluminescence.