Advanced Materials

A self-assembled hybrid of ultrananocrystalline diamond (UNCD) and carbon nanotubes (CNTs) is successfully prepared by their simultaneous growth in an argon-rich Ar/CH₄ plasma (see Figure and cover). Control of the relative fractions and configurations of UNCD and CNTs in the hybrid material is demonstrated. This new synthesis pathway enables the development of new nanocarbons with unique mechanical, tribological, and electrochemical properties.

A double hydrophilic block copolymer (DHBC) is used as a crystal-growth modifier for controlled self-assembly of complex and unusual calcite pancakes with multiple stacked and porous layers (see Figure), based on a polymer-directed crystallization mechanism. The results demonstrate that it is possible to manipulate the ability of selective adsorption and stabilization of the DHBCs in order to control the directed crystal growth process.

Electroactive luminescent bio-organic nanowires, 10 nm in width and with lengths up to 10 μm (see Figure), are generated through co-assembly of protein amyloid fibrils with conjugated oligoelectrolytes. The electro-optical properties of the wires are demonstrated with reversible electrochemical doping-induced fluorescence quenching, providing evidence for both electrical transport and electroactivity.

A temperature-sensing scheme that relies on kinetically trapping molecular mixtures of a sensor molecule and amorphous host materials in a thermodynamically unstable state is introduced. Subjecting the blends to temperatures above their glass transition leads to irreversible changes of their photoluminescence emission spectra due to phase separation and excimer formation, as shown in the Figure for blend films before (left) and after annealing at 150 °C for 42 h (right).

A lithographic method of patterning lipid bilayer membranes on the surface of colloidal particles is described. Three-dimensional, micrometer-resolution patterns on the single fluid lipid bilayer membranes supported on silica microspheres have been generated by in-situ UV photolithography (see Figure). This technique is based on the direct photochemical removal of lipids from the colloid surface in an aqueous environment.

A nanometer-sized ethyl alcohol meniscus induced between a conductive atomic force microscope tip and a silicon surface (see Figure) allows the fabrication of nanodots or nanowires of SiC_x at a predetermined position on the substrate. The meniscus size and kinetic parameters control the nanostructure size.

Spherical colloids with silica cores (300–500 nm diameter) and gold shells (20–60 nm thickness) are shown to deform to form oblate ellipsoids under ion-beam irradiation, as shown in the Figure. The deformation, which can be controlled by ion fluence, is attributed to an ion-induced anisotropic deformation in the amorphous silica that is constrained mechanically by the gold shell. The optical extinction of these samples is highly angle-dependent.

Thermoelectric nanowire-based devices are fabricated by the electrodeposition of n-type Bi₂Te₃ and p-type BiSbTe nanowire bundles within the same alumina nanotemplate (see Figure). The nanowire bundles are approximately 50 μm in diameter and consist of nanowires 200 nm in diameter and 40 μm in length. These nanostructured materials could be used to create higher-efficiency power generation or cooling devices.

Hyperbranched polyphenylene nanotubes are fabricated by Diels– Alder reactions of tetraphenylcyclopentadienones in the nanochannels of porous alumina membranes. Nanotubes with different structures and morphologies, and even highly porous carbon nanotubes (see Figure), can be obtained by adjusting the starting materials and the conditions of in-situ polymerization.

A self-assembled hybrid of ultrananocrystalline diamond (UNCD) and carbon nanotubes (CNTs) is successfully prepared by their simultaneous growth in an argon-rich Ar/CH₄ plasma (see Figure and cover). Control of the relative fractions and configurations of UNCD and CNTs in the hybrid material is demonstrated. This new synthesis pathway enables the development of new nanocarbons with unique mechanical, tribological, and electrochemical properties.

Superb antishock WS₂ inorganic fullerenes (IF) can sustain shock pressures up to 25 GPa, suggesting that these IFs are probably the toughest cage molecules known. The Figure shows images of a) pre- and b) post-shock WS₂ IF nanoparticles. These IFs may have great potential to withstand very high applied loads when used as solid-state lubricants.

Syndiotactic propylene–ethylene copolymers show entropic or enthalpic elasticity depending on ethylene concentration (see Figure). Enthalpic elasticity is due to a reversible transition between transplanar and helical polymorphic forms during stretching, and allows maintenance of elasticity even for highly crystalline materials.

Self-assembly of 100 μm spheres on a patterned electrode under the influence of an applied electric field is demonstrated. This process occurs for ordered arrays and arbitrary patterns, over areas up to ∼0.7 cm², with a defect rate (e.g., missing spheres or extra spheres, circled in Figure) of about 1 %. These arrays of microspheres can be transferred into polymeric matrices, such as poly(dimethylsiloxane), polyurethane, and epoxy.

A fully inorganic analogue of the nanostructured dye-sensitized solar cell is fabricated using an electrochemically grown n-ZnO/CdSe core–shell nanowire array (see Figure). Filling the voids between the nanowires with p-type wide-bandgap CuSCN by a solution-deposition technique leads to an extremely thin solar cell exhibiting 2.3 % energy-conversion efficiency.

High-porosity syndiotactic polystyrene aerogels characterized by nanofibrils that give rise to a microporous crystalline δ-phase (see Figure) present a high sorption capacity for volatile organic compounds at low concentrations, typical of the δ-phase, as well as high sorption kinetics, typical of aerogels. These sorption properties make these new aerogels very promising for industrial applications in chemical separations and water purification.

SiC nanowires (NWs) reinforce SiC matrix composites with high efficiency. With the incorporation of ∼ 6 vol.-% randomly oriented single-crystal SiC NWs in the matrices, the fracture toughnesses and flexural strengths of the composites doubled. The composites (see Figure) were fabricated in situ by a new process based on chemical vapor infiltration. Reinforcement efficiency of the NW is affected by the amount of C deposited on the NWs as the NW/matrix interfacial layer.

Patterning of organic field-effect transistors can be easily accomplished by microcontact printing combined with subsequent electroplating and electrode-peeling transfer. The method is based on area-selective electrodeposition and diffusion electropolymerization performed on metallized substrates with a previously patterned self-assembled monolayer, which is used as a template in the subsequent deposition of drain and source contacts (see Figure).

Si thin films, grown using ion-beam-assisted deposition of buffer layers on polycrystalline metal-alloy tapes (see Figure), show out-of-plane and in-plane mosaic spreads of 0.8° and 1.3°, respectively, and a room-temperature Hall mobility of 89 cm² V^–1 s^–1 for a doping concentration of 4.4 × 10¹⁶ cm^–3. These results provide proof-of-concept for a promising materials technology that does not require lattice-matched, single-crystal substrates for deposition of well-oriented, high-carrier-mobility semiconductor thin films.

Single-crystalline SiC nanowires (NWs) with a SiO₂ coating (see Figure) have been grown using electrospun polyacrylonitrile nanofibers as templates. SiC NWs produced in this process have uniform cross-sections, well-ordered structures, and very low concentrations of stacking faults, and contain no catalyst. Some bent or helical SiC NWs with single-crystalline structures are also observed.

A polymer matrix filled with nanoparticles, used as the gate material, makes solution-processable, low-voltage, organic transistors possible. The device shown here operates at very low voltages (see Figure). Atomic force microscopy shows a relatively homogeneous film, even with a high filling of nanoparticles.

Deformation of single, nanometer-sized metal crystals is monitored in situ by transmission electron microscopy (see Figure). Compressive forces from graphitic shells encapsulating Mo or W crystals lead to slow but considerable deformation. The formation of twins and grain boundaries is observed. Sustained or cyclic deformation leads to re-annealing of defects so that a permanent accumulation of defects in the crystals does not occur.

Patterned monolayers of gold nanoparticles are selectively formed on Hf⁴⁺-modified silicon dioxide. The 1.5 nm diameter particles are functionalized with a phosphonic acid ligand shell and assembled from solution on a native oxide surface that has been patterned with Hf⁴⁺ ions, as shown in the Figure. This system integrates nanoscale components and lithographic patterning. The technique used is precise and compatible with other lithographic techniques.

Preparation of a low-density, high- surface-area SnO₂ aerogel (see Figure inset), comprised of interconnected, randomly oriented crystalline (rutile) SnO₂ nanoparticles ∼3–5 nm in size is reported. X-ray absorption near-edge structure spectroscopy at the Sn M_4,5 edge reveals that the electronic structure of the SnO₂ aerogel is similar to that of tetragonal SnO, rather than SnO₂ or β-Sn, with additional Sn-related electronic states close to the conduction band minimum.

Magnetoresistive La_0.67Sr_0.33MnO₃ nanowires (NWs) have been synthesized using pulsed-laser deposition, with a template of MgO NWs. Transport studies reveal a remarkable metal–insulator transition at 325 K, accompanied by room-temperature colossal magnetoresistance (MR) of ∼ 10 % under a 1 T magnetic field. Shape-induced MR was observed for magnetic fields applied parallel or perpendicular to the NW (see Figure).

Rigiflex lithography combines the mold rigidity of imprint lithography, which permits fine patterning, with the mold flexibility of soft lithography, allowing intimate contact of the mold with the surface substrate over a large area. A UV-curable mold based on poly(urethane acrylate) is prepared as a film on a flexible poly(ethylene terephthalate) support, allowing nanopatterns to be prepared by a bilayer-transfer technique (see Figure).