Advanced Materials

Molecular nanowires for nanoelectronics may be built from guanine (G) tetrad building blocks. Spontaneous assembly of guanine-rich DNA sequences that form tetrads and further arrange into a tetrahelix structure produces long, continuous monomolecular G-wires (see Figure and cover), presumably G4-DNA, composed of single self-folded poly(G) strands of thousands of bases.

Conventional optical photolithography is used to create photoresist patterns on a preformed silica colloidal crystal film. Upon regrowth of the same silica colloidal crystal followed by removal of the photoresist patterns, air–core line defects are successfully introduced into the self-assembled silica colloidal crystal (see Figure and inside cover).

Outstanding examples of applications of scanning probe microscopy (SPM; see Figure) in materials science and the latest developments in techniques that show the full potential of SPM are introduced in this Progress Report. Starting with appealing visualization of matter, other focus points are the investigation of dynamics of processes, determination of properties and functionality, and manipulation of matter at the nanometer length scale.

The application of an electric field (E_cast) during solvent vaporization is shown to inhibit the formation of ordered domains in thin films of a poly(phenylenevinylene) derivative, resulting in a homogeneous environment favorable for charge transfer. An order-of-magnitude increase in charge-carrier mobility (see Figure) is achieved by the elimination of these commonly found domains.

Ethenylene groups within the silicate framework of hybrid mesoporous ethenylene-silica (HME) are successfully modified via a two-step chemical modification process (see Figure) to produce a sulfonic acid-functionalized hybrid mesoporous solid acid catalyst. The material exhibits high activity for various acid-catalyzed reactions and can be used repeatedly without deactivation. The Diels–Alder modification described can be extended to the creation of other functional materials.

Nanostructured TiO₂ (ns-TiO₂) films obtained by supersonic cluster beam deposition possess highly porous, defective structures, and allow efficient incorporation of carbon- containing molecules during thermal treatment. Carbothermal reduction modifies the electronic structure of the ns-TiO₂, narrowing the optical gap to 2 eV. This is within the range of visible solar radiation (see Figure), allowing more efficient photoconversion.

Organic dye molecules have been included in the crystalline regions of syndiotactic polystyrene (sPS) by soaking clathrate or glass films of sPS in an azulene solution containing a plasticizer (see Figure). Highly oriented films, in which the dye molecules are oriented, are easily obtained by applying a similar procedure to an oriented glass sample.

The ordered monodisperse ionic channels existing in lyotropic liquid-crystal (LLC) polymer films allow only the passage of water-soluble molecules which are smaller than the ∼ 1.2 nm diameter of the channels. When formed on an ultraporous polysulfone (PSf) support, the films are used effectively as size-selective sieves for water-soluble molecules. These membranes are able to completely reject molecules larger than their pore sizes.

The synthesis of efficient photoluminescent quantum dots via growth on a DNA template is reported for the first time. The nanoparticles emit in the second biological window of 1050–1200 nm with quantum efficiencies of 11.5 ± 1 % in aqueous solution, and are stable for over a week in blood plasma at 37 °C. The Figure shows an energy-filtered TEM image of PbS nanocrystals (Pb: orange; P in DNA: green).

Reactive “polymer nanosheets” consisting of N-dodecylacrylamide and a photocrosslinkable methacryloyl group in the polymer monolayer have been deposited onto solid substrates by the Langmuir–Blodgett technique. The polymer nanosheets have well-ordered molecular alignment and a controlled thickness on the nanoscale. Multiple photopatterning allows the formation of 3D nanostructures, such as pyramids, tracery patterns, etc. (see Figure), with nanometer thickness precision. The scale bar in the bottom figure represents 5.0 mm.

Electrostatic-force-driven self-assembling behavior of gelatin polypeptides has been investigated through the predominantly seeded-aggregation growth of denatured gelatin molecules on citrate-stabilized gold nanoparticles (see Figure). The resulting self-assembled gelatin aggregates have been used as soft templates to prepare nanometer-sized gold-loaded silica/gelatin nanocapsules. This synthetic approach has been extended to various silica-coated biomolecules and provides further insight for creating novel smart bionanostructures.

A simple approach to actively manipulate fluids in two-dimensional microfluidic networks based on the electrocapillary effect is reported. It allows not only patterning of biological solutions and yeast cells in a programmable manner, but also the growth of self-assembled colloidal crystals in the addressable microfluidic networks. The Figure shows a photonic display made by using colloidal particles of different diameters. The inset (scalebar: 200 μm) shows a microchamber filled with 250 nm colloidal crystals.

A thermosensitive polymer hydrogel can be used to transport cargo by propagating a volume-phase transition along its length (see Figure; red and blue arrows correspond to localized heating and cooling, respectively). Directional motion with velocities up to 15 μm s^–1 for cylinder diameters of approximately 1 mm are recorded. Miniaturization of this device could lead to increased gel speeds and microfluidic and medical applications.

ZnO nanocrystals with various shapes (see Figure) have been synthesized via non-hydrolytic ester elimination sol–gel reactions between zinc acetate and 1,12-dodecanediol. Uniform anisotropic cone-shaped, hexagonal cone-shaped, and rod-shaped ZnO nanocrystals have been synthesized using various surfactants.

Large-scale alignment of bilayer block copolymer films by applying in-plane shear is demonstrated. The method eliminates all disclinations and most dislocations from arbitrarily large samples, as evidenced by atomic force microscopy of the microdomain lattice (Figure, left) as well as its Fourier transform (Figure, right). The resulting films can act as ordered nanolithographic templates.

Layer-by-layer assembly is used to produce thin films of J-aggregates of cyanine dye molecules with an absorption constant of 10⁶ cm^–1. The films display high reflection and absorption at resonance (see Figure, ∼50 nm films) and nanoscale features that make them well suited for use in strong-coupling optoelectronic applications, enabling the creation of exciton–polariton optoelectronic devices that operate at room temperature.

Axis-selective two-photon excitation and polarization-preserved triplet energy transfer using a linearly polarized (LP) 800 nm femtosecond pulse laser generates an anisotropic photoreaction in photocrosslinkable-polymer liquid-crystalline films. The molecular orientation is controlled parallel to the polarization of the laser. The tightly focused laser beam generates a submicrometer-oriented structure, as shown in the Figure.

Perylene tetracarboxylic derivatives (PTCDs) display exceptionally high two-photon absorption (2PA) cross- sections (δ, see Figure). In addition, the 2PA saturation behavior and strong two-photon-pumped fluorescence suggest that PTCD compounds may be attractive candidates for applications in optical limiting and two-photon-pumped upconversion lasing.

Pyramid-like Fe₃O₄ nanostructures (see Figure) are formed over large areas on α-Fe₂O₃(0001) substrates using a plasma-sputtering technique. No catalysts or templates are used in the reaction process. This nanostructure resembles Egyptian pyramids, possessing many layers and standing perpendicular to the substrate surface. These structures may have potential applications in constructing nanoscale magnetic and high-density storage devices.

The ferroelectric relaxor terpolymer (P(VDF-TrFE-CFE) has a dielectric constant above 50 at room temperature and giant longitudinal strain. By adding only 0.5 wt.-% functionalized multiwalled carbon nanotubes, its crystallinity (light blue, see Figure), Young's modulus (green), dielectric constant (dark blue), and electromechanical response (maroon) can be simultaneously improved (see Figure).

Molecular nanowires for nanoelectronics may be built from guanine (G) tetrad building blocks. Spontaneous assembly of guanine-rich DNA sequences that form tetrads and further arrange into a tetrahelix structure produces long, continuous monomolecular G-wires (see Figure and cover), presumably G4-DNA, composed of single self-folded poly(G) strands of thousands of bases.

Embedding metal and metal-oxide nanoparticles into a Teflon AF matrix using two solution-phase synthesis techniques has been developed and exemplified using silver, gold, palladium, and nickel nanoparticles. The nanocomposite materials (see Figure) exhibit greatly improved chemical stability and can find applications in optoelectronics, catalysis, and as protective coatings.

Introducing structural defects into photonic crystals is a challenge that must be met for many photonic applications. Here, a method is demonstrated to tailor the local structure of silicon inverse opals, prepared from the self-assembly of colloidal microspheres, by combining multiphoton photopolymerization and silsesquioxanes (see Figure).

Chemically active polyelectrolyte planar defects (see Figure) are embedded into colloidal photonic crystals using both direct-coating and transfer-printing techniques. These planar defects introduce a transmitting state within the photonic stop band, which is dynamically adjusted with nanometer precision by pressure-controlled selective vapor sorption.

Conventional optical photolithography is used to create photoresist patterns on a preformed silica colloidal crystal film. Upon regrowth of the same silica colloidal crystal followed by removal of the photoresist patterns, air–core line defects are successfully introduced into the self-assembled silica colloidal crystal (see Figure and inside cover).