Advanced Materials

A simple, low-cost method for fabricating flexible copper wires on elastomeric substrates is demonstrated. The use of microcontact printing and electroless metal deposition rather than conventional photolithography and physical vapor deposition of metals makes the process inexpensive and operationally simple. Copper films on elastomers may be used to fabricate flexible electronic circuits and biocompatible electronic devices.

The method used to fabricate a superhydrophobic coating from aqueous dispersions of hybrid responsive nanoparticles with no application of surfactants, organic solvents or fluorinated organic materials is reported. The hybrid nanoparticles consisted of a silica core with a grafted mixed block copolymer brush of poly[styrene-block-(4-vinylpyridine)] constituting the responsive particle shell. The responsive shell was used to tune and stabilize the secondary aggregates of the particles of the appropriate size and morphology in an aqueous environment. The suspension of the particles formed a textured superhydrophobic coating on various substrates upon casting, evaporation of water and heating above the glass transition temperature.

Polymeric-DNA complexes (polyplexes) are constructed with multiple layers of counter-polyions as DNA/polyethylenimine/poly(acrylic acid)/polyethylenimine. The increased association of polyethylenimine achieved by the multilayer approach leads to substantial increases in expression of transgene for reporter plasmids without the need for excess free polymer typically required for non-viral gene delivery. This method of polyplex preparation provides the opportunity to improve transgene expression for gene therapy approaches to disease treatment.

Gold nanostructures consisting of nanoblocks separated by a few nanometer-wide gaps were fabricated, and found to exhibit strong photoluminescence due to enhancement of the optical near-field localized in the nanogaps. The fabricated structures demonstrate a nanostructured metallic material capable of efficient photoluminescence, whose efficiency can be adjusted by tailoring the nanogap width.

We present a nanowell (NW)-based biosensing platform for electrochemically detecting biological reactions on the level of single lipid vesicle. The NW geometry of a gently-sloped vertical wall is found to be optimal for selective deposition of single liposomes without capillary resistances. Also, the use of a hydrophilic, non-biofouling PEG copolymer is essential to provide distinctively separated FLV arrays without nonspecific adsorption.

The self assembly of peptide hydrogelators that carry aromatic substituents can be modeled by a novel nanocylindrical architecture. The proposed model suggests that the nanocylinders are formed by anti-parallel β-sheets interlocked by the π-stacking interactions of fluorenyl groups and phenyl rings. This explanation is consistent with the structures observed in TEM and the data obtained by a variety of spectroscopic techniques.

High aspect ratio, luminescent poly(9,9-dioctylfluorene) nanowires are synthesized by template wetting. Optical spectroscopic characterization indicates the formation of a significant fraction of the polymer β-phase. The results indicate that the wires essentially act as self-doped 1D nanostructures in which the PFO β-phase dominates the luminescence behavior following optical, electrochemical or electrical excitation.

A functioning dynamic memory device has been created using a polypyrrole composite material that contains immobilized anions and highly mobile cations in the form of a thin film spanning two metal electrodes in an interdigitated electrode array configuration. Dynamic asymmetric electronic behavior based on the movement of charge in response to the application of a field is demonstrated. The material system described has significant advantages for application in nanometer-scale electronics.

Dye-sensitized solar cells (DSSCs) comprising chemically synthesized nanorods and nanoparticles are investigated. In identical circumstances, except for the charge-collection efficiency, nanorod-based DSSCs show improved photovoltaic properties (6.2 % versus 4.3 % for NP-based DSSCs) owing to the characteristics of slightly enhanced electron transport and predominantly degraded charge recombination, compared with nanoparticle-based DSSC.

A simple, low-cost method for fabricating flexible copper wires on elastomeric substrates is demonstrated. The use of microcontact printing and electroless metal deposition rather than conventional photolithography and physical vapor deposition of metals makes the process inexpensive and operationally simple. Copper films on elastomers may be used to fabricate flexible electronic circuits and biocompatible electronic devices.

Transparent inorganic UV-protective coatings are prepared by an epoxide-derived sol-gel route at low temperature. The obtained coatings show high transparency in visible range and highly efficient absorption in the whole UV range, which makes them ideal candidates for the protection against UV radiation.

Tunable, room-temperature, amplified stimulated emission (ASE) is generated in quantum dot (QD)-doped nanocomposites through two-photon optical pumping in the near infrared (see figure). Utilizing a zirconia host matrix temporal stability comparable to that of ASE generated through optical pumping in the 1-photon excitation region is demonstrated.

Printing of well defined micro-structures using a soft lithographic technique based on liquid crystalline inks is presented. Monolithic structures with tunable macromolecular organization can be locally printed with a variety of optical functionalities. Applications in the fields of displays and security- features are shown.

Uniformly doped crystalline organic nanorods and nanowires are prepared by adsorbent-assisted physical vapor deposition. The emission color of the binary 1D nanomaterials can be controlled – and made to approach white light (see figure) – by changing the doping content, which is ascribed to intermolecular fluorescence resonance energy transfer between the two nanocrystalline components.

Bilayer membranes that are covalently conjugated in situ to an encapsulating hydrogel have been formed. These membranes are extremely long-lived, lasting over ten days in standard laboratory conditions, and are sufficiently fluid to support protein incorporation.

A high molecular-weight polymer – not a small molecule or surfactant – is superior for dispersing carbon nanotubes in water when processing a waterborne, polymeric nanocomposite. A polymeric dispersant above its entanglement molecular weight creates a brush structure on the nanotube that increases molecular friction on entangles with the matrix, yielding increased adhesion energy, as shown, along with greater toughness and energy dissipation during deformation. A dispersant can thereby be used to tune a nanocomposite's mechanical properties.

Silicon colloids with diameters from 0.5 μm to 5 μm are synthesized. Because of their spherical shape and smooth surface they work as optical microcavities with well-defined resonating modes in the near-infrared range. Silicon colloids are also the building blocks of photonic sponges formed by disorder networks of microspheres of different sizes that scatter light strongly in a wide range of wavelengths

Endothelial progenitor cells are cultured on nanotopographic substrates with a line-grating geometry and respond to these substrates through aligned and elongated morphology, reduced proliferation, and increased migration relative to flat substrates. The cells also form supercellular band structures, which lead to enhanced capillary tube formation upon the addition of matrigel. These results suggest that substrate nanotopography can be used to create organized vascular structures in vitro. Image taken at 250 × magnification.

A self organizing antimicrobial finish on acrylate-based materials was achieved by adding only 0.4 wt% of a biocidal macromer to the monomer mixture prior polymerization. The materials surface kills the infectious bacterium Staphylococcus aureus without releasing the biocide (Figure, lower section) and stays active even after 45 d of constant washing. Confocal Raman spectroscopy and fluorescence microscopy (Figure, upper section) reveal that the biocide has migrated to the surface of the materials during polymerization.

The spatial variability of polarization switching in ferroelectric lead zirconate-titanate nanoparticle arrays and within a single sub-100 nanometer nanoparticle is investigated by using switching spectroscopy piezoresponse force microscopy. Strong variations of switching properties within a single nanoparticle are observed and attributed to polarization pinning by geometric effects and interfacial dislocations. The spatial distributions of imprint bias and the thickness of the frozen polarization layer within the nanoparticle are reconstructed.

A GaN resonant cavity light emitting diode was built on a GaN/AlN distributed Bragg reflector grown on a silicon substrate. The electroluminescence output increased by 2.5 times for a GaN diode coupled to a properly designed resonant cavity. Theoretical calculations showed that this enhancement could increase up to four times for transmission through a semi-transparent metal contact design, and up to eight times for a flip-chip design.

Cyano-substituted oligo(p-phenylene vinylene) derivatives can display piezochromic fluorescence. This rare and desirable effect is achieved by balancing π–π and aliphatic interactions in these molecules through the variation of electron density in the central ring and the length of peripheral aliphatic tails. This leads to fluorophores which can adopt different supramolecular structures and as a result can change their solid-state emission characteristics upon compression.

Self-organization of colloidal spheres within a channel, of which a 1D periodic groove substrate is used as the bottom substrate, is studied. We demonstrate that high-quality monolayer square symmetric colloidal crystals can be achieved only when the colloidal suspension drying front is set parallel to close-packing rows of a commensurate square lattice of the 1D periodic grooves. Experimental optical characterization and theoretical simulations of the samples are presented and discussed.

Insoluble triplet-emissive layers were realized due to the introduction of an oxetane moiety into an orange-emitting iridium(III)-complex. Highly efficient and entirely solution processed multilayer devices were fabricated and the well-balanced charge injection and transport results in a maximum luminous efficiency of 18.4 cd A^–1 and a power efficiency of 14 lm W^–1 at a brightness of 100 cd m^–2. These results compare favorably with vacuum-processed devices reported in the literature.

The exact 3D geometry of nanometer-scale AlN pits is determined by Z-contrast imaging. The figure shows the 3D geometry of an AlN nano-pit and its corresponding GaN quantum dot. An atomic-resolution Z-contrast image is displayed in false color to clearly show the Z-contrast of the image, while the other panel displays a schematic 3D view.

Evaluation of the health risks associated with the use of nanometer-sized particles constitutes an important research field. Here, the effect of gold nanoparticles (AuNPs) on human embryonic lung fibroblasts is investigated. The figure shows the uptake of AuNPs by lung fibroblasts. Most nanoparticles are endocytosed and found in vesicles (arrows) around the nucleus (N). However, some particles are found in cytosol (red circle).

Monodisperse Cs₂Mo₆X₁₄@SiO₂(X = Cl, Br, I) luminescent nanoparticles are synthesized by a water-in-oil microemulsion technique. They emit in the red and near-infrared window (600–900 nm), a region of interest for bio-imaging technologies. Microscopy studies (SEM, TEM and HAADF-STEM, see figure) show a good dispersion of the [Mo₆X₁₄]^2– anions within the @SiO₂ nanoparticles and that the nanoparticles are homogeneous with a regular spherical shape of 45 nm diameter.

Copper nanotube arrays are synthesized by electrodeposition of copper into the porous alumina membranes in presence of a lateral rotating electric field. A computer simulation of the experiment gives the insight of growth mechanism. In principle, this method can be applied to synthesize nanotube arrays of all such materials which can be electrodeposited.

He'll weld with a mighty hand. Flash-welded polyaniline nanofiber actuators demonstrate unprecedented reversible, rapid actuation upon doping. An intense flash of light creates an asymmetric structure (see figure) with a thin dense layer on top of a thick porous nanofibrillar layer. On exposure to camphor sulfonic acid the asymmetric film curls more than 720°.

The generation of “nanograss” surfaces, where the surface chemistry of nanorough silicon is precisely adjusted by the photochemical immobilization of polymeric thin films, is reported. The wetting properties of the surfaces can range from superwetting to impaled drops and superhydrophobicity. Superhydrophobic nanograss is found to be “condensation resistant”.

We describe the first in a series of studies designed to develop and to characterize self-assembled monolayers containing isolated small-molecule probes. We insert tether molecules into preformed oligo(ethylene glycol)-terminated alkanethiolate monolayer matrices and covalently attach the neurotransmitter serotonin to the tethers. These monolayers selectively recognize serotonin antibodies and resist binding of nonspecific antibodies and proteins. We will use these capture materials for biosensor development and functionally-directed proteomics.

Well-aligned ZnO nanowires (NWs) with tunable n-type conductivity are synthesized by introducing Ga₂O₃ as a dopant source in thermal evaporation. The crystallographic orientation of the NWs depends on the dopant content. Electrical transport property measurements on single nanowires verify that the resistivity of ZnO NWs can be controlled, with high reproducibility, by the Ga impurities.

A liquid-crystalline (LC) monomer containing a bis(azobenzene)-based metallomacrocycle was synthesized and found to form a columnar hexagonal (Col_H) LC phase. Adding solvent to swell the cross-linked Col_H phase allows the azobenzene macrocycles to undergo photo-isomerization from the “closed” to “open” form with retention of LC order to afford a supramolecular polymer with photo-responsive nanopores.

The synthesis of helically coiled nanotubes and nanowires through the use of In and Sn catalysts, respectively, in a floating-catalyst-based CVD process, is demonstrated. The figure is a scanning electron microscopy image of helically coiled carbon nanowires prepared from a thermal decomposition of xylene and acetylene in the presence of Fe–Sn catalyst particles. The bright spot at the tip of each nanowire represents the catalyst particle.

The controlled assembly of active microtubule (MT)-based networks offers great promise in numerous technologies. The design and construction of these systems requires MT growth in 3D scaffolds such as gels. We report on the morphology of MTs grown in a crowded environment in the form of viscous fluids containing agarose, and in confined environments in the case of solid agarose gels. The experimental results are supported by a computational model.

We present STM and STS results obtained for double-walled carbon nanotubes. In the case displayed here, the STS results exhibit the Van Hove singularities corresponding to semi conducting tubes for both the outer and the inner shell and a finite density of states at the Fermi level (E_F) is observed for a DWNT. We associate this behavior to the presence of an intershell interaction.

Nano-embossed hollow spherical (NeHS) TiO₂ that features both good light scattering and charge generation shows a very promising performance in high-efficiency dye-sensitized solar cells. A bilayered film structure having the bifunctional NeHS TiO₂ particulate film as an overlayer exhibits conversion efficiencies as high as 10.34 % under AM-1.5G one sun light intensity.

The method used to fabricate a superhydrophobic coating from aqueous dispersions of hybrid responsive nanoparticles with no application of surfactants, organic solvents or fluorinated organic materials is reported. The hybrid nanoparticles consisted of a silica core with a grafted mixed block copolymer brush of poly[styrene-block-(4-vinylpyridine)] constituting the responsive particle shell. The responsive shell was used to tune and stabilize the secondary aggregates of the particles of the appropriate size and morphology in an aqueous environment. The suspension of the particles formed a textured superhydrophobic coating on various substrates upon casting, evaporation of water and heating above the glass transition temperature.