Advanced Materials

Thin oxide films with long-range ordered microstructures were fabricated by a wrinkling process initiated by photopolymerization. The faster polymerization of the film surface generates a buckling effect to create patterns in the films. The removal of the organic polymer by thermal treatment leaves titania microstructures having long-range order. This method of producing micropatterned structures can find several applications in photonics.

This paper describes a new pathway to neuroactive materials that relies on integration of neurotransmitter-like functional groups into synthetic polymers. A series of biodegradable polymers are synthesized with varying concentrations of acetylcholine-like functionalities (ALFs) using a modular design. The polymers with medium ALF contents resemble laminin in promoting neurite sprouting and extension while maintaining phenotypic protein expression of neurons.

An imprinted photonic polymer constructed by colloidal crystal and molecular imprinting technologies shows specific and rapid recognition with high sensitivity to the protein template, as demonstrated by shifts in the photonic crystal stop band (see figure) when it is soaked in various concentrations of proteins.

Various surfaces can successfully be coated with reactive polymer coatings and then patterned with DNA features using supramocular nanostamping (SuNS). Surfaces as different as silicon, quartz, polystyrene, PMMA and PDMS have been patterned using the same protocol. In addition to the previously demonstrated high resolution and high information transfer of SuNS this approach makes it a substrate-independent method.

Liquid supramolecular nanostamping (LiSuNS) is an efficient stamping technique that replicates various DNA features with no need of solid surface contact. LiSuNS is based on the specific interaction of complementary DNA strands. An original pattern composed of multiple DNA strands on a rough surface can be copied onto a liquid prepolymer that is subsequently hardened, leading to a solid surface that displays the mirror image of the master used.

Thin oxide films with long-range ordered microstructures were fabricated by a wrinkling process initiated by photopolymerization. The faster polymerization of the film surface generates a buckling effect to create patterns in the films. The removal of the organic polymer by thermal treatment leaves titania microstructures having long-range order. This method of producing micropatterned structures can find several applications in photonics.

In situ sol-gel polymerization is demonstrated for fabricating transparent poly(methyl methacrylate) (PMMA)-ZnO quantum dot (QD)- hybrid materials in bulk dimension. The transparent PMMA-ZnO QD hybrid materials exhibit enhanced UV-shielding effects in the entire UV range, even at concentrations as low as 0.02 wt %.

A C₆₀-terminated self assembled monolayer at the semiconductor/gate insulator interface of an organic thin film field effect transistor provides acceptor states optimized for photoinduced charge transfer. Charge densities of up to 10¹³ charges cm^–2 can be trapped in the C₆₀ acceptors.

Rod-shaped assemblies of FePt nanoparticles embedded amidst PtTe₂ nanoplatelets, formed by co-precipitation in the presence of sucrose and trioctylphosphine oxide. The (001) planes in each of the PtTe₂ nanoplatelets are stacked along directions close to the nanorod axis. Separate precipitation of FePt or PtTe₂ under identical conditions yield spheres or randomly shaped clusters platelets, underscoring the key influence of co-precipitation on the morphology of the nanostructure assembly.

Superhydrophobic surfaces are prepared based on silica colloids coated with multiple layers of block copolymer micelles (see figure). The hierarchical surface roughness can be tuned by adjusting the pH and molecular weight of the polymer segments. Optical functionality is imparted to the films by the inclusion of quantum dots or organic dyes in the hydrophobic cores, as depicted in the figure.

The incorporation of a small amount of salt in a block copolymer leads to strong modifications of the interfacial interactions, causing the microdomains to orient perpendicular to the surface during solvent evaporation. This approach can be used to prepare hexagonally ordered cylindrical arrays with high aspect ratios over large areas.

A method for producing self-organised arrays of nanometric metallic dots is reported. It consists on developing first the nanodot pattern by ion erosion on a semiconductor cover film and transferring it to a previously buried metallic layer. This procedure has been applied to Co, and the ferromagnetic behaviour of the dots at room temperature is demonstrated.

Free or mesh-supported nanomats can easily be developed by this novel application of the electrospinning technique in which electrospun nanofibers are neutralized with a cloud of electrospray-generated small counterions. The fibers condense into dense micrometer-thick nanomats because of the attraction between opposite charges on its sides (see figure).

Multifunctional Nanoparticles: A facile approach to create multi-functional nanopyramids has been demonstrated. The surfaces of bi-material Au/Ni nanopyramids were differentially modified with chemical and biological moieties. Dye-labeled nanopyramids were used as probes for dual-mode optical imaging (scattering and fluorescence). Under a magnetic field, these multi-functional Au/Ni NPs also assembled into 1D chains that exhibited polarization- dependent optical properties.

Creating many different complex structures from a single prepattern is achieved from either a master mold or stamping onto a solid substrate by patterning with a PDMS replica mold. Various metal patterns including ellipses, dots, rings, chains of dots (or rings), ribbons and wavy lines with various feature sizes can be generated from a single pattern of isolated ellipsoidal dots by simply varying the residual polymer film thickness and the reactive ion etching (RIE) time.

In addition to the well known ferroelastic domains formed by deformation twinning in rhombohedral perovskites, a monoclinic structure is observed by transmission electron microscopy in LaCoO₃-based materials. The monoclinic domains consist of a one-dimensional superstructure corresponding to doubling or tripling of the pseudo cubic unit cell due to twinning at the atomic scale, as shown in the figure.

This paper describes a new pathway to neuroactive materials that relies on integration of neurotransmitter-like functional groups into synthetic polymers. A series of biodegradable polymers are synthesized with varying concentrations of acetylcholine-like functionalities (ALFs) using a modular design. The polymers with medium ALF contents resemble laminin in promoting neurite sprouting and extension while maintaining phenotypic protein expression of neurons.

We demonstrate a brushing technique as a promising method for the mass production of efficient and flexible solar cells even on a non-flat surface such as roofing tiles. Higher device efficiency could be obtained compared to the spin-coated devices, resulting from the improved organization of polymer chains and domains induced by more effective application of shear stress to the polymer chains during the brushing process.

ZnO nanorod arrays are selectively grown on Si substrates using facet-controlled GaN micropatterns with highly anisotropic surface energies. Although we used facet-controlled GaN micropatterns for selective MOPVE growth, other micropatterns can be employed if the difference in surface energies between a top surface and the sidewalls of a micropattern is large enough to affect heteroepitaxial selective growth of the nanorods. This growth may be expanded to create many other position-controlled semiconductor nanorods.

Quantum dots are incorporated onto small beads made of various materials thanks to the versatile layer-by-layer method. The high contrast, tri-color gradient TEM image of a bead emphasizes quantum dots in red-yellow spots. Below, quantum dot coated magnetic beads demonstrate bimodality with their bright fluorescence and alignment along field lines. An hyperspectral imaging inspired technique allowed faster statistical characterization of optically coded beads on a setup typical of biological experiments.

A new approach to directly organize colloidal particles into patterned arrays using a nanostructured polymer template coated with polyelectrolyte multilayers is introduced. The topological template with both positive and negative charges provides a finely defined chemical nanopattern to guide selective deposition of colloidal particles onto the patterned surface upon Coulombic attraction (see figure).

Reversible polarity-dependent resistance (PDR) switching in phase-change (PC) films is feasible. Nanometer-scale crystalline marks are produced in amorphous Ge₂Sb_2+xTe₅ films by electrical pulses through an AFM tip. In these marks, PDR switching is demonstrated with three orders of magnitude current contrast using less than 1.5 V. No current contrast between the crystalline marks in the high- resistance state and the amorphous background is observed.

A new organic semiconductor based on a benzobisthiazole core has been studied as a hole transport material in field effect transistors; remarkably, the material self-assembles in the solid state to give intermolecular short contacts in all three dimensions.

We describe the fabrication of extremely high mass fraction polymer-nanotube composites displaying very high conductivity. Contrary to general expectations, the conductivity displays percolation-like scaling for all mass fractions from 22 % right up to 100 %. These are among the most conductive composites ever demonstrated.

An ultrathin photo-crosslinkable random copolymer film was designed as a substrate-independent imaging layer for block copolymer (BCP) thin films. Negative-tone resist chemistry was combined with the chemistry of neutral surfaces to formulate the imaging layer. The synthesis of the imaging layer, optimization of the photo-crosslinking conditions, and patterning of BCP thin films on the imaging layer is discussed. The mild room temperature crosslinking chemistry is especially attractive for BCPs containing temperature-sensitive monomers.

Films of a block copolymer fluid are deposited on surfaces bearing nanostripes of different wettability (see figure). The dewetting process of the fluid decodes the underlying pattern, opening trenches as narrow as 70 nm in the film, and creating fluid nanoribbons as narrow as 300 nm. The fluid ribbons are stabilized by the internal organization of the copolymer in the confined space of the ribbon.

White-emitting organic light-emitting diodes (OLEDs) notoriously suffer from brightness-dependent color shifts. Based on experimental data and fundamental considerations about charge-transport and trapping, a quantitative model is developed which gives insight into the origin of this shift and describes the experimental data extremely well. Having understood the major contribution to the spectral instability, a device architecture is designed that shows excellent color stability over a wide range of brightness levels.

Lipid bilayers in nanopores are stable for days. The stability depends on the nature of the lipid as well on the pore diameter as investigated by impedance spectroscopy. Bilayers formed of palmitoyl-oleoyl-phosphatidylcholine are stable up to 4 days in 200 nm pores regularly arrayed in a 300 nm thin silicon nitride support. The transport of K⁺ across bilayers by valinomycin demonstrates that this support material has a high potential to monitor functions of membrane proteins.

Local reactions are triggered by delivering molecules from an AFM probe tip, allowing for direct modification of chemically functionalized surfaces. Silicon wafer-bound acetylene moieties readily undergo 1,3-dipolar cycloadddition with solution-phase azides delivered from an AFM tip. This selective and robust technique allows for the facile creation and placement of sub-micrometer-sized features.

Diphenylalanine (FF) peptides self-assemble into well ordered, discrete, hollow nanotubular structures under relatively simple conditions. AFM is used to investigate alignment of FF tubes in strong magnetic fields. Using the direction of alignment, a constraint on the orientation of the phenylalanine aromatic rings is derived and compared to a molecular model structure. These arrays have potential in future applications as functional nanoscale materials.

Single crystalline boron nanocones are obtained by a simple chemical vapor deposition method. Electric conductivity values of boron nanocones are (1.0–7.3) × 10^–5 (Ω cm)^–1. Results of field emission show the low turn-on and threshold electric fields of about 3.5 V μm^–1 and 5.3 V μm^–1, respectively. Boron nanocones with good electrical transport and field emission properties are promising candidates for application in flat panel displays and nanoelectronics building blocks.

A method to suppress the scattering of inorganic nanoparticle inclusions within organic embedding media is presented. Suppression takes place by means of appropriate surface modification (using ATRP), such as to match the effective refractive index of the resulting core-shell particle to the refractive index of the embedding medium.

Photoluminescence measurements show that the tunable bandgap emissions of the alloyed ZnS_xSe_1–x nanowires shift continuously from 370 nm to 463 nm. According to the experimental results, predetermined bandgap emissions can be obtained via synthesizing alloyed ZnS_xSe_1–x nanowires with the corresponding composition x.

Nanostructured poly(p-xylylene) thin-film templates are used for Ni deposition. Noncovalent adsorption of metal-binding ligand to a thin film anchors a palladium catalyst and leads to selective metallization. The template facilitates complete control over the morphology and topology of the deposited Ni (see figure).

Doping of low levels of sodium onto the cation sites of ceria-zirconia mixed oxides allows reduction of the materials to take place at lower temperatures than undoped materials, a desirable property for practical applications in supports for redox catalysis. Synthesis is achieved in a single step under mild hydrothermal conditions directly from aqueous mixtures of metals salts at high pH.

Co₃O₄peration. Porous and polycrystalline Co₃O₄ nanotubes have been derived from Co₄(CO)₁₂ clusters on carbon nanotube templates. The prepared porous Co₃O₄ nanotubes exhibit superior Li-battery performance with good cycle life and high capacity (1200 mAh g^–1) owing to their hollow structure and small size. Moreover, this approach can be extended to synthesize other porous metal oxide nanotubes.

Nanosheet-based microspheres of ZnO:Eu (see figure) are fabricated via pyrolysis of Zn₅(OH)₆(CO₃)₂ hierarchical microspheres. Efficient ZnO→Eu³⁺ energy transfer is observed, which is attributed to surface defects at the nonpolar [11?00] surface of a ZnO nanosheet that couples with Eu³⁺ and stabilizes the Eu²⁺ trap level just below the conduction band of ZnO.

Laminated object manufacturing, a rapid prototyping method, is applied to paper sheets containing SiC filler particles. Upon pyrolysis and melt filtration of Si, the sheets can be transformed into dense ceramic objects with complex shapes such as the 18-layered gearwheel shown in the figure.

We demonstrate molecule-specific third-harmonic-generation (THG) microscopy by using silver nanoparticles as THG contrast agents. Through matching surface plasmon wavelength to THG wavelength, strong contrast can be provided by silver nanoparticles under THG microscopy. By conjugating anti-her2 antibodies with silver nanoparticles, the expression of the Her2/neu oncogene in the cancer cell membranes is successfully imaged under THG modality for the first time.

The properties of high-quality InN nanobelts fabricated by the metal-organic chemical vapor deposition technique are investigated. The figure shows the uniaxial strain ϵ₃ (, solid squares) and in-plane strain ϵ₁ (solid circles) as a function of excitation intensity. The reduction of the tensile in-plane strain gives rise to a noticeable increase of the band gap energy.

An electrochemically fabricated 1D photonic crystal of porous Si displaying a single reflectance peak is coupled to an optical fiber and embedded in activated carbon to sense the breakthrough of organic vapors (see figure). The sensor responds to various organic vapors, demonstrating filter end-of- service-life applications

High-resolution measurement of anisotropic electrical properties allows the probing of transport in organic materials as an explicit function of molecular orientation and proximity. A new device architecture facilitates the efficient measurement of these properties; 15° angular resolution is demonstrated for the rubrene single crystal.

A ‘bricks-and-mortar’ assembly approach can be used to create well- defined fibers on the microscale with alternating organic-inorganic arrangement through a simple ice-templating strategy. The fibers are constructed from closely packed monodisperse inorganic nanoparticles@PNIPAm core/shell microgels. A series of functional ‘bricks’, such as core/shell and hollow nanoparticles are prepared.

A selenophene analogue (P3HS) of poly(3-hexylthiophene), P3HT, has been investigated as a replacement for P3HT in bulk heterojunction solar cells. Polymer:PCBM films and devices of both materials are directly compared by studying morphology, optical properties, and device performance. Preliminary optimisation of P3HS:PCBM devices gave promising results with a power conversion energy slightly lower than that of an optimised P3HT:PCBM device measured under identical conditions.

Atom transfer radical polymerization is used to prepare a highly deliquescent hyperbranched polymer from a monomer containing polymerizable vinyl group and an initiation-ready site for branching and chain growth, as depicted in the figure. The figure also shows the very rapid deliquescence kinetics of this polymer originating from its hyperbranched structure.

A new crosslinking system based on azide-functionalized random copolymers has been defined for the preparation of substrates with controllable surface interactions. The azido group is used for both thermal- and photo-crosslinking, which is found to be very efficient. Furthermore, the use of UV irradiation for crosslinking enables the preparation of patterned surfaces by conventional photolithographic techniques, combining the “bottom-up” self-assembly of block copolymer strategies with traditional “top-down” photolithographic methods.

The electronic properties of graphite are discussed focusing on the 2D behavior of quasi-particles in bulk and few-layered graphite samples. The figure shows the occurrence of quantum oscillations in a highly oriented pyrolytic graphite sample at room temperature, corroborating that few-layered graphite rather than graphene may be optimally suited for quantum devices.

Rechargeable all-solid-state batteries prevent electrode degradation upon cycling and electrolyte leakage. Based on the excellent intercalation chemistry in Si thin films, a new 3D-integrated all-solid-state battery concept is proposed (see figure). High-aspect-ratio cavities and features, etched in silicon, will yield large surface area batteries with anticipated energy density of about 5 mWh μm^–1 cm^–2, i.e. more than 3 orders of magnitude higher than that of integrated capacitors.