Advanced Functional Materials

A surface with nanograssed micropyramidal arrays that allows for enhanced drop nucleation and departure simultaneously is successfully developed by harnessing the hierarchical roughness and heterogeneous wetting. On page 4617, Nikhil Koratkar, Shuhuai Yao, Zuankai Wang, and co-workers show that the surface yields a global superhydrophobity as well as local wettable patches (smooth structure). Synergistic co-operation between the hierarchical structure contributes directly to a continuous process of nucleation, coalescence, departure, and re-nucleation, enabling sustained drop-wise condensation over prolonged periods.

Ferroelectric nanolithography provides a pathway for the direct assembly of patterned metal nano-particle arrays. On page 4712, David Conklin, Dawn A. Bonnell, and co-workers show that the density of the arrays is controlled by the photon flux and the size of the nanoparticles is controlled by the interface. Nanoparticle arrays can be functionalized by a range of active molecules, in this case opti-cally active porphyrin complexes, to produce hybrid optoelectronic devices.

On page 4663, Christopher E. Patrick and Feliciano Giustino investigate the interface between TiO₂ and Sb₂S₃ found in semiconductor-sensitized solar cells by means of first principle calculations. An atomistic model of the TiO₂ and Sb₂S₃ interface is proposed and the interfacial energy-level alignment and ideal open-circuit voltage are determined. The analysis of other isostructural sensitizers indicates that anti-monselite (Sb₂Se₃) holds potential for delivering higher energy conversion efficiencies than the TiO₂/Sb₂S₃ system.

Various applications of scanned pipette techniques to conducting polymers are demonstrated. Micrometer-scale fabrication is shown, as is micrometer-scale cyclic voltammetry and voltammetric–amperometric mapping, for both PANI and PEDOT conducting polymer systems, and for a variety of morphologies: thin films, microspots, microribbons, extruded microstructures, and nanowires.

A surface with nanograssed micropyramid arrays that allows for enhanced drop nucleation and departure simultaneously is successfully developed by harnessing the heterogeneous wetting and hierarchical roughness. The surface yields a global superhydrophobity as well as local smooth (wettable) patches. Synergistic co-operation between the hierarchical structures contributes directly to a continuous process of nucleation, coalescence, departure, and re-nucleation enabling sustained dropwise condensation over prolonged periods.

A novel Lewis acid-catalysed self-healing system is investigated for implementation in epoxy-based fibre reinforced polymer composite materials. Healing is initiated when microcapsules are ruptured at the onset of crack propagation. Results show that a material recovery value of greater than 80% fracture strength is achieved when using a TDCB geometry.

Following rapid development over the last decade, superhydrophobic coatings have become very promising for practical applications. Superhydrophobic polyester textiles coated with silicone nanofilaments are fabricated by chemical vapor deposition of trichloromethylsilane as described by Junping Zhang and Stefan Seeger on page 4699. The coated textiles feature superwetting properties, flexibility, excellent reusability, oil/water separation efficiency, and selective oil absorption capacity, making them excellent candidates for, e.g., practical oil absorption.

Transparent mesoporous TiO₂ films with high porosity and good connectivity for improvement of cell performance are introduced to iodine-free solid-state dye-sensitized solar cells with conductive polymers. Highly conductive polymers as hole-transporting materials can effectively penetrate the TiO₂ pores, and can be polymerized by heating at mild temperatures. The fabricated devices exhibit one of the highest energy-conversion efficiencies (up to 6.8% in N719 dye) yet reported, which is a result of their enhanced light absorption and good hole conductivity.

P3HT aggregate morphology in P3HT:PCBMthin films is studied by analyzing the optical properties with a model developed by F. C. Spano. Films with non-optimized (CF cast) and nearly optimized initial morphologies (DCB cast, solvent-annealed) are thermally annealed directly at the target temperatures. Changes in the energetic disorder (σ), excitonic bandwidth (W) and degree of P3HT crystallinity are related to the glass transition range (light grey) and to the solar cell device performance.

A new approach to develop positive (T₁-weighted) contrast agents for MRI applications is proposed. This approach is based on GdSi_xO_y nanospheres exhibiting 3D interconnected mesopore network. These paramagnetic GdSi_xO_y-MSNs provide significant contrast enhancement at very low Gd concentrations. High ¹H relaxivities and low r₂/r₁ ratios were achieved. This establishes the impact of pore morphology on MR-relaxivity, in line with enhanced diffusivity of water in 3D networks.

The interface between TiO₂ and Sb₂S₃ found in semiconductor-sensitized solar cells is investigated by means of first-principles calculations. An atomistic model of the TiO₂/Sb₂S₃ interface is proposed, and the interfacial energy-level alignment and ideal open-circuit voltage are determined. The analysis of other isostructural sensitizers indicates that antimonselite (Sb₂Se₃) holds potential for delivering higher energy conversion efficiencies than the TiO₂/Sb₂S₃ system.

Nanocrystal superlattices from gold-poly-N-isopropylacrylamide (Au-PNIPAM) core– shell particles are prepared within a broad range of concentrations in aqueous dispersions. These superlattices show strong Bragg diffraction in the visible, tunable by the particle volume fraction as well as temperature. Structural changes (melting/recrystallization) upon changes in temperature are highly reversible.

Magnetostrictive Fe–Ga/Cu multilayered nanowires are synthesized using citrate-based electrochemistry, resulting in strong <110> textured growth. Coercivity versus applied field angle data reveal that, at high angles, the magnetization reversal mechanisms are different in continuous (curve A) to those of multilayered structures (curves B–E). This is attributed to mixed mode reversal involving vortex and coherent rotation modes in continuous wires.

Quantum simulations to calculate the relative activation energies for oxygen incorporation into yttria-stabilized zirconia (YSZ) and yttria-doped ceria (YDC) are reported. In addition, the epitaxial growth of thin YDC interlayers on YSZ substrates experimentally demonstrated, which shows improvement in the performance of surface-modified solid oxide fuel cells in terms of power density and electrode interface resistance.

Solution processed Gallium doped ZnO nanowires are aligned on substrates using an innovative shear coating technique. Nanowire alignment has shown improvement in ZnO nanowire transparent electrode conductivity. 2D network simulations in conjunction with electrical measurements have revealed different regimes of operation of nanowire thin films and provided a guideline for improving electrical performance of nanowire electrodes.

An iodine-free solid-state dye-sensitized solar cell (ssDSSC) with 6.8% efficiency can be fabricated using conductive polymers and organized mesoporous TiO₂. On page 4633, Eunkyoung Kim, Jong Hak Kim, and co-workers show the effects of polymer conductivity and transmittance of the interfacial TiO₂ layer on energy conversion efficiency. This method can be used for the fabrication of various photovoltaic cells.

Superhydrophobic and superoleophilic polyester materials are prepared by one-step growth of silicone nanofilaments onto the textile via chemical vapor deposition of trichloromethylsilane. Owing to the superwetting properties and flexibility of the coated textile, excellent reusability, oil/water separation efficiency and selective oil absorption capacity are observed, which make it a very promising material, e.g., for practical oil absorption.

An optically transparent thermoplastic self-healing system based on a poly(methyl methacrylate) matrix containing dibutylphthalate filled capsules is reported. Index matching minimizes light scatter from the capsules or healed material in the polymer film. Healing occurs via a solvent welding mechanism initiated by release of dibutylphthalate from ruptured capsules. After healing, the optical properties, protective capabilities, and mechanical strength of the polymer film are recovered.

The mechanisms of nucleation and growth of nanoparticles formed by polarization dependent photo-reduction on a ferroelectric surface are determined. The effects of photon flux, chemistry, and concentration on particle size and separation are quantified. This new understanding leads to control of the deposition required to demonstrate the fabrication of novel metal nanoparticle/porphyrin optoelectronic devices that exploit surface plasmons to produce enhanced photocurrent.

A higher internal quantum efficiency and a higher light extraction efficiency are simultaneously achieved by engraving an array of nanoholes into the p-GaN cladding layer, followed by partial filling with silver. The technique offers a practical approach to overcoming the limitation of the exponentially decayed surface plasmon field and to controlling the effective coupling energy. It is feasible for high-power lighting applications.

Monodisperse Co nanoparticles, stabilized by an organic coating, are synthesized and immobilized on a variety of self-assembled monolayers and chemical templates. The particles have an average diameter of ∼10 nm and consist of hcp cobalt covered by a thin (∼1 nm) oxide film. They exhibit pronounced ferromagnetic properties with a blocking temperature above 380 K stemming from the high magnetocrystalline anisotropy.

A biologically active thrombomodulin surface assembly to limit interfacial thrombin production was generated on the lumen of clinical ePTFE vascular grafts by site-specific covalent immobilization. Therapeutic capacity of this biomimetic surface engineering approach to attenuate thrombus formation was demonstrated in a clinically relevant in vivo model of prosthetic graft thrombosis.

One approach to alleviate issues associated with the organic light-emitting diode (OLED)-based sensing platform: A 2-D uniform 2 μm-pitch microlens array (μLA) integrated with the OLED and an O₂ sensing film leads to a ∼2.1–3.8 fold enhancement of the photoluminescence (PL) signal, enabling a more accurate determination of the (bio)analyte-dependent PL decay time, and hence its concentration. It also enables operation of the OLEDs at lower voltages, which enhances their operational lifetime.

Methyl-group-functionalized microporous metal frameworks can lead to significantly enhanced CO₂ adsorption capacity despite the reduction of surface area and pore volume caused by addition of the methyl group.

In electrostatically templated self-assembly, dielectric particles are attracted towards nonconductive regions of a patterned gold electrode. This method aligns and centers dielectric spheres on circular adsorption sites, but, due to edge effects and greater friction, produces poor quality assemblies of disks.

A general method for producing water dispersible superparamagnetic Fe₃O₄ nanoparticles is presented utilizing ring opening reactions between surface-bound epoxy-ligands and amine functionalities. PEG or arginine stabilized suspensions exhibit high r₁ values of 17 s−¹ mM⁻¹, and low r₂/r₁ ratios of 3.3–3.8. This demonstrates high magnetization and excellent water dispersibility of the nanocrystals, as required for applications as positive MRI contrast agents.

Inverted organic solar cells employing a solution processed V₂O₅ (sV₂O₅) hole-extraction-layer on top of the active organic layer are demonstrated. Even without any post-deposition treatment, the electronic structure of the sV₂O₅ layers is similar to that of thermally evaporated V₂O₅ (eV₂O₅) layers which have been exposed to ambient air. Optimized devices with sV₂O₅ layers show power conversion efficiencies similar to that of devices with eV₂O₅ layers.

Solution-processed silver nanowire (Ag NW) films are introduced as transparent electrodes for thin-film solar cells. Ag NWs are processed by doctor blade-coating at moderate temperatures and their morphological, optical, and electrical characteristics are presented. Additionally Ag NW electrodes are applied for a direct comparison with indium tin oxide electrode layers in poly(3-hexylthiophen-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) organic solar cells with comparable performances.

The addition of genipin (0.25–1 mM) to soluble type I collagen imparts substantial dose dependent increases in shear modulus immediately after gelation, as compared to collagen alone. This range of genipin concentrations is chosen because it is compatible with mesenchymal and neural stem cell encapsulation and survival within the gel.