Advanced Materials

Self-assembly, transfer, and integration of particles is achieved by combining self-assembly processes with an adhesion cascade (see Figure). This process complements and enhances existing fabrication methods as it allows the integration of particles into planar devices. Moreover, it is versatile in terms of particle size and materials, and can create arbitrary particle arrangements with functional particle–substrate connections.

Reversible tuning of an intragap transmitting state induced by redox cycling is accomplished using a redox-active polyelectrolyte multilayer planar defect embedded in a colloidal photonic crystal (CPC). The wavelength position of the defect state can be changed by changing the oxidation state of the ferrocene moieties in the polymer backbone (see Figure). This could find applications in electrochemically tunable microcavities and CPC-based laser sources.

The pressure to publish is borne by journals as well as by research scientists. The Editor discusses meeting the challenge of an ever-increasing number of manuscript submissions while simultaneously improving the quality of the journal and reducing publication times.

Field-effect transistors based on solution-processible organic semiconductors have experienced impressive improvements in both performance (see Figure) and reliability in recent years and are being developed for applications in printable electronics on flexible substrates. This article reviews their underlying materials, charge transport, and device physics, with a particular focus on what can be learnt about the electronic properties of active, organic semiconductor/dielectric heterointerfaces from studying such devices.

The machining of 3D microstructures in single-crystal artificial diamond is demonstrated with a focused ion beam (FIB)-assisted lift-off technique. A sacrificial buried layer is created with MeV ion implantation, followed by patterning of selected regions with the FIB technique; the sacrificial layer is then selectively etched, leaving 3D free-standing microstructures in the bulk (see Figure). Using this fabrication technique, light waveguiding through a microstructure in single-crystal diamond is demonstrated for the first time.

A new method for controlling the hole density in single-walled carbon nanotube field-effect transistors (SWCNT-FETs) by solution-based chemical doping is presented. The use of organic molecules that adsorb onto SWCNTs from solution is investigated. The transfer characteristics of the SWCNT-FETs exhibit continuous and precise shifts in threshold voltages (see Figure) upon doping with F₄TCNQ molecules, even in air.

Photosystem I (PS I), a multi-subunit protein–chlorophyll complex that mediates vectorial, light-induced electron transfer has been self-assembled as an oriented monolayer on a solid metal surface. Unique cysteine mutants are induced for the attachment of PS I through the formation of sulfide bonds. A photopotential of approximately +1 V is observed (see Figure) for single trimer molecules or the monolayer continuum.

Self-assembly, transfer, and integration of particles is achieved by combining self-assembly processes with an adhesion cascade (see Figure). This process complements and enhances existing fabrication methods as it allows the integration of particles into planar devices. Moreover, it is versatile in terms of particle size and materials, and can create arbitrary particle arrangements with functional particle–substrate connections.

Thin films of diblock copolymers with cylindrical microdomains oriented normal to the film plane are employed as planar optical waveguides in the Kretschmann configuration (see Figure). Their waveguiding properties were investigated by optical waveguide spectroscopy. The dielectric constants and the film thickness of the block copolymer layer can be independently obtained from fitting between the waveguide patterns for s- and p-polarization and Fresnel calculations.

A cylindrical-phase diblock copolymer ultrathin film is modified with vacuum UV light to selectively remove one of the surface domain components. The corrugated film then serves as a template for the self-organization of colloidal magnetic nanoparticles (see Figure). This hierarchical methodology is a general route to the nanoscale assembly of functional materials. This work has ramifications for potential future bit-patterned magnetic-storage media.

On the surface of a quantum dot (QD), maltose-binding protein (MBP, white and yellow in Figure) labeled with a cyanine dye (red) self-assembles, resulting in F?rster resonance energy transfer between the acceptor dye and the QD donor. Upon binding maltose, MBP undergoes a conformational change (white ⇌ yellow), causing concentration-dependent photoluminescence changes.

Reversible tuning of an intragap transmitting state induced by redox cycling is accomplished using a redox-active polyelectrolyte multilayer planar defect embedded in a colloidal photonic crystal (CPC). The wavelength position of the defect state can be changed by changing the oxidation state of the ferrocene moieties in the polymer backbone (see Figure). This could find applications in electrochemically tunable microcavities and CPC-based laser sources.

Deposition of CdS nanoparticles on SWCNTs produces a photoactive composite that undergoes charge transfer interactions following excitation with visible light (see Figure). The transient bleaching recovery in approximately 200 ps confirms quick deactivation of excited CdS on the SWCNT surface. Visible excitation of the CdS–SWCNT film produces a photocurrent and thus provides evidence for the electron-transfer pathway in the composite.

Rejection-wavelength tuning is achieved by combining the mechanochromic response of photonic bandgap composites with the intrinsic electroactive properties of dielectric thin films. By straining the composite electrode, the photonic crystal interparticle lattice constant is varied in situ (see Figure). These simple-to-make films may find use in photonic devices that require a compact light-propagation controlling component.

A Ti-Cr-MCM-48 photocatalyst prepared in a single step exhibits superior photocatalytic activity compared to TiO₂-Cr-MCM-48 prepared by a post-impregnation method. The high activity of the photocatalyst is attributed to the synergistic interaction between the Cr ions dispersed in the silica framework and the nanocrystalline nature of titania crystallites anchored onto the pore walls (see Figure).

Uniform ZnSe ultranarrow nanorods (1.3 nm × 4.5 nm) and 100–200 nm long nanowires with the same width have been produced and characterized, and the spectroscopic properties measured. The uniformity of the rods and wires is demonstrated in their spontaneous assembly into highly ordered 2D supercrystals (see Figure). Development of the rods from more spherical nuclei is demonstrated.

Microwave-induced plasmas of argon (see Figure) and dioxygen have been used to rapidly prepare ternary niobate and titanate phases directly in the solid state from precursors that do not exhibit microwave heating at room temperature. However, for some reactions heating of the microwave-induced plasma can promote dielectric loss, which allows access to local temperatures greater than the equilibrium plasma temperature.

Aligned arrays of ultrathin, high-quality ZnO nanotubes (see Figure) have been synthesized via hydrothermal growth methods on Si that has been pre-coated with a thin film of ZnO. The nanorods are single-crystalline, with typical wall thicknesses and outer diameters of 5–15 and 20–40 nm, respectively. Annealing the arrays in vacuum causes enhancement of UV photoluminescence.

Two-polymer microtransfer molding (2P-μTM), an advanced microtransfer molding technique, is developed for fabrication of 3D microstructures. The use of two different photocurable prepolymers and a simple and robust filling and coating method allows an extremely high yield in layer-by-layer microfabrication able to produce highly layered microstructures with high structural fidelity (see Figure).

PbS nanoparticles dispersed in polymer-fiber matrices by electrospinning are presented (see Figure). These PbS nanoparticles are roughly spherical in shape, each with a diameter of approximately 5 nm, and do not aggregate. This method will open up a wide route to functionalizing surfaces which can enable the fabrication of new types of optical, electric, and magnetic devices.

Highly efficient organic UV photodetectors that are not sensitive to visible radiation (“visible-blind”) but to UV-A radiation are fabricated using an organic donor–acceptor couple. High external quantum efficiencies (EQEs) comparable to commercial GaN devices, but covering the entire UV-A range (see Figure), make these devices promising for environmental and biomedical UV-sensing applications.

All the attributes necessary for good OLED performance (see Figure), namely, high electroluminescence efficiency (5.4 cd A^–1), long operational lifetime (10 000 h at an initial luminance of 100 cd m^–2), and deep-blue color (color saturation: (0.14, 0.13)) are demonstrated by an OLED incorporating a novel, composite hole-transport layer and an emitter based on a new mono(styryl)amine dopant in the stable, anthracene-based blue host material, 2-methyl-9,10-di(2-naphthyl)anthracene.

Practical lithium-metal batteries are the ultimate goal of battery researchers. The addition of a zwitterionic compound (see Figure) to an ionic liquid electrolyte doped with a lithium salt results in a 100% enhancement of the current densities achieved in the cycling of a lithium-metal cell. This phenomenon arises due to increased lithium-ion mobility or a reduced solid electrolyte interphase layer resistance.

Binary colloidal crystals (see Figure) have been fabricated via the confined convective assembly method. By adjusting the ratio of the diameters of the small and large particles and the concentration of the small particles, various superlattices, including the previously reported LS₂ and LS₃ structures along with the new LS₄ and LS₅ structures, have been prepared.

Well-dispersed Y₂O₃:Eu nanocrystals, with a size less than 10 nm, and self-assembled nanodisks (see Figure) could be synthesized by a simple organometallic route. Two strong emission peaks located between 610 and 630 nm, and a 2.6 % quantum yield, are achievable upon excitation at 330 nm. Excellent dispersibility, a long lifetime, and improved emission may allow Y₂O₃:Eu nanocrystals to be useful for biological labeling.

Highly ordered mesostructures of tin oxide have been obtained via the block-copolymer-assisted assembly of crystalline tin oxide nanoparticle sols. The 3.5 nm tin oxide nanoparticles obtained using low-temperature synthesis can be dispersed without the use of any stabilizers and are assembled via an evaporation-induced self-assembly (EISA) process (see Figure).