Advanced Materials

Hongbo Sun and co-workers report on p. 3204 on the synthesis of ferrofluids, stable colloidal mixtures composed of magnetic nanoparticles suspended in a photopolymerizable resins as carriers, which were then utilized as precursor materials for femtosecond laser direct writing of remotely controllable micro-/nanomachines. Such photopolymerizable ferrofluid-enabled machines can be envisioned performing functions such as drug delivery and in-situ clinical operation inside blood vessels.

The inside cover illustrates light-irradiated Au₂₅ clusters adsorbed on a nanoparticulate TiO₂ film. The clusters absorb visible light and inject electrons into the TiO₂ in the presence of an electron donor, resulting in conversion of light to electricity and demonstrating gold's potential as a photovoltaic material, as reported by Nobuyuki Sakai and Tetsu Tatsuma on p. 3185.

The Langmuir-Blodgett method for formation of ordered multilayers of spherical particles is reviewed with emphasis on how it has gradually been refined to allow the controlled formation of complex structures containing more than one particle size arranged in a regular pattern. The potential of the method is discussed and illustrated with a range of applications.

The realization of ferromagnetism in functional non-magnetic metal oxides, such as TiO₂ and ZnO, by dilute doping of magnetic impurities or controlled introduction of specific defect types is reviewed. An attempt is made to capture the scope and spirit of this field as it developed over the past decade highlighting the successes, concerns, and new questions. Future research directions are discussed as well.

AgBr nanowires within single-wall carbon nanotubes (SWCNTs) are extremely stable even under UV laser light illumination. The structure of AgBr nanowires within SWCNTs, which was confirmed by transmission electron microscopy, inhibits photoreduction to Ag by preventing the migration of Br atoms. Reduction of AgBr nanowires to Ag can be observed only when the outer SWCNT is structurally compromised by intense electron beam irradiation.

Single-crystallineCdS nanobelts demonstrate excellent field-emission properties for the first time. Individual CdS nanobelts are assembled for high-performance visible-light photodetectors with an ultrafast response time of ∼20 μs and ultrahigh quantum efficiency of 1.9 × 10⁷%. The results suggest a high potential of utilizing these CdS nanobelts as optoelectronic nanodevices.

Photochromic silver-containing mesoporous titania thin films are used as writable or rewritable data carriers. Continuous wave UV and visible laser radiations, respectively, can either repeatedly print and completely erase micropatterns on their surface or engrave permanent micropatterns, depending on the laser intensity.

A new fabrication approach, self-aligned membrane projection lithography, is used to create composite split ring resonators with a resonance near 10 μm. The composite resonators are oriented on the interior face of approximately-spheroidal cavities, and hence represent the first instance of fabrication of micrometer-scale SRRs with out-of-plane current flow.

Nanoscale light-emitting diodes (nanoLEDs) and arrays of nanoLEDs produced by laser controlled diffusion of interstitial manganese (Mn_i) donor ions out of the ferromagnetic semiconductor (GaMn)As towards the underlying layers of a quantum well heterostructure. The approach represents an alternative to deep etching for the creation of nanoscale current channels and nanoLEDs.

The crystal dissolution of sparingly soluble calcite microcrystals for the top-down fabrication of highly oriented nanoshoot arrays is reported. The successful demonstration of crystal dissolution at nanoscale offers new opportunities to design and synthesize architecturally controlled nanostructures with complex forms through systematic control of crystal dissolution along with crystal growth.

Glutathione-protected Au₂₅ as well as Au_n (n = 15, 18, 22, 29, 33, 39) clusters adsorbed on TiO₂ electrodes exhibit anodic photocurrents and negative shifts of photopotential in response to visible and/or near-infrared light (400 < λ < 900 nm) on the basis of HOMO−LUMO and similar transitions, indicating that the electrodes are applicable to the conversion of light to electricity (see figure).

Weaker triplet-triplet annihilation (TTA) is observed in organic solid mixed systems comprising the phosphorescent emitter Ir(ppy)₂(acac), which has a smaller dipole moment than the reference compound Ir(ppy)₃. Spectral and time-resolved analysis show that the weaker TTA can be explained by lower emitter aggregation, which reduces diffusion-based TTA.

Single-layer polymer light-emitting diodes are fabricated using poly (9,9′-dioctylfluorene)-co- benzothiadiazole (F8BT) as the emissive layer in contact with metal oxide injection layers ITO/ZnO/Cs₂CO₃/F8BT/MoO₃/Au. Luminous efficiencies of up to 23 cd A⁻¹ are achieved for polymer layer thicknesses near 1 μm.

Nanoelectronic biosensors based on readily fabricated networks of single-walled carbon nanotubes (SWNT-net) were used to non-invasively detect cellular bioelectrical signals. This nanotube approach promises applications in both fundamental research and high-throughput drug screening targeting on ion channels.

Design and fabrication of remote-controllable micromachines by femtosecond laser-induced two-photon polymerization (TPP) of novel ferrofluids resin composed of methacrylate groups modified Fe₃O₄ nanoparticles and photoresists is demonstrated. As two typical models, a micro-spring and a micro-turbine were successfully fabricated for precise motion control. The development of remotely controllable micro-nanomachines would shorten the distance between actionless micro-nanostructures and smart microrobots.

Hybrid materials represent a new field of basic research. The processing of nanostructured or hierarchical hybrid architectures involves cross-cutting synthetic strategies allowing the development of materials with various shapes with perfect mastery at different size scales, composition, porosity, functionality, and morphology. Their remarkable new properties and multifunctional nature allow the emergence of innovative industrial applications in extremely diverse fields.