Advanced Materials

Unique, three-dimensional structures—silicon pillars—are formed by millisecond long, single-pulse annealing of 110-GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition (HWCVD), as demonstrated by Fude Liu and co-workers on p. 3002. The cover shows a field-emission secondary-electron microscopy (FE-SEM) image of silicon pillars taken at a sample tilt angle of 52°.

On p. 2983 Michael J. Brett and co-workers demonstrate a template-directed technique to produce arrays of silicon nanotubes (SiNTs) with highly engineerable morphology. Fabrication steps include glancing angle deposition (GLAD) of the templates, low-pressure CVD of a shell-Si coating, ion milling to expose the templates, and wet-chemical etching for removal of the templates. The technique may be generally adapted to a wide variety of morphologies and NT materials.

The cover picture shows a series of SEM and AFM images of silica structures from several different diatom species. These images demonstrate remarkable structural diversity and unique porous architectures of diatoms justifying their status as the world's smallest nanofabrication factories. Further details can be found in the article by Nicolas Voelcker and co-workers on p. 2947.

The world's smallest silica nanofabrication factories: a remarkable diversity of shapes and pore architectures of diatom biosilica irrefutably demonstrates precision and brilliance of natural design at the micro and nanoscale, providing a range of lessons that current and future nanotechnology researchers can learn from diatoms.

The development of assembly of hard nanomaterials via the soft Langmuir–Blodgett technique is summarized in this review. After a brief summary on the basics of nanomaterials, examples of LB assemblies of nanomaterials are described according to types of nanomaterials: nanoparticles, nanorods, nanowires, nanotubes, and nanosheets, with description of remaining challenges for the LB films of hard nanomaterials upon comparison with soft material couterparts.

Arrays of silicon nanotubes (SiNTs) with controllable architectures, wall thicknesses and crystallinity are fabricated by a new template-assisted technique. The method includes a sequence of glancing angle deposition of the templates, low-pressure CVD shell-Si coating, ion-milling to expose the templates, and wet-chemical etching for template removal. The technique may be generally adapted to a wide variety of morphologies and NT materials.

Anisotropic mobility in spin-coated MEH-PPV films is due to an interfacial layer of several nanometers at the film-substrate interface with a higher electron density assisted by local chain alignment parallel to the substrate. This layer is formed via spin-coating. The strength of this interface effect is dependent on the solvent used.

The synthesis and characterization of an organic dye, P4, together with its performance in p-type dye-sensitized solar cells (DSSCs) is presented. A solar-cell device based on P4 and an electrolyte that contains the I⁻/I₃⁻ couple in acetonitrile yielded an IPCE value of 44% on a transparent NiO film only 1–1.4 μm thick, the highest value obtained so far.

Chitosan inverse opal scaffolds: Three-dimensional chitosan scaffolds with an inverse opal structure have been fabricated using a cubic close packed lattice of polymer beads as the template. The scaffolds have a uniform and interconnected pore structure as well as a fibrous morphology on the wall. They can be used as a model system for in vitro studies of cell culture and as clinically practical scaffolds for tissue engineering.

Silicon pillars are formed by millisecond-long, single-pulse annealing of 110 GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition. The image was taken at a sample tilt angle of 52° for a better 3D view.

Flexible, semi-transparent, and free-standing graphite oxide membranes are produced by a facile self-assembly process at the liquid/air interface, and the membranes are thickness controlled and area adjustable. Such macroscopic membranes are constructed from individual graphene oxide sheets by layer-by-layer stacking and show excellent mechanical and optical performance.

High-quality 3D photonic crystals are fabricated through electrodeposition into a polymer template created by multibeam interference lithography. Complete infilling of the template is achieved through electrodeposition of Cu₂O, and subsequent etching of the template results in a Cu₂O/air photonic crystal with the exact inverse structure of the template (see figure). The resultant photonic crystal shows a high peak reflectance at theoretically predicted wavelength.

The generation and conduction of photoelectrons in ligated metallic Au NPs are demonstrated, and their key factors include tunneling of photoexcited electrons, the close packing of the NP network, and increased photoelectron-to-intrinsic electron ratio associated with ligand passivation. In view of their inherent characteristics, metallic NPs may provide a promising alternative to semiconductors in photocurrent and photodetection applications.

Numerous thermodynamically favorable but kinetically limited reactions exist in complex hydride composites for on-board PEMFC vehicle applications. Catalyst- doping, nanoconfinement, tailoring thermodynamic driving forces, and self-catalyzing by in situ product seeding as shown in the figure have been explored to improve reaction kinetics at temperatures closer to thermodynamically feasible. We discuss such schemes and their underlying mechanisms.