Self-assembled nanostructures often exhibit unique properties that are distinct from those of bulk materials. During the past decade, significant progress has been made in the assembly of nanorods and understanding some of the self-directing assembly mechanisms, particularly related to gold nanorods. Nonetheless, methods that can be scaled up to large areas for device-scale applications are yet to be established. This review describes various routes that are being actively pursued to achieve assembly of nanorods. Self-assembly methods that utilize external forces such as electric field or gravitational forces are reviewed. Additionally, self-assembly schemes using chemical and biomolecule linkers are presented. Other important routes, such as template assisted assembly, Langmuir-Blodgett, and nanorod assembly methods carried out in solution phase are also discussed. The latter includes recently reported approaches to produce superstructured particles through self-assembly. Solvent evaporation and drying can also strongly contribute to the assembly of nanostructures. The final section presents self-assembly routes that primarily exploit the drying kinetics of solvents.

Nano-cellular foams were successfully produced from blends of styrenic and acrylic polymers by a two-step batch foaming process using carbon dioxide as the blowing agent. Addition of poly(ethyl methacrylate) or poly(methyl methacrylate-co-ethyl acrylate) to styrene-acrylonitrile copolymers, even at a low level, resulted in very homogeneous foams with smaller cell size and narrower cell size distribution than with the individual polymers. The best nanofoams produced from miscible blends have average cell sizes below 100 nm, cell densities up to 5 × 1015 cm−3 and medium-to-low relative densities (void fraction between 60 and 70%). Contrary to previous studies, it was found that blends with lower CO2 solubility gave higher cell density nanofoams. This suggests new mechanisms for the nucleation of foams from these blends at the nanoscale.

To overcome the low fabrication yield associated with single crystalline 3C–SiC diaphragm-based high temperature capacitive pressure sensors fabricated by wafer bonding, we have developed an alternative based on a polycrystalline SiC-on-Si architecture. The capacitive pressure sensing element, i.e., a thin film diaphragm, was fabricated using low stress and high conductivity low-pressure chemical vapor deposition poly-SiC thin films, and the sensing architecture was formed by wafer bonding a poly-SiC film to a Si substrate using phosphosilicate glass bonding films. With a geometric aspect ratio of up to 800:1 and a maximum deflection load eight times or more to their thickness, the poly-SiC diaphragm-based sensors presented repeatable pressure sensing characteristics up to 500 °C.

We report on Ni-modified TiO2 nanotubes with improved photocatalytic properties. Using the as-anodized TiO2 nanotubes as templates, Ni was electrodeposited using pulsed current waveforms. It was found that the Ni deposition was first initiated at the bottoms of the intertubular voids and then grew upward, resulting in a Ni/TiO2 coaxial nanostructure with Ni wrapping around the TiO2 nanotubes. Moreover, the tube inside was kept empty and tube openings unclogged for the fabricated Ni/TiO2 nanocomposites. Further photodegradation tests using methyl red revealed that the fabricated Ni/TiO2 nanocomposites possess higher photocatalytic efficiency than the counterparts of pristine TiO2 nanotubes. The observed improved photocatalytic efficiency is ascribed to the Schottky barriers formed between Ni and TiO2.

To understand the impact that the growth rate has on the residual stress of chemical vapor deposition-grown 3C–SiC heteroepitaxial films on Si substrates, growth experiments were performed. The film thickness was held constant at ∼2.5 μm independent of the growth rate so as to allow for direct film comparison as a function of the growth rate. Stress analysis performed by profilometer curvature measurement, μιχρο-Raman shift analysis and micro-machined freestanding structures, show an apparent disagreement about the stress nature. This incongruity between the experimental data can be explained assuming a strong stress field located in the substrate related to defects generated in the silicon during the growth process.

Photoanodes based on TiO2-polyheptazine (TiO2-PH) hybrids are, due to the energetics of photogenerated charges, very promising for solar water splitting in terms of possibly reduced need for external electric bias. Visible (λ > 420 nm) light-driven photooxidation of water at TiO2-PH electrodes loaded with two different metal oxide cocatalysts was investigated. As compared with TiO2-PH photoanodes loaded with colloidal [iridium (IV) oxide] IrO2 deposited by colloidal deposition, photoelectrodes modified with CoOx oxygen-evolving cocatalyst (Co-Pi) deposited by photoassisted deposition precipitation method showed both higher photocurrents and more efficient oxygen evolution under prolonged irradiation. The minimum external electric bias needed to observe complete photooxidation of water to dioxygen at TiO2-PH photoanodes modified with Co-Pi was estimated to be ∼0.6 V at pH 7. The key factor limiting the photoconversion efficiency at low bias potentials is the fast primary recombination of photogenerated charges.

A nanocomposite-modified electrode has been prepared by functionalizing multiwalled carbon nanotubes (MWCNTs) with N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (p-PDA). The physical characterization of the prepared composite has been done using infrared spectroscopy and ultraviolet-visible spectroscopy. The morphologies of the prepared p-PDA/MWCNTs/ionophore film have been characterized using scanning electron microscopy and transmission electron microscopy. The electrochemical studies of the prepared composite electrode have been investigated by cyclic voltammetry technique. We observed that the p-PDA/MWCNTs/ionomer composite has better electrochemistry, film adhesion with homogeneous dispersion at the electrode surface and an electrocatalytic activity toward the oxidation of dopamine (DA) in 0.1 M phosphate buffer solution (pH 7.0) at a potential of 50 mV. The linear range and detection limit for the detection of DA was found to be 62–625 and 5 µM respectively. The modified electrode also exhibited several attractive features such as simple preparation, fast response, good stability and repeatability.

In this paper, a process to introduce nanoscale cells in homogeneous polyetherimide (PEI) is presented. The nanofoams produced have a bulk porosity (void fraction) in the range of 25–64%, with the average cell sizes in the range of 40–100 nm. Uniform nucleation of cells throughout the volume of the PEI specimen was observed. Supercritical CO2 at 20 MPa was used as the blowing agent and the specimens were foamed in a hot press to ensure flatness for further processing and characterization. Sorption studies showed that at 20 MPa, PEI can absorb about 10% CO2 by weight and that a 1-mm thick specimen can reach an equilibrium concentration in approximately 100 h at 45 °C. The effects of desorption time, foaming temperature, clamping pressure, and foaming time were investigated. Several nanoscale morphologies were observed through changes in the foaming temperature, which ranged from 165 to 210 °C. In one experiment, it was found that when the clamping force is increased from 1 to 10 tons, the average cell size increased from 40 to 4000 nm or by a factor of 100. This points to the clamping force as an important process variable to control the nanostructure introduced in PEI. Optimal processing conditions for the production of defect-free nanofoams are presented.

Next-generation fission and fusion nuclear reactor materials will be exposed to very high temperatures, intense neutron radiation, corrosive environments, and, mostly, all three at once. Grand opening will be given to the material, if they have stability at high temperature operating favorable in the extreme environments, self-healing, thermal as well as irradiation properties. Owing to the superior properties of silicon carbide, nuclear scientists are closely evaluating SiC-based materials for various applications in nuclear reactors. In the present perspective, relevant properties, challenging issues, and recommendations are emphasized. Based on our recent experiments, attempt to solve various uses on SiC-based materials in nuclear applications is described in detail.

Microcellular foams, with cells of the order 10 μm, have been studied for over two decades. But little research has been done to study the effect of molecular weight on solid-state microcellular foaming. In this study, polyethylene terephthalate (PET) with a range of intrinsic viscosity (IV) 0.68–0.81 dL/g was used to investigate the effect of molecular weight on microcellular foaming process and resulting foam microstructures and properties. In the saturation step, IV showed negligible effect on sorption and desorption of CO2 in PET for all the conditions explored. In the foaming step, we found relative density increased with increasing IV. Also, as IV increased, cell size decreased and cell nucleation density increased. We hypothesize that lower chain mobility in higher IV samples led to more localized cell nucleation, resulting in a higher nucleation density, and also more constraints for cell growth, resulting in a smaller cell size. In addition, higher IV foams were found to have smaller skin thicknesses.

We report results of comparative study of photocatalytic properties of polycrystalline TiO2 nanotubes and single-crystalline nanorods. It is demonstrated that single-crystalline nanorods show superior photocatalytic properties compared to polycrystalline nanotubes due to low recombination of photoexcited carriers. Grain boundaries in polycrystalline nanotubes act as a barrier of the effective carrier pathway. Visible light activity of the TiO2 nanostructures is enhanced by the sensitization of CdS nanoparticles on TiO2. Subsequent heat treatment of the CdS/TiO2 heterostructures led to the dramatically enhanced photoresponse under both white and visible light irradiation, which was attributed to the improved crystallinity of CdS nanoparticles and TiO2nanostructures.

Data from the literature and our laboratory have been reviewed regarding the maximum homologous temperatures that can be attained by the addition of solute elements that may induce thermodynamic or kinetic (Zener pinning) stabilization of a nanocrystalline grain size (<100 nm) to elevated temperatures. The results of this review suggest that kinetic stabilization by Zener pinning by nanoscale second phases may be the more effective strategy for keeping a nanoscale grain microstructure at the highest homologous temperatures. More research is necessary to confirm this suggestion and to determine the influence of nanoscale grain boundary second phases on the mechanical behavior of the nanocrystalline matrix.