Organic photovoltaic devices are poised to fill the low-cost, low power niche in the solar cell market. Recently measured efficiencies of solid-state organic cells are nudging 5% while Grätzel’s more established dye-sensitized solar cell technology is more than double this. A fundamental understanding of the excitonic nature of organic materials is an essential backbone for device engineering. Bound electron-hole pairs, “excitons,” are formed in organic semiconductors on photo-absorption. In the organic solar cell, the exciton must diffuse to the donor–accepter interface for simultaneous charge generation and separation. This interface is critical as the concentration of charge carriers is high and recombination here is higher than in the bulk. Nanostructured engineering of the interface has been utilized to maximize organic materials properties, namely to compensate the poor exciton diffusion lengths and lower mobilities. Excitonic solar cells have different limitations on their open-circuit photo-voltages due to these high interfacial charge carrier concentrations, and their behavior cannot be interpreted as if they were conventional solar cells. This article briefly reviews some of the differences between excitonic organic solar cells and conventional inorganic solar cells and highlights some of the technical strategies used in this rapidly progressing field, whose ultimate aim is for organic solar cells to be a commercial reality.

After creep failure at 1300 °C, silica-based nanofibers with diameters of ∼250 nm and lengths of up to a few tens of microns were observed on the fracture surfaces of Ti3SiC2. A possible mechanism for the formation of these fibers is proposed.

We report enhanced thermal stabilities of nanostructured Cu films containing insoluble tungsten carbides prepared by sputter deposition. Tungsten carbides in the form of W2C are present in the supersaturated solid solution of Cu, as confirmed by x-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray diffraction analyses. Focused ion beam analysis revealed that the films are thermally stable during annealing when they are in contact with Si without a diffusion barrier, and the copper silicide was not formed up to an annealing temperature of 400 °C. Leakage current characteristic evaluation on SiO2/Si metal oxide semiconductor (MOS) structure also revealed the superior reliability of Cu with a dilute amount of tungsten carbides, indicating their usefulness in advanced barrierless metallization applications. The films with higher amount of tungsten carbides exhibited good thermal stability at high temperatures and could be rationalized as a consequence of a refined grain structure together with the strengthening effect of W2C.

A new series of rare earth-niobate, RE3NbO7 (RE=Y,Gd,Eu), buffer layers were developed for the growth of superconducting YBa2Cu3O7−δ (YBCO) films on biaxially textured Ni–W (3 at.%) substrates. Using chemical solution deposition, smooth, crack-free, and epitaxial RE3NbO7 (RE = Y,Gd,Eu) films were grown on cube-textured Ni–W substrate. YBCO film with a critical current density of 1.1 × 106 A/cm2 in self-field at 77 K was grown directly on a single Gd3NbO7-buffered Ni–W substrate using pulsed laser deposition.

Mg−Cu−Y alloys with optimal glass forming ability have been found at off-eutectic compositions. The critical size for bulk metallic glass formation at the pinpointed compositions more than doubles that of the previously discovered eutectic Mg65Cu25Y10 alloy, leading to fully glassy rods with near-centimeter diameters in the ternary system upon copper mold casting. The result is a striking demonstration of the strong composition dependence of the glass forming ability, as well as of the need to scrutinize off-eutectic compositions. The implications of the discovery are discussed.

Highest strength for 7075 Al alloy was obtained by combining the equal-channel-angular pressing (ECAP) and natural aging processes. The tensile yield strength and ultimate strength of the ECAP processed and naturally aged sample were 103% and 35% higher, respectively, than those of the coarse-grained 7075 Al alloy counterpart. The enhanced strength resulted from high densities of Guinier–Preston (G-P) zones and dislocations. This study shows that severe plastic deformation has the potential to significantly enhance the mechanical properties of precipitate hardening 7000 series Al alloys.

Recent progress in in situ observation of solid–liquid interfaces by means of transmission electron microscopy, carried out by the Nagoya group, was reviewed. The results obtained on pure materials are discussed based on Jackson's theory. The structure of the solid–liquid interfaces of eutectic alloys was also observed. The in situ observation technique of solid–liquid interface is applied to industrially important reactions which include liquid phases.

Herein we report on the room-temperature spontaneous growth of Ga freestanding nanoribbons from Cr2GaC surfaces. An oxidation-based model is proposed to explain the growth of the nanostructures. The nanoribbons present a unique opportunity to study the behavior of electrons confined to two dimensions. The production of these Ga nanostructures could be the first step in the manufacture of gallium arsenide or nitride devices with enhanced characteristics for photonic, electronic, and catalytic applications.

The relationship between crystal structure and piezo-response was investigated in epitaxially grown PbZr1−xTixO3 (PZT) thin films on Pt(001)/MgO(001) with a thin PbTiO3 interlayer. Insertion of the interlayer resulted in significant relaxation ofthe strain that could be developed in the course of deposition of the PZT films, consequently leading us to single out only the effect of composition. Composition of the morphotropic phase boundary (MPB), at which tetragonal and rhombohedral phases are mixed with the same volume fraction, was found to be ∼0.55 in Ti/(Zr + Ti) ratio in our films, which is close to the value for bulk polycrystalline PZT (∼0.50). The piezoelectric response peaks were two times higher in the MPB regime than in the single phase regime due to structural instability caused by the coexistence of two phases. The results indicate that epitaxial PZT films having the MPB composition are advantageous over those of other compositions for nano-storage devices based on scanning force microscopy.

The effects of residual stress induced during the annealing process on the microstructural evolution and electrical properties of Pb(Zr,Ti)O3 (PZT) films were investigated. PZT films were deposited on platinized silicon substrates by the radio frequency magnetron sputtering method using a single oxide target. Compressive stress was induced in the film by bending the silicon substrate during sputtering using a specially designed substrate holder and subsequently annealing the film without the holder. Without the residual stress, the PZT film was severely cracked when it was thicker than 2 μm due to the thermal expansion mismatch between the PZT and the Si substrate. On the other hand, when the residual stress was applied, no cracks were detected in the film for thicknesses of up to 4 μm. The suppression of crack formation was attributed to the residual compressive stress that compensated for the tensile stress generated during and/or after the annealing process. The electrical properties of the PZT film with the residual stress were improved compared to those of the PZT film without the residual stress.

This overview will describe briefly key segments of the hydrogen energy cycle from production using various feedstocks to its end use in fuel cells to generate electrical and thermal energy. The paper will also discuss the larger societal context, the so-called “hydrogen economy,” in which such production and use of hydrogen may take place. Although most of the public attention on hydrogen has been focused on its potential as an alternative energy source to petroleum and other fossil fuels, a hydrogen economy will encompass much more than a substitution of one energy source by another. Widespread use of hydrogen as an energy carrier can transform our society in much the same way that personal computing technologies have. This transforming power arises from the unique capability of hydrogen to link renewable energy resources and zero-emission energy conversion technologies. Hydrogen can be produced from locally available renewable resources, such as solar, wind, biomass, and water, and converted to electricity or fuel at or near the point of use with only heat and water vapor as “emissions.” Hydrogen also lies at the confluence of two emerging trends that will shape our energy future during the first quarter of this century: greater reliance on renewable energy sources and the shift from large, centralized power plants to smaller, decentralized facilities located at or near the point of use. This paper describes these emerging trends and the role of hydrogen in linking them in a way that could transform our society.

Gold nanoclusters were successfully deposited in the interior of TiO2 nanotubes fabricated as ordered arrays. This approach is a useful fabrication platform for miniature planar fuel cells, gas sensors, and heterogeneous catalysts. A pressure impregnation process was used to inject the titania and Au precursors into mesoporous alumina. After thermal treatment, Au nanoclusters were well-dispersed on the interior walls of nanotubular TiO2. The TiO2 nanotubes were shown by x-ray diffraction to be entirely anatase. Transmission electron microscopy imaging confirmed that 80% of the Au particles were 4.1 nm ± 2.0 nm in diameter. This material exhibited catalytic CO oxidation activity at low temperatures.

High-resolution transmission electron microscopy studies of hydrothermally derived platelike lead titanate nanoparticles reveal that below a critical size of approximately 70 nm, the single ferroelectric domain polarization axis reorients from perpendicular to parallel to the plate. We suggest that during particle growth, ions in the hydrothermal processing medium compensate for the ferroelectric depolarization energy. When the processing medium is removed by washing and drying, single domain nanoparticles minimize their depolarization energy by c-axis flipping.

In this study, we investigated the vibration properties of Sn–Zn and Sn–Zn–Al alloys. It is notable that, with a small amount of Al addition, Sn whiskers were generated during resonant vibration. This may be the first time that Sn whiskers were found on bulk materials. Microstructural refining and hardening caused by alloying of Al stunted the fiberous type Sn deformation within Sn–Zn eutectics. Vibration-induced extrusion of Zn-free regions in the vicinity of cell boundaries may account for the appearance of the whiskers.

A comparative study on the wet and dry milling of the intermediates for the Z-type hexagonal ferrite (Ba3Co2Fe24O41, Z phase) was performed. Phase-pure Z phase was synthesized by wet milling the intermediates comprising M and Y-type hexaferrites. The intermediates were obtained by calcining the stoichiometric powder mixture at 1080 °C. Subsequent wet milling by a planetary mill for 1 h increased the crystallization rate of Z phase upon subsequent heating at 1230 °C. In contrast, dry milling the intermediates resulted in the severe surface amorphization and led to heterogeneous crystalline states. The observed favorable effect of wet milling the intermediates was explained by the particle size reduction for the decrease of diffusion distance while preserving the basic layer units common to the related hexaferrites.

A method to observe the dispersion structure of carbon nanotubes buried inside a molding composite is described in this communication. The idea is that by utilizing the difference in ablation temperature between the tubes and the composite material, only the composite material, which has a lower ablation temperature, is ablated and buried tubes appear. This was applied to a rubber composite mixed with vapor-grown carbon fibers. A 150-fs pulse laser was prepared as an ablation source. In the ablation images observed with a field-emission secondary electron microscope, linear tubes, clusters, and connections of the tubes could be easily found in their original state.

We report a new compression shearing method for the production of bulk amorphous materials. In this study, amorphous Nd–Fe–B melt-spun ribbons were successfully consolidated into bulk form at room temperature by the compression shearing method. X-ray diffraction and transmission electron microscopy studies revealed that the amorphous structure was well maintained in the bulk materials. The resultant bulk materials exhibited the same magnetic properties as the original amorphous Nd–Fe–B materials.

Amorphous transition behavior of silica polymorphs under high pressure has been extensively studied by using diamond-anvil cells or shock wave technologies at ambient temperature. Here, we report the amorphization of crystalline silica fiber in cristobalite polymorph in the temperature range of 1050–1350 °C without pressure applied in vacuum. X-ray diffraction, infrared spectra, and Raman spectra illustrated the transition. Raman spectra revealed that no significant changes had happened to the SiO4 unit during the transition. It is suggested that the driven-off of interstitial oxygen attributed to the transition and the reaction between the diffusing hydrogen and interstitial oxygen promoted the process.

An alumina-based ceramic codispersed with 15 vol% zirconia and 15 vol% mullite (AZM) was synthesized by reactive processing, and the creep behavior was compared to alumina with 30 vol% zirconia (AZ). Constant stress compressive creep behavior for AZM exhibited a stress exponent of 2 and an activation energy of 770 KJ/mol, while a similar stress exponent but lower activation energy of 660 KJ/mol was found for AZ. The strain rate of AZM, however, was more than twice that of the AZ under the same deformation conditions, indicating a better potential for superplastic shape forming.

We report here on the utilization of variable band gap conjugated polymers for optoelectronic redox applications comprising organic photovoltaics, color tunable light emitting diodes, and electrochromics. For the evaluation of morphology in photovoltaicdevices, atomic force microscopy, and optical microscopy provided direct visualization of the blend film structure. The evolution of the morphology in two and three component blends incorporating poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenlenevinylene] (MEH-PPV), poly(methylmethacrylate) (PMMA), and [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) was investigated. It was found that while insulating PMMA can be used to modulate the phase separation in these blends, a bicontinuous network of donor and acceptor was required to achieve the best device results. Similarily, a MEH-PPVcopolymer with a decreased conjugation length has been used for investigating inter- and intramolecular photoinduced charge transfer in the presence of PMMA and PCBM.We fabricated MEH-PPV/PCBM solar cells that have power conversion efficiencies up to 1.5% with a range of 0.7–1.5%, dependent on the nature of the MEH-PPV used. This further indicates that in addition to blend morphology, polymer structure is critical for optimizing device performance. To this end, the concept of an ideal donor for photovoltaic devices based on poly[2,5-di(3,7-dialkoxy)-cyanoterephthalylidene] is described and two donor-acceptor polymers based on cyanovinylene (CNV) and dioxythiophene are discussed as representative examples of soluble narrow band gap polymers synthesized in our group. For light emitting applications, utilization of two blue emitting conjugated polymers poly (9,9-dioctylfluorene) (PFO) and poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,ethyl-3,6-carbazole)] (PFH-PEtCz)is presented for a color tunable polymer light emitting diode that emits orange, green, and blue light with a voltage range of 7–10 V as a function of the total conjugated polymer content in PMMA and is attributed to the phase separation between the conjugated polymers. Finally, the narrow band gap conjugated polymer, poly[bis(3,4-propylenedioxythiophene-dihexyl)]-cyanovinylene has been characterized for its electrochromic properties, illustrating the multifunctional nature of variable band gap conjugated polymers.