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.

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.

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.

The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen density and are among the most promising solid-state hydrogen-storage materials. In this work, the crystal structure and electronic structure of pure and mixed-alkali alanates were calculated by ground-state density-functional band-structure calculations. The results are in excellent correspondence with available experimental data. The properties of the pure alanates were compared, and the relatively high stability of the Li3AlH6 phase was pointed out as an important difference that may explain the difficulty of hydrogenating lithium alanate. The alkali alanates are nonmetallic with calculated band gaps around 5 eV and 2.5–3 eV for the tetra- and hexahydrides. The bonding was identified as ionic between the alkali cations and the aluminohydride complexes, while it is polar covalent within the complex. A broad range of hypothetical mixed-alkali alanate compounds was simulated, and four were found to be stable compared to the pure alanates and each other: LiNa2AlH6, K2LiAlH6, K2NaAlH6, and K2.5Na0.5AlH6. No mixed-alkali tetrahydrides were found to be stable, and this was explained by the local coordination within the different compounds. The only alkali alanate that seemed to be close to fulfilling the international hydrogen density targets was NaAlH4.

Hydrogen isotherms on a variety of single-walled carbon nanotube (SWNT) samples were measured using a differential pressure adsorption apparatus, which provides highly accurate data. A number of these SWNT samples were modified by a non-destructive cutting process, which reduced the aspect ratio of the nanotube bundles by two orders of magnitude. There were no apparent differences in the microporosity of SWNT as a function of aspect ratio. The adsorption of helium on SWNT is shown to be non-negligible and results in artificially low hydrogen capacities using conventional adsorption methodology. With no accounting for helium adsorption, the hydrogen adsorption results show that cut and uncut SWNT have similar hydrogen capacities of <1 wt% at 25 °C and pressures up to 110 bar. However, an analysis of hydrogen capacity versus N2 Brunauer–Emmett–Teller surface area suggests that there is an enhanced heat of adsorption of hydrogen for SWNT versus activated carbon.

Organic solar cells based on conjugated polymer:fullerene blends show nowadays efficiencies above 4%. After briefly presenting the science of bulk-heterojunction solar cells, we report herein a shelf lifetime study performed by encapsulating the cells in a flexible and transparent gas barrier material. This method allows lifetimes as reported for glass encapsulation. Moreover, we propose a new approach to pattern organic solar cells and design large-scale modules. This technique, based on selective Nd:yttrium aluminum garnet (YAG) laser etching, potentially enables low-cost, high-speed roll-to-roll operation.

Over the last ten years there has been substantial experimental and theoretical effort in understanding the transport properties of filled skutterudite compounds to optimize their thermoelectric properties. One such approach involves partially filling the voids in attempting to optimize the electrical properties while minimizing the thermal conductivity. We illustrate the importance of this approach by plotting and comparing the figure of merit of CoSb3 over a large range of carrier concentrations and thermal conductivity values. The thermal conductivity of partially filled skutterudites AxCo4Sb12, where A = La, Eu, and Yb, is analyzed using the Debye model to correlate the data with the type of filler atom in evaluating the role of the filler in affecting the thermal conductivity. Partial void filling has resulted in relatively high thermoelectric figures of merit at moderately high temperatures.

Hollow and nanoporous particles of zero-valent iron (ZVI) were prepared with template-directed synthesis. Polymer resin beads (0.4 mm diameter) were coated with nanoscale iron particles by reductive precipitation of ferrous iron [Fe(II)] with sodium borohydride. The resin was calcinated at 400 °C to produce hollow and nanoporous iron spheres. The nanoporous iron oxides were then reduced to metallic iron by hydrogen at 500 °C. Scanning electron microscope images of the reduced iron spheres showed that the particles were hollow. The shell thickness was approximately 5 μm and highly porous. Brunauer–Emmett–Teller specific surface area was 2100 m2/kg. In comparison, the theoretical specific surface area of solid iron particles of the same size is just 1.9 m2/kg. Batch tests showed that the surface area normalized reactivity of the porous particles were 14–31% higher than microscale iron particles with similar surface areas for the transformation of hexavalent chromium [Cr(VI)], azo dye Orange II {4-[(2-hydroxyl-1-naphthalenyl)azo]-benzenesulfonic acid monosodium}, and trichloroethene. The combined performance enhancement (larger surface area and higher surface activity) is significant (>1200 times).

In this study, the transport of water-stable “nano-C60 particles” (a term used to refer to underivatized C60 crystalline nanoparticles, stable in water for months) through a soil column (packed with Lula soil, 0.27% organic carbon) was investigated for the first time. Nano-C60 particle breakthrough experiments were conducted at different flow rates, while other column operating parameters remained fixed through all the experiments. Nano-C60 particles were observed to be more mobile at higher flow velocity: at the flow velocity of 0.38 m/d, the maximum percent of nano-C60 breakthrough (C/C0) was 47%; at the flow velocity of 3.8 m/d, the plateau value of nano-C60 breakthrough was 60%; and at the flow velocity of 11.4 m/d, the plateau value of nano-C60 breakthrough was almost 80%. At the low flow velocity (0.38 m/d), which is typical of groundwater flow, nano-C60 particles showed very limited mobility: after about 57 pore volumes, they deposited to the soil column so rapidly that virtually no nano-C60 was detected in the effluent. This observed “favorable deposition” (attachment efficiency α = 1) was probably due to “filter ripening.” Also the release of nano-C60 particles after flow interruption was observed. The transport of naphthalene through the same soil column containing 0.18% nano-C60 particles deposited was measured. A retardation factor of about 13 was observed, possibly suggesting that sorbed nano-C60 particles in the soil column sorbed naphthalene similar to soil organic carbon. An asymmetric naphthalene breakthrough curve was observed, which is possibly due to “sorption nonequilibrium.”

Numerous studies have examined arsenic adsorption on varying adsorbents including iron oxides, aluminum hydroxides, alumina, and carbon as a means of arsenic removal in drinking water treatments. The objectives of this study were to evaluate the effect of magnetite particle size on the adsorption and desorption behavior of arsenite and arsenate, and to investigate the competitive adsorption between natural organic matter (NOM) and arsenic. Increases in adsorption maximum capacities for arsenite and arsenate were observed with decreasing magnetite particle size. Arsenic desorption is hysteretic, more so with the smaller nanoparticles. Such desorption hysteresis might result from a higher arsenic affinity for magnetite nanoparticles. In the presence of NOM, substantial decrease in arsenic sorption to magnetite nanoparticles was observed. It would be beneficial to thoroughly investigate adsorption and desorption of arsenic on magnetite nanoparticles for further practical purposes.

Electron paramagnetic resonance (EPR) spectra were obtained for samples of Ti-doped NaAlH4 subjected to different numbers of cycles of dehydrogenation/re-hydrogenation. Ti is observed to evolve from its initial Ti(III) state through a series of Ti(0) species during the first 5 cycles. Although the conversion of Ti(III) to Ti(0) occurs much more readily for TiCl3-doped samples than those prepared with TiF3, in both cases the evolution of Ti follows the same sequence that involves 3 distinguishable Ti(0) species and ends in the predominance of the same single Ti(0) species. The spectrum of a sample of NaAlH4 containing 2 mol% of cubic Al3Ti is distinctly different than any of those observed for the Ti(0) species that arise during the hydrogen cycling of the hydride. The major changes in the nature of the predominant Ti species have little if any effect on the dehydrogenation kinetics, which strongly suggests that the profoundly enhanced hydrogen cycling kinetics of Ti-doped NaAlH4 are due to a Ti species present in only a relatively minor amount.

A unique combination of in situ synchrotron x-ray diffraction and in situ micro-Raman spectroscopy was used to study the growth process of YBa2Cu3O6+x films obtained by metal organic decomposition using trifluoroacetate precursor on LaAlO3 substrates. The techniques give complementary information: x-ray diffraction gives insight into the structural growth, whereas micro-Raman spectroscopy gives information of the chemical composition with additional information on the texture. To perform both experiments in situ, a special high-temperature process chamber was designed.

A thin film of a stiff material, patterned as a serpentine on a flat elastomeric substrate, can elongate substantially when the substrate is pulled. We showed that the film elongates by twisting out of plane, accommodated by the compliance of the substrate and the pattern of the film. Consequently, large elongations of the substrate induce small strains in the film, even when the width of the film is much larger than its thickness. Such a wide serpentine, or other compliant patterns of stiff materials, can serve as a platform on which electronic circuits can be fabricated. This architecture will make electronics elastically stretchable.

We review recent advances in the growth of Si1−xGex islands and Ge dots on (001) Si. We first discuss the evolution of the island morphology with Si1−xGex coverage and the effect of growth parameters or post-growth annealing on the shape of the islands and dots. We outline some of the structural and optical properties of Si1−xGex islands and assess progress in the determination of their composition and strain distribution. Finally, we discuss various approaches currently being investigated to engineer Si1−xGex quantum dots and in particular to control their size, density, and spatial distribution. For example, we show how C pre-deposition on Si (001) can influence the nucleation and growth of Ge islands.

Magnetoresistive biosensors use a new detection method for molecular recognition reactions based on two recently developed techniques and devices: Magnetic markers and XMR sensors, where XMR means either giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR). The markers are specifically attached to the target molecules, and their magnetic stray field is picked up by an embedded magnetoresistive sensor as a change of the electrical resistance. Compared to established, e.g., fluorescent, detection methods, magnetic biosensors have a number of advantages, including low molecular detection limits, flexibility, and the direct availability of an electronic signal suitable for further automated analysis. This makes them a promising choice for the detection units of future widespread and easy-to-use lab-on-a-chip systems or biochips. In this article, we discuss recent advances in this field and compare possible approaches toward single molecule detection.

Pseudo-simulated body fluids (SBFs) were used in in vitro experiments to promote chitosan porous membrane calcification. Common SBFs, which had concentrations of phosphate or calcium ions doubled, were so named because they do not replicate, by rigor, a genuine body fluid ion concentration. The objective of using such calcification fluids was to study the influence of phosphate and calcium excess in solution on mineralization deposit characteristics. SEM-EDS analyses showed that morphology and composition of deposits varies depending on which ion (phosphate or calcium) is in excess; x-ray diffractograms show that deposits are poorly crystalline (like biological apatites) but still show better crystallinity in deposits generated from P-rich SBF. This result, added to previous ones [such as those reported by Beppu and Santana Mater. Res.5, 47 (2002)] where a difference in the interconnectivity of the inorganic and organic (matrix) phases was stressed, suggests different deposition processes for each situation.

The concentration of hydroxyl (–OH) groups in epitaxial barium titanate (BaTiO3) films (thickness ∼ 200 nm), deposited on single-crystal strontium titanate (SrTiO3) at 150 °C by a hydrothermal technique, was investigated using x-ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. After hydrothermal treatment, a broad FTIR resonance for the hydroxyl groups indicated a significant concentration of surface –OH groups in the films. The as-deposited films were subsequently treated hydrothermally with D2O, and the kinetics of the exchange reaction between –OH incorporated into the film and –OD from the D2O were studied using FTIR. For reactions carried out intermittently, the kinetics of the exchange reaction between –OH by –OD depended not only on the total reaction time, but also on the duration of each treatment. The broad FTIR hydroxyl resonance in the as-deposited hydrothermal film was significantly reduced only after heating for 1 h at 600–800 °C.

Nanocomposite thin films consisting of Au nanoparticles embedded in yttria-stabilized zirconia (YSZ) were synthesized at room temperature by radio frequency magnetron co-sputtering from YSZ and Au targets and subsequently annealed in an argon atmosphere. Au microstructure and particle size were characterized as a function of annealing temperature from 600 to 1000 °C by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Rutherford backscattering spectroscopy. Spectroscopic ellipsometry was also used to determine the optical constants of the resulting films. In particular, the refractive index of the nanocomposites was found to undergo an anomalous dispersion in the spectral region where the extinction coefficient achieves its maximum. Additionally, the incorporation of Au in the YSZ matrix was found to increase the refractive index in comparison to that of YSZ. At annealing temperatures higher than 800 °C, a good agreement was found between experimental findings and theoretical models using bulk dielectric functions for Au, as modified to account for a reduced mean free path for scattering than that for free electrons. However, for annealing temperatures below 800 °C, an additional offset was required for the optical constants of Au to obtain good agreement between theory and experiment. This behavior was attributed to a relatively high atomic Au concentration in the YSZ matrix.

Five different mixed-perovskite (AA′)(BB′)O3 single crystals were grown, where A = La, Nd; A′ = Sr; B = Al, Ga; and B′ = Ta, Nb. The as-grown crystals were yellowish/brownish. After annealing in air, the coloration was more intense. Annealing in a reducing atmosphere decreased coloration. The crystals were investigated by transmission spectroscopy, electron spectroscopy for chemical analysis (ESCA), and single-crystal x-ray diffraction. Additional broad absorption bands in the transmission spectra were observed for the as-grown samples. They are in line with the changes of the shape of O(1s) ESCA peaks. Redundant interstitial oxygen ions were recognized as the reason for the crystal coloration. All structures were solved and refined in different space groups of the regular system. Some of the unit cells have a doubled lattice constant: (i) lanthanum strontium gallium niobate, Pm3m, 3.9323(5) Å, at 100 K, 3.9270(5) Å; (ii) neodymium strontium aluminum tantalate, Pm3m, 3.8353(4) Å; (iii) lanthanum strontium aluminum tantalate, Pn3m, 7.720(1) Å, annealed in reducing atmosphere, 7.708(1) Å; (iv) neodymium strontium aluminum niobate, Fm3m, 7.744(4) Å.