Optical design of multilayer antireflection coatings for indoor solar cell applications.

Multilayer antireflection coatings (ARCs) for solar cells are conventionally designed to enhance the photocurrent level obtained at normal incidence. This is mainly because outdoor solar panels are usually placed such that they can receive strong midday sunlight at a nearly vertical angle. However, in the case of indoor photovoltaic devices, the direction of light changes considerably with changes in the relative position and angle between the device and light sources; therefore, it is often difficult to predict the incident angle. In this study, we explore a method to design ARCs suitable for indoor photovoltaics by essentially taking into account the indoor lighting environment, which is different from the outdoor conditions. We propose an optimization-based design strategy that aims to enhance the average level of the photocurrent generated when a solar cell receives irradiance randomly from all directions. We apply the proposed method to design an ARC for organic photovoltaics, which are expected to be promising indoor devices, and numerically compare the resultant performance with that obtained using a conventional design method. The results demonstrate that our design strategy is effective for achieving excellent omnidirectional antireflection performance and allows the realization of practical and efficient ARCs for indoor devices.

Lateral voltage as a new input for artificial lipid bilayer systems.

In this work, we propose lateral voltage as a new input for use in artificial lipid bilayer systems in addition to the commonly used transmembrane voltage. To apply a lateral voltage to bilayer lipid membranes, we fabricated electrode-equipped silicon and Teflon chips. The Si chips could be used for photodetector devices based on fullerene-doped lipid bilayers, and the Teflon chips were used in a study of the ion channel functions in the lipid bilayer. The findings indicate that the lateral voltage effectively regulates the transmembrane current, in both ion-channel-incorporated and fullerene-incorporated lipid bilayer systems, suggesting that the lateral voltage is a practicable and useful additional input for use in lipid bilayer systems.

Structure of hydrated cobalt ions confined in the nanospace of single-walled carbon nanotubes.

The structure of hydrated Co ions confined in the nanospace of single-walled carbon nanotubes (SWNTs) has been studied using the X-ray absorption fine structure (XAFS) technique. Water adsorption isotherms on Co-impregnated SWNTs indicate a high affinity of Co ions to water molecules. The results of XAFS analysis provided the information on the proportion of dissolved species in nanospaces against the total amount of cobalt ions adsorbed on the open-pored SWNT. The structural information of the first shell around a Co ion was expressed in terms of the hydration number, Co-O distance and Debye-Waller factor. The actual coordination number and the interatomic distance of Co-O for the dissolved species were remarkably reduced compared to the bulk aqueous solution indicating the dehydration of water molecules from Co ions and a compact hydrated structure in the micropore of SWNTs.

Oxygen vacancy mediated room-temperature ferromagnetism and band gap narrowing in DyFe0.5Cr0.5O3 nanoparticles.

We report on the magnetic and optical properties of DyFe0.5Cr0.5O3 nanoparticles synthesized by a sol-gel method. Rietveld refinement of a powder X-ray diffraction (XRD) pattern confirms the formation of an orthorhombic disordered phase with the Pnma space group. The formation of nano-sized particles, with an average size of 42(±12) nm, was approximated by the transmission electron microscopy (TEM) image analysis. X-ray photoelectron spectroscopy (XPS) of this compound reveals the presence of Fe2+/Fe3+ and Cr2+/Cr3+ mixed-valence states as a consequence of oxygen vacancies present at the surface of nanoparticles. The temperature-dependent magnetization (M-T) shows a finite non-zero magnetization up to 300 K and the field-dependent magnetization (M-H) curve exhibits a weak ferromagnetic (WFM) nature at 300 K with a clear hysteresis loop, which is quite appealing compared to that of the previously reported micron-sized DyFe0.5Cr0.5O3. These observations indicate that the large concentration of uncompensated surface spin of nanoparticles could be responsible for the observed room-temperature ferromagnetism. Moreover, DyFe0.5Cr0.5O3 nanoparticles show a significantly narrow band gap (Eg ∼ 2.0 eV). Meanwhile, the oxygen vacancies may generate shallow trap energy levels within the band gap as observed from photoluminescence (PL) spectroscopy. The observed band gap narrowing by Fe doping and the effect of oxygen vacancies on the band gap are consistent with the predictions of density functional theory (DFT) calculations. The evidence of room-temperature ferromagnetism in DyFe0.5Cr0.5O3 nanoparticles compared to their bulk counterparts and the significantly narrow band gap in the visible range manifest the potential of this material in spintronic and optical applications.

Modulation of Photoinduced Transmembrane Currents in a Fullerene-Doped Freestanding Lipid Bilayer by a Lateral Bias.

We report on a novel lipid bilayer system, in which a lateral bias can be applied in addition to a conventional transmembrane voltage. Freestanding bilayer lipid membranes (BLMs) doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were formed in a microaperture, around which metal electrodes were deposited. Using this system, it was possible to modulate and amplify photoinduced transmembrane currents by applying a lateral bias along the BLM. The results indicate that the microfabricated Si chip with embedded electrodes is a promising platform for the formation of transistor-like devices based on PCBM-doped BLMs and have potential for use in a wide variety of nanohybrid devices.

Simple top-down preparation of magnetic Bi0.9Gd0.1Fe1-xTixO3 nanoparticles by ultrasonication of multiferroic bulk material.

We present a simple technique to synthesize ultrafine nanoparticles directly from bulk multiferroic perovskite powder. The starting materials, which were ceramic pellets of the nominal compositions Bi0.9Gd0.1Fe1-xTixO3 (x = 0.00-0.20), were prepared initially by a solid state reaction technique, then ground into micrometer-sized powders and mixed with isopropanol or water in an ultrasonic bath. The particle size was studied as a function of sonication time with transmission electron microscopic imaging and electron diffraction that confirmed the formation of a large fraction of single-crystalline nanoparticles with a mean size of 11-13 nm. A significant improvement in the magnetic behavior of Bi0.9Gd0.1Fe1-xTixO3 nanoparticles compared to their bulk counterparts was observed at room temperature. This sonication technique may be considered as a simple and promising route to prepare ultrafine nanoparticles for functional applications.