Examination of gas desorption by B4C resin for use in neutron scattering experiment

Gas desorption rates for several types of B(4)C resins were investigated using a throughput method. The investigation was particularly focused on determining the out gas composition, effects of dry air, grain size (density) effects on the gas desorption rates. It is found that water is the main component of out gas and that dry air can effectively reduce gas desorption.     

Coherence filters and their uses. I. Basic theory and examples

Abstract

The phenomenon of correlation-induced spectral changes, discovered several years ago and extensively studied since then, is shown to offer the possibility of contructing novel types of spectral filter which have several properties that are not achievable with conventional filters. For example such filters can have different prescribed filtering properties in different directions of observation. In this paper the underlying theory is discussed and is illustrated by a few examples.     

Space charge limited current measurements on conjugated polymer films using conductive atomic force microscopy

We describe local (~150 nm resolution), quantitative measurements of charge carrier mobility in conjugated polymer films that are commonly used in thin-film transistors and nanostructured solar cells. We measure space charge limited currents (SCLC) through these films using conductive atomic force microscopy (c-AFM) and in macroscopic diodes. The current densities we measure with c-AFM are substantially higher than those observed in planar devices at the same bias. This leads to an overestimation of carrier mobility by up to 3 orders of magnitude when using the standard Mott-Gurney law to fit the c-AFM data. We reconcile this apparent discrepancy between c-AFM and planar device measurements by accounting for the proper tip-sample geometry using finite element simulations of tip-sample currents. We show that a semiempirical scaling factor based on the ratio of the tip contact area diameter to the sample thickness can be used to correct c-AFM current-voltage curves and thus extract mobilities that are in good agreement with values measured in the conventional planar device geometry.     

Quantum dot/plasmonic nanoparticle metachromophores with quantum yields that vary with excitation wavelength

Coupled plasmonic/chromophore systems are of interest in applications ranging from fluorescent biosensors to solar photovoltaics and photoelectrochemical cells because near-field coupling to metal nanostructures can dramatically alter the optical performance of nearby materials. We show that CdSe quantum dots (QDs) near single silver nanoprisms can exhibit photoluminescence lifetimes and quantum yields that depend on the excitation wavelength, in apparent violation of the Kasha-Vavilov rule. We attribute the variation in QD lifetime with excitation wavelength to the wavelength-dependent coupling of higher-order plasmon modes to different spatial subpopulations of nearby QDs. At the QD emission wavelength, these subpopulations are coupled to far-field radiation with varying efficiency by the nanoprism dipolar resonance. These results offer an easily accessible new route to design metachromophores with tailored optical properties.     

Fracture behavior and toughening mechanism in Zanchor reinforced composites under mode II loading

The mode II interlaminar fracture behavior and the toughening mechanism of Zanchor reinforced composite laminates were investigated by using the End Notched Flexure (ENF) and Interlaminar Shear (ILS) specimens. The ENF test results demonstrated that the Zanchor process was highly effective to improve the mode II fracture toughness of composite laminates, where the fracture toughness increased almost linearly with the Zanchor density. The R-curves of Zanchor composites were roughly divided into the transition and stable regions, where the width of the transition region became larger as the Zanchor density increased. The macroscopic fracture behavior of the Zanchor composites was still brittle under mode II loading like that of the base composite, where the crack tip process zone was estimated to be rather small regardless of the Zanchor density. The ILS test results demonstrated that the square of the normalized shear strength increased linearly with the Zanchor density and agreed quantitatively with the normalized fracture toughness. The wedge effect was supposed to be the dominant toughening mechanism against the mode II fracture, where the entangled fiber bundles partly sustained the shear stress in the vicinity of the crack tip. The entangled fiber bundles played an important role to form the mode II fracture surface, where the microscopic fracture pattern of the entangled fiber bundles was mainly the breakage of the fiber bundles rather than the pull-out or debonding of the fiber bundles.     

Toward the β-FeSi2p-n homo-junction structure

β-FeSi₂ thin films were prepared on various substrates, and the influence of the thermal expansion coefficient (TEC) and the softening temperature on the film quality were discussed. It was clarified that a crack-free β-FeSi₂ film could be formed on a glass material substrate with a TEC close to that of β-FeSi₂, and when the softening point of the substrate is close to the crystal growth temperature of β-FeSi₂. A (β-FeSi₂)/(MoSi₂)/(Corning 1737 glass) stacked structure without leak current was prepared to demonstrate the possibility of a MoSi₂ back electrode layer. Furthermore, the (Al-doped p-β-FeSi₂)/(Ni-doped n-β-FeSi₂) homo-junction was also prepared by the vacuum evaporation and thermal diffusion method. We have succeeded in achieving current-rectification to a β-FeSi₂ thin film, although the anode current was small.     

InP/InGaAs buried-structure avalanche photodiodes

Planar InP/InGaAs avalanche photodiodes with a new guardring structure have been designed and fabricated. The diodes had a buried n-InP layer and an n?-InP multiplication region under p-n junctions. A successful guardring effect was obtained. The diode exhibited a uniform multiplication over the active region, a maximum multiplication factor of 30, low dark currents of around 20 nA at 90% of breakdown voltage and a flat frequency response up to 1 GHz. Multiplication noise was measured up to a multiplication factor of 17.     

Radiation Efficiency of Partially Coherent Planar Sources with Various Intensity Distributions

Abstract

A general expression is derived for radiation efficiency, which is defined as a ratio of the radiated energy flux to the source-integrated intensity, of partially coherent planar sources with arbitrary intensity distributions. On the basis of the expression, radiation efficiencies of the sources with various intensity distributions are quantitatively investigated as a function of both the coherence condition and the intensity distribution across the source. By stemming from the present source model whose spatial coherence is characterized by Bessel functions, a physical origin of the variation in radiation efficiency is satisfactorily presented in connection with the spatial frequency spectrum of the source associated with evanescent waves. As a result, it is found that the broad spread in spatial frequency spectrum of the source results in the reduction of radiation efficiency for the sources with arbitrary intensity distributions including the quasi-homogeneous ones and that the behaviour of this kind is independent of the presence of evanescent waves, at least, for the quasi-homogeneous sources.     

Effects of quaternary ammonium compounds with 0.1% sodium hydroxide on swine vesicular disease virus

The purpose of the present study was to evaluate the role of central alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate type of glutamate receptors in the control of ACTH and corticosterone release under basal and stress conditions. AMPA/ kainate competitive receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), which does not penetrate the blood-brain barrier, was administered intracerebroventricularly (i.c.v.). A modified method for i.c.v. drug administration in conscious freely moving rats was employed. DNQX or artificial cerebrospinal fluid (aCSF) was injected into lateral ventricle through a thin polyethylene cannula with a steel needle on the end which was inserted and moved via large polyethylene cannula to the guide stainless steel cannula. This procedure was performed out of the cage. ACTH and corticosterone release under basal conditions and during immobilization stress were investigated. Intracerebroventricular administration of DNQX resulted in an increase of ACTH and corticosterone in plasma reaching maximal values at 15 min after drug injection. During immobilization stress, i.c.v. DNQX induced a mild reduction in plasma ACTH levels compared to those in aCSF pretreated rats. Corticosterone secretion was high throughout the whole period of stress exposure. These findings indicate that endogenous excitatory amino acids (EAA) acting at AMPA/kainate receptors may interfere with the control of ACTH release under both basal and stress conditions, but the mechanisms involved remain to be elucidated.