640 × 512 pixel narrow-band, four-band, and broad-band quantum well infrared photodetector focal plane arrays

A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane.     

Solid state extrusion of thermoplastic elastomers 4

A solid state extrusion technique is applied as to produce oriented block copoly(ether ester) under various physical conditions. The morphology of the extruded samples is characterized in relation to the extrusion parameters and hard segment compositions of the polymer, using thermal analysis and X-ray methods. The lateral dimensions of the crystalline domains are found to be approximately 150 Å depending on the extrusion conditions. The statistics of the long range periodicity of the structure along the extrusion direction is in agreement with a one-dimensional two phase model, the crystalline portion of which does not vary much in thickness (35 – 45 Å). The unexpected increase in the long period and the thermal shrinkage suggest the existence of strained interlamellar amorphous chains (tie molecules). The observed variations in tensile properties are interpreted under the assumption that both the number of such tie molecules and their fully extended lengths are determined by the hard segment composition and the extrusion conditions. It is also argued that the increase in the glass transition temperature is not only a function of the composition of hard segments in the amorphous phase but also of the number of strained tie molecules.Herrn Dr. Dr. h. c. H. Hellmann zum 70. Geburtstag gewidmet.Part 3 cf. lit [11]     

Time evolution studies of the H2O/quartz interface using sum frequency generation, atomic force microscopy, and molecular dynamics

Many interfacial studies on solid surfaces, for example, quartz/water, assume that a standard cleaning procedure regenerates the surface reproducibly. In the reported work, the results of two surface specific techniques, sum frequency generation (SFG) spectroscopy and atomic force microscopy, show that the effects of prolonged exposure to Nanopure water and to pH 10 NaOH are distinctly different. In conjunction with the experimental data, molecular mechanics is used to correlate the SFG spectral frequencies to the hydrogen stretching vibrations of the surface-bound water molecules. It is found that after 17 days of soaking in water, water molecules penetrate into the SiO2 matrix to produce a swollen and amorphous layer; it is likely that broken Si-O bonds from the polishing process serve as nucleation sites for hydration and swelling. Disorder introduced in the interfacial water layer is detected by the rising intensity of the weakly hydrogen-bonded SFG peak at 3450 cm(-1). Dominance of the 3450 cm(-1) is absent in a pH 10, NaOH-soaked quartz disk, indicating that the strong hydrogen-bonded network in water remains intact.     

Tricarbonyliron complexes of some blocked cyclohexadienes

Complexation commencing with some substituted 1,3- or 1,4-cyclohexadienes with Fe(CO)₅ indicates that the steric direction is controlled by classical hindrance with groups such as alkyl, but probably involves transmission of the entering group through intermediate complexation with CO₂Me. The results help to define methods of obtaining desired stereoisomers in the series.     

The two-phase structure of segmented block copoly(ether ester)

The annealing induced morphological changes in isotropic block copoly(etherester)s are investigated by small angle X-ray scattering methods. The observed results are consistent with a lamellar model which is comprised of a crystalline core of thickness 35 to 45 Å, a diffuse boundary zone of width 9 Å, and an amorphous layer which is varying strongly in thickness. The enhanced crystallinity of the samples annealed at higher temperatures is mainly due the lateral growth of the lamellae; the long period increases by not more than 20%. The scattering power of the samples is explained by means of an equivalent two-phase model in which the crystalline phase has the same structure as theα-form of poly(butylene terephthalate), whereas the amorphous phase is a mixture of the uncrystallized ester segments and the ether segments. The crystallinity determined from the scattering power is very much higher than that determined from thermoanalytical investigations.     

Precursor decomposition and nucleation kinetics during platelike apatite synthesis

Self-organization of calcium and phosphorus precursors in solution containing acetic acid and ethylene glycol produces a nanosized lamellar acetate-phosphonate hybrid containing two acetate and one phosphonate components. The lamellar morphology of the hybrid precursor is responsible the formation of platelike apatite product after thermal treatment at or above 400 degrees C. However a preliminary preheating stage (300 degrees C, 24 h) is crucial in determining the morphology of the apatite. Activation energy measurements by nonisothermal thermogravimetric analysis show that decomposition of the hybrid precursor involves at least two steps. Among the three components, it appears that the calcium acetate bidentate chelate component is stable below or at 300 degrees C. However, the calcium phosphonate and calcium acetate monodentate components are decomposed at this temperature. Above 360 degrees C, nuclear magnetic resonance and infrared spectroscopic data reveal the decomposition of more stable calcium acetate bidentate chelate. It is evident that the bond rupture of the bidentate calcium acetate species in the precursor results in the start of crystalline apatite formation but the other components must be decomposed by heating prior to this critical step in order to produce platelike apatite.     

Glycosides from Grewia damine and Filicium decipiens

Chemical investigation of n-butanol extract from the methanol extract of leaves of Grewia damine furnished lupeol, sitosterol beta-D-glucoside, flavone C-glycosides vitexin, isovitexin where as the same extracts from the leaves of Filicium decipiens furnished sitosterol beta-D-glucoside, 3-O-beta-D-glucopyranosyl kaempferol, 3-O-beta-D-glucopyranosylquercetin and 3-O-alpha-L-rhamnopyranosyl(1--> 2)-beta-D-glucopyranosylkaempferol.     

Antifeedant activity of some Sri Lankan plants

Twenty nine solvent extracts from twenty Sri Lankan plants were examined for antifeedant activity against the fourth instar larvae of Mexican bean beetle, Epilachna varivestis Muls., Coccinellidae. Extracts of Sarcococca brevifolia (Buxaceae), Strychnus nux vomica (Loganiaceae), Diploclisia glaucescens, Coscinium fenestratum (Menispermaceae), Syzygium caryophyllatum (Myrtaceae), Pittosporium zeylanicum (Pittosporaceae), Lasianthus gardneri (Rubiaceae), Ferronia limonia (Rutaceae) and Allophylus cobbe (Sapindaceae) have shown strong antifeedant activity.     

A polymer electrolyte containing ionic liquid for possible applications in photoelectrochemical solar cells

Various iodide ion conducting polymer electrolytes have been studied as candidate materials for fabricating photoelectrochemical (PEC) solar cells and energy storage devices. In this study, enhanced ionic conductivity values were obtained for the ionic liquid tetrahexylammonium iodide containing polyethylene oxide (PEO)-based plasticized electrolytes. The analysis of thermal properties revealed the existence of two phases in the electrolyte, and the conductivity measurements showed a marked conductivity enhancement during the melting of the plasticizer-rich phase of the electrolyte. Annealed electrolyte samples showed better conductivity than nonannealed samples, revealing the existence of hysteresis. The optimum conductivity was shown for the electrolytes with PEO:salt = 100:15 mass ratio, and this sample exhibited the minimum glass transition temperature of 72.2 °C. For this optimum PEO to salt ratio, the conductivity of nonannealed electrolyte was 4.4 × 10⁻⁴ S cm⁻¹ and that of the annealed sample was 4.6 × 10⁻⁴ S cm⁻¹ at 30 °C. An all solid PEC solar cell was fabricated using this annealed electrolyte. The short circuit current density (I _SC), the open circuit voltage (V _OC), and the power conversion efficiency of the cell are 0.63 mA cm⁻², 0.76 V, and 0.47% under the irradiation of 600 W m⁻² light.