ZnO nanostructures as efficient antireflection layers in solar cells

An efficient antireflection coating (ARC) can enhance solar cell performance through increased light coupling. Here, we investigate solution-grown ZnO nanostructures as ARCs for Si solar cells and compare them to conventional single layer ARCs. We find that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance. Compared with a silicon nitride (SiN) single layer ARC, ZnO nanorod arrays display a broadband reflection suppression from 400 to 1200 nm. For a tapered nanorod array with average tip diameter of 10 nm, we achieve a weighted global reflectance of 6.6%, which is superior to an optimized SiN single layer ARC. Calculations using rigorous coupled wave analysis suggest that the tapered nanorod arrays behave like modified single layer ARCs, where the tapering leads to impedance matching between Si and air through a gradual reduction of the effective refractive index away from the surface, resulting in low reflection particularly at longer wavelengths and eliminating interference fringes through roughening of the air-ZnO interface. According to the calculations, we may further improve ARC performance by tailoring the thickness of the bottom fused ZnO layer and through better control of tip tapering.     

Effects of temperature and soil components on emissions from pyrolysis of pyrene-contaminated soil

Effects of temperature and soil on yields and identities of light gases (H2, CH4, C2H2, C2H4, C2H6, CO, and CO2) and polycyclic aromatic hydrocarbons (PAH) from thermal treatment of a pyrene-contaminated (5 wt%) soil in the absence of oxygen were determined for a U.S. EPA synthetic soil matrix prepared to proxy U.S. Superfund soils. Shallow piles (140-170 mg) of contaminated soil particles and as controls, neat (non-contaminated) soil (140-160 mg), neat pyrene (10-15 mg), neat sand (230 mg), and pyrene-contaminated sand (160 mg), were heated in a ceramic boat inside a 1.65 cm i.d. pyrex tube at temperatures from 500 to 1100 degrees C under an axial flow of helium. Volatile products spent 0.2-0.4s at temperature before cooling. Light gases, PAH and a dichloromethane extract of the residue in the ceramic boat, were analyzed by gas chromatography or high pressure liquid chromatography (HPLC). Over 99% pyrene removal was observed when heating for a few tens of seconds in all investigated cases, i.e., at 500, 650, 750, 1000, and 1100 degrees C for soil, and 750 and 1000 degrees C for sand. However, each of these experiments gave significant yields (0.2-16 wt% of the initial pyrene) of other PAH, e.g., cyclopenta[cd]pyrene (CPP), which mutates bacterial cells and human cells in vitro. Heating pyrene-polluted soil gave pyrene conversions and yields of acetylene, CPP, and other PAH exceeding those predicted from similar, but separate heating of neat soil and neat pyrene. Up to 750 degrees C, recovered pyrene, other PAH, and light gases accounted for all or most of the initial pyrene whereas at 1000 and 1100 degrees C conversion to soot was significant. A kinetic analysis disentangled effects of soil-pyrene interactions and vapor phase pyrolysis of pyrene. Increase of residence time was found to be the main reason for the enhanced conversion of pyrene in the case of the presence of a solid soil or sand matrix. Light gas species released due to the thermal treatment, such as acetylene and methane, lead the formation of other, pyrene-derived PAH, e.g., methylpyrenes, cyclopenta[cd]pyrene, and benzo[a]pyrene. Implications of these findings for the chemistry of soil thermal decontamination and for diagnosing potential defects in soil thermal cleaning, e.g., incomplete elimination of targeted pollutants and formation of adverse by-products, are discussed.     

Limits to the uncertainty achievable in force transfer

The increasing number of international comparison measurements carried out during the past years were the reason for the tests of the force transducers described in this paper. Various influences which affect the uncertainty of measurement, such as longtime behaviour, short-time behaviour and interactions, will be shown. These errors are described by means of examples. Methods are presented which may lead to a reduction of these errors.     

Prozeßvergleich von Umkehrosmose und Elektrodialyse am Beispiel der Nitrat-Entfernung aus Grundwässern

Comparison of reverse osmosis and electrodialysis for removal of nitrate from groundwater . Reverse osmosis and electrodialysis are membrane processes suitable for desalination of aqueous solutions. Both processes were tested on a pilot scale in a waterworks for removal of nitrate from groundwater. A combination of the processes was also considered with a view to very high concentration of the residual water. The article shows how information gathered from long-term reverse osmosis trials and the experiments with the electrodialysis plant with industrial membrane dimensions can provide a basis for safe design of large plants. Treatment costs for large capacities are shown for the example of the above feed water. The advantages and disadvantages of reverse osmosis and electrodialysis are compared. This comparison demonstrates fitting applications of the two processes in other areas (chemical industry, sewage treatment).     

Bildung von Aluminiumoxid-Deckschichten auf Eisenbasislegierungen

Formation of alumina layers on iron-base alloys The formation of Al₂O₃-layers has been studied for ferritic alloys Fe-6 Al-M and austenitic alloys Fe-27 Ni-4 Al-M where M – Ti, Zr, V, Nb, W, B, Si… (concentrations in wt%). One or more alloying elements M had been added and in some cases carbon. The oxidation was performed at 1000 °C in H₂O-H₂ mixtures at PO₂ = 10^?19 bar. After ½ h oxidation the oxide layers were investigated by X-ray structures analysis, scanning electron microscopy and Auger electron spectroscopy (AES). The alloy Fe-6 Al and most doped alloys form badly adherent layers, however, on alloys with additions of 0.1 to 1% Ti, Zr, V or Y the oxide layers are fine-grained and well-adherent. The Ti-doped ferritic alloys showed very protective layers, which is caused by the formation of a Ti(C, O)-layer beneath the α-Al₂O₃. The presence of the oxicarbide induces nucleation and improves the adherence of α-Al₂O₃, according to epitaxial relations between ferrite and oxicarbide and between oxicarbide and alumina. The favourable influence of Ti and Zr on the Al₂O₃ formation is also effective on the austenitic alloys.     

Friction in turbulent flow of solids-gas systems

Two-phase solids-in-air flow was experimentally studied in a once-through circular tube flow system using nominal 25μ and 50μ spherical glass beads. At mass flow ratios up to 1.6, the friction factor was found to be generally higher than that for air flow alone but considerably less than that for a single-phase fluid having a density the same as that of the mixture. The pressure drop experienced by the 2 phase system of 25μ beads and air was found to show true drag reduction. A continuum mechanics analysis showed the viscous stresses and Reynolds stresses to be significantly affected by solid particle addition.     

A miniature high-power KrF laser excited with a capacitively coupled discharge

A KrF excimer laser excited in a capacitively coupled discharge device made out of commercial BaTiO3doorknob capacitors is described. The discharge volume of 1.4 cm³is formed by a 3 mm bore into four capacitors glued together in a line. A maximal laser output energy of 1.7 mJ (1.2 J/l) in a 5.0 ns long pulse was achieved.     

Polyester-Polyether Block Copolymers II. Thermal and Mechanical Properties of Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers

The melting and crystallisation behaviour of crystalline phases in poly (hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been investigated in relation to copolymer composition and polyether block molecular weight (m.w.). In contrast to that in corresponding homopolymer blends, the polyester crystallinity in the block polymers is greatly reduced by incorporation of polyether units, though some persists even at low polyester contents. Concomitant changes in the glass transition temperatures show part of the polyester component to form a homogeneous component of the amorphous phase. The mechanical properties change with composition in parallel with the changes in copolymer crystallinity and T_g. Copolymers with 20-60 w % of poly(oxytetramethylene) units of m.w. 2000 are highly extensible elastomers. Those with higher m. w. polyether blocks have higher modulus and strength but suffer a serious loss of properties at 60d?C. The observations are interpreted in terms of a model in which polyester crystallites (and polyether crystallites also, for the higher m. w. polyether blocks) are supported within an amorphous matrix by tie-molecules whose nature changes with the copolymer compositions. The results are compared with those for analogous polyester-polyethers having different structural components.