Ray tracing for the optics at nano‐textured ZnO–air and ZnO–silicon interfaces

We investigate the scattering behavior of nano‐textured ZnO–Air and ZnO–Silicon interfaces for the application in thin film silicon solar cells. Contrary to the common approach, the numerical solution of the Maxwell's equations, we introduce a ray tracing approach based on geometric optics and the measured interface topography. The validity of this model is discussed by means of scanning near‐field optical microscopy (SNOM) measurements and numerical solutions of the Maxwell's equations. We show, that the ray tracing model can qualitatively describe the formation of micro lenses, which are the dominant feature of the local scattering properties of the investigated interfaces. A quantitative analysis for the ZnO–Silicon interface at λ = 488 and 780 nm shows that the ray tracing model corresponds well to the numerical solution of the Maxwell's equations, especially within the first 1.5 µm distance from the interface. Direct correlations between the locally scattered intensity and the interface topographies are found. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical characterization of hydroxyapatite obtained by wet chemistry in the presence of V,Co, and Cu ions

A model system for the precipitation of hydroxyapatite (HA) from saturated solutions at basic pH was utilized to investigate the effects of V, Co, and Cu ions on crystallography and stoichiometry of the produced apatites. X-ray diffraction (XRD) was applied to analyze phase composition and crystallinity of powders obtained with different metal ion concentrations and annealed at different sintering temperatures. This procedure used the temperature-dependent phase transitions and decompositions of calcium phosphates to analyze the particular influences of the metal ions on apatite mineralization. Comparative XRD measurements showed that all metal ion species reduced crystallinity and crystallite size of the produced apatites. Furthermore the transformation of amorphous calcium phosphate (ACP) to HA was partially inhibited, as was deduced from the formation of α-tricalcium phosphate (α-TCP) peaks in XRD patterns of the heated powders as well as from the reduced intensity of the OH stretch vibration in FTIR spectra. The thermally induced formation of β-TCP indicated a significantly reduced Ca/P ratio as compared to stoichiometric HA. This effect was more pronounced with rising metal ion content. In addition, the appearance of metal oxides in the XRD patterns of samples heated to higher temperatures indicated the incorporation of metal ions in the precipitated apatites. Peak shifts showed that both the apatitic as well as the β-TCP phase apparently had incorporated metal ions.     

Melaminharzbasierende duromere WPC – Steuerung der Verarbeitung und der Eigenschaften

This article exemplarily describes the influence of wood, two thermoplastic additives and process conditions on the processability and subsequently on the obtained bending properties of melamine-resin based wood polymer compounds. Before a wood-melamine resin-compound can be processed its reactivity has to be understood. This allows for estimating if and how the process can be realised. Besides previous chemical plasticization of the melamine resin, some additives need to be employed. These in turn influence the reactivity of the compound as well as the mechanical properties of the resulting composites. The main parameters controlling these effects are compatibility and acidity. Even the wood type affects the cross-linking reaction of the melamine resin with regard to temperature and time. Depending on adaptations to the process and the respective formulations processing as well as the properties of the final product can vary substantially. Only if all these effects regarding formulation and extrusion parameters are taken into account, melamine-resin based wood polymer composites of high quality can be produced.     

S-Layer Protein Self-Assembly

Crystalline S(urface)-layers are the most commonly observed cell surface structures in prokaryotic organisms (bacteria and archaea). S-layers are highly porous protein meshworks with unit cell sizes in the range of 3 to 30 nm, and thicknesses of ~10 nm. One of the key features of S-layer proteins is their intrinsic capability to form self-assembled mono- or double layers in solution, and at interfaces. Basic research on S-layer proteins laid foundation to make use of the unique self-assembly properties of native and, in particular, genetically functionalized S-layer protein lattices, in a broad range of applications in the life and non-life sciences. This contribution briefly summarizes the knowledge about structure, genetics, chemistry, morphogenesis, and function of S-layer proteins and pays particular attention to the self-assembly in solution, and at differently functionalized solid supports.     

Optimizing Single‐Walled‐Carbon‐Nanotube‐Based Saturable Absorbers for Ultrafast Lasers

The application of single‐walled carbon nanotubes (SWCNTs) as saturable absorbers (SA) in a Nd:glass femtosecond laser is verified as a promising alternative to traditional semiconductor saturable‐absorber mirrors (SESAMs). The shortest laser pulses achieved with a SWCNT‐SA fabricated by the slow‐evaporation method are reported herein. Nearly Fourier‐limited 288 fs pulses are obtained with negative‐dispersion soliton mode‐locking. The importance of the properties of the starting material, such as the degree of purity and the chirality, and the successive slow‐evaporation deposition method is proven by using a multitechnique approach based on X‐ray diffractometry, scanning electron microscopy, and μ‐Raman spectroscopy. The high degree of nanotube alignment on the glass substrate and also the slight metallic character due to electron transfer between the glass matrix and the nanotubes themselves are identified as the main features responsible for the good laser response.     

Crystalline Organic Heterostructures Engineering Based on Vanadyl Phthalocyanine and Rod‐Like Conjugated Organic Semiconductors with Selected Central Groups

The effect of groups in conjugated molecules on films’ interface morphology, electronic structure, and charge transport behavior is explored utilizing a series of crystalline organic heterostructures that are constructed by four rod‐like molecules and vanadyl phthalocyanine (VOPc). The four rod‐like molecules, which possess the same biphenyl endgroup but different central groups, present similar growth behavior along with different thin film structural parameters and electronic structures. The changes of the structure parameters result in diverse morphology of the VOPc/rod‐like molecule heterostructure because of the different lattice mismatch. The electronic structure differences in rod‐like molecules cause different interface electronic structure of the heterostructure. Under the conjunct effect of morphology and interface electronic structure, the transistors based on the crystalline heterostructures present diverse charge transport behavior and field‐effect mobilities. These results provide a clue for the development of crystalline organic heterostructure engineering and tailoring overall organic device performance through molecular design in local inducing layer.     

Modelling the removal of p-TSA (para-toluenesulfonamide) during rapid sand filtration used for drinking water treatment

A finite element model was set-up to determine degradation rate constants for p-TSA during rapid sand filtration (RSF). Data used for the model originated from a column experiment carried out in the filter hall of a drinking water treatment plant in Berlin (Germany). Aerated abstracted groundwater was passed through a 1.6 m long column-shaped experimental sand filter applying infiltration rates from 2 to 6 m h⁻¹. Model results were fitted to measured profiles and breakthrough curves of p-TSA for different infiltration rates using both first-order reaction kinetics and Michaelis-Menten kinetics. Both approaches showed that degradation rates varied both in space and time. Higher degradation rates were observed in the upper part of the column, probably related to higher microbial activity in this zone. Measured and simulated breakthrough curves revealed an adaption phase with lower degradation rates after infiltration rates were changed, followed by an adapted phase with more elevated degradation rates. Irrespective of the mathematical approach and the infiltration rate, degradation rates were very high, probably owing to the fact that filter sands have been in operation for decades, receiving high p-TSA concentrations with the raw water.     

Microchip electrospray: improvements in spray and signal stability during gradient elution by an inverted postcolumn makeup flow

Dynamic changes in mobile phase composition during high-performance liquid chromatography (HPLC) gradient elution coupled to mass spectrometry (MS) sensitively affect electrospray modes. We investigate the impact of the eluent composition on spray stability and MS response by infusion and injection experiments with a small tetrapeptide in water-acetonitrile mixtures. The employed HPLC/electrospray (ESI)-MS configuration uses a microchip equipped with an enrichment column, a separation column, and a makeup flow (MUF) channel. One nano pump is connected to the separation column, while a second one delivers solvent of exactly inverted composition to the MUF channel. Both solvent streams are united behind the separation column, before the ESI tip, such that the resulting electrosprayed solution always has identical composition during a gradient elution. Analyte peak parameters without and with MUF compensation are determined and discussed with respect to the electrospray mode and eluent composition. The postcolumn MUF significantly improves spray and signal stability over the entire solvent gradient, without compromising the performance of the HPLC separation column. It can also be conveniently implemented on microchip platforms.