Hydrogen interaction with defects and impurities in 6H-SiC

The dynamics of hydrogen capture and release from trapping centers in 6H-SiC after plasma hydrogenation and annealing was investigated by low-temperature photoluminescence (PL). Indications of competing processes of hydrogen capture by different trapping centers were observed. Passivation of Al acceptors with hydrogen is the dominating process during plasma hydrogenation or plasma etching. Irreversible release of hydrogen from Al-trapping centers and additional trapping of hydrogen by Si vacancy (V_Si) to form a V_Si+H complex occurred during annealing at temperatures above 300°C. It is suggested that the V_Si+H complex may be playing an important role in keeping hydrogen in SiC after higher temperature treatment.     

Sphärische Multipolanalyse der Beugung elektromagnetischer Wellen an einer ideal leitenden elliptisch berandeten Kugelschale

Übersicht In dieser Arbeit wird die sphärische Multipolanalyse zur Berechnung der Beugung an einer elliptisch berandeten Kugelschale herangezogen. Dieses Randwertproblem mit Laméschen Differentialgleichungen. Die numerische Auswertung umfaßt einerseits die Berechnung von Stromverläufen und Richtcharakteristiken für den dipolerregten elliptisch konturierten Kugelflächenreflektor. Andererseits werden charakteristische Streuparameter für eine Hohlkugel mit elliptischer Apertur berechnet. Die dabei benötigte Multipolentwicklung der ebenen Welle in elliptischen Kegelkoordinaten wird angegeben.

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Diffraetion of electromagnetic waves by a perfectly conducting spherical shell with elliptical contour a spherical multipole analysis

Contents In this paper the spherical multipole analysis is used in order to treat the diffraction by a spherical shell with elliptical contour. This boundary value problem can be reduced to a two-parametric eigenvalue problem with two Lamé equations. Numerical data are presented like current distributions and radiation patterns for a spherical reflector with elliptical contour. Furthermore computed scattering characteristics for a spherical cavity with an elliptical aperture are shown.

     

Numerical implementation of the S-matrix algorithm for modeling of relief diffraction gratings

A new numerical implementation is developed to calculate the diffraction efficiency of relief diffraction gratings. In the new formulation, vectors containing the expansion coefficients of electric and magnetic fields on boundaries of the grating layer are expressed by additional constants. An S-matrix algorithm has been systematically described in detail and adapted to a simple matrix form. This implementation is suitable for the study of optical characteristics of periodic structures by using modern object-oriented programming languages and different standard mathematical software. The modeling program has been developed on the basis of this numerical implementation and tested by comparison with other commercially available programs and experimental data. Numerical examples are given to show the usefulness of the new implementation.     

Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films

Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.     

Molecular Level Characterisation of the Surface of Carbohydrate-Functionalised Mesoporous silica Nanoparticles (MSN) as a Potential Targeted Drug Delivery System via High Resolution Magic Angle Spinning (HR-MAS) NMR Spectroscopy

Atomistic level characterisation of external surface species of mesoporous silica nanoparticles (MSN) poses a significant analytical challenge due to the inherently low content of grafted ligands. This study proposes the use of HR-MAS NMR spectroscopy for a molecular level characterisation of the external surface of carbohydrate-functionalised nanoparticles. MSN differing in size (32 nm, 106 nm, 220 nm) were synthesised using the sol-gel method. The synthesised materials displayed narrow particle size distribution (based on DLS and TEM results) and a hexagonal arrangement of the pores with a diameter of ca. 3 nm as investigated with PXRD and N₂ physisorption. The surface of the obtained nanoparticles was functionalised with galactose and lactose using reductive amination as confirmed by FTIR and NMR techniques. The functionalisation of the particles surface did not alter the pore architecture, structure or morphology of the materials as confirmed with TEM imaging. HR-MAS NMR spectroscopy was used for the first time to investigate the structure of the functionalised MSN suspended in D₂O. Furthermore, lactose was successfully attached to the silica without breaking the glycosidic bond. The results demonstrate that HR-MAS NMR can provide detailed structural information on the organic functionalities attached at the external surface of MSN within short experimental times.     

Liquid‐selenium‐enhanced grain growth of nanoparticle precursor layers for CuInSe2 solar cell absorbers

Large‐grained CuInSe₂ absorber layers are synthesized using a non‐vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide‐based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H₂ or H₂Se gasses. Lateral grain sizes up to 4 µm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe₂ enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low‐cost, non‐vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes. Copyright © 2014 John Wiley & Sons, Ltd.     

Automated streamflow measurements in high-elevation Alpine catchments

Salt dilution is a well-established streamflow measurement method in creeks, which works particularly well downstream of turbulent flow sections as the mixing of the salt tracer is enhanced. Usually, salt dilution measurements are performed manually, which considerably limits the observations of rare peak flow events. These events are particularly important for constructing robust rating curves and avoiding large uncertainties in the extrapolation of streamflow values. An additional challenge is the variability of the river cross section, especially after larger discharge events, leading to nonstationary rating curves. Therefore, discharge measurements well distributed over time are needed to construct a reliable streamflow–water level relationship and to detect changes caused by erosion and deposition processes. To overcome these two issues, we used an automated streamflow measuring systems at three different sites with contrasting hydrological and hydraulic characteristics in the Alps. This system allowed us to measure discharge at nearly maximum flow of the observation period (2020–2021) at all three sites and to detect abrupt changes in the rating curve by performing event-based salt injections. The uncertainty in the measurements was quantified, and the streamflow was compared with official gauging stations in the same catchment. Based on a very large dataset of almost 300 measurements, we were able to evaluate the reliability of the system and identify the primary sources of uncertainty in the experimental setup. One key aspect was the site selection for the downstream electrical conductivity sensors, as measurement location strongly controls the signal-to-noise ratio in the recorded breakthrough curves.