Thin film silicon solar cells are an attractive option for the production of sustainable energy but their low response at long wavelengths requires additional measures for absorption enhancement. The most successful concepts are based on light scattering interface textures whose understanding is greatly facilitated by considering a superposition of periodic textures that diffract the light into oblique angles, ideally beyond the critical angle of total internal reflection. Because the thickness of the active layers is on the same scale as the wavelength, interference of diffracted waves gives rise to resonance phenomena. We discuss the absorption enhancement in terms of a perturbation approach using the modal structure of a corresponding device with flat interfaces.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

EURECA (European Underground Rare Event Calorimeter Array) is an astro-particle physics facility aiming to directly detect galactic dark matter. The Laboratoire Souterrain de Modane has been selected as host laboratory. The EURECA collaboration unites CRESST, EDELWEISS and the Spanish-French experiment ROSEBUD, thus concentrating and focussing effort on cryogenic detector research in Europe into a single facility. EURECA will use a target mass of up to one ton, enough to explore WIMP – nucleon scalar scattering cross sections in the region of 10-9 – 10-10 picobarn. A major advantage of EURECA is the planned use of more than just one target material (multi target experiment for WIMP identification).

In the nip or substrate configuration thin film silicon solar cells, the choice of front TCO contact is critical because there is a trade off between its transparency which influences the current in the solar cell and its conductivity which influences the series resistance. Here, we investigate the optical behavior of two different TCO front contacts, either a 70 nm thick, nominally flat ITO or a 2 μm thick rough LPCVD ZnO. The back contact consists of LP-CVD ZnO with random texture. First we investigate the influence of the rough and flat front TCOs in μc-Si:H and a-Si:H solar cells. With the back contact geometries used in this work, the antireflection properties of ITO are effective at providing as much light trapping as the rough LP-CVD ZnO. In the second part, we demonstrate that total of 25 to 26 mA/cm2is achievable in nip micromorph tandem cells and show short circuit current up to 11.7 mA/cm2 using an SIO based intermediate reflector.

For thin film silicon solar cells it is vital to increase the optical path of light in the absorber because this allows for thinner cells with better stability and higher production throughput. We discuss the effect of periodically textured interfaces for the case of thin film silicon solar cells in n-i-p configuration using embossed plastic substrate which allows us studying the effect of a wide range of random or periodic textures. Due to the moderate thickness of the individual layers the texture is carried into each interface with a high degree of conformity even for the front contact which is the last layer. Solar cells on periodic structures show excellent performance; in a microcrystalline cell on a simple sinusoidal grating we achieved a gain in current density of 30%. Furthermore, the periodicity serves as a useful tool for the study of light management because the underlying phenomena like diffraction or grating coupling to plasma excitations of the metallic back reflector are governed by a relatively low number of well defined parameters like the periodicity and the amplitude of the grating.

We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 μas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and — amongst others — will allow the study of motion within a few times the event horizon size of the Galactic Center black hole.

Carbon nanotubes (CNTs) are of great interest because of several unsurpassable physical (mechanical, electrical, thermal, and chemical) properties. Especially their large elastic modulus and breaking strength make them highly attractive for their use as reinforced agents in forming a new class of multifunctional advanced materials - onanocomposites, in addition to high conductivity (either in semiconducting or metallic regimes) achieved through lower percolation thresholds for several electronic applications. Among the known conducting polymers, polyaniline (PANI) has a high potential due to its ease of synthesis, excellent environmental, and thermal stability and reversible control of its electrical/electronic properties. In this work, PANI-single-/multiwalled NTs composites films containing different nanotube content of both kinds were synthesized by spin-cast preceded by ultrasonic mixing of the constituents. They were characterized using complementary techniques including scanning electron microscopy, X-ray diffraction, infrared and Raman spectroscopy, and conductivity revealing their microscopic structure and physical properties thus helping in establishing process-structure-property correlations. The present work will discuss some of these findings in terms of a) self-alignment of nanotubes in conducting polymer b) their optical and electrical properties, and c) their design with a view to electronic and sensor applications, all ascribed due to long range π-π interaction between the constituents.

Electron spin resonance investigations on the angular dependence of carbon nanotubes are reported. It is proved that the resonance line is a convolution of three lines one due to electron delocalized over carbon nanotubes, the second assigned either to amorphous carbon or to conducting electrons in interaction with metallic impurities, and the last one originating from catalyst residues.

Progressive switching of grains in ferroelectric materials leads to internal stresses, which may give rise to degradation of the material or even fracture. Here we propose a two-dimensional multigrain model for ferroelectric polycrystal. The numerical computations employ the nonlinear micromechanics model of Huber et al. [1] for each grain. Results for the macroscopic response, butterfly and hysteresis loops, as well as internal stress and electric field distributions are presented.

Cu(In, Ga)Se2 (CIGS) layers were grown with different vacuum evaporation recipes and the effects of sodium on the grain growth were investigated by scanning electron microscopy. A reduced grain size mainly in the lower part of films grown with the 3-stage process was observed when Na was available during growth. The growth kinetics were found to be influenced during the second stage of the process. In contrast, no clear change in grain size could be observed for CIGS layers grown with constant evaporation rates, with a bi-layer and with an ’extreme’ bi-layer process. A mechanism for the action of Na is proposed, which is based on the assumption that Na passivates CIGS grain boundaries and that this results in a surfactant effect. The mechanism explains the different influences of Na on CIGS growth for different evaporation recipes, the occurrence of reduced grain size in the 3-stage process and the surface smoothing effect observed mainly for CIGS grown with the bi-layer process.

In-diffusion of Na after CIGS growth is shown to be an alternative Na incorporation method that does not reduce the CIGS grain size. A conversion efficiency improvement from 10.4% to 14.2% was achieved due to the post-deposition treatment on CIGS absorbers grown without Na at a maximum substrate temperature of 450°C.

Neat Fibers of HiPco single wall carbon nanotubes extruded from strong acid suspensions exhibit preferred orientation along fiber axes. We characterize the extrusion-induced alignment using x-ray fiber diagrams and polarized Raman scattering, using a model which allows for some fraction of the sample to remain completely unaligned. We show that both x-ray and Raman data are required for a complete texture analysis of SWNT fibers.

Low substrate temperatures have to be used for polymer substrates. Therefore, using soda- lime glass (SLG) substrates with and without an alkali barrier (Al2O3), a three-step CIGS coevaporation process for a substrate temperature of 450 °C has been developed and compared to film deposition with constant evaporation rates. The three-step process was found to enhance grain nucleation. An efficiency of 14.0 % has been achieved with this process for solar cells on SLG. Since polymers in general do not contain Na, a way of Na addition to the absorber is needed. It is shown that NaF coevaporation can be used to control the Na content in CIGS. Also incorporation of Na in CIGS by diffusion from a NaCl layer through a polyimide is demonstrated. With such SLG/NaCl/polyimide structures flexible solar cells can be obtained using a lift-off process. A cell efficiency of 11.6 % (0.99 cm2 area) has been achieved.

A polished diamond (110) surface was observed to undergo surface rearrangement above ˜700 °C to a micro faceted diamond surface when in contact with a nickel film and in the presence of hydrogen. Formation of a graphitic layer at the diamond-nickel interface above 700 °C was observed in the absence of hydrogen. The presence of 0.1 Torr of hydrogen was shown to be sufficient to prevent graphite formation at the nickel-diamond interface.

Systems of different technological levels have been developed for the mass-rearing of cassava mealybugs, Phenacoccus manihoti, cassava green mites, Mononychellus tanajoa and their natural enemies. Prototypes have been built and are being evaluated for host plant growth, host insect and mite production and output of natural enemies. One of the prototypes uses a paternoster system in which trays each holding 66 cassava plants rotate around a light source. After each rotation the trays receive and empty a given amount of nutrient solution. The other uses a perforated vertical cylinder holding up to 250 cassava cuttings. The plants are irrigated through a pump or gravity system. Six to eight weeks are required to complete the cycle from planting to harvest of the natural enemies in either system. These systems reduce significantly the labour input required for conventional rearing systems and at the same time improve the reliability and quality of the end product.

A description is given of the Danish Twin Register which is based on the total twin population born in Denmark in the years 1870-1910 with a more recent addition of all same-sexed pairs from the period 1911-1920. Twins belonging to pairs where one or both partners are found to have died before attaining the age of six years are disregarded in the more intensive studies whereas the remaining part of the twin population is being followed by periodical inquiries.

The methods used in the collection of the material, in the establishment of the zygosity diagnosis and in specific investigations of selected diseases and abnormalities are described and discussed.

A survey is given of the more important results of the research based on the Register. In the group of somatic diseases, greatest attention has so far been paid to malignant growths, diabetes mellitus and peptic ulcer. A number of psychiatric disorders and deviations are at present being studied with schizophrenia and criminality as the first subjects for intensive research. Some of the main results obtained are given as illustrations of the potentialities and scope of this approach to the application of twin studies in a broad variety of research areas.