Charakterisierung von Kieselsäuresolen mit Röntgenkleinwinkelstreuung,Elektronenmikroskopie und Stickstoff-Adsorption

Zusammenfassung Es werden die mittleren Dimensionen der Teilchen dreier Kieselsäuresole mit derRKWS und demE. M. bestimmt. Entgegen der Angabe anderer Autoren ergibt sich dabei bei Berücksichtigung der Teilchengrößenverteilung nahezu völlige Übereinstimmung beider Methoden.RKWS undE. M. ergeben angenähert auch die gleiche mittlere Schwankung _m der Teilchendurchmesser. Die mit derRKWS bestimmte spezifische Oberfläche ist stets größer als die aus der N₂-Adsorption bestimmte, und zwar nimmt der relative Unterschied mit dem mittleren Teilchendurchmesser zu. Die mit derRKWS bestimmte innere Hydratation liegt bei 0,15–0,26 g H₂O/g SiO₂.

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Characterization of silica sols by means of X-ray small angle scattering, electron microscopy and nitrogen adsorption

X-ray small angle scattering and electron microscopy are used to determine average dimensions of particles in three silica sols. In contradiction to findings of other authors, a nearly complete agreement of both methods is found if the particle size distribution is taken into account. Identical average variations _m of the particle diameters are obtained for both methods. The inner surface determined by means of the X-ray small angle scattering is in all cases larger than that obtained from N₂-adsorption, the difference increasing with average particle diameter. The inner hydration determined by means of the X-ray small angle scattering lies at 0.15–0.26 g H₂O/g SiO₂.

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Mit 8 Abbildungen

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Herrn Professor Dr. Dr. h. c.Otto Kratky zum 70. Geburtstag mit den herzlichsten Glückwünschen gewidmet.     

Ultrafast X-ray experiments on structural changes in single crystals of polar molecules

Intramolecular charge transfer in aminobenzonitrile (DIABN) single crystals is studied by a combination of ultrafast techniques. The intramolecular dynamics is probed by time-resolved spectroscopy in the UV/Vis and mid-IR. The intermolecular structural response is investigated by transient X-ray scattering and transmission experiments. A theoretical analysis shows that diffuse scattering and dipole solvation determine the X-ray data. The observed dynamics results from charge transfer reaction leading to strong local changes of molecular dipole moments and related structural rearrangements in the crystal.     

光学特异材料的设计

In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials（MMs） at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numer ical simulations. Particular emphasis is put on the significance of such tailored effective properties of optical MMs     

Interaction of femtosecond light filaments with obscurants in aerosols

The interaction of ultrashort laser pulses with opaque droplets in the atmosphere is examined numerically. Intense filaments resulting from the balance between self-focusing and ionization of air molecules are shown to be robust against obscurants sized up to 2/3 of the filament diameter. (3D+1)-dimensional numerical simulations confirm recent experimental data [F. Courvoisier et al., Appl. Phys. Lett. 83, 213 (2003)]. The filament is rapidly rebuilt with minimal loss of energy over a few cm after the interaction region. The replenishment of the pulse mainly proceeds from the nonlinear attractor responsible for the formation of a spatial soliton modeling the filament core.     

Improving the efficiency of thin film tandem solar cells by plasmonic intermediate reflectors

Thin film tandem solar cells made of amorphous and microcrystalline silicon provide renewable energy at the benefit of low material consumption. As a drawback, these materials do not posses the high carrier mobilities of their crystalline counterpart which limits the feasible material thickness. For maintaining the light absorption as high as possible, photon management is required. Here we show that metallic nanodiscs that sustain localized plasmon polaritons can increase the efficiency of such solar cells if they are incorporated into the dielectric intermediate reflector separating the top and the bottom cell. We provide quantitative estimates for the possible absorption enhancement of optimized bi-periodic nanodiscs that are feasible for fabrication. Emphasis is also put on discussing the impact of obliquely incident sun light on the solar cell performance.