Structural,thermal, and spectral characterization of the different crystalline forms of Alq3, tris(quinolin-8-olato)aluminum(III), an electroluminescent material in OLED technology

The interest in organic materials for use in organic light-emitting diodes (OLEDs) began with the pioneering report of efficient green electroluminescence from Alq₃, tris(quinolin-8-olato)aluminum(III), by Tang and Van Slyke [C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913]. After more than 20 years of intense research and development in OLEDs, Alq₃ continues to be a widely used electroluminescent material in OLED technology. Alq₃ is used in the electron-transport and/or electron-injecting layer in multilayer device structures and also as an effective host material for various dyes. Much is known about the properties of this metal chelate complex, yet much remains unknown despite numerous studies. In recent years, five crystalline phases (α, β, γ, δ, and ε) of Alq₃ have been identified. In the present report, a combined structural, thermal, and spectroscopic (Raman, fluorescence, and nuclear magnetic resonance) analysis of different crystalline phases of Alq₃ is presented.     

Thermocapillary flow on a gas-liquid surface under normal and reduced gravity

The aim of the present work is the study of the thermocapillary flow phenomenon at 1-g, μ-g conditions and the transition between 1-g and μ-g. The experimental results were observed with a novel high speed imaging system using a combination of a monochrome high speed CCD camera and a liquid crystal tunable filter. The flow velocity and the temperature patterns could be measured simultaneously from the seeded thermochromic liquid crystals, which change colour depending on their temperature. We investigated the thermocapillary flow with an experimental setup, where a bubble is positioned in a liquid matrix under a heated wall. The µ-g experiments were conducted in the drop tower of the ZARM-Institute of the University of Bremen. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alternative precursors for MOVPE growth of InN and GaN at low temperature

We report on the use of dimethylhydrazine (DMHy) and tertiarybuthylhydrazine (TBHy), as alternative nitrogen precursor for GaN low-temperature growth, as well as to improve the InN growth rate. Lowering the GaN growth temperature, would allow growing InN/GaN heterostructures by MOVPE, without damaging the InN layers. Increasing the low InN MOVPE growth rate is of major importance to grow reasonably thick InN layers. In this respect, triethylindium (TEIn) was also used as an alternative to trimethylindium (TMIn).     

InN excitonic deformation potentials determined experimentally

We report the experimental determination of the interband deformation potentials of indium nitride by combining both optical spectroscopy investigations and high-resolution X-ray measurements performed on a series of InN films grown by metal organic vapour-phase epitaxy. Our approach, which follows the one used for GaN by Shan et al. [Phys. Rev. B. 54 (1996) 13460], gives here for InN a₁=−7.66 eV, a₂=−2.59 eV, b₁=5.06 eV, and b₂=−2.53 eV.     

Experimental investigation of the particle-wall-impact under particular consideration of the wall surface influence on the particle trajectory and the transition between sliding and adhering impact

We present results of the experimental investigation of the impact of particles on a rough wall. The particle-wall impact influences considerably the behavior of particle laden gas flows. The aim of the present work is to study the influence of the wall roughness on the particle trajectory and the particle rotation after impact. The measurements were carried out in a special test facility, which allows the investigation of single particle-wall impacts. Particle velocities and trajectories were recorded by a video system and evaluated by using a particle tracking technique. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Compression of a suspension of helical Yukawa rods

ABSTRACT

We present a Monte Carlo simulation study of the compression of helical Yukawa rods under isobaric conditions. The model is a chiral liquid crystal mesogen, which mimics, for instance, cellulose nanocrystals. It has several parameters (e.g. surface charge and internal pitch), which influence the compression route and the final structure. The strongest dependence of the structure of the condensed phase is found for the internal pitch of the charge helix: decreasing the internal pitch reduces the maximum density under otherwise equal conditions.     

Die kombinierte Simplex-Methode

Zusammenfassung Einsparung von Operationen durch Vermeidung der künstlichen Schlupfvariablen.

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Summary The combined Simplex-Method considered in the paper avoids artificial slack variables and saves computational steps.

     

Histochemical localization of high-sulfur keratins with silver nitrate

Colloid and Polymer Science - The treatment of merino wool with ammoniacal silver nitrate results in a selective staining of high-sulfur proteins. The method has been applied to unmodified and...     

Widely tunable pulse durations from a passively mode-locked thin-disk Yb:YAG laser

We demonstrate a passively mode-locked thin-disk Yb:YAG laser that generates solitonlike pulses with durations that are continuously tunable in a very wide range from 3.3 to 89 ps or from 0.83 to 1.57 ps. The average powers are typically ~12 W . Previously [Opt. Lett. 25, 859 (2000)], only pulse durations in a narrow range near 0.7 ps could be obtained from such lasers because of the effect of spatial hole burning. We achieved this much wider range by constructing a laser cavity with two different angles of incidence on the thin disk, which greatly reduces the effect of spatial hole burning.