Luminescence investigations of the GaP-based dilute nitride Ga(NAsP) material system

Multi-quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown, pseudomorphically strained to GaP-substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature-dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material, the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation.     

1,2-Bis-triphenylphosphoranylidenamino-äthan als zweizähniger Ligand in Übergangsmetallkomplexen

1,2-Bis-(triphenylphosphorane-ylidene-amino)ethane as a Bidentate Ligand in Transition Metal Complexes The reactions of Ph₃P?N? C₂H₄? N?PPh₃ with transition metal halogenides MX₂ give according to eq. (1) novel bisiminophosphorane complexes of the type M(Ph₃PNC₂H₄ NPPh₃)X₂ (M ? Co, X ? Cl 1 a , Br 1 b , J 1 c ; M ? Ni, X ? Cl 2 a , Br 2 b , J 2 c , M ? Hg, X ? Cl 3 , M ? Cd, X ? Cl 4 ). The preparation, properties, magnetic moments, and structure of the new complexes are reported     

Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates

Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminated olefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.     

Nature of low-energy dipole strength in nuclei: the case of a resonance at particle threshold in 208Pb

A high-resolution (gamma,gamma') study of the electric dipole response in 208Pb at the S-DALINAC reveals a resonance structure centered around the neutron emission threshold. Microscopic quasiparticle phonon model calculations in realistic model spaces including the coupling to complex configurations are able to describe the data in great detail. The resonance is shown to result from surface density oscillations of the neutron skin relative to an approximately isospin-saturated core. It also forms an integral part of a toroidal E1 mode representing an example of vortex collective motion in nuclei.     

Heat transfer between two nanoparticles through near field interaction

We introduce a thermal conductance by using the fluctuation-dissipation theorem to analyze the heat transfer between two nanoparticles separated by a submicron distance. Using either a molecular dynamics technique or a model based on the Coulomb interaction between fluctuating dipoles, we derive the thermal conductance. Both models agree for distances larger than a few diameters. For separation distances smaller than the particle diameter, we find a transition regime characterized by a thermal conductance larger than the contact conductance.     

Microscopic nature of the pygmy dipole resonance: the stable Ca isotopes

The electric dipole strength distribution in 44Ca has been measured up to 10 MeV in high resolution photon scattering experiments for the first time. The data obtained have been compared to earlier measurements on (40,48)Ca in order to view the evolution of the electric pygmy dipole resonance (PDR). Calculations that were performed within the framework of the microscopic extended theory of finite Fermi systems, which adds contributions of the quasiparticle-phonon coupling to random phase approximation calculations, give a qualitative agreement with the experimental data for all three isotopes. We have shown that it is necessary to include this coupling to describe the PDR.