Polarographische Bestimmung von Eisen(III)-dimethyldithiocarbamidat (Ferbam)

Zusammenfassung Eine Methode zur polarographischen Bestimmung von Ferbam wird beschrieben. Die Messung erfolgt klassisch polarographisch in Citrat-Phosphat-Puffer und impulspolarographisch (Single-Sweep-Verfahren) in Natriumacetat-Natriumcitrat-Grundlösung. Die untere Nachweisgrenze liegt für die konventionelle Gleichspannungspolarographie bei 2 g/ml und für die Impulspolarographie bei 0,2 g/ml.

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Summary A new method is described for the polarographic determination of Ferbam. The measurement is carried out for the classical d.c. method in citratephosphate buffer, and for the single-sweep method in a supporting electrolyte of sodium citrate and acetate. The lower limit of detection is 2 g/ml for the conventional d. c. polarography and 0.2 g/ml for the pulse polarography (singlesweep method).

     

Coupled-resonator optical waveguides doped with nanocrystals

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual cavity modes into coherently coupled waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. To demonstrate the formation of multisphere photon states, we use a bent linear array of microresonators and probe the properties of the cavity photon field by the spatially and spectrally resolved measurement of the nanocrystal emission. Photon mode coupling is evidenced by the observed mode splitting and emission intensity distributions along the CROW structure.     

Coherent dynamics in InGaAs quantum dots and quantum dot molecules

We measure the dephasing time of the exciton ground state transition in InGaAs quantum dots (QD) and quantum dot molecules (QDM) using a sensitive four-wave mixing technique. In the QDs we find experimental evidence that the dephasing time is given only by the radiative lifetime at low temperatures. We demonstrate the tunability of the radiatively limited dephasing time from 400 ps up to 2 ns in a series of annealed QDs with increasing energy separation of 69–330 meV from the wetting layer continuum. Furthermore, the distribution of the fine-structure splitting δ₁ and of the biexciton binding energy δ_B is measured. δ₁ decreases from 96 to with increasing annealing temperature, indicating an improving circular symmetry of the in-plane confinement potential. The biexciton binding energy shows only a weak dependence on the confinement energy, which we attribute to a compensation between decreasing confinement and decreasing separation of electron and hole. In the QDM we measured the exciton dephasing as function of interdot barrier thickness in the temperature range from 5 to 60 K. At 5 K dephasing times of several hundred picoseconds are found. Moreover, a systematic dependence of the dephasing dynamics on the barrier thickness is observed, showing how the quantum mechanical coupling in the molecules affects the exciton lifetime and acoustic-phonon interaction.     

Selectivity of Molecular Recognition Displayed by Monoclonal Antibodies as Compared to Receptors – a New Approach to Screen Combinatorial Libraries

Photolabeled monoclonal antibodies generated against a potent antagonist of the glycoprotein receptor GPIIb‐IIIa have been used to demonstrate that antibodies can be employed to replace receptors for on‐bead screening of combinatorial libraries.     

A continuously tunable low-threshold organic semiconductor distributed feedback laser fabricated by rotating shadow mask evaporation

We have theorized that a photonic band gap can be induced in a submicron periodically poled LiNbO₃ (SPPLN) with a uniform electrical field applied along the Y axis of the structure. The width of the band gap can be modulated by the intensity of the Y-directional electrical field. Moreover, for such a periodical structure with a duty cycle other than 0.5, the central location of the gap can be tuned by applying an additional electrical field along the Z axis of the sample.     

Propagation oscillations in the near-field response of traveling surface waves launched by metallic nanoapertures

We discuss the implications of a frequency-dependent complex dielectric function ε(ω) of a metal for the interpretation of scanning near-field optical microscopy (SNOM) measurements in the vicinity of metallic nanoapertures. For subwavelength slits in gold films we observe distinct spatial intensity oscillations in the near-field signal for specific wavelengths in the visible spectrum. These oscillations of the SNOM signal far away from the nanoslit are ascribed to a constructive interference between the propagating surface plasmon (SP) with light scattered parallel to the gold–air interface. In these spatial SNOM-signal oscillations information about the surface plasmon dielectric function is encoded which can be extracted, for example, in surface plasmon interferometry for applications as sensors or waveguides.