CO laser stabilization using the optogalvanic Lamb-dip

Frequency stabilization of the CO laser using a CO lamb-dip is achieved in the range from 5.0–6.3 m. The CO saturation signal is obtained from a low-pressure discharge in absorption and is detected using optogalvanic, detection. The frequency stability and reproducibility has been verified to be better than 100 kHz; this is an improvement of more than one order of magnitude compared with locking techniques using CO laser gain profiles.Alexander von Humboldt Awardee from National Bureau of Standards, Boulder, Colorado, USA     

Feller's One-Dimensional Diffusions as Weak Solutions to Stochastic Differential Equations

A continuous strong Markov process X on the line generated by Feller's generalized second order differential operator D_mD is considered. Supposed that the canonical scale p is locally the difference of two bounded convex functions, that the speed measure m contains a strictly positive absolutely continuous component, and that both boundaries of the state space R are inaccessible. Then the process X is characterized as a weak solution to a stochastic differential equation involving local time.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXX. Elektronenmikroskopische Untersuchung in Hochauflösung an metastabilen Niob-Wolfram-Oxiden Vergleich mit der rechnerischen Simultation

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXX. High Resolution Electron Microscopy Investigation of Metastable Niobium Tungsten Oxides. Comparison with Computer Simulated Images . Starting with solid solution series (Nb, W)O_x, where WO₃ + NbO₂ was substituted for Nb₂O₅, a gentle oxidation leads from the original block sizes of [3 × 4], [4 × 4], [4 × 5] or [5 × 5] octahedra to a doubling of blocks in the new ternary oxides, e. g. 2 × [5 × 5] → [5 × 10]. As HRTEM of the oxidation products revealed, these new larger blocks are connected in a special way including so-called “L-type-tunnels”. Using a LaB₆-cathode with our electron microscope, we now for the first time can directly see the positions of these tunnels.     

Influence of substrate morphology on organic layer growth: PTCDA on Ag(1 1 1)

By UV-excited photoelectron emission microscopy (UV-PEEM) we investigated the microscopic growth behavior of organic thin films using 3,4,9,10-perylene-tetracarboxylicacid dianhydride (PTCDA) on a Ag(1 1 1) single crystal substrate as example. Direct, real time observation allows to correlate the initial growth modes and the related kinetic parameters with substrate properties like terrace width, step density, and step bunches from the submonolayer range up to 5 layers or more. Above room temperature PTCDA grows in a Stranski–Krastanov fashion: after completion of the first two stable layers three-dimensional islands are formed. The nucleation density strongly depends on the temperature and the substrate morphology thus affecting the properties of the organic film.     

Selective influencing of the migration time of SO4(2-) by forming neutral species with Pb2+ in capillary zone electrophoresis.

Organic and inorganic anions are analyzed using capillary zone electrophoresis with indirect fluorescence detection. As electrolyte 2,5-dihydroxybenzoic acid is used. By adding Pb2+ to the electrolyte the migration time of SO4(2-) can be selectively influenced and the separation of Cl- and SO4(2-) considerably improved. The fluorescence intensity of 2,5-dihydroxybenzoic acid increases in the presence of Pb2+ up to a concentration of 6*10(-4) mol/L Pb2+. Limits of detection in the lower mumol/L range were obtained.     

A Stochastic Differential Equation for a Class of Feller's One-dimensional Diffusion

A class of one-dimensional continuous strong Markovian processes is considered. Such process X were first described by William Feller in a purely analytical way, using the generalized second-order differential operator D_mD. In the case of natural boundaries of the state space R and a trivial road map p(x)= x, these diffusion processes are martingales. In the present paper it is additionally assumed that the speed measure m contains a nonvanishing absolutely continous component. Then a stochastic differential equation is derived, which has the diffusion X as a weak solution.     

Metal Assisted Synthesis of Cationic Sulfidobismuth Cubanes in Ionic Liquids

Bi₂S₃ was dissolved in the presence of either AuCl/PtCl₂ or AgCl in the ionic liquids [BMIm]Cl ⋅ xAlCl₃ (BMIm=1-n-butyl-3-methylimidazolium; x=4–4.3) through annealing the mixtures at 180 or 200 °C. Upon cooling to room temperature, orange, air-sensitive crystals of [BMIm](Bi₄S₄)[AlCl₄]₅ ( 1 ) or Ag(Bi₇S₈)[S(AlCl₃)₃]₂[AlCl₄]₂ ( 2 ) precipitated, respectively. 1 did not form in the absence of AuCl/PtCl₂, suggesting an essential role of the metal cations. X-ray diffraction on single-crystals of 1 revealed a monoclinic crystal structure that contains (Bi₄S₄)⁴⁺ heterocubanes and [AlCl₄]⁻ tetrahedra as well as [BMIm]⁺ cations. The intercalation of the ionic liquid was confirmed via solid state NMR spectroscopy, revealing unusual coupling behavior. The crystal structure of 2 consists of (Bi₇S₈)⁵⁺ spiro-dicubanes, [S(AlCl₃)₃]²⁻ tetrahedra triples, isolated [AlCl₄]⁻ tetrahedra, and heavily disordered silver(I) cations. No cation ordering took place in 2 upon slow cooling to 100 K.