Neutral-pion photoproduction off protons in the energy range 0.3 GeV<E(gamma)<3 GeV

Single pi(0) photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of approximately 98% of 4pi. Differential cross sections dsigma/dOmega have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gammap-->N(*)(Delta(*))-->ppi(0). A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.     

Ultra-trace analytical monitoring of silicon wafer surfaces by capillary electrophoresis

Several methods are presented for the routine ultra-trace analytical monitoring of inorganic and organic anions and cations on the surface and in the native oxide of silicon wafers--the wafer-surface water-extraction method, the vapor-phase-decomposition method, and the re-dissolving method. Electrokinetic injection, sample stacking, and electrolyte composition were, therefore, optimized and made robust. For electrokinetic injection with transient isotachophoretic preconcentration a linear range of 0.05 to 0.5 micromol L(-1) was obtained; for sample stacking the linear range was 0.5 to 10 micromol L(-1), even in the presence of up to 750 micromol L(-1) hydrofluoric acid. Inorganic anions and monovalent carboxylic acids are predominately dissolved in the aqueous layer on the wafer surface whereas dicarboxylic acids are chemically bonded to the silanol groups and form esters.     

Vowel identification and vowel masking patterns of hearing-impaired subjects

Confusion matrices for seven synthetic steady-state vowels were obtained from ten normal and three hearing-impaired subjects. The vowels were identified at greater than 96% accuracy by the normals, and less accurately by the impaired subjects. Shortened versions of selected vowels then were used as maskers, and vowel masking patterns (VMPs) consisting of forward-masked threshold for sinusoidal probes at all vowel masker harmonics were obtained from the impaired subjects and from one normal subject. Vowel-masked probe thresholds were transformed using growth-of-masking functions obtained with flat-spectrum noise. VMPs of the impaired subjects, relative to those of the normal, were characterized by smaller dynamic range, poorer peak resolution, and poorer preservation of the vowel formant structure. These VMP characteristics, however, did not necessarily coincide with inaccurate vowel recognition. Vowel identification appeared to be related primarily to VMP peak frequencies rather than to the levels at the peaks or to between-peak characteristics of the patterns.     

The influence of a transverse magnetic field on a subnormal glow discharge in air

In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G) some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed in these oscillations.     

Modeling of Cu gettering in p- and n-type silicon and in poly-silicon

Based on experimental findings we set up calculations of numerical modeling of gettering efficiencies for Cu in various silicon wafers. Gettering efficiencies for Cu were measured by applying a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by a thermal treatment to redistribute the metallic impurity. Subsequently, the wafers were analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. We investigated p/p+ and n/n+ epitaxial wafers with different doping levels and different substrate-doping species. We have also investigated gettering efficiencies of phosphorus-diffused p- and n-type wafers. Heavilyboron doped silicon exhibited a gettering efficiency of ∼100%, while gettering by n+ silicon occurred for doping levels >3×10¹⁹ atoms/cm³ only. In another set of experiments we investigated the dependence of the gettering efficiency of p-type wafers with poly-silicon back sides for different cooling rates and Cu spiking levels. A strong dependence on both parameters was found. Cu gettering in p/p+ epitaxial wafers was modeled by calculating the increased solubility of Cu in p+ silicon compared to non-doped silicon taking into account the Fermi-level effect, which stabilizes donors in p+ silicon, and the pairing reaction between Cu and B. Calculated gettering efficiencies were in very good agreement with experimental results. Gettering in n+ silicon was similarly modeled in terms of pairing reactions and the Fermi-level effect. But, for n-type silicon, many experimental uncertainties existed; thus, we applied our expressions to solubility data of Hall and Racette to obtain the unknown parameters. The empirical calculations were in good agreement even with results on n/n+ wafers. For phosphorus-diffused wafers we had to consider an excess vacancy concentration of 1.2–5.5 times the equilibrium concentration to explain the experimental findings by the model. Gettering by poly-silicon back sides was simulated by solving the time-dependent diffusion equation with boundary conditions that take into account different surface reaction rates of silicon point defects. Using this advanced model, the experimentally measured gettering efficiencies were reproduced within the uncertainty of the measurement. Received: 3 September 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

3D holographic PIV with a forward-scattering laser sheet and stereoscopic analysis

 A new 3D PIV system combining holography and stereoscopic PIV is presented. The double pulsed holographic recording relies on the forward scattering of particles in the laser sheet. The holographic images of the particles are used for a stereoscopic PIV analysis. An imaging system with a rightangle prism is used to acquire a stereoscopic pair of images. The application of the system to the vortex flow from an inclined delta wing shows the prospects and limitations of the technique. Received: 23 December 1996/Accepted: 1 June 1997     

Synthesis and characterization of sodium titanates Na2Ti3O7 and Na2Ti6O13

Na₂Ti₃O₇ and Na₂Ti₆O₁₃ were synthesized by sol-gel method in order to obtain pure phases. Different heat-treatments were applied on powders and pellets of these materials. The effects were studied by XRD, dilatometry, TGA-DTA, SEM and electrochemical impedance spectroscopy. Pure Na₂Ti₃O₇ was obtained at 973 K. Sintering at 1373 K caused a partial decomposition into Na₂Ti₆O₁₃. The Na₂Ti₃O₇ powder sintered at 1273 K showed polygonal microstructure. Na₂Ti₃O₇ pellets sintered at 1323 K for 10 h exhibited large structures. This latter microstructure decreased the electrical conductivity of Na₂Ti₃O₇. Pure Na₂Ti₆O₁₃ was obtained at 873 K. Sintering at 1073 K caused a partial decomposition into TiO₂ (rutile). Na₂Ti₆O₁₃ pellets sintered at 1323 K for 10 h exhibited common shrinkage behavior. This shrinkage process increased the electrical conductivity of this material. The presence of TiO₂ resulted in a oxygen partial pressure dependence of the electrical conductivity.     

Trace analytical performance, epistemology and engineering creativity

Analytics is a professional and systematic compilation of instances for the inference of problem solving truths. Relevant analytical results are the starting point of inductive learning in engineering. In the semiconductor industry, diagnostic investigations must be based on both process and product monitoring using trace-analytical methods. The analyst’s strive for detection power and an increasing number of analytes are the key and flywheel of engineering knowledge. Received: 9 October 1995 / Accepted: 14 May 1996