Model for the amorphous roughening transition in amorphous semiconductor deposition

The evolution of surface roughness on hydrogenated amorphous silicon (a-Si:H) films prepared by plasma-enhanced chemical vapor deposition exhibits initial smoothening due to nuclei coalescence, a region of surface stability, and finally a prominent roughening transition (designated a → a) at a critical thickness. The thickness at which the a → a transition occurs, as measured by real time spectroscopic ellipsometry (SE), is found to correlate closely with the electronic properties of the film. Thus, the transition has been incorporated into deposition phase diagrams that have been applied successfully to optimize solar cell performance and stability. A simple continuum model for the evolution of the 1D surface profile using an initial condition designed to be consistent with the nucleation characteristics measured by real time SE is sufficient for insights into the correlation between the roughness evolution and film properties. Good agreement between the experimental results and model calculations support the concept that optimum electronic properties of the films are associated with weakly reactive surfaces and long lifetime radicals that lead to adsorbed precursors with large surface diffusion lengths.     

Numerical modeling of thermally-stimulated currents for the density-of-states determination in thin-film semiconductors

The paper reports on thermally stimulated conductivity studies used for characterization of the density of states profile in thin film semiconductors, by numerically solving the non-linear time-dependent rate equations for free and trapped charge. We explore the derivation of energy and density scales from temperature and conductivity data. We examine the distinction between ‘strong’ and ‘weak’ re-trapping and the use of low ‘effective’ values of attempt-to-escape frequencies in establishing an energy scale, and the ad hoc inclusion of a temperature-dependent lifetime. It is confirmed for several illustrative model systems that the technique can afford surprisingly good fidelity in recovery of the density of states under a range of conditions.     

Alpha decay rate enhancement in metals: An unlikely scenario

It has been recently suggested that one might drastically shorten the alpha lifetime of nuclear waste products, if these are embedded in metals at low temperatures. Using quantum mechanical tunneling arguments, we show that such an effect is likely to be very small, if present at all.     

Die-swell,splashing drop and a numerical technique for solving the Oldroyd B model for axisymmetric free surface flows

This work deals with the development of a numerical method for simulating viscoelastic axisymmetric free surface flow of an Oldroyd B fluid. A novel formulation is developed for the computation of the non-Newtonian extra-stress components on rigid boundaries and on the symmetry axis. The full free surface stress conditions are employed. The resulting governing equations are solved by finite differences on a Marker-and-cell (MAC) type grid. Validation is provided by simulating a pipe flow problem. The classical die-swell problem is solved and swelling ratios are provided. The height of the splash caused by a falling liquid drop for various Reynolds and Weissenberg numbers is then studied, and the height of the splash is shown to diminish with increasing viscoelasticity.     

Stereoselective synthesis of (+)-boronolide and (−)-5-epi-boronolide

Stereoselective synthesis of boronolide and 5-epi-boronolide was achieved from d-(−)-tartaric acid. The key step involves the reduction of a keto Weinreb amide for the synthesis of boronolide, and a single pot construction of a diketone from the bis-Weinreb amide of tartaric acid and subsequent reduction with L-Selectride for 5-epi-boronolide.     

Laser ablation and ionization time-of-flight mass spectrometer with orthogonal sample introduction and axial field rf-only quadrupole cooling

We describe a laser ablation and ionization time-of-flight mass spectrometer with orthogonal sample introduction and axial field rf-only quadrupole cooling device. Experimental results have shown the fairly uniform sensitivities for different metal elements, and a satisfactory resolving power. Little interference is shown in the spectrum. The detection limits are about 10^− 7–10^− 8 g/g for most of the metal elements.     

Electrochemical modification of poly-aniline films in the presence of guaiacol–sulfonic acid

Poly-aniline (PANI) films when subjected to cyclic voltammetry in the presence of guaiacol–sulfonic acid (GSA) undergo a modification which alters their red–ox activity and extends electroactivity to neutral pH. A plausible mechanism of the modification reaction is discussed. The PANI–GSA film modified electrodes electrocatalyze the oxidation of ascorbic acid (AA) in neutral phosphate buffer (pH 7.4) with ca. 250 mV reduction of the oxidation peak potential.     

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C1–C4 aliphatic alcohols near ambient pressure

Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.