Laser‐induced dielectric breakdown in tetramethylgermane/tetramethyltin mixtures: deposition of nanostructured Sn/Ge/C and Ge?Sn/C films

Transversely Excited Atmospheric (TEA) CO₂ laser‐irradiation of gaseous tetramethylgermane (TMG)–tetramethyltin (TMT) mixtures in Ar results in decomposition of both organometallic compounds and in chemical vapour deposition of nanostructured films analyzed by FTIR and Raman spectroscopy, X‐ray diffraction and electron microscopy. They were shown to have similar morphology and elemental composition and constituents dependent on the TMG–TMT ratio. The analyses confirm the presence of nanosized carbon‐rich (graphitic) structures that incorporate C? M and M? M (M ?Ge, Sn) bonds containing an amorphous phase together with crystalline, either β‐Sn or metastable Sn‐rich Ge? Sn alloy. The unique latter constituent is favored at high concentrations of TMG precursor. Copyright © 2010 John Wiley & Sons, Ltd.     

Breakdown kinetics of aggregates from poly(ethylene glycol‐bl‐propylene sulfide) di‐ and triblock copolymers induced by a non‐ionic surfactant

We explored the effects of addition of the nonionic surfactant Triton X‐100 on the stability of aggregates of poly(ethylene glycol‐bl‐propylene sulfide) di‐ and triblock copolymers. Fluorescence spectra of pyrene, used as a probe molecule, elucidated the various stages of transformation from pure copolymeric micelles to surfactant‐rich micelles. Turbidity measurements yielded insight into the mechanism of the interaction, the hydrophobicity of the copolymer driving the process. Triton X‐100 tends to strongly interact with highly hydrophobic copolymers by inserting into the core of the micellar aggregates. On the other hand, Triton X‐100 tends to interact with the corona of micelles formed by less hydrophobic copolymers which, for this reason, are more stable upon addition of this destabilizing agent. Kinetic data give evidence that only monomers, not micelles of surfactant, interact with the copolymer micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2477–2487, 2008     

Laser-induced breakdown spectroscopy for branching ratio and atomic lifetime measurements in singly-ionized neodymium and gallium

Precision laboratory astrophysics measurements can be made in laser-induced plasmas created for laser-induced breakdown spectroscopy. Branching ratios from highly-energetic levels in singly-ionized neodymium may be measured by observing spontaneous emission in laser-induced plasmas in an argon environment at decreased pressures (~ 7.7 mbar). Utilizing a broadband Èchelle spectrometer with a spectral range from 200–840 nm, the spontaneous emission intensities from hundreds of transitions originating in 138 energy levels in Nd I, Nd II, and Nd III have been observed simultaneously, allowing the determination of branching ratios for these energy levels for branches greater than 1% in the visible wavelength range. In this study, eight branching ratios from the 23,229.991 cm^− 1 level in Nd II were measured and compared to previously determined values as a method for optimizing experimental conditions such as buffer gas pressure and observation delay time. The branching ratios of the eight branches were found to be in excellent agreement with three previously determined values from both experiment and theory. A plan to utilize this laser-induced plasma apparatus to measure the lifetime of the 4s5p³P₂ level at 118,727.89 cm^− 1 in singly-ionized gallium using a cascade-photon-coincidence method is also presented. Utilizing a solid Ga target ablated in a helium environment, “start photons” at 541.6 nm from a transition into the 4s5p³P₂ level and “stop photons” at 633.4 nm from a transition out of that Ga II energy level were observed. Single-photon detection will be accomplished using avalanche photodiodes with narrowband interference filters and delay times between the detection of coincident photons from these two transitions will be measured.     

Formative Time Delay in Nitrogen Discharges at Low Pressure

In this paper the formative time delay in nitrogen was determined from statistically based measurements of electrical breakdown time delay. The measurements were carried out under different conditions on a newlydesigned gas tube with a plane‐parallel electrode system made from copper. The avalanche growth was followed based on a simple analytical model agreeing well with the experimental data. The dependencies of the formative time delay on the working voltage and the electron yields in the interelectrode space originating from residual states were found. A developed approximate model for the formative time delay has shown fits with the experimental data better than other models discussed in the literature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the melt flow direction on the treeing process in polymeric insulation

This paper presents the results of a study of the effect of the residual mechanical stress formed in solid polymers at the stage of production on the initiation and growth of an electrical tree. It is shown that the time to tree initiation and the time to breakdown of polycarbonate samples can be determined from the results of investigation of treeing parameters. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 85–94, January–February, 2009.     

Morphology and electrical breakdown properties of LDPE‐polypropylene copolymer blends

In this study, the specimens of low‐density polyethylene (LDPE) and blend polymers of LDPE and a random copolymer of ethylene and propylene were prepared by the blowing process and T‐die method. The differences in electrical breakdown properties and morphology between the specimens made by the two different methods were studied. It was found that the specimen made by the T‐die method had a higher electrical breakdown strength than the specimen made by the blowing process, except for the DC breakdown strength in some cases at 30 °C. The morphology of the specimens was investigated by means of the measurements of thermal shrinkage, infrared dichroism, and X‐ray diffraction. The specimen made by the T‐die method has a stronger orientation in both the crystalline and amorphous phases than the specimen made by the blowing process. The difference in morphology is supposed to be correlated with the difference in electrical breakdown properties between the specimens made by the two different methods. It was concluded that the electrical breakdown properties are strongly affected by the orientation of chains in the specimen. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1741–1748, 2001     

Absolute characterization of laser-induced breakdown spectroscopy detection systems

A quantitative comparison of the performance of four different laser-induced breakdown spectroscopy detection systems is presented. The systems studied are an intensified photodiode array coupled with a Czerny–Turner spectrometer, an intensified CCD coupled with a Czerny–Turner spectrometer, an intensified CCD coupled to an Echelle spectrometer, and a prototype multichannel compact CCD spectrometer system. A simple theory of LIBS detection systems is introduced, and used to define noise-equivalent spectral radiance and noise-equivalent integrated spectral radiance for spectral detectors. A detailed characterization of cathode noise sources in the intensified systems is presented.     

Rôle du soufflage dans le contrôle de l'éclatement tourbillonnaire sur une aile delta

According to flow visualizations performed in water tunnel and referring to a simple phenomenological model describing the nature of exchanges occurring within a two-dimensional mixing layer, a model was built up to specify the nature of flows ensuring the recirculating zone equilibrium over the upper surface of a delta wing at high angle of attack. Perturbing the flows equilibrium leads to delay the vortex breakdown. To cite this article: O. Rodriguez, J. Pruvost, C. R. Mecanique 333 (2005).     

Multivariate analysis of remote laser-induced breakdown spectroscopy spectra using partial least squares,principal component analysis,and related techniques

Quantitative analysis with laser-induced breakdown spectroscopy traditionally employs calibration curves that are complicated by chemical matrix effects. These chemical matrix effects influence the laser-induced breakdown spectroscopy plasma and the ratio of elemental composition to elemental emission line intensity. Consequently, laser-induced breakdown spectroscopy calibration typically requires a priori knowledge of the unknown, in order for a series of calibration standards similar to the unknown to be employed. In this paper, three new Multivariate Analysis techniques are employed to analyze the laser-induced breakdown spectroscopy spectra of 18 disparate igneous and highly-metamorphosed rock samples. Partial Least Squares analysis is used to generate a calibration model from which unknown samples can be analyzed. Principal Components Analysis and Soft Independent Modeling of Class Analogy are employed to generate a model and predict the rock type of the samples. These Multivariate Analysis techniques appear to exploit the matrix effects associated with the chemistries of these 18 samples.     

Laser ablation of powdered samples and analysis by means of laser-induced breakdown spectroscopy

The presented work proves the capacities of laser-induced breakdown spectroscopy (LIBS) as a fast, universal, and versatile technique for analysis of complex materials as ceramics. This paper reports on the analysis of ceramic raw materials (brick clays and kaolin) submitted to laser ablation in the form of pressed pellets. Spectrographic study was provided by standard single-pulse LIBS technique and orthogonal reheating double-pulse LIBS. It was found that both methods are comparable in terms of analytical performance, if adequate experimental parameters and signal detection systems are used.