Nanosecond laser ablation and deposition of silicon

Nanosecond-pulsed KrF (248 nm, 25 ns) and Nd:YAG (1064 nm, 532 nm, 355 nm, 5 ns) lasers were used to ablate a polycrystalline Si target in a background pressure of <10⁻⁴ Pa. Si films were deposited on Si and GaAs substrates at room temperature. The surface morphology of the films was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Round droplets from 20 nm to 5 μm were detected on the deposited films. Raman Spectroscopy indicated that the micron-sized droplets were crystalline and the films were amorphous. The dependence of the properties of the films on laser wavelengths and fluence is discussed.     

Pyrolytic studies of phenoxarsine derivatives

The predicted pyrolyzate of phenoxarsine derivatives from their mass spectra is diphenylene oxide. The prediction is verified by the experiment.     

Katalyse durch Polymerkomplexe. 5. Mitt. Die heterotropische Wechselwirkung von Histamin und Hydroxamat enthaltenden Polymerkatalysatoren mit hydrophoben Ammoniumsalzen bei der Phenylesterhydrolse

Ohne Zusammenfassung     

Synchronization of ultraviolet-preionization in a Marx-driven TEA CO2 laser

In a TEA CO₂ laser a two-stage spark gap was used to control the predischarge, which produced the ultraviolet-preionization, and to generate a trigger pulse for the Marx bank, which excited the main discharge. The time-sequence of the predischarge and the trigger pulse could be reversed so that the main discharge could commence before the preionization process. This set-up has enabled temporal synchronization on the laser performance, or basically the time delay between the pre- and the main discharges, to be investigated from about − 150 ns to 600 ns.     

Superintense laser fields in circular array: effects of phase and pulse jitters

Extremely intense laser field that makes nonlinear quantum vacuum can be generated by coherent superposition of multiple lasers in circular configuration that incorporates optical fibers synchronization scheme and piecewise mirrors in circular array operating below typical damage threshold. Coherent amplification and large laser beams can produce intensity reaching nonlinear quantum vacuum regime. The effects of phase jitter and envelope timing of the pulses due to imperfect synchronization are simulated and analyzed for both linear and circularly polarized pulses. We obtain simple analytical expressions that well describe the envelope jitter and phase jitter. Several practical aspects are discussed, including implications of scaling the laser dimension and pulse duration, with possibility for giant laser facility.     

Thermally and electron-impact-induced rearrangements of dimethylthioncarbamates in gaseous phase

The thermally and electron-impact-induced rearrangements of the dimethylthioncarbamates to the dimethylthiolcarbamates are discussed. Owing to the competition with the ion fragmentation reactions in the mass spectrometric time, < 10^?6 seconds, the extent of the mass spectrometrically observed ion isomerization cannot be predicted from that of the thermal induced one. In the ion fragmentations of the non-rearranged molecular ions, it was found that the relative abundance of the ion (CH₃)₂NC?O^⊕ to the total ionization is larger than that of the ion (CH₃)₂NC?S^⊕. This is believed to be attributable to the differences in the dissociation energies of the C? S bond and the C? O bond and in the stabilities of the two ions.     

Experimental and quantum‐chemical studies of 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with picolines

¹H, ¹³C and ¹⁵N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with picolines, [Au(PIC)Cl₃], trans‐[Pd(PIC)₂Cl₂], trans/cis‐[Pt(PIC)₂Cl₂] and [Pt(PIC)₄]Cl₂, were performed. After complexation, the ¹H and ¹³C signals were shifted to higher frequency, whereas the ¹⁵N ones to lower (by ca 80–110 ppm), with respect to the free ligands. The ¹⁵N shielding phenomenon was enhanced in the series [Au(PIC)Cl₃] < trans‐[Pd(PIC)₂Cl₂] < cis‐[Pt(PIC)₂Cl₂] < trans‐[Pt(PIC)₂Cl₂]; it increased following the Pd(II) → Pt(II) replacement, but decreased upon the trans → cis‐transition. Experimental ¹H, ¹³C and ¹⁵N NMR chemical shifts were compared to those quantum‐chemically calculated by B3LYP/LanL2DZ + 6‐31G**//B3LYP/LanL2DZ + 6‐31G*. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrodynamics of two-phase flow in vertical up and down-flow across a horizontal tube bundle

Flow patterns, void fraction and friction pressure drop measurements were made for an adiabatic, vertical up-and-down, two-phase flow of air–water mixtures across a horizontal in-line, 5×20 tube bundle with a pitch-to-diameter ratio of 1.28. The flow patterns in the cross-flow zones were obtained and flow pattern maps were constructed. The data of average void fraction were less than the values predicted by a homogenous flow model and showed a strong mass velocity effect, but were well-correlated in terms of the Martinelli parameter X_tt and liquid-only Froude number Fr_LO. The two-phase friction multiplier data could be well-correlated with the Martinelli parameter.     

Simulations of V-I characteristics in a plasmafocus fun

The voltage and current characteristics in a plasma focus gun are simulated to yield the current efficiency and the rundown velocity of the current sheath. Since the discharge circuit is strongly influenced by the rundown dynamics of the current sheath, the simple snowplow model, which is modified to include the time-varying current and mass efficiencies, us used. The computer simulations are carried out for two separate experiments using deuterium and argon gas. A steady state of constant rundown velocity and saturated sheath current for both gases is correlated to the maximum holding voltage of the glass insulator. As much as 27% of the total discharge current for the deuterium gas and 33% for argon gas stay behind as leakage currents around the glass insulator when the radial compression phase begins