Broadband semiconductor saturable-absorber mirror for a self-starting mode-locked Cr:forsterite laser

We report a low-loss broadband semiconductor saturable-absorber mirror (SESAM) that uses gold film as the reflector. A semiconductor- SiO(2) double-layer stack enhances the reflectivity of the gold film. This low-loss SESAM was used in a mode-locked Cr:forsterite laser to produce self-starting 20-fs-scale laser pulses at 1.3 microm . The structure can be applied to SESAM's for other wavelengths.     

NHC-coordinated palladacycle catalyzed 1,2-addition of arylboronates to unactivated ketones

Abstract

Palladium catalyzed intermolecular 1,2-addition of arylboronate to unactivated ketone was investigated. NHC-coordinated palladacycle 4c exhibited catalytic activity for the reactions and provided the corresponding tertiary alcohols and γ,γ-disubstituted γ-lactones in good to excellent yields.     

A new type of laser-induced surface damage of GaAs

The damage of surface layers of GaAs induced by a laser pulse with 15 ns and 600 ns duration has been studied by means of channeling. It is found that damage induced by 600 ns pulses is much more pronounced than that by shorter pulses and that 600 ns pulses produce As-rich layers at the surface. Results are discussed on the basis of calculated temperature rise during and after a laser pulse.     

Differential cross section and photon-beam asymmetry for the gamma n --> K+ Sigma- reaction at E gamma = 1.5-2.4 GeV

Differential cross sections and photon-beam asymmetries have been measured for the gamma n --> K+ Sigma- and gamma p --> K+Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of E gamma = 1.5-2.4 GeV at 0.6 < cos ThetacmK< 1. The cross section ratio of sigma K+ Sigma-/sigma K+ Sigma0, expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+ Sigma- reaction, large positive asymmetries are observed, indicating the dominance of K* exchange. The large difference between the asymmetries for the K+ Sigma- and K+ Sigma0 reactions cannot be explained by simple theoretical considerations based on Regge model calculations.     

Determination of formal potential of NADH/NAD+ redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes

The electrochemical regeneration of NADH/NAD⁺ redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be ? 0.365 ± 0.002 V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2 M NaClO₄/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670 mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2 M H₂SO₄ solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 10³–10⁴ M^?1 s^? 1 depending on the preparation conditions of the PPS-modified electrodes.     

An XPS depth-profile study on electrochemically deposited TaO x

Through the use of XPS and controlled Ar⁺ etching, the surface composition and oxide species of tantalum oxides (TaO _x ), which were electrodeposited on glassy carbon electrodes by cyclic voltammetric and constant-potential electrolyses, are quantified along the depth profile. Electrodeposition exhibits efficacy in depositing TaO _x with a distribution of various TaO _x : TaO, TaO₂, and Ta₂O₅. The distribution gradient from the outer surface of TaO _x is such that Ta₂O₅?>?TaO₂?>?TaO. TaO is found to be the dominant species in the underlying layer of TaO _x . Such a unique structure of the electrode surface is analogous to that of nanoparticles with a core–shell structure, with the core being suboxides and the surface being that of the saturated pentoxide, Ta₂O₅. The electrochemically induced nonhydrolytic condensation route is proposed to be capable of producing TaO _x with a distribution gradient of Ta₂O₅, TaO₂, and TaO in the depth direction.     

Effects of a magnetic force on surface-enhanced Raman spectra of a cysteamine linking magnetic particle and a silver colloid plate.

The effects of a magnetic force on magnetic particles linked by cysteamine to a silver colloid plate were analyzed with surface-enhanced Raman scattering spectroscopy. Cysteamine molecules were stretched by a force exerted on the magnetic particles with the external magnetic field gradients generated by two Nd-Fe-B magnets. The spectra showed that the relative intensity ratio of C-S (trans) to C-S (gauche) of cysteamine was increased 2 - 3 times within 30 min under the application of magnetic field gradients. Also, the shift of C-S (T) was observed up to 4 cm(-1) to higher frequency. These results suggested that an extension of the distance between a magnetic particle and a silver colloid induced isomerization from the gauche conformation to the trans conformation, accompanied by probable thiolate migration on the silver colloid surface.     

Direct synthesis and properties of polybenzodipyrrolediones from dibenzylidenebenzodifurandiones and various diamines

Aromatic and aliphatic polybenzodipyrrolediones have been synthesized directly by the solution cyclopolycondensation of two dibenzylidenebenzodifurandiones with four different diamines in refluxing m-cresol or o-phenylphenol in the presence of boric acid. The polymerizations proceeded smoothly in a homogeneous solution and afforded the heterocyclic polymers having inherent viscosities as high as 1.0 almost quantitatively. All the polymers were readily soluble in a wide range of solvents, including N-methyl-2-pyrrolidone (NMP), hot m-cresol, and hot pyridine. Tough, transparent, yellow films could be cast from NMP solutions of the polymers. Thermogravimetric analysis of the aromatic polybenzodipyrrolediones showed a 10% weight loss temperature of 460–500°C under nitrogen. The results also indicated that the aromatic polymers were somewhat less thermally stable than wholly aromatic polypyromellitimides.     

Preparation and properties of ordered and random polyamide-esters from 4-(4-amino-α,α-dimethylbenzyl)phenol and aromatic diacyl chlorides

Random polyamide-esters were prepared directly by the interfacial and solution polycondensation of 4-(4-amino-α,α-dimethylbenzyl)phenol (I) with iso- and terephthaloyl chlorides. Authentic samples of ordered polyamide–esters with an amide-amide–ester-ester structure were synthesized by the two-step procedure; that is, the preparation of amide–bisphenol monomers from I and subsequent polycondensation with aromatic diacyl chlorides. The random and ordered polyamide–esters differed from one another with respect to solubility in organic solvents and glass transition temperature, whereas all the random and ordered polymers were of equal low crystallinity. All of these polymers began to decompose around 350°C in both air and nitrogen atmospheres.