Pure-silica optical waveguides, fiber couplers, and high-aspect ratio submicrometer channels for electrokinetic separation devices

A new fabrication procedure for integration of ultraviolet transparent pure-silica planar waveguides, fiber couplers and high-aspect ratio submicrometer channels is presented. Only a single photolithographic mask step is required. The channels are 80-90 microm deep and the width can be reduced to about 0.5 microm, corresponding to a height-to-width ratio of more than 150. The core of the waveguides consists of pure silicon dioxide, which is favorable over doped silica, due to the absence of absorption centers associated with the dopants. This furthermore improves the long-term stability of the waveguides, because of an increased radiation resistance of the glass. The propagation loss decreases from 1.0 dB/cm at 200 nm to 0.2 dB/cm at 800 nm, which, to our knowledge, is the lowest propagation loss reported for integrated planar waveguides in the ultraviolet wavelength region to date. The effective optical path length is 1.2 mm for an absorbance cell with a nominal length of 1.0 mm, indicating effective suppression of stray light. The limit of detection for paracetamol when present in the entire channel network was determined to 3 microg/mL. Finally, the applicability of the fabricated devices for capillary electrophoresis was evaluated by separation of caffein, paracetamol and ketoprofone using absorbance detection at 254 nm.     

Synthesis of 2-acyl-3-methylthiofurans from 3-methylthio-2-pentene-1,5-dione enolates

2-Acyl-3-methylthiofurans 3 are obtained in fair yields from 3-methylthio-2-pentene-1,5-dione enolates 1 by reaction with iodine. In a similar reaction 1-phenyl-3-methylthio-4-nitro-2-buten-1-one gave 3-methylthio-2-nitro-5-phenylfuran 11. In the crystalline state the 2-benzoyl-3-methylthio-5-phenylfuran 3b showed a non-bonded sulfur-oxygen interaction as inferred from an X-ray diffraction determination, with a S····O distance of 2.871(5)Å.     

Performance of an in-plane detection cell with integrated waveguides for UV/Vis absorbance measurements on microfluidic separation devices

A microfluidic device with integrated waveguides and a long path length detection cell for UV/Vis absorbance detection is presented. The 750 microm U-cell detection geometry was evaluated in terms of its optical performance as well as its influence on efficiency for electrophoretic separations in the microdevice. Stray light was found to have a strong effect on both, the sensitivity of the detection and the available linear range. The long path length U-cell showed a 9 times higher sensitivity when compared to a conventional capillary electrophoresis (CE) system with a 75 microm inner diameter (ID) capillary, and a 22 times higher sensitivity than with a 50 microm ID capillary. The linear range was comparable to that achieved in a 75 microm ID capillary and more than twice as large as in a 50 microm ID capillary. The use of the 750 microm U-cell did not contribute significantly to band broadening; however, a clear quantification was made difficult by the convolution of several other band broadening sources.     

A Study of picosecond dehalogenation of chlorobenzene anions in liquids by positronium inhibition measurements

Radiation chemistry and results of Ps yields indicate that the following processes occur in the positron spur in solution of halogen-substituted hydrocarbons, RX_n: e⁺ + e^? → Ps, e^? + RX _n → (RX_n)^? → RX_n?1 + X^?, e⁺ + (RX_n)^? → Ps + RX_n, e⁺ + X^? → [X^?, e⁺]. Hence the trapped electron can form Ps only if (RX _n)^? is stable or has a lifetime that is longer than o comparable to the Ps formation time. Previous studies have shown that some of the strongly chlorinated benzenes (n = 4.5 give reasonable inhibition in benzene but not in linear hydrocarbons. The reason is very probably that the dechlorination time is much shorter in benzene than in saturated hydrocarbons because Cl^? is more strongly solvated in benzene than in non-aromatic hydrocarbons. To test those ideas further we have begun detailed studies of solutions of the possible “intermediate” inhibitors, viz. 1,2,3,5- and 1,2,4,5-C₆H₂Cl₄, in mixtures of C₆H₆/C₆H₁₄ different methyl-substituted benzene aniline, anisole, dioxane and ethylbenzene. The results are discussed and interpreted in terms of the spur model. The Ps inhibition efficiency of the two isomeric forms of tetrachlorobenzene studied, appears most probably to depend on intramolecular electron transfer with subsequent dehalogenation of the molecular anion on a picosecond timescale. The divergence in inhibitor efficiency obtained for the chlorobenzenes when dissolved in aromatic solvents compared to the same solutes when dissolved in a saturated alkane appears most probably to be caused by complex formation between the initially formed chlorobenzene anion and benzene molecules, which permits a rapid relaxation of the molecular anion with subsequent bond stretching and expulsion of the chloride anion.     

Electrical conductivity in HMTSF-TNAP under pressure

The resistivity of the organic conductor HMTSF-TNAP has been measured at pressures up to 25 kbar and at temperatures down to 1.2 K. Under pressure the increase in the stacking axis resistivity of HMTSF-TNAP (Δ^2,2 -Bi(4,5-trimethylene-1,3-diselenole)-11,11′,12,12′-tetracyano-2m6- naphtoquinodimethane) below 47 K is reduced, although the transition temperature T_p falls at only 0.7 K kbar^?1. This weak pressure dependence compared to that of HMTSF-TCNQ correlates with the larger resistivity anisotropy in the TNAP salt.     

Modifications of interface chemistry of LSM-YSZ composite by ceria nanoparticles

A porous composite electrode LSM-YSZ (lanthanum strontium manganite and yttria stabilized zirconia) was impregnated with different amounts of SDC (samarium substituted ceria) nanoparticles. The materials were investigated with X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy to determine the microstructure, the interface chemistry and the surface chemistry of the various impregnated samples. The SDC nanoparticles cover the surface of the LSM-YSZ backbone to a large extent; they are approximately 5-20 nm in diameter and have a cubic crystal structure. Low concentrations of lanthanum and manganese originating from LSM were detected within SDC particles. It was also observed that the relative atomic concentration of strontium increased on the LSM-YSZ surface with increasing amount of SDC nanoparticles. These findings are related to the applied nanoparticle impregnation method. It is indicated that interactions between surfactant, nanoparticles, impregnation solution and the LSM-YSZ composite take place which can locally affect the surface and interface chemistry of the investigated materials.