The Trifluoromethyl Anion

First evidence for the existence of free trifluoromethyl anion CF₃^? has been obtained. The 3D‐caged potassium cation in [K(crypt‐222)]⁺ is inaccessible to CF₃^?, thus rendering it uncoordinated (“naked”). Ionic [K(crypt‐222)]⁺ CF₃^? has been characterized by single‐crystal X‐ray diffraction, solution NMR spectroscopy, DFT calculations, and reactivity toward electrophiles.     

Gas chromatography-mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry in quantifying fatty acids

This critical overview covers current analytical methods and future developments in quantitative determination of fatty acids (FAs), emphasizing sample extraction, derivatization and instrumental analysis with gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS²). We compare the benefits and the drawbacks of these two analytical techniques.We consider the well-established GC/MS method with pre-derivatization to be a traditional technique in terms of highly standardized sample-preparation procedures, affordability and readily available library searching for compound identification. However, the complicated derivatization steps required prior to instrumental analysis with GC/MS take a long time, with loss and transformation of FAs, low recovery and poor reproducibility.HPLC/MS² without derivatization shows the benefits of simple, mild sample-processing conditions, satisfactory recovery, short running time and high selectivity and sensitivity, which may allow it to become a viable alternative to GC/MS for the analysis of FAs in the years ahead.     

Effect of sterilization on non-woven polyethylene terephthalate fiber structures for vascular grafts

Non-woven polyethylene terephthalate (PET) fibers produced via melt blowing and compounded into a 6 mm diameter 3D tubular scaffold were developed with artery matching mechanical properties. This work compares the effects of ethylene oxide (EtO) and low temperature plasma (LTP) sterilization on PET surface chemistry and biocompatibility. As seen through X-ray photoelectron spectroscopy (XPS) analysis, LTP sterilization led to an increase in overall oxygen content and the creation of new hydroxyl groups. EtO sterilization induced alkylation of the PET polymer. The in vitro cytotoxicity showed similar fibroblastic viability on LTP- and EtO-treated PET fibers. However, TNF-α release levels, indicative of macrophage activation, were significantly higher when macrophages were incubated on EtO-treated PET fibers. Subcutaneous mice implantation revealed an inflammatory response with foreign body reaction to PET grafts independent of the sterilization procedure.     

High-energy femtosecond laser pulse compression in single- and multi-ionization regime of rare gases: experiment versus theory

We report experimental and numerical results on the post-compression of 40 fs duration pulses down to 10 fs at high energy level (multi-mJ). The spectral broadening is achieved through the self-phase modulation resulting from optical-field-ionization of different noble gases (He, Ne, Ar) by the 40-fs laser pulse propagating in a low-pressure gas-filled hollow capillary. We discuss the influence of the multi-ionization dynamics, through the gas dependence, on the laser energy carried by the capillary, as well as on the duration and temporal shape of the post-compressed pulses. In all the different experimental conditions investigated in this article (pressures and gases used), the experimental data is in good agreement with the numerical results from a three-dimension propagation code. Through this study, we demonstrate the robustness of the proposed post-compression technique with regard to multi-ionization, indicating that it can be used on a large intensity range by judiciously choosing the gas.     

Approach for dislocation free GaN epitaxy

The characteristics of confined epitaxial growth are investigated with the goal of determining the contributing effects of mask attributes (spacing, feature size) and growth conditions (V/III ratio, pressure, temperature) on the efficiency of the approach for dislocation density reduction of GaN. In addition to standard (secondary electron and atomic force) microscopy, electron channeling contrast imaging (ECCI) is employed to identify extended defects over large (tens of microns) areas. Using this method, it is illustrated that by confining the epitaxial growth, high quality GaN can be grown with dislocation densities approaching zero.     

Electrical stress effects on ultrathin (2.3 nm) oxides

Oxide reliability is a major concern for deep-submicron technologies as the dielectric thickness decreases. We study the dependence of the interface states and stress induced leakage current increase as a function of electrical stresses at different temperatures. The experiments were performed on ultrathin gate oxide (2.3 nm) metal oxide semi-conductor devices. Charge pumping and gate current as a function of the gate voltage were used to analyze both processes. Stress induced leakage current is still observable when the sensing gate voltage ranges from −1.2 to 0.6 V. We also observe an increase of interface states after different stresses. We show that, for a given stress, the stress induced leakage current increases with the temperature. From the experimental data we show that the general relation of both interface states and stress induced leakage current increases follow a power law with the stress voltage and temperature.     

Chiral resolution by crystallization of host-guest supramolecular complexes

The crystallization behaviour and the physical characterization of supramolecular complexes formed between permethylated-α-cyclodextrin (TMα-CD) and the enantiomers of phenylethanol (PE) are investigated. According to crystal structure analyses, complexes containing the pure guest enantiomers are almost isomorphous, indicating that the host presents a poor ability to distinguish PE enantiomers at a molecular level. Nevertheless, crystallizations from racemic PE in water induce an efficient chiral discrimination and allow the enantio-separation of the guests despite the existence of a solid solution revealed by XRPD and coupled TG-DSC analyses. The enantiodifferentiation is explained by solubility differences between the two diastereomeric complexes in the studied temperature range. Moreover, it is shown that the diastereomeric complex TMα-CD/(S)-PE crystallizes in two distinct phases: a monohydrate and an anhydrous form, with a transition temperature close to 37°C. The insertion of a water molecule in the crystals grown below 37°C does not involve any other change of the crystal packing nor of the molecular conformation, but leads to different crystal growth mechanisms inducing different morphologies and distinct thermal behaviours. This revised version was published online in July 2006 with corrections to the Cover Date.     

About the theory of optical grating coupler-waveguide systems

It is well known that photoresist gratings can be used for coupling light into and out of optical waveguides. To understand the coupling phenomena, and as a first step of a theoretical study, we deal here with the diffraction of a plane electromagnetic wave by a photoresist grating lying on a dielectric optical guide. Using a rigorous electromagnetic formalism, we find the sharp resonances already described by Hope and relate them with the existence of modes in the optical guide.     

Determination of the coupling coefficient of a holographic thin film coupler

In two previous papers, we proposed a rigorous electromagnetic formalism to study the coupling resonances which occur when a plane wave illuminates a grating coupler waveguide system under a convenient angle of incidence. We deal here with the case when a limited incident beam impinges on the system, and we try to optimize the parameters of the beam in order to get the best coupling coefficient. Numerical results are given for both lossless and lossy photo-resists.