Quantum electronic transport: Linear and nonlinear conductance from the Keldysh approach

This is a review of the derivation of the Landauer conductance using the Keldysh non-equilibrium Green's function (NEGF) formalism and the equations-of-motion (EOM) method. We consider the elastic quantum electronic transport through a multi-lead device and treat the conductor in the mean-field approximation. This is suitable for open quantum dots as well as for several molecular systems where charging effects are negligible. The focus of the presentation is to unveil the technical issues involved in the formalism. We show how the Landauer conductance emerges as a linear term in the current-voltage I-V characteristics and indicate how to go beyond this regime. We address the connection of the NEGF approach to recent developments in molecular transport and discuss the problems that arise when one tries to include interaction effects beyond the mean field.     

Phase behaviour of binary systems of lactones in carbon dioxide

Experimental phase equilibrium data for binary systems involving ε-caprolactone, δ-hexalactone, and γ-caprolactone with carbon dioxide have been measured applying the synthetic method using a high-pressure, variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa. For the systems investigated, (vapour + liquid) (VLE), (liquid + liquid) (LLE), and (vapour + liquid + liquid) (VLLE) equilibrium were visually recorded. It was observed that an increase in temperature or in carbon dioxide concentration led to a pronounced raise in transition pressure values. The experimental results were modelled using the Peng–Robinson equation of state with the conventional quadratic mixing rule, affording a satisfactory representation of the experimental values.     

Phase behaviour of the ternary system {poly(ε-caprolactone) + carbon dioxide + dichloromethane}

Recently, production of biocompatible and biodegradable polymer microparticles has been a matter of growing interest in pharmaceutical and food areas such as drug or active compounds delivery. To conduct production of microparticles, polymeric particle coating, impregnation of active compounds in polymeric films, the knowledge of phase behaviour involving the biodegradable polymer in supercritical carbon dioxide in the presence of a modifier may be needed to allow developing new industrial applications. In this sense, the aim of this work was to investigate the phase behaviour of the ternary system formed by the biodegradable polymer poly(ε-caprolactone) in (carbon dioxide + dichloromethane). Experimental phase transition (bubble and cloud point) values were obtained by applying the static-synthetic method using a variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa, in the CO₂ overall composition range of (25–46) wt%, while polymer concentrations studied were (1, 3, 5, and 7) wt%. For the system investigated, depending on the polymer concentration, vapour–liquid, liquid–liquid, and vapour–liquid–liquid phase transitions were verified.     

pH effect on the photochemistry of 4-methylcoumarin phosphate esters: caged-phosphate case study

There are numerous reports of coumarin ester derivatives, in particular phosphate esters, as photocleavable cages in biological systems. Despite the comprehensive analysis of the photocleavage mechanism, studies of 4-methylcoumarin caged phosphates and/or nucleotides were always performed at constant pH. In this work, we present the study of the pH effect on the photochemistry of (7-diethylaminocoumarin-4-yl)methyl phosphate (DEACM-P). Fluorescence and photocleavage quantum yields, as well as the fluorescence decay times were measured as a function of the pH. It was found that the pH produces significant changes in the overall photochemical quantum yield of DEACM-P, and the observed changes are complementary to those obtained from the fluorescence quantum yield. Deprotonation of DEACM-HPO(4)(-) to yield DEACM-PO(4)(2-), produces a decrease in the photochemical quantum yield (from 0.0045 to 0.0003) and an increase in the fluorescence quantum yield (from 0.072 to 0.092). Moreover, from the analysis of the decay times, we have also found that hydroxyl ion is not only relevant, but it is mechanistically involved in the photoreaction of DEACM-HPO(4)(-).     

Ethylbenzene to chemicals: Catalytic conversion of ethylbenzene into styrene over metal-containing MCM-41

Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeO_x/IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N₂ adsorption isotherms and temperature programmed reduction (TPR). Cu²⁺, Co²⁺, and Cr⁴⁺/Cr³⁺ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeO_x/IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO₂. However, MeO_x/IM catalysts had a low performance in styrene production (activity less than 15 × 10^?3 mmol h^?1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni²⁺ or Fe³⁺ coordinated with the MCM-41 framework, as well as NiO_x and Fe₂O₃ extra-framework species, is continuously oxidized by the CO₂ to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe³⁺ species produced active sp² carbon compounds, which are removed by CO₂; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni²⁺ and Ni⁰ species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO₂ plays a role in furnishing the lattice oxygen to maintain the Fe³⁺ active sites in the dehydrogenation of ethylbenzene to form styrene.     

Failure analysis case study on a Cu/low-k technology in package: New front-side approach using laser and plasma de-processing

Because of its advantages (reduction of thickness, improvement of the signal delay and of the thermal dissipation…), Cu/low-k technologies are more and more used for RF applications in semiconductor industry. The failure analysis of such devices becomes a new challenge. This paper deals with a failure analysis case study on copper and low-k dielectric structure encapsulated in a plastic package. It shows the limitations of the techniques used in a standard failure analysis flow and presents a new sample preparation combining laser package ablation and specific RIE process for front-side decapsulation. This innovative sample preparation flow has been found mandatory for solving the failure analysis case: it was demonstrated that there was not any defect at the surface of the die and this method enabled the access to an EOS defect located between two metal layers.     

Spectrofluorimetric Determination of Coumarin in Commercial Tablets

A simple, rapid and effective analytical method based on fluorescence spectroscopy for the determination of coumarin in pharmaceutical formulations without pre-treatment or pre-concentration step was development. Coumarin had maximum excitation and emission at 310 nm and 390 nm, respectively. Optimum conditions for the detection of coumarin were investigated. Under optimized conditions, we observed a linear behavior for the sign of coumarin in the concentration range of 2.5 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹, with linearity of 0.998 and sensitivity of 2.9 × 10¹⁰ u.a/mol L⁻¹. The proposed method was validated in terms of accuracy, precision and specificity of coumarin using the standard addition and external calibration. It was noted that the results support (P < 0.05), indicating that the matrices were not an interference in the determination of coumarin by fluorescence spectroscopy. The results were favorable compared with those obtained by reference chromatographic methods.     

Electronic and elastic properties of expanded radialenes carbon nanotubes

The series of expanded radialenes of molecular formulae C_2n H _n and C_3n H _n are obtained by inserting acetylene or diacetylene groups between each pair of methylene units of radialenes C _n H _n . This paper reports on the new theoretical investigation of electronic and elastic properties of some carbon nanotubes based on expanded radialenes with different diameters and with the armchair and zigzag edges Using the ABINIT software package, which is based on the density functional theory (DFT), we found that all studied carbon nanotubes based on expanded radialenes possess metallic behavior. Also, the calculations show that the elastic properties of the nanotubes depend on the form of the rolling up (armchair (m,m) or zigzag (m,0)). The Young’s modulus is slightly smaller for the (m,0) nanotubes and a bit larger for (m,m) nanotubes.