Characteristics and nature of the halogen-bonding interactions between CCl3F and ozone: a supermolecular and SAPT study

The strength and nature of the halogen-bond interactions in CCl₃F···O₃ complexes were examined by means of ab initio quantum-chemical calculations and symmetry-adapted perturbation theory (SAPT). Our calculations predict a trifurcated C–Cl···O interaction for the global minimum of CCl₃F···O₃ complex and several local minima, differing slightly in energy, separated by very low barriers. The calculations, which include a rigorous decomposition of the interaction energies, also indicate that the interaction of CCl₃F molecule with O₃ is characterised by contributions from both electrostatic and dispersion energies, with the contribution of the latter being dominant. The evaluated SAPT interaction energies for the CCl₃F···O₃ complexes are generally in good agreement with those obtained using the supermolecule CCSD(T) method, suggesting that SAPT is a proper method to study the intermolecular interactions in these complexes.     

Normal distribution profile for doping concentration in multilayer tunnel junction

In this paper, the effect of doping concentration and layer thickness on the performance of tunnel junctions (TJs) is studied. We investigate the behavior of single, double and triple layer structures of TJs. Triple layer structure shows better performance in comparison with the other structures and can reach the higher tunneling current besides lower voltage drop. Also, the behavior of the triple layer TJ with different doping concentration profiles is studied. We propose a new normal distribution profile for doping concentration in multilayer TJs which shows better performance in comparison with the linear and graded doping concentration profiles. The higher $\upalpha $ parameters in normal distribution enhance the device performance with increasing the smoothness of doping variations in the center and edge of the TJ. Finally, we examine different thicknesses of triple layer TJ in order to achieve the optimum structure.     

A fast and sensitive nanosensor based on MgO nanoparticle room-temperature ionic liquid carbon paste electrode for determination of methyldopa in pharmaceutical and patient human urine samples

In this study, we describe an ionic liquid–MgO nanoparticle modified carbon paste electrode (MgO/NPs/IL/CPE) was used as a simple, fast, and sensitive tool for the investigation of the electrochemical oxidation of methyldopa (MDOP) using voltammetric methods. The MgO/NPs was characterized with different methods such as TEM, SEM, and XRD. The oxidation peak potential of the MDOP at a surface of MgO/NPs/IL/CPE appeared at 450 mV that was about 100 mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode (CPE) under similar conditions. The electro-oxidation of MDOP occurred in a pH-dependent 2e^? and 2H⁺ process, and the electrode reaction followed a diffusion-controlled pathway. Under optimal conditions at pH 7.0, the anodic peak currents increased linearly with the concentration of MDOP in the range of 0.08–380 μmol L^?1 with a detection limit of 0.03 μmol L^?1 (3σ). The proposed sensor was successfully applied to the determination of MDOP in real samples such as drug and urine.     

Design considerations to improve high temperature characteristics of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers: Strain in barriers

Uncooled multiple quantum well lasers have great attraction because of their lower power dissipation and smaller size than traditional semiconductor lasers. In this study we will investigate the strain effect in barriers of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers. We simulate a laser structure using a band-to-band transition approach. Single effective mass theory has been used for conduction band and Kohn-Luttinger Hamiltonian has been solved for valance band to obtain quantum states and envelope wave functions in the structure. In the case of unstrained barriers, the results have good agreement with a real device fabricated and presented in one of the references. Our main work is proposal of 0.2% compressive strain in the structure Barriers that cause 20% improvement in mode gain-current density characteristic. Significant reduction in leakage current density and Auger current density characteristics is also obtained at 85 °C. Optical gain-photon energy spectrum is increased more than 3% proportional to unstrained barriers.     

Numerical analysis of InGaAs–InP multiple-quantum well laser emitting at 2 {\upmu }m

Multiple-quantum well InGaAs laser structures emitting at 2  \(\upmu \) m with different barriers are modeled using commercial software that combines gain calculation with 2-D simulations of carrier transport and waveguiding. The model is calibrated using experimental results. The simulated results show a non-uniform distribution of carriers in different quantum wells with InGaAlAs barriers which affects their contribution to the gain. The carrier uniformity and a reduction in threshold current density are observed when we use an InGaAs barrier material. The quantum well number was varied from 2 to 4 in both structures and a comparison of the threshold current and its variation with temperature were investigated.     

Modified-DBR-based semi-omnidirectional multilayer anti-reflection coating for tandem solar cells

In this paper, multilayer antireflection coatings are designed by modifying the thickness of two and three paired layer distributed Bragg reflector （DBR） structure. Our proposed DBR-based structures show antireflection behaviors, in spite of the reflection treatment in traditional DBR structures. Firstly, the proposed structures are designed to be equivalent to the theoretical ideal triple-layer （TL） antireflection coating （ARC）. Therefore, the problem of finding a suitable material for the middle layer of triple structure is solved. Simulation results show the significant equivalency for the reflectance of proposed structures to the ideal TL ARC at the same wavelengths and incident angles. Also, the design of the structure is changed in order to present the constant reflectance coefficient over a wide range of wavelengths. This structure enhances the omni-directionality of the multilayer ARC.     

Phase separation, crystallization and leaching of microporous glass ceramics in the CaO-TiO2-P2O5 system

Microporous glass ceramics belonging to the CaO-TiO₂-P₂O₅ system were prepared with the assumption of a 2:1 mole ratio for β-Ca₃(PO₄)₂:CaTi₄(PO₄)₆, the anticipated crystalline phases in the end product. The glasses formulated according to the above composition were melted and cast onto a steel mold and were crystallized to glass ceramics containing the above phases. Dilatometric/differential thermal analysis (DTA) techniques were utilized to determine the appropriate phase separation-nucleation and crystallization temperatures. The crystalline products and resulting microstructures in various stages of process were determined and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By leaching the resulting glass ceramics in HCl, β-Ca₃(PO₄)₂ was dissolved out leaving a porous skeleton of CaTi₄(PO₄)₆. It was found that the volume porosity, specific surface area and mean pore diameter of microporous glass ceramics can be managed through the proper selection of heat treatment conditions. In the optimized conditions for fabricating glass ceramics of minimum mean pore size the values of 41 ± 4%, 26 ± 3 m²/g and 14.3 ± 2 nm were obtained for porosity, surface area and pore diameter respectively.     

Comparing Long‐Chain Branching Mechanisms for Ethylene Polymerization with Metallocenes and Other Single‐Site Catalysts: What Simulated Microstructures Can Teach Us

Three different long‐chain branch (LCB) formation mechanisms for ethylene polymerization with metallocenes in solution polymerization semi‐batch and continuous stirred‐tank reactors are modeled to predict the microstructure of the resulting polymer. The three mechanisms are terminal branching, C–H bond activation, and intramolecular random incorporation. Selected polymerization parameters are varied to observe how each mechanism affects polymer microstructure. Increasing the ethylene concentration during semi‐batch polymerization reduces the LCB frequency of polymers made with the terminal branching and intramolecular mechanisms, but has no effect on those made with the C–H bond activation mechanism, which disagrees with most previous data published in the literature. The intramolecular mechanism predicts that LCB frequencies hardly depend on polymerization time or ethylene conversion, which also disagrees with the published experimental data for these systems. For continuous polymerization reactors, experimental data relating polydispersity to LCB frequency can be well described with the terminal branching mechanism, but both C–H bond activation and intramolecular models fail to describe this experimental relationship. Therefore, detailed simulations confirm that the terminal branching mechanism is indeed the most likely mechanism for LCB formation when ethylene is polymerized with single‐site coordination catalysts such as metallocenes in solution polymerization reactors.     

Electrochemical preconcentration of ultra-trace Cd2+ from environmental and biological samples prior to its determination using carbon paste electrode impregnated with ion imprinted polymer nanoparticles

Cadmium (Cd) is known as one of the most toxic elements among the heavy metals. This study proposes an electrochemical preconcentration method using the ion imprinted polymer nanoparticles modified carbon paste electrode (IIP-CPE) for the stripping voltammetry determination of Cd²⁺ in the environmental and biological samples. These IIP NPs were synthesised using ethylene glycol dimethacrylate as the cross-linker, 2,2?-azobisisobutyronitrile as the free radical initiator and 4?-(4-vinylphenyl)-2,2?:6?,2?-terpyridine as the Cd-binding ligand. The calibration plot was linear in the concentration range of 4–500 nM (R² = 0.9936) with a sensitivity of 918 µA µM^?1 cm^?2. The LOD based on 3S_b/m (where m is the slope of the calibration curve and S_b is the standard deviation for five blank measurements) was found to be 1.94 nM. The relative standard deviations (RSDs) for single-electrode repeatability and electrode-to-electrode reproducibility were 3.0% and 5.6% (n = 5), respectively. The accuracy of the current method was confirmed by the analysis of urine quality control material (QCM, Seronorm^TM Trace Elements Urine, REF NO 201205, Norway) and spiked blood, rice and water samples. Recoveries were found to be above 95.0% for all samples, which confirms the good performance of the proposed voltammetry method.     

Surface free energy effects on the postbuckling behavior of cylindrical shear deformable nanoshells under combined axial and radial compressions

In the traditional continuum mechanics, the effects of surface free energy are generally ignored. However, this cannot be the case for nanostructures because of their high surface to volume ratio; surface energy plays an important role in the mechanical responses. In the present study, the nonlinear buckling and postbuckling characteristics of cylindrical nanoshells subjected to combined axial and radial compressions are investigated in the presence of surface energy effects. To this end, Gurtin–Murdoch elasticity theory is implemented into the classical first-order shear deformation shell theory to develop an efficient size-dependent shell model incorporating surface free energy effects. Subsequently, a boundary layer theory is employed including surface effects in conjunction with the nonlinear prebuckling deformations, the large postbuckling deflections and the initial geometric imperfection. Finally, a solution methodology based on a two-stepped singular perturbation technique is utilized to obtain the size-dependent critical buckling loads and equilibrium postbuckling paths corresponding to the both axial dominated and radial dominated loading cases. It is observed that for the both axial dominated and radial dominated loading cases, surface free energy effects cause to increase the both critical buckling load and critical end-shortening of shear deformable nanoshell made of silicon.