Determination of carbon nanotube density by gradient sedimentation

Density gradient centrifugation is a high-resolution technique for the separation and characterization of large molecules and stable complexes. We have analyzed various nanotube structures by preparative centrifugation in sodium metatungstate-water solutions. Bundled, isolated and acid-treated single-walled nanotubes (SWNTs) and multiwall nanotubes (MWNTs) formed sharp bands at well-defined densities. The structure of the material in each band was confirmed by transmission electron microscopy and Raman spectroscopy. Our data suggest respective densities of 1.87, 2.13, 1.74, and 2.1 g/cm(3) for bundled, isolated, and acid-treated SWNTs and MWNTs. These measured results compare well with their calculated densities.     

Improving the dielectric constant of Al2O3 by cerium substitution for high-k MIM applications

Process compatible high-k dielectric thin films are one of the key solutions to develop high performance metal–insulator–metal (MIM) structures for future microelectronic devices. Engineered cerium–aluminate (Ce_xAl_2–xO₃) thin films were deposited on titanium nitride metal electrodes by electron-beam co-evaporation of ceria and alumina in a molecular beam deposition chamber. X-ray photoelectron spectroscopy clearly reveals that Ce cations can be stabilized in the 3+ valence state in Ce_xAl_2–xO₃ up to x = 0.7 by accommodation in the alumina host matrix. Higher Ce content was observed to result in cerium dioxide segregation in cerium aluminate matrix, probably due to the chemical tendency of Ce cations to exist rather in the 4+ than in the 3+ state. Electrical characterization of the X-ray amorphous Ce_0.7Al_1.3O₃ films reveals a dielectric constant value of about 11 and leakage current lower than 10^?4 A/cm². No parasitic low-k interface formation between the high-k Ce_0.7Al_1.3O₃ film and the TiN metal electrode is detected.     

A 3D Analogue of Phenyllithium: Solution‐Phase,Solid‐State,and Computational Study of the Lithiacarborane [Li−CB11H11]−

The lithiacarborane [Li?CB₁₁H₁₁]^? plays a central role in carborane chemistry, as it is a key intermediate to achieve the selective functionalization of the monocarba‐closo‐dodecaborate [CB₁₁H₁₂]^? for applications in various fields. Also, it is an organometallic species of fundamental interest because it represents a 3D analogue of phenyllithium featuring an exo C?Li bond in addition to the delocalized negative endo charge of the spherical cluster. For the first time, the elusive and highly reactive endo/exo formal dianion [CB₁₁H₁₁]^2? has been isolated as its lithiate as well as zincate in pure form and fully characterized. DFT calculations corroborate the experimental findings and underscore the remarkably high reactivity of the lithiacarborane. Subsequent derivatizations demonstrate the relevance of its initial clean formation.     

Subcomponent Self-Assembly of a Cyclic Tetranuclear FeII Helicate in a Highly Diastereoselective Self-Sorting Manner

An enantiomerically pure diamine based on the 4,15-difunctionalized [2.2]paracyclophane scaffold and 2-formylpyridine self-assemble into an optically pure cyclic metallosupramolecular Fe₄L₆ helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self-assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple-stranded helicate, and hence, leads to the larger strain-free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic chiral self-sorting manner given the fact that the assembly contains ten stereogenic elements, which can in principle give rise to 149 different diastereomers. The metallosupramolecular aggregates could be characterized by NMR, UV/Vis and CD spectroscopy, mass spectrometry, and X-ray crystallography.     

Photocured characteristics of fast photocurable acrylic formulations and investigations by differential photo calorimeter

Nanofluids are obtained by suspending metallic or non-metallic nanoparticles in conventional base liquids and can be employed to increase heat transfer rate in various applications. In this study, the effects of adding three types of nanofluids on turbulent convective heat transfer at the entrance region of a constant wall heat flux tube were experimentally studied. The nanofluids were mixtures of aluminium oxide, copper oxide, and silicon carbide at various nanoparticle volume fractions ranging from 0.0002 to 0.002 in water. The convective heat transfer coefficient was measured at different Reynolds numbers of 10,000–50,000. At these concentrations and Reynolds numbers, a maximum of 11–18% of convection heat transfer coefficient was observed as compared to the base fluid, showing a 6–9% increase on average. In this study, it was observed that changes in the nanoparticle type had no considerable effect on heat transfer coefficient increase. According to the model proposed here, the dimensionless thickness of laminar sub-layer is specified as a functional equation of the volume fraction of nanoparticles for each material.

     

Focusing of a vortex carrying beam with Gaussian background by an apertured system in presence of coma

In this paper, diffraction pattern of a vortex carrying beam with a Gaussian background has been studied by using Fresnel-Kirchhoff diffraction integral, in the presence of third-order coma. Results of intensity distribution and encircled energy at the Gaussian plane have been presented for two values of the topological charge. Positional shift and splitting of the dark core have been investigated in detail. It is noticed that the diffraction pattern of a beam with double topological charge is affected more by comatic aberration in comparison to the beam with single topological charge. We have also verified our results by using the optical transfer function approach. Propagation of an apertured Gaussian background vortex beam through a π-phase shifter has also been studied for two values of the topological charge.     

Focusing of linearly-, and circularly polarized Gaussian background vortex beams by a high numerical aperture system afflicted with third-order astigmatism

Effects of third-order astigmatism on the focused structure of linearly and circularly polarized Laguerre-Gaussian beams have been investigated by using vectorial Debye-Wolf integral. The results have been presented for total intensity distribution and squares of the polarization components at the focal plane of a high numerical aperture system, for two values of the topological charge. Astigmatism results in the stretching of the intensity pattern as well as of the squares of the polarization components. A split is observed in the intensity pattern of a focused beam having double topological charge, and also in the pattern of the longitudinal polarization component of circularly polarized beam even with unit topological charge.     

Vertically aligned N-doped carbon nanotubes by spray pyrolysis of turpentine oil and pyridine derivative with dissolved ferrocene

Vertically aligned nitrogen-doped carbon nanotubes were synthesized from the pyrolysis of a mixture of turpentine oil, 4-tert-butylpyridine (C₉H₁₃N) and ferrocene on silicon and quartz substrate in nitrogen atmosphere at 700 °C by simple spray pyrolysis technique. SEM, TEM, TGA/DTA, Raman spectroscopy, XPS and electron probe micro analysis (EPMA) techniques were used to characterize the structural analysis and composition of the as-grown N-doped carbon nanotubes. Morphology of the films was greatly affected by the nature of the substrate. From the XPS and EPMA data, it was found that nitrogen content of the nanotubes were 1.6 at.% and 2 at.% on silicon and quartz substrate, respectively. Our studies show that two different types of N atoms can be present in these materials. These are ‘pyridinic’ and ‘graphitic’ nitrogen with binding energies of 398.2 eV and 400.4 eV, respectively. Raman spectroscopy reveals that graphitization of carbon nanotubes grown on silicon is better than nanotubes grown on quartz substrate. Thermogravimetric analysis showed that the thermal stability of as-prepared nanotubes grown on silicon substrate is higher than the nanotubes deposited on quartz substrate.     

Flattened Gain Profile of Raman-Fiber Optical Parametric Hybrid Amplifier in C+L Band for SD-WDM System

Journal of Russian Laser Research - Variations in gain with the least noise figure and noise are the challenging issues for the hybrid amplifier. This is resolved in the proposed model of...     

Meticulous assessment of natural compounds from NPASS database for identifying analogue of GRL0617, the only known inhibitor for SARS-CoV2 papain-like protease (PLpro) using rigorous computational workflow

Molecular Diversity - The latest global outbreak of 2019 respiratory coronavirus disease (COVID-19) is triggered by the inception of novel coronavirus SARS-CoV2. If recent events are of any...