Controllable growth of Se nanotubes and nanowires from different solvent during the sonochemical process

Selenium (Se) nanotubes and nanowires have been controllably prepared by a solution-phase approach consisting of hydrothermal process and subsequent sonochemical process in different solvent including methanol, ethanol, acetone, dimethyl formamide, water, isopropanol and ethylene glycol. It is revealed that the formation of the Se nanotubes or nanowires is dependent on the breakage or not of the in-situ generated Se nanoparticles. The effects of the solvents on the morphology of Se nanostructures have been preliminarily discussed. Finally, Se nanotubes and nanowires have been characterized by X-ray powder diffraction (XRD), field emission scan electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy.     

TeO2 liquid phase: Viscosity measurements and evaluation of the thermal conductivity from crystal growth experiments

Current applications of paratellurite TeO₂ in optics and nuclear physics require improving the yield and optical quality of synthesized single crystals. Modelling of the growth process is a useful tool for such purpose, however, involving the knowledge of several thermodynamic parameters of both solid and liquid phase of the compound. This work describes the determination of two main unknown ones, namely dynamic viscosity η and thermal conductivity λ_l of the liquid phase. Measurements of η are performed by means of a specifically designed apparatus; over a 40 K temperature interval above the melting point we find a mean value of 0.028 Pa.s. This data is used in commercial software to depict the evolution of the solid-liquid interface in our Bridgman growth set-up. Comparison of the distribution of defects observed in grown ingots with the results of modelling allows estimating λ_l as lying in the range 3.50-3.75 W m⁻¹ K⁻¹.     

Fullerene-like CPx: A first-principles study of the relative stability of precursors and defect energetics during synthetic growth

Inherently nanostructured CP_x compounds were studied by first-principles calculations. Geometry optimizations and cohesive energy comparisons show stability for C₃P, C₂P, C₃P₂, CP, and P₄ (P₂) species in isolated form as well as incorporated in graphene layers. The energy cost for structural defects, arising from the substitution of C for P and intercalation of P atoms in graphene, was also evaluated. We find a larger curvature of the graphene sheets and a higher density of cross-linkage sites in comparison to fullerene-like (FL) CN_x, which is explained by differences in the bonding between P and N. Thus, the computational results extend the scope of fullerene-like thin film materials with FL-CP_x and provide insights for its structural properties.     

The impact of STEM on the growth of wealth at varying scales,ranging from individuals to firms and countries: The performance of STEM firms during the pandemic across different markets

Researchers have not yet reached consensus on whether there is a difference in performance between STEM and non-STEM firms across different financial markets during economic expansion and through economic downturns, such as pandemics and recessions. It is unclear as to whether STEM or non-STEM firms, but also graduates with STEM or non-STEM education contribute more, less, or equally to economic inequality. By analysing total wealth at varying scales, ranging from individuals, to firms, to entire countries, we demonstrate that the Zipf exponent, serving as a proxy for wealth inequality, persistently ramps up as the scale of a system increases. At an individual level, analysing the Zipf plots separately for the world's richest individuals with STEM and non-STEM graduation degree, we begin by demonstrating that STEM education contributes more to inequality than non-STEM. At a firm level, in contrast to the DAX and CAC40 indexes, for firms comprising the S&P 500 index, the average growth rate of STEM constituents has been significantly higher than those calculated for non-STEM constituents during the most recent economic expansion and the coronavirus pandemic. This insight is particularly useful for the financial sector. Secondly, we demonstrate a functional dependence between a country's number of patents and its STEM graduates. Finally, motivated by the fact that the U.S. heavily surpasses the E.U. in terms of Venture Capital, we model wealth inequality at different scales of the economy.