Free Atoms Research Articles

Construction of silver-epoxy adhesive with suppressed silver migration rate based on thiol-silver interaction

The silver migration limits the application of silver based conductive adhesives in wet environment. The existing methods for inhibiting silver migration in epoxy conductive silver adhesives involve one or more issues such as cost, complexity, and inhibition of conductivity. Moreover, there is currently a lack of strategies that can suppress the silver migration effect while ensuring good dispersion of silver fillers in the matrix and constructing a good filler matrix interface. Herein, a facile method was reported suppressing the silver migration in silver-epoxy conductive adhesive. Tetrafunctional thiopentaerythritol tetramercaptoacetate (PERTMA) was introduced into 1,4-cyclohexanedimethanol diglycidyl ether (CHDMGE) epoxy resin as the curing agent. This method utilized the strong interaction between silver and thiols, including coordination and covalent bonding, to achieve good compatibility between filler and matrix. By tightly combining silver with the resin system, the content of free silver atoms was reduced, capturing and inhibiting the hydrolysis of silver atoms and their migration with current, and the conductivity of the conductive silver adhesive was not greatly degraded due to the silver-thiol interaction. At the same time, the introducing of PERTMA was able to reduce the surface hydrophilicity of epoxy resin, which also helped suppressing the silver migration effect under humid circumstances. The interaction between silver and thiol was characterized, and the influence of silver content on the curing behavior, material mechanical performance, conductivity, resistivity on silver migration and flexibility was explored. The CHDMGE/PERTMA/Ag conductive adhesive based on strong thiol-silver interaction had excellent resistance to silver migration, which occurred after 3500s, which was 10.67 times longer than the control group. In addition, the silver filler enhanced the tensile strength of the matrix resin by this thiol-silver interaction. This study will provide new ideas for the design and development of silver migration resistant conductive adhesives based on matrix filler interaction.

Nature of magnetic circular dichroism and absorption spectra of f-f transitions in Na0.4Ho0.6F2.2 single crystal

We present first study of magnetic circular dichroism (MCD) spectra of Ho3+ ion in C4v local symmetry, which it has in fluorite Na0.4Ho0.6F2.2. Optical absorption and MCD spectra were studied in this single crystal in the region of 5I8→ 5F3, 5F2, 3K8 and 5G5 transitions in the temperature range 3.6–––90 K. It was revealed, that number of transitions observed in the MCD and absorption spectra coincides with the number of transitions only from the doublet E state to singlet excited states. The E-E type transitions are not active in MCD, but they are not observed in the absorption spectra either. Paramagnetic magneto-optical activities (MOA) of the absorption bands and their temperature dependences were measured and interpreted with the help of the theory based on the nature of f-f transitions allowance. The MCD spectra were also analyzed in approximation of the J,±MJ wave functions of the free atom. It was shown in particular, that the lowest initial state of the transitions observed at T > 10 K had MJ = 7, but this is not the lowest state of the holmium ion in the crystal. A little lower there is a quasi-doublet with MJ = 8 and, accordingly, with a higher magneto-optical activity of transitions from it. However, the intensity of transitions from this state is low.

Compton Profile Investigation for Aluminum (Al)

This paper presents a study on the Compton Profile (CP) for aluminum in the face-centered cubic (fcc) crystal structure. Renormalized -Free Atom (RFA) model has been used to calculate the CP for the (3s-3p) subset of configurations. It is found that the RFA calculation for the (3s2-3p1) configuration provides a better agreement with experimental values and the Plane Wave Generalized Gradient Approximation (PW-GGA) than the free atom model. CP was chosen for all values within the momentum region (PZ= 0 7a.u) and compared the theoretical results with the available experimental values. The results were in good agreement with the available experimental values.

The role of radiation pressure in lithium deficit for stars in the stage of late accretion: failure of lithium test for young stellar clusters

ABSTRACT We study the behaviour of lithium atoms in the radiation field of main-sequence (MS) stars. The radiation pressure on atoms in the resonant lines of the ${\rm Li\, {\small I}}$ 6708 Å doublet exceeds the gravity at Teff > 3000 K. The lifetime of ${\rm Li}$ atoms before their ionization is sufficient to achieve the escape velocity. Free ${\rm Li}$ atoms cannot approach the pre-main sequence (PMS) and MS stars if the surrounding gas is sufficiently transparent. Accretion of small bodies (SBs) can partially restore the lithium abundance when SB directly falls on to the star in elongated orbits. In the case of accretion from discs consisting of SB fragments, when the parent bodies move in quasi-circular orbits, the boundary of the SB sublimation region plays a decisive role. Near hot stars, the free ${\rm Li}$ atom is rapidly ionized and participates in accretion on to the star in the form of ions, contributing to an increase in the ${\rm Li}$ abundance. Low-mass stars with low temperatures cannot hold lithium atoms. Near stars with Planck energy distribution in the radiation field, lithium deficiency occurs if 3000 K < Teff < 3400 K. New stars with [Fe/H] = 0.0 may indicate a lithium deficiency at Teff < 5000 K. Failure of the lithium test to estimate the age of a stellar cluster may indicate a significant contribution of accretion in the form of debris discs consisting of SBs.

Degradation of Tolonium Chloride Dye by Phosphate Ion in Aqueous Acidic Solution: Kinetic Approach

The degradation of tolonium chloride (TC+) dye by phosphate ion (PO43-) in an aqueous acidic solution was studied using spectrophotometric analysis at 301 K, I= 1.0 M, [TC+]= 1.5 × 10-5 M, [H+]= 1.0×10-3 M, and ʎmax 600 nm. To determine the potency and rate of the reactant species, an aqueous acidic medium was employed. The reaction's direction and tendency were predicted using a thermodynamic analysis at an interval of 5.0 K and a temperature range of 301-321 K. Without the presence of intermediate complex/free atoms formation, a reaction that produced phenyl sulphoxide, phenylamine, and HPO32- as products of the reaction was obtained with a molar ratio of 1:1 for both reactants. First-order tolonium chloride reactivity was found in the reaction and first-order for the phosphate ion, resulting in a second-order reaction overall. The reaction process accelerated as the concentration of hydrochloric acid rose. The response time decreased with an increase in ionic strength concentration and added Ca2+ and Cl- did catalyze the reaction positively. A straight line that went through the origin was produced by plotting 1/ko vs PO43- concentration. The spectroscopic analysis showed no discernible shift from λmax of 600 nm. Additionally, an increase in temperature accelerated the reaction process. The reaction has a negative free energy change, G (-3.13–1.12 KJ/mol) which indicates that it is spontaneous and that the reactants have more free energy than that of the products. While the enthalpy of activation, H is positive and indicates that the reaction was endothermic and followed an associative path, the entropy of activation, S, is also negative (-7.45–1.10 KJ/mol), indicating that the reaction is less disordered. Due to the added ions catalysis and absence of free atoms during the course of the reaction, an outer-sphere mechanism was suggested for the reaction.

Quantitative reconstruction of atomic orbital densities of neon from partial cross sections

The approach of photoemission orbital tomography, i.e., the orbital density reconstruction from photoemission of planar molecular layers by using a formalism equivalent to a Fourier transformation, is transferred to free atoms. Absolute radial orbital densities of neon 1s, 2s, and 2p orbitals are reconstructed with a central-field one-electron model, using well-known atomic photoionization data. The model parameters are optimized by a Markov chain Monte Carlo method with Bayesian inference from which uncertainties for the reconstructed orbital densities are derived. The presented model opens the path for photoemission orbital tomography as a powerful tool, as well as for a quantitative analysis. Published by the American Physical Society 2024

Factors Affecting the Cracking Resistances of a Spring Steel Tempered at Different Temperatures

Cracking resistance is vital to the practical application of spring steels, which consists of fracture toughness (KIC) under the quasistatic loading condition and fatigue crack propagation (FCP) resistance under the cyclic loading condition. In the present study, the relation between the KIC/FCP resistance and microstructure of the 50CrMnSiVNb spring steel tempered at various temperatures is studied. In the results, it is shown that the dislocation density is the main factor influencing the KIC and FCP resistances, and the carbide size/quantity and morphology can also affect the KIC and FCP resistances. Thus, reducing the dislocation density is the most effective method to enhance the cracking resistance of the investigated steel. Moreover, decreasing the aspect ratio and obtaining a moderate size of tempered carbides are also beneficial to the cracking resistance. In addition, free hydrogen atoms can cause intergranular fracture on the fracture surface, worsening the FCP rate. To enhance the FCP resistance, smelting processes need to be improved to reduce the hydrogen content of the investigated steel.

Mixture of hydrogen and methane under planetary interior conditions.

We employ first-principles molecular dynamics simulations to provide equation-of-state data, pair distribution functions (PDFs), diffusion coefficients, and band gaps of a mixture of hydrogen and methane under planetary interior conditions as relevant for Uranus, Neptune, and similar icy exoplanets. We test the linear mixing approximation, which is fulfilled within a few percent for the chosen P-T conditions. Evaluation of the PDFs reveals that methane molecules dissociate into carbon clusters and free hydrogen atoms at temperatures greater than 3000 K. At high temperatures, the clusters are found to be short-lived. Furthermore, we calculate the electrical conductivity from which we derive the non-metal-to-metal transition region of the mixture. We also calculate the electrical conductivity along the P-T profile of Uranus [N. Nettelmann et al., Planet. Space Sci., 2013, 77, 143-151] and observe the transition of the mixture from a molecular to an atomic fluid as a function of the radius of the planet. The density and temperature ranges chosen in our study can be achieved using dynamic shock compression experiments and seek to aid such future experiments. Our work also provides a relevant data set for a better understanding of the interior, evolution, luminosity, and magnetic field of the ice giants in our solar system and beyond.

The formation mechanism of Sc-based metallofullerenes: a molecular dynamics simulation study.

The practical applications of endohedral metallofullerenes (EMFs) are mainly constrained by their low yields. Understanding the formation mechanisms is therefore crucial for developing methods for high-yield and selective synthesis. To address this, a novel force-field parameter set, "CSc.ff", was created using a single-parameter search optimization method, then molecular dynamics simulations of various systems with a carbon-to-scandium atomic ratio of 12.5 were carried out. The simulations were run under a constant atomic number, volume, and energy (NVE) ensemble. The influence of the working gas, helium, as well as temperature gradients on the formation process was examined. Our simulations reveal that the cage growth patterns of Sc-based EMFs (Sc-EMFs) closely resemble those of hollow fullerenes, evolving from free carbon atoms to chains, rings, and, ultimately, to cage-shaped clusters. Importantly, the Sc-EMFs formed in the simulation frequently exhibit structural defects or under-coordinated carbon atoms. Scandium atoms, whether at the periphery or on the surface of these cages, can be incorporated into the cages, forming Sc-EMFs. Helium was found to not only promote the formation of carbon cages but also facilitate the encapsulation of scandium atoms, playing a crucial role in the formation of cluster fullerenes. Moreover, cooling effectively inhibits the uncontrollable growth of the carbon cage and is essential for forming stable, appropriate-sized cages. This study enhances our understanding of the formation of Sc-EMFs and provides valuable insights for developing more efficient synthetic methods.

Exploring structural and optical properties of a new series of soft salts based on cyclometalated platinum complexes.

A series of nine new soft salts based on two platinum(II) complexes, namely ([Pt(C^N)(CN)2]-[Pt(C^N)(en)]+) (en = ethane-1,2-diamine), has been developed and synthesized. Their photophysical properties in both solution and the solid state were described. All soft salt complexes exhibit phosphorescence emission with PLQY in the solid state up to 0.36. Most of these materials displayed aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) in water/DMSO solutions as the water ratio increased. Structure-property relationships were analyzed in relation to emission properties. The presence of the free nitrogen atoms in soft salt complexes with a C^N pyrimidine-based ligand allowed for reversible sensitivity to acidic vapors, resulting in the quenching of phosphorescence emission. Additionally, for selected soft salts, we described reversible vapochromism behaviour, making these new materials interesting for multi-detection purposes in anti-counterfeiting applications.

P-block doped semi-metallic xenes as highly selective and efficient transition-metal free single atom catalysts for electrochemical CO reduction

Electronic structure of boron-doped silicene is optimized for CORR and selective towards methanol with an overpotential of less than 0.1 V.

Configuration average, state, orbital, Coulomb and exchange energies of confined beryllium atom

We have analysed the electronic structure for the ground and excited configurations of the confined beryllium atom under impenetrable spherical walls by using Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) methods. The wavefunction is built up from the one-electron wavefunctions which constitute the Slater-type basis sets. When the dot radius increases, all energies approach the corresponding values of free beryllium atom. In addition, in large dot radii, the ratio of the average potential energy to the total kinetic energy for each configuration approaches to the virial coefficients for free atoms (−2). It is found that the Coulomb interaction energy between the electrons occupying the 1s orbital is the biggest. For the 1s22s2p configuration, in small dot radii, while the 2s orbital energy is larger than the 2p orbital energy, the 2s orbital energy is smaller than that of 2p in large dot radii.

High-temperature photoluminescence properties of various defects in hydrothermally grown ZnO microrods

High-temperature photoluminescence properties of hydrothermally grown ZnO microrods were reported. Photoluminescence spectra of ZnO microrods deconvoluted into three Gaussian components: near band edge (NBE) emission, Violet emission (VL) and Yellow emission (YL) peaks corresponding to free excitons, zinc vacancies and interstitial oxygen atoms, respectively. Increasing the temperature caused a redshift of the energy position of the NBE and VL peaks and a blueshift of the energy position of the YL peak were observed. In the temperature range from 300K to 473K, the intensities of the NBE and VL bands varied based on a nonlinear pattern. Intensity of these emission bands decreases from temperature 473K–673K. As the temperature increases, changes in the energy and crystal structures of the material due to decrease in the concentration of defects cause a blueshift of the emission bands related to interstitial atoms, and a redshift of the emission bands related to vacancies.

High-resolution spectroscopic imaging of atoms and nanoparticles in thin film vaporization

We introduce a spectroscopic absorption imaging method in the UV regime (225–400 nm) to study tin vapor created by irradiating a thin film with a low intensity 108 W cm−2 nanosecond laser pulse, a case inspired by current developments around “advanced target shaping” in industrial laser-produced plasma sources for extreme ultraviolet light. The 4-ns-time-resolved, 10-μm-spatial-resolution images contain a 10-cm−1-resolution spectrum of the vapor in each pixel 100 ns after the vaporization. The images allow us to reveal a homogeneous temperature profile throughout the vapor of around 3000 K. We obtain a density map of the atoms (with a peak density of 5 × 1018 cm−3) and nanoparticles (1012 cm−3 for the best fitting 20 nm radius case), which both are shown to be present in the vapor. For each free atom, approximately three appear to be clustered in nanoparticles, and this composition is invariant over space and density. The density and temperature maps of the free atoms are combined to estimate the electron density (peaking at 1013 cm−3) in the vapor.

Hydrogen embrittlement of iron nanowires: investigating size and orientation dependence on loading behaviour

ABSTRACT With the ever-increasing use and applications of nanowires it has never been more imperative to understand how environmental interactions modify their unique mechanical properties and loading behaviour. While experimental research has shown that atomic hydrogen degrades mechanical properties through hydrogen embrittlement, results are limited and often do not directly quantify the hydrogen concentration or consider small diameter nanowires. In this study, we have used molecular dynamics simulations to the study the effect of atomic hydrogen on iron nanowires with various orientations and diameters. Results demonstrate that with increasing hydrogen concentration there is a clear reduction in the elastic modulus and yield stress as compared to the hydrogen free case for all diameters and orientations considered. In addition, this reduction in mechanical properties appears to exhibit a size dependence, with larger reductions being found in nanowires with larger cross-sectional diameters. We suggest that smaller diameter nanowires, with a higher ratio of surface to bulk atoms, are more influenced by free surface atoms than lattice distortions from atomic hydrogen. As this ratio of surface to bulk atoms is decreased, the larger diameter nanowires become less affected by free surfaces and more susceptible to the effect of atomic hydrogen.

A Review on Medicinal uses of Moringa oleifera

There are about thirteen species of Moringa trees in the family Moringaceae. Moringa oleifera Lam. (synonym: Moringa pterygosperma Gaertn.) is the most widely known species. All part of the Moringa tree is useful in some way and people depends on it for their livelihood. The leaves of the Moringa tree are an excellent source of Nutrients like Minerals, Protein and Vitamins (A and C). Moringa tree has approximately 46 antioxidants and it is one of the cheapest sources of natural anti-oxidants. Anti-oxidants supply the free atoms needed by the human body and mitigate the effect of free radicals. M. oleifera contains active compounds such as flavonoids, tannins, saponins, alkaloids, phenolics, and triterpenoids which possess antibacterial effects. Moringa leaves contains flavonoids and tannins that are thought to have anti-inflammatory effects Moringa oleifera has high mineral and protein content and has been previously investigated for its potential in treating different oral soft tissue diseases. Present review summarises the various medicinal uses of Moringa oleifera.
 Keywords: Moringa oleifera, Anti-oxidants, Oral diseases, dentistry

Hierarchical Structuring of Black Silicon Wafers by Ion-Flow-Stimulated Roughening Transition: Fundamentals and Applications for Photovoltaics.

Ion-flow-stimulated roughening transition is a phenomenon that may prove useful in the hierarchical structuring of nanostructures. In this work, we have investigated theoretically and experimentally the surface texturing of single-crystal and multi-crystalline silicon wafers irradiated using ion-beam flows. In contrast to previous studies, ions had relatively low energies, whereas flow densities were high enough to induce a quasi-liquid state in the upper silicon layers. The resulting surface modifications reduced the wafer light reflectance to values characteristic of black silicon, widely used in solar energetics. Features of nanostructures on different faces of silicon single crystals were studied numerically based on the mesoscopic Monte Carlo model. We established that the formation of nano-pyramids, ridges, and twisting dune-like structures is due to the stimulated roughening transition effect. The aforementioned variety of modified surface morphologies arises due to the fact that the effects of stimulated surface diffusion of atoms and re-deposition of free atoms on the wafer surface from the near-surface region are manifested to different degrees on different Si faces. It is these two factors that determine the selection of the allowable "trajectories" (evolution paths) of the thermodynamic system along which its Helmholtz free energy, F, decreases, concomitant with an increase in the surface area of the wafer and the corresponding changes in its internal energy, U (dU>0), and entropy, S (dS>0), so that dF=dU - TdS<0, where T is the absolute temperature. The basic theoretical concepts developed were confirmed in experimental studies, the results of which showed that our method could produce, abundantly, black silicon wafers in an environmentally friendly manner compared to traditional chemical etching.

Tunable Diode Lasers for Analytics and Diagnostics

Continuous-wave diode lasers (DLs) with tunable emission wavelengths have become extensively used in various fields of analytical spectroscopy and diagnostics. Working in the near and mid-IR spectral region, tunable diode lasers are particularly effective in detecting simple molecules, making them invaluable for environmental monitoring, industrial process control, and diagnostics of subsonic and supersonic gas flows. However, the lack of commercial diode lasers operating in the spectral region shorter than 400 nm has restricted their applicability to elemental analysis, as many resonance lines of free atoms of elements lie in the region 250–400 nm. This review aims to highlight various applications of continuous diode lasers, which are lesser-known to analytical chemists. We briefly overview their main characteristics and discuss their advantages, enabling their successful implementation in traditional analytical spectroscopy tasks, as well as for diagnosing parameters of remote gas objects, including combustion processes in mixing gas flows.

Tunable Diode Lasers for Analytics and Diagnostics

Continuous-wave diode lasers (DLs) with tunable emission wavelengths have become extensively used in various fields of analytical spectroscopy and diagnostics. Working in the near and mid-IR spectral region, tunable diode lasers are particularly effective in detecting simple molecules, making them invaluable for environmental monitoring, industrial process control, and diagnostics of subsonic and supersonic gas flows. However, the lack of commercial diode lasers operating in the spectral region shorter than 400 nm has restricted their applicability to elemental analysis, as many resonance lines of free atoms of elements lie in the region 250–400 nm. This review aims to highlight various applications of continuous diode lasers, which are lesser-known to analytical chemists. We briefly overview their main characteristics and discuss their advantages, enabling their successful implementation in traditional analytical spectroscopy tasks, as well as for diagnosing parameters of remote gas objects, including combustion processes in mixing gas flows.

Electrocatalysis of formic acid oxidation on Pt–Ru alloys modified with Pb adatoms

Abstract Catalytic effect of lead adatoms, deposited at under-potentials, in the oxidation of formic acid on platinum ruthenium alloys was discovered. With increasing the degree of coverage with the lead adatoms, the catalytic activity of Pt–Ru electrodes increases, reaches its maximum and subsequently decreases. No firmly adsorbed intermediates at the Pt–Ru surface were observed at the optimal coverage degree. Then, its catalytic activity is about 200 mV higher than that on pure Pt in the current density range of 10−4 mA cm−2 to 10−1 mA cm−2. Two effects are responsible for the catalysis of formic acid oxidation. The lead adatoms decrease the number of assemblies of few adjacent free atoms of Pt, on which firmly bound intermediates should form. Positive residual charge of lead adatoms improves their interaction with oxy species, placed on the adjacent atoms of ruthenium. The established interaction stabilizes the energetic state of these oxy species causing the increase in their concentration. A larger concentration of the oxy species accelerates oxidation of firmly bound intermediates and thus releases the Pt atoms for the oxidation of subsequent molecules of formic acid.