Increase In Number Of Atoms Research Articles

Dominance of the density effects in the magnetic sublevel population and circular polarization of x-ray radiation

On the basis of the fully relativistic distorted-wave treatment of impact excitation by a longitudinally polarized electron beam, we have assessed the influence of density effects on the magnetic sublevel population and circular polarization of x-ray radiation, taking the 1s2p 3P2 1s2 1S0 line of selected He-like Ne8+, Ar16+, and Kr34+ ions as an example. Starting from the most general method of rate equation, we carried out specific analytic expressions in terms of the magnetic sublevel-to-magnetic sublevel collisional-radiative model, corresponding to different states. It is shown that the density contributions to the magnetic sublevel population can be considerable. These dramatic influences also lead to a remarkable decrease in the circular polarization of x-ray radiation, yet the character of which weakens as the incident energy and/or atomic number increases. The Breit interaction and radiative cascade contributions are also estimated, and found to be generally important in these systems. These findings originate a better understanding of the fundamentals of x-ray radiation arising from various kinds of plasmas. Comparisons of our results with other theoretical predictions, when available, are made.

Influence of multipole effects on the cross section and alignment following inner-shell ionization of atoms by a linearly polarized photon

On the basis of the fully relativistic Dirac-Fock treatment of single ionization by a linearly polarized photon with regard to the E1, M1, E2, M2, and E3 multipoles of the radiative field as well as their interference, we have assessed the influence of multipole effects on the cross sections and alignment parameters A20 and A22 of the residual ions, taking the 3p3/2 and 3d3/2 vacancies of selected Zn and Zn-like Kr6+, Cd18+, and Xe24+ ions as examples. Starting from the most general method of density matrix theory, we carried out specific analytic expressions in terms of the reduced matrix elements of multipole fields, corresponding to different ion-core states. It is shown that the multipole contributions to the photoionization cross sections can be considerable, the character of which becomes more evident as the incident energy and/or atomic number increases. These dramatic influences also lead to a remarkable increase in the alignment parameter A20 of the residual ions, yet virtually independent of the nuclear charge for A22. The present results in Coulomb gauge and Babushkin gauge excellently agreed with each other, suggesting that there is a high degree of convergence achieved in this study. Comparison of our results with experimental data and other theoretical predictions, when available, is made.

Fisher information of radial wavefunctions for relativistic hydrogenic atoms

We calculate Fisher information and the inverse participation ratio normalised by the electric binding energy for the relativistic hydrogenic atoms based on the radial wavefunctions in position space. Fisher information rapidly decreases as the atomic number increases, but it increases again for heavy atoms for S1/2 and P1/2 states due to the relativistic effect. We consider not only the ground state but also excited states by numerically evaluating the generalised Laguerre polynomials in the exact Dirac’s relativistic radial wavefunctions. This study contrasts with the previous studies of the relativistic many-electron systems (i.e., ground-state neutral atoms), where numerical densities were employed.

CRYSTAL STRUCTURE AND CHEMICAL BOND IN INTERMEDIATE COMPOUNDS OF Tl2Se–In2Se3–”P2Se4” SYSTEM

Perspective compounds that are widely used in production of working elements for semiconductor IR and laser technology, thermal generation, solar power, are materials based on complex chalcogenide compounds. Special attention is paid to compounds of the M2P2Se6 type, derived from Sn2P2S6(Se6). Modification of the composition of M2P2Se6 type compounds by isovalent substitutions of the chalcogen S®Se, which form the sublattice of the anionic group [P2X6]4–, as well as Sn2+®Pb2+, heterovalent substitutions 2Sn2+®4M1+ (M1 – K+, Na+, Rb+, Tl+, Ag+, Cu+), 2Sn2+®M1++M23+ (M2 – In3+, Sb3+, Bi3+, Fe3+) leads to the formation of new structures with different structure of cation sublattice, which is accompanied by a change in crystal-chemical parameters.Study of physical-chemical interaction in the Tl2Se–In2Se3–“P2Se4” system showed that intermediate complex selenides which melts congruently In2Se3 (1192 К), TlInSe2 (1023 К), Tl4P2Se6 (758 К), In4(P2Se6)3 (880 К), TlInP2Se6 (875 К) form five quasi-binary eutectic type sections with formation of limited solid solution.Crystalstructure studies of complex chalcogenides of the Tl2Se–In2Se3–“P2Se4” system were carried out by a powder method. Refinement of the structural parameters of intermediate compounds was carried out by the Rietveld method. Crystal-chemical parameters of compounds in the Tl2Se–In2Se3–“P2Se4” system are: In2Se3 hexagonal, Р61, a=7.129, c=19.381 A; Tl2Se tetragonal, Р/n, а=8,540; с=12,380 A; TlInSe2 tetragonal, I4/mcm, a=8.064, c=6.833 A; Tl4P2Se6 monoclinic, P121/c1, a=12.239, b=9.055, c=12.328 A, b=98.83о; In4(P2Se6)3 trigonal, R3h, a=6.381, c=20.014; TlInP2Se6 triclinic, P-1(2), a=6.449, b=7.542, c=12.166 A,a=100.72, b=93.63 о, g=113.32 о.The crystal-chemical analysis of the М2P2Se6 type compounds showed that in their structure anionic group of atoms [P2Se6]4– can be isolated in the form of two fused tetrahedron, a pair of P–P from Phosphorus atoms occupy octahedron voids between the planes of Selenium atoms, cations of atoms (Tl, In) occupy position between layers of atoms of anionic groups. In the transition of In4(P2Se6)3®TlInP2Se6®Tl4P2Se6 with a decrease in the total electronegativity of the atoms of the cationic group (an increase in the total number of cations atoms per anionic group [P2Se6]4–), there is a corresponding decrease in the interatomic distances between a pair of Phosphorus P–Р atoms from 3,082 A®2,278 A®2,217 A, as well as the connections of P–Se 2,193¸2,233 A® 2,184¸2,235 A®2,100¸2,246 A, indicating an increase in the stability of the anionic group [P2Se6]4–. For compound Tl4P2Se6 there is a discernible deformation of fused tetrahedron [P2Se6]4–.An analysis of crystal-chemical studies has shown that binary compounds characterized by a mixed type of chemical bond – ionic-covalent. Transition from binary compounds to complex compounds TlInSe2, TlInP2Se6, In4(P2Se6)3 and TlInP2Se6, due to trans-effects in the Tl–P–Se bonds system, increases the polarization of Tl–Se bonds, indicating an increase in contribution ionic component of chemical bonding. The opposite processes is observed for In–Se bonds, the polarization of which decreases, which leads to an increase in the power of the covalent component. An increase in the ion bond between cations of Tl+, In3+ and Se2– anionic groups also leads to decrease in the contribution of the metallic component in the ternary and quartery compounds to binary selenides.

Driven-dissipative quantum dynamics in ultra-long-lived dipoles in an optical cavity

We study the quantum dynamics of many-body arrays of two-level atoms in a driven cavity subject to collective decay and interactions mediated by the cavity field. We work in the bad cavity limit accessible, for example, using long-lived electronic clock states of alkaline-earth atoms, for which the bare atomic linewidth is much less than the cavity linewidth. In the absence of interactions, our system reduces to previously studied models of collective fluorescence. We show that while interactions do not qualitatively change the steady-state properties they lead to a drastic change in the dynamical properties. We find that, for some intervals of driving strengths, the system shows two very distinct types of transient behaviors that depend on the initial state of the system. In particular, there is a parameter regime where the system features oscillatory dynamics with a period of oscillation that becomes much shorter than the duration of the overall transient dynamics as the atom number increases. We use both mean-field and exact numerical calculations of the quantum system to investigate the dynamics.

Theoretical calculation of atomic spectrum for 1s23l4l′ states of beryllium-like ions

Using the saddle-point variation and saddle-point complex-rotation methods, energies, radiative, and Auger rates are calculated for the doubly-excited states 1s23l4l′ of beryllium-like ions. The total wave function is expanded by the restricted variation method to saturate the functional space and improve the nonrelativistic energy. Relativistic corrections and mass polarization effects are taken into account by the first-order perturbation theory. The partial Auger rates for these states are studied. The calculated Auger electron energies are compared with the experimental results which are observed in high resolution electron spectroscopy. The total radiative rates and the total Auger rates for these doubly-excited states 1s23l4l′ in the beryllium-like ions are also analyzed along with the increase of atomic number Z. Calculated results show that the total Auger rates are several orders of magnitude larger than the total radiative rates for these low-Z systems.

Strain effects on the mechanical properties of Group-V monolayers with buckled honeycomb structures

Based on first-principles calculations, we study systematically the ideal tensile stress-strain relations of three monoatomic group-V monolayer two dimensional (2D) materials with buckled honeycomb lattices: blue phosphorene, β-arsenene, and β-antimonene. The ideal strengths and critical strains for these 2D materials are investigated under uniaxial and equibiaxial strains. It is found that the ideal strengths decrease significantly as the atomic number increases, while the critical strains change not so much. In particular, the ideal strength of antimonene along armchair direction is found to exceed Griffith strength limit. The distributions of charge density, buckling heights, bond lengths and bond angles are also studied under different types of strains. It can be concluded that the critical strain is determined by the stretch and rotation of bonds simultaneously. Furthermore, the phonon dispersions, phonon instabilities, and failure mechanism of these materials under three types of strains are also calculated and explored.

Origin of the anomalous trends in band alignment of GaX/ZnGeX2 (X = N, P, As, Sb) heterojunctions

Utilizing first-principles band structure method, we studied the trends of electronic structures and band offsets of the common-anion heterojunctions GaX/ZnGeX2 (X = N, P, As, Sb). Here, ZnGeX2 can be derived by atomic transmutation of two Ga atoms in GaX into one Zn atom and one Ge atom. The calculated results show that the valence band maximums (VBMs) of GaX are always lower in energy than that of ZnGeX2, and the band offset decreases when the anion atomic number increases. The conduction band minimums (CBMs) of ZnGeX2 are lower than that of GaX for X = P, As, and Sb, as expected. However, surprisingly, for ZnGeN2, its CBM is higher than GaN. We found that the coupling between anion p and cation d states plays a decisive role in determining the position of the valence band maximum, and the increased electronegativity of Ge relative to Ga explains the lower CBMs of ZnGeX2 for X = P, As, and Sb. Meanwhile, due to the high ionicity, the strong coulomb interaction is the origin of the anomalous behavior for nitrides.

Molecular discovery of half-metallic one-dimensional metal-organic framework

The metal-organic framework (MOF) is a large family of nanomaterials with tunable structural and electronic properties. Discovering half-metallic MOF can broaden the selection pool of half-metals for specific applications in the areas of electronics and catalysis. In this study, seven one-dimensional first-row transition metal-dithiolene MOFs have been systematically investigated using the first-principles density functional theory method. Our theoretical outcomes reveal that the electrical conductivities of these MOFs are determined by the electronic configurations of the metal cations. They can change from a semiconductor to a half-metal and further to a metal as the atomic number increases. Among all MOFs we considered, Cr(III)/Mn(III)/Fe(III)/Co(III)-dithiolene MOFs are promising candidates for spintronic applications.

Decay processes of doubly-excited 1s23lnl′ 1, 3S resonances of Be-like ions

Energies, radiative and Auger decay rates for the doubly-excited states 1s23lnl′ 1, 3S (n=3–4) of Be-like ions are calculated by the saddle-point variation and saddle-point complex-rotation methods. The configuration structure of the doubly-excited series is checked by the relative contribution to the normalization of the angular-spin components. Relativistic corrections and mass polarization effects are taken into account by the first-order perturbation theory. The partial Auger decay rates and the Auger branching ratios for these states are studied. The calculated Auger electron energies are compared with the high resolution electron spectroscopy. The total fluorescence yield of these doubly-excited states 1s23lnl′ 1, 3S in the Be-like ions are also analyzed along with the increase of atomic number Z.

Ab initio investigation of structural and electronic properties of selenium and tellurium clusters

Structural and electronic properties of selenium (Sen; n = 8–31, 35 and 40) and tellurium clusters (Ten; n = 6–24, 30 and 32) have been investigated within the framework of density functional formalism. Genetic algorithm based code USPEX and molecular dynamics have been used to obtain at least 70 distinct equilibrium geometries for each cluster. Strikingly, all the ground state geometries as well as a few low energy structures are ring like, closed one dimensional structures. Despite the fact that the small clusters of these elements tend to have one dimensional geometries, it is unusual to have such stable ring geometries for large clusters of the order of 40 atoms. Our work brings out a very interesting trend of order–disorder–order transitions in the growth pattern of these clusters. Although, the size of the ring increases with an increase in number of atoms, the variation in the bond angles and bond lengths is rather small. Remarkably, binding energy per atom is almost constant. The nature of bonding has been analyzed by examining individual charge densities of all the molecular orbitals. It turns out that the amount of buckling and the angle between three adjacent atoms involved along the ring plays a crucial role in forming covalent bonds in a variety of ways. The pattern of Eigenvalues of all the clusters show a very interesting character. The “bands” are formed out of almost pure atomic orbitals with negligible hybridization between s and p. The lowest n energy levels show text book like tight binding character having constant width. The manifold of p bands is separated from s band by a large gap, a consequence of large separation between atomic s and p levels. Unlike the case of infinite helix we find that all the character of the occupied p bands show all the three components, px, py and pz. Further, non bonding orbitals are found to lie below the HOMO level.

Diffusion Rates of Components in Metal-Silicides Depending on Atomic Number of Refractory Metal Component

Interdiffusion studies conducted in group IVB, VB and VIB metal-silicon systems are discussed in detail to show a pattern in the change of diffusion coefficients with the change in atomic number of the refractory metal (M) component. MSi2and M5Si3phases are considered for these discussions. It is shown that integrated diffusion coefficients increase with the increase in atomic number of the refractory component when the data are plotted with respect to the melting point normalized annealing temperature. This indicates the increase in overall defect concentration facilitating the diffusion of components. This is found to be true in both the phases. Additionally, the estimated ratios of tracer diffusion coefficients indicate the change in concentration of antisite defects in certain manner with the change in atomic number of the refractory components.

Complexation properties and structural character of lanthanides complexes of O,N-hetero donor ligand BIZA

ABSTRACTComplexation properties of N-methyl-N-tolyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide (MeTolBIZA) with trivalent lanthanides were investigated by spectroscopic titration study and discussed based on structural character determined by X-ray crystallography. As a result, it is revealed that one or two MeTolBIZA molecules coordinate with lanthanide ions as tridentate ligand via two nitrogen atoms in 2-(1H-benzimidazol-2-yl)pyridine moiety and one oxygen atom in amide group. The stability constant of 1:2 metal–ligand complex decreases with increase of atomic number of lanthanide, and the 1:2 complex cannot be formed with heavier lanthanides. This result can be attributed to steric hindrance between ligand molecules.Abbreviations: MeTolBIZA: N-methyl-N-tolyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; An3+: trivalent actinides; Ln3+: trivalent lanthanides; TPTZ: 2,4,6-tris(2-pyridyl)-1,3,5-triazine; BTP: 2,6-bis(1,2,4-triazin-3-yl)pyridine; PTA: N-alkyl-N-phenyl-1,10-phenanthroline-2-carboxamide; BIZA: N-alkyl-N-aryl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; MePhBIZA: N-methyl-N-phenyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; D2EHPA: di-2-ethylhexyl phosphoric acid; EXAFS: extended X-ray absorption fine structure

Gas Breakdown and Discharge Formation in High-Power Impulse Magnetron Sputtering

Discharge behaviors of high-power impulse magnetron sputtering with different targets have been investigated. Distinct current–voltage curves and target current waveforms are observed. Breakdown voltage and the maximum target current show a periodic drop with the increase of atomic number in subgroups and periods. The target current density is found to be mainly affected by the secondary electron emission yield. Thus, its magnitude is unable to directly evaluate the ionization degree of sputtered atoms in high-power impulse magnetron sputtering (HiPIMS) process. In this paper, the interactive influence of secondary electron emission, sputter yield, and ionization energy on the ionization degree of sputtered atoms is discussed based on the analysis of the voltage and current characteristics. As a result, targets can be categorized into three sorts according to the ionization degree: 1) low ionization degree targets, such as Ag and C less than 10%; 2) intermediate ionization degree targets like Cr and Cu with 55% and 35%; 3) Ti, Zr, and Mo targets with the second ionization processes. These results provide institutive operation ranges for the state-of-the-art HiPIMS applications.

The stability and electronic properties of Si-doped ZnO nanosheet: a DFT study

This work deals with stability, structural and electronic properties of perfect ZnO nanosheet and substiutionally doped ZnO nanosheet with Si are simulated and optimized successfully using density functional theory (DFT) with the help of SIESTA program in the generalized gradient approximation (GGA). The substitution atoms have been replaced on the oxygen site in line and zigzag doping. The stability of perfect ZnO nanosheet and ground state structures of Sin-ZnO (n = 1–6) are studied in terms of binding energy, show that a maximum stabilized of one Si in line doping and two Si in zigzag doping due to the dopant located in the center of nanosheet is a more stable. The electronic properties of ZnO nanosheet and Si-doped are discussed using ionization potential, electron affinity, HOMO–LUMO gap, electronegativity, and hardness. The results showed the presence of silicon atoms substitution expands the bond length with respect to perfect ZnO nanosheets. The obtained values of HOMO and LUMO are slightly different and this suggests that different of position dopant play significant roles on electronic properties and large electron affinity at four silicon atoms doped ZnO nanosheet in two cases that it improved the electron more accepting ability. The study of HOMO-LUMO gap reveals that the gap decreases with the increase in number of Si dopant atoms in ZnO nanosheet. These results global gave molecular electronics important electronic applications and help us to replace some oxygen atoms instead of silicon atoms in ZnO nanosheet.

Photocatalytic oxidation of aniline over MO/TiO2 (M = Mg, Ca, Sr, Ba) under visible light irradiation

MO/TiO2 (M = Mg, Ca, Sr & Ba; TiO2: Evonik Aroxide P25) composites were prepared for photocatalytic aniline oxidation under visible light irradiation. The conversion efficiencies of aniline over the samples are revealed as follow order: BaO/TiO2>SrO/TiO2>CaO/TiO2>MgO/TiO2. The combined results of XPS and CO2 TPD indicate that the electron density of lattice oxygen and the surface basicity for the photocatalysts became higher and higher with the atomic number increase of the alkaline metal elements, in accordance with the order of the conversion efficiency. The sample SrO/TiO2 shows the highest nitrosobenzene selectivity. BaO/TiO2 with highest surface basicity may facilitate the further aniline transformation to nitrobenzene and azobenzene, resulting in lower selectivity for nitrosobenzene. Surface complexes formed on the basic sites of the catalysts via aniline chemsorption would be acted as active sites and be excited for the photocatalytic oxidation of aniline under visible light irradiation.

Effect of heating rate, impurity concentration of Cu, atomic number, temperatures, time annealing temperature on the structure, crystallization temperature and crystallization process of Ni1−xCux bulk;x= 0.1, 0.3, 0.5, 0.7

This paper studies the effects of heating rate 4 × 10[Formula: see text] K/s, 4 × 10[Formula: see text] K/s, 4 × 10[Formula: see text] K/s; impurity concentration of Cu on Ni[Formula: see text]Cu[Formula: see text] bulk with x = 0.1, x = 0.3, x = 0.5, x = 0.7; atom number (N), N = 4000 atoms, 5324 atoms, 6912 atoms, 8788 atoms at temperatures (T), T = 300 K; N = 6912 atoms at T = 300 K, 400 K, 500 K, 600 K, 700 K, 800 K; N = 6912 atoms at T = 600 K after time annealing temperature (t), t = 500 ps on the structure, crystallization temperature and crystallization process of Ni[Formula: see text]Cu[Formula: see text] bulk by molecular dynamics (MD) method with interactive embedding Sutton–Chen (ST) and periodic boundary conditions. The structural characteristics were analyzed through radial distribution function (RDF), energy total (E[Formula: see text]), size (l) and common neighborhood analysis (CNA) method; temperature (T), crystallization temperature (T[Formula: see text]), crystallization process through relationship between E[Formula: see text], T. The results showed Ni[Formula: see text]Cu[Formula: see text] bulk and links Ni–Ni, Ni–Cu, Cu–Cu always exist in 03 types structures: FCC, HCP, Amor. When time annealing temperature increases then Ni[Formula: see text]Cu[Formula: see text] bulk moves from a crystalline state to an amorphous state. When increases impurity concentration of Cu in Ni[Formula: see text]Cu[Formula: see text] bulk, then the structure unit number FCC, HCP decreases and then increases, structure unit number Amor increases and then decreases. When atom number (N) increases, decreasing T and increasing time annealing temperature lead to structure unit number FCC, HCP increases, Amor decreases and structural, crystallization temperature, crystallization process of Ni[Formula: see text]Cu[Formula: see text] bulk change.

Three-photon laser excitation of mesoscopic ensembles of cold rubidium Rydberg atoms

The spectra of three-photon laser excitation (according to the 5S1/2 → 5P3/2 → 6S1/2 → 37P3/2 scheme) of mesoscopic ensembles of cold Rb Rydberg atoms in a magneto-optical trap, using cw single-frequency lasers in each stage, have been investigated. The ensembles consisted of 1 to 5 atoms, and their presence was recorded by the selective field ionisation method with postselection according to the number of atoms. The dependence of the spectral shape on the excitation laser pulse duration has been studied. For 2-μs pulses, the minimum spectral width was found to be 1.3 MHz; it was determined by the laser linewidth and the spectral width of laser pulse. For pulses shorter than 0.5 μs, additional spectral broadening and occurrence of Rabi oscillations in the wings of three-photon resonances have been observed, a fact indicative of implementation of coherent three-photon laser excitation of Rydberg atoms. An analysis of the spectra within the four-level theoretical model based on optical Bloch equations showed good agreement between the experimental and theoretical results. The dependence of the shape of three-photon excitation spectrum on the number of recorded atoms was also studied. An increase in the average number of atoms leads to the occurrence of a dip in the single-atom excitation spectra; this dip is due to the specificity of the excitation and detection statistics of Rydberg atoms. The results obtained are important for applications of Rydberg atoms in quantum informatics.

Investigation of bismuth borate glass system modified with barium for structural and gamma-ray shielding properties.

In the present paper, transparent and non-toxic Bi2O3-B2O3 glasses doped with BaO have been prepared by the authors which may replace the standard radiation shielding concretes and lead based commercial glasses for gamma ray shielding applications. The effects of BaO on the structural and optical properties of the prepared glass system have been investigated by Raman, FTIR and UV-Visible techniques. It has been observed that barium plays the role of a modifier and it is responsible for conversion of triangular [BO3] units to tetrahedral [BO4] units along with formation of non-bridging oxygen and increase in ionic character. It also improves the radiation shielding abilities of the glass system. The mass attenuation coefficients for gamma-ray photons at 662 keV energy by using 137Cs radioactive source have been measured by employing narrow beam transmission geometry. This was accompanied by theoretical computation of mass attenuation coefficients in the wide photon energy range varying from 1 keV to 100 GeV. It has been found that values of mean free path and tenth value layer decrease whereas, density and effective atomic number increase with the increase of barium oxide content. As compared with barite concrete and commercial shielding glass RS-360, our prepared Bi2O3 - BaO - B2O3 glasses have shown better gamma ray shielding properties. This implies that the prepared glass system is a better gamma ray absorber and it has the potential for use in gamma-ray shielding applications.

Formation energetics and magnetism in Ca/TM doped CaZrO3: DFT investigation

Spin-polarized density functional theory is used to investigate the formation energetics and magnetic properties of Ca/transition metal TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped CaZrO3 systems. A strong interdependence of formation energy and TM dopant size (ionic radii) is evident, which increases solely with the increase of dopant atomic number. Our results elucidate that Co@Zr, Cr@Zr, Fe@Zr, and V@Zr doped systems show half-metallic nature due to partial filling of d-orbitals with a reasonable charge carrier density of ∼1021 cm−3, while Ca@Zr and Cu@Zr doped systems exhibit p-type ferromagnetism because of deficiency of electrons. In contrast, Sc-dopant reveals as p-type non-magnetic due to strong hybridization. Furthermore, Ti@Zr, Mn@Zr, and Ni@Zr doped CaZrO3 systems, depict non-magnetic behavior. Interestingly, Mn@Zr doped system contains high magnetic moment of 3μB and show insulating nature. The findings of present calculations yield a wide avenue for practical applications of these doped systems in spintronics.