Atomic Positions Research Articles

Simulated TEM imaging of a heavily irradiated metal

We recast the Howie–Whelan equations for generating simulated transmission electron microscope (TEM) images, replacing the dependence on local atomic displacements with atomic positions only. This allows rapid computation of simulated TEM images for arbitrarily complex atomistic configurations of lattice defects and dislocations in the dynamical two beam approximation directly from standard atomistic simulation output files. Large-scale massively-overlapping cascade simulations, performed with molecular dynamics, are used to generate representative high-dose nanoscale defect and dislocation microstructures in tungsten at room temperature. We then compare the simulated TEM images to experimental TEM images with similar irradiation and imaging conditions. The simulated TEM shows ‘white-dot’ damage in weak-beam dark-field imaging conditions, in agreement with our experimental observations and as expected from previous studies, and in bright-field conditions a dislocation network is observed. In this work we also compare the simulated images to the nanoscale lattice defects in the original atomic structures, and find that at high dose the white spots are not only created by small dislocation loops, but rather arise from nanoscale fluctuations in strains around curved sections of dislocation lines.

A Review on Binary Alkaline‐Earth Trielides: an Overview of Compositions and Structures, of their Stabilities and Energetics and of Criteria for the Validity of the Zintl‐Concept

AbstractOmitting alloys with a compositional range we present a compilation of binary alkaline earth trielides AExTRy together with results of DFT calculations to estimate total energies and energies of formation in comparison and to analyse the distribution of charges at the atomic positions in a Bader analysis of the electron density. In a comparison of many structures, we furthermore analyse the effect of bonding on this charge distribution and reflect on the real bonding patterns in comparison with our expectations according to the Zintl concept, and we find mechanisms blocking an electron transfer as favoured by the electronegativity differences. We have subjected a variety of structural parameters together with the DFT results to a Principal Component Analysis to explore their relationship which we describe in the form of correlation matrices and biplots. The Zintl rules turn out to be a very slack guideline in rationalizing the structures of these compounds.

Long-range dipole-dipole exchange-induced atomic grating

We propose a theoretical scheme for dipole exchange-induced grating (DEIG) based on a hybrid coherent atomic system. The system consists of an ultra-cold rubidium (87Rb) atomic ensemble and movable Rydberg spin atoms. The optical response of the grating appears as a superposition of three- and four-level configurations, which is similar to the cooperative optical nonlinearity caused by the dipole blockade effect. The far-field diffraction properties of the cooperative optical nonlinear grating are tuned by the probe field (intensity and photon statistics). However, our Rydberg atomic grating uniquely responds to the spatial positions of spin atoms, which offers a novel approach to dynamically control electromagnetically induced gratings (EIG).

DFT formalism studies on the structural and electronic properties of hexagonal graphene quantum dot with B, N and Si substitutional impurities

The study of carbon-based nanostructured materials is a highly active research field, that has made significant progress in the study of twodimensional materials and nanotechnology. The interest in these materials is mainly attributed to the fascinating properties they exhibit, as seen in the case of graphene as a 2D material, as well as emergence on numerous novel 2D materials and their heterostructures. Additionally, there is important interest in systems such as 2D quantum dots. Therefore, this work focuses on the systematic study of graphene quantum dots of various sizes, all within the framework of first-principles density functional theory. We started with the simplest graphene quantum dot (GQD) structure, benzene (C6H6), which consist of six carbon atoms passivated with hydrogen atoms. We then increased its size by adding more aromatic rings, resulting in the following GQD configurations: C24H12, C54H18, C96H24, C150H30 and C216H36. We report the density of states (DOS) and the imaginary part of the dielectric function (ε2) for the system, analyzing both the pristine configuration and the effect of both single and double (boron, nitrogen and silicon, denoted as Sa). The double substitutional atom study was done considering random, ortho-, meta-, and para-director positions just for the C94H24Sa2 GQD. In general, we can conclude that as the GQD increases in size, the HOMO-LUMO energy decreases. Furthermore, it is observed that boron and nitrogen exhibit their expected n-, and p-type doping characteristics, but this differs between single and double Sa substitutions. Additionally, the imaginary part of the dielectric function is highly sensitive to the positions of single and double substitutional atoms, as well as the polarization of incident light. Therefore, we suggest that these differences can be used to clearly determinate the type of substitutional atoms and their positions from optical measurements.

Imino(dialkylamino)isoindolines: Structures and dynamic behavior

In 1956, Elvidge and coworkers investigated the synthesis of a series of isoindoline compounds derived from phthalonitrile. They produced a series of secondary amine-modified isoindolines known as the imino(dialkylamino)isoindolines, and in this report, we revisit this chemistry. In addition to confirming the previously observed reactivity, we structurally characterized three examples and observed a double bond character between the isoindoline carbon atom and the secondary nitrogen atom position. This results in a rotational barrier about this bond, which we observed by NMR spectroscopy and probed using computational methods. The barriers are comparable to those seen in bis-substituted amides.

Halogen Bonding to the π-Systems of Polycyclic Aromatics.

The propensity of the π-electron system lying above a polycyclic aromatic system to engage in a halogen bond is examined by DFT calculations. Prototype Lewis acid CF3I is placed above the planes of benzene, naphthalene, anthracene, phenanthrene, naphthacene, chrysene, triphenyl, pyrene, and coronene. The I atom positions itself some 3.3-3.4 Å above the polycyclic plane, and the associated interaction energy is about 4 kcal/mol. This quantity is a little smaller for benzene, but is roughly equal for the larger polycyclics. The energy only oscillates a little as the Lewis acid slides across the face of the polycyclic, preferring regions of higher π-electron density over minima of the electrostatic potential. The binding is dominated by dispersion which contributes half of the total interaction energy.

In-depth research on azole corrosion inhibitors - effect of N atoms position and quantity on copper corrosion inhibition performance in alkaline environments: Experimental evaluation and theoretical analysis

Copper's superior electrical properties make it ideal for multi-layer interconnections in integrated circuits. Chemical mechanical polishing (CMP) is the main method for achieving copper wiring flatness. However, copper is susceptible to corrosion in glycine-based alkaline polishing solutions. This study examines benzimidazole, indazole, and benzotriazole as corrosion inhibitors for copper in an alkaline environment (pH=9), focusing on the impact of nitrogen atom arrangement on inhibition efficiency. Through electrochemical, contact angle, static corrosion, and surface characterization tests, it's demonstrated that these inhibitors protect copper surfaces effectively. The adsorption of these inhibitors follows the Langmuir equation with a mixed adsorption mode. X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy tests, and density functional theory calculations elucidate the adsorption configuration and corrosion inhibition mechanism. The scope of this research extends beyond merely analyzing the performance of the three corrosion inhibitors; more importantly, it has yielded novel insights that are broadly applicable to the field of corrosion inhibitors. The findings are as follows: 1. The coupled structure of dinitrogen and trinitrogen facilitates charge accumulation, manifesting as the formation of additional Cu-N bonds, which prevents desorption; 2. The multi-nitrogen coupled structures provide sites for the formation of intermolecular hydrogen bonds, which is essential for the establishment of an orderly and dense passivation layer. It is expected that this study will provide valuable insights into the development and design of new and efficient copper corrosion inhibitors.

Microphases deriving from Ba2ZrF8 structure type: III: Structural approach of dis-Sr17Zr9F70, Sr23Zr12F94, Pb29Hf15F118. General model of formation of M′2p-1MpF8p-2 microphases

The domain Sr1-xZrxF2+2x studied at 670 °C between the limits 0.340 ≤ x ≤ 0.353 show the presence of a new phase Sr17Zr9F70 and of modulated phases, all deriving from Ba2ZrF8 structure type. In the same domain studied below 600 °C, Sr17Zr9F70 tends to lose its long range ordering between Sr cations and Sr vacancies, tripling the b lattice parameter; moreover a new monoclinic superstructure Sr23Zr12F94 [a = 3sinβ×a (Ba2ZrF8); b = b (Ba2ZrF8); c = c (Ba2ZrF8), β = 105.31°] is also characterized. The homologous Hf phases are isostructural.With Pb, between 555 and 530 °C, another superstructure Pb29Zr15F118 [a = 5 × a (Ba2ZrF8); b = b (Ba2ZrF8); c = c (Ba2ZrF8] and its isotypic Pb29Hf15F118 are evidenced and their structure is solved in great part with a similar cationic disorder between Pb cations and Pb vacancies. Between 530 and 510 °C, a second much more complex superstructure exists but has not been characterized.Moreover, at 630 °C, single crystals of Pb2HfF8 are obtained which allows to confirm that, contrary to Ba2ZrF8, Pb2HfF8 is non-centrosymmetric (Pn21a space group). but the atomic positions deviate only slightly from centrosymmetry.A general structural model for all these M′2p-1MpF8p-2 (p = 6, 9, 12, 15) microphases is developed.

Thermosetting benzoxazoles with endo-alkynyl groups: Excellent thermal stability and low dielectric loss

In this study, six thermosetting benzoxazole monomers with endo-alkynyl groups are prepared, and the effect of the endo-alkynyl groups and substituent group on the curing behavior and solubility of monomers, and on the thermal properties and dielectric properties of polybenzoxazoles are investigated. Our findings reveal that incorporating endo-alkynyl groups enhances the cross-linked network in the benzoxazole monomers, thereby improving their thermal stability, hydrophobicity, and dielectric constant. However, this modification also results in decreased solubility and curing properties of the monomers. In addition, the position of the fluorine atoms can affect the curing behavior of monomer and the dielectric properties of polybenzoxazoles. When a fluorine atom is positioned ortho to the cyano group, it impedes the curing of the cyanide group, which increases the curing reaction temperature. Moreover, while it is generally believed that the addition of fluorine typically lowers the dielectric constant of a material, the placement of fluorine atoms ortho to the cyano group can lead to overlapping electronic effects. This overlap may increase the polarity of the curing network, which increases the dielectric constant and dielectric loss of the polybenzoxazoles. Among the six thermosetting benzoxazole monomers studied, poly (2 F-JQ) containing m-diethynyl groups exhibit a 5 % thermal decomposition temperature (Td5) of 610 °C, and a low dielectric loss of 0.0045 at 1 MHz. Compared with other polybenzoxazoles, poly (2 F-JQ) possesses a moderate dielectric constant, excellent thermal stability, and extremely low dielectric loss. In summary, this study provides a new approach for preparing resins that feature high-temperature resistance and low dielectric loss.

Porphyrin photosensitizers compatible with both aqueous and non-aqueous conditions: Acid dependent spectral, solubility and photocatalytic properties of meso-tetra(pyridyl)porphyrins

The aerobic photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a specific singlet oxygen quencher was studied in the presence of meso-tetra(aryl)porphyrins (aryl = 2-pyridyl, 3-pyridyl and 4-pyridyl) and their diprotonated and hexaprotonated derivatives to investigate the influence of the position of pyridine nitrogen atom, solvent, core protonation (with HCl or dichloroacetic acid) and full protonation of the porphyrins on their photocatalytic activity and photooxidative stability. The pseudo-first order rate constants (kobs) for the oxidation of DPBF with singlet oxygen were determined to compare the relative activity of the photosensitizers. 1,4-benzoquinone as a scavenger of superoxide anion radical provided evidence for the absence of this species in these photocatalytic systems. The singlet oxygen quantum yields (φΔ) of the porphyrin photosensitizers were estimated by determining the initial rate constants for the oxidation of DPBF. H4T(2-Py)P(Cl)2 and H4T(2-Py)P(CHCl2COO)2 were the most efficient photosensitizers of the series of the meso-tetra(2-, 3- or 4-pyridyl)porphyrins and the protonated derivatives.

Tunable atomic spontaneous radiation in cylindrical waveguide

The chiral interaction between light and matter has brought chiral quantum optics into a flourishing stage. Here, we explore the perfect chiral interaction between the atoms with elliptically polarized dipoles and waveguide modes, and find that ideal unidirectional radiation can be obtained by adjusting the position and polarization of atoms. When there are two waveguide modes in the system, by controlling the polarization of the dipoles, the dipoles can radiate not only the unidirectional single waveguide mode, but also two seperated waveguide modes.

Excitonic correlations in the system of gated metallic wires with the applied Zeeman magnetic field

We have studied the electron–electron interactions in the system composed of two metallic one-dimensional point contact and zero-sized wires, in the applied electric field and exposed to the influence of the external Zeeman magnetic field. The interactions between the electrons within wires have been taken into account within the usual Hubbard model. We have considered different limits of particle-filling on the atomic lattice site positions. We show the existence of the excitonic pairing in this one-dimensional system in different limits of the electron–electron interactions, magnetic field, and temperature. We demonstrate that the usual Hubbard-U interaction leads to strong electron localization, which enhances the local antiferromagnetic order in the system.

The role of local structure and preferential site occupancy on the saturation magnetization of the Y2.97Gd0.03Fe5O12 ferrite

Herein, we present a comprehensive crystallographic and magnetic study of the Gd0.03Y2.97Fe5O12 ferrite, synthesized via the sol–gel method. Rietveld refinement and Raman spectrum confirmed the single-phase cubic structure formation. Furthermore, the atomic positions, the local structure distortion, lattice parameters (12.398(1) Å), volume (1905.6(4) Å3), and the average crystallite size (68.3(9) nm) were also determined. Using a phenomenological model was confirmed that the Gd3+ ions prefer to occupy the dodecahedral sites. The micrographic images obtained by scanning electron and transmission microscopies corroborated the agglomerated coral style of the particles. From the magnetic study, it was verified that the Gd3+ ions induce a negative contribution to the net magnetic moment in the Gd0.03Y2.97Fe5O12 ferrite. In addition, was demonstrated that the a-d super-exchange interaction weakening is not the main mechanism that determines the saturation magnetization for the studied compound. Instead, the negative contribution of the Gd3+ ion’s magnetic moment in dodecahedral sites is the determining physical mechanism of saturation magnetization.

First principles study on the electronic structure and optical properties of Janus WSeTe with defects and strains

A Janus monolayer can be described as a two-dimensional material with distinct anions on either side of each layer. Two of these distinct chalcogen atoms are situated in the mirror-symmetric lattice positions of the transition metal atoms and are referred to as Janus transition metal dichalcogenides (TMDs). This material breaks the out-of-plane mirror symmetry and thus has excellent properties not found in conventional TMDs. However, during material synthesis, it can generate a number of defects that can substantially alter its properties. Therefore, in this article, the changes in the electronic structure and optical properties of Janus WSeTe when generating single vacancy defects, double vacancy defects and antisite defects have been investigated using first principles study. Assess the stability of the material through computations of its phonon spectrum, AIMD simulation and defect formation energy. Analyse its bandstructure, projected density of states, and optical absorption coefficient to present the change in its properties. The results show that the easiest and most stable form of defect is the substitution of Se atom for Te atom. These defect types change the bandgap value in different ways in Janus WSeTe, which further changes the peak optical absorption coefficient. The lattice constants undergo alterations during the defect generation process. For this purpose, we also investigated the changes in the properties of Janus WSeTe and its defects when subjected to biaxial tensile and compressive strains ranging from −9% to 9 %. As the tensile and compressive strains increase, a gradual decrease in the band gap value is observed. Our findings may serve as a theoretical basis for experiments in the synthesis of Janus WSeTe and the development of electronic devices using monolayer Janus WSeTe.

Energetic and spectroscopic properties of n-type and p-type C60 fullerene

C60 organic diodes have received considerable attention as components in low-cost and high-speed rectifiers. Regarding to that the geometric, electronic, and energetic properties, of substitutional C59X and exohedral and endohedral C60X fullerenes (X = B, N) were investigated using DFT method. This work demonstrates for the first time the energy barriers required for passing the doping B and N atoms from inside to outside the cavity of C60 fullerene and vice versa. One exciting finding is the duality behavior of C60B fullerene as n- and p-types in addition to the ability of IR and Raman spectra to distinguish between them. Moreover, the substitutional C59X and the exohedral and endohedral C60X fullerenes (X = B, N) are classified into n-type and p-type C60 fullerenes according to type and position of doped atoms. Finally, the obtained results can open the way for the formation of new organic electronic devices based on C60 fullerene.

Halogen-doped CQDs as a modulation of fractional function sensing in ZIF composites

This study draws inspiration from the partition-function sensing mechanism of plant cells for purifying harmful gas molecules. The size of the pore size of ZIF-8 sieving gas molecules was modulated by halogen-doped carbon quantum dots (CQDs) during the formation of ZIF-8. Notably, the difference in electronegativity of different halogens makes the sieving pore size of ZIF-8 tunable in the nanometer range, which greatly enhances the selectivity of the composite. In addition, the halogen-doped carbon quantum dots modulate the structure, band gap, and impedance of the composites, enabling the detection of specific gases on the order of ppb. Using X-ray photoelectron spectroscopy, simulation data and density-functional theory, we find that halogen-doped CQDs can fine-tune the pore size of ZIF-8 by influencing the chemical bond lengths by affecting the positions of atoms on the imidazole ring. Plants in nature are similarly characterized in that different components act as sensors for characteristic gas components and synergistically promote the adsorption and purification processes of gas molecules. This study provides an innovative means of modifying the structure and properties of ZIF materials and introduces the concept of plant-like gas multi-sensing in the field of gas sensing research.

Unveiling the magic of twist angle: Thermal transport in Two-dimensional Graphene/MoS2/Graphene Heterostructures

Thermal transport properties of two-dimensional vdW heterostructures have attracted considerable research interests in electron-related devices due to their powerful capability of multi-functional integration. Herein, we investigated the in-plane and out-of-plane thermal conductivity of graphene/MoS2 heterostructures under various twist angles utilizing molecular dynamics simulations. It was found that the in-plane thermal conductivity of MoS2 layer in heterostructures decreases with twist angle. Notably, the lowest thermal conductivity occurs at a twist angle of 10.893°, just 47.3 % of that in untwisted MoS2 layers in heterostructure. In addition, the interlayer interfacial thermal resistance between graphene and MoS2 layer increases with the twist angle but decreases with the layer numbers of graphene. The atomic position deviation, potential energy surface, phonon state of density are calculated to reveal the regulation mechanism of thermal conductivity by twist angle. Interestingly, it is found that the twist angles and the layer numbers of graphene can control the atomic vibration arising from potential energy surfaces and phonon transport through the overlap of phonon density of states between graphene and MoS2 layers. This study can provide valuable insights into the thermal conductivity modulation and phonon transport mechanism of heterostructures.

Predicting the One-Particle Density Matrix with Machine Learning.

Two of the most widely used electronic-structure theory methods, namely, Hartree-Fock and Kohn-Sham density functional theory, require the iterative solution of a set of Schrödinger-like equations. The speed of convergence of such a process depends on the complexity of the system under investigation, the self-consistent-field algorithm employed, and the initial guess for the density matrix. An initial density matrix close to the ground-state matrix will effectively allow one to cut out many of the self-consistent steps necessary to achieve convergence. Here, we predict the density matrix of Kohn-Sham density functional theory by constructing a neural network that uses only the atomic positions as information. Such a neural network provides an initial guess for the density matrix far superior to that of any other recipes available. Furthermore, the quality of such a neural-network density matrix is good enough for the evaluation of interatomic forces. This allows us to run accelerated ab initio molecular dynamics with little to no self-consistent steps.

Photonic topological Anderson insulator in a two-dimensional atomic lattice

Disorder in atomic positions can induce a topologically nontrivial phase - topological Anderson insulator (TAI) - for transverse electric optical quasimodes of a two-dimensional honeycomb lattice of immobile atoms. TAI requires both time-reversal and inversion symmetries to be broken to similar extents. It is characterized by a nonzero topological invariant, a reduced density of states and spatially localized quasimodes in the bulk, as well as propagating edge states. A transition from TAI to the topological insulator (TI) phase can take place at a constant value of the topological invariant, showing that TAI and TI represent the same topological phase.

Binding ability of chloride ion with platinum and rhodium dinuclear complex containing ethylenediamine as co-ligand

In this study, the binding capability for Cl− ion was investigated with amidate-bridged platinum–rhodium dinuclear complex axially coordinated PPh3 to the rhodium atoms containing ethylenediamine (=en) as co-ligand. Mixing [PtRhCl3(piam)2(en)]·3H2O (2Cl) with PPh3 and NaPF6 provided [PtRhCl2(piam)2(en)(PPh3)]PF6 (2(PPh3)·PF6) which can bind Cl− ion at the axial position of platinum atom to be [PtRhCl2(piam)2(en)(PPh3)]Cl (2(PPh3)·Cl), where both crystal structures were determined by single-crystal X-ray analyses. UV–vis titration demonstrated that the formation constant of 2(PPh3)·PF6 with Cl− is 1.6 × 103 M−1, significantly smaller than that with NH3 as a co-ligand, which suggests that multinucleation is necessary for effective hydrogen bonds as well as the affinity of metals.