High Atomic Density Research Articles

COHERENCE ASSEMBLY IN STRUCTURES WITH HEAVY METAL CLUSTERS

A crystallographic analysis of two structures, monoclinic Nа8[{Re4(PO)4}(CN)12]⋅18H2O⋅CH3OH (I) and orthorhombic [(C6H5)4P]4 [Ta6I12(CN6)] (II), in which clusters of heavy atoms are significantly rarefied in space, so that their mutual arrangement cannot be explained only in terms of chemical interaction, has been performed. In structure I the crystallographic planes with a high atomic density (“skeletal” planes) are located in the regions with dhkl = 10–5.5 Å and dhkl 3 Å. The planes in which atomic groups [Re4(PO)4] (playing the role of unified bulk objects) are concentrated are in fact selected in the first region. In the second region, ordering is implemented at the level of individual atoms. A crystallographic analysis showed that the structure basis is determined by the sites of heavy Re cations. A striking fact is that there are 1152 subcells and only 32 Re atoms per unit cell in this structure; i.e., only the fraction of 1/144 provides the basis of structure stability. In structure II “skeletal” planes are also absent in the range of dhkl from ∼7 to ∼4 Å. The planes in the range of large dhkl characterize cluster ordering, whereas the planes in the range of small dhkl characterize ordering of separate atoms. The geometry and local symmetry of the cluster group (Та6 octahedron) dictates the basis of translational symmetry—unified sublattice of sites, most of which are free of these atoms. The considered structures demonstrate the key role of heavy atoms in the formation of translational symmetry—the fundamental difference of the crystalline state from other condensed states. The newly formed structure retains partially local symmetry of cores (templates) of atomic groups, bound by strong chemical interactions, including the interactions between heavy and light atoms. The process of formation of a crystal structure from randomly oriented and randomly located templates—coherence assembly—is implemented according to the laws of dynamics of elastic media, where masses of atoms rather than their chemical characteristics are important.

Li vaporization behavior and mechanical properties of Li8ZrO6 under high temperature reducing atmosphere

Li8ZrO6 sintered compacts are one of the promising candidates for innovative tritium breeding materials from the viewpoint of lithium density, but there are concerns such as a decrease in lithium atomic density and mechanical strength due to Li2O vaporization. In this study, we fabricated a two-phase mixed sintered body of Li8ZrO6 with a high lithium atomic density, as the main component, and relatively a large amount of Li2O, and thermally annealed it in an environment simulating actual use conditions to vaporize lithium. It is shown that this material is stable at 320°C, which is the main temperature in the blanket space, Li2O vaporizes and part of Li8ZrO6 changes to Li6Zr2O7 at least above 700°C, and vaporization of Li2O occurs more rapidly to finally become to a single phase of Li2ZrO3 at 800−900°C. In addition, it is shown that this material has a higher lithium density than Li2TiO3, one of the Japanese candidate materials, in a wide temperature range below 770 °C during the expected period of practical use of three years. Finally, it is concluded that loading Li8ZrO6-based material and Li2TiO3 in the high and low temperature regions, respectively, achieves the highest lithium density.

High Density Single Fe Atoms on Mesoporous N-Doped Carbons: Noble Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acidic and Alkaline Media.

It remains a challenge to develop efficient noble metal-free electrocatalysts for the oxygen reduction reaction (ORR) in various renewable energy systems. Single atom catalysts have recently drawn great attention as promising candidates both due to their high activity and their utmost atom utilization for electrocatalytic ORR. Herein, the synthesis of an efficient ORR electrocatalyst that is composed of N-doped mesoporous carbon and a high density (4.05 wt%) of single Fe atoms via pyrolysis Fe-conjugated polymer is reported. Benefiting from the abundant atomic Fe-N4 sites on its conductive, mesoporous carbon structures, this material exhibits an excellent electrocatalytic activity for ORR, with positive onset potentials of 0.93 and 0.98V in acidic and alkaline media, respectively. Its electrocatalytic performance for ORR is also comparable to that of Pt/C (20 wt%) in both media. Furthermore, it electrocatalyzes the reaction almost fully to H2 O (or barely to H2 O2 ). Additionally, it is durable and tolerates the methanol crossover reaction well. Furthermore, a proton exchange membrane fuel cell and a zinc-air battery assembled using it on their cathodedeliver high maximum power densities (320 and 91mW cm-2 , respectively). Density functional theory calculation reveals that the material's decent electrocatalytic performance for ORR is due to its atomically dispersed Fe-N4 sites.

Geometric Tuning of Single-Atom FeN4 Sites via Edge-Generation Enhances Multi-Enzymatic Properties.

Single-atom nanozymes (SAzymes) are considered promising alternatives to natural enzymes. The catalytic performance of SAzymes featuring homogeneous, well-defined active structures can be enhanced through elucidating structure-activity relationship and tailoring physicochemical properties. However, manipulating enzymatic properties through structural variation is an underdeveloped approach. Herein, the synthesis of edge-rich Fe single-atom nanozymes (FeNC-edge) via an H2 O2 -mediated edge generation is reported. By controlling the number of edge sites, the peroxidase (POD)- and oxidase (OXD)-like performance is significantly enhanced. The activity enhancement results from the presence of abundant edges, which provide new anchoring sites to mononuclear Fe. Experimental results combined with density functional theory (DFT) calculations reveal that FeN4 moieties in the edge sites display high electron density of Fe atoms and open N atoms. Finally, it is demonstrated that FeNC-edge nanozyme effectively inhibits tumor growth both in vitro and in vivo, suggesting that edge-tailoring is an efficient strategy for developing artificial enzymes as novel catalytic therapeutics.

Investigation on spatial distribution of atomic density in a supersonic planar symmetric gas jet by simulations

As a special gas target with large aspect ratio, the planar symmetric gas jet has attracted some interests in High Harmonic Generation (HHG). It can be produced by gas adiabatic expansion through a supersonic slit nozzle into vacuum. In this work, the spatial distributions of atomic density are investigated in detail along the short side, the long side and the gas jet flow of the planar symmetric argon gas jet based on ANSYS Fluent. The results indicate that along the long side, the planar symmetric jet provides the advantages of high atomic density and the large dimension of uniform atomic density distribution. The density distribution profile is similar to the Gaussian one along the short side. The atomic density at the center of the jet outside the nozzle is lower and decreases much faster than that expected by idealized straight streamline model due to the lateral expansion of gas jet at slit nozzle width.

TALIF at H− ion sources for the determination of the density and EDF of atomic hydrogen

The production of H− ions in negative ion sources relevant for particle accelerator facilities and neutral beam injection systems is based predominantly on the surface conversion of H atoms at a low work function surface covered with caesium (the plasma grid (PG)). Therefore, the H atom density n H and energy distribution function (EDF) close to the PG determine the amount of surface produced H− ions. As a direct method for the density and EDF determination, two-photon absorption laser induced fluorescence (TALIF) on H atoms was implemented at the ion source of the teststand BATMAN Upgrade (BUG) being the first time that this was accomplished at an H− ion source. Several challenges had to be overcome concerning the application of the diagnostic at the complex facility and the evaluation of the fluorescence signals against a bright H background. The observed line profiles suggest a Maxwellian EDF with an H atom temperature of K. The presence of highly energetic H atoms (measured by optical emission spectroscopy, (OES)) could not be resolved by the TALIF system due to the insufficient signal-to-noise ratio. Atomic densities were measured for H2 and D2 plasmas for varying ion source parameters at BUG resulting in values between m−3 and m−3 for hydrogen. For the operation with deuterium, higher atomic densities are observed for similar ion source parameters which agree well with the previous results obtained with OES.

Atomic and electronic structures of interfaces between amorphous (Al2O3)1−x(SiO2)x and GaN polar surfaces revealed by first-principles simulated annealing technique

We report first-principles molecular-dynamics calculations with the simulated annealing technique that clarify the atomic and electronic structures of the semiconductor–insulator interfaces consisting of GaN (0001) and (0001¯) faces and the amorphous (Al2O3)1−x(SiO2)x. We confirm that the obtained interfaces are free from dangling bonds, as predicted by our previous calculations, irrespective of the thickness of the amorphous (Al2O3)1−x(SiO2)x layer. This is due to the high atomic density and large mean coordination number near the interfaces caused by atomic diffusion from inside of the insulator to the interfaces. The calculated local density of states of the (Al2O3)1−x(SiO2)x/GaN system quantitatively shows clear band offsets and, more importantly, the absence of deep states in the GaN energy gap. Interestingly, we find that the band alignment causing the offset is not abrupt at the interface but varies gradually near the interface, predicting the existence of transition layers. We determine the thicknesses of the transition layers in the (Al2O3)1−x(SiO2)x/GaN system to be about 10 Å. We argue that those structural characteristics prevent the formation of the dangling-bond origin carrier traps at the interface, and this is a superior feature of the (Al2O3)1−x(SiO2)x as a gate oxide for the GaN-based metal–oxide–semiconductor devices.

Gas Chromatography Mass Spectrometry based metabolomic investigation on five different rice cutivars (Oryza sativa L.) under different induced Cadmium stress

Heavy Metals (HMs) are naturally occurring elements with high atomic weight and density. In this study, the metabolite profiling of five different indica rice varieties namely, IR-36, Triguna, IR-64, Muktasree and Ajit exposed to cadmium stress in concentrations from 0 µmolL−1, 25 µmolL−1, 50 µmolL−1 and 100 µmolL−1 has been performed using GC-MS. The score plots of PCA, PLS-DA and OPLS-DA analyses showed clear discrimination between control and Cd-treated seedlings of each variety. GC-MS based metabolomic study specified that HM like cadmium exposure could cause changes in metabolite levels mainly on amino acids, organic acids, sugars and their derivatives, phenolics, nitrogen bases and purine metabolites. These metabolomic responses are related with a reduction in shoot and root growth i.e, their photosynthetic capacity especially in IR-36, Triguna, IR-64 and Ajit variety. Only Muktasree showed a consistent increase in shoot and root length in the course of Cd exposure. Biochemical pathway analyses also demonstrated that exposure to cadmium affected the secondary metabolism pathways along with primary metabolism.

Construction of dense H-bond acceptors in the channels of covalent organic frameworks for proton conduction

Two-dimensional (2D) COFs with a high density of oxygen atoms along the pore walls as a host loaded with H3PO4facilitated the formation of hydrogen-bond networks along the pores, further facilitating proton transport.

Groundwater contamination status in Malaysia: level of heavy metal, source, health impact, and remediation technologies.

Groundwater is defined as water that exists underground in voids or gaps in sediments and is extracted for human consumption from aquifers. It is critical to our daily lives because it contributes to the sustainability of our natural ecosystem while also providing economic benefits. Heavy metals are metallic compounds with a relatively high atomic weight and density compared to water. In Malaysia, heavy metal contamination of groundwater has become a concern due to rapid population growth, economic development, and a lack of environmental awareness. Environmental factors or their behaviors, such as density, viscosity, or volume, affect the distribution and transportation of heavy metals. The article discusses the difficulties created by the presence of heavy metals in groundwater supplies and the resulting health problems. Additionally, remediation methods are discussed for managing contaminated water to preserve the ecological environment for current and future generations, as well as their advantages and disadvantages.

PdAu Nanosheets for Visible-Light-Driven Suzuki Cross-Coupling Reactions.

Combining a two-dimensional (2D) morphology and plasmonic photocatalysis represents an efficient design for light-driven organic transformations. We report a one-pot synthesis of surfactant templated PdAu nanosheets (NSs). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses show the formation of 2D PdAu structures was initiated through nanoparticle seeds dispersed in the alkyl ammonium salt surfactant which acted as a template for the growth into NSs. The PdAu NSs were used for visible-light-enhanced Suzuki cross coupling. The PdAu bimetallic NSs outperformed monometallic Pd NSs and commercial Pd/C in room-temperature Suzuki cross-coupling reactions. The high catalytic activity is attributed to a combination of the 2D morphology giving rise to plasmon-enhanced catalysis and a high density of surface atoms, the electron-rich Pd surface due to alloying, and the presence of weakly bound amines. A comparative study of surfactant-assisted NSs and CO-assisted NSs was also carried out to assess the influence of surface ligands on the catalytic and photocatalytic enhancement of NSs with similar morphology. The surfactant-assisted NSs showed substantially superior performance compared to the CO-assisted for room-temperature Suzuki coupling reactions.

Intermetallic Pd3Pb nanobranches with low-coordinated surface atoms for highly efficient ethanol oxidation reaction

Pd based bimetallic nanocrystals (NCs) with low-coordinated surface atoms endow a tremendous ability to modify electronic properties and have the synergistic effect to improve electrocatalytic performance. Among various bimetallic NCs with different compositions, intermetallic Pd-Pb NCs can improve the poisoning tolerance of surface active sites during electrocatalytic reactions. In addition, Pb can provide abundant oxygen-containing species (OHads) and has the ability to cleavage the C–C bond during electrocatalysis that can hinder the production of COads intermediate species, thereby improving ethanol oxidation reaction (EOR) performance. Herein, we report a wet-chemical method for synthesizing highly uniform Pd3Pb nanobranches (NBs). The growth process of Pd3Pb NBs was controlled using ascorbic acid as a reductant, oleylamine as a solvent, 1-octadecene as a surfactant, and ammonium bromide as a shape-directing agent. Their unique NB morphology makes them suitable as electrocatalysts, attributed to the effective adsorption of ethanol and (OH)ads and enhanced removal capability of intermediates adsorbed on the active site of Pd3Pb NBs due to the intermetallic Pd–Pb composition and high density of low-coordinated surface atoms in Pd3Pb branches that can enhance EOR in alkaline media. The prepared Pd3Pb NBs exhibited significantly higher mass activity than Pd3Pb nanocubes and commercial Pd/C catalysts.

Crystallization behavior and defect analysis on induction growth of hexagonal GaN in isothermal relaxation

Gallium nitride (GaN) plays a vital role in the devices of many fields, including communication, display, and lighting. The key to fabricating high-performance GaN devices lies in the growth quality of GaN, exploring the growth mechanism is crucial. In this study, molecular dynamics was used to simulate the induced crystallization processes of wurtzite crystals of GaN based on solid-liquid models. Additionally, the results were studied using a variety of methods for investigating its growth mechanism and perform defect analysis. The results show that the qualities of the crystal growth at low temperatures are not optimal, with a high density of defective atoms and dislocations density, and disordered structures form. The lamellar structure with the overlapping arrangement of the wurtzite and zinc-blende structures forms at high temperatures, where the crystal growth quality is better than that at low temperatures. Dislocation and void defects are observed in the system, however, the number of these two defects changes in opposite trends during the relaxation process. Void defects are more conducive to structural stability than the formation of dislocations and the random arrangement of disordered atoms. This research can contribute to a further understanding of the crystal formation of GaN.

Surface Assessment via Grid Evaluation (SuAVE) for Every Surface Curvature and Cavity Shape.

The surface assessment via grid evaluation (SuAVE) software was developed to account for the effect of curvature in the calculations of structural properties of chemical interfaces regardless of the chemical composition, asymmetry, and level of atom coarseness. It employs differential geometry techniques, enabling the representation of chemical surfaces as fully differentiable. In this article, we present novel developments of SuAVE to treat closed surfaces and complex cavity shapes. These developments expand the repertoire of curvature-dependent analyses already available in the previous version of SuAVE (e.g., area per lipid, density profiles, membrane thickness, deuterium-order parameters, volume per lipid, and surface curvature angle) to include new functionalities applicable to soft matter (e.g., sphericity, average radius, principal moment of inertia, and roundness) and crystalline porous materials (e.g., pore diameter, internal void volume, total area, and the total void volume of the unit cell structure). SuAVE can accurately handle chemical systems with high and low atom density as demonstrated for two distinct chemical systems: the lipid A vesicle and a set of selected metal–organic frameworks. The SuAVE software v2.0 is fully parallel and benefits from a compiler that supports OpenMP. SuAVE is freely available from https://github.com/SuAVE-Software/source and https://www.biomatsite.net/.

Evaluation of TlBr semiconductor detector in gamma camera imaging: Monte Carlo simulation study

Among the detector materials available at room temperature, thallium bromide (TlBr), which has a relatively high atomic number and density, is widely used for gamma camera imaging. This study aimed to verify the usefulness of TlBr through quantitative evaluation by modeling detectors of various compound types using Monte Carlo simulations. The Geant4 application for tomographic emission was used for simulation, and detectors based on cadmium zinc telluride and cadmium telluride materials were selected as a comparison group. A pixel-matched parallel-hole collimator with proven excellent performance was modeled, and phantoms used for quality control in nuclear medicine were used. The signal-to-noise ratio (SNR), contrast to noise ratio (CNR), sensitivity, and full width at half maximum (FWHM) were used for quantitative analysis to evaluate the image quality. The SNR, CNR, sensitivity, and FWHM for the TlBr detector material were approximately 1.05, 1.04, 1.41, and 1.02 times, respectively, higher than those of the other detector materials. The SNR, CNR and sensitivity increased with increasing detector thickness, but the spatial resolution in terms of FWHM decreased. Thus, we demonstrated the feasibility and possibility of using the TlBr detector material in comparison with commercial detector materials.

Investigation of the Gamma-ray Shielding Performance of CuO-CdO-Bi2O3 Bentonite Ceramics.

The purpose of this research is to identify the radiation shielding capability of ceramics adding CuO, CdO, and Bi2O3 with diverse wt (%). The chemical compositions of the raw ceramics were documented through Energy Dispersive X-ray “EDX” techniques. For aesthetic appeal and solidification, CuO has been chosen to be added to ceramic. Moreover, in the interest of increasing the radiation shielding ability, the high atomic number and density of both CdO and Bi2O3 were suggested for the raw ceramics. To obtain the morphological features of the prepared ceramic samples, a Scanning Electron Microscope, or SEM, was utilized. To verify the experimental results, the MCA value obtained from the Phy-X software was compared to the experimental value collected from the HPGe detector. At energies 0.06 MeV, 0.662 MeV, 1.173 MeV, and 1.333 MeV the linear and mass attenuation coefficients of the prepared ceramics have been measured using a high purity germanium “HPGe” detector as well as three different point sources. Moreover, the relationship between ln(I) and the thickness of the ceramics has been presented here, and the comparison between the LAC of the prepared ceramics with other materials has also been displayed. Bentonite ceramic containing CuO (15 mol %)-CdO (15 mol %)-Bi2O3 (20 mol %) with density 3.6 showed the lowest HVL, MFP, and TVL at all studied energies, yet pure Bentonite ceramic containing only CuO (50 mol %), having density 3.4, presented the greatest values. Hence, it can be concluded that the addition of CdO and Bi2O3 enhances the radiation shielding ability.

Co-Exsolution Method Via Seeded Effect for Catalytically Active Anode in Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) have great potential in terms of reducing the operating temperature (400-600oC), because of the low activation energy of proton conduction in oxides compared to oxygen ion conduction. These characteristics provide a pathway to overcome the limitation of conventional SOFC (600-1000oC) such as durability, degradation of catalysts. However, poor catalyst activity at low operating temperatures still remains a problem to be solved. One promising way to improve catalytic activity is in-situ exsolution of various metal nanoparticles. Exsolved nanoparticles not only increase the active catalytic area but also have excellent resistance to thermal agglomeration and carbon coking. Unfortunately, it is difficult to achieve a high population density of metal nanoparticles due to the low exsolution kinetics (diffusion, nucleation) in the anode atmospheres of PCFC. In this study, we designed an A-site deficiency proton-conducting oxide, Ba0.9(Zr0.1Ce0.7Y0.1Yb0.1)0.95M0.05O3-d, as a host material to maximize exsolution behaviors. In addition, a co-exsolution strategy with Cu, which has the highest reducibility among transition metals, was introduced to achieve a high population density of exsolved atoms at low temperatures. A single doped Ni metal in the designed host material exhibited a population density value of 1.13 particles/um2 in reducing atmosphere at 600oC. The single doped Cu metal showed 24.1 particles/um2, but Co-doped with Ni and Cu metal produced the highest particle population of 98.31/um2, which is 87 times greater than a single Ni doping. These results follow the seeded growth mechanism induced by the additional surface energy of pre-exsolved Cu. This suggests a new synergy effect on exsolution phenomena that enhances segregation and nucleation kinetics Figure 1

Dielectric engineering for improvement of mobility and photoelectric performance in 2D BiI3

Two-dimensional (2D) bismuth triiodide (BiI3) has been emerging as a potential layered material for optoelectronic applications due to its air stability and high atomic density. Although much effort has been devoted to improvements of carrier mobility, conductivity and photoelectric response, performance is still very limited. Here, we report a simple and scalable strategy for greatly improving the electrical and optical properties of 2D BiI3 through high-κ dielectric engineering. Upon covering with a high-κ dielectric oxide (Al2O3), air isolation and dielectric screening effects can lead to the reduction of the contact barrier, passivation of trap states, and suppression of Coulomb scattering. As a result, BiI3-based phototransistors can increase carrier mobility by three orders of magnitude and improve photoresponsivity by three orders of magnitude up to 8.05 × 103 A W−1. This work develops a new 2D BiI3 material and efficient dielectric engineering for improving mobility and photoelectrical performance, expanding the family of 2D materials and offering a promising strategy for potential nano-device applications.

Inexpensive and highly controlled growth of zinc oxide nanowire: Impacts of substrate temperature and growth time on synthesis and physical properties

Zinc oxide nanowires (ZnO NWs) were synthesized using a simple reactive-evaporation method without the use of catalysts. The NWs growth was precisely controlled by adjusting the experimental conditions mainly growth times and substrate temperatures. These experimental parameters are crucial for the growth of NWs. The typical diameter and length of the highly crystalline NWs obtained are several tens and several hundred nanometers, respectively. The nature of early-stages growth, morphology, structure and photoluminescent properties of the NWs grown at low temperatures have been explained and give the basic reasons behind these growth mechanisms. Self-organized ZnO nuclei are primarily formed on FTO pits due to high density of Zn atoms. It can be ascribed to vapour-solid with an area selected growth of NWs which provide a continuous pathway for carrier transport due to direct contact with the substrate. These features are crucial for the application of electronic devices, solar cells, etc.

Controlling the mechanical properties and corrosion behavior of biomedical TiZrNb alloys by combining recrystallization and spinodal decomposition

Excellent comprehensive mechanical properties and corrosion resistance of TiZrNb equiatomic ratio medium-entropy alloy were obtained through recrystallization and spinodal decomposition. In addition to solid solution strengthening and recrystallization, the excellent mechanical properties can also be attributed to the hindering effect of nanoprecipitation formed via spinodal decomposition on the movement of dislocations. The high atomic arrangement density due to spinodal decomposition reduces the surface energy of the alloy passivation film, thereby increasing the activation energy of dissolution and the bonding energy between atoms, which improve the corrosion resistance and stability of the alloy passivation film. This work provides a new strategy to control the mechanical properties and corrosion resistance by combining recrystallization and spinodal decomposition.