Atomic Energy Research Articles

Neural Network Model for Predicting the Atomization Energy of Multi-Atomic Molecules Based on Sorted Coulomb Matrices

Neural Network Model for Predicting the Atomization Energy of Multi-Atomic Molecules Based on Sorted Coulomb Matrices

Simulation for Elucidating a Formation Mechanism of 6-Coordinated Si in Phosphate Glass

Phosphate glasses are materials that are expected to have a wide range of applications, including highly ion-conductive materials in fuel cells and biomaterials that supply therapeutic ions. Diffusion of ions in glasses plays an important role in designing glasses for these applications. The diffusion of protons is one of the most important properties of fuel cells, and the diffusion of network-modified cations such as Na+ and Ca2+ ions is closely related to glass dissolution and hydration reactions. In general, these diffusion properties are strongly dependent on the atomic-scale glass structure. We found that the difference in the morphology of PO4 tetrahedra (P-Qn : number of bridging oxygen) greatly affects the diffusion of protons and Na+ ions in phosphate glass, where these ions can diffuse much more easily near P-Q2 than near P-Q3 , and suggested that ionic conductivity and glass solubility can be designed by controlling the P-Qn distribution of phosphate glasses [1]. We also suggested that the P-Qn distribution can be controlled using 6-coordinated Si (6cSi), which is formed in phosphate glasses containing more than 40 mol% P2O5 [2]. However, the formation mechanism of 6cSi is not clear. In this study, we aim to elucidate the formation mechanism of 6cSi in phosphate glasses based on first-principles molecular dynamics (MD) simulations.The glass models for 55.0P2O5-21.3SiO2-23.7Na2O (mol%) were generated by quenching from the melt using classical MD simulations with the DL POLY [3] program. Subsequently, first-principles MD simulations using the SIESTA code [4] were performed to observe the reaction process from 4cSi to 5/6cSi. Atomic energies were calculated using orbital decomposition of the total energy by the OpenMX code [5]. For these electronic structure calculations, a localized basis with the GGA-PBE functional was used.In obtained models, atomic energies for non-bridging oxygen (NBO) are higher than those for bridging oxygen (BO). In the first-principles MD simulation, the formation of chemical reaction from "4cSi + P-Q2 " to " 5/6cSi + P-Q3 " was observed as shown in Fig. 1. The energy decreases by the change from a NBO in P-Q2 to a BO in P-Q3 is larger than the energy increase by the change for 4cSi to 5c/6cSi.It will be possible to design highly functional glasses by applying the 6cSi formation mechanism and controlling the amount of 6cSi formed.Reference:[1] K. Takada, T. Tamura, H. Maeda, and T. Kasuga, Phys. Chem. Chem. Phys. 23, 14580 (2021). [2] K. Takada, T. Tamura ,and T. Kasuga, RSC Adv. 12, 35043 (2022). [3]T. Todorov et al., J. Chem. 16, 1911 (2006). [4] J. Solar et al., J. Phys. Cond. Matt. 14, 2745 (2000). [5] T. Ozaki, Phys. Rev. B 67, 155108 (2003). Figure 1

High Sensitivity of Energy Dispersive X-Ray Spectroscopy Measurement Using Liquid Cell with Electron Transmittance Window Ultra-Thinned by a Gas Cluster Ion Beam

In recent years, enclosing liquid in a “liquid cell” (Fig. 1) has made it possible to analyze the chemical composition of the liquid sample and map samples in the liquid-solid interface using XPS, EDX, SEM in ultra-high vacuum (UHV). The most important part of the cell is the electron transmission window that allows electrons to input to or extract from the liquid sample. Silicon nitride (SiNx) is the most suitable material as the window, which has excellent mechanical properties. R. Endo et. al. has successfully measured the concentration of CsCl solution using a SiNx window with the film thickness of 5 nm1. However, the transmittance of 1 keV photoelectron is about 10% with the thickness of SiNx membrane. When the membrane thickness is decreased to 2 nm, the transmittance can be improved to more than 40%, which means that even higher sensitivity can be achieved. However, the burst pressure must be 1 atm or more because the membrane needs to perform enclosing a liquid sample in UHV. In previous research, we demonstrated low damage etching of an SiNx film using gas cluster ion beam (GCIB) for thinning the window2. Herein, GCIB is composed of aggregates of several thousands of atoms, and the energy of the individual atoms in the GCIB reduces to several eV/atom with an acceleration voltage of several kV. This enables irradiation on the target surface with little damage. Combining O2-GCIB irradiation and exposure of acetylacetone (Hacac) gas enable reactive etching of SiNx2.In this study, we utilized the above techniques to ultra-thin SiNx films and investigate whether the low-damage irradiation effect of GCIB is effective for SiNx films. In addition, Proof-of-principle of high sensitivity in liquid sample detection using ultra-thinning SiNx films is demonstrated using SEM/EDS.We have evaluated the burst pressure of ultra-thinned SiNx membranes of TEM window chips (SiMPore, Inc.) by reactive etching with O2-GCIB and Hacac gas, where the thickness was originally 11 nm. The SiNx membrane was also etched in the same way using 400 eV Ar+ beam, and the burst pressure was evaluated. These irradiation doses were controlled so that the remaining SiNx membrane thickness was 4.5 nm. As a result, the burst pressure was 1 atm in the case of Ar+ beam, whereas it was 2.5 atm in the case of the GCIB etching. Therefore, it was found that low damage irradiation of GCIB was valid for thinning SiNx membrane.We sealed pure water in the liquid cell shown in Fig. 1 and performed EDS measurement. When electron beam with the energy of 5 keV was injected at the SiNx/water, generated characteristics X-ray of oxygen which photon energy is 0.52 keV could be observed. On the other hands, no O peak was observed in the SiNx/Si region. This result indicates that the O peak originated from the pure water under the SiNx membrane. Next, we carried out the measurements on a pristine SiNx membrane (t = 11 nm) and the GCIB-etched SiNx membrane (t = 4.5 nm), and compared their O peak characteristic X-ray intensities. Herein, the incident electron energies were 1.0 and 1.5 keV. The peak intensity of the GCIB-etched SiNx membrane was 1.6 times stronger than that of the pristine membrane at 1.5 keV. At 1.0 keV, the O peak was observed in GCIB-etched SiNx, but not in pristine SiNx. This is because the penetration depth of electrons in the SiNx film decreases with decreasing electron energy. From the above results, we have shown that the ultrathin SiNx membrane thinned by GCIB could be used for highly sensitive detection of pure water. Acknowledgement This work was supported by JSPS KAKENHI Grant Numbers 23K13236 and 22K04930.

Generalized rate theory for void and bubble swelling and its application to δ-plutonium

A rate theory for void and bubble swelling is derived that allows both vacancies and self-interstitial atoms to be generated by thermal activation at all sinks. In addition, they can also be produced by displacement damage from external and internal radiation. This generalized rate theory (GRT) is applied to swelling of gallium-stabilized δ-plutonium in which α-decay causes the displacement damage. Since the helium atoms produced also become trapped in vacancies, a distinction is made between empty and occupied vacancies. The growth of helium bubbles observed by transmission electron microscopy in weapons-grade and in material enriched with Pu238 is analyzed, using different values for the formation energy of self-interstitial atoms (SIA) and two different sets of relaxation volumes for the vacancy and for the SIA. One set allows preferential capture of SIA at dislocations, while the other set gives equal preference to both vacancy and SIA. It is found that the helium bubble diameters observed are in better agreement with GRT predictions if no preferential capture occurs at dislocations. Therefore, helium bubbles in δ-plutonium will not evolve into voids. The helium density within the bubbles remains sufficiently high to cause thermal emission of SIA. Based on a helium density between two to three helium atoms per vacant site, the sum of formation and migration energies must be around 2.0 eV for SIA in δ-plutonium.

Reactive Force-Field Molecular Dynamics Study for Analysis of Silicon Nanocrystal Formation Process in Silicon Oxide Film

Recently, Tunnel Oxide Passivated Contact (TOPCon) solar cells using ultra-thin silicon oxide (SiO x ) films as passivation films have attracted attention due to the high conversion efficiency of 25.7% [1]. Generally, thick SiO x films exhibit excellent passivation performance and lead to long-term reliability of the solar cells[2]. However, in TOPCon solar cells, the thickness of the passivation film is limited to 1~2 nm due to the high electrical resistance of the SiO x film. Therefore, a new SiO x film (named NATURE contact) with improved conductivity through silicon nanocrystals (Si NCs) have been developed by Tsubata et al. [3]. The left figure shows the structure of NATURE contact. It consists of three SiO x layers with different oxygen concentrations. The Si NCs formed in the thin Si-rich layer in the center functions as a carrier transport pathway. The passivation film with the NATURE contact has shown a good passivation performance and conductivity even for relatively thick SiO x films. Since the effects of multidimensional process parameters during NATURE contact formation have been neither elucidated nor optimized, there is significant room for performance improvement in NATURE contact. Therefore, it is of crucial importance to understand the atomic level growth process of Si NCs during formation of NATURE contact and its impact of the oxygen concentration and temperature.We employed Reactive force-field molecular dynamics (ReaxFF MD) method, which reproduces chemical reactions using a bond order-dependent concept. The method has been used in studies such as Si deposition simulations [4]. The periodic boundary conditions were applied to the simulation box for all directions in the size of 65 Å × 40 Å × 45 Å. Crystalline silicon was placed throughout the simulation box and the atoms of the simulated Si NC section were fixed in the center of the box. Crystals other than the fixed portion are then made amorphous using the Melt-Quench method. Finally, the fixation was released to allow the entire box to react. Crystallinity was evaluated by the average radius calculated from the number of atoms constituting the crystal. It is noted that the average radius is evaluated up to 25 Å due to the size of the simulation box. Annealing was performed in the following three processes: pre-moistening, amorphization, and crystal growth. We varied the temperature of crystal growth at 1500 - 2500 K and the oxygen concentration at 0 - 5 %. We investigated the effects of temperature and oxygen concentration on the growth of Si NCs in a-SiO x .The right figure shows the transition of the mean radius of the Si NCs at different temperatures. As a result, when the temperature was varied, a peak in the size of crystal growth was observed at 2250 K, and the crystals disappeared at 2500 K. The trend of maximum crystal growth at a certain temperature and the qualitative agreement were experimentally confirmed [5]. This result suggests that the change in the size of Si NCs occurred because the kinetic energy of Si atoms is larger than the energy barrier required from a-Si to c-Si. The initially placed Si NC of 269 atoms was appropriately shaped or grown. This is consistent with the nucleation theory[6]. When the oxygen concentration was increased, no crystal growth was observed. Experiments have shown that increasing oxygen concentration tends to suppress crystallization [3]. This result suggests that the change in the size of Si NCs was caused by the interdiffusion of silicon and oxygen.

Pyrazinamide-based Co(II), Ni(II) and Cu(II) complexes: DFT exploration of structure, reactivity properties and in silico ADMET profiles.

In this paper, we present a theoretical study on the complexation of Co(II), Ni(II), and Cu(II) with a pyrazinamide ligand (PZA), which plays an important role in the treatment of tuberculosis and has biological and pharmacological benefits. It is a hybrid organic/inorganic material involving coordination between a metal ion and PZA ligand containing different coordination sites. This allows it to have different binding modes with metal ions and, therefore, provides a versatile ability to coordinate with metals. This study aimed to optimize the structures of the [M(PZA)2Cl2] complexes using density functional theory (DFT) at the B3LYP/6-311G + (d,p) level and the M06-2X functional is a high-nonlocality functional of double the amount of nonlocal exchange 2X. Various properties, including geometrical parameters, natural bonding orbital (NBO) to determine atomic charges, HOMO-LUMO energies, electronic properties, reactivity (ELF, LOL), NCI-RDG, and molecular electrostatic potential (MEP) on the surfaces of key metal-PZA complexes were determined and described. The AIM method has also been used to examine the chemical bonds. Furthermore, an in silico analysis aiming to explore the ADMET profiles of the compounds under investigation revealed promising aqueous solubility, oral bioavailability and gastrointestinal absorption, in addition to favorable druglikeness non-toxic and non-carcinogenic characteristics. The DFT method was carried out using Gaussian 09 software and GaussView 5.0. Avogadro software was used to define the geometry of the complexes. The Multiwfn program was used to produce scatter plots of the reduced density gradient (RDG), non-covalent interactions (NCI), ELF, LOL, and to define the parameters selected for the topological analysis of the BCPs using Bader's AIM.

Evaluation of the Seismicity Index for Nigerian Nuclear Installations

Seismic Hazard Assessment (SHA) is a quantitative measure of assessing the seismic hazard or risk involved for a given site. The parameter computed for such an assessment is needed for building engineers or national decision makers especially when it concerns nuclear installations. Even though the International Atomic Energy Agency (IAEA) currently makes it mandatory to provide such an index before undertaking any form of development or construction of a nuclear installation, this computation has not been done for Nigeria. Data over long period of time is usually necessary for a quantitative seismic hazard assessment, but because such information is scarce in Nigeria a fractal approach is therefore used in this research. A SHA index called the b-value is evaluated by determining the fractal dimension of the network of locations of recorded past tremor events within Nigeria. In this work a b-value of 0.43 which quantitatively measures the seismic hazard or risk of a given region is computed for Nigeria. Aeromagnetic data was used in producing analytic signal maps that accurately mapped faults that could have been responsible for causing the earth tremors, and the coordinates of these faults or lineament were used in calculating the fractal dimension of the system of faults. The fractal dimension of 0.8568 was obtained by determining the slope of line of best-fit of the plot of the log of the average number of tremor locations <N(R)> within radius R of each location against log of radius R, which was in turn used to determine the b-value. A b-value of 0.43 obtained indicates that Nigeria is in a less seismically active region and this can be used in the IAEA safety guidelines for nuclear installations.

RADIATION PROTECTION WHEN USING SOURCES OF IONIZING RADIATION IN MEDICINE

Problem statement. The use of sources of ionizing radiation (SIR) in medicine is necessary for establishing diagnoses and treating patients, as well as measures for visualization and localization of various formations when using radiopharmaceuticals to study the functions and structure of organs. But when using sources of ionizing radiation, risks from radiation exposure to patients and staff are possible. Such risks are safety concerns in nuclear medicine procedures. The application of SIR requires proper radiation protection in accordance with the norms and rules of nuclear and radiation safety. Purpose of the article is to develop recommendations for improving radiation safety measures in medical institutions of Ukraine on the basis of an analytical review of regulatory and scientific and technical literature on radiation safety when using ionizing radiation in nuclear medicine in the countries of the world. Conclusions. During medical research using sources of ionizing radiation, risks from radiation exposure to patients and staff are possible. Radiation safety should consider: duration of exposure, distance of patients and staff from the source of radiation and use of appropriate protection. Dosimeters for measuring the total radiation dose must be worn by all personnel of the radiology department of the hospital. For interventional radiologists, lead aprons and thyroid shields are the primary means of radiation protection that must be worn at all times during the procedure. It is recommended that criteria for clinical audits be included in standards and accreditation and certification programs related to medical practice using ionizing radiation. It is advisable to introduce the teaching of clinical audit into the initial and continuing education and curricula of the professional training of medical workers, including administrative and managerial profiles. In the radiological laboratories of Ukraine, it is expedient to implement the recommendations of the EU Atomic Energy Commission in accordance with Council Directive 2013/59/Euratom. Clinical audit of medical radiological procedures will provide an opportunity to improve the quality and safety of medical services, as well as patient health care.

Optimization of Input Parameters for Enhanced Production of Technetium-99 using the EXIFON Code

Radioisotopes are critical in nuclear medicine for both imaging and therapeutic applications. In this work, the optimization of input parameters for enhanced production of technetium-99 using the EXIFON code have been studied. The reaction 100Mo(p, 2n)99mTc was examined within an incident proton energy range of 0 - 40 MeV. The calculated excitation function for the reaction channel reached a peak value of 1003.7 mbat about 21.00 MeV incident energy. Results obtained from the EXIFON code were compared with evaluated nuclear cross-sections data (ENDF) and experimentally measured cross-sections data (EXFOR) from the International Atomic Energy Agency (IAEA) nuclear database. Our findings show good agreement with the evaluated nuclear data and disagreement with the experimental data within the investigated energy range.

WAYS TO INFLUENCE THE ECONOMIC REGULATION OF LABOR PROTECTION, TAKING INTO ACCOUNT THE RISK-ORIENTED APPROACH

Statement of the problem. In recent years, the state of safety and working conditions at Ukrainian production facilities has continued to be difficult and dangerous, especially at construction companies (one of the ten most injury-prone industries), as evidenced by official statistics on occupational injuries, while Ukraine is living in a state of war. Huge sums of money from the state reserve funds, the Pension Fund, and the owners of enterprises themselves are spent on eliminating the consequences of industrial accidents, accidents, occupational diseases, and on helping victims and families of those killed at work. Ukraine has adopted many laws and regulations on occupational health and safety, including those that, in accordance with the Association Agreement between Ukraine, on the one hand, and the European Union, the European Atomic Energy Community and their Member States, on the other hand, have adapted Ukrainian legislation to that of the European Union, within the framework of which work is actively underway to implement a risk-based approach at the state level in the system of managing the economic safety and health of employees who are citizens of Ukraine. Business leaders (employers) understand the responsibility for the life and health of employees, the need to create proper, safe and healthy working conditions, and care about the economic development of the business, despite the high risks of today's hazards. Objective. To analyze the most effective ways of economic impact of occupational health and safety regulation, taking into account the risk-oriented approach, while maintaining the economic development of the company. Conclusion. The analysis of the most effective ways of economic impact of occupational health and safety regulation, taking into account the risk-oriented approach, shows that in the current conditions of development of enterprises in our country, it is difficult to find a universal solution that would simultaneously meet the requirements for the budget for financing occupational health and safety measures, the speed and quality of its implementation, and at the same time reduce risks in the field of occupational health and safety at workplaces. Therefore, it is difficult to predict which of these ways plays a primary role and which are acceptable, and how to ensure the efficiency of the entire system. Professional, comprehensive occupational health and safety cost planning will help to find the perfect balance between the measures taken and their economic benefits. The complexity of applying several options for economic regulation of occupational health and safety will allow the company to operate smoothly, without conflicts and have a sustainable operation, which will allow for economic growth, the organization's development strategy for the near future, and will also reduce risks in the field of occupational health and safety by taking effective preventive measures.

The Out‐of‐Plane C─S Bonds Boosting Reversible Redox in Copper Sulfide Cathodes for Ultradurable Magnesium Battery

AbstractAs a typical conversion‐type cathode material, CuS has shown great potential in the field of rechargeable magnesium batteries (RMBs) due to its excellent energy density, stable voltage platforms, and low cost. However, the poor phase conversion reversibility in CuS cathodes has resulted in low Coulombic efficiency and short cycling life, impeding its further development. Herein, an abundance of CS heterointerfaces is meticulously crafted by the CuS nanoparticles anchored on rGO nanosheets (CuS@G). The out‐of‐plane C─S bonds effectively reduce the activation energy of sulfur atoms within Cu‐S tetrahedrons, facilitating the formation of S─S bonds in the Cu₂S crystal structure and driving the reversible phase conversion between Cu₂S and CuS during the charge/discharge process. Furthermore, a more reversible phase conversion could diminish copper ion dissolution induced by volume expansion. Consequently, the CuS@G cathode exhibits one of the most remarkable rate performances to date (160.5 mAh g−1 at 1 A g−1), retaining 64.7% of its capacity after 1000 cycles. Additionally, a durable CuS@G||Mg pouch cell is successfully assembled, delivering a high capacity of 9.5 mAh. These fundamental insights provide valuable guidance for the design of high‐performance conversion cathode materials for next‐generation RMBs.

Investigation on the microscopic mechanism of low-energy argon ion irradiation on calcium fluoride

Calcium fluoride (CaF2) crystals are considered ideal materials for optical windows due to their high UV transmittance and exceptional optical anisotropy. Ion beam processing enables the fabrication of CaF2 crystals with high machining accuracy and minimal damage. This study established molecular dynamics, monte carlo simulations, and theoretical models to explore the processes and mechanisms involved in ion beam machining of CaF2 crystals. It was found that the incident energy and angle of argon ion incidence were closely related to changes in the density and kinetic energy of the recoil atoms. While the increase in the density and kinetic energy of the recoil atoms will improve the processing efficiency, it also leads to the increase in defects and deterioration of surface morphology. Additionally, it was observed that backscattering occurs when ions are not incident vertically. To avoid irregular changes in surface morphology and defects, the incidence angle should be controlled to below 40°, and ionization loss caused by recoil ions should be minimized to prevent drastic temperature fluctuations and significant temperature rises during processing. This paper reveals the sputtering mechanism of CaF2 crystals bombarded by low-energy argon ions under various process parameters, provides guidance for optimization of the ion-beam process, and proposes an innovative research method to understand the evolution of calcium fluoride crystals under argon ion radiation from the atomic perspective. The research results will provide significant theoretical support for optimizing the ion beam processing process and enhancing the material properties.

Calculation of the correlation, relativistic, and QED corrections to the total electron binding energy in atoms and their nuclear charge dependence

Calculation of the correlation, relativistic, and QED corrections to the total electron binding energy in atoms and their nuclear charge dependence

Post-CCSD(T) Thermochemistry of Chlorine Fluorides as a Challenging Test Case for Evaluating Density Functional Theory and Composite Ab Initio Methods.

Quantum chemistry plays a key role in exploring the chemical properties of highly reactive chlorine polyfluoride compounds (ClFn). Here, we investigate the thermochemical properties of ClFn species (n=2-6) by means of high-level thermochemical procedures approximating the CCSDT(Q) and CCSDTQ5 energies at the complete basis set limit. We consider total atomization energies (TAEs), Cl-F bond dissociation energies (BDEs), F2 elimination energies (F2 elim.), ionization potentials (IPs), and electron affinities (EAs). The TAEs have significant contributions from post-CCSD(T) correlation effects. The higher-order triple excitations, CCSDT-CCSD(T), are negative and amount to -0.338 (ClF2), -0.727 (ClF3), -0.903 (ClF4), -1.335 (ClF5), and -1.946 (ClF6) kcal/mol. However, the contributions from quadruple (and, where available, also quintuple) excitations are much larger and positive and amount to +1.335 (ClF2), +1.387 (ClF3), +2.367 (ClF4), +2.399 (ClF5), and +3.432 (ClF6) kcal/mol. Thus, the contributions from post-CCSD(T) excitations exceed the threshold of chemical accuracy in nearly all cases. Due to their increasing hyper-valency and multireference character, the ClFn series provides an interesting and challenging test case for both density functional theory and low-level composite ab initio procedures. Here, we highlight the limitations in achieving overall chemical accuracy across all DFT and most composite ab initio procedures.

Crystalline Carbon Deposition on Piston Ring Substrates and Its Effects on Tribological Characteristics, Engine Performance, and Emissions

Electron cyclotron resonance‐chemical vapor carbon deposition technique was altered via incorporation of nitrogen gas in the methane (CH4)‐based plasma, thermal annealing of the substrates, and Arduino‐controlled sample rotating mechanism to bombard the contact surface of the piston ring samples. By placing the substrates very close to the plasma gun, various carbon‐based structures including graphene oxide, nanodiamond, and reduced graphene oxide were successfully deposited. The formed structures were characterized via scanning electron microscopy, atomic force microscopy, Raman spectroscopy, X‐ray diffraction, and energy dispersive X‐ray. Related tribological analyses such as surface hardness‐roughness, coefficient of friction (COF), and wear rate were also carried out on the coated surfaces. The morphology and chemical composition of the worn surfaces were observed via SEM and EDX. The coated samples were installed in a small spark‐ignition engine to determine the effect of coating on brake power (Pe), specific energy consumption (β), carbon monoxide (CO), and unburned hydrocarbon (UHC) emissions. Very promising results of 14% increase in surface hardness, 11% reduction in β, 15% enhancement in Pe, 50% decrease in COF, 12.5% and 9% improvements in CO, and UHC emissions were obtained.

Design of polymers with higher atomization energy with help of machine learning and chemical space generation

Designing materials with desired properties is a challenging task, often hindered by the laborious and expensive nature of conventional experimental methods, especially for large-scale screening. To overcome these limitations, a more viable solution lies in the realm of machine learning (ML) guided exploration. In our current investigation, various ML models were employed to predict the atomization energy of polymers, Hist Gradient Boosting model has emerged as the most effective one. A comprehensive polymer database was generated, and ML model was used for rapid prediction of atomization energy. The generated database of polymers is visualized and analyzed. Structural behavior of chosen polymers is studied using chemical similarity analysis. Synthetic accessibility assessment that done using synthetic accessibility (SA) score has indicated that majority of selected polymers are easy to synthesize. This innovative approach proves to be highly beneficial for the virtual screening of materials, offering a more efficient and cost-effective means for designing and identifying polymers.

Role of sputtered atom and ion energy distribution in films deposited by physical vapor deposition: A molecular dynamics approach

We present a comparative molecular dynamics simulation study of copper film growth between various physical vapor deposition (PVD) techniques: a constant energy neutral beam, thermal evaporation, dc magnetron sputtering, high-power impulse magnetron sputtering (HiPIMS), and bipolar HiPIMS. Experimentally determined energy distribution functions were utilized to model the deposition processes. Our results indicate significant differences in the film quality, growth rate, and substrate erosion. Bipolar HiPIMS shows the potential for an improved film structure under certain conditions, albeit with increased substrate erosion. Bipolar HiPIMS (+180 V and 10% Cu+ ions) exhibited the best film properties in terms of crystallinity and atomic stress among the PVD processes investigated.

Exploration of Hydrogen Storage Exhibited by Rh‐Decorated Pristine and Defective Graphenes: A First‐Principles Study

ABSTRACTWe utilized density functional theory (DFT) to ascertain the storage of hydrogen in Rh‐decorated pristine (PG) and defective graphenes, primarily graphitic‐N (GNG) and pyridinic‐N (PNG). The binding energy of a single Rh atom on PG, GNG, and PNG was found to be −1.87, −2.18, and −4.01 eV, respectively. PG exhibits a weak adsorption energy of hydrogen molecules (−0.06 eV/H2). On the other hand, Rh‐decorated pristine and defective graphenes show incredibly higher hydrogen adsorption energy. As per the latest guidelines of the U.S. Department of Energy (DOE), the Rh‐decorated GNG (Rh@GNG) is found to be the best hydrogen storage material out of the three systems investigated here. The single Rh atom‐decorated GNG adsorbs up to 4H2. Uniform decoration of graphene surfaces with Rh atoms is necessary to improve hydrogen storage performance. Both sides of GNG surfaces are decorated with 8Rh atoms, which can adsorb up to 24H2 molecules, with an average adsorption energy of −0.33 eV/H2. The mechanism of H2 adsorption on the host system has been explored based on DFT‐evaluated deformation of charge density, partial density of states (PDOS), and non‐covalent interaction (NCI) plots. For a better understanding of the adsorption process, the diffusion energy barrier of Rh metal is computed using the climbing image nudged elastic band (CI‐NEB) method, and the thermal stability has been evaluated through ab initio molecular dynamics (AIMD) simulations.

Molecular dynamics assessment of primary damage efficiency for fusion relevant elements

Accurate computational modeling of fusion reactors depends upon precise figures of merit for radiation damage. The Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model, a gold standard parameter for characterizing primary damage in solids, has been shown to overestimate surviving Frenkel defects in materials under high-energy irradiation. Here, we investigate the NRT-dpa model at higher primary knock-on atom (PKA) energies for six pure metals of interest in fusion. We compute updated defect production efficiency values and athermal recombination corrected (ARC)-dpa efficiency parameters for each element, which can be used for increased accuracy in neutronics simulations and fitting other extensions to the NRT-dpa.

Theoretical analysis and predictions for the two-neutrino double electron capture of 124Xe

Abstract We provide a complete theoretical description of the two-neutrino electron capture in 124Xe, improving both the nuclear and the atomic structure calculations. We improve the general formalism through the use of the Taylor expansion method, leading to higher-order terms in the decay rate of the process. The nuclear part is treated with pn-QRPA and interacting shell model (ISM) methods. The nuclear matrix elements (NMEs) are calculated with the pn-QRPA method with isospin restoration by fixing the input parameters so that the experimental decay rate is reproduced, resulting in values significantly lower than in previous calculations. The validity of the pn-QRPA NMEs is tested by showing their values to be comparable with the ones for double-beta decay with the emission of two antineutrinos of 128,130Te, which have similar pairing features. Within the ISM, we reproduce the total experimental half-life within a factor of two and predict the capture fraction to the KK channel of about 74%. We also predict the capture fractions to other decay channels and show that for the cumulative decay to the KL1–KO1 channels, a capture fraction of about 24% could be observed experimentally. On the atomic side, calculations are improved by accounting for the Pauli blocking of the decay of innermost nucleon states and by considering all s-wave electrons available for capture, expanding beyond the K and L1 orbitals considered in previous studies. We also provide improved atomic relaxation energies of the final atomic states of 124Te, which may be used as input for background modeling in liquid Xenon experiments.