Penetration Of Atoms Research Articles

Role of graphene layers on the radiation resistance of copper–graphene nanocomposite: Inhibiting the expansion of thermal spike

Metal–graphene nanocomposites are expected to have excellent radiation resistance. The intrinsic role of the graphene layers (GrLs) in their performance has not been fully understood. Five copper–graphene nanocomposite (CGNC) systems were used to investigate the detailed mechanisms underpinning this behaviour by atomistic simulation. Results showed that GrLs can reduce the formation, growth, and intensity of the thermal spike of CGNC; this effect became more evident with the increasing number of layers of graphene. The role of the GrLs can be explained by three mechanisms: first, the ultra-strength C–C bonds of graphene hindered the penetration of high-energy atoms, second, the number of recoiled atoms decreased with the increasing number of layers of graphene, and third, the energy dissipation along the graphene planes also indirectly weakened the damage caused to the entire system. These mechanisms may provide a pathway to prevent material degradation in extreme radiation environments.

Improved Long-Term Stability of Transparent Conducting Electrodes Based on Double-Laminated Electrosprayed Antimony Tin Oxides and Ag Nanowires

AbstractWe fabricated double-laminated antimony tin oxide/Ag nanowire electrodes by spin-coating and electrospraying. Compared to pure Ag nanowire electrodes and single-laminated antimony tin oxide/Ag nanowire electrodes, the double-laminated antimony tin oxide/Ag nanowire electrodes had superior transparent conducting electrode performances with sheet resistance ~19.8 Ω/□ and optical transmittance ~81.9%; this was due to uniform distribution of the connected Ag nanowires because of double lamination of the metallic Ag nanowires without Ag aggregation despite subsequent microwave heating at 250°C. They also exhibited excellent and superior long-term chemical and thermal stabilities and adhesion to substrate because double-laminated antimony tin oxide thin films act as the protective layers between Ag nanowires, blocking Ag atoms penetration.

Theoretical Study of Cu Intercalation through a Defect in Zero-Layer Graphene on SiC Surface

Cu atom penetration through a defect in zero-layer graphene (ZLG) epitaxially grown on an SiC substrate was theoretically investigated, using density functional theory calculations, as a possible mechanism for pure single-layer graphene formation by Cu intercalation on an SiC surface. Our model calculation predicted that a Cu monolayer formed by Cu intercalation causes a lift of the graphene surface of about 0.2 nm, which supports our previous experimental observation. Our calculations on Cu intercalation through a graphene defect implied the possibility that a transition of the defect shape from a 5–8–5 to a double-vacancy model causes the timing of the passage of the Cu atom through the ZLG surface to reduce the potential barrier for the penetration. In addition, it was found that the SiC substrate stabilizes the Cu atom after penetration via an Si–Cu interaction. Furthermore, a preceding intercalated Cu atom was found to be capable of facilitating subsequent Cu penetration by suppressing its inverse re...

Dissolution of oxygen in polycrystalline palladium at $${P_{{O_2}}}$$ P O 2 = 100 Pa and temperatures of 500 to 950 K

The dissolution of oxygen in polycrystalline palladium Pd(poly) at an O2 pressure of 100 Pa and temperatures of 500–950 K has been investigated by temperature-programmed desorption. At 500 K, the process yields a surface palladium film that includes an oxide-like reconstructed structure on a rarefied metal surface layer. At this temperature, palladium sorbs ~2 monolayers (ML) of oxygen. At 600–800 K, palladium dissolves up to ~140 ML of oxygen as a result of O2 chemisorption on the surface of the oxide film, penetration of Oads atoms under the oxide film, and their diffusion into the metal bulk. The dependence of the amount of oxygen sorbed by Pd(poly) (n) on the time of exposure to an O2 atmosphere is described by a nearparabolic function, n = atb, indicating that oxygen atoms diffuse in the metal lattice. The activation energy of this diffusion, Е dif, is ~83.5 kJ/mol. At high temperatures (800–950 K), palladium sorbs much less oxygen (≤10 ML). This is due to the complete decomposition of the surface oxide film, a process that markedly hampers the insertion of Oads atoms under the surface layer of the metal.

Hydrogen dissociation and incorporation on Mg17Al12(100) surface: A density functional theory study

Hydrogen adsorption, dissociation, and penetration on (in) Mg17Al12 (100) surface are studied extensively by DFT total-energy calculations. The adsorption geometries, dissociation barriers, various diffusion pathways, penetrative processes, and electronic structures were investigated. Results show that the atomic and molecular hydrogen forms prefer to be adsorbed on the Mg3-Mg3 bridge sites (C sites). Hydrogen molecules are dissociated on the surface with the minimum barrier energy of 0.63eV. There are two stages in the process of hydrogen incorporation, which are hydrogen diffusion on the surface and the penetration from the surface into the subsurface. Two possible pathways of atomic hydrogen penetration from surface into subsurface are found. The calculations of electronic structures show that the hybridization between the s orbital of H and the s orbitals of Mg is major. The Mg-Mg bond on the outmost surface is shortened from 4.48Å to 3.30Å after the hydrogen adsorption on C sites, showing the strong interaction between Mg and H atoms.

Molecular dynamic simulations of the high-speed copper nanoparticles collision with the aluminum surface

With the use of the molecular dynamic simulations, we investigated the effect of the high-speed (500 m/s, 1000 m/s) copper nanoparticle impact on the mechanical properties of an aluminum surface. Dislocation analysis shows that a large number of dislocations are formed in the impact area; the total length of dislocations is determined not only by the speed and size of the incoming copper nanoparticle (kinetic energy of the nanoparticle), but by a temperature of the system as well. The dislocations occupy the whole area of the aluminum single crystal at high kinetic energy of the nanoparticle. With the decrease of the nanoparticle kinetic energy, the dislocation structures are formed in the near-surface layer; formation of the dislocation loops takes place. Temperature rise of the system (aluminum substrate + nanoparticle) reduces the total dislocation length in the single crystal of aluminum; there is deeper penetration of the copper atoms in the aluminum at high temperatures. Average energy of the nanoparticles and room temperature of the system are optimal for production of high-quality layers of copper on the aluminum surface.

Effect of Mg addition on mechanical and thermoelectrical properties of Al–Al2O3 nanocomposite

The effects of Mg addition on mechanical thermo-electrical properties of Al–Mg/5%Al2O3 nanocomposite with different Mg contents (0, 5%, 10% and 20%) produced by mechanical alloying were studied. Scanning electron microscopy analysis (SEM), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were used to characterize the produced powder. The results show that addition of Mg forms a predominant phase (Al–Mg solid solution). By increasing the mass fraction of Mg, the crystallite size decreases and the lattice strain increases which results from the atomic penetration of Mg atoms into the substitutional sites of Al lattice. The microhardness of the composite increases with the increase of the Mg content. The thermal and electrical conductivities increase linearly with the temperature increase in the inspected temperature range. Moreover, the thermal conductivity increases with the increase of Mg content.

Dissociation and diffusion of hydrogen on defect-free and vacancy defective Mg (0001) surfaces: A density functional theory study

First-principles calculations with the density functional theory (DFT) have been carried out to study dissociation and diffusion of hydrogen on defect-free and vacancy defective Mg (0001) surfaces. Results show that energy barriers of 1.42eV and 1.28eV require to be overcome for H2 dissociation on defect-free and vacancy defective Mg (0001) surfaces respectively, indicating that reactivity of Mg (0001) surface is moderately increased due to vacancy defect. Besides, the existence of vacancy defect changes the preferential H atom diffusion entrance to the subsurface and reduces the diffusion energy barrier. An interesting remark is that the minimum energy diffusion path of H atom from magnesium surface into bulk is a spiral channel formed by staggered octahedral and tetrahedral interstitials. The diffusion barriers computed for H atom penetration from the surface into inner-layers are all less than 0.70eV, which is much smaller than the activation energy for H2 dissociation on the Mg (0001) surface. This suggests that H2 dissociation is more likely than H diffusion to be rate-limiting step for magnesium hydrogenation.

High-speed collision of copper nanoparticle with aluminum surface: Molecular dynamics simulation

We investigate the effect of the high-speed collision of copper nanoparticles with aluminum surface by means of molecular dynamic simulations. Studied diameter of nanoparticles is varied within the range 7.2–22nm and the velocity of impact is equal to 500 or 1000m/s. Dislocation analysis shows that a large quantity of dislocations is formed within the impact area. Overall length of dislocations is determined, first of all, by the impact velocity and by the size of incident copper nanoparticle, in other words, by the kinetic energy of the nanoparticle. Dislocations occupy the total volume of the impacted aluminum single crystal layer (40.5nm in thickness) in the form of intertwined structure in the case of large kinetic energy of the incident nanoparticle. Decrease in the initial kinetic energy or increase in the layer thickness lead to restriction of the penetration depth of the dislocation net; formation of separate dislocation loops is observed in this case. Increase in the initial system temperature slightly raises the dislocation density inside the bombarded layer and considerably decreases the dislocation density inside the nanoparticle. The temperature increase also leads to a deeper penetration of the copper atoms inside the aluminum. Additional molecular dynamic simulations show that the deposited particles demonstrate a very good adhesion even in the case of the considered relatively large nanoparticles. Medium energy of the nanoparticles corresponding to velocity of about 500m/s and elevated temperature of the system about 700–900K are optimal parameters for production of high-quality layers of copper on the aluminum surface. These conditions provide both a good adhesion and a less degree of the plastic deformation. At the same time, higher impact velocities can be used for combined treatment consisting of both the plastic deformation and the coating.

Zirconium–nickel crystals—hydrogen accumulators: Dissolution and penetration of hydrogen atoms in alloys

The calculation of the free energy, thermodynamic equilibrium equations, and kinetic equations of the intermetallic compound Zr2NiHx has been carried out based on molecular-kinetic concepts. The equilibrium hydrogen concentration depending on the temperature, pressure, and energy parameters has been calculated. The absorption–desorption of hydrogen has been studied, and the possibility of the realization of the hysteresis effect has been revealed. The kinetics of the dissolution and permeability of hydrogen is considered, the time dependence of these values has been found, and conditions for the extremum character of their time dependence have been determined. Relaxation times of the dissolution and permeability of hydrogen into the alloy have been calculated. The calculation results are compared with the experimental data available in the literature.

Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300–400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θSm = 0.2–0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).

On the mechanism of biological activation by tritium

The mechanism of biological activation by beta-emitting radionuclide tritium was studied. Luminous marine bacteria were used as a bioassay to monitor the biological effect of tritium with luminescence intensity as the physiological parameter tested. Two different types of tritium sources were used: HTO molecules distributed regularly in the surrounding aqueous medium, and a solid source with tritium atoms fixed on its surface (tritium-labeled films, 0.11, 0.28, 0.91, and 2.36 MBq/cm2). When using the tritium-labeled films, tritium penetration into the cells was prevented. The both types of tritium sources revealed similar changes in the bacterial luminescence kinetics: a delay period followed by bioluminescence activation. No monotonic dependences of bioluminescence activation efficiency on specific radioactivities of the films were found. A 15-day exposure to tritiated water (100 MBq/L) did not reveal mutations in bacterial DNA. The results obtained give preference to a “non-genomic” mechanism of bioluminescence activation by tritium. An activation of the intracellular bioluminescence process develops without penetration of tritium atoms into the cells and can be caused by intensification of trans-membrane cellular processes stimulated by ionization and radiolysis of aqueous media.

Core/shell formation and surface segregation of multi shell icosahedral silver-palladium bimetallic nanostructures: A dynamic and thermodynamic study

Core/shell formation and surface segregation of multi shell icosahedral bimetallic silver-palladium nanostructures with the size of 55 and 147 atoms were studied by using the Molecular Dynamics simulations, and calculating Helmholtz free energy changes in the penetration of palladium atoms from shell to core, core to shell transition of silver and melting temperatures by using statistical mechanical densities of states. In 55 atoms icosahedra, two core–shell motifs, Ag13Pd42 and Pd13Ag42 with their isomers Pd13(Pd29Ag13) and Ag13(Ag29Pd13) were considered. Similarly in 147 atoms icosahedra, all mutations corresponding to the occupations of either silver atoms or palladium atoms in the core, inner shell or outer shell and their isomers generated by interchanging thirteen core atoms with thirteen atoms of the other type in the inner and outer shells were considered. It is found that the palladium-core clusters are more stable than the silver-core clusters and cohesive energy increases with the palladium composition. Phase transition of each cluster was studied by means of constant volume heat capacity. The trend in variation of melting temperature is accordance with the energy trend. Helmholtz free energy changes in palladium penetration, core to shell transition of silver and in surface mixing and segregation revealed the thermodynamic stability of the formation of PdcoreAgshell structures especially at silver rich environment and the surface segregation of silver.

Defect-Mediated Reduction in Barrier for Helium Tunneling through Functionalized Graphene Nanopores

We investigate the separation of helium isotopes by quantum tunneling through graphene nanopores, recently proposed as an alternative to conventional methods for 3He production. We propose here a novel defective nanopore created by removing two pentagon rings of a Stone–Thrower–Wales (STW) defect, which significantly decreases the helium tunneling barrier by 50–75%. The barrier height is fine-tuned by adjusting the effective pore size, which is achieved by pore rim passivation using an appropriate functionalizing atom. This fine-tuning leads to positive deviation in the tunneling probability of 3He compared to that of 4He in the low-energy region, and thereby to high selectivity and transmission of the former isotope. It is found that fluorine-passivated nanopores restrict helium atom penetration because of their highly reduced pore size. Defective nanopores in nitrogen- and oxygen-passivated structures exhibit relatively high transmission values of 10–3 for the oxygen variant and improved selectivity val...

Structural evolutions of supported Co clusters with different configurations on the Cu(010) substrate

Structural evolutions of Co561 clusters supported on the Cu(010) substrate were studied by molecular dynamics simulation using an embedded atom method. Energy, snapshot, pair distribution function and epitaxial factor were used to analyze the effects of supported position, configuration and temperature on the structural evolutions. It is found that the energy of the cluster changes significantly with varying the supported position and the original configuration. The most stable supported position is (111) facet. As a function of configuration the stability decreases in the order: icosahedron > truncated octahedron > decahedron > cuboctahedron > sphere. Supported (111) facet changes to stack along the (100) of substrate. Epitaxial growth on the substrate occurs for all configurations. The epitaxial temperature and the amount of epitaxial atoms are related to the configuration. The epitaxial growth is adverse to the stability of the cluster, while the epitaxy has no effect on the crystal structure of the supported cluster. The energy of the cluster is reduced by the epitaxial growth and atomic penetration into the substrate but is enhanced by the distortion of the cluster on the substrate.

Effects of idling time between depositions of organic layers and metal electrode in organic photovoltaic device

Deposition of metal cathode in organic photovoltaic (OPV) devices is known to cause serious metal atom penetration into the active layers and as a remedy, exciton blocking layer (EBL) is implemented. It is found that the metal penetration through EBL can be controlled by optimizing the idling time between the depositions of EBL and cathode layers. Both electrical and optical data show that the resistance of BPhen layer (EBL) to metal (Mg:Ag) penetration increase with increasing idling time. Also, significant variation in power conversion efficiency (PCE) is observed in subphthalocyanine chloride (SubPc)/fullerene (C60) based organic photovoltaic (OPV) cells by simply adding idling time as an additional control parameter. Device with optimized BPhen thickness and idling time resulted in a PCE of 2.8% whereas that of no idling time consideration has PCE limited at 2.3%. These observations are attributed to slow processes of self-organization in BPhen after their depositions.

Ab initio and empirical modeling of lithium atoms penetration into silicon

A process of lithium atoms penetration into silicon (100) subsurface layers was investigated with the help of DFT method. It was shown that, while the concentration of lithium adatoms on reconstructed (100) silicon surface is low, the bonding energy of lithium atoms in the subsurface layers is smaller than the bonding energy on the surface, so lithium atoms are unlikely to migrate into the crystal. When the (100) silicon surface is covered by 2 layers of lithium, migration into the subsurface layer becomes favorable. In addition to this, the reconstruction of the surface changes to the form with symmetric dimers as the concentration increases. Thus, all possible lithium migration paths become energy-wise equal, so the rate of lithium atom transfer into silicon crystal rises.In addition to the ab initio calculations, an ad-hoc empirical interatomic potential was developed and the kinetics of lithium diffusion into silicon were studied. It was shown that lithium penetration proceeds in a layer-by-layer way with a sharp border between undoped and lithiated silicon. This is accounted for the fact that, once a tetrahedral interstice is occupied by a lithium atom, the migration barriers between the adjacent interstices become lower and the rate of diffusion increases.

Adsorption and reaction of silver on an oxidized Si(0 0 1) surface

The adsorption and reaction of silver on an oxidized Si(001) surface were investigated on the basis of Si 2p, Ag 3d and O 1s core-level photoemission measurements at room temperature (RT). We compared the present results with those obtained in the case of titanium in our previous study. We found that silver on an oxidized Si(001) surface at RT causes a reduction in the intensity of the Si1+ and Si2+ states and an increase in the intensity of the Si3+ and Si4+ states. Based on an analysis of the Ag 3d and O 1s states, we concluded that the change in the Si 2p oxidized states upon silver adsorption is due to charge transfer rather than conformation change, although the applicability of the charge transfer scheme may be dependent on the thickness of the silver layer. We also deduced that penetration of silver atoms through a thin silicon oxide film occurs.

TOP-electrode-eliminated organic bi-stable devices and their two switching modes in different atmospheres

An OBD device fabrication method without top electrode deposition is presented to investigate organic bi-stable mechanisms, showing that the bi-stable phenomenon can appear without penetration of metal atoms into the organic layer. Two switch modes, unipolar switch usually present in organic devices and bipolar switch usually present in both organic and inorganic devices, were found in the same organic device when measured in nitrogen and air atmospheres, respectively. It has been observed that pre-bias of the opposite polarity promotes the switch in air atmosphere. Atomic force microscopy showed protrusions could form at the anode/organic interface. A possible mechanism relating needle-tip formation to atmospheres is proposed, which could unify both organic and inorganic memory behaviors.

Gamma-ray energy buildup factor calculations and shielding effects of some Jordanian building structures

Abstract The shielding properties of three different construction styles, and building materials, commonly used in Jordan, were evaluated using parameters such as attenuation coefficients, equivalent atomic number, penetration depth and energy buildup factor. Geometric progression (GP) method was used to calculate gamma-ray energy buildup factors of limestone, concrete, bricks, cement plaster and air for the energy range 0.05–3 MeV, and penetration depths up to 40 mfp. It has been observed that among the examined building materials, limestone offers highest value for equivalent atomic number and linear attenuation coefficient and the lowest values for penetration depth and energy buildup factor. The obtained buildup factors were used as basic data to establish the total equivalent energy buildup factors for three different multilayer construction styles using an iterative method. The three styles were then compared in terms of fractional transmission of photons at different incident photon energies. It is concluded that, in case of any nuclear accident, large multistory buildings with five layers exterior walls, style A, could effectively attenuate radiation more than small dwellings of any construction style.