Interaction Of Metal Atoms Research Articles

The influence of metals on the phase transformations of fullerenes at high pressure and high temperatures

Phase transformations in crystalline fullerenes C60 and C70 with additions of two groups of metals (7 at. % each): carbide-forming (V and nichrome Ni20Cr80) and non-carbide-forming (Ag and Ni) at a high pressure of 8 GPa and high temperatures of 500–1100 °C have been investigated by X-ray diffraction and Raman spectroscopy. The measurements were carried out ex situ after a thermobaric treatment. Two groups of phase transformations were found: crystalline fullerenes into amorphous graphite and the formation of carbides VC, V2C and Cr3C2. The addition of V and nichrome stabilizes fullerene molecules and raises the temperature of transformation of crystalline fullerene into amorphous graphite by hundreds of degrees, while the addition of Ag and Ni does not have such an effect. Thus, the described effect is explained by chemical interaction. Carbides in systems with V and nichrome are formed mainly in the interaction of metal with amorphous graphite, and not with crystalline fullerene. The result is explained on the basis of a comparison of the interaction of metal atoms with fullerene molecules and with individual carbon atoms.

Formation of carbides in the interaction of Fe and Al with fullerenes at high pressures and high temperatures

Phase transformations in crystalline and amorphous fullerenes C60 and C70 with additions of Fe or Al (7 at% each) at high pressures of 2 and 8 GPa and high temperatures of 500–1100 °C have been investigated by X-ray diffraction. Two groups of phase transformations were found: amorphous or crystalline fullerenes into disoriented graphite and the formation of carbides Fe3C, Fe7C3, or Al4C3. It was shown that the introduction of Fe or Al significantly increases the transformation temperature of crystalline fullerene and does not affect the transformation of amorphous fullerenes. Carbides in most of the studied fullerene – metal systems are not formed upon the interaction of Fe or Al with crystalline fullerenes, but are formed only upon interaction with disordered graphite. The results obtained are explained on the basis of a comparison of the interaction of metal atoms with fullerene molecules and with individual carbon atoms.

Adsorption and dissociation of CO on metal clusters

Adsorption and dissociation of carbon monoxide on metal clusters M13 (M = Ag, Co, Cu, Fe, Ni and Ru), has been studied. Structure stabilities of metal clusters, adsorption sites, adsorption energies and the activation energies for the dissociation of CO were determined using density functional theory. Cohesive and binding energies of metal atoms in M13 clusters of studied metals were calculated, showing the different strength interaction of metal atoms in each particle. Three active adsorption sites on the M13 particles studied have been identified, showing that CO adsorption with covalent nature can occur on different sites depending of the metal cluster. Charge density difference in the M13-CO interaction on all the adsorption sites of all metal clusters showed a strong accumulation of charge density in the MC bonding. Of the group of metal cluster modeled, Ru13, Cu13 and Co13 present higher adsorption energies. On the other hand, Fe13, Co13 and Ru13 present lower activation energies. In all cases, endothermic behavior of CO dissociation was observed. The initial stages of CO interaction with several metal clusters, in comparison with metal surfaces, is presented.

Effect of light elements impurity atoms on grain boundary diffusion in FCC metals: a molecular dynamics simulation

Effect of carbon and oxygen impurity atoms on diffusion along the tilt grain boundaries with <100> and <111> misorientation axis in metals with FCC lattice was studied by mean of molecular dynamics method. Ni, Ag, and Al were considered as metals. Interactions of metal atoms with each other were described by many-particle Clery-Rosato potentials constructed within the framework of tight binding model. To describe interactions of atoms of light elements impurities with metal atoms and atoms of impurities with each other, Morse pair potentials were used. According to obtained results, impurities in most cases lead to an increase in self-diffusion coefficient along the grain boundaries, which is caused by deformation of crystal lattice near the impurity atoms. Therefore, additional distortions and free volume are formed along the boundaries. It is more expressed for carbon impurities. Moreover, with an increase in concentration of carbon in the metal, an increase in coefficient of grain-boundary self-diffusion was observed first, and then a decrease followed. This behavior is explained by formation of aggregates of carbon atoms at grain boundary, which leads to partial blocking of the boundary. Oxygen atoms had smaller effect on diffusion along the grain boundaries, which is apparently explained by absence of a tendency to form aggregates and lesser deformation of crystal lattice around impurity. The greatest effect of impurities on self-diffusion along the grain boundaries among the examined metals was observed for nickel. Nickel has the smallest lattice parameter, impurity atoms deform its lattice around itself more than aluminum and silver, and therefore they create relatively more lattice distortions in it and additional free volume along the grain boundaries, which lead to an increase in diffusion permeability. Diffusion coefficients along the high-angle boundaries with misorientation angle of 30° turned out to be approximately two times higher than along low-angle boundaries with a misorientation angle of 7°. Diffusion along the <100> grain boundaries flowed more intensively than along the <111> boundaries.

Initial Stages of Metal Films Growth on a SiO2-Cristobalite Surface

Using the density functional theory approach and pseudopotentials we studied energetics and electron structures of metal layers (Al, Cu, Ni, and Cr) deposited on a cristobalite surface. We have found that the properties of the first adsorbed layers decide by interaction of metal atoms with oxygen atoms of a substrate surface. Aluminum as an easily oxidized metal, is characterized by the high adhesion, it is followed by nickel and chromium, and copper closes the studied group of metals. Further plating is characterized by significant reduction of binding energy; the properties of films tend to properties of bulk metals

INTERACTION OF HYDROGEN IMPURITY WITH NANOCRYSTALLINE PALLADIUM AND NICKEL

The interaction of hydrogen atoms with nanocrystalline palladium and nickel in the work was studied by the molecular dynamics method. The nanocrystalline structure of palladium and nickel was created in the model by crystallization from the liquid state at the presence of several specially introduced crystalline embryos. After solidification, the calculation blocks, in addition to the crystalline phase, contained grain boundaries and triple junctions of grain boundaries. The interactions of metal atoms with each other were described by the multi-particle Cleri-Rosato potential constructed in the framework of the tight-binding model. Morse potentials were used to describe the interactions of hydrogen atoms with metal atoms and with each other. The parameters of Morse potentials were calculated from the experimental data of theabsorption energy, the activation energy of the above-barrier diffusion of hydrogen in a metal (at normal and high temperatures), the binding energy with a vacancy, dilatation. According to the results obtained in the present work, at a high concentration of hydrogen (the concentration of 10% from the metal atoms was considered), the hydrogen atoms combine into aggregates, which are formed predominantly near the surface of the metal. The aggregates contained, as a rule, several dozen hydrogen atoms and had low diffusion activity. The binding energy of hydrogen atoms with these aggregates was greater than with the metal crystal lattice or grain boundaries in it. In palladium, hydrogen aggregates were formed farther from the surface than in nickel. Apparently, this is due not so much to the relatively low energy of hydrogen absorption by palladium (–0.1 eV) in comparison with nickel (0.16 eV), but rather to the difference in lattice parameters of the metals under consideration: 3.89 Å for Pd and 3.524 Å for Ni. For the same reason, conspicuously, hydrogen aggregates in a pure crystal lattice were more often observed in Pd than in Ni. In Ni, aggregates, as a rule, were formed in defect areas containing an excess free volume: near the free surface, in grain boundaries and in triple junctions.

THE STUDY OF HYDROGEN INTERACTION WITH PALLADIUM AND NICKEL NANOPARTICLES BY THE METHOD OF MOLECULAR DYNAMICS

Hydrogen interaction with Pd and Ni nanoparticles was studied by the method of molecular dynamics. The metal particle in the model was created by cutting a ball from the fcc crystal. The interaction of metal atoms with each other was described with the aid of the multiparticle Cleri-Rosato potential, constructed within the tight binding model. To describe the interactions of hydrogen atoms with metal atoms and with each other, the Morse potential was used, the parameters of which were calculated from the experimental data of absorption energy, activation energy of the above-barrier diffusion of hydrogen in the metal (at normal and high temperatures), binding energy with the vacancy and dilatations. Temperatures from 300 to 1100 K were considered. During the computer experiment the temperature in calculation block was constant. The concentration of hydrogen atoms introduced into the calculation block corresponded to a pressure of 10 and 20 MPa. The initial positions of the hydrogen atoms in the calculation block (in the metal particle or outside it) did not affect the final equilibrium distribution of hydrogen, which was established after some time of the computer experiment, depending on the temperature. As it was shown by the molecular dynamics simulation, nanoparticles are effective hydrogen accumulator having a high velocity of reversible sorption-desorption process of hydrogen. At room temperature, Pd and Ni nanoparticles sorb substantially all hydrogen which is unevenly distributed in the particle volume in an effort to form aggregates containing a few tens of hydrogen atoms. In the case of Ni particles hydrogen predominantly is located near the surface. In the Pd particles, by contrast, hydrogen strongly connected with the Pd lattice, and at increasing temperature it form larger aggregates. Intensive evaporation of hydrogen from the Pd and Ni particles occurs at temperatures above 700 K. At the same time, according to the obtained data, hydrogen is more strongly associated with the particles of Pd than with Ni particles, and the work that needs to be spent for hydrogen evacuation (desorption) in the case of Pd particles is higher than for Ni particles.

Ab initio studies on the adsorption and implantation of Al and Fe to nitride materials

The formation of transfer material products on coated cutting and forming tools is a major failure mechanism leading to various sorts of wear. To describe the atomistic processes behind the formation of transfer materials, we use ab initio to study the adsorption energy as well as the implantation barrier of Al and Fe atoms for (001)-oriented surfaces of TiN, Ti0.50Al0.50N, Ti0.90Si0.10N, CrN, and Cr0.90Si0.10N. The interactions between additional atoms and nitride-surfaces are described for pure adhesion, considering no additional stresses, and for the implantation barrier. The latter, we simplified to the stress required to implant Al and Fe into sub-surface regions of the nitride material. The adsorption energies exhibit pronounced extrema at high-symmetry positions and are generally highest at nitrogen sites. Here, the binary nitrides are comparable to their ternary counterparts and the average adhesive energy is higher (more negative) on CrN than TiN based systems. Contrary, the implantation barrier for Al and Fe atoms is higher for the ternary systems Ti0.50Al0.50N, Ti0.90Si0.10N, and Cr0.90Si0.10N than for their binary counterparts TiN and CrN. Based on our results, we can conclude that TiN based systems outperform CrN based systems with respect to pure adhesion, while the Si-containing ternaries exhibit higher implantation barriers for Al and Fe atoms. The data obtained are important to understand the atomistic interaction of metal atoms with nitride-based materials, which is valid not just for machining operations but also for any combination such as interfaces between coatings and substrates or multilayer and phase arrangements themselves.

<i>Ab Initio</i> Study of the Oxygen Effect on Magnetic Interactions within 3d Metal Nanowires on Vicinal Rh (553) Surface

We present ab initio study of the magnetic properties of monatomic 3d transition metal (Mn, Fe, Co, Ni) nanowires without and with oxygen atoms on vicinal Rh (553) surface. We considered different experimentally observed submonolayer quantities of oxygen atoms. It was found that monatomic 3d metal nanowires without oxygen are in magnetic states. Within oxidized metal nanowires oxygen atoms affect on the magnetic moments and magnetic interaction of metal atoms. This influence leads to reduced (in the case of Mn, Fe and Co atoms) or quenched (in the case of Ni atoms) magnetic moment for these metal atoms.

Kinetic Monte Carlo simulation of electrodeposition using the embedded-atom method

A kinetic Monte Carlo (KMC) method for deposition is presented and applied to the simulation of electrodeposition of a metal on a single crystal surface of the same metal under galvanostatic conditions. This method utilizes the multi-body embedded-atom method (EAM) potential to characterize the interactions of metal atoms and adatoms. The method accounts for collective surface diffusion processes, in addition to nearest-neighbor hopping, including atom exchange and step-edge atom exchange. Steady-state deposition configurations obtained using the KMC method are validated by comparison with the structures obtained through the use of molecular dynamics (MD) simulations to relax KMC constraints. The results of this work support the use of the proposed KMC method to simulate electrodeposition processes at length (microns) and time (seconds) scales that are not feasible using other methods.

A computational study of the insertion of Li, Na, and Mg atoms into Si(111) nanosheets

Based on first principles calculations, we study the interaction of metal atoms (Li, Na, and Mg) with Si(111) nanosheets of different thicknesses. We show that the chemistry of the interactions is sensitive to both the nanosheet thickness and the dopant–surface distance. Both Li and Na atoms adsorb strongly on the nanosheet surface, accompanied by large charge transfers (∼0.9e) from the metal atoms to surrounding atoms. In contrast, Mg atoms have weak adsorption. Compared to bulk Si, we show that nanosheet Si is expected to improve the charge/discharge rate of Li/Na/Mg-ion batteries. Nevertheless, due to large insertion barriers (up to the prohibitive ∼2.1 and ∼3.1eV for Mg and Na, respectively) and significant energy differences between surface and sub-surface sites (∼1.0 and ∼1.9eV for Mg and Na, respectively), the theoretical capacities of Si for both Na-ion and Mg-ion batteries cannot be achieved at realistic charge/discharge rates.

Synthesis, Structure, Photoluminescence and Thermal Properties of Sodium Ethene‐Bis‐Nitrobenzenesulfonate

AbstractAbstract. Sodium ethene‐bis‐nitrobenzenesulfonate, [Na2(ENS)·6H2O]n(1) was synthesized through coupling reaction of o‐nitrotoluenesulfonic acid in NaOH solution and characterized by single crystal X‐ray diffraction, elemental analysis, IR and 1H NMR spectroscopy, XRPD, DSC and TGA (where ENS2– = ethene‐bis‐nitrobenzenesulfonate). The asymmetrical unit of (1) consists of two octahedral NaI ions, and the neighboring metal centers are bridged by μ2 water molecules resulting in the formation of an inorganic tetranuclear unit. The tetranuclear units were connected through the ENS2– ligands into a 2D topology net. The weak π–π stacking and H‐bonding interactions further stabilized the structure. The crystals of (C7H6NO5S)–·(H5O2)+ (2) were obtained by post‐processing the unreacted raw material to recycle. Furthermore, the rigidity and the conjugation effect of the aromatic system in compound 1 were increased through the coordination interactions of metal atoms to ligands, resulting in the emission coming from ligand enhanced with red‐shifting about 9 nm of the maximal wavelength. The conjugation effects and the steric arrangement of the substituent groups play the main role to the luminescence intensity and red‐shift effect.

Charge transfer and formation of reduced Ce3+ upon adsorption of metal atoms at the ceria (110) surface

The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce(3+), while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.

The role of the organic layer functionalization in the formation of silicon/organic layer/metal junctions with coinage metals

The design of silicon/alkyl layer/metal junctions for the formation of optimal top metal contacts requires knowledge of the mechanistic and energetic aspects of the interactions of metal atoms with the modified surface. This involves (a) the interaction of the metal with the terminal groups of the organic layer, (b) the diffusion of metal atoms through the organic layer and (c) the reactions of metal atoms with the silicon surface atoms. The diffusion through the monolayer and the metal catalyzed breakage of Si-C bonds must be avoided to obtain high quality junctions. In this work, we performed a comprehensive density functional theory investigation to identify the reaction pathways of all these processes. In the absence of a reactive terminal group, gold atoms may penetrate through a compact alkyl monolayer on Si(111) with no energy barrier. However, the presence of thiol terminal groups introduces a high energy barrier which blocks the diffusion of metals into the monolayer. The diffusion barriers increase in the order Ag < Au < Cu and correlate with the stability of metal-thiolate complexes whereas the barriers for the formation of metal silicides increase in the order Cu < Au < Ag in correlation with the increasing metallic radii. The reactivity of gold clusters with functionalized Si(111) surfaces was also investigated. Metal silicide formation can only be avoided by a compact monolayer terminated by a reactive functional group. The mechanistic and energetic picture obtained in this work contributes to understanding of the factors that influence the quality of top metal contacts during the formation of silicon/organic layer/metal junctions.

Electron donor–acceptor properties of metal atoms interacting with pterins

Many animal colorants have been described as scavengers of free radicals. Pterins, also known as pteridines, represent one of these pigments. These molecules are analogous to guanine and consist of heterocyclic compounds, which have the highest nitrogen content of any colorant analyzed from animals. One of the mechanisms used for scavenging free radicals is that of the electron transfer reaction, which can be analyzed in terms of the electron donor–acceptor properties of these molecules. The interaction of metal atoms with pterins modifies the properties of pterins, in such a way that they manifest altered electron transfer properties. In this paper, Density Functional Approximation calculations are used to analyze the interaction of pterins (pterin, isoxanthopterin and sepiapterin) with metal atoms (M = Cu, Ag, Au, Zn, Cd or Hg). Neutral (in gas phase), cations and di-cations (in water) are analyzed in order to assess the effect of the positive charge in the M–pterin interaction. Evidently, there is a correlation between the dissociation energy involved in the removal of the metal atom and the ionization energy of the metal atom. Those pterins containing certain cationic metals (such as Zn, Cd and Hg) are depicted as better antioxidants than other pterins, and likewise the interaction with Cu, Ag and Au (di-cations) produces compounds that may act as electron acceptors. The electron transfer reaction between metal–pterins and HO˙ is exergonic only when pterins are bonded to Zn, Cd and Hg (cations). This new information may contribute to elucidate the way pterins participate in oxidative stress. Besides this, these results may inspire new experiments similar to those reported previously for the reaction of guanine with metal atoms.

STRUCTURAL AND ELECTRONIC PROPERTIES OF METAL-DOPED ORGANIC SEMICONDUCTORS

Interaction of metal atoms with organic thin films is a fundamental issue in the optimization performances of novel devices. The computational investigations, based on density functional theory, reveal that a realistic description of the reactive processes is obtained when the organic thin film is modeled by its crystallographic structure. In this case, the metal atoms can react with multiple organic molecules present in the solid forming complexes where they are bound both to O atoms and to aromatic C atoms of the molecules. Calculated band gap states, induced by chemical reaction upon deposition, reproduce quite well the measured density of states as a function of the metal concentration in the solid. Simulated core level shift spectra for N (1s), O (1s) and Al (2p) in doped systems are in good agreement with experimental spectra and the electronic structure analysis provides a microscopic description of reaction processes. Interestingly, K atoms in PTCDA solid are ionically bound to anhydride O atoms and are able to form quasi mono-dimensional chain along the stack direction of the organic material.

Rotational Invariance and Double Frustration in the Structures of Gold Clusters Growing around the Fs-Defected MgO (100) Surface

The interaction of small gold clusters (Au(n), n = 1-4, 20) and a gold monolayer with the MgO (100) surface surrounding a neutral oxygen vacancy (F(s) center) is investigated using density-functional (DF) calculations. It is found that the presence of the defect modifies the interaction of gold not only with the vacancy itself, but also with the oxygen and magnesium atoms around it by increasing both the adhesion energy and the equilibrium bond distances. This is at variance with the interaction of metal atoms with the regular MgO (100) surface or the F(s) defect itself, in which an increase of the adhesion energy is associated with a shortening of the metal-surface distance. The resulting double frustration and cylindrical invariance of the metal-surface interaction cause small gold clusters growing around an F(s) nucleation center to be highly fluxional in terms both of rotational freedom and of multiple competing structural motifs. Fragmentation energies of the gold clusters are also discussed, finding that the lowest-energy pathway corresponds to the detachment of a dimer.

Interactions of Li, Ca, and Al with aromatic carbon materials: An ab initio study

The interactions of benzene (C6H6), naphthalene (C10H8), and perinaphthene (C13H9) with metal atoms (Li, Ca, and Al) were studied using second-order Møller-Plesset perturbation theory. By analyzing the frontier molecular orbitals, geometric structures, binding energies, and charge transfers, it was found that these metal atoms can bond strongly with C13H9, but can only bond weakly with C6H6 and C10H8. The bonding nature between a metal atom and C13H9 at their ground state depends significantly on the valence orbital of the metal atom and the pi-bonding distribution of the aromatic hydrocarbons. The spindly shaped 3p valence orbital of an Al atom results in the deviation of the adsorption site to the edge of C13H9, whereas the ball-shaped 2s/4s valence orbitals of a Li and a Ca atom facilitate their overlap with the second lowest unoccupied molecular orbital of C13H9. Further, Hartree-Fock and density-functional theory methods were demonstrated generally to be unreliable in describing the interactions of metal atoms with these pi systems.

Interface properties of metal/cytosine/Si(1 1 1):H heterostructures studied by means of SERS and DFT

In this work the interface formation between cytosine and hydrogen-passivated Si(1 1 1) substrates, the growth of cytosine layers as well as the interface between a metal (In or Ag) and the cytosine layers are studied. Cytosine was thermally evaporated by organic molecular beam deposition (OMBD) onto H-passivated Si(1 1 1) substrates under ultra-high vacuum conditions. Metal deposition on monolayers (∼0.4 nm) of cytosine leads to an enhancement of the Raman signal via the surface-enhanced Raman scattering (SERS) effect. The interaction with metals is found to be very different due to the large difference in the ionisation potential of Ag and In (IP Ag = 7.58 eV, IP In = 5.78 eV). The signal enhancement arises mainly from contributions due to molecule–metal charge transfer. Density functional theory calculations were employed for modelling the interaction of metal atoms with cytosine. Computational approaches were carried out on silver–cytosine and indium–cytosine complexes using the B3LYP density functional with the LANL2DZ basis set.

Static SIMS study of the behavior of K atoms on CH 3, CO 2H and CO 2CH 3 terminated self-assembled monolayers

Time-of-flight secondary ion mass spectroscopy has proven to be a very powerful tool in the study of the interaction of metal atoms with organic thin films since analysis of the emitted molecular cluster ions provide clear information about the presence of chemical reactions, metal penetration and metal nucleation. In this work, this approach is employed to examine the behavior of K atoms evaporated onto S(CH 2) 15CH 3, S(CH 2) 15CO 2H and S(CH 2) 15CO 2CH 3 self-assembled monolayers on Au substrates. On the CH 3 surface, no chemical reaction is observed, and the sticking probability of K atoms is quite low. However, we find that K atoms react with CO 2H and CO 2CH 3 groups, forming CO 2K moieties at the vacuum interface, but do not react with the (CH 2) n  backbone. Additional exposure of K to the system results in K remaining at the vacuum interface, not penetrating through the organic layer. The results imply that the CO 2K may act as a possible buffer layer to prevent chemical reactions when other types of metal atoms are employed.