Binding Energy Of Atom Research Articles

Adsorption of hydrogen and hydrogen–containing gases on Pd– and Ag–single atoms doped on anatase TiO2 (1 0 1) surfaces and their sensing performance

The Pd– and Ag–doped anatase TiO2 (1 0 1) surfaces were investigated and the binding energies of single atom of Pd (−2.15 eV) and Ag (−2.38 eV) on the anatase (1 0 1) surfaces, respectively denoted as Pd/TiO2 and Ag/TiO2, were obtained. Binding sites for Pd and Ag atoms toward the TiO2 surface atoms are three atoms (Ti5C and two O2C atoms) and two O2C atoms of the TiO2 (1 0 1) surface, respectively. Due to adsorptions of H2 and hydrogen–containing (H2O, NH3, and CH4) gases on the Pd/TiO2 and Ag/TiO2, adsorption abilities on the Pd/TiO2 and Ag/TiO2 are in decreasing orders: NH3 > H2O > H2 > CH4 and NH3 > H2O > CH4 > H2, respectively. Mulliken–charge transfers from the Pd and Ag atoms to adsorption atoms of the anatase TiO2 (1 0 1) surface and the adsorption of hydrogen and hydrogen–containing gases to the Pd/TiO2 and Ag/TiO2 were observed. The Pd/TiO2 and/or Ag/TiO2 have high potentials to be NH3 sensing materials based on the electric conductivity measurement. The Pd/TiO2 has high potential to be CH4 sensing device based on the electric conductivity and surface charge measurements.

Mass and heat transfer between evaporation and condensation surfaces: Atomistic simulation and solution of Boltzmann kinetic equation

Boundary conditions required for numerical solution of the Boltzmann kinetic equation (BKE) for mass/heat transfer between evaporation and condensation surfaces are analyzed by comparison of BKE results with molecular dynamics (MD) simulations. Lennard–Jones potential with parameters corresponding to solid argon is used to simulate evaporation from the hot side, nonequilibrium vapor flow with a Knudsen number of about 0.02, and condensation on the cold side of the condensed phase. The equilibrium density of vapor obtained in MD simulation of phase coexistence is used in BKE calculations for consistency of BKE results with MD data. The collision cross-section is also adjusted to provide a thermal flux in vapor identical to that in MD. Our MD simulations of evaporation toward a nonreflective absorbing boundary show that the velocity distribution function (VDF) of evaporated atoms has the nearly semi-Maxwellian shape because the binding energy of atoms evaporated from the interphase layer between bulk phase and vapor is much smaller than the cohesive energy in the condensed phase. Indeed, the calculated temperature and density profiles within the interphase layer indicate that the averaged kinetic energy of atoms remains near-constant with decreasing density almost until the interphase edge. Using consistent BKE and MD methods, the profiles of gas density, mass velocity, and temperatures together with VDFs in a gap of many mean free paths between the evaporation and condensation surfaces are obtained and compared. We demonstrate that the best fit of BKE results with MD simulations can be achieved with the evaporation and condensation coefficients both close to unity.

Expansion of an ultracold Rydberg plasma

We report a systematic experimental and numerical study of the expansion of ultra-cold Rydberg plasmas. Specifically, we have measured the asymptotic expansion velocities, $v_0$, of ultra-cold neutral plasmas (UNPs) which evolve from cold, dense samples of Rydberg rubidium atoms using ion time-of-flight spectroscopy. From this, we have obtained values for the effective initial plasma electron temperature, $T_{e,0} = m_{ion} v_0^2/k_B$ (where $m_{ion}$ is the Rb$^+$ ion mass), as a function of the original Rydberg atom density and binding energy, $E_{b,i}$. We have also simulated numerically the interaction of UNPs with a large reservoir of Rydberg atoms to obtain data to compare with our experimental results. We find that for Rydberg atom densities in the range $10^7 - 10^9$ cm$^{-3}$, for states with principal quantum number $n > 40$, $T_{e,0}$ is insensitive to the initial ionization mechanism which seeds the plasma. In addition, the quantity $k_B \, T_{e,0}$ is strongly correlated with the fraction of atoms which ionize, and is in the range $0.6 \times |E_{b,i}| \lesssim k_BT_{e,0} \lesssim 2.5 \times |E_{b,i}|$. On the other hand, plasmas from Rydberg samples with $n \lesssim 40$ evolve with no significant additional ionization of the remaining atoms once a threshold number of ions has been established. The dominant interaction between the plasma electrons and the Rydberg atoms is one in which the atoms are deexcited, a heating process for electrons that competes with adiabatic cooling to establish an equilibrium where $T_{e,0}$ is determined by their Coulomb coupling parameter, $\Gamma_e \sim 0.01$.

Structures and electronic properties of $$\hbox {W}_{m}\hbox {Cu}_{n}\,(n + m \le 7)$$ W m Cu n ( n + m ≤ 7 ) clusters

Geometric and electronic structures of \(\hbox {W}_{m}\hbox {Cu}_{n}\, (m + n \le 7)\) cluster have been systematically calculated by density functional theory at the generalized gradient approximation level for ground-state structures. \(\hbox {W}_{m}\hbox {Cu}_{n}\) clusters with \(n = 1, 3, 5\) tend to form bipyramid structures, whereas \(\hbox {WCu}_{n}\) favour planar shapes except for \(\hbox {WCu}_{5}\). The configurations of \(\hbox {W}_{m}\hbox {Cu}_{n}\) clusters are more sensitive to the Cu atoms than the W atoms, while the average atomic binding energies and the total magnetic moments are determined by W atoms. The calculated second-order differences in energies and HOMO–LOMO energy gaps show pronounced odd–even oscillating behaviours. From the Mulliken electron population analysis, we found that Cu 4p and W 6p orbitals exhibit electronic charges and both Cu 4s and W 6s orbitals transfer electronic charges to the W 5d orbital, which lead to the extension of W–Cu bond lengths.

Deposition of Pd nanoparticles on the walls of cathodically hydrogenated TiO2 nanotube arrays via galvanic displacement: A novel route to produce exceptionally active and durable composite electrocatalysts for cost-effective hydrogen evolution

Noble metal-based materials are inevitable components of cathodes for the hydrogen evolution reaction (HER) in future water electrolysis systems for clean hydrogen fuel production. However, designing active and durable nanostructured catalysts with low amount of costly noble metals is still a great challenge. Herein, we show that Pd nanoparticles (NPs) can be synthesized on the highly developed surface of anodically grown TiO2 nanotube (TNT) arrays by applying a simple galvanic displacement strategy. In a two-step procedure, air-annealed TNT arrays are first cathodically protonated and then partially reoxidized by Pd(II) ions from a PdCl2 solution while providing a scaffold for the metallic Pd deposit. Structural and electrochemical characterizations reveal that the Pd content and the width of the Pd-populated zone of the tube walls are in correlation with the tube length. The Pd@TNT composites display remarkable HER activity in 1 M HClO4 delivering a current density of −10 mA cm−2 at an overpotential of −38 mV and a Tafel slope of only −13 mV/dec. More impressively, the mass and apparent activity of the Pd@TNTs is superior to even commercial Pt/C at higher current densities. The composites also show stable chronopotentiometric response over 25 h and a negligible HER overpotential increase after potential cycling tests. The exceptional performance of the Pd@TNT cathodes is assigned to the unique semiconducting properties of the three-dimensional, interactive TNT supporting structures that, on the one hand, provide abundance of Pd active sites with optimized atomic hydrogen binding energy for the cathodic HER, but on the other hand, prevent anodic degradation of the Pd catalyst.

Electronic and optical properties of hydrogenated silicon carbide nanosheets: A DFT study

Density-functional theory has been applied to investigate the effect of hydrogen adsorption on silicon carbide (SiC) nanosheets, considering six, different configurations for adsorption process. The chair-like configuration is found to be the most stable because of the adsorption of hydrogen atoms by silicon and carbon atoms on the opposite sides. The pure and hydrogenated SiC monolayers are also found to be sp2- and sp3-hybridized, respectively. The binding energy of the hydrogen atoms in the chair-like structure is calculated about −3.845 eV, implying the system to be much more stable than the same study based on graphene, though with nearly the same electronic properties, strongly proposing the SiC monolayer to be a promising material for next generation hydrogen storage. Optical properties presented in terms of the real and the imaginary parts of the dielectric function also demonstrate a decrease in the dielectric constant and the static refractive index due to hydrogen adsorption with the Plasmon frequency of the chair-like, hydrogenated monolayer, occurring at higher energies compared to that of the pure one.

Binding maps for the study and prediction of bimetallic catalyst surface reactions: The case of methanol oxidation

AbstractFocusing on the competing pathways of methanol oxidation on platinum and platinum/gold bimetallic catalysts, we explore a novel density functional theory (DFT)‐based approach to the study of reactions on catalyst surfaces. Traditionally, DFT has been used to compute binding energies of products and intermediates as proxies for catalytic activity, and to compute full reaction pathways and their activation energy barriers. Merging the computational simplicity and intuitive clarity of binding energy calculations with the site sensitivity of transition state calculations, we construct maps of the binding energies of relevant atoms and molecules at all sites on a surface. We show that knowledge of the arrangement of strong and weak binding sites on a surface is powerful in rationalizing the ease with which a reaction step proceeds on a given local motif of surface atoms. We highlight the prospects and challenges of this approach toward catalyst screening and prediction.

Novel catalysis mechanisms of benzohydroxamic acid adsorption by lead ions and changes in the surface of scheelite particles

To improve the floatability of tungsten minerals, lead ions (lead nitrate) were used to modify the surface properties of the minerals and benzohydroxamic acid (BHA) was used as a collector in the flotation system. Pb2+-BHA complexes are inevitably present in this process and the role of it is unclear. This investigation is going to describe a new approach and the mechanism of catalyzing BHA adsorption onto scheelite by lead ions. Chemical speciation, zeta potential, FTIR, and XPS studies were conducted to establish the important role of lead ions. Indeed, Pb2+-BHA complexes were shown to be the active species responsible for flotation. The speciation and zeta potential results showed the presence of the adsorbed Pb2+-BHA complexes on the scheelite. The XPS results for atomic composition and binding energies confirmed Pb2+-BHA species adsorbed on the scheelite surface, which contributed to more adsorption of BHA. The new method would increase the recovery of scheelite, simplify the flowsheet and reduce the processing cost.

Transformation of Carbides in Prolonged Rail Operation

The evolution of the carbide phase in the surface layers of bulk-quenched rails (after the passage of 500 and 1000 million t of traffic) and differentially quenched rails (after the passage of 691.8 million t) to a depth of 10 mm at the central axis of the rail cross section and at the nearby rounded section is studied by transmission electron-diffraction microscopy. The grains of plate pearlite, ferrite–carbide mixture, and structure-free ferrite are analyzed. The carbide phase in the surface layers of the steel changes in two mutually complementary processes during rail operation: (1) cleavage of cementite particles with subsequent entrainment in ferrite grains or plates (in the pearlite structure); (2) cleavage and dissolution of cementite particles, with transfer of carbon atoms to dislocations (in Cottrell atmospheres and in dislocational cores), which transport them to the ferrite grains (or plates), where cementite nanoparticles are formed again. In the previous location of the plates, fragmented dislocational substructure appears. The boundaries of the fragments are found at the positions previously occupied by cementite α-phase boundaries. The solution of cementite is mainly due to the energy of carbon atoms at dislocation cores and subboundaries in comparison with the cementite lattice. The binding energy of the carbon atom and the dislocations is 0.6 eV and the binding energy of the carbon atom and the subboundary is 0.8 eV, as against 0.4 eV for the carbon atom in cementite. Elastoplastic stress fields are formed; their stress concentrators are intra- and interphase boundaries of ferrite and pearlite grains, cementite plates and ferrite of the pearlite colonies, and globular cementite and ferrite particles. Those are also the basic sources of curvature and torsion in the crystal lattice of the rail steel. On approaching the contact surface, the number of stress concentrators increases, and the internal long-range stress fields are of greater amplitude.

Effects of Focusing for Atoms Sputtered from a Ni (001) Face with Angle and Energy Resolution

The focusing and overfocusing of atoms sputtered from Ni (001) face are studied with the use of molecular dynamics computer simulations. When a crystal transitions from the paramagnetic to the ferromagnetic state, there is a reduction in the number of focused and overfocused sputtered atoms. The evolution of distributions of sputtered atoms with the simultaneous energy and polar angle resolution due to changes in the azimuthal angle and binding energy of atoms at a surface is studied.

Квазиклассический метод анализа и оценки орбитальных энергий связи в многоэлектронных атомах и ионах

Квазиклассический метод анализа и оценки орбитальных энергий связи в многоэлектронных атомах и ионах

Sputtering of redeposited material in focused ion beam silicon processing

Sputtering of the redeposited material was experimentally studied with the use of test structures specially prepared by the focused beam of gallium ions with different energies. The consequent milling of the structures and their characterization utilizing transmission electron microscopy revealed that the milling rate for the redeposited material is 1.3 times higher than for crystalline silicon. The dynamic Monte-Carlo simulations of sputtering were performed with the introduced discrete-continuous variation model for the surface binding energy of the silicon atoms, which takes into account the formation of the gallium precipitates in the surface layer of the bombarded material. The calculations allowed obtaining not only the correct values of redeposited material milling rate, but also the distributions of gallium atoms in the sputtered materials which were in the qualitative agreement with the experimental data.

Photoluminescence excitation study of split-vacancy centers in diamond

Two known representatives of the split-vacancy complexes in diamond, the negatively charged silicon-vacancy ${\mathrm{SiV}}^{\ensuremath{-}}$ and recently discovered germanium-vacancy ${\mathrm{GeV}}^{\ensuremath{-}}$ defects, were comparatively studied for their photoluminescence (PL) and complementary optical absorption spectra. The observed strong difference between luminescence and absorption spectra indicates a strong frequency defect, that is the difference of binding energies of impurity atom in the ground and excited electronic states, in these color centers. The presence of frequency defect is well supported by first-principle calculations. The obtained results accompanied with isotopic effects shed light on the structure of these centers in the ground and excited electronic states that would open the doorway to their theoretical description.

An efficient cluster model to describe the oxygen reduction reaction activity of metal catalysts: a combined theoretical and experimental study.

A simple and efficient cluster model containing only seven metal atoms was proposed to investigate the oxygen reduction reaction (ORR) activity of various metal catalysts by density functional theory (DFT) calculation. The model was validated by comparing ORR volcano plots obtained from the cluster model in this work and the slab model in the literature. We then used this model to investigate the influence of the support of Ag nanoparticles on ORR activity, which is hard to describe by the slab model. The calculations revealed the binding energy of oxygen atoms on Ag/COOH-CNTs or Ag/OH-CNTs changed to 2.04 and 2.09 eV respectively, in comparison to that of Ag/CNTs (2.13 eV). As a result, the ORR current density improved to 2.24 and 1.88 mA cm-2 at the potential of 0.7 V (vs. RHE) for Ag/COOH-CNTs and Ag/OH-CNTs respectively, in comparison to that of Ag/CNTs (1.66 mA cm-2). The cluster model could simultaneously reduce the computing time and make it possible to consider the influence of catalyst supports, which would provide new insight to design more effective ORR metal catalysts.

Dependence on Ionization Degree and Relativistic Effects in Electron Binding Energies in Free Atoms and Ions

Dependence on Ionization Degree and Relativistic Effects in Electron Binding Energies in Free Atoms and Ions

Theoretical Insights on the Inefficiency of RNA Oxidative Damage under Aerobic Conditions.

Oxidative damage to RNA has been linked to change or loss of RNA function and development of many human age-related diseases. However, knowledge on the nature of RNA oxidative damage is relatively limited. In this study, oxidative damage to RNA is investigated under anaerobic and aerobic conditions by exploring the properties and reactions of 5-hydroxyl-2'-uridin-6-yl and its peroxyl diastereoisomers in the RNA strand, respectively. Selective addition of OH to the nucleic base from the 5'-end is studied at the molecular level for the first time, explaining the large number of the 5S-isomer available for further reactions. Our results provide clear evidence that the efficiency of C2'-H2' bond activation in the peroxyl isomers is lower than in the carbon radical species. An exception is observed for the isomer cis-(5S,6R)-A1, whose internucleotidyl H2'-abstraction barrier is far smaller than that in the corresponding C6-yl radical. However, analysis of the equilibrium species distribution reveals that the amount of cis-(5S,6R)-A1 is very small among the peroxyl diastereoisomers, and hence the resulting products from direct strand scission should be a less important component in RNA oxidative damage. The species with maximum distribution is the cis-(5S,6R)-B1 isomer, which is derived from cis-(5S,6R)-A1 and has a moderate intranucleotidyl H2'-abstraction barrier. More importantly, the reaction is mildly exothermic. These results show that the main fraction of the intranucleotidyl H2'-abstraction intermediates can be formed from the cis-(5S,6R)-B1 isomer. The absolute reduction potentials, the hydrogen atom binding energies, and the key structural parameters of the C6-peroxyl species are used to understand the diverse reactivity of the cis-(5S,6R) diastereoisomers toward the C2'-H2' bonds activation. The present study shows that in addition to the selectivity of the OH radical addition, there is a strong correlation between the conformation of the modified uracil base and its reactivity in RNA oxidative damage.

High Edge Selectivity of In Situ Electrochemical Pt Deposition on Edge-Rich Layered WS2 Nanosheets.

Recent studies show that the Pt electrode can be slowly dissolved into the acidic media and regenerate on the working electrode along with the long-time hydrogen evolution reaction (HER) test. However, to date, the relationship between the Pt deposition and the intrinsic properties of the working electrode remains elusive. Herein, for the first time, the edge selectivity of in situ electrochemical Pt deposition on layered 2H-WS2 nanosheets, whose edge surface with rich dangling bonds is chemically active to regulate their properties, especially the interfacial reaction occurring between the electrode surface and the adjacent thin layer of the solution, is theoretically elucidated and experimentally verified by controlling the cathode polarization test using Pt wire as the counter electrode in H2 SO4 solution. It is revealed that the layered WS2 nanosheets with rich exposed edges show much stronger interaction with Pt atoms because the terminated S22- or S2- ligands on the edge exhibit much lower binding energy for Pt atoms compared with the apical S2- ligands on the terrace surface. The in situ electrochemical Pt-deposited WS2 nanosheets with rich exposed edges can act as a highly active hybrid electrocatalyst to accelerate HER kinetics and exhibit commercial Pt-like HER performance, especially in the alkaline media.

Investigation of the scintillation properties of LuAG:Tb[formula omitted] nanocrystalline powders and nanoceramic prepared by SPS method

1 mole percent Tb3+ doped lutetium aluminium garnet (LuAG:Tb3+) nanocrystalline powders were prepared by Pechini method. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) measurements confirmed the atomic binding energy and crystal structure. The XRD results showed that the nanocrystalline powders had cubic structure with grain sizes of 11 and 34 nm at minimum and maximum annealing temperatures, respectively. The morphology of the nanocrystalline powders with grain sizes 11 and 34 nm was characterized by transmission electron microscopy (TEM) analysis. The UV–Vis–NIR analyses were done to obtain energy absorption values and to investigate the effect of different grain sizes on absorption spectra of nanocrystalline powders. Excitation, emission spectra and decay time were measured for different grain sizes of the nanocrystalline powders. The results showed that increasing grain size was caused an increasing in emission intensity. The different grain sizes and quenching parameter such as an OH group affected the decay time of the LuAG:Tb3+ nanocrystalline powders. Then the LuAG:Tb3+ nanoceramics were fabricated at 1500°C by spark-plasma sintering (SPS) method for the first time from nanopowders prepared by the Pechini method at 900°C. The comparison of photoluminescence spectra and decay time of LuAG:Tb3+ powder and ceramic which were measured at room temperature in ultraviolet (VU) region, was done. Moreover, the X-ray excitation luminescence measurements of LuAG:Tb3+ nanoceramic were investigated.

Synthesis of dimethyl carbonate on single Cu atom embedded in N-doped graphene: Effect of nitrogen species

The synthesis of dimethyl carbonate (DMC) by oxidative carbonylation of methanol on atomic Cu supported on N-doped graphene (Cu1/NG) was explored by density-functional theory. The configurations with which the Cu atom is anchored to pyridinic- (Cu/PNG), graphitic- (Cu/GNG) and amino-N (Cu/ANG) doped graphene have been systematically investigated and compared with Cu-doped monovacancy graphene (Cu/MG) and pristine graphene (Cu/PG). The binding energy of the Cu atom was found to decrease in the order Cu/GNG>Cu/ANG>Cu/MG>Cu/PNG>Cu/PG. On Cu1/NG, DMC can be formed via CO insertion into CH3O to form CH3OCO, which then reacts with additional methoxide. The barrier energies of the rate-limiting reaction of CO insertion into methoxide on Cu/PNG, Cu/GNG, Cu/MG, and Cu/ANG surfaces have been found to be 31.0, 52.1, 73.5, and 92.0kJ/mol, respectively. And the corresponding reaction energies are −38.2, −51.3, −44.6, and −63.4kJ/mol, respectively. The activity of the Cu1/NG catalysts increases in the order Cu/PNG<Cu/GNG<Cu/MG<Cu/ANG. To summarize, the presence of pyridinic- and graphitic-N in Cu1/NG catalysts is beneficial to the oxidative carbonylation of methanol, while amino-N has a negative effect on DMC formation.

Effects of AC and DC corona on the surface properties of silicone rubber: Characterization by contact angle measurements and XPS high resolution scan

This study utilized a multi-needle corona electrode system to investigate the influence of AC and DC coronas on the surface properties of high temperature vulcanized (HTV) silicone rubber. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) analysis were performed to characterize the chemical structure and hydrophobicity changes in state of the silicone rubber surface after corona exposure. The results indicated that the effects of AC corona were greater than that of DC corona, and the effects of negative DC corona were slightly greater than that of positive DC corona. XPS results showed that the C elemental content on the silicone rubber surface decreased, whereas the O elemental content increased. High-resolution scan on Si 2p XPS spectra proved that surface oxidation occurred during corona exposure and caused the high binding energies of Si atoms and silica-like layer. High-resolution C 1s XPS spectra showed that corona exposure destroyed the Si-CH3 groups on the surface. Some C-O and C=O bonds appeared following the corona exposure. High-resolution O 1s XPS spectra confirmed the formation of Si-OH groups and chemically absorbed water, which was ignored in the past research. Chemically absorbed water was detected as one of the essential factors that caused the loss of hydrophobicity of silicone rubber after corona exposure, together with Si-OH groups and silica-like layer.