Interaction Of Atomic Hydrogen Research Articles

Theoretical models of hydrogen-induced defects in amorphous silicon dioxide

We used density functional theory (DFT) calculations to model the interaction of hydrogen atoms and molecules with strained bonds and neutral oxygen vacancies in amorphous silica $({\text{a-SiO}}_{2})$. The results demonstrate that the interaction of atomic hydrogen with strained Si--O bonds in defect-free ${\text{a-SiO}}_{2}$ networks results in the formation of two distinct defect structures, which are referred to as the ${[{\text{SiO}}_{4}/\text{H}]}^{0}$ and the hydroxyl ${\text{E}}^{\ensuremath{'}}$ center. To study the distribution of each defect's properties, up to 116 configurations of each center were calculated. We show that the hydroxyl ${E}^{\ensuremath{'}}$ center can be thermodynamically stable in the neutral charge state. In order to understand the origins and reactions of this defect, different mechanisms of formation, passivation, and depassivation have been investigated. The interaction of H with a single-oxygen vacancy in ${\text{a-SiO}}_{2}$ was studied in 144 configurations, all resulting in the hydrogen bridge defect. The reaction of the hydrogen bridge defect with the second H atom is barrierless and fully passivates the O vacancy. The latter defect reacts with atomic H with a small barrier, restoring the hydrogen bridge defect. These results provide a better understanding of how atomic and molecular hydrogen can both passivate existing defects and create new electrically active defects in amorphous-silica matrices.

Hydrogen adsorbed at N-polar InN: Significant changes in the surface electronic properties

The interaction of atomic hydrogen and ammonia with as-grown N-polar InN surfaces is investigated using in situ photoelectron spectroscopy. Changes in the surface electronic properties, including the band alignment and work function, as well as the chemical bonding states of the substrate and adsorbates are characterized. Ammonia molecules are dissociating at the InN surface, resulting in adsorption of hydrogen species. Consequently, the considerable changes of the chemical and electronic properties of the InN surface during ammonia interaction are almost identical to those found for adsorption of atomic hydrogen. In both cases, hydrogen atoms preferentially bond to surface nitrogen atoms, resulting in the disappearance of the nitrogen dangling-bond-related occupied surface state close to the valence band edge at $\ensuremath{\sim}1.6$ eV binding energy and the formation of new occupied electron states at the conduction band edge. Furthermore, a decrease in work function during adsorption from 4.7 to 3.7--3.8 eV, as well as an increase in the surface downward band bending by 0.3 eV, confirm that hydrogen is acting as electron donor at InN surfaces and therefore has to be considered as one main reason for the surface electron accumulation observed at N-polar InN samples exposed to ambient conditions, for example as the dissociation product of molecules. The measured formation and occupation of electronic states above the conduction band minimum occur in conjunction with the observed increase in surface electron concentration and underline the relationship between the energy position of occupied electron states and surface band alignment for InN as a small-band-gap semiconductor.

Hydrogen–vacancy interactions in ferromagnetic and paramagnetic bcc iron: Ab initio calculations

Simulation of the paramagnetic state is still a challenge for computer material science. At the same time, for iron alloys the region of the paramagnetic state is important from the viewpoint of processing. The paper presents results of ab initio modeling of interaction of hydrogen atom with a vacancy in both ferromagnetic and (for the first time) paramagnetic bcc iron. The interaction energy calculations are carried out in the framework of the local spin density approximation (LSDA) by using the supercell LAPW‐WIEN‐2k method. To obtain the disordered distribution of magnetic moments the program package BINAR was used. Fifteen nonequivalent magnetic configurations were obtained. Five of them having the lowest energy were chosen for further analysis. The H–O site distance is 0.23 Å in both paramagnetic and ferromagnetic bcc iron. The energy of hydrogen trapping by the vacancy is 0.60 and 0.27 for paramagnetic and ferromagnetic state, respectively. It is found that weakening of the H–V interaction in the paramagnetic state is the consequence of magnetic effects.

Ambient-temperature high damping capacity in TiPd-based martensitic alloys

Shape memory alloys (SMAs) have attracted considerable attention for their high damping capacities. Here we investigate the damping behavior of Ti50(Pd50−xDx) SMAs (D=Fe, Co, Mn, V) by dynamic mechanical analysis. We find that these alloys show remarkably similar damping behavior. There exists a sharp damping peak associated with the B2–B19 martensitic transformation and a high damping plateau (Q−1~0.02–0.05) over a wide ambient-temperature range (220–420K) due to the hysteretic twin boundary motion. After doping hydrogen into the above alloys, a new relaxation-type damping peak appears in the martensite phase over 270–360K. Such a peak is considered to originate from the interaction of hydrogen atoms with twin boundaries and the corresponding damping capacity (Q−1~0.05–0.09) is enhanced by roughly twice that of the damping plateau for each alloy. Moreover, the relaxation peaks are at higher temperatures for the TiPd-based alloys (270–370K) than for the TiNi-based alloys (190–260K). We discuss the influence of hydrogen diffusion, mobility of twin boundaries and hydrogen–twin boundary interaction on the temperature range of the relaxation peak. Our results suggest that a martensite, with appropriate values for twinning shear and hydrogen doping level, provides a route towards developing high damping SMAs for applications in desired temperature ranges.

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While the metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.

Expanding the structural versatility of thiostannate(iv) complexes

The synthesis of new thiostannate(IV) complexes is of key importance for further progress in the formation of both extended thiostannate compounds and multinary tin sulphide containing functional materials. Here we report on the crystal structures of three new thiostannate(IV) compounds with complex structures: ((CH3C(NH2)2)8Sn2S6SnS41, ((CH3)2NH2)(NH4)SnS32 and (NH4)6Sn3S9·1.3H2O 3). They have been synthesised by utilising different crystallisation solvents (DMF and acetonitrile) starting from the same ammonium thiostannate(IV) containing solution. The size and shape of the thiostannate(IV) complexes take the form of discrete monomeric [SnS4]4− and dimeric [Sn2S6]4− complexes in 1, infinite linear [SnS3]2− chains in 2 and as a trimeric six-membered [Sn3S9]6− complex in 3. Hirshfeld surface analysis shows that the number of interacting hydrogen atoms with the thiostannate(IV) complex in 3 is responsible for elongation of the Sn–S bonds, regardless of the origin of the hydrogen atom (neutral water molecules or charged ammonium cations). Furthermore, statistics on the bond distances and angles for the most common dimeric thiostannate(IV) complex [Sn2S6]4− is collected and compared with the three thiostannate(IV) structures obtained here.

Ab-initio Simulation of Hydrogen Atom Interaction with Tungsten

The results of calculations of stable configurations of atomic hydrogen in the tungsten bulk, in the presence of vacancies, as well as on the surface (100) and in the near-surface layers are given. Activation barriers for interstitial diffusion, on-surface diffusion, trapping in a vacancy, detrapping from the vacancy, and transitions between on-surface and under-surface sites are calculated. Hydrogen-vacancy interaction is considered for the case of several H atoms trapped in a vacancy.

Rydberg states in the strong field ionization of hydrogen by 800, 1200 and 1600 nm lasers

We study the population of Rydberg excited states in the strong field interaction of atomic hydrogen with 800, 1200 and 1600 nm laser pulses. The total excitation probability displays strong out-of-phase modulation with respect to the weak modulation in the total ionization probability as the laser intensity is increased. The results are explained in terms of channel closing, to demonstrate multiphoton ionization features in the strong tunnel ionization regime. We also explain the stability of high Rydberg states in strong laser fields in contrast to other previous ionization stabilization models.

Two-color ionization of hydrogen close to threshold with keV photons

In a recent Letter [H. Bachau, M. Dondera, and V. Florescu, Phys. Rev. Lett. 112, 073001 (2014)] we considered the hydrogen atom in interaction with an electromagnetic field consisting in the coherent superposition of two keV pulses centered around two frequencies ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$ that differ by a few atomic units. The analysis of the results obtained from the resolution of the time-dependent Schr\odinger equation focused on stimulated Compton scattering (SCS). We have developed in parallel an approach based on perturbation theory and it proved to be an appropriate and useful tool in complement to the nonperturbative approach. In this paper we present a detailed analysis of the electron spectra obtained for $\ensuremath{\hbar}{\ensuremath{\omega}}_{1}=$ 55 a.u. and two values of $\ensuremath{\hbar}{\ensuremath{\omega}}_{2}$, 50 and 54 a.u. Emphasis is put on the case $\ensuremath{\hbar}{\ensuremath{\omega}}_{2}=54$ a.u., where the electron emitted through SCS has the lowest energy, showing in particular that in the vicinity of the ionization threshold the cross section increases as $\ensuremath{\hbar}{\ensuremath{\omega}}_{1}\ensuremath{-}\ensuremath{\hbar}{\ensuremath{\omega}}_{2}$ decreases. We calculate photoelectron energy and angular distributions at various relative directions of propagation of the pulses. We discuss the limitations of the approximations underlying the numerical and analytical approaches used in this work.

Mechanism of the formation of hydrogen tetroxide and peroxide via low-temperature interaction between hydrogen atoms and molecular oxygen

A mechanism and kinetic model for the synthesis of peroxide radical condensate via the low-temperature interaction of hydrogen atoms with O2 molecules is proposed. The main components of the reaction, hydrogen tetroxide H2O4 and hydrogen peroxide H2O2, are formed in a low-temperature liquid layer formed near the cold surface during synthesis. Molecules of H2O4 and H2O2 are stabilized by transitioning to the solid phase. The dependences of the \(N_{O_2 } /N_{H_2 O_2 }\) ratio on the ratio of concentrations of H and O2 in the gas phase, calculated on the basis of the model, are consistent with the experimental data.

A molecular dynamics simulation of hydrogen atoms collisions on an H-preadsorbed silica surface

The interaction of hydrogen atoms and molecules with a silica surface is relevant for many research and technological areas. Here, the dynamics of hydrogen atoms colliding with an H-preadsorbed β-cristobalite (0 0 1) surface has been studied using a semiclassical collisional method in conjunction with a recently developed analytical potential energy surface based on density functional theory (DFT) calculations. The atomic recombination probability via an Eley–Rideal (E–R) mechanism, as well as the probabilities for other competitive surface processes, have been determined in a broad range of collision energies (0.04–3.0 eV) for off-normal (θv = 45°) and normal (θv = 0°) incidence and for two different surface temperatures (TS = 300 and 1000 K). H2,gas molecules form in roto-vibrational excited levels while the energy transferred to the solid surface is below 10% for all simulated conditions. Finally, the global atomic recombination coefficient (γE–R) and vibrational state resolved recombination coefficients (γ(v)) were calculated and compared with the available experimental values. The calculated collisional data are of interest in chemical kinetics studies and fluid dynamics simulations of silica surface processes in H-based low-temperature, low-pressure plasmas.

Semi-analytical model of hydrogen ionization by strong laser pulse at low field frequencies

We consider the interaction of hydrogen atom with a very intense low frequency laser pulse. The Henneberger-Kramers representation of the time-dependent Schrödinger equation is the most appropriate one for this purpose. It is shown that in the case of very low frequencies, the quantum dispersion of the electron wave packet plays a dominant role in the dynamics of the atom.

Deuterium adsorption on (and desorption from) SiC(0 0 0 1)-(3 × 3), R30°, R30° and quasi-free-standing graphene obtained by hydrogen intercalation

We present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C–H (C–D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp2-to-sp3 rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate.

An experimental test of the weak equivalence principle for antihydrogen at the future FLAIR facility

We present new experimental ideas to investigate the gravitational interaction of antihydrogen. The experiment can first be performed in an off-line mirror measurement on hydrogen atoms, as a testing ground for our methods, before the implementation with antihydrogen atoms. A beam of hydrogen atoms is formed by launching a cold beam of protons through a cloud of trapped electrons in a nested Penning trap arrangement. In the next step, the atoms are stopped in a series of pulsed electromagnetic coils — so-called atomic coilgun. The stopped atoms are confined in a magnetic quadrupole trap and cooled by single-photon laser cooling. We intend to employ the method of Raman interferometry to study the gravitational interaction of atomic hydrogen — and later on antihydrogen at the FLAIR facility — with high sensitivity.

Investigation of the Adsorption and Diffusion of Hydrogen in Iron Clusters by the Method of Density Functional

We construct a cluster model of interaction of atomic hydrogen with α - and γ -iron surfaces and perform quantum-chemical computations of the Fe–H system by the method of density functional with the RPBE-GGA exchange-correlation functional. We obtain the curves of the potential energy of interaction of atomic hydrogen with iron clusters of BCC and FCC structures and establish the activation barriers of its adsorption, penetration into the subsurface layer, and migration between tetrahedral and octahedral positions of clusters. The energies of dissolution of atomic hydrogen at different absorption sites of the clusters are computed and the stable energy states of hydrogen in the octahedral positions of FCC iron clusters are revealed. We analyze the charge state of atomic hydrogen both on the surface and in the bulk sites of the clusters and confirm the mechanism of partial charge transfer in the iron–hydrogen system.

Formation of Hydrogen Polyoxides As Constituents of Peroxy Radical Condensate upon Low-Temperature Interaction of Hydrogen Atoms with Liquid Ozone

The composition of low-temperature condensates obtained by the reaction of hydrogen atoms with liquid ozone has been determined from the Raman spectra and data on the molar ratio of O2 to H2O2 in the decomposition products. The main constituents are hydrogen tetroxide H2O4, trioxide H2O3, and peroxide H2O2 in comparable amounts and also water H2O. The mechanism and quantitative kinetic model of their formation have been proposed. H2O4, H2O3, and H2O2 are formed in the diffusion-controlled reactions between OH and HO2 in the liquid ozone layer and stabilized by transfer to the solid phase. OH and HO2 radicals are generated via a sequence of the reactions initiated by the interaction H + O3(liq). The model adequately reproduces the properties of the real condensates.

Frist-Principles Study of Hydrogen Atom Diffusion on Transition Metal Doped Mg(0001) Surface

First-principles calculations within the density functional theory (DFT) have been carried out to study the interaction of hydrogen atom with transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) doped Mg (0001) surfaces. First we have calculated the stability of the transition metals atom on the Mg surface, On the basis of the energetic criteria, all the elements except Zn prefer to substitute one of the Mg atoms from the second layer, while Zn tend to substitute one of the Mg atoms from the first layer. In the second step, we have studied the interaction between hydrogen atom and the transition metals doped Mg (0001) surface.we have studied the interaction of a hydrogen atom with the transition metals doped Mg (0001) surface. The results show that for transition metals atoms doped Mg (0001) surface in the second layer, it not only enhances the chemisorption interaction between hydrogen atom and Mg surface, but also it benefits hydrogen atom diffusion in Mg bulk with relatively more diffusion paths. However, when the Mg surface doped by elements such as Sc, Ti, V, Cu and Zn, hydrogen atom chooses to bond with transition metals atom and block the diffusion of hydrogen atom into Mg bulk, while when the Mg surface doped by elements such as Cr, Mn, Fe, Co and Ni, hydrogen atom chooses to leave from transition metals atom thereby promoting the diffusion of hydrogen atom diffusion into Mg bulk. Charge density difference plots shows that electrons are transferred from electronic states of transition metals atom to the orbital of hydrogen atom which cause attractive interactions between hydrogen atom and transition metals atom and reduce the energy barrier of the hydrogen atom diffusion into Mg bulk. Our results show that useing transition metals (Cr, Mn, Fe, Co and Ni) as catalysts for the hydrogenation/dehydrogenation of Mg bulk samples and provide more diffusion paths of hydrogen atom, they are beneficial for the diffusion of hydrogen atom to Mg bulk and improve significantly the hydrogenation kinetics property of Mg surface.

The electronegativity equalization method fused with molecular mechanics: a fluctuating charge and flexible body potential function for [Emim][Gly] ionic liquids

Recently, experimental and theoretical studies on amino acid ionic liquid (AAIL) systems have attracted much attention. A transferable intermolecular potential approach that includes fluctuating charges and a flexible body based on a combination of the electronegativity equalization method and molecular mechanics (EEM/MM), and its application to an AAIL system containing 1-ethyl-3-methylimidazolium ([Emim](+)) and glycine ([Gly](-)) are explored and tested in this study. A consistent integration of EEM with MM requires the input of the EEM charges of all atoms into the MM intermolecular electrostatic interaction term. Compared with ionic liquid (IL) force fields, the EEM/MM model has an outstanding feature: the EEM/MM model not only presents the electrostatic interaction of atoms and their changes in response to different ambient environments but also introduces "the H-bond interaction region" in which a new parameter kHB(RHB) is used to describe the electrostatic interaction of hydrogen atoms in [Emim](+) and oxygen atoms in [Gly](-), which can form hydrogen bonds. The EEM/MM model gives quite accurate predictions for gas-phase state properties of [Emim](+), [Gly](-), and ion pairs, such as optimized geometries, dipole moments, vibrational frequencies, and cluster interaction energies. Due to its explicit description of charges and hydrogen bonds, the EEM/MM model also performs well for the liquid-phase properties of [Emim][Gly] under ambient conditions. The calculated properties, such as density, heat of vaporization, the self-diffusion coefficient, and ionic conductivity, are fairly consistent with available experimental results.

Hydrogen evolution from water through metal sulfide reactions

Transition metal sulfides play an important catalytic role in many chemical reactions. In this work, we have conducted a careful computational study of the structures, electronic states, and reactivity of metal sulfide cluster anions M2S(X)(-) (M = Mo and W, X = 4-6) using density functional theory. Detailed structural analysis shows that these metal sulfide anions have ground state isomers with two bridging sulfide bonds, notably different in some cases from the corresponding oxides with the same stoichiometry. The chemical reactivity of these metal sulfide anions with water has also been carried out. After a thorough search on the reactive potential energy surface, we propose several competitive, energetically favorable, reaction pathways that lead to the evolution of hydrogen. Selectivity in the initial water addition and subsequent hydrogen migration are found to be the key steps in all the proposed reaction channels. Initial adsorption of water is most favored involving a terminal metal sulfur bond in Mo2S4(-) isomers whereas the most preferred orientation for water addition involves a bridging metal sulfur bond in the case of W2S4(-) and M2S5(-) isomers. In all the lowest energy H2 elimination steps, the interacting hydrogen atoms involve a metal hydride and a metal hydroxide (or thiol) group. We have also observed a higher energy reaction channel where the interacting hydrogen atoms in the H2 elimination step involve a thiol (-SH) and a hydroxyl (-OH) group. For all the reaction pathways, the Mo sulfide reactions involve a higher barrier than the corresponding W analogues. We observe for both metals that reactions of M2S4(-) and M2S5(-) clusters with water to liberate H2 are exothermic and involve modest free energy barriers. However, the reaction of water with M2S6(-) is highly endothermic with a considerable barrier due to saturation of the local bonding environment.

Chemical and structural properties of polymorphous silicon thin films grown from dichlorosilane

We have examined the effects of hydrogen dilution (RH) and deposition pressure on the morphological, structural and chemical properties of polymorphous silicon thin films (pm-Si:H), using dichlorosilane as silicon precursor in the plasma enhanced chemical vapor deposition (PECVD) process. The use of silicon chlorinated precursors enhances the crystallization process in as grown pm-Si:H samples, obtaining crystalline fractions from Raman spectra in the range of 65–95%. Atomic Force Microscopy results show the morphological differences obtained when the chlorine chemistry dominates the growth process and when the plasma–surface interactions become more prominent. Augmenting RH causes a considerable reduction in both roughness and topography, demonstrating an enhancement of ion bombardment and attack of the growing surface. X-ray Photoelectron Spectroscopy results show that, after ambient exposure, there is low concentration of oxygen inside the films grown at low RH, present in the form of SiO, which can be considered as structural defects. Instead, oxidation increases with deposition pressure and dilution, along with film porosity, generating a secondary SiOx phase. For higher pressure and dilution, the amount of chlorine incorporated to the film decreases congruently with HCl chlorine extraction processes involving atomic hydrogen interactions with the surface. In all cases, weak silicon hydride (SiH) bonds were not detected by infrared spectroscopy, while bonding configurations associated to the silicon nanocrystal surface were clearly observed. Since these films are generally used in photovoltaic devices, analyzing their chemical and structural properties such as oxygen incorporation to the films, along with chlorine and hydrogen, is fundamental in order to understand and optimize their electrical and optical properties.