Concentration Of Hydrogen Atoms Research Articles

Concentration of atomic hydrogen in a dielectric barrier discharge measured by two-photon absorption fluorescence

Two-photon absorption laser-induced fluorescence (TALIF) was utilized for measuring the concentration of atomic hydrogen in a volume dielectric barrier discharge (DBD) ignited in mixtures of Ar, H2 and O2 at atmospheric pressure. The method was calibrated by TALIF of krypton diluted in argon at atmospheric pressure, proving that three-body collisions had a negligible effect on quenching of excited krypton atoms. The diagnostic study was complemented with a 3D numerical model of the gas flow and a zero-dimensional model of the chemistry in order to better understand the reaction kinetics and identify the key pathways leading to the production and destruction of atomic hydrogen. It was determined that the density of atomic hydrogen in Ar–H2 mixtures was in the order of 1021 m−3 and decreased when oxygen was added into the gas mixture. Spatially resolved measurements and simulations revealed a sharply bordered region with low atomic hydrogen concentration when oxygen was added to the gas mixture. At substoichiometric oxygen/hydrogen ratios, this H-poor region is confined to an area close to the gas inlet and it is shown that the size of this region is not only influenced by the chemistry but also by the gas flow patterns. Experimentally, it was observed that a decrease in H2 concentration in the feeding Ar–H2 mixture led to an increase in H production in the DBD.

Impact of chemical vapour deposition plasma inhomogeneity on the spatial variation of sp2 carbon in boron doped diamond electrodes

The impact of plasma inhomogeneity on the sp2 content of thin film (∼micron) boron doped diamond (BDD) electrodes, grown using microwave chemical vapour deposition (MW-CVD) under different methane (CH4) concentrations (1% and 5%), is investigated. The sp2surface content (critical for interpreting electrochemical data) is comparatively assessed using a variety of electrochemical measurements: capacitance; solvent window analysis and quinone surface coverage. For all growths, distinctive regions containing appreciably differing amounts of sp2 carbon are identified, across the wafer. For example, on the 1% CH4 wafer, some areas exhibit electrochemical signatures indicative of high quality, minimal sp2 content BDD, whereas others show regions comprising significant sp2 carbon. Note Raman microscopy was unable to identify these variations. On the 5% CH4 wafer, no region was found to contain minimal levels of sp2 carbon. Changes in sp2 content across the BDD films indicates spatial variations in parameters such as temperature, methane and atomic hydrogen concentrations during growth, in this case linked directly to the use of a commonly employed multi-moded (overmoded) chamber for MW-CVD BDD synthesis, operated under low power density conditions. Varying sp2 levels can have significant impact on the resulting electrochemical behaviour of the BDD.

Enhanced Sodium-Ion Mobility and Electronic Transport of Hydrogen-Incorporated V2O5 Electrode Materials

Although α-V2O5 as an attractive electrode material for electrochemical energy storage devices exhibits a high theoretical capacity, its atomic structure with the confined size of channels for Na-ion transport and low electronic conductivity lead to the poor rate performance. Here we demonstrate that hydrogen incorporation in α-V2O5 is an effective way to improve the kinetics of ionic and electronic transports by using the density functional theory. Among various structures of hydrogen-incorporated α-V2O5, H2V2O5 presents enlarged diffusion channels along the [010] and [001] directions where the diffusion energy barriers decrease to 0.844 eV (−34.93%) and 1.737 eV (−41.81%), respectively. Improved electronic conductivity is also achieved for H2V2O5 due to the insulator–metal transition attributed by the high concentration of hydrogen atoms. As H2V2O5 has smaller volume expansion occurring during the Na-intercalation process, H2V2O5 at the comparable specific capacity exhibits higher rate capability and cyclability than α-V2O5.

Diameter control of gold nanoparticles synthesized in gas phase using atmospheric-pressure H2/Ar plasma jet and gold wire as the nanoparticle source: Control by varying the H2/Ar mixture ratio

This report describes diameter control of gold nanoparticles (AuNPs) during synthesis using an atmospheric-pressure H2/Ar plasma jet drive with pulse-modulated ultrahigh frequency, employing Au wire as the NP source material. During this process, where most of the AuNPs are regarded as formed through condensation from Au vapor derived by the Au wire etching, the mean diameter varied in the approximate range of 2–12 nm with H2 volume ratios up to 3.9%. In plasma diagnostics, results showed that the H2 volume ratio influences the plasma discharge behaviour, which affects the heat flux density flowed into the Au wire, and the atomic hydrogen concentration in the plasma. Both seemed to influence the etching rate of the Au wire per unit area, which is directly related to the concentration of Au vapor in the plasma. The concentration is one factor affecting the particle size evolution because of the collisions among vapor species in reaction field. Therefore, the AuNP size variation with the H2 volume ratio was discussed from the perspective of the etching rate of the Au wire at each H2 volume ratio.

Numerical Investigation of the Role of Volumetric Transformation Strain on the Relaxation Stress and the Corresponding Hydrogen Interstitial Concentration in Niobium Matrix

The effects of relaxation stress on the hydrogen concentration in Niobium- (Nb-) H media were investigated by iterative numerical modeling approach. To calculate the transformation strain, relaxation stress, and corresponding relaxed hydrogen concentration around an edge dislocation, a new third-order polynomial formulation was utilized in the model. With the aid of this polynomial, hydrogen induced relaxation stress never exceeds the dislocation stress, which indicates that the total stress field never turns to compressive state and diverges the results. The current model calculates the hydrogen concentration not only in the vicinity of an edge dislocation but also far away from the dislocation. Furthermore, the effect of relaxation stress on the interaction energy was also captured in the model. Overall, the current findings shed light on the complicated hydrogen embrittlement mechanisms of metallic materials by demonstrating that hydrogen induced relaxation has a significant effect on the hydrogen atom concentration and the interaction energy between the existing internal stress field and the solute hydrogen atom.

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.

First-principles study on hydrogen adsorption on nitrogen doped graphene

In this paper we have investigated the adsorption of Hydrogen on Nitrogen doped graphene in detail by means of first-principles calculations. A comprehensive study is performed of the structural, electronic and optical properties of hydrogen atoms adsorbed on dopant atoms sites and on carbon atoms neighboring dopant atoms. The effect of doping has been investigated by varying the concentration of doping atoms from 3.125%( one atom of nitrogen in 32 host atoms) to 6.25% ( two nitrogen atoms in 32 host atoms). Similarly the effect of adsorption has been investigated by varying the concentration of hydrogen atoms and also varying the adsorption sites. Band structure, partial density of states (PDOS) and optical properties of pure, nitrogen doped and hydrogen adsorbed graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with nitrogen doped graphene and Hydrogen adsorbed graphene sheet. It is found that upon nitrogen doping the Dirac point in the graphene band structure shifts below the Fermi Energy level and energy gap appears at the high symmetric K-point. On the other hand, by adsorption of Hydrogen atom, there is further change in the band structure near the Fermi level and also the energy gap at the high symmetric K-point is increased. There is change in the dielectric function and refractive index of the graphene after H atoms adsorption on N-doped graphene. The overall absorption spectra is decreased in case of nitrogen doping and after adsorption process of Hydrogen atoms. However a significant red shift in absorption towards visible range of radiation is found to occur for hydrogen atoms adsorbed on nitrogen doped graphene sheet. The reflectivity peak of graphene increases in low energy region after H adsorption on N-doped graphene. The results can be used to tune the Fermi Energy level and to tailor the optical properties of graphene sheet in visible region.

Safe and simple detection of sparse hydrogen by Pd-Au alloy/air based 1D photonic crystal sensor

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy.

Fluorescence (TALIF) measurement of atomic hydrogen concentration in a coplanar surface dielectric barrier discharge

Spatially and temporally resolved measurements of atomic hydrogen concentration above the dielectric of coplanar barrier discharge are presented for atmospheric pressure in 2.2% H2/Ar. The measurements were carried out in the afterglow phase by means of two-photon absorption laser-induced fluorescence (TALIF). The difficulties of employing the TALIF technique in close proximity to the dielectric surface wall were successfully addressed by taking measurements on a suitable convexly curved dielectric barrier, and by proper mathematical treatment of parasitic signals from laser–surface interactions. It was found that the maximum atomic hydrogen concentration is situated closest to the dielectric wall from which it gradually decays. The maximum absolute concentration was more than 1022 m−3. In the afterglow phase, the concentration of atomic hydrogen above the dielectric surface stays constant for a considerable time (10 μs–1 ms), with longer times for areas situated farther from the dielectric surface. The existence of such a temporal plateau was explained by the presented 1D model: the recombination losses of atomic hydrogen farther from the dielectric surface are compensated by the diffusion of atomic hydrogen from regions close to the dielectric surface. The fact that a temporal plateau exists even closest to the dielectric surface suggests that the dielectric surface acts as a source of atomic hydrogen in the afterglow phase.

Coupling of Plasma Chemistry, Vibrational Kinetics, Collisional‐Radiative Models and Electron Energy Distribution Function Under Non‐Equilibrium Conditions

The coupling between the electron energy distribution function (eedf) and the kinetics of vibrationally and electronically excited states is discussed. The first case study concerns the role of heterogeneous recombination in affecting the concentration of atomic hydrogen in RF plasmas, with consequences on eedf and negative ion formation. The coupling of eedf and a collisional‐radiative model for atomic hydrogen is discussed for optically thin and thick plasmas, finding large differences in the creation of eedf plateaux. The last case study deals with a self‐consistent coupling of eedf and kinetics of vibrationally and electronically excited states in CO2 cold plasmas emphasizing the role of pure vibrational mechanisms in the dissociation of CO2.

Influence of power density on high purity 63 mm diameter polycrystalline diamond deposition inside a 2.45 GHz MPCVD reactor

63 mm diameter polycrystalline diamond (PCD) films were synthesized via a microwave plasma chemical vapor deposition (MPCVD) reactor in 99% H2–1% CH4 atmosphere. Two different conditions, i.e. the typical condition (input power of 5 kW and gas pressure of 13 kPa) and the high power density condition (input power of 10 kW and gas pressure of 18 kPa), were employed for diamond depositions. The color changes of the plasma under the two proposed conditions with and without methane were observed by photographs. Likewise, the concentrations of hydrogen atoms and carbon active chemical species in plasma were analyzed by optical emission spectroscopy (OES). The morphologies and purity of the PCD films were investigated by scanning electron microscopy (SEM) and Raman spectroscopy, respectively. Finally, the transmission spectrum of the polished PCD plates was characterized by a UV–Vis–NIR spectrometer. Experimental results showed that both the concentrations of hydrogen atoms and carbon radicals increased obviously, with the boost input power and higher pressure. The films synthesized under the high power density condition displayed higher purity and more uniform thickness. The growth rates in 10 kW and 18 kPa reached ~7.7 µm h−1, approximately 6.5 times as much as that occurred in the typical process. Moreover, the polished plates synthesized under the high power density condition possessed a relatively high optical transmittance (~69%), approaching the theoretical values of approximately 71.4% in IR. These results indicate that the purity and growth rate of big-area PCD films could be simultaneously increased with power density.

Diagnostics of low-pressure hydrogen discharge created in a 13.56 MHz RF plasma reactor

A 13.56 MHz RF discharge in hydrogen was studied within the pressure range of 1–10 Pa, and at a power range of 400–1000 W. The electron energy distribution function and electron density were measured by a Langmuir probe. The gas temperature was determined by the Fulcher-α system in pure H2, and by the second positive system of nitrogen using N2 as the probing gas. The gas temperature was constant and equal to 450 ± 50 K in the capacitively coupled plasma (CCP) mode, and it increased with pressure and power in the inductively coupled plasma (ICP) mode. Also, the vibrational temperature of the ground state of hydrogen molecules was determined to be around 3100 and 2000 ± 500 K in the ICP and CCP mode, respectively. The concentration of atomic hydrogen was determined by means of actinometry, either by using Ar (5%) as the probing gas, or by using H2 as the actinometer in pure hydrogen (Q1 rotational line of Fulcher-α system). The concentration of hydrogen density increased with pressure in both modes, but with a dissociation degree slightly higher in the ICP mode (a factor 2).

Effect of the electron energy distribution on the measurement of the atom concentration by optical actinometry

The oxygen and hydrogen atom concentrations in the hollow cathode discharge with water vapor additives are determined using small argon and xenon additives as optical actinometers. The problem of the rejection of measurements of the electron plasma component parameters is discussed.

Modelling of measured optical properties of Pd–Au alloy ultrathin film for room temperature hydrogen sensing

A theoretical framework is presented to describe optical properties of palladium gold alloy ultra‐thin film of thickness about 5 nm. Density functional theory is employed to calculate complex dielectric function of hydrogen loaded Pd3Au alloy. Using Bruggeman's effective medium theory, the effective dielectric function of hydrogenated alloy is calculated in case of non‐uniform diffusion of hydrogen starting from very low concentration. Reflectance of deposited film on silica substrate is calculated using transfer matrix method and results are compared with the measured reflectance of sputter deposited thin film of alloy on identical substrate. The change of reflectance with hydrogen concentration is also calculated and verified experimentally. In both the cases, hydrogen loaded films show low reflectance due to reduction of the available electronic states near Fermi level compared to unloaded films. From TEM images and Grazing Incidence X‐ray diffraction analyses, crystal structure of the deposited alloy film is predicted. Using this alloy a four‐layered plasmonic waveguide is designed for room temperature hydrogen sensing. Analytical calculations show that absorption loss of fundamental TM mode of the waveguide at 633 nm changes almost linearly with hydrogen concentration variation. The loss will decrease about 5 dB/100% atomic concentration of hydrogen for 10 µm device length.

Beneficial effect of hydrogen in aluminum oxide deposited through the atomic layer deposition method on the electrical properties of an indium–gallium–zinc oxide thin-film transistor

ABSTRACTDescribed herein is the role of hydrogen in aluminum oxide (Al2O3) gate dielectrics in amorphous indium–gallium–zinc oxide (a-InGaZnO or a-IGZO) thin-film transistors (TFTs). Compared to a-IGZO TFTs with a low-temperature (150°C) Al2O3 gate dielectric, a-IGZO devices with a high-temperature (250–300°C) Al2O3 gate dielectric exhibit poor transistor characteristics, such as low mobility, a high subthreshold slope, and huge hysteresis. Through DC and short-pulsed current–voltage (I–V) measurements, it was revealed that the degradation of the transistor performance stems from the charging and discharging phenomenon at the interface traps located in the interface between the a-IGZO semiconductor and the Al2O3 gate insulator. It was found that the low-temperature Al2O3 atomic layer deposition processed film contains a higher density of hydrogen atoms compared to high-deposition-temperature films. The study results show that a high concentration of hydrogen atoms can passivate the defect sites in the interface and bulk, which produces excellent transistor characteristics. This study demonstrated that hydrogen has a beneficial effect on the defect passivation for oxide TFTs.

Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

Atomic concentration of hydrogen in tetra- and hexaamine heteroligand chromium(III) complexes with cyclic tetraamines

Based on the revealed dependence of the atomic concentration of hydrogen (NH) on the composition and structure of tetra- and hexaamine heteroligand chromium(III) complexes with cyclic tetraamines, routes to new materials with high NH for preparing effective composites for protection from neutron radiation were suggested.

CO2 hydrogenation to methanol over Cu/ZrO2 catalysts: Effects of zirconia phases

Structure–activity relationships of amorphous (a-), tetragonal (t-), monoclinic (m-) ZrO2 phase supported copper catalysts for methanol synthesis from CO2 hydrogenation were investigated with X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), N2O chemisorption, H2-temperature programmed reduction (H2-TPR), X-ray absorption spectroscopy (XAS), H2 and CO2 temperature-programmed desorption (H2- and CO2-TPD). The order of copper surface area is found to be as follows: Cu/a-ZrO2>Cu/t-ZrO2>Cu/m-ZrO2. The increased yield of methanol is correlated to the increase of copper surface area. However, normalization of the copper site specific activity (TOFmethanol) of Cu/t-ZrO2 is about 1.10–1.50 times and 1.62–3.59 times higher than Cu/a-ZrO2 and Cu/m-ZrO2, respectively. The high TOFmethanol is caused by a strong Cu–ZrO2 interaction and a high surface concentration of atomic hydrogen to CO2.

Tuning the properties of a complex disordered material: Full factorial investigation of PECVD-grown amorphous hydrogenated boron carbide

A multiresponse 25 full factorial experiment is performed to investigate the effects of growth conditions (temperature, power, pressure, total flow rate, partial precursor flow rate) on the chemical, mechanical, dielectric, electronic, and charge transport properties of thin-film amorphous hydrogenated boron carbide (a-BxC:Hy) grown by plasma-enhanced chemical vapor deposition (PECVD) from ortho-carborane. The main and interaction effects are determined and discussed, and the relationships between properties are investigated via correlation analysis. The process condition with the strongest influence on growth rate is pressure, followed by partial precursor flow rate, with low pressure and high partial flow rate conditions yielding the highest growth rates. The atomic concentration of hydrogen (at.% H) and density are controlled primarily by temperature and power, with low temperature and power conditions leading to relatively soft, hydrogen-rich, low-density, porous films, and vice versa. The B/C ratio is controlled by temperature, power, pressure, and the power*pressure interaction, and is uncorrelated to hydrogen concentration. Thin-film dielectric and electronic structure properties, including high-frequency dielectric constant (ε1), low-frequency/total dielectric constant (κ), optical band gap (ETauc/E04), and Urbach energy (EU), are correlated strongly with at.% H, and weakly to moderately with B/C ratio. These properties are dominated by the influence of temperature, with a second significant influence from the power*pressure interaction. The interaction of power and pressure leads to two opposite growth regimes—high power and high pressure or low power and low pressure—that can produce a-BxC:Hy films with similar dielectric or electronic structure properties. Charge transport properties also show a correlation with at.% H and B/C, but not with the electronic structure and disorder parameters, which suggests a complicated relationship between the two. The range of properties measured highlights the potential of thin-film a-BxC:Hy for low-κ dielectric and neutron detection applications, and suggests clear pathways for future material property optimization.

２光子吸収レーザ誘起蛍光法を用いた壁面の化学的消炎における水素吸着の影響評価

Hydrogen atom concentration in CH4/air premixed flame in a narrow channel is measured using a newly-developed two-photon absorption LIF (H-TALIF) setup with improved THG efficiency at 205nm. Laser fluence smaller than 0.09 J/cm2 is used for H-TALIF measurement free of the interference from photodissociation. Numerical simulations considering only the adsorption of hydrogen atom on the wall are also conducted. The initial sticking coefficient of the H atom is estimated as 0.1 for SUS321 and 0.01 for quartz by fitting simulated H atom distribution to the H-TALIF measurement result.