Hydrogen Incorporation Research Articles

Effect of main gas and carrier gas on ZnO thin films deposited by atmospheric pressure plasma jet

The effect of main gas flow rate and gas type of carrier gas on the electrical and optical properties of Ga-doped ZnO films deposited by atmospheric pressure plasma jet was investigated. Adding Ar and H2 in the carrier gas reduces the sheet resistance of the films from 230 to 90Ω/□ and increases the deposition rate by 38% due to the incorporation of hydrogen as a shallow donor and the lower breakdown potential of Ar, respectively. The effect of the main gas flow rate is less significant compared with the gas type of the carrier gas, but a proper flow rate is required to produce the film with lower resistivity. The lowest resistivity of 1.25×10−3Ωcm was achieved with a carrier gas mixture percentage of 75% and a main gas flow rate of 30slm at a substrate temperature of 180°C in open air. All the samples presented in this study exhibit average transmittance above 80% in the visible region and low haze below 5.5%.

Influence of hydrogen incorporation and coating thickness on the corrosion resistance of carbon based coatings deposited by magnetron sputtering

Hydrogenated and non-hydrogenated carbon based coatings with two different thicknesses (300nm and 1μm) were deposited on 316L stainless steel by magnetron sputtering and the coating morphology, structure and corrosion resistance were evaluated. The morphological and structural characterizations were performed by scanning electron microscopy and Raman spectroscopy respectively, while the corrosion resistance was evaluated by potentiodynamic test and electrochemical impedance spectroscopy. The results revealed that hydrogenated coatings present a more protective behavior and the variations in coating thickness did not promote changes in the electrochemical behavior.

The hard sphere view of the outer core

The hard sphere model for liquids attempts to capture the physical behavior of a real liquid in a simple conceptual model: a fluid of fixed size spheres that only interact repulsively when they come into contact. Is the model good enough to use for modeling internal planetary structure? To answer this question, I survey variants of hard sphere liquid theory by applying them to the Earth’s outer core to determine which of them explains wavespeeds in the outer core best. The variants explored here are the Carnahan-Starling hard sphere model, the Mansoori-Canfield extension to hard sphere mixtures, the transition metal hard sphere liquid, and the Lennard-Jones hard sphere liquid with attractive forces. With an empirical addition of a temperature dependence to the liquid’s hard sphere diameter, all of the variants explored can replicate wavespeeds in most of the radius range of the outer core. The hard sphere model for liquid transition metals explains the wavespeed best because it yields a mean liquid atomic weight of 48.8 g mol −1 at 10 wt% light element abundance in the core which is in good cosmochemical agreement with core light element models. Other variants also fit core wavespeeds but require implausibly low liquid mean atomic weight implying excessive incorporation of hydrogen or helium in the core. Applied to the detailed wavespeed structure of the Earth’s outermost outer core, the model suggests that the mean atomic weight could be reduced by up to 1.74% or the temperature could be increased by up to 400 K relative to an adiabatic profile, or there could be 8% fewer valence electrons in the liquid.

Synthesis of Iron Oxide Nanoparticles from Iron Acetylacetonate and Cyclopentadienyliron Dicarbonyl Dimer in Low Pressure Plasma — Effect of Plasma Parameters on Morphology and Magnetic Properties

Iron oxide nanoparticles are synthesized using organometallic precursors namely, iron (III) acetylacetonate and cyclopentadienyliron dicarbonyl dimer in a capacitively coupled low pressure plasma system. They are characterized using High Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD), magnetization studies and Raman spectroscopy. The role of hydrogen and RF (Radio Frequency) power on the crystalline and magnetic properties of the nanoparticles is studied. Incorporation of hydrogen to the Plasma-Enhanced Chemical Vapor Deposition (PECVD) chamber during the synthesis facilitates both crystallization of iron oxide nanoparticles and reduction of carbon content in the product. The saturation magnetization of iron oxide nanoparticles synthesized using iron (III) acetylacetonate and cyclopentadienyliron dicarbonyl dimer in presence of hydrogen at 200 W RF power is higher than that synthesized in the absence of hydrogen at 50 W RF power. In case of nanoparticles synthesized using iron (III) acetylacetonate, the saturation magnetization increases from 1.5 emu g-1 to 19 emu g-1, and for the same synthesized from cyclopentadienyliron dicarbonyl dimer it increases from 3.2 emu g-1 to 22.4 emu g-1.

Hydrogen-induced mechanical properties of amorphous silicon thin films

Mechanical properties of thin films such as residual stress and hardness are of paramount importance from the device fabrication point of view. Intrinsic stress in sputtered films can be tensile or compressive as decided by the number density and the energy of the plasma species striking the growing film. In the presence of hydrogen we analyzed the applicability of idealized stress reversal curve for amorphous silicon thin films deposited by DC, pulsed DC (PDC) and RF sputtering. We are successfully able to correlate the microstructure with the stress reversal and hardness. We observed a stress reversal from compressive to tensile with hydrogen incorporation. It was found that unlike in idealized stress reversal curve case, though the energy of plasma species is less in DC plasma, DC deposited films exhibit more compressive stress, followed by PDC and RF deposited films. A tendency towards tensile stress from compressive stress was observed at ~13, 18 and 23at%H for DC, PDC and RF deposited films respectively, which is in exact agreement with the vacancy to void transition in the films. Regardless of the sputtering power mode, the hardness of a-Si:H films is found to be maximum at CH~10at%H. Enhancement in hardness with CH (up to CH~10at%H) is attributed to increase of Si–H bonds. Beyond CH~10at%H, hardness starts falling.

Hydrous species in feldspars: A reassessment based on FTIR and SIMS

Recent interest in hydrogen incorporation in feldspars has been driven by the potential of this common mineral species to record magmatic water contents. Accurate measurement of H concentrations in feldspars by Fourier transform infrared (FTIR) spectroscopy is hampered by the need to collect polarized spectra in three mutually perpendicular directions, which can be impractical for crystals characterized by small dimensions, polysynthetic twinning, and/or chemical zoning. SIMS is an attractive alternative to FTIR, offering high spatial resolution, high precision, and the feasibility of attaining low detection limits. In this study we compare FTIR and SIMS data for 19 feldspars, including plagioclase, anorthoclase, sanidine, microcline, and orthoclase. We present adjustments to previously published FTIR data on some of these samples. Our new SIMS and FTIR data are well correlated and we demonstrate the feasibility of quantitatively measuring H concentrations as low as 1–2 ppmw H_2O using SIMS. Combination of the new data together with re-evaluation of the NMR calibration of Johnson and Rossman (2003) indicates that the IR absorption coefficients for hydrous species in feldspar increase with decreasing frequency of their O-H absorptions, in accord with theory. We derive new molar integral IR absorption coefficients (I) for feldspars with the following hydrous species as defined by Johnson and Rossman (2003): Type I and II H_2O (microcline and orthoclase): I = 120 470 ± 11 360 L·mol^(−1) H_2O cm^(−2) Type IIb OH (sanidine): I = 150 000 ± 15 000 L·mol^(−1) H_2O cm^(−2) Type IIa OH (plagioclase and anorthoclase): I = 202 600 ± 20 260 L·mol^(−1) H_2O cm^(−2) These absorption coefficients depend on critical assumptions with regards to SIMS matrix effects. If accurate, one important implication is that the H concentrations of plagioclase crystals estimated in the literature are too high by up to a factor of two, requiring revision of previously estimated plagioclase-melt H partitioning coefficients.

(Invited) Stability and Defect Chemistry of High-Temperature Piezoelectric Single Crystals

Piezoelectric single crystals of the langasite family exhibit piezoelectrically excited bulk acoustic waves up to temperatures of about 1400 °C. Therefore, the materials show the potential to be operated as resonant microbalance at extremely high temperatures. Such piezoelectric transducers enable, for example, film deposition monitoring or gas sensing by determination of atmosphere dependent mass changes of thin films already deposited on the resonators. Further, langasite based surface acoustic wave devices are increasingly operated at elevated temperatures. Consequently, the stability and operation limits of these crystals need to be determined and correlated with the transport kinetics of the constitutive elements and of dopants. In this work, the high-temperature stability of the piezoelectric single crystals CTGS (Ca3TaGa3Si2O14) and LGS (La3Ga5SiO14) is reviewed and related to their defect chemistry and the atomistic transport processes occurring in the crystals. First, the resonance frequency of CTGS and LGS bulk acoustic devices is determined up to temperatures as close as possible to their ultimate operation limit which is the melting point. The figure shows the relative frequency shift in comparison to common piezoelectric crystals such as quartz. It is obvious that the maximum operation temperature of langasite type crystals exceeds that of quartz significantly. The diffusion coefficients of oxygen and hydrogenous species follow from tracer diffusion runs and subsequent secondary ion mass spectrometry as well as optical absorption spectroscopy. The electrical conductivity is determined by impedance spectroscopy as function of temperature, oxygen partial pressure and crystal orientation. Key issues limiting the high-temperature operation are the evaporation of gallium, the formation of oxygen vacancies and the incorporation of hydrogen. For example, a dominant role of hydrogen is observed in hydrogenous atmospheres since the diffusion coefficient of hydrogenous species is orders of magnitude higher than that of oxygen. Further, the loss mechanisms are correlated with the transport kinetics. Its effect on the electromechanical properties such as mechanical stiffness, piezoelectric and dielectric constant, effective viscosity and electrical conductivity is evaluated. Thereby, the electromechanical properties are extracted from resonance spectra using a one-dimensional physical model. The viscoelastic damping in langasite, expressed as viscosity, governs the total loss up to about 650 °C. Between 400 and 650 °C, the temperature dependence of the property can be described by a single activation energy. Above about 600 °C, the electrical conductivity impacts the total loss noticeable. In contrast, the loss in CTGS is virtually not affected be the conductivity. In addition, the damping of the piezoelectric devices is determined by monitoring the amplitude of the displacement by laser vibrometry. Comparing CTGS and LGS, the former shows significantly lower losses at high temperatures which is caused to some extent by its fully ordered structure. Finally, application relevant aspects such as use of piezoelectric resonators are briefly presented. One example is the determination of thermodynamic properties of thin films. Figure 1

Evolution of OH groups in diopside and feldspars with temperature

Using in situ FTIR and heating/cooling stage, we have investigated the temperature evolutions of OH bands in natural diopside, plagioclase and anorthoclase. The frequencies of three main resolved OH bands (3645, 3464 and 3361 cm −1 called band 1, 2 and 3, respectively) in diopside shift linearly with temperature. With increasing temperature, band 1 shifts to lower wavenumbers, band 2 exhibits almost no shift while band 3 shifts to higher wavenumbers. The integral absorbance of band 1, 2 and 3 decreases by 18.8, 10.1 and 31.4 %, respectively, from −50 to 400°C. No simultaneous growth and decline of OH bands is observed during the whole process, excluding H proton transfer. In contrast to OH defects in diopside, the bands at lower frequencies in feldspars weaken while their bands at higher frequencies strengthen with increasing temperature, indicating H protons change positions in the crystal structure from one site with stronger H bond to another site with weaker H bond. These results reflect different local environments of OH defects and temperature dependent OH absorption coefficients in diopside, and change of H sites in feldspar structure with temperature. It provides important constraints on the microscopic mechanisms of hydrogen incorporation in these minerals.

ChemInform Abstract: Recent Advances in Asymmetric Organocatalysis Mediated by Bifunctional Amine—Thioureas Bearing Multiple Hydrogen‐Bonding Donors

AbstractReview: [50 refs.

Electron trap level of hydrogen incorporated nitrogen vacancies in silicon nitride

Hydrogen incorporation into nitrogen vacancies in silicon nitride and its effects on electron trap level are analyzed using simulation based on density functional theory with temperature- and pressure-dependent hydrogen chemical potential. If the silicon dangling bonds around a nitrogen vacancy are well separated each other, hydrogen incorporation is energetically stable up to 900 °C, which is in agreement with the experimentally observed desorption temperature. On the other hand, if the dangling bonds strongly interact, the incorporation is energetically unfavorable even at room temperature because of steric hindrance. An electron trap level caused by a nitrogen vacancy becomes shallow by the hydrogen incorporation. An electron is trapped in a deep level created by a silicon dangling bond before hydrogen incorporation, whereas it is trapped in a shallow level created by an anti-bonding state of a silicon-silicon bond after hydrogen incorporation. The simulation results qualitatively explain the experiment, in which reduced hydrogen content in silicon nitride shows superior charge retention characteristics.

Conversion of Dimethyl Ether to 2,2,3-Trimethylbutane over a Cu/BEA Catalyst: Role of Cu Sites in Hydrogen Incorporation

Recently, it has been demonstrated that methanol and/or dimethyl ether can be converted into branched alkanes at low temperatures and pressures over large-pore acidic zeolites such as H-BEA. This process achieves high selectivity to branched C4 (e.g., isobutane) and C7 (e.g., 2,2,3-trimethylbutane) hydrocarbons. However, the direct homologation of methanol or dimethyl ether into alkanes and water is hydrogen-deficient, resulting in the formation of unsaturated alkylated aromatic residues, which reduce yield and can contribute to catalyst deactivation. In this paper we describe a Cu-modified H-BEA catalyst that is able to incorporate hydrogen from gas-phase H2 cofed with dimethyl ether into the desired branched alkane products while maintaining the high C4 and C7 carbon selectivity of the parent H-BEA. This hydrogen incorporation is achieved through the combination of metallic Cu nanoparticles present on the external surface of the zeolite, which perform H2 activation and olefin hydrogenation, and Lewis acidic ion-exchanged cationic Cu present within the H-BEA pores, which promotes hydrogen transfer. With cofed H2, this multifunctional catalyst achieved a 2-fold increase in hydrocarbon productivity in comparison to H-BEA and shifted selectivity toward products favored by the olefin catalytic cycle over the aromatic catalytic cycle.

Photo-assisted proton exchange and chemical etching on Fe-doped lithium niobate crystals.

We report the photo-assisted proton exchange and chemical etching on Fe-doped LiNbO(3) crystals. Selective proton exchange and chemical etching are realized through the 455nm-laser irradiation on the crystal surface in pyrophosphoric acid. Optical microscopy and Micro-IR spectroscopy analysis show that the hydrogen incorporation is confined spatially by the laser irradiation. Moreover, under the laser irradiation, + z surface is found to be more easily etched than -z surface. This unexpected etching anisotropy is attributed to the photogalvanic effect of the crystal.

Giant conductivity enhancement of ferrite insulators induced by atomic hydrogen.

Hydrogen behavior in oxides has triggered much interest for its scientific and technological importance in a wide range of research fields from novel ion conductors to astrochemistry. Here, we report a giant conductivity enhancement in ZnFe2O4 ferrite insulators to the metallic state by over eleven orders of magnitude induced by electrochemically generated atomic hydrogen at room temperature. The conductivity and the amount of incorporated hydrogen increased in an exponential function with time. An activation energy for the atomic hydrogen chemisorption was measured to be 8.23 kJ mol(-1). Quantitative kinetics correlations among the adsorption of atomic hydrogen, hydrogen incorporation and conductivity enhancement are established, based on which hydrogen incorporation process is clarified herein. We demonstrate that the hydrogen incorporation in oxides can be adjusted by manipulating the kinetic factors. These findings have implications for research into hydrogen behavior in oxides in environments containing hydrogen atoms and offer possibilities for utilizing and controlling the modifications of oxide materials induced by atomic hydrogen.

Complex transition metal hydrides incorporating ionic hydrogen: thermal decomposition pathway of Na2Mg2FeH8 and Na2Mg2RuH8.

Complex transition metal hydrides have potential technological application as hydrogen storage materials, smart windows and sensors. Recent exploration of these materials has revealed that the incorporation of anionic hydrogen into these systems expands the potential number of viable complexes, while varying the countercation allows for optimisation of their thermodynamic stability. In this study, the optimised synthesis of Na2Mg2TH8 (T = Fe, Ru) has been achieved and their thermal decomposition properties studied by ex situ Powder X-ray Diffraction, Gas Chromatography and Pressure-Composition Isotherm measurements. The temperature and pathway of decomposition of these isostructural compounds differs considerably, with Na2Mg2FeH8 proceeding via NaMgH3 in a three-step process, while Na2Mg2RuH8 decomposes via Mg2RuH4 in a two-step process. The first desorption maxima of Na2Mg2FeH8 occurs at ca. 400 °C, while Na2Mg2RuH8 has its first maxima at 420 °C. The enthalpy and entropy of desorption for Na2Mg2TH8 (T = Fe, Ru) has been established by PCI measurements, with the ΔHdes for Na2Mg2FeH8 being 94.5 kJ mol(-1) H2 and 125 kJ mol(-1) H2 for Na2Mg2RuH8.

Synthesis of hydrogen-doped zinc oxide transparent conductive films by RF magnetron sputtering

Hydrogen-doped ZnO (ZnO:H) thin films were synthesized on glass substrates by using an RF magnetron sputtering system and adding H2 to Ar sputtering gas. The doping effects of hydrogen on ZnO thin films were systematically investigated under various deposition conditions. Resistivity decreased with increasing H2 fraction from 0 to 5%. The Hall effect and infrared reflectance measurements showed that the increase in H2 fraction induced increases in hydrogen incorporation amount and carrier density. These results can be understood by considering that hydrogen acts as a donor, as was previously reported. Effective hydrogen doping in ZnO during synthesis was realized by the suppression of the increase in substrate temperature not only in the bulk but also at the top surface. The lowest resistivity of 1.5 × 10−3 Ω·cm and the highest carrier density of 2.7 × 1020 cm−3 were obtained under optimized conditions without metal dope.

Ultra high amorphous silicon passivation quality of crystalline silicon surface using in-situ post-deposition treatments

A parametric study of post-deposition hydrogen plasma treatment of intrinsic a:Si:H films is performed. We demonstrate a significant improvement in passivation of c-Si(100) promoting epitaxy after an in-situ hydrogen plasma treatment depending mainly on the pressure and slightly on the power. Plasma diagnostic indicates an increase of Hα* signal with high power and low pressure. However, our analysis reveals a better hydrogen incorporation with high pressure and a slight increase in monohydride with high power. Longer H2 plasma duration up to 50 s shows no detrimental effect on the passivation quality. Optimizing the in-situ H2 plasma treatment, high minority carrier lifetime over 15 ms was achieved after short thermal annealing. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Diamond-like carbon films from CO source gas by RF plasma CVD method

Diamond-like carbon (DLC) films were fabricated by RF CO plasma chemical vapor deposition (CVD) to avoid hydrogen incorporation into the deposited films. Broadband optical emissions confirmed a hydrogen-free process without atomic hydrogen emissions. The fabricated films were characterized by Raman scattering spectroscopy, Rutherford backscattering spectrometry (RBS) with elastic recoil detection analysis (ERDA) methods, and FT-IR spectroscopy with comparison to conventional DLC films fabricated from C2H2 gas. The hydrogen concentration in the DLC films was reduced to 4 at. % using a CO source while the conventional DLC films prepared from C2H2 contained 27 at. %. The DLC films made from CO gas contained a large amount of oxygen, approximately 20 at. %, a larger number of graphite structures than the conventional DLC film, and characteristic triple bonds (C≡C) of carbon atoms in the FT-IR spectrum.

Organic and mineral matter changes due to oil generation, saturation and expulsion processes based on artificial maturation experiments

Hydrous pyrolysis experiments were conducted on immature organic-rich rock with type-I kerogen to evaluate petroleum generation, saturation and expulsion processes. The experiments were carried out under isothermal conditions at ten different temperatures (280° through 360°C) for nine different time spans between 18 and 144h. Rock samples recovered from the experiments were analyzed for total organic carbon (TOC–weight%), Rock-Eval pyrolysis, vitrinite reflectance (Ro%), spectral fluorescence and visual characterization of organic matter under the microscopy. TOC, S2 and HI tend to decrease with increasing temperature and duration of the experiments as expected. The Ro% values reach up to 1.14% in the most severe experiment (i.e. 360°C/96h). The Ro% is believed to be suppressed due to hydrogen incorporation from bitumen. The bitumen production was observed with the increase of transformation index (TI) and two types of bitumen were differentiated by fluorescence color. The bitumen with yellow fluorescence was mainly composed of saturate and aromatic hydrocarbons that were probably generated earlier than the bitumen with brown fluorescence which is rich in NSO compounds. The greatest bitumen saturation occurs at TI around of 41% to 45%, when the S1 reaches its highest values. The decrease of bitumen saturation and consequent oil expulsion is marked by a reduction in S1 values and fluorescence color. This phenomenon occurs simultaneously with the development of fractures and voids in the mineral matrix which reduces the oil retention capability and facilitates the expulsion process. These observations enhanced the understanding of oil generation and saturation processes, as well as primary migration, expulsion and type of generated bitumen.

STUDY OF THE PLASMA EMISSION IN A MAGNETRON SPUTTERING SYSTEM FOR A-SI:H PRODUCTION

The use of hydrogenated amorphous silicon, a-Si:H, for solar cell applications has shown interesting possibilities for increasing the efficiency of heterojunctions and reducing costs of solar cells. Hydrogen incorporation in thin films of amorphous silicon is crucial for obtaining good electrical properties because it passivates the dangling bonds in the structure. The study of several parameters that influence the formation of films is necessary to optimize the material properties. In this paper, the optical emission of plasma during film growth by sputtering was studied in order to evaluate the hydrogenation process, at different levels of hydrogen in a H-Ar plasma. The results show the possibility to control such a process through optical emission spectroscopy (OES) without the need to introduce further analysis tools in the reactors.

Structural and photoconductivity properties of silicon carbon thin films

AbstractNanostructured films composed of silicon crystallites dispersed in an hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition from silane‐methane mixtures diluted in hydrogen by varying the rf power. Compositional, structural, optical and photoconductivity properties of the films have been investigated. The increase in rf power in the 40‐80 W range enhances the incorporation of carbon and hydrogen in the amorphous matrix and decreases the volume fraction and size of the silicon crystallites leading to an enlargement of the optical band gap from 2.07 to 2.20 eV. Steady state photoconductivity measurements, performed under monochromatic radiations in the visible range, have demonstrated the occurrence of monomolecular recombination kinetics in the samples under illumination and that the mobility‐lifetime product of the free electrons as a function of the optical gap decreases from 1.9 × 10–7 to 2.5 × 10–9 cm2V–1 as in the case of device quality films deposited by silane‐methane mixtures diluted in hydrogen. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)