Incorporation Of Hydrogen Atoms Research Articles

Amino acid synthesis from an amorphous substance composed of carbon, nitrogen, and oxygen

Hydrogen cyanide, formaldehyde, and ammonia are considered important intermediates in amino acid synthesis by electric discharge. In this study, however, amino acid precursors were synthesized from a CO–N2 mixture free of hydrogen atoms. An amorphous film composed of carbon, nitrogen, and oxygen was given from a highly activated plasma. When exposed to atmospheric moisture, this film incorporated hydrogen atoms to yield amino acid. This is a mechanism for amino acid synthesis without involving hydrogen cyanide, formaldehyde, and ammonia.

Structure of hydrogenated amorphous Ni 56Dy 44

The structure of amorphous Ni 56Dy 44, loaded with 32 at% and 60 at% hydrogen, was investigated by X-ray and neutron diffraction using the isotopic substitution method. The results are discussed on the basis of the pair distribution functions. The incorporation of hydrogen atoms causes a change of the Ni–Dy matrix, i.e., an increase of the atomic distances and of the coordination numbers, in particular those of the Dy–Dy correlations. The H-atoms are preferentially located in a tetrahedral Dy-coordination, but also some hydrogen–Ni coordination was found. The hydrogen–metal distances agree with the distances between tetrahedral interstitial sites and the metal atoms in the crystalline hydrides DyH 2 and Ni 57H 43. A distance correlation between the hydrogen atoms was found at 2.78 Å.

Hydrogen, Acceptors, and H-Acceptor Complexes in GaN

ABSTRACTWe present ab-initio calculations on energetics and geometries of atomic hydrogen, of several candidate acceptors, and of H-acceptor complexes in wurtzite GaN For the H-Mg complex in Mg-doped GaN, we calculate the vibrational frequencies of H. Hydrogen is found to be a negative-U center. H-acceptor complex formation is always exothermic. Substitutional Be has a low formation energy and a shallow impurity level, which makes it a good candidate for p-doping in MBE growth. CN appears not to be shallow. Atomic hydrogen incorporation in undoped GaN is disfavored in an H2 atmosphere; it becomes favorable in p and n-type conditions in atomic H environments.

Low-temperature interaction of hydrogen with methane-precovered thin palladium films

The interaction of hydrogen with methane-precovered thin palladium films at 78 K has been studied by means of a combination of thermal desorption mass spectrometry (TDMS) and surface potential change (ΔSP) measurements. The results show that preadsorption of methane under high pressure (≈ 1 Torr) strongly hinders the adsorption and incorporation of hydrogen atoms into the bulk of Pd films. Only exposure to a pressure of H 2 ⩾ 10 −3 Torr leads to PdH x formation. Decomposition of the bulk PdH x is limited by the preadsorbed CH 4. The TD spectra point to a significant enrichment of subsurface and surface states of hydrogen due to interaction with preadsorbed methane.

Diamond epitaxy on a Si(001) substrate: a comparison of structural models

A previous proposal for the atomic structure at the interface of a diamond (001) adfilm growing epitaxially on Si(001) in a 45 degree rotated orientation, is extended by the inclusion of Si atoms in the second adfilm layer. In addition, two new models for growth in 3:2 registry in a parallel orientation are investigated, including versions with and without incorporation of hydrogen atoms into the structure. For each model, a total energy optimisation of the geometry is carried out using quantum chemical calculations with the PM3 Hamiltonian applied to periodically repeated atomic clusters containing up to eight atomic layers. Due to the non-stoichiometric nature of the interface layers, comparisons of the relative energetics of the models are performed by the introduction of carefully defined interface and adhesive bonding energies. It is found that the rotated model has a very low intrinsic interface energy and is favourable for very thin adfilms, but due to the smaller elastic deformation needed for registry the parallel growth mode becomes most favourable for thicker layers. Detailed atomic geometries for the optimised structures of all three models are given.

Low pressure chemical vapor deposition (LPCVD) of β–SiC on Si(100) using MTS in a hot wall reactor

Stoichiometric β–SiC thin films with a high preferred orientation of (111) planes were successfully deposited on Si(100) substrates at a relatively low temperature of 1050 °C from the mixture of methyltrichlorosilane (CH3SiCl3 or MTS) and H2 in a hot wall LPCVD reactor. No etching of the Si substrate and smooth topography of the deposit were observed at high H2/MTS ratios and/or low deposition pressures. The presences of excess silicon, excess carbon, or incorporated hydrogen atoms in the films were not detected. Poor topography, degradation in preferred orientation, and etching of the Si substrate were observed at high values of deposition pressure, MTS concentration, and temperature. The etching on the Si substrate was due to the out-diffusion of Si atoms from the substrate and the presence of Cl-containing radicals resulting from the decomposition of MTS molecules while transporting to the Si substrates. A deposition mechanism was proposed to model the deposition of SiC in a hot wall reactor by using (1) gas phase decomposition of MTS molecules, (2) adsorption of the intermediates on the surface, and (3) reaction of the adsorbed intermediates to form SiC. The deposition rates were predicted very well for various deposition conditions in a hot wall LPCVD reactor.

Photoluminescence and electroluminescence at the TiO 2—electrolyte interface

The photoluminescence (PL) and electroluminescence (EL) of polycrystalline TiO 2 film electrodes with anatase and rutile structure were studied in aqueous electrolyte solutions. The main difference between the PL spectrum of anatase samples and that of rutile samples was the presence of a band peaking at 850 nm in the latter. The dependence of this band intensity on the penetration depth of exciting light is well described within the framework of the dead-layer model. On the basis of this description, the luminescent centers responsible for the appearance of the 850 nm band were concluded to be mainly bulk states whose nature is discussed. The EL behaviour of TiO 2 film electrodes under negative polarization was shown to depend, to a considerable extent, on the nature of the alkali metal cation in the solution. The PL and EL bands in the visible spectral region (λ max = 580–650 nm) observed at potentials more negative than E fb are assigned to the luminescent centers produced by the penetration of alkali metal cations into the near-surface region of the electrode. Electroluminescence with a wide spectrum observed at potentials at which the hydrogen evolution reaction proceeds is attributed to the radiative recombination of holes injected into the valence band from electrogenerated radicals with electrons located at the states produced by the incorporation of atomic hydrogen into the oxide lattice. The possible mechanisms of the transfer of charges involved in the EL process through the TiO 2—electrolyte interface are discussed.

Effect of hydrogenation on deep-level traps in InP on GaAs

Deep levels in the heteroepitaxial undoped InP layers grown directly on GaAs substrates by organometallic vapor-phase epitaxy have been investigated by deep-level transient spectroscopy. Two electron traps have been observed with activation energies of 0.4 and 0.57 eV in the temperature range between 150 and 310 K. The trap concentrations of these levels are in the order of 1015 cm−3 for samples with a carrier concentration of 1016 cm−3. Incorporation of atomic hydrogen into the InP layer by a photochemical vapor deposition system produces substantial decreases of the trap concentrations to 1014 cm−3 and of the carrier concentration to 1015 cm−3.

High-purity InP and the role of hydrogen

Extremely high-purity InP has been grown in an atmospheric-pressure MOCVD reactor over the unusually large temperature range from 57-700 degrees C. The apparent purity of the material was enhanced by the incorporation of atomic hydrogen. At 650 degrees C, a temperature at which many device structures are grown, a 77 K electron mobility of 190000 cm2 V-1 s-1 was obtained with an electron concentration of 1.6*1014 cm-3. Removal of the hydrogen resulted in a decrease in the electron mobility and an increase in the electron concentration. After removal of the atomic hydrogen, samples grown at 650 degrees C had 77 K electron mobilities of approximately 140000 cm2 V-1 s-1 at an electron concentration of approximately 3.6*1014 cm-3. Analysis of the temperature dependence of the electron mobility indicates that the atomic hydrogen, which comes from the thermal decomposition of the phosphine on epilayer cool-down, neutralises both donors and acceptors. The incorporation and removal of hydrogen does not affect the optical characteristics of the material as measured by photoluminescence and far-infrared photoconductivity.

Influence of hydrogen passivation on the infrared spectra of Hg0.8Cd0.2Te

Hydrogen passivation has been investigated in Hg0.8Cd0 2Te using infrared transmission measurements. The ability of atomic hydrogen to passivate the activities of residual impurities or defects is demonstrated by the fact that the absorption edge is moved to the short wave direction and the absorption below the energy gap is reduced after the incorporation of atomic hydrogen using an rf glow discharge system. It is also found that Hg vacancies can be effectively passivated after hydrogenation. Hydrogen injection and passivation of residual impurities or defects are also observed in Hg0.8Cd0.2Te boiled in water.

Rearrangement of surface steps of the Ni(7911) surface by hydrogen adsorption

Chemisorption of hydrogen on a Ni(7911) stepped surface was studied by LEED, AES, UPS and work function measurements. Atomic hydrogen is chemisorbed on this surface and causes a rearrangement of steps. Hydrogen molecules are found to be inactive for such an effect. It is concluded that the step rearrangement is induced by the incorporation of atomic hydrogen into the subsurface region through step sites. Structural models for the step-rearranged states produced by hydrogen chemisorption are discussed.

Hydrogenation of GaAs-on-InP

Incorporation of atomic hydrogen into heteroepitaxial Si-doped GaAs layers grown directly on InP substrates by organometallic vapor phase epitaxy produces substantial increases in the reverse bias breakdown voltage of TiPtAu Schottky diodes fabricated on the GaAs-on-InP. Plasma hydrogenated diodes annealed at 400 °C to restore the electrical activity of the passivated shallow donors have reverse breakdown voltages (VB) of ∼6.5 V compared to 4.5 V for untreated samples. The increases in VB are stable to 500 °C annealing for 5 min. Atomic profiling of deuterated samples showed substantial outdiffusion of deuterium from the GaAs at 600 °C, with increasing accumulation at the heterointerface. The deuterium in this disordered region after 600 °C annealing is in a relatively immobile, electrically inactive state.

Hydrogen passivation of high purity n-type InP

It has been shown for the first time that the concentration of ionised impurities in n-type InP can be reduced by incorporation of atomic hydrogen. The temperature dependence of the electron mobility indicates that donors as well as acceptors are passivated, although the hydrogen is more strongly bound when passivating acceptors.

Electronic structure of amorphous Ge:F(H) alloys

The authors study the electronic structure of fluorinated and hydrogenated amorphous germanium using a linear combination of atomic orbitals. All the nearest-neighbour and the F-F or H-H second neighbour interactions are considered. The interaction integrals for the Ge-H or (Ge-F) bonds are determined by using a 1/d2 law, d being the bond length. The calculated energies for the various molecular orbitals of GeH4 compare very well with the availability experimental data. The local density of states at H(F) and Ge atoms has been computed both for the s and p orbitals. For a-Ge:H alloys, the computed peaks occur at -10.4 and -3.5 eV for the GeH unit, at -10.3, -4.9 and -2.5 eV for GeH2 and at -10.6, -4.9 and -2.3 eV for GeH3. The peaks near -10 and -2.4 eV originate from the s-like and p-like states of the germanium matrix, respectively. The hydrogen-induced peaks are at -3.5 and -4.9 eV. A reduction in the electronic states is observed near the top of the valence band. For a-Ge:F alloys, the authors obtain fluorine-induced peaks at -12.4 and -10.1 eV for GeF, at -12.9, -10.7, -10.0, -9.5 and -9.2 eV for GeF2 and at -13.3, -11.1, -10.6, -9.9, -9,4 and -8.8 eV for GeF3. Again, a large reduction in the electron states near the top of the valence band is observed. The electronic spectra arising from the simple GeFnHm units, and the (GeFH)n chain-like configurations in amorphous germanium are also given. In these the locations of the peaks induced by fluorine atoms remain undisturbed by the incorporation of hydrogen atoms. However, the positions of the hydrogen-induced peaks are altered significantly by the presence of the fluorine atoms. These results are in reasonable agreement with the available photoemission data. However, more careful photoemission measurements on these alloys need to be performed to detect the predicted electronic structure.

Bonding and Release of Hydrogen in a-Si:C:H Alloys

AbstractHydrogen evolution and infrared absorption studies of a-Si:C:H films prepared from mixtures of hydrocarbon (CH4' C2H6' C2H4) and silane gases (SiH4 'Si2H6)by the glow-discharge process show that both the absolute hydrogen content and the hydrogen bonding is uniquely determined by the carbon content. Up to a carbon concentration of ∼45 % the widening of the optical gap is mainly due to an increase of the hydrogen content. For a hydrogen density NH > 1- 2x1022cm-3 the incorporated hydrogen atoms lead to the formation of voids, resulting in thermal instability of the bonded hydrogen and in a deterioration of the electronic quality of the amorphous material.

Incorporation of hydrogen atoms from deuterated water and stereospecifically deuterium-labeled nicotinamide nucleotides into fatty acids with the Escherichia coli fatty acid synthetase system

The mechanism of hydrogen incorporation into fatty acids was investigated with intact Escherichia coli cells, a crude enzyme preparation and purified reductases of fatty acid synthetase system. The distributions of deuterium atoms incorporated into fatty acids from 2H 2O and stereospecifically deuterium-labeled NADPH or NADH were determined by mass spectrometry. When E. coli was grown in 2H 2O, almost every hydrogen atom of cellular fatty acids was incorporated from the medium. When fatty acids were synthesized from acetyl-CoA, malonyl-CoA and NADPH in the presence of a crude enzyme preparation of either E. coli or Bacillus subtilis, almost every hydrogen atom was also incorporated from the medium. In contrast to these results, purified β-ketoacyl acyl carrier protein reductase directly transferred the H B hydrogen of NADPH to β-ketoacyl acyl carrier protein, and purified enoyl acyl carrier protein reductase also transferred the H B hydrogen of NADPH and NADH directly to enoyl acyl carrier protein. In the crude enzyme preparation of E. coli, we found high activities which exchanged the H B hydrogen of NADPH with the deuterium of 2H 2O. The conflicting results of the origin of hydrogen atoms of fatty acids mentioned above are explained by the presence of enzymes, which catalyzed the rapid exchange of NADPH with the deuterium of 2H 2O prior to the reaction of fatty acid synthetase.

Stereochemical studies of hydrogen incorporation from nucleotides with fatty acid synthetase from Brevibacterium ammoniagenes.

The biosynthesis of fatty acids from malonyl-CoA and acetyl-CoA was investigated with an enzyme preparation which was purified 100-fold from Brevibacterium ammoniagenes. Fatty acids synthesized in the presence of D2O and stereospecifically deuterated NADPH and NADH were isolated and analyzed by mass chromatography to examine the localization of deuterium in the molecule. The following results were obtained: 1) HB hydrogen of NADPH was used for beta-ketoacyl reductase. 2) HB hydrogen of NADH was used for enoyl reductase. 3) Hydrogen atoms from water were found on the even-numbered methylene carbon atoms (2-hydrogen atoms per carbon atom) and some were also found on the odd-numbered methylene carbon atoms. 4) Hydrogen atoms from NADPH was found on the odd-numbered methylene carbon atoms (1 hydrogen per carbon). 5) Hydrogen atoms from NADH was also found on the odd-numbered methylene carbon atoms, but the number of incorporated hydrogen atoms was less than expected. The exchange of HB hydrogen of NADH with water catalyzed by enoyl reductase was suspected. 6) The exchange of methylene hydrogen atoms of malonyl-CoA with protons of water was suggested by 13C NMR analysis.

Stereochemical studies of hydrogen incorporation from nucleotides with fatty acid synthetase from Brevibacterium ammoniagenes.

The biosynthesis of fatty acids from malonyl-CoA and acetyl-CoA was investigated with an enzyme preparation which was purified 100-fold from Brevibacterium ammoniagenes. Fatty acids synthesized in the presence of D2O and stereospecifically deuterated NADPH and NADH were isolated and analyzed by mass chromatography to examine the localization of deuterium in the molecule. The following results were obtained: 1) HB hydrogen of NADPH was used for beta-ketoacyl reductase. 2) HB hydrogen of NADH was used for enoyl reductase. 3) Hydrogen atoms from water were found on the even-numbered methylene carbon atoms (2-hydrogen atoms per carbon atom) and some were also found on the odd-numbered methylene carbon. 4) Hydrogen atoms from NADPH were found on odd-numbered methylene carbon atoms (1-hydrogen per carbon). 5) Hydrogen atoms from NADH were also found on the odd-numbered methylene carbon atoms, but the number of incorporated hydrogen atoms was less than expected. The exchange of HB hydrogen of NADH with water catalyzed by enoyl reductase was suspected. 6) The exchange of methylene hydrogen atoms of malonyl-CoA with proton of water was suggested by 13C NMR analysis.

Potentialausbildung an der Mangandioxid-Elektrode als oxidelektrode mit nichtstöchiometrischem oxid

A critical summary of the previous interpretations of the potential of the manganese-dioxide electrode is given; this potential is discussed on the basis of a general thermodynamic theory of Vetter. The dependence of the potential of a Pt/γ-MnOn . (2 - n)H2O-electrode on pH (1·40–4·54), concentration of Mn2+ (5 × 10−2 - 5 × 10−6 mol/1) and the oxidation degree n has been determined. A potentiometric method of analysis is described by which it is possible to determine the oxidation degree n of 0,5 mg manganese dioxide (layer thickness 0·2 μm), with a maximum error in Δn of ±0·003. It could be shown, in accordance with the theory, that the value of pH and the concentration of Mn2+ in the solution determines the oxidation degree n of the oxide, which is in equilibrium with the given solution. Establishment of equilibrium was attained in a few hours, or up to 2 days.The solubility product P2(n) = [Mn2+][OH−]2 of the non-stoichiometric (valency 2n) manganese oxide and its dependence on the oxidation degree n has been evaluated. The free enthalpy of formation ΔG0(n) of manganese oxide and its variation with n has been calculated from electrochemical data.The chemical formula of γ-manganese dioxide is discussed on the basis of X-ray and thermogravimetric measurements (as carried out by other authors), and has been found to be MnO2n-2(OH)4-2n = MnO2H4-2n = MnOn(2 - n)H2O. The incorporation of hydrogen atoms during the reduction process takes place through diffusion of H+ and e−. The results of previous investigations of Vosburgh, Brenet, Bode, Feitknecht, Glemser and their co-workers are compared with our own.