Hydrogen Complexes Research Articles

Boron–hydrogen complexes in diamond and their vibrational properties

Diamond is a promising candidate material for high power, high temperature and high frequency electronics. Boron is well known as a shallow acceptor in diamond. Recently diamond has been successfully shallow n-type doped by introducing an excess of deuterium in high quality B doped diamond, enabling a reversible p-type to n-type conversion of B doped diamond. However, the nature of this new shallow donor has been the subject of debate. We calculate the properties of boron and its complexes with hydrogen in diamond, using accurate ab initio plane wave Density Functional Theory (DFT) methods, and show that BH 2 centres are stable with small binding energies of 0.23 to 0.71 eV, consistent with experimentally observed dissociation of the new donor at relatively low temperatures of 200 °C, and explain the two-step deuteration process in high quality boron doped diamond. Our ab initio Plane Wave periodic supercell DFT theory calculations confirm the existence of a BH induced level at E c – 0.96 eV. We further show that the BH 2 centre possesses a very deep donor level, excluding the possibility of BH 2 doping the BH impurity band previously suggested. To facilitate experimental determination of the nature of the new shallow donor, we determine the Local Vibrational Modes of BH and BH 2 centres in different charge states, together with isotope shifts, which may be compared with experiment, towards establishing the nature of the new donor.

Hydrogenation of platinum introduced in silicon by radiation enhanced diffusion

Hydrogenation of deep-lying platinum layers in silicon is reported. Two methods of hydrogenation were compared – rf hydrogen plasma exposure at 250 °C and proton implantation – both followed by annealing up to 400 °C. Several platinum–hydrogen complexes were identified by deep-level transient spectroscopy and their annealing characteristics were established. Result show that proton implantation allows local hydrogenation of platinum atoms at the range of implanted protons. On the other hand, platinum atoms substantially accelerate annealing of radiation defects introduced by implanted protons.

A theoretical study of the hydrogen bonding between the vic-, cis- and trans-C 2H 2F 2 isomers and hydrogen fluoride

MP2/6-31++G(d,p) and B3LYP/6-31++G(d,p) theoretical calculations have been employed to investigate the hydrogen bonding formation involving the vic-, cis- and trans-C 2H 2F 2 isomers and hydrogen fluoride. Our calculations have revealed for each isomer the preferential existence of two possible hydrogen-bonded complexes: a non-cyclic complex and a cyclic complex. For all the three isomers the binding energies for the non-cyclic and cyclic hydrogen complexes are essentially equal using both the MP2 and B3LYP calculations, being that the cyclic structure is slightly more stable. For instance, the binding energies including BSSE and ZPE corrections for the non-cyclic and cyclic structures of cis-C 2H 2F···HF are 8.7 and 9.0 kJ mol −1, respectively, using B3LYP calculations. The cyclic complex formation reduces the polarity, in contrast to what occurs with the non-cyclic complex. This result is more accentuated in vic-C 2H 2F 2···HF. In this latter, Δ μ(cyclic) is −3.07 D, whereas Δ μ(non-cyclic) is +1.92 D using B3LYP calculations. Their corresponding MP2 values are +0.44 D and −1.89 D, respectively. As expected, the complexation produces an H F stretching frequency downward shift, whereas its IR intensity is enhanced. On the other hand, the vibrational modes of the vic-, cis- and trans-C 2H 2F 2 isomers are little affected by complexation. The new vibrational modes due to hydrogen bonding formation show several interesting features, in particular the HF bending modes which are pure rotations in the free molecule.

Electronic structure of boron-doped diamond with B–H complex and B pair

The electronic structure of boron–hydrogen complex and boron pair in diamond are studied by first-principles density-functional calculations with supercell models. The electronic structure calculated for the B–H complexes with C2v or C3v symmetry and the nearest-neighbor B pair is used to interpret recent experimental results such as B 1s x-ray photoemission spectroscopy, 11B nuclear quadruple resonance and B K-edge x-ray absorption spectroscopy, which cannot be explained solely by the isolated substitutional boron.

Investigation of negative electron affinity in hydrogen complex deactivated surface of InP:Zn (100)

Ultraviolet photoemission spectroscopy is used to investigate the development of negative electron affinity at the surface of hydrogenated Zn-doped InP (100). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultrahigh vacuum show a dramatic change in the work function of the material within a set annealing temperature range suggesting the establishment of negative electron affinity at the surface. The strength of the negative electron affinity is 1.08eV. This value is consistent with the deactivation energy of the H–Zn complex (1.14eV) determined previously. Spectral features are also shown to be sensitive to sample temperature. Hydrogen retrapping at the surface limits the effect and it is dependent on whether the surface is smooth or roughened. The electron affinity of the material is thus controlled with defect density and annealing temperature.

Shallow donors in diamond: Be and Mg

Abstract The electronic properties of the impurities Be, Mg and the hydrogen complexes Be–H, Mg–H in diamond have been investigated by first-principle calculations. It is found that the interstitial Be- or Mg- doped diamond are of n-type metal conductivity character. Even at low impurity concentration the doped diamond also appears n-type behavior. The further results indicate that the interstitial Be or Mg doping diamond should be synthesized at H-poor conditions to obtain the n-type material because most of hydrogen atom may result in interstitial Be- and Mg- doped diamond p-type semiconductor or insulator. The substitutional Be and Mg show acceptor behaviors and may compensate other interstitial donors in -diamond. Our results are very helpful to the research of n-type doping in diamond for the future experimental work.

Electrical passivation by hydrogen plasma treatment of transition metal impurities in germanium

Transition metal impurities in germanium introduce deep levels in the band gap, which may influence the lifetime of carriers and leakage currents of devices. In this work it is shown that Ti, Cr and Fe centres in germanium can be passivated using plasma hydrogenation. The metals have been implanted at 90 keV in n- and p-type wafers and in-diffused during a 5 min thermal anneal at 500 °C. Samples have been hydrogenated using a DC plasma for 4 h at 200 °C and Schottky diodes were made for measurement using DLTS. It is found that the levels of metal impurities are passivated by hydrogenation. Characteristic hole and electron traps are assigned to the irradiation damage induced by the direct plasma exposure. Metal-specific levels are tentatively assigned to transition metal–hydrogen-related centres. Two hole traps at 0.05 and 0.10 eV above the valence band are only present in the Cr-doped samples and are tentatively assigned to chromium–hydrogen complexes. A comparison is made with copper–hydrogen in germanium.

Effects of Residual Carbon and Hydrogen Atoms on Electrical Property of GaAsN Films Grown by Chemical Beam Epitaxy

The electrical behavior of nitrogen–hydrogen (N–H) complexes and carbon (C) atoms in GaAsN films grown by the chemical beam epitaxy (CBE) method have been studied by comparing H concentrations and hole concentrations. The contributions of H and C concentrations ([H] and [C]) to ionized impurity scattering have been also investigated. In the GaAsN films, there were three acceptor levels (A0, A1, and A2). The energy levels of A1 and A2 were 130 and 55 meV, respectively. The concentration of the deepest acceptor (A0) was more than 1019 cm-3, which was higher than [H] and [C]. A2 was observed only in films with a high [C]. The amount of A1 was proportional to [H]. Most of the residual H formed N–H complexes; thus, it is concluded that the N–H complex behaved as an acceptor in GaAsN films. At low temperatures, ionized impurity scattering limited the total hole mobility. The inverse numbers of the coefficients for the ionized scattering were consistent with [C] instead of [H]. This suggests that all the residual C atoms were ionized owing to compensation by the donors. A disagreement between N composition and alloy scattering has been also detected. This might indicate a fluctuation in the N composition in the GaAsN films.

Stress-Induced Splitting and Shift of Infrared Absorption Lines of Platinum–Hydrogen Complexes in Si

We have studied the stress-induced splitting and shift of infrared (IR) absorption lines of platinum–hydrogen complexes in Si by Fourier-transform IR (FT-IR) spectroscopy at 10 K combined with the application of uniaxial stress. We observed several peaks at 1873.0, 1880.7, 1891.8, 1922.3, 1929.9, and 1943.0 cm-1. These peaks may be due to the previously observed local vibrational modes (LVMs) of various platinum–hydrogen complexes, that is, the antisymmetric-stretching mode of (Pt–H2)0, the LVM of (Pt–H1)0, the symmetric-stretching mode of (Pt–H2)0, LVMs of (Pt–H3)- and (Pt–H3)0, and the LVM of an unidentified platinum–hydrogen complex, respectively. The peaks of (Pt–H1)0 and (Pt–H2)0 split into two components under <100 > compressive stress, while those of (Pt–H3)- and (Pt–H3)0 did not split. We measured the stress dependence of the two split components of the (Pt–H1)0 peak. The low-wavenumber component shifted by -3.2 cm-1/GPa, and the high-wavenumber component shifted by 4.2 cm-1/GPa. We show that these wavenumber shifts are equal to the piezospectroscopic tensor elements, A1 and A2, respectively. We propose a structural model of the Pt–H1 complex, where a hydrogen atom is bonded to one of four Si neighbors of the Pt atom in the {110} mirror plane perpendicular to the <110 > symmetric axis with C1h symmetry.

Hydrogen complexes of O-vinylacetoxime with trifluoroacetic acid

According to B3LYP/6-31G** calculations, the stable antiperi-, antiperiperiplanar and antiperi-, synperiperiplanar conformers of O-vinylacetoxime (1) form with trifluoroacetic acid strong H complexes of two types: with N···H-O and O···H-O hydrogen bonds. The former are more stable. Complexation changes N-O and C-O bond lengths in molecule 1, as well as mutual orientation of its vinyl and azomethine groups. The structural effect depends on the orientation of the H bond, which, in its turn, is determined by the nature of the electron-donor center. When the nitrogen atom of oxime 1 is involved in complex formation, the H bond lies in the molecular plane, whereas the H bond involving the oxygen atom is directed in parallel with its lone electron pair.

Inherent safety key performance indicators for hydrogen storage systems

The expected inherent safety performance of hydrogen storage technologies was investigated. Reference schemes were defined for alternative processes proposed for hydrogen storage, and several storage potentialities were considered. The expected safety performance of alternative process technologies was explored estimating key performance indicators based on consequence assessment and credit factors of possible loss of containment events. The results indicated that the potential hazard is always lower for the innovative technologies proposed for hydrogen storage, as metal or complex hydrides. This derived mainly from the application of the inherent safety principles of “substitution” and “moderation”, since in these processes hydrogen is stored as a less hazardous hydride. However, the results also evidenced that in the perspective of an industrial implementation of these technologies, the reliability of the auxiliary equipment will be a critical issue to be addressed.

Hydrogen and interstitial Mn complexes inMnxGa1−xAs dilute magnetic semiconductors

Complexes formed by H and Mn interstitials(Mnint)in MnxGa1−xAs dilute magnetic semiconductors (DMSs) have been investigated by using first-principles densityfunctional theory (DFT) methods both in gradient corrected spin density and HubbardU approximations. In agreement with previous results for complexes of H with substitutional Mn(MnGa), present results confirm the importance of electron correlation effects, as the HubbardU treatment weakens the H–Mn bonds even in theH–Mnint complexes. They also indicate that H compensates (without passivating) theMnint by formingMnint–H donor–acceptor(D–A) pairs and, then, Mnint–H complexes. In the H–Mnint and H–MnGa complexes, the H–Mn D–A interaction is always mediated by a host atom, thusleading to the formation of H–Ga bonds for interstitial Mn and of H–As bonds forsubstitutional Mn. This implies quite different H vibrational frequencies for theH–Mnint and H–MnGa complexes, thus suggesting that H can be used as a probe to discriminate between the twoMn forms through vibrational spectroscopy measurements. Finally, a higher stability of theH–Mnint with respectto the H–MnGa complexes has been found, which suggests the use of hydrogenation procedures to control the effectsof Mnint onthe MnxGa1−xAs properties.

Effects of saccharin on the electrodeposition of Ni–Co nanocrystalline coatings

Nickel–Co nanocrystalline coatings were electrodeposited onto a carbon steel substrate with and without saccharin addition. In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished as two effective parameters causing nanocrystalline electrodeposits. In the latter case, the growth active sites can be blocked easily at low current densities. By increasing the current density, a lower degree of adsorption was associated by a significant increase in surface diffusion of adions resulting in grain growth. Although, the nucleation rate is expected to increase with current density, it seems that the Ni–Co grain size is not reduced by the nucleation rate. Adsorption of saccharin molecules and/or decomposed sulfide species occurred in the saccharin contained bath, resulting in slow surface diffusion of adions. Therefore, finer grains were obtained which produced a smooth morphology instead of the pyramidal forms obtained in the absence of saccharin.

&lt;b&gt;STUDIES ON SOLVENT EXTRACTION OF FREE HYDROGEN CYANIDE FROM RIVER WATER&lt;/b&gt;

A method for free and strongly complexed cyanide measurement in river water was developed. Recovery tests from solution with and without river water, using various solvent combinations and background control were investigated to obtain an accurate and precise extraction method for the measurement of hydrogen cyanide in Kaduna River, Nigeria. The method enhanced the determination of undissociated hydrogen cyanide and the equilibria between hydrogen cyanide, cyanide ion and complex cyanides. A small portion of the hydrogen cyanide was extracted by equilibrating the sample with methylchloroform (1,1,1-trichloroethane), methanol, hexane and 2-octanol inclusions, respectively, in the solvent matrix with 2.5 M NaOH. The extracted hydrogen cyanide is transferred into tetrasodium pyrophosphate solution and determined colorimetrically. A total cyanide concentration of 0.03 mg/L in the river water and 0.40 mg/L in an effluent water sample, respectively, were obtained by the proposed method compared to 0.020 and 0.45 mg/L from the established diffusion method. The proposed method was sensitive and reproducible in the range of 0 to 5 mgL -1 of hydrogen cyanide with detectable limit of about 0.01 mgL -1 . KEY WORDS : Solvent extraction; Free hydrogen cyanide; River water Bull. Chem. Soc. Ethiop. 2007 , 21(3), 305-313.

Hydrogen complexes in ZnO grown by chemical vapor transport

The renewed interest in zinc oxide (ZnO) has provided a great number of details that could lead to a commercially viable alternative to gallium nitride (GaN) for use in high-efficiency, wide band-gap devices. The difficulty in obtaining such devices is that as-grown, large single crystals of ZnO are n type. Past research has shown that hydrogen plays an important role in the n-type conductivity of ZnO. However, other impurities cannot be eliminated as possible donors in as-grown ZnO. In an attempt to study the controlled doping of ZnO, we grew polycrystalline samples via the chemical vapor transport (CVT) method, using graphite as the transport agent. After diffusing hydrogen into these crystals, some clearly showed both the OH-related infrared (IR) absorption peak at 3327 cm −1, as reported in our earlier publications, and the 3611 cm −1 absorption peak reported by Lavrov [Physica B 340–342 (2003) 195]. Additionally, a third hydrogen-related absorption peak appears at 3150 cm −1. Suspecting a contaminant in our original source of graphite, we changed to a high-purity source of graphite. The resulting growth yielded no hydrogen-related absorption peaks after hydrogen diffusion into the sample. However, growing samples in ammonia recreated the 3150 cm −1 IR absorption peak.

Manganese–hydrogen complex in GaP

Manganese (Mn) acceptors are well known to form complexes with hydrogen (H) in InP and GaAs crystals. However, to our knowledge, the formation of such complexes in GaP has not been reported yet. The difficulty in formation of Mn–H complexes in GaP can be explained by unfavorable mutual positions of H and Mn energy levels in GaP band structure. A series of GaP samples intentionally doped with Mn and some of them co-doped with zinc (Zn) and containing also unintentional H and carbon (C) has been investigated. In very slightly p-type samples, a local vibration mode at 2369.4 cm −1 at 6 K was found, which we ascribed to Mn–H complexes by comparison of energy positions corresponding to analogical “Mn–H” complexes in other semiconductors. In more strongly p-type samples, these complexes were not found but Zn–H and C–H complexes were present.

Electron Density Topological Properties Are Useful To Assess the Difference between Hydrogen and Dihydrogen Complexes

B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) calculations for a series of hydrogen- and dihydrogen-bonded systems have been carried out in order to analyze the topology of the electron density and the energy densities at the respective energy-optimized bond critical points. Even though there are no significant differences when these properties are represented as a function of the dimerization energy, they can be separated into two well-defined sets if those properties are correlated with intermolecular distances. When analyzing the dependence of various properties with equilibrium bond lengths, the specific trends of dihydrogen bond systems consist of (a) lower electron density at the bond critical point, and (b) lower concentration/depletion of that density which can be translated in a different behavior for the Laplacian components. Furthermore, the sets of molecules form two different plots which allow for a valuable classification between hydrogen- and dihydrogen-bonded systems.

Cationic Dihydrogen/Dihydride Complexes of Osmium: Structure and Dynamics

Reaction of Cp*Os(CO)2Cl with (Et3Si )(BArF4) under hydrogen gas affords the cationic hydrogen complex [Cp*Os(CO)2(H2)][BArF4] (1), (Cp* = C5Me5; ArF = C6F5). When this reaction is carried out with HD gas, complex 1-d1 results, with JHD = 24.5 Hz. When solutions of complex 1 are monitored by 1H NMR spectroscopy over several days, the gradual formation of a trans dihydride species is observed. Similarly, reaction of CpOs(dppm)Br with NaBArF*4 (ArF* = 3,5-(CF3)2C6H3) under hydrogen affords the cationic dihydride complex [CpOs(dppm)H2]BArF*4 (2). At 295 K, complex 2 exists as a 10:1 mixture of cis and trans isomers. The 1H NMR spectrum of the cis form in the hydride region exhibits a triplet with JHP = 6.5 Hz, due to rapid exchange of the hydrogen atoms. At low temperature, static spectra of the HH'PP' spin system can be obtained, revealing quantum mechanical exchange coupling between the two hydride ligands. The observed JHH' is temperature dependent, varying from 133 Hz at 141 K to 176 Hz at 198 K. This is the first report of detectable exchange coupling between pairs of chemically equivalent hydrogen atoms. Research at the University of Washington was supported by the National Science Foundation. Research at Brookhaven National Laboratorymore » was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and was supported by its Division of Chemical Sciences, Office of Basic Energy Sciences. Research at Pacific Northwest National Laboratory (PNNL) was funded by LDRD funds. PNNL is operated by Battelle for the US Department of Energy.« less

Role of Annealing in Constant Period of Voltage Stress on the Burn-in Effect Suppression of InGaP/GaAs Heterojunction Bipolar Transistors

Rapid thermal annealing (RTA) is proved to be more efficient in dissociating hydrogen complexes than using a constant period of voltage stress (CPVS). Without waiting for the bond breaking of complexes by minority carrier injection, RTA favors the critical base–emitter voltage (VBE) responsible for the occurrence of burn-in (BI) from 1.75 to 1.4 V and thus assists CPVS in reducing VBE by about 25% used in BI suppression. Besides eliminating the BI, the sample first prepared by RTA and followed by CPVS has larger base and collector current densities at VBE>1.1 V and reaches 6 times those at VBE>1.3 V compared with the sample only using by CPVS.

Rh-Catalyzed Hydrogenation of Olefins with Zn Metal and Water

A very simple and highly practical method for the reduction of double bonds, including α,β-unsaturated ketones, is described. Zinc and water are used as reducing agents. The process does not require special precautions needed for the handling of flammable hydrogen gas or complex hydrides or the use of a pressure apparatus. In the case of α,β-enones, including cyclic systems, the reaction is completely selective for the C=C reduction, so that it complements well the Luche method for the reduction of enones to allylic alcohols. This method can be conveniently used for the preparation of deuterium-labeled compounds, using cheap D2O as the deuterium source.