Hydrogen Defects Research Articles

Temperature Induced Evolution of Bond-Centered Hydrogen (BCH) Defects in Crystalline Silicon: Dynamical, Electronic, Vibrational and Optical Signatures

ABSTRACTThe thermal stability, evolution and structure of the bond-centered-hydrogen (BCH) defect in crystalline silicon, its temperature induced dissociation, and the new H complexes formed have been studied in the temperature range from 50 K to 650 K by first-principles molecular dynamics (MD). We demonstrate that BCH is stable at 60 K, but decays at and above 310 K in agreement with experimental results. The dissolved BCH forms new complexes: transitional interstitials, stable monohydride-like and monohydride/dihydride-like complexes. The calculated asymmetric vibrational frequency of H in the BCH complex is 2000 cm-1, very close to the experimental values. Calculated vibrational frequencies, electron charge densities, electron densities of states (DOS), and optical spectra demonstrate noticeable differences for the different geometries with the BCH, interstitial and monohydride-like complexes, especially in the vicinity of the energy gap. The BCH complex is found to induce characteristic donor states below the conduction band, and raises the Fermi level to above the donor state energies.

Defect Interactions of ${\hbox{H}}_{2}$ in ${\hbox{SiO}}_{2}$: Implications for ELDRS and Latent Interface Trap Buildup

The energetics of the interactions between molecular hydrogen and common defects in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> that are typically associated with O deficiency have been obtained using atomic-scale quantum mechanical calculations. H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> does not easily crack at neutral vacancies, but it will crack efficiently at O vacancy sites that have captured a hole and relaxed into the puckered configuration of an E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">γ</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> defect, releasing a proton into the oxide. Isolated Si dangling bonds also can play a role in cracking H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , depending on their concentration in the oxides. These results provide significant insight into the underlying causes of latent interface trap buildup in MOS devices and enhanced low-dose-rate sensitivity in linear bipolar devices.

Hydrogen defect saturation in natural pyroxene

Dehydration via the redox reaction: OH- + Fe2+ ↔ O2- + Fe3+ + ½H2, is believed to be a commonly occurring process in pyroxenes and other nominally anhydrous minerals (NAMs) from the upper mantle an ...

Radiation and Thermal Transformations of Hydrogen Defects in Li6F and LiF:OH

Hydrogen and tritium defects formed in LiF under the action of neutron radiation under different conditions have been studied. It is shown that U-centers are registered in LiF:OH without additional heating of the sample after irradiation. The behavior of H0 and T0 atoms in Li6 F irradiated at 20 K was studied, and the places of their stabilization were established.

Appearance of a correlation between the Hall coefficient and electrical resistivity upon dihydrogenation of yttrium

To shed light on the correlation between the Hall coefficient (RH) and electrical resistivity (ρ), we performed simultaneous measurements of these two transport coefficients in fcc dihydride phase of yttrium (YHx), having H/Y values ranging from 1.73 to 2.04. Unlike the typical behavior of metals, an approximately linear relationship was observed between RH and ρ at room temperature after dihydrogenation of yttrium. Interpretation of this relationship, based on the Boltzmann–Bloch scheme, reveals that the transverse (cyclotron) relaxation rate (1/τc) of the carriers is relatively insensitive to the generation of hydrogen defects in the dihydride phase of yttrium, unlike the longitudinal relaxation rate (1/τ), which is affected by the presence of hydrogen defect. Low-temperature (77 K) measurements of RH and ρ on the same samples show that the approximately linear relationship observed at room temperature disappears but a certain nonlinear relationship may exist at 77 K.

Role of Schottky Defects in Hydrogen and Metal Diffusion in NaH, MgH2, and NaMgH3

The diffusion of hydrogen in metal hydrides is crucial to the kinetics of H2 storage in these materials. Although the role of charged H-related defects in several metal hydrides has been studied previously, little is known about the possible role of charged defects associated with metal sites. We describe a comprehensive set of first-principles calculations examining Schottky, Frenkel, and anti-Frenkel defects in NaH, MgH2, and NaMgH3 to address this issue. Our calculations give information on the diffusivities of H and metal atoms in these materials and show that defects associated with metal sites can play a crucial role in net atomic transport. We also consider doping of NaH by heterovalent MgH2, finding that this doping can significantly enhance the diffusivity of H.

The effect of isotope on the interaction between hydrogen and irradiation defect in pure iron

There are many works on the interaction between helium and irradiation defects, but not so many on hydrogen. Especially, the isotopic atoms of hydrogen, deuterium or tritium would exist in the environment of fusion reaction. However, few works were reported about the isotope effect of hydrogen on irradiation damage. This work used ion accelerator to implant ions of hydrogen or deuterium into the samples of pure iron at R.T., followed by annealing at high temperature to make the defects develop into large dislocation loops. The electron irradiation by high voltage electron microscope was carried out to check the nature of loops. The isotopic effect on the bias of dislocation loops was discussed.

Charge states of a hydrogen defect with a local vibrational mode at3326 cm−1in ZnO

An IR absorption study is presented of a hydrogen defect in ZnO that gives rise to a local vibrational mode at $3326\text{ }{\text{cm}}^{\ensuremath{-}1}$ [M. D. McCluskey et al., Appl. Phys. Lett. 81, 3807 (2002)]. It is shown that a subband gap illumination results in the appearance of a new IR absorption line at $3358\text{ }{\text{cm}}^{\ensuremath{-}1}$ at the expense of the main signal at $3326\text{ }{\text{cm}}^{\ensuremath{-}1}$. Based on the anticorrelation between the two lines as well as on the results of isotope substitution experiments it is concluded that both signals are due to stretch modes of an O-H bond of the same defect in different charge states. The energy of the subband gap light strongly suggest that this defect has a deep rather than shallow level in the band gap of ZnO. Additionally, the results on thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented.

Optically active point defects in high quality single crystal diamond

AbstractWe use density functional theory to investigate the optical properties of vacancy di‐nitrogen, vacancy–nitrogen–hydrogen and vacancy di‐hydrogen defects. The first is a common defect found in irradiated natural type IaA diamonds while the second is found in as‐grown CVD diamond. The last has not yet been detected. We find that these defects possess at least two charge states which can lead to photochromic behaviour. In the neutral and negative states, the three defects have optical bands due to internal transitions and two weaker optical absorption bands coming from charge state changes. Thus at least four absorption bands are expected for these defects. Vibrational modes of the hydrogen defects are reported.

Candidate theories to explain the anomalous spectroscopic signatures of atomic H in molecularH2crystals

We analyze a number of proposed explanations for spectroscopic anomalies observed in atomic hydrogen defects embedded in a solid molecular hydrogen matrix. In particular, we critically evaluate the possibility that these anomalies are related to Bose-Einstein condensation (both global and local). For each proposed mechanism we discuss which aspects of the experiment can be explained and make predictions for future experiments.

μSR in diamond

It has recently become possible to take advantage of the interesting properties of diamond, as the synthesis of diamond has reached a point that material with impurities in the low the part per billion range and residual strain in the order of ten nano-radians has been realized. Hyperfine interactions have played a key role in the study of diamond and the emergence of novel applications. This relates to the characterization of defects and the development of engineered few spin systems. A particular aspect of the defect studies is the elusive hydrogen defect. In μSR studies, muonium is considered a light isotope of hydrogen with very similar chemical properties, but with very interestingly different dynamical properties, due to its much lighter mass. It offers a unique opportunity to study the behaviour of hydrogen in diamond at very low concentrations. The studies have revealed details of the elementary muonium atom as well as a molecule involving muonium in the diamond lattice. The dynamics of the muonium, which include quantum diffusion and ionization have also been studied. This contribution reviews μSR in diamond in the context of diamond as a modern material hosting advanced applications.

Stable p-Type Doping of ZnO Film in Aqueous Solution at Low Temperatures

Zinc oxide (ZnO) is a wide band-gap material with excellent optical properties for optoelectronics applications. However, device fabrication has been hampered by difficulties in obtaining a stable p-type doping. Here, we present the first report on the growth and doping of ZnO film through the incorporation of potassium (K) from group I in aqueous solution at 90 °C to yield a stable p-type doping. The contribution of potassium toward p-type conductivity is confirmed using Hall effect measurements and SIMS. A new growth strategy was introduced to obtain a good film coverage with a lower native defect density without the use of surfactants. Photoluminescence measurements confirmed the reduction of defect-related emissions and enhancement of UV band-edge emissions. Variation of carrier concentrations with temperature points to the presence of unstable hydrogen donors that can be removed by annealing at temperatures above 400 °C for extended durations. The instability of these hydrogen defects is attributed t...

Ab initio studies of hydrogen and acceptor defects in rutile TiO2

The behaviour of hydrogen in both defect free and acceptor doped bulk rutile TiO2 is investigated through defect calculations performed within the density functional theory formalism. Both interstitial and substitutional hydrogen defects are shown to behave as shallow donors in the material, thereby existing as effectively positive hydroxide defects, OH*(O), and substitutional hydrogen defects, H*O. Of the investigated isolated hydrogen defects, the OH*(O) defect is shown to have the lowest formation energy over the whole Fermi level range under both oxidising and reducing conditions. However, the formation energy of H*O is only 0.35 eV higher under conditions where TiO2 is in equilibrium with Ti2O3, indicating that it exists as a minority defect in rutile TiO2 under highly reducing conditions such as under growth of TiO2 on a Ti metal surface. The enthalpy of hydration of oxygen vacancies is calculated to be -1.64 and -1.60 eV for the 2 x 2 x 3 and 3 x 3 x 3 supercells, indicating that OH*(O) defects will prevail in wet atmospheres, even at high temperatures. Hydrogen incorporated in the material can furthermore be expected to associate significantly with various acceptor centres (e.g., substitutional N and Al acceptors and Ti vacancies). The binding energies of the substitutional NH(x)O (imide) defect and of the association complexes between H and fully ionised substitutional Al, (Al'Ti x OH*(O)), and Ti vacancies, (V(Ti)x OH*(O)and (V(Ti) x 4OH*(O)) (i.e., Ruetschi type defects), are calculated to be -0.36, -0.12, -0.47 and -0.82 eV, respectively.

First-Principles Estimation of Hydrogen Occupancy around Lattice Defects in Al

Estimations of the fundamental relationship between hydrogen and lattice defects are important for understanding hydrogen embrittlement mechanisms and for predicting the amount of penetrating hydrogen. In this paper, hydrogen-trap energy around the lattice defects (e.g., atomic vacancy, stacking fault, grain boundaries, and free surfaces) within the Al lattice are calculated using first-principles calculations based on Generalized Gradient Approximation (GGA) and Ultra-Soft (US) pseudo potential. The hydrogen-trap energies obtained are 0.30 eV at the atomic vacancy, 0.002 eV at the stacking fault, 0.02 eV at the Σ3{111} Symmetrical Tilt Grain Boundary (STGB), 0.19 eV at the Σ3{112} STGB, and 0.45-0.60 eV at the free surfaces. Moreover, the hydrogen occupancies at the hydrogen-trap sites around the lattice defects are evaluated for several hydrogen gaseous environments using the obtained hydrogen-trap energies. Hydrogen occupancies around the lattice defects are extremely low under the pure hydrogen gaseous conditions. However, according to experimental data, hydrogen concentration can become higher for Al structures due to the hydrogen atoms generated by the surface oxidation process under a moist environment or other reasons. In such cases, the vacancy has a strong interaction with the hydrogen atoms.

Hydrogen Defect Passivation of Silicon Transistor on Plastic for High Performance Flexible Device Application

The electrical characteristics of a transistor on a transferred silicon ribbon are demonstrated. The process temperature is limited to 200°C for potential use on plastic sheets. Additional hydrogen annealing reduces the threshold voltage and improves the transistor properties. A high mobility of around 160 cm 2 /V s, with a high on/off ratio and an off current of as low as < 10 11 A, is achieved. The flexibility of the device is evaluated after applying stress in the bended condition. The device shows very little change in properties with a bending radius <4 mm. Overall, good electrical and mechanical properties are demonstrated for future use on flexible device applications.

Quantum Chemical Molecular Dynamics Simulations of Dynamic Fullerene Self-Assembly in Benzene Combustion

Using density-functional tight-binding (DFTB)-based quantum chemical molecular dynamics at 2500 and 3000 K, we have performed simulations of benzene combustion by gradually reducing the hydrogen to carbon (H/C) ratio. The accuracy of DFTB for these simulations was found to be on the order of 7-9 kcal/mol when compared to higher-level B3LYP and G3-like quantum chemical methods in extensive benchmark calculations. Ninety direct-dynamics trajectories were run for up to 225 ps simulation time, during which hydrocarbon cluster size, curvature, and C(x)H(y) composition, carbon hybridization type, and ring count statistics were recorded. Giant fullerene cage formation was observed only after hydrogen was completely eliminated from the reaction mixture, with yields of around 50% at 2500 K and 42% at 3000 K. Cage sizes are mostly in the range from 152 to 202 carbon atoms, with the distribution shifting toward larger cages at lower temperature. In contrast to previous simulations of dynamics fullerene assembly from ensembles of C(2) molecules, we find that the resulting cages show smaller number of attached carbon chains (antenna) surviving until cage closure. Again, no direct formation pathway for C(60) from smaller fragments was observed. Our results challenge the idealized picture of "ordered" growth of PAHs along a route involving only maximally condensed and fully hydrogenated graphene platelets, and favor instead fleeting open-chains with ring structures attached, featuring a large number of hydrogen defects, pentagons, and other nonhexagon ring species.

Structure and elasticity of hydrous ringwoodite: A first principle investigation

First principle calculations were performed to investigate structural, IR, and elastic properties of hydrous ringwoodite and their evolution with pressure up to 36 GPa. Hydrogen defects are introduced by creating Mg- or Si-vacancies Mg 1.875H 0.25SiO 4, Mg 1.75H 0.5SiO 4 and Mg 2Si 0.875H 0.5O 4. Energy considerations imply that the Mg-vacancy coupled substitution will be the easiest to form, but, in the Earth, both vacancies will participate in the process. Calculated IR spectra, when compared with reported observations, suggest that both types of defects are abundant in synthetic samples. We find that (d ln V S /d ln V P ) for lateral variations in the H content of ringwoodite will be quite small, suggesting that this quantity will be a sensitive metric for identifying the presence of dissolved water in the transition zone. The calculated bulk modulus decreases linearly with increasing water content with d K / d ( C H 2 O ) = − 7.1 ( GPa / wt % ) at room pressure, decreasing to −6.0 (GPa/wt%) at 20 GPa. The shear modulus similarly demonstrates a decrease with increased water content given, averaged over the substitution models, by d G / d ( C H 2 O ) = − 3.0 ( GPa / wt % ) at room pressure, decreasing to −1.8 (GPa/wt%) at 20 GPa. Over this pressured range, the water induce variation of d ln( V S )/d ln( V P ) is 0.62 at 0 GPa to 0.2 at 20 GPa.

Hydrogen, porosity and oxide film defects in liquid Al

This article reports results from an experiment where a bubble of air was held at a constant temperature in a liquid Al melt, with the volume of the bubble monitored continuously using real-time X-ray equipment. When the H content of the surrounding melt was low, the volume of the trapped air bubble reduced with time, as the O and N in the bubble atmosphere reacted with the Al to form Al2O3 and AlN. When the H content of the melt was increased to about 0.3 ml 100 g−1 Al, the H in solution passed into the air bubble causing its expansion. In an Al casting the same effect would cause an entrained double oxide film defect to act as a site for the growth of H-driven gas porosity. The way in which the oxide film defects might behave in forming H porosity has been discussed.

Diamonds from the V. Grib pipe, Arkhangelsk kimberlite province, Russia

A large collection (717 samples) of diamonds from the V. Grib deposit, discovered in 1996 in the Verhotinskoe field of the Arkhangelsk kimberlite province, was studied. The diamond crystals are characterized by high transparency and preservation. The collection consists of complete crystals (71%), chipped and damaged crystals (preservation > 50%; 14%), and fragments (preservation < 50%; 15%). Resorption is generally moderate resulting in a dominance of octahedral and mixed octahedral–dodecahedral shapes. Moderate resorption points to rapid ascent of the transporting kimberlite magma. A characteristic feature of V. Grib is a large number of green diamonds. This may relate to the close proximity of radioactive deposits. Microscopic green surface spots have no cathodoluminescence. The internal diamond morphology was studied by UV- and cathodoluminescence. The main typomorphic feature of diamond crystals from the V. Grib pipe is a high percentage of crystals without UV-luminescence. Presence of sectorial growth was also identified by luminescence. Analysis of mineral inclusions, carbon isotopic composition, nitrogen content and nitrogen aggregation state provided important genetic information. Peridotitic inclusions (olivine, chromian spinel and pyrope) predominate, sulfides are almost completely absent. The carbon isotopic composition of the host diamonds is typical for peridotitic diamonds worldwide. IR-spectroscopy suggests the presence of two diamond populations with low and high nitrogen concentrations. Three sub-populations may be identified based on a combination of morphology, nitrogen and hydrogen defects. Residence temperatures ( T Nitrogen), based on a mantle residence time of 3 Ga, fall between 1050 and 1170 °C. Diamond crystallization in V. Grib occurred in multiple stages. This is documented through luminescence patterns, data on nitrogen concentration and aggregation state, and the presence of “diamond-in-diamond” inclusions.

First-Principle Calculations of Solvated Electrons at Protic Solvent−TiO2 Interfaces with Oxygen Vacancies

Heterogeneous electron transfer dynamics at molecule−metal or molecule−metal oxide interfaces are a central issue for many fields in surface science. Recent time-resolved two-photon photoemission studies observed electron solvation at protic molecule−metal or −metal oxide interfaces in photoinduced charge transfer processes. Although the solvated electron is expected as a functional state (for instance, highly catalytic active site, promoter of charge transfer at devices), details are not yet well understood because of the strong dependence of specific atomistic-level solvent−substrate interactions on interfaces, e.g., ordered hydrogen bonds or defects at surfaces. We focus on the interfaces of H2O/TiO2(110) and CH3OH/TiO2(110) and have applied ab initio DFT calculations for several structures with changing coverage and adsorption types and after inserting oxygen vacancies. The electronic structures of wet-electron states and hydrogen bonds at interfaces have been analyzed using the calculated results.