Hydrogen Defects Research Articles

The effect and nature of the radiation induced oxide-interface traps on the performance of the Yb2O3 MOS device

Modifications in the crystal properties, chemical compositions and bond contents as a result of irradiation of Yb2O3/Si structures annealed at different temperatures in the dose range of 1–50 kGy were investigated. Beside, comprehensive results on the effect of the structural changes on radiation response of the MOS capacitors produced with these structures was presented in this study. 122 nm-thick Yb2O3 films were grown on p-type Si by RF magnetron sputtering, and the Yb2O3/Si structures were annealed at 200 °C, 400 °C, 600 °C, 800 °C under nitrogen ambient. The radiation exposure disrupts the crystalline properties of the film. Yb 4 d and O 1s spectra were taken from different depths in the Yb2O3/Si structures with X-ray photoelectron spectroscopy. Reasons of the right-side shift in the capacitance voltage (C–V) curves of the as-deposited and 200 °C-Yb2O3 MOS capacitors with radiation exposure were determined as increasing 2+ oxidation state occurring with the trapping of the electrons in the Yb3+ defect centers, decreasing Si–Si bond contents causing the positive charge trapping at Yb2O3/Si interface, existence of the hydrogen defect precursors. Events causing the left-side shift of the C–V with radiation exposure may be the silicate layer developing at the interface, increase in the trapping of the positive charges in the Si–Si defect centers, and decreasing Yb–Yb and 2+ contents. The radiation responses of the 400 °C, 600 °C, 800 °C-Yb2O3 MOS capacitors could not be measured at the frequencies lower than 2 MHz due to high charge trapping, high binding energies of the Yb–O and Yb3+ peaks, increasing 2+ oxidation content. The C–V curve shifted to the left-side at the relatively lower dose of 1 kGy for only device composed of 200 °C-Yb2O3 film. The sensitivities of the 200 °C-Yb2O3 MOS capacitor were found to be 16.3 mV/Gy for 70 Gy.

Displacement cascade evolution in tungsten with pre-existing helium and hydrogen clusters: a molecular dynamics study

Abstract The effects of radiation damage on bcc tungsten with preexisting helium and hydrogen clusters have been investigated in a high-energy environment via a comprehensive molecular dynamics simulation study. This research determines the interactions of displacement cascades with helium and hydrogen clusters integrated into a tungsten crystal generating point defect statistics. Helium or hydrogen clusters of atoms~0.1% of the total number of atoms have been randomly distributed within the simulation model and primary knock-on-atom (PKA) energies of 2.5, 5, 7.5 and 10 keV have been used to generate displacement cascades. The simulations quantify the extent of radiation damage during a simulated irradiation cycle using the Wigner-Seitz point defect identification technique. The generated point defects in crystals with and without pre-existing helium/hydrogen defects exhibit a power relationship with applied PKA energy. The point defects are classified by their atom type, defect type, and distribution within the irradiated model. The presence of pre-existing helium and hydrogen clusters significantly increases the defects (5 - 15 times versus pure tungsten models). The vacancy composition is primarily tungsten (e. g., ~70% at 2.5 keV) in models with pre-existing helium, but the interstitials are primarily He (e. g., ~89% at 10 keV). On the other hand, models with pre-existing hydrogen have a vacancy composition that is primarily tungsten (more than 90% irrespective of PKA energy), and the interstitial composition is more balanced between tungsten (average 46%) and hydrogen (average 54%) interstitials across the PKA range. The distribution of the atoms reveals that the tungsten point defects prefer to reside close to the position of cascade initiation, but helium or hydrogen defects reside close to the positions where clusters are built.

Effect of Isovalent Doping on Hydrogen Passivated Vacancy-oxygen Defect Complexes in Silicon: Insights from Density Functional Theory

Using the hybrid density functional theory (DFT) computational approach, we examine the effect of hydrogen passivation and isovalent doping on the vacancy(Vn)-oxygen interstitial(Oi), i.e., Vn-Omi (n, m = 0,1,2) defect complexes in silicon. Specifically, we study the structural properties, relative stability and defect levels induced by the V, V2, VOi, V2Oi VO2i defect complexes. We found that hydrogen passivation improve the electrical activity of silicon vacancy and divacancy, but has negative or undesirable effect on the electrical activity of VOi, V2Oi VO2i defect complexes. To remove the negative effect of hydrogen passivation, isovalent doping of VOi, V2Oi VO2i defect complexes with each of Ge, Sn and Pb is carried out. This is found to improve the electrical activity of the defect complexes by shifting the defect-induced acceptor and shallow donor levels deep into the valence and the conduction bands, respectively. Our work emphasizes the importance of isovalent doping in improving the electrical activity of silicon containing hydrogen and vacancy-oxygen defect complexes.

Well-behaved Ge n+/p shallow junction achieved by plasma immersion ion implantation

Ge n+/p junctions fabricated by conventional ion implantation (CII) and plasma immersion ion implantation (PIII) are compared in this work. To achieve low junction leakage current, PIII-implanted Ge n+/p junctions require higher annealing temperature to eliminate the Shockley-Read-Hall generation current, which may be contributed to the residual hydrogen and hydrogen-related defects. It is demonstrated that with 500 °C annealing, well-behaved Ge n+/p junction with ultra-shallow junction depth (<50 nm) can be achieved by PIII. With 600 °C annealing, best Ge n+/p junction performance with current on/off ratio ~9 × 105 and ideality factor ~1.07 is achieved by PIII.

Effect of H Defects on Li Transport during the Deposition Process on an H‐Diamond Surface: A First‐Principles Calculation Analysis

AbstractTo explore the feasibility and rationality of a hydrogen‐terminated diamond surface film as an solid electrolyte interface (SEI) for lithium‐sulfur batteries, the adsorption and migration behavior of lithium atoms on the hydrogen‐terminated diamond surface with different amounts of hydrogen defects are determined by first‐principles calculations. Since a hydrogen deficiency in the row direction is denser than a hydrogen deficiency in the chain direction, hydrogen deficiency can drive lithium‐ion deposition. Thus, lithium atoms are more stable on the surface of hydrogen‐terminated diamonds with a hydrogen deficiency in the direction of the dimer row. The adsorption of lithium atoms on hydrogen‐terminated diamond films lacking three hydrogens is more stable due to the absence of dangling chemical bonds on the surface of the hydrogen‐terminated diamond. Therefore, lithium atoms cannot be adsorbed on an all‐H‐diamond surface. The low adsorption energy of lithium atoms on a clean diamond surface indicates that it is a simple physical adsorption. H termination increases the adsorption energy and migration activation energy of Li on the diamond surface. H termination changes the migration path of Li on the diamond surface. The atomic deposition of Li is driven by the center of the H defect region on the H‐diamond surface.

Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation

A series of coesite, coexisting with or without a liquid phase, was synthesized in the nominal system SiO2–H2O at 800–1450 ​°C and 5 ​GPa. Micro-Raman spectroscopy was used to identify the crystalline phase, electron microprobe and LA-ICP-MS were employed to quantify some major and trace elements, and unpolarized FTIR spectroscopy was applied to probe the different types of hydrogen defects, explore water-incorporation mechanisms and quantify water contents. Trace amounts of Al and B were detected in the coesite. Combining our results with the results in the literatures, we have found no positive correlation between the Al contents and the “Al”-based hydrogen concentrations, suggesting that previously proposed hydrogen-incorporation mechanism H+ ​+ ​Al3+ ↔ Si4+ does not function in coesite. In contrast, we have confirmed the positive correlation between the B contents and the B-based hydrogen concentrations. The hydrogen-incorporation mechanism H+ ​+ ​B3+ ↔ Si4+ readily takes place in coesite at different P-T conditions, and significantly increases the water content at both liquid-saturated and liquid-undersaturated conditions. For the SiO2–H2O system, we have found that type-I hydrogarnet substitution plays a dictating role in incorporating water into coesite at liquid-saturated condition, type-II hydrogarnet substitution contributes significantly at nearly dry condition, and both operate at conditions in between. The water solubility of coesite, as dictated by the type-I hydrogarnet substitution, positively correlates with both P and T, cH2O ​= ​−105(30) ​+ ​5.2(32) ​× ​P ​+ ​0.112(26) ​× ​T, with cH2O in wt ppm, P in GPa and T in °C. Due to its low water solubility and small fraction in subducted slabs, coesite may contribute insignificantly to the vertical water transport in subduction zones. Furthermore, the water solubility of any coesite in exhuming ultra-high pressure metamorphic rocks should be virtually zero as coesite becomes metastable. With an adequately fast water-diffusion rate, this metastable coesite should be completely dry, which may have been the key factor to the partial preservation of most natural Coe. As a byproduct, a new IR experimental protocol for accurate water determination in optically anisotropic nominally anhydrous minerals has been found. Aided with the empirical method of Paterson (1982) it employs multiple unpolarized IR spectra, collected from randomly-orientated mineral grains, to approximate both total integrated absorbance and total integrated molar absorption coefficient. Its success relies on a high-level orientation randomness in the IR analyses.

IR Features of Hydrous Mg2SiO4-Ringwoodite, Unannealed and Annealed at 200–600 °C and 1 atm, with Implications to Hydrogen Defects and Water-Coupled Cation Disorder

Three batches of Mg2SiO4-ringwoodites (Mg-Rw) with different water contents (CH2O = ~1019(238), 5500(229) and 16,307(1219) ppm) were synthesized by using conventional high-P experimental techniques. Thirteen thin sections with different thicknesses (~14–113 μm) were prepared from them and examined for water-related IR peaks using unpolarized infrared spectra at ambient P-T conditions, leading to the observation of 15 IR peaks at ~3682, 3407, 3348, 3278, 3100, 2849, 2660, 2556, 2448, 1352, 1347, 1307, 1282, 1194 and 1186 cm−1. These IR peaks suggest multiple types of hydrogen defects in hydrous Mg-Rw. We have attributed the IR peaks at ~3680, 3650–3000 and 3000–2000 cm−1, respectively, to the hydrogen defects [VSi(OH)4], [VMg(OH)2MgSiSiMg] and [VMg(OH)2]. Combining these IR features with the chemical characteristics of hydrous Rw, we have revealed that the hydrogen defects [VMg(OH)2MgSiSiMg] are dominant in hydrous Rw at high P-T conditions, and the defects [VSi(OH)4] and [VMg(OH)2] play negligible roles. Extensive IR measurements were performed on seven thin sections annealed for several times at T of 200–600 °C and quickly quenched to room T. They display many significant variations, including an absorption enhancement of the peak at ~3680 cm−1, two new peaks occurring at ~3510 and 3461 cm−1, remarkable intensifications of the peaks at ~3405 and 3345 cm−1 and significant absorption reductions of the peaks at ~2500 cm−1. These phenomena imply significant hydrogen migration among different crystallographic sites and rearrangement of the O-H dipoles in hydrous Mg-Rw at high T. From the IR spectra obtained for hydrous Rw both unannealed and annealed at high T, we further infer that substantial amounts of cation disorder should be present in hydrous Rw at the P-T conditions of the mantle transition zone, as required by the formation of the hydrogen defects [VMg(OH)2MgSiSiMg]. The Mg-Si disorder may have very large effects on the physical and chemical properties of Rw, as exampled by its disproportional effects on the unit-cell volume and thermal expansivity.

Roasted coffee wastes as a substrate for Escherichia coli to grow and produce hydrogen.

After brewing roasted coffee, spent coffee grounds (SCGs) are generated being one of the daily wastes emerging in dominant countries with high rate and big quantity. Escherichia coli BW25113 wild-type strain, mutants with defects in hydrogen (H2)-producing/oxidizing four hydrogenases (Hyd) (ΔhyaB ΔhybC, ΔhycE, ΔhyfG) and septuple mutant (ΔhyaB ΔhybC ΔhycA ΔfdoG ΔldhA ΔfrdC ΔaceE) were investigated by measuring change of external pH, bacterial growth and H2 production during the utilization of SCG hydrolysate. In wild type, H2 was produced with rate of 1.28mL H2 (g sugar)-1 h-1 yielding 30.7mL H2 (g sugar)-1 or 2.75L (kg SCG)-1 during 24h. In septuple mutant, H2 production yield was 72mL H2 (g sugar)-1 with rate of 3mL H2 (g sugar)-1 h-1. H2 generation was absent in hycE single mutant showing the main role of Hyd-3 in H2 production. During utilization of SCG wild type, specific growth rate was 0.72±0.01 h-1 with biomass yield of 0.3g L-1. Genetic modifications and control of external parameters during growth could lead to prolonged and enhanced microbiological H2 production by organic wastes, which will aid more efficiently global sustainable energy needs resulting in diversification of mobile and fixed energy sources.

Review of Hydrogen Embrittlement in Metals: Hydrogen Diffusion, Hydrogen Characterization, Hydrogen Embrittlement Mechanism and Prevention

Hydrogen dissolved in metals as a result of internal and external hydrogen can affect the mechanical properties of the metals, principally through the interactions between hydrogen and material defects. Multiple phenomena such as hydrogen dissolution, hydrogen diffusion, hydrogen redistribution and hydrogen interactions with vacancies, dislocations, grain boundaries and other phase interfaces are involved in this process. Consequently, several hydrogen embrittlement (HE) mechanisms have been successively proposed to explain the HE phenomena, with the hydrogen-enhanced decohesion mechanism, hydrogen-enhanced localized plasticity mechanism and hydrogen-enhanced strain-induced vacancies being some of the most important. Additionally, to reduce the risk of HE for engineering structural materials in service, surface treatments and microstructural optimization of the alloys have been suggested. In this review, we report on the progress of the studies on HE in metals, with a particular focus on steels. It focuses on four aspects: (1) hydrogen diffusion behavior; (2) hydrogen characterization methods; (3) HE mechanisms; and (4) the prevention of HE. The strengths and weaknesses of the current HE mechanisms and HE prevention methods are discussed, and specific research directions for further investigation of fundamental HE mechanisms and methods for preventing HE failure are identified.

Optical spectroscopy of muon/hydrogen defects in 6H-SiC

Positive muons can be implanted into silicon carbide (SiC), where they model the isolated hydrogen defect in the negative, neutral, or positive charge states and act as either an acceptor or a donor with midgap energy levels [Lichti et al., Phys. Rev. B 70, 165204 (2004); Lichti et al., Phys. Rev. Lett. 101, 136403 (2008)]. The charge states evolve after implantation depending on the temperature and material doping. We have measured optically induced effects on muons implanted in 6H-SiC using a pulsed, tunable laser [Yokoyama et al., Rev. Sci. Instrum. 87, 125111 (2016)]. In n-type 6H-SiC at 85 K and 40 K, with a laser pulse of energy below the bandgap, we observe photoionization of the doubly occupied level (Mu−) to the neutral defect Mu0 and also ionization of Mu0 to Mu+. Varying the timing of the laser pulse relative to muon arrival confirms that the laser interacts directly with the muons in a stable or metastable state. There is no evidence of any interaction when the laser pulse is timed to arrive before the muons, so either few free carriers are generated by absorption at other dopant sites or the excess carriers have a very short lifetime (≪100ns). Wavelength scans show absorption edges corresponding to the possible interstitial sites within the structure. Combining these data and the existing muon results shows that at low temperature, we have co-existence of Mu0 and Mu− charge states, with the muon or hydrogen acting as a deep compensating impurity. The technique can be applied to many other semiconductors where the muon has been observed to be electrically active, modeling hydrogen.

Study of defects in diamond Schottky barrier diode by photocurrent spectroscopy

Defects in vertical diamond Schottky barrier diodes have been investigated by photocurrent spectroscopy in supercontinuum light photon energy ranging from 1.24 to 3.1 eV, and from 170 to 296 K. The photocurrent spectra exhibit three thresholds located around 1.3, 2.2 and 2.5 eV, which are related to defects energy levels in the active layer of diamond Schottky diodes (a slightly doped boron layer). Although the origin of the reported defects is still under discussion, they can be ascribed to hydrogen and nitrogen related defects. Moreover, the generated photocurrent can be explained by a two-photon process.

Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods.

Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical nanorod arrays. The ability to define the morphology and structure of the nanorods is essential to maximizing the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show that the O-polar nanorods (∼0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (∼0.37 eV). Oxygen plasma treatment is shown by cathodoluminescence spectroscopy to affect midgap defects associated with radiative emissions, which improves the Schottky contacts from weakly rectifying to strongly rectifying. Interestingly, the plasma treatment is shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc-vacancy-related hydrogen defect complexes (VZn-nH) in Zn-polar nanorods that evolve to lower-coordinated complexes. The effect on HO in the O-polar nanorods coincides with a large reduction in the visible-range defects, producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled, enhancing devices such as dynamic photodetectors, strain sensors, and light-emitting diodes while showing that the O-polar nanorods can outperform Zn-polar nanorods in such applications.

The evolution of hydrogen induced defects and the restoration of [formula omitted]-plasmon as a monitor of the thermal reduction of graphene oxide

In this article, we study the modification of the optical, chemical and electronic properties of graphene oxide (GO) during thermal reduction in ultra-high-vacuum by combining the results of several electron spectroscopies. We find that the fraction of oxygen moieties on the surface, as deduced from the evolution of C 1s core level in photoemission, is progressively reduced upon increasing the annealing temperature from 150 to 650 °C. The intensity of the CH stretching mode, associated with CH defects on GO surface and measured in the low energy region of electron energy loss spectra (EELS), decreases as a function of the annealing temperature. The removal or the reduction of such hydrogen or oxygen defects induces a restoration of sp2 carbon hybridization. The presence of such hybridization is confirmed by the capability to excite π-plasmon as observed in the EELS spectra. In particular we find a critical annealing temperature (Tann = 300 °C) at which π-plasmon excitation via electron scattering is accessible suggesting the formation of graphene-like domains with size comparable with the plasmon wavelength (λp~5 nm). The linear dispersion of π-band close to Fermi level, as measured in UPS, confirms the formation of graphene-like domains.

CHAPTER 5 Effect of Water Vapour on the High Temperature Oxidation of Stainless Steels

This chapter primarily reviews the nature of water vapour when it presents in bulk gas. The change in a ratio between water vapour and corresponding dissociated hydrogen, which determine the thermodynamic stability of the oxide formation, is analysed when the oxidation kinetics are linear and parabolic. When water vapour reaches the solid/gas interface, chromium species volatilisation and oxidation controlled by surface reaction can occur. The adsorbed water vapour can be further incorporated into the oxide possibly in the form of hydrogen defects. The role of these defects on altering the defect structure of the oxide is discussed. Finally, characteristics of the oxide scale on stainless steels formed in the atmosphere containing water vapour are reviewed.

Zr vacancies and their complexes with hydrogen in monoclinic zirconia: formation energies and positron lifetimes

Cation vacancies in metal oxides have high formation energies and, thus, are not as abundant as their oxygen-related counterparts. Nonetheless, they can be readily created during non-equilibrium processes. Positron-annihilation spectroscopy (PAS) is a well suited technique of probing such defects since negatively-charged lattice vacancies are deep potential wells which can act as positron traps. The present study reports first-principles calculations of positron trapping at Zr monovacancies in monoclinic zirconia. The binding of positrons and associated lifetimes for these defects were obtained within two-component density-functional theory under different approximations for the electron–positron correlation. The role of hydrogen was also explored. Low-energy vacancy–hydrogen defect complexes were determined for one and two hydrogen atoms bound to a single Zr monovacancy. Hydrogen decoration of the vacancy affected the localization of the positron leading to an appreciable decrease of the lifetime. The study was supplemented with PAS measurements on samples of monoclinic zirconia. From the PAS data two distinct, high-intensity components were resolved originating from different defect states. The corresponding lifetimes of 187 and 225 ps were very close to the theoretical predictions.

Hyperfine interaction of H-divacancy in diamond

We present a first principles density functional theory study of microscopic properties of hydrogen defect centres in diamond. Several configurations, involving interstitial hydrogen impurities, have been considered either forming with other defects, such as hydrogen defects and vacancies. The atomic structures, and hyperfine parameters of hydrogen result compared with the experimental data on electrically active centres in synthetic diamond. Based on Local density functional theory our calculations are in excellent agreement with one interpretation of electron paramagnetic resonance of hydrogen in diamond.

Molecular dynamics studies of hydrogen diffusion in tungsten at elevated temperature: Concentration dependence and defect effects

Influence of hydrogen concentration and defects introduced by neutron irradiation on hydrogen diffusion in tungsten has been investigated by molecular dynamics simulation at elevated temperatures. Hydrogen diffusion is shown to be significantly restrained at high concentrations due to spontaneous formation of platelet-like hydrogen clusters. For neutron irradiation defects, self-interstitials, mono-vacancies and vacancy clusters are considered. By clustering and acting as dislocation loops, self-interstitials show considerable trapping effects on hydrogen, leading to the suppression of hydrogen effective diffusion and the change of diffusion model in which hydrogen mainly diffuses along dislocation lines instead of hopping between tetrahedral interstitial sites. Moreover, an equation connecting hydrogen diffusion parameters and the total length of dislocation loops is empirically established. Different influences of mono-vacancies and vacancy clusters on hydrogen diffusion have been carefully identified. With the same vacancy concentration, hydrogen diffusivity is lower with mono-vacancies than that with vacancy clusters because more isolated trapping sites are provided by mono-vacancies. This work is not only helpful for understanding the synergistic effects of neutron irradiation and plasma interaction, but also potentially applicable for larger scale simulations as input data.

Computational and experimental identification of hydrogen defect vibrational modes in zinc sulfide

The characteristic extrinsic infrared absorption in bulk chemical vapor deposited (CVD) ZnS has been unambiguously identified. High resolution absorption measurements and ab initio vibrational calculations identify the absorption of 1760–1580 cm−1 as due to defects of the form (ZnHn)S, with n = 3 being the highest concentration. Multiple absorption peaks in this spectral region are due to Zn-H stretching from different bond lengths. Phonon spectra calculations of hexagonal ZnO impurities do not account for the spectral position of the absorption without three-phonon processes and thus are unlikely to be responsible for the extrinsic infrared absorption in CVD ZnS. This work shows the complementary utility of computational and experimental work for identifying defect structures in semiconductors.

Formation and annealing of radiation defects in silicon, implanted with hydrogen ions

Energy spectrum of radiation defect levels in n-type epitaxial silicon irradiated with 300 keV hydrogen ions was studied by DLTS (deep level transient spectroscopy) method. The increase in the amplitude of DLTS peak with the increase in the temperature of its registration was found. This indicates the formation of areas of defects accumulation with displacement density lower initial level of doping. After exposure of irradiated samples at room temperature for several months, these areas decay with isolated point A-, E-centers and hydrogen defects with an Ec – 0.31 eV level formation. It is shown that complexes with an Ec – 0.31 eV level are formed by attaching hydrogen atoms to A-center. At Т &gt; 150 °С, this defect begins to anneal, and at the same time A-center concentration is increased.

The Itinerant 2D Electron Gas of the Indium Oxide (111) Surface: Implications for Carbon- and Energy-Conversion Applications.

Transparent conducting oxides (TCO) have integral and emerging roles in photovoltaic, thermoelectric energy conversion, and more recently, photocatalytic systems. The functional properties of TCOs, and thus their role in these applications, are often mediated by the bulk electronic band structure but are also strongly influenced by the electronic structure of the native surface 2D electron gas (2DEG), particularly under operating conditions. This study investigates the 2DEG, and its response to changes in chemistry, at the (111) surface of the model TCO In2 O3 , through angle resolved and core level X-ray photoemission spectroscopy. It is found that the itinerant charge carriers of the 2DEG reside in two quantum well subbands penetrating up to 65 Å below the surface. The charge carrier concentration of this 2DEG, and thus the high surface n-type conductivity, emerges from donor-type oxygen vacancies of surface character and proves to be remarkably robust against surface absorbents and contamination. The optical transparency, however, may rely on the presence of ubiquitous surface adsorbed oxygen groups and hydrogen defect states that passivate localized oxygen vacancy states in the bandgap of In2 O3 .