Investigation of the interaction between hydrogen and irradiation defects in titanium by using positron annihilation spectroscopy

The formation of mono-vacancy, vacancy clusters and hydrogen-vacancy complexes with 30 keV H ion-irradiated pure titanium at different doses and temperatures was measured using by Positron annihilation spectroscopy (PAS). Results show a large number of H_mV_n clusters and vacancy-like defects in the samples irradiated at for room temperature, and that the formation of H_mV_n (m > n) at the sample irradiated at a high dose inhibits the increase of the S parameter. At increased irradiation temperature, the shrinkage of vacancy clusters and the effective open volume of defects decrease the S parameters. The high-temperature irradiation results in decreased vacancy-type defect concentration, and some hydrogen atoms diffuse from the cascade region to the track region, forming a large number of hydrogen-vacancy complexes in the track region. The coincidence Doppler broadening spectroscopy, an element analysis method, used to detect hydrogen in the ion-irradiated pure titanium sample, and results show hydrogen-related peaks in the high-momentum region, which may be due to the information of positron annihilation in the covalent bond formed by the H and the Ti elements. The increased radiation dose and temperature contribute to the formation of the hydrogen vacancy-complex, and the positron annihilation in high-momentum regions easily obtain hydrogen-related information.     

Micro-defects evolution of (Al0.33Cr0.21Fe0.28Zr0.18)O2 and (Al0.33Cr0.2Mn0.09Fe0.22Zr0.16)O2 induced by hydrogen ions irradiation

The micro-defects evolution of (Al_0.33Cr_0.21Fe_0.28Zr_0.18)O₂ and (Al_0.33Cr_0.2Mn_0.09Fe_0.22Zr_0.16)O₂ thin films irradiated with low energy (60 eV) hydrogen ions (H⁺) is investigated through Transmission Electron Microscopy (TEM) and the slow positron Doppler broadening spectroscopy (DBS) technique in this work. The results revealed that some perfect dislocation loops with Burgers vector b = a/2<1 1 0> were observed as the quaternary (Al_0.33Cr_0.21Fe_0.28Zr_0.18)O₂ irradiated with a fluence of 5.2 × 10²² cm^?2. The micro defects are mainly vacancy (V), hydrogen vacancy complex (i.e. H–V complex), and vacancy dislocation loops. However, after the fluence increased to 1.2 × 10²³ cm^?2, the phase of (Al_0.33Cr_0.21Fe_0.28Zr_0.18)O₂ transformed from FCC structure to amorphous, suggesting that the weak ionic bonds between the cations with O. The defects mainly exist as large amounts of hydrogen bubbles, some H–V complex and few voids. As the addition of little Mn element, the phase of quinary (Al_0.33Cr_0.2Mn_0.09Fe_0.22Zr_0.16)O₂ was unstable and easily produce precipitate under the irradiation temperature. And the micro-defects in (Al_0.33Cr_0.2Mn_0.09Fe_0.22Zr_0.16)O₂ irradiated with 5.2 × 10²² cm^?2 mainly exist as V, H–V complex and some vacancy clusters. While the fluence increase to 1.2 × 10²³ cm^?2, the defects mainly exist as H–V complex and hydrogen bubbles.     

Hydrogen diffusion coefficient in monoclinic zirconia in presence of oxygen vacancies

To better understand the hydrogen diffusion mechanisms in monoclinic zirconia that take place in fuel rod cladding during reactor operation, we calculate the diffusion paths of different defects involving hydrogen and oxygen vacancies using Density Functional Theory with hybrid functionals, and use them to obtain the hydrogen and oxygen diffusion coefficients. We find a hydrogen diffusion coefficient varying between 10^?10 to 10^?20 cm²?s^?1 at 600 K, strongly depending on the hydrogen to oxygen vacancy ratio. We find that the interstitial hydrogen atoms are the main diffusing species even though they are not the dominant configuration of hydrogen atoms. We confirm the existence of different huge trapping effects, which slow the hydrogen diffusion. The main mechanism is either the trapping of hydrogen atoms in oxygen vacancies or the formation of interstitial dihydrogen molecules depending on the hydrogen to oxygen vacancy ratio.     

Effect of helium implantation on the hydrogen retention of Cr2O3 films formed in an ultra-low oxygen environment

To simulate and investigate the irradiation damage of neutron and transmutation effect (He production) on the hydrogen isotope trapping behavior, in the present study, a new monoclinic hydrogen permeation barrier composed of Cr₂O₃ was fabricated and helium implantation with different fluences was tentatively employed. First, pure chromium samples were oxidized in an ultra-low oxygen partial pressure (1.7 × 10⁻²³ Pa) environment to obtain a single Cr₂O₃ layer. Then a dense layer of helium bubbles was formed in a substrate using a helium ion implantation method. Finally, the samples were treated in a hydrogen plasma environment at 500 °C. The damage, vacancy, and helium distribution in these samples were then simulated by SRIM. The morphology, phase, surface characteristics, thermal desorption, and electrochemical properties were subsequently characterized and evaluated. Thermal desorption spectrum analysis (TDS) was used to study the thermal desorption of hydrogen and helium at different temperatures. Our results showed that the inhibitory effect of the composite hydrogen barrier layer on the hydrogen diffusion in the substrate first increased and then decreased with the increase of the helium ion implantation fluence.     

Influence of microstructure on hydrogen trapping and diffusion in a pre-deformed TRIP steel

Austenitic steels are known to exhibit a low hydrogen diffusion coefficient and hence a good resistance to hydrogen embrittlement. Therefore, it is an experimental challenge to investigate their hydrogen diffusion properties. In this study, the electrochemical permeation technique is used to determine the hydrogen diffusion coefficients in different pre-deformed states (φ = 0, 0.32, 0.39, 0.49) of the high-alloy austenitic TRIP steel X3CrMnNiMoN17-8-4 in a temperature range of 323 K–353 K. In combination with microstructural analysis, a correlation between phase transformation from γ-austenite to α′-martensite and dislocation density is shown. As a result of the lattice transformation from fcc to bcc, the diffusion rate of hydrogen is significantly increased (D_{app, φ = 0} = 3.6 × 10^?12 cm² s^?1, D_{app, φ = 0.32} = 1.6 × 10^?11 cm² s^?1at 323 K). With higher degrees of deformation, the dislocation density also increased in the martensite islands, resulting in a degressive growth of the diffusion coefficient (D_{app, φ = 0.39} = 5.3 × 10^?11 cm² s^?1, D_{app, φ = 0.49} = 1.1 × 10^?10 cm² s^?1at 323 K). Moreover, detailed calculations are performed to describe the way of hydrogen trapping and to give a possible mechanism of diffusion.     

Theoretical studies in the stability of vacancies in zeolite templated carbon for hydrogen storage

In this work, we report DFT calculations of the energy formation and stability of multi-vacancies in a unit of Zeolite Template Carbon (C₃₉H₉). We label as V_n the respective vacancy where n carbon atoms have been removed from the pristine C₃₉H₉ structure. The results show that V₂, V₄, V₆ and V₉ are the most stable vacancies on the ZTC structure. This result agrees with many other studies. Besides, the most stable vacancy of ZTC structure is when nine carbon atoms are removed (V₉) from the ZTC structure. The formation of pentagon rings in the reconstruction of the ZTC vacancy give drastic effect on the energetics stability. Therefore, the formation of pentagon rings eliminates the dangling bonds thus lowering the energy formation. It is also carried out the decoration of ZTC vacancy with Lithium and Calcium atoms, this is the way to use de ZTC vacancy decorated as a medium for hydrogen storage. The results show that the ZTC vacancy decorated with 3 Lithium atoms can adsorb a maximum of nine hydrogen molecules (3 hydrogen molecules per Lithium atom). This gives a gravimetric storage capacity of 4.44 wt percent (wt. %), which is not enough for meeting DOE gravimetric target. On the other hand, to reach DOE gravimetric target, the study of ZTC vacancy decorated with 3 Calcium atoms is carried out, which can adsorb maximum of fifteen hydrogen molecules (5 hydrogen molecules per Calcium atom), this gives gravimetric storage capacity of 5.81 wt %, which meet DOE gravimetric targets, besides the binding energy of hydrogen molecules on ZTC vacancy decorated with 3 Calcium is calculated. These energies are in the range 0.2453–0.2053 eV/H₂, which are desirable energies for hydrogen adsorption. This is demonstrated by building isotherm adsorption path. The results show that forming vacancies on ZTC structure decorated with three Calcium atoms (3CaC₃₀H₉) is good candidate as medium for hydrogen storage.     

Hydrothermally/electrochemically decorated FeSe on Ni-foam electrode: An efficient bifunctional electrocatalysts for overall water splitting in an alkaline medium

A new hybrid catalyst based on Ni foam (NF) and FeSe was prepared by a facial hydrothermal method, in which Se-decorated NF was subsequently electrochemically doped by Fe. Binder-free catalyst containing electrodes were directly tested for the hydrogen and oxygen evolution reaction (HER/OER). The FeSe/NF electrode displayed an OER current density of 100 mA cm⁻² at potential of 1.42 V, and a relatively small Tafel slope of 109 mV dec⁻¹ in a 1 M KOH solution. Also, FeSe/NF electrode exhibited reasonable HER overpotential of 200 mV at 10 mAcm⁻² current density with Tafel slope of 145 mV dec⁻¹. The XRD and TEM studies revealed that the formation of heterogeneous interfaces of NiSe₂ and FeSe₂,generated more active sites that can promote better ions and electron transport in the electrode/electrolyte interfaces. Furthermore, HRTEM analysis indicates that FeSe₂ rich in Se vacancy defects can be created with suitable M − O and M − H bond for better OER and HER performance, respectively. In a-two electrode alkaline water electrolyzer, current densities of 10 mA cm⁻² and 50 mA cm⁻² were obtained at cell voltages of 1.52 V and 1.85 V, respectively, using pure FeSe–NF as both the cathode and anode.     

Tailoring cation vacancies in Co,Ni phosphides for efficient overall water splitting

High-efficiency water splitting catalysts are competitive in energy conversion and clean energy production. Herein, a bifunctional water splitting catalyst CoNiP with cation vacancy defects (CoNiP–V) is constructed through defect engineering. The results show that abundant cation vacancy defects in CoNiP–V are bifunctional active centers in the process of water electrolysis, which enhance the activity of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In 1.0 mol L^?1 potassium hydroxide, CoNiP–V requires a pretty low overpotential of 58 mV to reach a geometrical current density of 10 mA cm^?2 for HER. To deliver a current density of 100 mA cm^?2, only 137 mV and 340 mV of overpotential are needed for HER and OER, respectively. Moreover, the cell with CoNiP–V as both cathode and anode exhibits good stability, which only needs 1.61 V to achieve a current density of 100 mA cm^?2, and the cell voltage barely rises 10% after 100 h’ test under 100 mA cm^?2. Therefore, CoNiP–V is promising for the development of efficient water splitting catalysts.     

Engineering the semiconducting CdS nanostructures by N-doped rGO for enhancing the adsorption sites: Promising electrocatalyst for hydrogen evolution reaction

The development of non-noble electrocatalysts for hydrogen production from water is of immense interest as it is clean and eco-friendly. The present work explores the electrocatalytic performance of morphologically varied CdS NPs synthesized using different sulphur source and ionic liquids via hydrothermal treatment, in catalyzing hydrogen evolution reaction (HER). The hierarchical flower shaped morphology denoted as CdS–N3 outperformed other prepared electrocatalysts with a Tafel slope value of 118 mV dec^?1 and a low overpotential 344 mV @ a current density of 10 mA/cm². However, the outperformed CdS–N3 catalyst when blended with N doped rGO, it showed a superior activity with a low overpotential of 201 mV at 10 mA/cm². The catalyst disclosed a small Tafel slope of 70 mV dec^?1 corroborating that the catalyst contains more electroactive sites and oxygen vacancy voids for the adsorption-desorption of charge carriers generated from the heteroatom doping. The CdS/N-rGO catalyst also revealed a higher TOF value of 5.18 × 10^?3 s^?1, which further proves that catalyst is more efficient in releasing H₂ molecules and this findings affirms that CdS/N-rGO catalyst can be an efficient candidate for initiating HER kinetics with endurable stability in acidic medium for high purity hydrogen production.     

High photocatalytic performance for hydrogen production under visible light on the hetero-junction Pani-ZnO nanoparticles

The present work is devoted to the preparation of the hetero-junction of Polyaniline-Zinc oxide nanoparticles (Pani-ZnO_Nps) and its photo-electrochemistry to assess its photocatalytic properties for the water reduction into hydrogen. The semiconducting characterization of the Pani-ZnO_Nps synthetized by in situ chemical oxidative polymerization was studied for the hydrogen evolution reaction (HER) upon visible light illumination. The forbidden bands E_g (= 1.64 eV, Pani) and (3.20 eV, ZnO_NPS) were extracted from the UV–Visible diffuse reflectance data. The Electrochemical Impedance Spectroscopy (EIS) showed the predominance of the intrinsic material with a bulk impedance of 71 kΩ cm². The semi conductivity was demonstrated by the capacitance measurements with flat band potentials (E_fb = - 0.7 and - 0.3 V_SCE) and carriers concentrations (N_A = 1.77 × 10¹⁹ and N_D = 4.80 × 10²⁰ cm^?3) respectively for Pani and ZnO_NPS. The energetic diagram of the hetero-junction Pani-ZnO_Nps predicts electrons injection from Pani to ZnO_NPS in KOH electrolyte. An improvement of 78% for the evolved hydrogen was obtained, compared to Pani alone; a liberation rate of 61.16 μmol g^?1 min^?1 and a quantum yield of 1.15% were obtained. More interestingly, the photoactivity was fully restored after three consecutive cycles with a zero-deactivation effect, indicating clearly the reusability of the catalyst over several cycles.     

Investigation on different valence B-site ions doped Pr0.6Sr0.4FeO3-δ ceramic membrane for hydrogen production from water splitting

This study investigates the different valence B-site ions doped on perovskite-type oxygen transport membrane for hydrogen production by water splitting. Perovskite-type Pr_0.6Sr_0.4Fe_0.9M_0.1O_3-δ (PSFM, M = Fe, Al, Zr, and W) are fabricated successfully by the sol-gel method and form dense membranes with orthorhombic structure. The microstructure, chemical stability, and hydrogen production performance of membranes are studied systematically. The doping of Al³⁺, Zr⁴⁺, and W⁶⁺ ions can enhance membranes chemical stability and long-term stability significantly, which is due to the increase of average binding energy and decrease of the valence of B-site ions. Because of higher oxygen vacancy content and lower oxygen vacancy formation energy, the PSFA membrane shows the highest hydrogen production rate of 1.07 mL min⁻¹·cm⁻² at 900 °C and stabilizes at about 1.0 mL min⁻¹·cm⁻² on long-term test. The performance degradation of PSFM membranes is attributed to the much valence variation of B-site Fe^3+/4+ ions and the oxygen vacancy-related phase transition.     

Transport of hydrogen and deuterium in 316LN stainless steel over a wide temperature range for nuclear hydrogen and nuclear fusion applications

The permeation of hydrogen and deuterium through 316LN stainless steel (316LN SS) was investigated over a wide temperature range of 300–850 °C for nuclear hydrogen and nuclear fusion applications. We presented the first complete datasets of permeability Φ, diffusivity D, and solubility S for both hydrogen (H) and deuterium (D) in 316LN SS. Φ_H and Φ_D were 3.47 × 10⁻⁷exp(−66.6 × 10³/RT) and 2.71 × 10⁻⁷exp(−67.5 × 10³/RT) mol·m⁻¹ s⁻¹ Pa^−0.5, respectively. D_H and D_D were 15.9 × 10⁻⁷exp(−56.5 × 10³/RT) and 13.8 × 10⁻⁷exp(−56.8 × 10³/RT) m²∙s⁻¹, respectively. The estimated isotope effect ratios of Φ_H/Φ_D, D_H/D_D, and S_H/S_D were ~1.4, ~1.2, and ~1.2, respectively. The previously reported results for 316LN SS were extrapolated to the temperature range used herein and were compared with the results of this study. Although some discrepancies were observed between the results of this study and previous studies, they were within the acceptable scattering range.     

Effect of cyclic plastic deformation on hydrogen diffusion behavior and embrittlement susceptibility of reeling-pipeline steel weldments

The hydrogen embrittlement (HE) susceptibility and hydrogen permeation behavior of reeling-pipeline welded joint with/without cyclic plastic deformation (CPD) were studied using the electrochemical hydrogen charging technique. Results indicated that the surface of welded joint emerged hydrogen-induced damage containing cracks and blisters. The degree of hydrogen-induced damage increased with the increase of hydrogen charging time and current density. When the hydrogen charging current density and time was 50 mA/cm² and 4 h, respectively, the area ratio of hydrogen-induced damage of overall welded joint with CPD process was reduced from 6.61% to 2.28%, and the damage ratio of different sub-zones in welded joint was also decreased. The oxidized inclusions enriching Al–Mg–Ca elements acted as the initiation sites for hydrogen-induced damages. The effective diffusion coefficient of as-welded joint was 2.63 × 10⁻⁶ cm²/s, while that of welded joint with CPD showed a smaller value of 1.36 × 10⁻⁶ cm²/s. The welded joint with CPD process presented better resistance to HE, which was attributed to the increased density of hydrogen traps and the formation of dislocation cells to disperse hydrogen uniformly and reduce the possibility of local accumulation and recombination of diffusible hydrogen. Sub-zones in welded joint without CPD process were considerably more sensitive to hydrogen-induced damage, which indicated the important role of microstructure and dislocation density in HE mechanisms. The order of HE susceptibility from low to high was weld metal, base metal and heat affected zone.     

Evaluation of layered perovskites YBa1−xSrxCo2O5+δ as cathodes for intermediate-temperature solid oxide fuel cells

This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa_1−xSr_xCo₂O_5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18–0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm⁻¹ at 400–700 °C in air. The results demonstrate the promising performance of YBa_1−xSr_xCo₂O_5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21–0.59 Ω cm² at 700 °C. The lowest ASR, 0.44 Ω cm², and the cathodic overpotential, −40 mV at a current density of −136 mA cm⁻², are obtained in YBaCo₂O_5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo₂O_5+δ cathode.     

Stability of a hydrogen molecule in a vacancy of palladium hydrides

We report our ab-initio calculations of energy states of equilibrium H–H separation in a vacancy of palladium and palladium hydrides at a variety of H/Pd loading ratios. In a vacancy of pure palladium, the H₂ molecule has a shallow local energy minimum only in the [001] direction at a separation of 0.96 Å and it dissociates into positions near interstitial sites due to its high energy state. Increasing the H/Pd ratio to the beta phase deepens the energy well of the H₂ molecule and results in a shorter H–H separation. At a loading ratio around 1, the H₂ molecule is mostly affected by surrounding hydrogen neighbors and the H–H separation reaches 0.77 Å. The H₂ molecule is then fairly stable and its energy state is comparable to that of nearby interstitial sites. Our calculations suggest that the loading ratio of hydrogen in palladium has a significant effect on the stability of the H₂ molecule in the vacancy.     

Comparative study on hydrogenation properties of Pd capped Mg and Mg/Al films

Recent emergence of Mg as a promising hydrogen storage material with 7.6 wt% hydrogen encourages study on its thin films to understand physics of storage mechanism. The present study investigates the variations in hydrogen storage properties of Pd sandwiched Mg films upon introduction of Al layer. Multilayered stack of Pd/Mg/Pd and Pd/Al/Mg/Pd were grown on Si substrate using vapor deposition method and further hydrogenated at 150° C under 2 bar H₂ pressure for 2 h. Elastic Recoil Detection Analysis (ERDA) technique with 120 MeV Ag⁹⁺ ions was used to obtain hydrogen concentration versus incident ion fluence. ERDA study reveals that Pd/Mg/Al/Pd films absorb 6.01 × 10¹⁸hydrogen atoms/cm² in comparison to 4 × 10¹⁷ atoms/cm² absorbed by Pd/Mg/Pd system.     

Substitution of nickel in Mg2Ni and its hydride with elements from groups XIII and XIV: An ab initio study

We have performed ab initio calculations with equilibrium supercells of the Mg₂Ni compound and its hydride Mg₂NiH₄ doped with elements X = Al, Ga, In, Si, Ge and Sn. Two concentrations of X in both structures have been set: (1) every 16th, and (2) every fourth Ni atom has been substituted by X. Total energy calculations yielded the Mg₂NiH₄ hydrogen absorption enthalpy ΔH_abs according to the chemical reaction Mg₂Ni + 2H₂ → Mg₂NiH₄. Reduction of the hydrogen absorption enthalpy was reported for both concentrations of X. When doping the Mg₂NiH₄ hydride with X = In in a low concentration (1), the value of hydrogen desorption enthalpy decreases from 68.22 to 55.96 kJ(mol H₂)^?1. Doping with X = In in a high concentration (2) further decreases the hydrogen desorption enthalpy to 5.50 kJ(mol H₂)^?1. Further, the electronic structure of Mg₂(Ni–In)H₄ hydride with a low In concentration indicates weaker Ni–H bonds in comparison with the pristine Mg₂NiH₄. Attraction between H and In atoms induced enhanced bonding between Mg and H atoms compared to the pristine Mg₂NiH₄.     

Copper(II) phthalocyanine/metal organic framework electrocatalyst for hydrogen evolution reaction application

Copper(II)phthalocyanine-incorporated metal organic framework (CuPc/MOF) composite material was synthesized for application as an electrocatalyst for hydrogen evolution reaction (HER). The composite exhibited excellent electroactivity compared to the unmodified MOF, as confirmed by the diffusion coefficients (D) values of 3.89 × 10⁻⁷ and 1.57 × 10⁻⁶ cm² s⁻¹ for MOF and CuPc/MOF, respectively. The D values were determined from cyclic voltammetry (CV) experiments performed in 0.1 mol L⁻¹ tetrabutylammonium perchlorate/dimethyl sulfoxide (TBAP/DMSO) electrolyte. The Tafel slope determined from the CV data of CuPc/MOF-catalysed HER for 0.450 mol L⁻¹ H₂SO₄, was 176.2 mV dec⁻¹, which was higher than that of the unmodified MOF (158.3 mV dec⁻¹). The charge transfer coefficients of MOF and CuPc/MOF were close to 0.5, signifying the occurrence of a Volmer reaction involving either the Heyrovsky or the Tafel mechanism for hydrogen generation. For both MOF and CuPc/MOF, the exchange current density (i₀) improved with increase in the concentration of the hydrogen source (i.e. 0.033–0.45 mol L⁻¹ H₂SO₄) Nonetheless, the CuPc/MOF composite had a higher i₀ value compared with the unmodified MOF. Thus CuPc/MOF has promise as an efficient electrocatalyst for HER.     

Helium and hydrogen interaction in tungsten simultaneously irradiated by He+-H2+ at high temperature

Tungsten (W) is one of the most promising candidates for plasma facing materials in the fusion reactor. Helium (He) in W can influence the retention of hydrogen isotopes. In the present study, W targets were simultaneously irradiated by He⁺-H₂⁺ or He⁺-D₂⁺ ion beams with the energies of 1 keV or 3 keV, at fixed temperatures in a range of room temperature (R.T.) to 1073 K. Mechanisms of He and hydrogen interaction in W were discussed, especially from the point of He retention, which was characterized by the high-temperature thermal desorption spectroscopy (TDS) and glow-discharge optical emission spectroscopy (GD-OES) measurements. It is found that He desorption shifts to a lower temperature range for the W simultaneously irradiated by 3 keV He⁺-1 keV H₂⁺ at 573 K, under He⁺ fluence up to 1 × 10²² He⁺m⁻². Transmission electron microscope (TEM) observation and annealing treatment at the temperature of 873–1073 K show that the increased He uptake is caused by the formation of dislocation. Enhanced retention amounts for the hydrogen isotopes were also confirmed. Amounts of the dislocation loops introduced by the H₂⁺-only irradiation can be reduced by annealing treatment at 873 K, while that introduced by He⁺ irradiation are quite stable, which grows larger at elevated temperatures. With an increase of H₂⁺ energy, Helium uptakes at both weak trapping sites and bubbles are increased, while the amounts of hydrogen retention are decreased. It suggests that hydrogen ion has a significant influence on the He trapping sites at the irradiation temperature up to 573 K, while the hydrogen retention is determined by the distribution of He bubbles and dislocation loops.     

In situ observation of H2 dissociation on the ZnO (0001) surface under high pressure of hydrogen using ambient-pressure XPS

The interaction of H₂ molecules with a ZnO (0001) single crystal surface has been studied over a wide pressure (10^?6–0.25 Torr) and temperature (300–600 K) range using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). ZnO is well-known for interstitial hydrogen and hydrogen atoms in ZnO are believed to be incorporated by the dissociative adsorption of H₂ molecules in the atmosphere and their subsequent diffusion into the bulk. The dissociative adsorption of H₂ has been investigated at elevated pressures because H₂ molecules are not dissociated on the ZnO single crystal surface under ultrahigh vacuum (UHV) conditions. When the pressure is increased to several mTorr, the dissociative adsorption of H₂ takes place to form OH bonds on the surface. At 0.25 Torr, the ZnO surface is saturated with H atoms and the coverage is estimated to be 1.1 × 10¹⁵ atoms/cm² at 300 K. At higher surface temperatures, the equilibrium between the dissociative adsorption of gas-phase H₂ molecules and the associative desorption of surface H atoms is established. While maintaining the equilibrium, the surface has been monitored successfully in situ by utilizing AP-XPS.