Defects In Nickel Research Articles

Fast-switching electrochromic smart windows based on WO3 doped NiO thin films

Nickel oxide (NiO) is a very promising material for the counter electrode in electrochromic devices (ECDs). In the current research, WO3 incorporated NiO thin films were fabricated via RF sputtering to enhance the electrochromic performance of NiO thin films. An XRD analysis revealed that the addition of WO3 to the cubic NiO thin film disrupts its long-range crystalline structure, resulting in an amorphous state. FESEM revealed the formation of columnar structure which favours ECDs. XPS analysis revealed that the addition of WO3 into NiO enhanced the hole concentration by creating nickel vacancies (nickel defects). Compared to pristine NiO, WO3 mixed NiO thin films showed enhanced optical modulation (66 %) with rapid switching speed (0.6 s/1.0 s for bleaching/colouring). This is mainly because the defect- induced amorphous structure of the nickel tungsten oxide thin film can provide large number of diffusion channels which facilitates the rapid ion intercalation process, and can accommodate large number of ions, and hence enhances the electrochromic performance. This advancement might have a substantial impact on the development of nickel tungsten oxide as a potential counter electrode in high-performance energy saving smart windows.

Spin-orbit coupling and Jahn-Teller effect in Td symmetry: an ab initio study on the substitutional nickel defect in diamond.

We analyse the spin-orbit and Jahn-Teller interactions in [Formula: see text] symmetry that are relevant for substitutional transition metal defects in semiconductors. We apply our theory to the substitutional nickel defect in diamond and compute the appropriate fine-level structure and magneto-optical parameters by means of hybrid density functional theory. Our calculations confirm the intepretations of previous experimental findings that the 2.56 and 2.51 eV optical centres are associated with this defect. Our analysis of the electronic structure unravels possible mechanisms behind the observed optical transitions and the optically detected magnetic resonance signal, too. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Effect of substrate temperatures on structural, optical and dispersion energy parameters of RF sputtered nickel oxide thin films

Thin films of nickel oxide (NiO) have been widely identified as a promising ion storage layer in electrochromic devices owing to their excellent electrochemical properties. There is, however, a lack of accurate description of their optical parameters, which are quite important to explore the optical and electrochromic characteristics of NiO. In the present investigation, nickel oxide (NiO) thin films have been deposited using radio frequency (RF) magnetron sputtering at different substrate temperatures (Tsub) viz. 100, 200 and 300 °C. The consequences of substrate temperature on the structural, morphological, optical, and vibrational properties were examined. The XRD pattern showed increased crystallinity with an increase in substrate temperature. Surface morphology revealed an ultrafine and smooth morphology. The average optical transmittance varied between 64% and 85%. Shrinkage in the energy bandgap was observed with the change in substrate temperature. The values of optical parameters like refractive index (n), extinction coefficient (k), the real part of the dielectric constant (ε1), the imaginary part of the dielectric constant (ϵ2), and porosity of NiO films were found to change with an increase in substrate temperature. The effect of substrate temperature on dispersion energy parameters (Eo and Ed) derived from the Wemple-DiDomenico model was calculated and discussed in detail. Room temperature photoluminescence studies revealed peaks along 3.39 eV (365 nm) and 2.95 eV (420 nm) nm as a consequence of band-band PL phenomena for nickel oxide and defects. In the Raman spectrum, one predominant peak around 560 cm−1 corresponds to the one-phonon LO mode, and another minor peak at 1100 cm−1 owing to the two-phonon LO mode were observed, which arises from Ni–O vibrations. The observed results reveal the potential application of the NiO films in optoelectronic and electrochromic device applications.

Formation and time dynamics of hydrogen-induced vacancies in nickel

The formation of hydrogen-induced defects in nickel was investigated by positron annihilation lifetime spectroscopy (PALS) and the time dynamics of those defects during room temperature aging was tracked with an unprecedented time resolution of the order of minutes using an ultrahigh-flux slow positron beam. Those measurements showed the formation of a large number of atomic vacancies simply by hydrogen addition at room temperature. Low-temperature PALS measurements indicated that they were monovacancy-level defects and low-temperature coincidence Doppler broadening measurements proved that hydrogen was trapped and bound to those vacancies during the hydrogen charge. Room temperature aging, i.e. below the stage III temperature in Ni, and the concomitant hydrogen desorption induced the agglomeration of those monovacancies into large vacancy clusters which remained even after all the hydrogen had desorbed and hydrides had disappeared. These results constitute the first empirical evidence that vacancy-hydrogen complexes are induced in Ni only by hydrogen charging and demonstrate that hydrogen has a primary role in the formation and stabilization of vacancies even at room temperature.

Decoration of growth sector boundaries with nitrogen vacancy centers in as-grown single crystal high-pressure high-temperature synthetic diamond

Large (> 100 mm$^3$), relatively pure (type II) and low birefringence single crystal diamond can be produced by high pressure high temperature (HPHT) synthesis. In this study we examine a HPHT sample of good crystalline perfection, containing less than 1 ppb (part per billion carbon atoms) of boron impurity atoms in the {001} growth sector and only tens of ppb of nitrogen impurity atoms. It is shown that the boundaries between {111} and {113} growth sectors are decorated by negatively charged nitrogen vacancy centres (NV$^-$): no decoration is observed at any other type of growth sector interface. This decoration can be used to calculated the relative {111} and {113} growth rates. The bulk (001) sector contains concentrations of luminescent point defects (excited with 488 and 532 nm wavelengths) below 10$^{11}$ cm$^{-3}$ (10$^{-3}$ ppb). We observe the negatively charged silicon-vacancy (SiV$^-$) defect in the bulk {111} sectors along with a zero phonon line emission associated with a nickel defect at 884 nm (1.40 eV). No preferential orientation is seen for either NV$^-$ or SiV$^-$ defects, but the nickel related defect is oriented with its trigonal axis along the <111> sector growth direction. Since the NV$^-$ defect is expected to readily re-orientate at HPHT diamond growth temperatures, no preferential orientation is expected for this defect but the lack of preferential orientation of SiV$^-$ in {111} sectors is not explained.

Statistics of primary radiation defects in pure nickel

Molecular dynamics simulations were applied to study radiation damage formation in collision cascades initiated by primary knock-on atoms (PKA) with energy EPKA = 5, 10, 15 and 20 keV in pure nickel at temperature T = 100, 300, 600, 900 and 1200 K. A series of 24 collision cascades per EPKA,T set was simulated to assure statistical reliability of the results. The number of Frenkel pairs, NFP, the fraction of vacancies, σvac, and self-interstitials (SIA), σSIA, in point defect clusters, the average size of vacancy and SIA clusters, Nvac and NSIA, respectively, and the average vacancy and SIA cluster per cascade yield, Yvac and YSIA, respectively, were evaluated as functions of EPKA,T. It is found that NFP∝EPKA under all simulated conditions. Both σvac and σSIA demonstrate similar dependence on EPKA. σvac matches Yvac, while σSIA correlates with NSIA and is affected by SIA diffusivity. Nvac is determined by the irradiation temperature and thermal stability of vacancy clusters. They are stable at T⩽ 300 K and Nvac∝EPKA, whereas at 600 K ⩽T⩽ 900 K, Nvac≈6 and 10, which corresponds to the sizes of regular stacking fault tetrahedra. SIA cluster per cascade yield YSIA∝NFP and therefore ∝EPKA under all simulated irradiation conditions.

Accelerated oxygen evolution kinetics on NiFeAl-layered double hydroxide electrocatalysts with defect sites prepared by electrodeposition

NiFe layered double hydroxides (LDHs) is considered to be one of the LDHs electrocatalyst materials with the best electrocatalytic oxygen evolution properties. However, its poor conductivity and inherently poor electrocatalytic activity are considered to be the limiting factors inhibiting the electrocatalytic properties for oxygen evolution reaction (OER). The amorphous NiFeAl-LDHs electrocatalysts were prepared by electrodeposition with nickel foam as the support, and the D-NiFeAl-LDHs electrocatalyst with defect sites was then obtained by alkali etching. The mechanism of catalysts with defect sites in OER was analyzed. The ingenious defects can selectively accelerate the adsorption of OH−, thus enhancing the electrochemical activity. The D-NiFeAl-LDHs electrocatalyst had higher OER electrocatalytic activity than NiFe-LDHs electrocatalyst: its accelerated OER kinetics were mainly due to the introduction of iron and nickel defects in NiFeAl-LDHs nanosheets, which effectively adjusted the surface electronic structure and improved OER electrocatalytic performance. There was only a low overpotential of 262 mV with the current density of 10 mA cm−2, and the Tafel slope was as low as 41.67 mV dec−1. The OER electrocatalytic performance of D-NiFeAl-LDHs was even better than those of most of the reported NiFe-LDHs electrocatalysts.

Self-healing mechanism of irradiation defects in nickel–graphene nanocomposite: An energetic and kinetic perspective

The self-healing mechanism of radiation-induced defects in nickel–graphene nanocomposite is investigated by atomistic simulations. Compared with pure nickel, nickel–graphene nanocomposite has less defects remained in the bulk region after collision cascades, illustrating self-healing performance. Nickel–graphene interfaces (NGIs) serve as sinks for radiation-induced defects and preferentially trap interstitials over vacancies. Energetic and kinetic calculations reveal that the defect formation energy and diffusion barrier are reduced in the vicinity of NGIs, and the reduction are pronounced for interstitials. When NGIs are loaded with interstitials, their segregation ability on radiation-induced defects improves significantly, and the radiation-induced defects near the NGIs diffuse more easily. Especially, the vacancies (or interstitials) near the NGIs tend to annihilate (or aggregate) with the interstitials trapped at the NGIs, which only happens at the interstitial-loaded side of NGIs. Therefore, nickel–graphene nanocomposite exhibits excellent radiation tolerance and shows promise as a structural material for advanced nuclear reactors due to its NGIs with the energetic and kinetic driving forces acting on radiation-induced defects.

Necessary Duration of Molecular Dynamics Simulation for Calculation of Self-Diffusion Coefficient during Migration of Different Point Defects in Nickel

The evaluation of the necessary duration of molecular dynamics experiment for the calculation of the selfdiffusion coefficient during migration of different point defects in Ni (vacancy, bivacancy, self-interstitial atom, hydrogen atom) is conducted in this paper. The mentioned defects have different mobility that results in different intensities of atoms displacements caused by migration of the defect. The accuracy of diffusion coefficient calculation is related to the accuracy of estimation of rootmean-square changes of atoms coordinates. Consequently, the accuracy increases with the increase of moleculardynamic experiment duration t, the temperature T, and the mobility of the defect initiating the diffusion. To describe the interatomic interactions, the multi-particle Cleri-Rosato potential is used in the study. It is shown that the simulation duration of 100 ps is enough to calculate the diffusion coefficient when the temperature is higher than 0.6 of melting point. When calculating the diffusion coefficient of impurity in a metal crystal (for example, the hydrogen impurity), it is possible to decrease the root mean square error of displacement evaluation of impurity atoms by increasing the number of impurity atoms.DOI 10.14258/izvasu(2018)1-06

Insights into the C–H Bond Activation on NiO Surfaces: The Role of Nickel and Oxygen Vacancies and of Low Valent Dopants on the Reactivity and Energetics

For the development of nickel oxide (NiO) as an oxidation catalyst, a fundamental understanding of the role of surface morphology and of nickel and oxygen vacancy defects is essential, since they govern the reactivity of the surface. Using density functional theory (DFT) calculations, we investigated the reactivity of two different crystal facets of NiO and reveal the contribution of the coordinatively unsaturated Ni–O pairs, nickel and oxygen vacancies, and low valent dopant Li in determining and altering the reactivity of the surfaces. The most stable surface, NiO(100), is relatively inactive for methane C–H activation with an activation barrier of 136.6 kJ mol–1. However, the relatively less stable NiO(110) surface is extremely active and can dissociate methane with an activation barrier of 57.1 kJ mol–1. The coordinative unsaturation and comparatively low binding strength of the four-coordinated surface lattice oxygen on the NiO(110) surface leads to strong chemisorption of the dissociated H, facilitating extremely low activation barriers for methane dissociation. The presence of a Ni vacancy on the inactive NiO(100) surface brings down the activation barrier for methane dissociation to 90 kJ mol–1. This is a result of weakening of the binding strength of the oxygen, allowing strong chemisorption of the dissociated H. In this work, we predict that an equivalent increase in the surface reactivity can be achieved by doping the inactive NiO(100) surface with low valent metals like Li, which also weakens the binding strength of surface oxygen. The hydrogen chemisorption energy on the oxygen site is identified as a descriptor for estimating the reactivity of surfaces.

Spectroscopic analysis of microdiamonds in ophiolitic chromitite and peridotite

Microdiamonds ∼200 μm in size, occurring in ophiolitic chromitites and peridotites, have been reported in recent years. Owing to their unusual geological formation, there are several debates about their origin. We studied 30 microdiamonds from 3 sources: (1) chromitite ore in Luobusa, Tibet; (2) peridotite in Luobusa, Tibet; and (3) chromitite ore in Ray-Iz, polar Ural Mountains, Russia. They are translucent, yellow to greenish-yellow diamonds with a cubo-octahedral polycrystalline or single crystal with partial cubo-octahedral form. Infrared (IR) spectra revealed that these diamonds are type Ib (i.e., diamonds containing neutrally charged single substitutional nitrogen atoms, N s 0 , known as the C center) with unknown broad bands observed in the one-phonon region. They contain fluid inclusions, such as water, carbonates, silicates, hydrocarbons, and solid CO 2 . We also identified additional microinclusions, such as chromite, magnetite, feldspar (albite), moissanite, hematite, and magnesiochromite, using a Raman microscope. Photoluminescence (PL) spectra measured at liquid nitrogen temperature suggest that these diamonds contain nitrogen-vacancy, nickel, and H2 center defects. We compare them with high-pressure–high-temperature (HPHT) synthetic industrial diamond grits. Although there are similarities between microdiamonds and HPHT synthetic diamonds, major differences in the IR, Raman, and PL spectra confirm that these microdiamonds are of natural origin. Spectral characteristics suggest that their geological formation is different but unique compared to that of natural gem-quality diamonds. Although these microdiamonds are not commercially important, they are geologically important in that they provide an understanding of a new diamond genesis.

Cathodoluminescence of synthetic diamonds annealed at high temperature without stabilizing pressure

Nitrogen-containing synthetic diamonds heated at temperatures 1800, 2000 and 2500°C in hydrogen atmosphere (LPHT annealing) have been studied by cathodoluminescence (CL). After LPHT annealing, the transformations of nickel and nitrogen related defects were found similar to those occurred after annealing under high stabilizing pressure (HPHT annealing). An assumption is made that LPHT annealing may remove yellow color of synthetic HPHT-grown diamonds in areas where nickel and nitrogen have “matching” concentrations. The areas with excessive concentration of nickel, or nitrogen remain yellow even after 48h LPHT annealing at temperature 1800°C.

Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys.

Energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance.

Development of a pair potential for Ni–He

An interatomic potential for helium in bulk nickel was developed by fitting first-principles calculation results. This two-body Ni–He potential can give a good description of relative stability and migration of interstitial and substitutional He defects in bulk nickel. The zero-temperature binding energies of additional He to existing He-vacancy clusters and interstitial He clusters were studied and found in agreement with first-principles calculations.

Defect-related photoluminescence properties of as-synthesized and annealed NiO nanostructures via hydrothermal method

A hydrothermal-based synthesis technique was used to produce both amorphous and nano-grained NiO nanowires. The scanning electron microscopy images showed the morphologies before and after annealing treatment at 350 and 400°C for 2h. The microstructural features of the mixed amorphous and local crystalline in as-synthesized NiO and polycrystalline in annealed NiO were characterized by X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy, respectively. The corresponding elemental compositions were determined via energy-dispersive X-ray. In addition, annealing-dependent effects on the photoluminescence spectra were observed in at least two different energy band regions, e.g., at ~395, 660, and 680nm. The photoluminescence properties, including intensity and energy, of the individual NiO nanowires varied significantly with microstructural changes arising from nickel and oxygen defects from annealing the as-synthesized amorphous NiO. The microstructural and optical origin of as-synthesized amorphous and annealed nano-grained NiO nanowires is discussed on the basis of the aforementioned results.

Defect Formation of Nickel-Incorporated Large-Diameter Czochralski-Grown Silicon and Their Effect on Gate Oxide Reliability

Nickel, the related defect distribution of as-grown nickel-incorporated p-type Czochralski-grown silicon crystals, and its effect on the gate oxide reliability were investigated with respect to the boron doping concentration. The segregation of nickel at the surface was more likely in the doping range of 5.5–7.4 × 1014 cm−3 than in the doping range of 1.1–1.7 × 1015 cm−3, which was due to the active formation of Ni–B pairs in the crystal with a higher boron doping concentration. The formation of surface defects was affected by the atomic nickel distribution; that is, the surface defect density was relatively high in the crystal with a lower boron doping concentration. The gate-oxide reliability was aggravated by nickel-related defects, but this effect was noticeably suppressed in the crystal with a higher boron doping concentration. From the breakdown yield and measured laser scattering tomographic defect density, we found the “transferred portion” of bulk nickel defects that causes a degradation in the gate-oxide reliability.

Grain-Subgrain Structure and Vacancy-Type Defects in Submicrocrystalline Nickel at Low Temperature Annealing

Grain-Subgrain Structure and Vacancy-Type Defects in Submicrocrystalline Nickel at Low Temperature Annealing

Analysis of Nickel Defect in Diamond with Photoluminescence upon Excitation near 200 nm

Photoluminescent (PL) spectra of synthetic diamond powders at temperatures between 10 and 300 K were excited with synchrotron radiation in the wavelength range 125-375 nm. Prominent spectral PL features were detected at 484.6 and 489.0 nm (2.559 and 2.535 eV), associated with nickel defect. During our measurement of PL excitation (PLE) spectra of Ni defect in diamond, we observed a distinct PLE line at 215 nm for the first time. We thereby suggest the use of UV-PL spectra excited in the region 200-220 nm to analyze and to identify nickel defect in diamonds.

Positron spectroscopy of defects in submicrocrystalline nickel after low-temperature annealing

Using the method of measuring the positron lifetime spectra and Doppler broadening annihilation line spectroscopy, the annealing of defects in submicrocrystalline nickel produced by equal channel angular pressing has been studied. In as-prepared samples, the positrons are trapped by dislocation defects and vacancy complexes inside crystallites. The size of vacancy complexes decreases with increasing annealing temperature in the interval ΔT = 20–300°C. However, at T = 360°C, the complexes start growing again. The dependence of S-parameter on W-parameter derived from the Doppler broadening spectroscopy has two parts with different inclinations to axes that correspond to different types of primary centers of positron trapping in submicrocrystalline nickel. It has been elucidated that, at recovery stage in the temperature interval ΔT = 20–180°C, the main centers of positron trapping are low-angle boundaries enriched by impurities, while at in situ recrystallization stage in the temperature interval ΔT = 180–360°C, the primary centers of positron trapping are low-angle boundaries.

The separation effect of radiation-induced defects in nickel

Pure nickel, the model material for austenitic steels used in reactors, with an electrical resistivity ratio of ρ300 K/ρ4.2 K ~ 300 has been investigated under electron and neutron irradiation at TIRR ~ 320-340 K. Three of its states have been subjected to irradiation: a recrystallized state at 873 K, a deformed one to 90%, and an annealed one at 450 K after deformation to remove deformationinduced vacancies. It is has been experimentally shown that neutron and electron irradiation of the deformed nickel results in the sepa� ration of radiationinduced defects. This separation occurs because a significant portion of the radia� tioninduced interstitial atoms is captured by disloc ation sinks and does not participate in recombina� tion with vacancies. As a result, the concentration of accumulated vacancies in the deformed nickel can exceed their concentration in the annealed nickel and be almost twice as high. At higher doses of neutron irradiation, above 10 18 cm -2 , separation does not occur, since vacancy sinks in the form of clusters are more powerful than dislocation sinks.