Point defects in sputtered NiO films

Jang, Wei-Luen; Lu, Yang‐Ming; Hwang, Weng-Sing; Hsiung, Tung Li; Wang, H. Paul

doi:10.1063/1.3081025

Cited by 127 publications

(75 citation statements)

References 10 publications

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“…Such relaxation of atomic structure, induced by the presence of nickel vacancy, plays significant role in the average structure relaxation, especially for the first coordination shell of nickel, as was found recently. 42 The results of our simulations are in excellent agreement with those from the recent ab initio calculations 65,66 of the structure relaxation around Ni vacancy, which predict the relaxation of O atoms by about 0.17Å outwards from the vacancy. This fact confirms the ability of our simple force-field potential model to reproduce well structure relaxation around nickel vacancies.…”

Section: Resultssupporting

confidence: 80%

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Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

et al. 2012

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Nanocrystalline NiO samples have been studied using the Ni K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy and recently developed modeling technique, combining classical molecular dynamics with ab initio multiple-scattering EXAFS calculations (MD-EXAFS). Conventional analysis of the EXAFS signals from the first two coordination shells of nickel revealed that (i) the second shell average distance R(Ni-Ni2) expands in nanocrystalline NiO compared to microcrystalline NiO, in agreement with overall unit cell volume expansion observed by x-ray diffraction; (ii) on the contrary, the first shell average distance R(Ni-O1) in nanocrystalline NiO shrinks compared to microcrystalline NiO; (iii) the thermal contribution into the mean-square relative displacement σ 2 is close in both microcrystalline and nanocrystalline NiO and can be described by the Debye model; (iv) the static disorder is additionally present in nanocrystalline NiO in both the first Ni-O1 and second Ni-Ni2 shells due to nanocrystal structure relaxation. Within the MD-EXAFS method, the force-field potential models have been developed for nanosized NiO using as a criterion the agreement between the experimental and theoretical EXAFS spectra. The best solutions have been obtained for the 3D cubic-shaped nanoparticle models with nonzero Ni vacancy concentration Cvac: Cvac ≈ 0.4-1.2% for NiO nanoparticles having the cube size of L ≈ 3.6-4.2 nm and Cvac ≈ 1.6-2.0% for NiO thin film composed of cubic nano-grains with a size of L ≈ 1.3-2.1 nm. Thus, our results show that the Ni vacancies in nanosized NiO play important role in its atomic structure relaxation along with the size reduction effect.

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Section: Resultssupporting

confidence: 80%

“…It was concluded that nickel vacancies, being the dominant point defects, are responsible for the electrical conductivity of the films 42 and for the film decomposition under annealing in vacuum above 400…”

Section: 43mentioning

confidence: 99%

Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

et al. 2012

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“…As for the point defect structure of NiO, it has been investigated earlier with different experimental techniques including thermogravimetry, 47 electrical conductivity, 48,49 and perturbed angular correlation spectroscopy. 50 Thus, there is a general agreement that the primary point defects in NiO are metal vacancies.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, our positron annihilation results are consistent with previous experimental results. [47][48][49][50][51] Fig . 5 shows τ 1 , τ 2 and the corresponding intensities (I 1 , I 2 ) in the NiO nanocrystals annealed at different temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…50 Thus, there is a general agreement that the primary point defects in NiO are metal vacancies. [49][50][51] Zhang et al 29 investigated stability and magnetism of vacancies in NiO using the GGA+U First-principle computation method, and they found that Ni vacancy is the predominant defect and the doubly ionized cation vacancy is the most stable defect under oxygen-rich conditions. From the literature, 29,48 we also see that the Ni vacancy could be in singly, doubly, or mixed charge states in the case of NiO.…”

Section: Resultsmentioning

confidence: 99%

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Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Chen¹,

Chen²,

Zhang³

et al. 2017

ECS J. Solid State Sci. Technol.

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Pure NiO nanoparticles were subjected to isochronal thermal treatments in open air from 100 to 1000 • C. X-ray diffraction (XRD) patterns indicate that all annealed samples exhibit a single phase of face-centered cubic (FCC) crystalline structure, obvious grain growth occurs only above 400 • C and the average crystallite size increases from 20 to 80 nm. X-ray photoelectron spectroscopy (XPS) shows that only very few amount of Ni 3+ and no impurity element have been found in the annealed samples. Positron annihilation measurements reveal that large number of Ni-vacancy defects exist in the grain surface region. These surface defects begin to recover after annealing above 400 • C, and most of them are removed at 1000 • C. Room temperature ferromagnetism is obviously observed for the samples annealed at 100 and 400 • C. The saturation magnetization gradually decreases with the increase of the annealing temperature, and it almost disappears at 800 and 1000 • C. The disappearance of ferromagnetism shows good coincidence with the recovery of Ni-vacancies. Our results suggest that the anomalous ferromagnetic behavior in NiO nanoparticles might be due to the surface Ni-vacancy defects instead of grain size effects. 2 It is well known that the bulk AF materials are magnetically compensated and have zero net magnetic moment in zero applied field, while fine particles of an AF material should display either weak ferromagnetism (FM) or superparamagnetism (SPM).3 Since Richardson and Milligan first reported anomalous magnetic properties in NiO nanoparticles, 4 ferromagnetic behaviors were found in an increasing number of AF nanomaterials. Consequently, it is important to investigate the magnetic mechanism of AF nanomaterials extensively. Among the various nanostructured AF transition metal monoxides, NiO has been widely investigated, because it is a unique metal-deficient p-type semiconductor presenting a wide band-gap (3.6-4.0eV), and its bulk form possesses a relatively high Néel temperature T N (523 K). As a consequence, it can cause high storage density of magnetic recording media due to allowing magnetic stability at very low volumes far above room temperature. 17 In the recent few decades, great efforts have been devoted to exploring the unexpected magnetic properties in NiO nanomaterials, such as large magnetic moments, enhanced coercivity, spin glass freezing and hysteretic loop shifts. However, up to now the underlying mechanism for the FM is still unclear. It has been reported that the FM might come from the surface and finite size effects, or a net magnetic moment probably arises from uncompensated spins. Several models, such as the two-sublattice model, 3 multi-sublattice model, 10 and core-shell model 9,12-14,18-24 have been used to illustrate the anomalous properties of NiO nanoparticles. However, different groups reported that * Electrochemical Society Fellow.z E-mail: czy2004hust@163.com; chenzq@whu.edu.cn; mascher@mcmaster.ca surface effects and size effects on the ferromagnetic properties of the nanomater...

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Metal Oxides for Photoelectrochemical Fuel Production

Rizzi

Girardi

2022

Tailored Functional Oxide Nanomaterials

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Point defects in sputtered NiO films

Cited by 127 publications

References 10 publications

Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Metal Oxides for Photoelectrochemical Fuel Production

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