Magnetic resonance identification of hydrogen at a zinc vacancy in ZnO

Són, Nguyên Tiên; Isoya, Junichi; Ivanov, Ivan Gueorguiev; Ohshima, Takeshi; Janzén, Erik

doi:10.1088/0953-8984/25/33/335804

Cited by 15 publications

(4 citation statements)

References 23 publications

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“…The peak shape is also highly symmetrical and totally different from the asymmetric feature from ionized V O and Zn i defects with g factors less than 2 . We therefore assign it to the ionized V Zn defect, which has been identified as the g factor between 2.0018 and 2.056. − Since V Zn is a surface-sensitive defect in ZnO, , mild vacuum annealing can modify the surface structure of NCs with high specific surface and lead to the formation of V Zn defects. We have further analyzed the introduction of V Zn defects by using PL and Raman spectra in Figure S5 as well as the positron annihilation lifetime spectra in Figure S8.…”

Section: Resultsmentioning

confidence: 95%

Concurrent Improvement of Photocarrier Separation and Extraction in ZnO Nanocrystal Ultraviolet Photodetectors

Yuan

et al. 2019

J. Phys. Chem. C

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Polycrystalline film photodetectors often suffer from several drawbacks, such as uncontrollable defect species, grain boundary scattering, and surface oxygen trapping/detrapping, hindering their practical applications in high-performance UV photodetection. In this work, we induce an acceptor-type zinc vacancy (VZn) defect in zero-dimensional ZnO nanocrystals by a dual thermal annealing process, which has been closely examined by a defect-sensitive electron paramagnetic resonance technique. The optimization of annealing parameters can well tune the VZn concentration and induce a considerable self-powered behavior, which is believed to result from ionized acceptor enhanced charge separation. On the other aspect, the capping of metallic Zn can lead to the formation of abundant interface conducting channels for the highly efficient charge transport and extraction. The optimized responsivity is enhanced from 5.3 × 10–3 to 15.3 A W–1, and the average rise and decay times remain at 36.6 and 101.8 ms, respectively. Conductive atomic force microscopy confirms a uniform photocurrent distribution in the annealed polycrystalline films, suggesting the significance of synergies of lattice defects and grain boundary conductive channels. This study unambiguously demonstrates a new route to engineer the photodetection in nanocrystalline oxides, providing a promising prospect for future low-cost, low-power-consumption micro-/nano-optoelectronic devices.

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Section: Resultsmentioning

confidence: 95%

Concurrent Improvement of Photocarrier Separation and Extraction in ZnO Nanocrystal Ultraviolet Photodetectors

Yuan

et al. 2019

J. Phys. Chem. C

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“…On the other hand, if the spin localizes on the axial O, the symmetry of the system remains C 3v . Experimentally both of these cases have been observed in the work of Galland and Herve [43] and the V Zn EPR center was also studied by Son et al [44], who identified a separate center with H attached to the O in the V Zn . Here, we only discuss the V Zn .…”

Section: G-tensormentioning

confidence: 83%

Calculated electron paramagnetic resonance $g$-tensor and hyperfine parameters for zinc vacancy and N related defects in ZnO

Dabsamut,

Boonchun,

Lambrecht

2022

Preprint

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Various defects in ZnO, focused on substitutional NO and N2 in various sites, O-site, interstitial and Zn-site are studied using first-principles calculations with the goal of understanding the electron paramagnetic resonance (EPR) center reported for N2 in ZnO and substitutional N on the O-site. The g tensors are calculated using the gauge including projector augmented wave (GIPAW) method and compared with experiments. The g-tensor of the free N + 2 and N − 2 radicals and their various contributions within the GIPAW theory are analyzed first to provide a baseline reference for the accuracy of the method and for understanding the N2 behavior in ZnO. Previous controversies on the site location of N2 in ZnO for this EPR center and on the shallow or deep nature and donor or acceptor nature of this center are resolved. We find that the N2 on the Zn site is mostly zinc-vacancy like in its spin density and g-tensor, while for the O-site, a model with the N2 axis lying in-the basal plane and the singly occupied πg-orbital along the c axis provides good agreement with experiment. For the interstitial location, if the N2 is not strongly interacting with the surroundings, no levels in the gap are found and hence also no possible EPR center. The calculated g-tensors for NO and VZn are also found to be in good agreement with experiment. The effects of different functionals affecting the localization of the spin density are shown to affect the g-tensor values.

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“…[31,42] Aside from the intended incorporation of foreign ions, ZnO exhibits color center defects [43] , oxygen interstitial sites [44,45] and hydrogen defects [46,47] as naturally occurring defects at ambient conditions. Even though hydrogen defects have been evidenced experimentally by IR [48] , RAMAN [49] , EPR [50] and optical spectroscopy [51] and have been studied by quantum chemical calculations, [52,53] it is not clear if the concentration of these defects is high enough to have any impact on catalytic activity. With respect to solid-state 1 H NMR, two different 1 H NMR signals, including a fairly sharp signal at ~4.3 ppm, were observed in ZnO and ZnO:Al, which were claimed to correspond to interstitial H positions or the particle surface.…”

Section: Introductionmentioning

confidence: 99%

A method for surface characterization using solid-state nuclear magnetic resonance spectroscopy demonstrated on nano-crystalline ZnO:Al

Konrad Wied,

Mockenhaupt,

Schürmann

et al. 2024

Preprint

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Nano-scale zinc-oxide doped with aluminium ZnO:Al is studied by different techniques targeting surface changes induced by the conditions at which ZnO:Al is used as support material in the catalysis of methanol. While it is well established, that a variety of 1H and 27Al resonances can be found by solid-state NMR for this material, it was not clear yet which signals are related to species located close to the surface of the material and which to species located in the bulk. To this end, a method is suggested which makes use of a paramagnetically impregnated material to suppress NMR signals close to particle surface in the blind-sphere around the paramagnetic metal atoms. It is shown that it is important to use conditions which guarantee a stable reference system relative to which it can be established whether the coating procedure is conserving the original structure or not. This method, called Paramagnetically Assisted Surface Peak Assignment (PASPA), helped to assign the 1H and 27Al NMR peaks to the bulk and the surface layer defined by the blind- sphere of the paramagnetic atoms. The assignment results are further corroborated by the results from heteronuclear 27Al{1H} dipolar dephasing experiments, which indicate the hydrogen atoms are preferentially located in the surface layer and not in the particle core.

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Magnetic resonance identification of hydrogen at a zinc vacancy in ZnO

Cited by 15 publications

References 23 publications

Concurrent Improvement of Photocarrier Separation and Extraction in ZnO Nanocrystal Ultraviolet Photodetectors

Concurrent Improvement of Photocarrier Separation and Extraction in ZnO Nanocrystal Ultraviolet Photodetectors

Calculated electron paramagnetic resonance $g$-tensor and hyperfine parameters for zinc vacancy and N related defects in ZnO

A method for surface characterization using solid-state nuclear magnetic resonance spectroscopy demonstrated on nano-crystalline ZnO:Al

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