Rectangular nanovoids in helium-implanted and thermally annealed MgO(100)

Kooi, Bart J.; Veen, A. van; Hosson, J.T.M. de; Schüt, H.; Fedorov, A. V.; Labohm, F.

doi:10.1063/1.125954

Cited by 38 publications

(27 citation statements)

References 15 publications

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“…Dislocation loops are formed at smaller depths in the MgO top layer ͑layer 1͒ and below the ion implantation layer. 40 The presence of dislocation loops in MgO does not affect the S parameter significantly, but it does shorten the diffusion length compared to the bulk values. In the layer below the ion implantation layer ͑layer 3͒ there are not only dislocation loops but also a tail of implanted species as observed by NDP, 20 possibly because of channeling effects.…”

Section: Methodsmentioning

confidence: 99%

“…The choice for this model is mainly based on defect analysis performed on previously ion-implanted MgO samples that were analyzed with techniques such as transmission electron microscopy, positron annihilation spectroscopy, and neutron depth profiling. 20,40,41 In particular, there is a subsurface layer containing the ion implanted species and the main implantation defects ͑layer 2͒. Dislocation loops are formed at smaller depths in the MgO top layer ͑layer 1͒ and below the ion implantation layer.…”

Section: Methodsmentioning

confidence: 99%

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Positron confinement in embedded lithium nanoclusters

et al. 2002

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Quantum confinement of positrons in nanoclusters offers the opportunity to obtain detailed information on the electronic structure of nanoclusters by application of positron annihilation spectroscopy techniques. In this work, positron confinement is investigated in lithium nanoclusters embedded in monocrystalline MgO. These nanoclusters were created by means of ion implantation and subsequent annealing. It was found from the results of Doppler broadening positron beam analysis that approximately 92% of the implanted positrons annihilate in lithium nanoclusters rather than in the embedding MgO, while the local fraction of lithium at the implantation depth is only 1.3 at. %. The results of two-dimensional angular correlation of annihilation radiation confirm the presence of crystalline bulk lithium. The confinement of positrons is ascribed to the difference in positron affinity between lithium and MgO. The nanocluster acts as a potential well for positrons, where the depth of the potential well is equal to the difference in the positron affinities of lithium and MgO. These affinities were calculated using the linear muffin-tin orbital atomic sphere approximation method. This yields a positronic potential step at the MgOʈLi interface of 1.8 eV using the generalized gradient approximation and 2.8 eV using the insulator model.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Positron confinement in embedded lithium nanoclusters

et al. 2002

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“…The specimen preparation is dis-cussed elsewhere. 19 The sample treatment and main observations are listed in Table I.…”

Section: Methodsmentioning

confidence: 99%

Formation of solid Kr nanoclusters in MgO

et al. 2003

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The phenomenon of positron confinement enables us to investigate the electronic structure of nanoclusters embedded in host matrices. Solid Kr nanoclusters are a very interesting subject of investigation because of the very low predicted value of the positron affinity of bulk Kr. In this work, positron trapping in solid Kr nanoclusters embedded in MgO is investigated. The Kr nanoclusters were created by means of 280 keV Kr ion implantation in single crystals of MgO͑100͒ and subsequent thermal annealing at a temperature of 1100 K. The nanoclusters were observed by cross-sectional transmission electron microscopy in high-resolution mode. The fcc Kr nanoclusters are rectangularly shaped with sizes of 2 to 5 nm and are in a cube-on-cube orientation relationship with the MgO host matrix. From the Moiré fringes in high-resolution recordings, the lattice parameter of the solid Kr was deduced and found to vary from 5.3 to 5.8 Å. The corresponding pressures are 0.6 -2.5 GPa as found using the Ronchi equation of state. The relationship between lattice parameter and cluster size was investigated and it was found that the lattice parameter increases linearly with increasing nanocluster size. The defect evolution during annealing was monitored by means optical absorption spectroscopy and positron beam analysis. No evidence of positron trapping was found despite the very low positron affinity of solid Kr. Alternative definitions of the positron affinity are proposed for application to insulator materials.

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“…The specimen preparation was discussed elsewhere. 19 In order to facilitate comparison with the formation of Zn-clusters, 15 an additional set of samples was implanted in the same batch with Zn + ions only and annealed simultaneously with the coimplanted samples. Figure 1͑a͒ shows representative positron depth profiles of the Doppler W and S parameters for the Zn and Zn plus O coimplanted samples after the annealing step at 770 K, using momentum windows of 8.…”

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confidence: 99%

“…The specimen preparation was discussed elsewhere. 19 In order to facilitate comparison with the formation of Zn-clusters, 15 an additional set of samples was implanted in the same batch with Zn + ions only and annealed simultaneously with the coimplanted samples. 10 While W provides a measure for positron annihilation with semicore electrons, 10,17 providing chemical sensitivity to the positron trapping site, S is a measure of annihilation with valence electrons, providing sensitivity to the electronic structure and the presence of vacancies.…”

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Formation and stability of rocksalt ZnO nanocrystals in MgO

Eijt

Roode

Schüt

et al. 2007

Applied Physics Letters

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Coimplantation of Zn and O ions into a single crystalline MgO and subsequent thermal annealing were applied in the synthesis of ZnO nanocrystals. Electron microscopy showed that rocksalt instead of wurtzite ZnO stabilizes for relatively large nanocrystals up to ϳ15 nm, resulting from its small lattice mismatch with MgO of ϳ1.7%. The vacancies initially created by implantation induce favorable nanocrystal growth kinetics and are effectively absorbed during the nucleation and growth processes. The optical band edge of the ZnO nanocrystals was detected at ϳ2.8 eV. 2-4 and can be tailored in band gap in the deep-ultraviolet range between ϳ4.8 eV for x ϳ 0.55 up to ϳ7.8 eV for MgO. ZnO is polymorphic and it is known to exist in two cubic structures. Stabilization of a rocksalt ZnO phase can be achieved as a result of external pressure. 5,6 Furthermore, ZnO also exists in a metastable sphalerite structure. The wurtzite and sphalerite arrangements are very much alike, with the wurtzite phase slightly more stable at about the same equilibrium density. 7Rocksalt ZnO is characterized by a significant ϳ0.8 eV /formula unit 7 smaller equilibrium cohesive energy at a ϳ25% higher density. Stabilization of a rocksalt phase in general may also occur for nanocrystals ͑NCs͒ typically in the range of 1 -10 nm as a result of the increasingly important influence of surfaces for colloidal quantum dots [8][9][10] or of interfaces for NCs embedded in the host matrices.11,12 The use of nanoparticles further leads to a size-dependent increase in optical band gap. 8,13 Synthesis of ZnO NCs embedded in MgO can therefore pave the way to extending the tunability of the rocksalt band gap by including the blueviolet to ultraviolet range between ϳ3 and ϳ5 eV.A promising all-solid-state synthesis route for compound NCs consists of sequential implantation of both types of ions and subsequent thermal annealing, 11,14 which is particularly interesting because the passivation of surface states can be achieved robustly by incorporation of the NCs in a wide band gap material such as MgO. Previous studies 15 approached the synthesis of embedded ZnO NCs using high dose Zn + ion implantation in MgO͑100͒ single crystals followed by thermal annealing under oxidizing conditions. However, this leads to the formation of metallic Zn NCs exclusively, 15 with interesting optical properties related with a pronounced Mie scattering resonance. Coimplantation of Zn and O ions, on the other hand, will directly lead to a situation of local supersaturation for both types of ions and is therefore a promising candidate for the synthesis of embedded ZnO NCs.MgO͑100͒ single crystals were implanted using 40 keV O + and 140 keV Zn + ions at a dose of 1 ϫ 10 17 ions/ cm 2 each. The stopping and range of ions in matter ͑SRIM͒ calculations 16 showed that maximum Zn and O concentrations of ϳ20 and 17 at % were reached at a depth of 62 and 66 nm, respectively, after implantation ͓see inset of Fig. 1͑a͔͒. The evolution of the implanted samples was monitored after each subsequent ...

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Rectangular nanovoids in helium-implanted and thermally annealed MgO(100)

Cited by 38 publications

References 15 publications

Positron confinement in embedded lithium nanoclusters

Positron confinement in embedded lithium nanoclusters

Formation of solid Kr nanoclusters in MgO

Formation and stability of rocksalt ZnO nanocrystals in MgO

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