Positron confinement in embedded lithium nanoclusters

Huis, Marijn A. van; Veen, A. van; Schüt, H.; Falub, C.V.; Eijt, S.W.H.; Mijnarends, P.E.; Kuriplach, J.

doi:10.1103/physrevb.65.085416

Cited by 40 publications

(39 citation statements)

References 41 publications

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“…12͒ compared to that of MgO. 5 So why do the Doppler broadening and 2D-ACAR results not give evidence of positron trapping in the Kr nanoclusters?…”

Section: Positron Beam Analysismentioning

confidence: 99%

“…However, the differences in calculated energies between various theoretical models are approximately 1 eV. 12,5 Furthermore, we have combined experimental and theoretical results, and the electronic and positronic data for Kr given in Table III are only valid for a lattice parameter of 5.72 Å, while in reality there is a distribution. Therefore, we estimate the systematic error in ⌬E AB,ϩ to be at least 1.5 eV, so that it is not clear whether positrons will trap in Kr nanoclusters when the vacuum levels are aligned.…”

Section: ͑9͒mentioning

confidence: 99%

“…5 If ⌬E AB,ϩ Ͼ0, the cluster acts as a potential barrier. Finally, the possibility should be considered that positrons are trapped at the interface.…”

Section: Positron Trapping and Positron Affinitiesmentioning

confidence: 99%

“…The shape of the 511 keV peak is characterized by the so-called S ͑shape͒ parameter, which gives the ratio of the number of counts in the center of the peak to the number of counts in the whole peak. 18,5 By using a monoenergetic positron beam with variable energy, the S parameter can be recorded as a function of depth. However, at larger depths the depth resolution decreases due to broadening of the implantation profile of the implanted positrons.…”

Section: Positron Beam Analysismentioning

confidence: 99%

“…However, positron confinement only works when the positron affinity of the nanocluster is lower than the positron affinity of the host material and when the host-nanocluster interface is without defects so that the positron will not become trapped at the interface. Looking through the literature that has predicted positron affinity for almost all metals, 9 a number of semiconductors, 10 a few insulators, 5,11 and rare gases, 12 it is obvious that the solid noble gases have by far the lowest positron affinity of all elements ͑less than Ϫ10 eV), making them the most interesting candidates to further pursue and exploit the phenomenon of positron confinement. In this work, we have created solid Kr nanoclusters as observed by means of transmission electron microscopy ͑TEM͒ and investigated positron trapping in this host-nanocluster system.…”

Section: Introductionmentioning

confidence: 99%

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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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“…12͒ compared to that of MgO. 5 So why do the Doppler broadening and 2D-ACAR results not give evidence of positron trapping in the Kr nanoclusters?…”

Section: Positron Beam Analysismentioning

confidence: 99%

Section: ͑9͒mentioning

confidence: 99%

“…5 If ⌬E AB,ϩ Ͼ0, the cluster acts as a potential barrier. Finally, the possibility should be considered that positrons are trapped at the interface.…”

Section: Positron Trapping and Positron Affinitiesmentioning

confidence: 99%

Section: Positron Beam Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formation of solid Kr nanoclusters in MgO

et al. 2003

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Positron studies of surfaces, structure and electronic properties of nanocrystals

Eijt

Barbiellini

Houtepen

et al. 2007

Phys. Status Solidi (c)

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A brief review is given of recent positron studies of metal and semiconductor nanocrystals. The prospects offered by positron annihilation as a sensitive method to access nanocrystal (NC) properties are described and compared with other experimental methods. The tunability of the electronic structure of nanocrystals underlies their great potential for application in many areas. Owing to their large surface-to-volume ratio, the surfaces and interfaces of NCs play a crucial role in determining their properties. Here we focus on positron 2D angular correlation of annihilation radiation (2D-ACAR) and (two-detector) Doppler studies for investigating surfaces and electronic properties of CdSe NCs.1 Introduction Nanoscale particles have become extremely important in the tailoring of materials for a wide range of applications [1][2][3]. In particular, semiconductor nanocrystals (NCs) have attracted wide interest because their electronic and optical properties can be tuned by variation of their size and shape [2,3]. At small sizes, the surface or interface energy becomes a very significant factor in establishing not only the interior crystal structure but also the specific surface structure and ad-atom termination of the NCs. These special properties underlie the large potential of NCs for applications in areas of nanostructured thin-film solar cells [4], opto-electronics [3] and spintronics [5], fission/fusion reactor vessel steels [6], metal hydrides for hydrogen storage [7], and fluorescence-based detection of biomolecules [3].During the last decade, it has been shown that positrons (e + ) act as a sensitive, self-seeking probe of embedded and colloidal NCs [8][9][10][11][12][13][14][15][16][17][18][19][20], revealing the local structural properties and electronic structure via a measurement of the electron momentum density [21]. Positron methods are thus capable of extracting valuable information on properties at specific surface, interface or defect sites in the NCs, which are difficult to access by other methods such as transmission electron microscopy, X-ray diffraction (XRD), and EXAFS. Furthermore, insight into the electronic structure of buried or embedded NC systems is gained, which is difficult to obtain with e.g. STM or XPS.

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