Electronic Excitations in LiF: 10-70 eV

Fields, J. R.; Gibbons, P. C.; Schnatterly, S. E.

doi:10.1103/physrevlett.38.430

Cited by 56 publications

(26 citation statements)

References 13 publications

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“…The intensities of these characteristic losses grow with LiF coverage while their energy positions are stable. Moreover, all these peaks coincide (within the limit of experimental error) with peaks measured for LiF single crystals [5,6]. Such behaviour may be attributed to the strong localization of the electronic states to which the observed characteristic losses correspond.…”

supporting

confidence: 57%

Electron Excitations in the Li Enriched LiF Clusters

Gołek

Sobolewski

1998

phys. stat. sol. (b)

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It is known that the electron bombardment of alkali halide causes radiation damages and considerable decomposition in the surface region [1,2]. In the electron stimulated desorption (ESD) process the halogen is more effectively desorbed leaving the alkali metal enriched target surface. In some cases, the alkali atoms agglomerate to form clusters [3]. Such clusters can serve as a convenient tool for studying the properties of finite alkali and alkali halide grains. In this note, we present results of the electron energy loss spectroscopy (EELS) in the reflectance mode of the LiF/Si(100) system. LiF does not grow epitaxially on Si(100) [4], therefore the sizes of clusters of alkali-halide in this system are expected to be coverage dependent. Our low energy electron diffraction (LEED) data indicate that layer structure substantially depends on the deposition temperature. In particular, at 100 K the substrate two-domain (2 Â 1) pattern vanishes for the coverage of about one ML 1 ) and no other pattern appears. At room temperature, the substrate LEED pattern transforms into (1 Â 1) reconstruction for about one ML and becomes more diffuse during the subsequent deposition of a few ML of LiF. This suggests that LiF islands are much smaller for the lowtemperature deposition than in the case of the room-temperature layer formation.The experiments were performed in a UHV system (5 Â 10 ± ±10 mPa) equipped with several surface analyses instruments, but only the four-grid LEED optics and hemispherical spectrometer were used in this experiment. Primary electron beam of 120 eV and 100 nA/mm 2 (normal to the sample surface) was applied for the loss spectra measurement. LiF films were vapour-deposited from 99.9 % purity LiF crystal pieces onto the Si (100) wafers. The layer deposition rate was about 1.2 ML/min. Hemispherical analyser, used for EELS measurements, was fixed for the measuring of the secondary beam under an angle of 15 to the surface normal. Fig. 1 shows the evolution of EELS spectra with increasing film thickness and, hence, with increasing grain sizes. As it is seen, the LiF features emerge at energies of 10.8 eV, 14 to 18 eV, and about 24.5 eV. The intensities of these characteristic losses grow with LiF coverage while their energy positions are stable. Moreover, all these peaks coincide (within the limit of experimental error) with peaks measured for LiF single crystals [5,6]. Such behaviour may be attributed to the strong localization of the electronic states to which the observed characteristic losses correspond. This suggests that not only excitons but also valence electron plasmons (25 eV peak) are localized excitations. Measurements of EELS for LiF layers deposited at 100 K lead to a similar conclusion. An additional confirmation of this conclusion comes from the experiment in which the 6 ML LiF layer was continually bombarded by an electron beam and the loss spectra were measured after variable irradiation doses. In the course of irradiation, all LiF peaks vanish with rates similar one to the other and with...

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supporting

confidence: 57%

Electron Excitations in the Li Enriched LiF Clusters

Gołek

Sobolewski

1998

phys. stat. sol. (b)

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“…1 permits some immediate observations about the exciton. First, its binding energy is large, suggestive of a local character (16,17). However, it is also dispersive, following (k) ϭ 0 ϩ 8t cos(ka/2), with 0 ϭ 14.2 eV and t ϭ Ϫ0.065 eV, which is a nonlocal effect.…”

Section: Resultsmentioning

confidence: 99%

Dynamical reconstruction of the exciton in LiF with inelastic x-ray scattering

Abbamonte

Graber

Reed

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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The absorption of light by materials proceeds through the formation of excitons, which are states in which an excited electron is bound to the valence hole it vacated. Understanding the structure and dynamics of excitons is important, for example, for developing technologies for light-emitting diodes or solar energy conversion. However, there has never been an experimental means to study the time-dependent structure of excitons directly. Here, we use causality-inverted inelastic x-ray scattering (IXS) to image the charge-transfer exciton in the prototype insulator LiF, with resolutions ⌬t ‫؍‬ 20.67 as (2.067 ؋ 10 ؊17 s) in time and ⌬x ‫؍‬ 0.533 Å (5.33 ؋ 10 ؊11 m) in space. Our results show that the exciton has a modulated internal structure and is coherently delocalized over two unit cells of the LiF crystal (Ϸ8 Å). This structure changes only modestly during the course of its life, which establishes it unambiguously as a Frenkel exciton and thus amenable to a simplified theoretical description. Our results resolve an old controversy about excitons in the alkali halides and demonstrate the utility of IXS for imaging attosecond electron dynamics in condensed matter.attoscience ͉ Wannier function

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“…This momentum transfer dependence of the near edge structure has been used to study the symmetries of the core excited states in solids [6,13,14,15,16,17,18,22,23,24,25]. It may also be possible to use this momentum transfer dependence to obtain information about intermediate-and long-range structure, which are contained in the EXAFStype oscillations χ q (k).…”

Section: B Central Atom Contributionmentioning

confidence: 99%

“…The dependence of x-ray edges on the magnitude of the momentum transfer has been investigated in Ref. [6,21,22], and more recently in Ref. [23].…”

Section: Introductionmentioning

confidence: 99%

Inelastic scattering from core electrons: A multiple scattering approach

2005

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The real-space multiple-scattering (RSMS) approach is applied to model non-resonant inelastic scattering from deep core electron levels over a broad energy spectrum. This approach is applicable to aperiodic or periodic systems alike and incorporates ab initio, self-consistent electronic structure and final state effects. The approach generalizes to finite momentum transfer a method used extensively to model x-ray absorption spectra (XAS), and includes both near edge spectra and extended fine structure. The calculations can be used to analyze experimental results of inelastic scattering from core-electrons using either x-ray photons (NRIXS) or electrons (EELS). In the low momentum transfer region (the dipole limit), these inelastic loss spectra are proportional to those from XAS. Thus their analysis can provide similar information about the electronic and structural properties of a system. Results for finite momentum transfer yield additional information concerning monopole, quadrupole, and higher couplings. Our results are compared both with experiment and with other theoretical calculations.

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Electronic Excitations in LiF: 10-70 eV

Cited by 56 publications

References 13 publications

Electron Excitations in the Li Enriched LiF Clusters

Electron Excitations in the Li Enriched LiF Clusters

Dynamical reconstruction of the exciton in LiF with inelastic x-ray scattering

Inelastic scattering from core electrons: A multiple scattering approach

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