<i>Ab initio</i>calculation of ELNES/XANES of BeO polymorphs

Gao, Shang

doi:10.1002/pssb.200945574

Cited by 9 publications

(7 citation statements)

References 41 publications

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“…There is also a broad low intensity peak at ~139 eV. The first peak is due to a core exciton and the overall spectrum is reproduced quite well by theoretical calculations (Soininen et al 2001;Gao 2010) but there has been no detailed analysis of the individual peaks.…”

Section: Alkalis (Li Na K Rb Cs)mentioning

confidence: 99%

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Henderson

Groot

Moulton

2014

Reviews in Mineralogy and Geochemistry

271

155

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In addition to the XANES region, at higher energies the extended X-ray absorption fine structure (EXAFS) region is found. The spectral shape in the near-edge region is determined by electronic density of states effects and gives mainly information about the electronic properties and the local geometry of the absorbing atom. The EXAFS region is dominated by single scattering events of the outgoing electron on the neighboring atoms, providing mainly information about the local geometric structure around the absorbing site. In this chapter we will focus on XANES. XANES SpectroscopyIn XPS the ground state (Ψ 0 ) is excited to the ground state plus a core hole (c), where the electron (ε) is excited to higher energy, while in XAS the ground state is excited with a coreto-valence excitation (cv). The XPS binding (E B ) is defined as the photon energy (Ω) minus the measured kinetic energy of the electron (E k ) and corrected for the work function (φ):The work function is the minimal energy to emit an electron from the material. In metals the XAS edge energy can be assumed to be equal to the XPS binding energy, because exactly at the XPS binding energy a transition is possible to the lowest empty state. Experimentally the XAS edge energy can be slightly higher than the XPS binding energy, for example if the transition to the lowest empty state is forbidden by selection rules. Single electron excitation approximation and selection rulesIn first approximation XANES can be described as the excitation of a core electron to an empty state. In the Fermi golden rule, the initial state wave function is rewritten as a core wave function and the final state wave function (ε) as a valence electron wave function (ν). This implicitly assumes that all other electrons do not participate in the X-ray induced transition. In this approximation, the Fermi golden rule can be written as:The X-ray absorption selection rules determine that the dipole matrix element is non-zero if the orbital quantum number of the final state differs by one from the initial state (∆L = ± 1, i.e., s → p, p → s or d, etc.) and the spin is conserved (∆S = 0). In the dipole approximation, the shape of the absorption spectrum should look like the partial density of the (∆L = ± 1) empty states projected on the absorbing site, convoluted with a Lorentzian. This Lorentzian broadening is due to the finite lifetime of the core-hole, leading to an uncertainty in its energy according to Heisenberg's principle. The single electron approximation gives an adequate simulation of the XANES spectral shape if the interactions between the electrons in the final state are relatively weak. This is the case for all excitations from 1s core states (K-edges).

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Section: Alkalis (Li Na K Rb Cs)mentioning

confidence: 99%

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Henderson

Groot

Moulton

2014

Reviews in Mineralogy and Geochemistry

271

155

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“…Briefly, under the dipole approximation, the intensity is represented by the square modulus of the position‐operator matrix element between the core state (1s) and the unoccupied states (π*,σ*), which are explicitly evaluated, with core‐hole effects taken into account by employing a specially constructed pseudopotential for the excited atom in a sufficiently large supercell . The ELNES dependence on the direction of the momentum transfer manifests the anisotropy of the electron orbitals . Due to strong anisotropy between the in‐plane sp 2 bonding and the π‐bonding formed by p z orbitals, h‐BeO core‐loss spectra differ drastically for q ∥ c and q

⊥

c , where q is the momentum transfer upon inelastic scattering and c ∥ z ∥[0001] (Figure S7).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Honeycomb‐Structured Beryllium Oxide via Graphene Liquid Cells

et al. 2020

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Using high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy, we show that beryllium oxide crystallizes in the planar hexagonal structure in a graphene liquid cell by a wet‐chemistry approach. These liquid cells can feature van‐der‐Waals pressures up to 1 GPa, producing a miniaturized high‐pressure container for the crystallization in solution. The thickness of as‐received crystals is beyond the thermodynamic ultra‐thin limit above which the wurtzite phase is energetically more favorable according to the theoretical prediction. The crystallization of the planar phase is ascribed to the near‐free‐standing condition afforded by the graphene surface. Our calculations show that the energy barrier of the phase transition is responsible for the observed thickness beyond the previously predicted limit. These findings open a new door for exploring aqueous‐solution approaches of more metal‐oxide semiconductors with exotic phase structures and properties in graphene‐encapsulated confined cells.

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“…This is different to the shape of the hexagonal wurtzite BeO spectrum, which, in addition to the core-exciton, also displays noticeable features at higher energies. This difference is retained for BeO in the zinc-blende structure, as shown by supercell core-hole calculations [37]. The spectral features can be understood by analyzing the excitations derived from solving the Bethe-Salpeter equation.…”

Section: Discussionmentioning

confidence: 99%

“…[29,30,31,32]). The Be 1s edge was investigated by Soininen et al [33], using a pseudopotential-based BSE technique [34,35] and, more recently, by pseudopotential (PP) supercell calculations within the core-hole approximation [36,37]. Regarding the beryllium chalcogenides, there are several theoretical studies on their properties in the literature, see e.g.…”

Section: Introductionmentioning

confidence: 99%

The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment

Olovsson

Weinhardt

Fuchs

et al. 2013

J. Phys.: Condens. Matter

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Abstract. We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe-Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core excitons and higher energy excitations.The Be K-edge in beryllium oxide and chalcogenides 2

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Ab initiocalculation of ELNES/XANES of BeO polymorphs

Cited by 9 publications

References 41 publications

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Synthesis of Honeycomb‐Structured Beryllium Oxide via Graphene Liquid Cells

The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment

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