Anisotropy of hexagonal boron nitride core absorption spectra by x-ray Raman spectroscopy

Watanabe, Noboru; Hayashi, Hisashi; Udagawa, Yasuo; Takeshita, Kunikazu; Kawata, Hiroshi

doi:10.1063/1.117439

Cited by 44 publications

(27 citation statements)

References 15 publications

(20 reference statements)

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“…The core hole is on the nitrogen atom, but the electron in the conduction band is still concentrated on the boron atoms. Excitonic effects and oscillator strengths are therefore expected to be weaker, which is the case: The measured EELS signals are much weaker and therefore less accurate, and the spectra show broader and less "atomiclike" features, in agreement with previous studies [34,35,37,40,42].…”

Section: A Core Losses At the Boron K Edgesupporting

confidence: 74%

“…The different peaks are sharp and related to well-known transitions with typical symmetries between the deep 1s level and the first unoccupied π * states (192 eV) and σ * states (199 eV) [32][33][34][35][36][37][38][39]. Energy-filtered scattering patterns have been recorded in the 185-215 eV range for the three samples.…”

Section: A Core Losses At the Boron K Edgementioning

confidence: 99%

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Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

et al. 2017

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Electron energy loss spectra were measured on hexagonal boron nitride single crystals employing an electron energy loss spectroscopic setup composed of an electron microscope equipped with a monochromator and an in-column filter. This setup provides high-quality energy-loss spectra and allows also for the imaging of energy-filtered diffraction patterns. These two acquisition modes provide complementary pieces of information, offering a global view of excitations in reciprocal space. As an example of the capabilities of the method we show how easily the core loss spectra at the K edges of boron and nitrogen can be measured and imaged. Low losses associated with interband and/or plasmon excitations are also measured. This energy range allows us to illustrate that our method provides results whose quality is comparable to that obtained from nonresonant x-ray inelastic scattering but with advantageous specificities such as an enhanced sensitivity at low q and a much greater simplicity and versatility that make it well adapted to the study of two-dimensional materials and related heterostructures. Finally, by comparing theoretical calculations to our measures, we are able to relate the range of applicability of ab initio calculations to the anisotropy of the sample and assess the level of approximation required for a proper simulation of our acquisition method.

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Section: A Core Losses At the Boron K Edgesupporting

confidence: 74%

Section: A Core Losses At the Boron K Edgementioning

confidence: 99%

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

et al. 2017

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“…Such a superposition of wave functions from different atomic sites would not generate a single spherical harmonic wave function. This is a significant refinement of the prior understanding of this exciton peak as a 1s − π * transition 21,24,34 .…”

mentioning

confidence: 99%

“…The crystallite size is of the order of 1000Å with a mosaic spread about 2 to 3 degrees along the c-axis 24 . The orientation within the basal plane is assumed to be random.…”

mentioning

confidence: 99%

Exciton spectroscopy of hexagonal boron nitride using nonresonant x-ray Raman scattering

et al. 2008

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We report non-resonant x-ray Raman scattering (XRS) measurements from hexagonal boron nitride for transferred momentum from 2 to 9Å −1 along directions both in and out of the basal plane. A symmetry-based argument, together with real-space full multiple scattering calculations of the projected density of states in the spherical harmonics basis, reveals that a strong pre-edge feature is a dominantly Y10-type Frenkel exciton with no other s-, p-, or d -components. This conclusion is supported by a second, independent calculation of the q-dependent XRS cross-section based on the Bethe-Salpeter equation. The physics of low-energy photoelectrons in solids is a complex, many body problem 1 . All aspects of the electronic structure of the material must be taken into account 2,3 , including the interaction between the photoelectron and the complementary hole 3,4,5,6 . This latter effect allows for similar long-lived bound states in metals (generally called Fermi-edge singularities) 7 and in insulators (called excitons) 8 . As a canonical example of a many body problem in condensed matter physics, core-excitons are a topic of continuing interest 4,5,6 .The present synergy between steadily progressing ab initio theoretical treatments 2,3,9,10 and on-going improvements in instrumentation 11 in studies of nonresonant x-ray Raman scattering (XRS) shows a strong potential for rapid progress on this old problem 5,6 . XRS is the inelastic scattering of hard x-rays from bound electrons, and XRS studies have seen a recent explosion in the number and range of applications 5,6,11,12,13,14,15,16,17 . In comparison with q-resolved electron energy loss spectroscopy (EELS) 18 , XRS is more suited for bulk condensed matter systems 13 due to the large penetration length afforded by the relative high-energy incident and scattered photons. The measured q-dependent XRS provides direct information about multipole contributions to the dynamic structure factor S(q, ω) 5,6,14,15,16 . It can be directly compared with theoretical calculations of S(q, ω) 6,14,15,16 , and can in some cases be inverted to provide an experimental measure of the perturbed projected density of states (l -DOS) 10,19 , which can again be compared to theory.XRS has shown itself to be especially suitable for spectroscopy of the angular characteristics of core excitons at the near edge region. For example, XRS studies 5,6 on LiF and icosahedral B 4 C convincingly demonstrated s-, and p-type excitons at the F and B K-edges, respectively, which can be attributed to atoms located at a center of inversion symmetry of the unit cell with parity a good quantum number for the final states 6 . Here, we demonstrate that for some systems one can learn not only the ∆l selection rule for the exciton but also a full description of its angular characteristics in terms of spherical harmonics, Y lm .We present measurements of the q-dependent XRS of hexagonal boron nitride (h-BN), an anisotropic system with all atoms sitting at positions with reflection symmetry to the basal plane (Figure 1,...

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“…X-ray Raman spectroscopy (XRS) is an alternative hard x-ray based technique that can extract soft-XAS information. [4][5][6][7][8][9][10][11][12] This hard x-ray photon-in/photon-out technique combines the advantages of a hard x-ray probe with the sensitivity of soft x-ray XAS. In particular it enables bulk studies of low-Z systems under many conditions including extreme pressure/temperature environments, flow tubes, furnaces, liquids, in situ cells, etc.…”

Section: Introductionmentioning

confidence: 99%

A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource

Sokaras

Nordlund

Weng

et al. 2012

Review of Scientific Instruments

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We present a new x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station is located at wiggler beamline 6-2 equipped with two monochromators-Si(111) and Si(311) as well as collimating and focusing optics. It consists of two multi-crystal Johann type spectrometers arranged on intersecting Rowland circles of 1 m diameter. The first one, positioned at the forward scattering angles (low-q), consists of 40 spherically bent and diced Si(110) crystals with 100 mm diameters providing about 1.9% of 4π sr solid angle of detection. When operated in the (440) order in combination with the Si (311) monochromator, an overall energy resolution of 270 meV is obtained at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers (not diced), is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. The solid angle of this spectrometer is about 0.9% of 4π sr, with a combined energy resolution of 600 meV using the Si (311) monochromator. These features exceed the specifications of currently existing relevant instrumentation, opening new opportunities for the routine application of this photon-in/photonout hard x-ray technique to emerging research in multidisciplinary scientific fields, such as energyrelated sciences, material sciences, physical chemistry, etc.

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Anisotropy of hexagonal boron nitride core absorption spectra by x-ray Raman spectroscopy

Cited by 44 publications

References 15 publications

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

Exciton spectroscopy of hexagonal boron nitride using nonresonant x-ray Raman scattering

A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource

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