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128. The interlayer structure of trioctahedral lithian micas: an AXANES spectroscopy study at the potassium K-edge

Author

Cibin, Giannantonio, Mottana, Annibale, Marcelli, Augusto, Cinque, Gianfelice, Xu, Wei, Wu, Ziyu, and Brigatti, Maria Franca

Subjects
Mica -- Structure, Mica -- Composition, Potassium -- Research, Crystals -- Structure, Crystals -- Analysis, Earth sciences
Abstract

We recorded angle-dependent XANES (AXANES) spectra at the potassium K-edge for three compositionally intermediate polylithionite-siderophyllite trioctahedral 1M-micas using polarized synchrotron radiation. We evaluated the experimental spectra for both their in-plane and out-of-plane component fractions of the electric dipole contribution using the analytical formulae of Brouder (1990), referring to theory to extract the origin of their multiple-scattering pathways of Natoli et al. (2003). This analysis was extended to a fourth lithian mica studied previously and allowed characterization of the local environment and ordering around the potassium atoms in the interlayer of the entire set of micas. The AXANES in-plane components are notably similar to the XANES spectra recorded on randomly oriented powders, provided these are oriented at the 'magic angle' (Pettifer et al. 1992). Most observed contributions arise from multiple-scattering interactions of the photoelectron ejected from the potassium absorber colliding with atoms located in the interlayer itself. Note that this includes not only interactions with other coplanar potassium and/or alkali atoms distributed along the interlayer plane, but also with their near- and next-nearest neighboring oxygen atoms which lie on the basal planes of the tetrahedral sheets facing the interlayer. By contrast, the AXANES out-of-plane component suggests that several multiple-scattering pathways cross the energetic and structural barrier represented by the tetrahedral sheets. They reach not only the X anions that are located on the upper level of the octahedral sheets, at the center of the open cavity in the tetrahedral sheet, but also the metal cations centering the octahedral sheet itself. Therefore, the out-of-plane components provide indirect information on the number of independent octahedral sites, the cation oxidation state, and the trans- vs. cis-orientation of the anionic sites. Keywords: Polylithionite, siderophyllite, X-ray absorption pleochroism, XAFS, XANES, MXAN DOI: 10.2138/am.2010.3344

Published
2010

131. Quasi‐1D ZrS3 as an Anisotropic Nano‐Reflector for Manipulating Light–Matter Interactions.

Author

Guo, Junqing, Xiao, Zhenyang, Wu, Ziyu, Liao, Xiaxia, Wan, Siyuan, Fu, Xuewen, and Zhou, Yangbo

Subjects
OPTICAL modulation, OPTOELECTRONIC devices, ISOTROPIC properties, CRYSTAL symmetry, OPTICAL properties, RAMAN scattering
Abstract

2D layered materials with low crystal symmetries exhibit unique anisotropic physical properties. Here the systematic studies on the optical modulation effects of such anisotropic 2D materials to isotropic 2D materials in their stacked van der Waals (vdW) heterostructures are reported. By applying angle‐resolved polarization spectroscopic characterizations on the MoS2/ZrS3 vdW heterostructure, periodic intensity variations of the Raman scattering and photoluminescence (PL) emission modes of monolayer MoS2 are observed, which are closely correlated to the anisotropic optical properties of the underlying ZrS3 layers. Such anisotropic optical modulation effects can be identified with the thickness of ZrS3 reduced to few layers (≈6 nm), and are attributed to the strong birefringence and dichroism effects in ZrS3 that cause reflection difference between its crystal axis, thus modulating the Raman/PL intensities of MoS2 via Fabry–Pérot interference effect. Furthermore, the polarized photocurrent response of the heterostructure is also demonstrated, where its major contribution originates from MoS2. This work develops a new methodology to tune the light–matter interactions and properties of isotropic 2D materials by the combination with anisotropic 2D materials, which substantially broadens the application of low symmetry layered materials in polarization sensitive optoelectronic devices. [ABSTRACT FROM AUTHOR]

Published
2022
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