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Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite.

ABSTRACT: Crystalline silica (SiO₂) is a major material used in many technologies, yet the exact surface structures of silica polymorphs are still mostly unknown. Here we perform a comprehensive study of surface reconstructions of ?-cristobalite (001), ?-quartz (001) and stishovite (110) and (100) using evolutionary algorithm USPEX in conjunction with ab initio calculations. We found the well-known "dense surface" to be among low-energy reconstructions of ?-quartz (001), as well as its previously proposed distorted version, which we call "shifted surface". For cristobalite and stishovite we show the formation of reconstructions without dangling bonds which share common features with well-known "dense surface" of ?-quartz (001). We call them "dense cristobalite" and "dense stishovite" - all of these have honeycomb arrangements of corner-sharing SiO₄-tetrahedra in the surface layers. These tetrahedral honeycombs have very low surface energies, and such tetrahedral surface pattern is observed even in stishovite (the bulk structure of which has SiO₆-octahedra, rather than SiO₄-tetrahedra).

SUBMITTER: Feya OD

PROVIDER: S-EPMC6085356 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite.

Feya Oleg D OD Wang Qinggao Q Lepeshkin Sergey V SV Baturin Vladimir S VS Uspenskii Yurii A YA Oganov Artem R AR

Scientific reports 20180809 1

Crystalline silica (SiO<sub>2</sub>) is a major material used in many technologies, yet the exact surface structures of silica polymorphs are still mostly unknown. Here we perform a comprehensive study of surface reconstructions of α-cristobalite (001), α-quartz (001) and stishovite (110) and (100) using evolutionary algorithm USPEX in conjunction with ab initio calculations. We found the well-known "dense surface" to be among low-energy reconstructions of α-quartz (001), as well as its previous ...[more]

PMID: 30093648

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Project description:Two-dimensional (2D) topological insulators have fascinating physical properties which are promising for applications within spintronics. In order to realize spintronic devices working at room temperature, materials with a large nontrivial gap are needed. Bismuthene, a 2D layer of Bi atoms in a honeycomb structure, has recently attracted strong attention because of its record-large nontrivial gap, which is due to the strong spin-orbit coupling of Bi and the unusually strong interaction of the Bi atoms with the surface atoms of the substrate underneath. It would be a significant step forward to be able to form 2D materials with properties such as bismuthene on semiconductors such as GaAs, which has a band gap size relevant for electronics and a direct band gap for optical applications. Here, we present the successful formation of a 2D Bi honeycomb structure on GaAs, which fulfills these conditions. Bi atoms have been incorporated into a clean GaAs(111) surface, with As termination, based on Bi deposition under optimized growth conditions. Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/S) demonstrates a well-ordered large-scale honeycomb structure, consisting of Bi atoms in a √3 × √3 30° reconstruction on GaAs(111). X-ray photoelectron spectroscopy shows that the Bi atoms of the honeycomb structure only bond to the underlying As atoms. This is supported by calculations based on density functional theory that confirm the honeycomb structure with a large Bi-As binding energy and predict Bi-induced electronic bands within the GaAs band gap that open up a gap of nontrivial topological nature. STS results support the existence of Bi-induced states within the GaAs band gap. The GaAs:Bi honeycomb layer found here has a similar structure as previously published bismuthene on SiC or on Ag, though with a significantly larger lattice constant and only weak Bi-Bi bonding. It can therefore be considered as an extreme case of bismuthene, which is fundamentally interesting. Furthermore, it has the same exciting electronic properties, opening a large nontrivial gap, which is the requirement for room-temperature spintronic applications, and it is directly integrated in GaAs, a direct band gap semiconductor with a large range of (opto)electronic devices.

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Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite.

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Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite.

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