The Atomic Structure of Two-Dimensional Silica

Büchner, Christin; Lichtenstein, Leonid; Heyde, Markus; Freund, Hans‐Joachim

doi:10.1007/978-3-319-15588-3_16

Cited by 9 publications

(10 citation statements)

References 84 publications

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“…If the high temperature annealing during the bilayer preparation is continued under 5 × 10 –6 mbar O 2 , the disordered (usually called vitreous) bilayer phase can be obtained, indicated by the transformation of the (2 × 2) superstructure into a ring in LEED and characterized in real space by a range of variable Si ring sizes with a definite size distribution. , Thus, this phase is characterized by a very special, two-dimensional disorder in which the correlation between the two Si–O networks of the BL is fully maintained and the BL becomes disordered only in the plane. Since in this way a realization of the disorder in bulk silica glass, suggested more than 80 years ago by Zachariasen, can be obtained, this is a very interesting process which can be used as a model for disordered silica …”

Section: Results and Interpretationmentioning

confidence: 99%

“…It is counterbalanced by the energy necessary to strain the local chemical bonds in length and angle in the silica layer and/or from it to the Ru, to produce defects. The two phases accommodate the misfit to the Ru periodicity , differently. The rotated ML phase shows a moiré pattern, i.e.…”

Section: Results and Interpretationmentioning

confidence: 99%

“…In recent years a multitude of well-defined ultrathin silica films supported on different transition metal substrates have been produced and investigated. − On the Ru(0001) support, the existence of various silica polymorphs has been reported. On the one hand, two different types of chemisorbed monolayers (ML) were reported where corner sharing SiO 4 tetrahedra represent the basic construction unit of the film .…”

Section: Introductionmentioning

confidence: 99%

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Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods

et al. 2018

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Silica mono-and bilayer films on Ru(0001) can be physisorbed or chemisorbed, with ordered or vitreous structures, depending on the particular preparation procedures applied. Using the SMART spectro-microscope at BESSY-II with its capabilities for μspectroscopy, μ-diffraction, and LEEM imaging with lateral resolution below 5 nm, in situ and in real time and applied to identical areas, we have investigated the formation of these layers, defined and characterized their properties and their connected morphology, and followed their evolution. Two distinct chemisorbed monolayers and three bilayers (physisorbed crystalline and vitreous, and chemisorbed zigzag phases), and some transitions between them, have been studied. We found that, apart from the deposited silicon amount, the most important parameter for steering the evolution to a particular well-defined layer is the oxygen content at the Ru interface. Nucleation and growth of all layers are homogeneous on the scale of our resolution, leading to rather small domains (20−40 nm), mostly of the same phase, separated by defect lines. We discuss these and other basic findings in context and point out open questions. We also offer alternative recipes for the preparation of some phases, to obtain more homogeneous layers on a mesoscopic scale.

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Section: Results and Interpretationmentioning

confidence: 99%

Section: Results and Interpretationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods

et al. 2018

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“…Recently, the atomic-level structure of an amorphous silica bilayer grown on Ru(0001) was resolved in real space (Figure ). , This system offers exciting opportunities to probe its structure–reactivity relationships. The silica bilayer is amorphous in the xy -plane (substrate plane), although it is ordered in the z -direction and atomically flat at the surface.…”

Section: Experimental and Computational Approaches In The Investigati...mentioning

confidence: 99%

Beyond Ordered Materials: Understanding Catalytic Sites on Amorphous Solids

et al. 2017

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Amorphous materials are widely used as components of solid catalysts, and have been the subject of much applied research. In some instances, their catalytic performance is demonstrably superior to that of their crystalline counterparts, due in part to their greater flexibility. Amorphous or disordered phases can also be generated from crystalline phases under reaction conditions, thus ex-situ observations of long-range order may provide an incomplete or misleading picture. Until recently, theorists and experimentalists have mostly neglected these important materials in fundamental studies, preferring instead to study “well-defined” (often crystalline) catalysts that are potentially more tractable and amenable to computational modeling of their structure-activity relationships. The amorphous materials were assumed to be simply non-uniform versions of compositionally-similar materials with long-range order, having the same key features at short and medium length scales. In this Perspective, shortcomings of this assumption are discussed, as well as challenges inherent in tackling amorphous catalysts more directly, namely, identifying and describing the active sites (especially under reaction conditions), discerning how subtle structural variations modulate site activity, and building atomically detailed models of amorphous catalysts. Three important classes of amorphous catalytic materials are highlighted to illustrate key issues: amorphous oxides, metal ions atomically dispersed on amorphous supports, and supported metal clusters. Amorphous and disordered silicas, aluminas, and silica-aluminas, are discussed in terms of challenges and progress toward identifying how their local structural disorder and surface heterogeneity may impact the behavior of active sites. Promising models of amorphous materials with atomistic detail and increased fidelity to experiment are becoming available. However, for reactions in which small fractions of sites dominate the total activity, computational estimates of the observed kinetics will require statistical sampling methods, even for the most detailed catalyst models. Further developments in in situ and operando characterization techniques and computational modeling will advance our understanding of amorphous catalytic materials and the impact of structural disorder

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“…The recently reported epitaxial, solid solution, single-crystalline Ni–Pd alloy films with continuously tunable lattice constant open possibilities to tackle this challenge . This paper focuses on the growth of 2D silicates on transition-metal substrates that have gained interest as 2D analogues of zeolites. − It will be shown that silica deposition onto a Ni–Pd alloy substrate in an oxygen-rich environment results in the self-limited growth of a 2D Ni silicate in a dioctahedral clay structure not seen in bulk Ni silicates.…”

Section: Introductionmentioning

confidence: 99%

Structure of a Two-Dimensional Silicate Layer Formed by Reaction with an Alloy Substrate

et al. 2019

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The ability to synthesize two-dimensional (2D) oxide layers with nonbulk structures on transition-metal surfaces has attracted attention as a method to expand the range of 2D structures and properties beyond those accessible by thinning known layered materials. In this paper, a combination of surface spectroscopies, scanning tunneling microscopy (STM), and density functional theory (DFT) show that the reaction of silicon and oxygen with a Ni–Pd alloy surface extracts Ni from the substrate to produce a non-bulk-structured 2D Ni silicate. The surface spectroscopies reveal that high-temperature annealing in an oxygen-rich environment causes substrate Ni to segregate toward the surface where it can oxidize to form a 2D crystalline layer that includes Ni–O–Si bonds. STM images of the 2D crystalline layer reveal a local honeycomb structure consistent with six-membered rings of corner-sharing SiO4 tetrahedra overlaid on a larger-scale moiré pattern that arises from the lattice mismatch between the 2D layer and the substrate. The DFT calculations identify a thermodynamically favorable 2D Ni silicate structure composed of a layer of six-membered rings of corner-sharing SiO4 tetrahedra bonded to an octahedrally coordinated Ni–O layer that can explain the observed STM contrast. The structure resembles a single layer of a dioctahedral clay with bonds to the substrate replacing O–H bonds in clays. The dioctahedral Ni clay stands in contrast to known bulk materials in which Ni is only observed in trioctahedral clays. Theory indicates that the formation of the 2D Ni silicate is not strongly dependent on the alloy composition while experiments suggest that its formation is self-limited; that is, once it forms, continued exposure to oxidizing conditions does not alter the structure. The results highlight the potential for using alloy substrates with a reactive component to form unique 2D surface layers with a broad processing window and without tight constraints on composition control.

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The Atomic Structure of Two-Dimensional Silica

Cited by 9 publications

References 84 publications

Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods

Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods

Beyond Ordered Materials: Understanding Catalytic Sites on Amorphous Solids

Structure of a Two-Dimensional Silicate Layer Formed by Reaction with an Alloy Substrate

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