We have employed a suitable combination of atomic-scale modeling techniques in order to explore the adsorption properties of dichlorobenzene (DClB) isomers in the potassium-exchanged X-type faujasite (KX). To describe the preferential locations of the DClB isomer within the faujasite porosity and the main interactions, we applied Density Functional Theory (DFT). In addition to multiple hydrogen bonds established between hydrogen atoms of DClB species and framework oxygen atoms, the adsorption is stabilized by electrostatic interaction between the potassium cations and DClB atoms bearing a negative charge, i.e. the chlorine atoms and/or the carbon atoms opposite to the chlorine atoms. The ortho-DClB isomer high value of interaction energy with KX is explained by the possibility of simultaneous stabilizing electrostatic interactions due to the large size of the K+ cation. Using Monte Carlo (MC) simulation, we have extracted the absolute adsorption isotherms of DClB isomers in the KX zeolite and the adsorption heat evolution as a function of loading and compared it with accessible experimental and calculated data. In addition, we explain the underlying microscopic adsorption mechanism in play, for various uptakes, supported by the cumulative snapshots. We show that the type of interaction depends on the K+ location and on the relative position of the chlorine atoms on the DClB isomer. Finally, we have evidenced a slight redistribution of K+ cations upon increasing adsorbed amount, with a tendency of these cations to shift towards the supercage, especially at crystallographic positions III and III ’.

The formation of one dimensional semiconductors offers exciting potential for the development of nanoscale devices. Germanium (Ge) nanoribbons can be formed on metallic substrates with specific structural and electronic properties. In this study, we investigate the structure of Ge nanoribbons grown on an Al(110) substrate by molecular beam epitaxy. We used low energy electron diffraction, scanning tunneling microscopy and density functional theory calculations techniques. We show the successful formation of an ordered network of single-width Ge-based nanoribbons, with a (10 × a[-110]) periodicity along the [-110] direction of the Al(110) crystal surface. Individual Ge nanoribbons structure is determined via an energetic theoretical study based on Ge chemical potential, and a comparison of calculated and experimental images to validate a stacked dimers model.

Since germanene cannot be exfoliated from a bulk material, and since Ge-based surface alloys are more stable than pure Ge monolayers (MLs) on metal surfaces, the synthesis of germanene flakes remains challenging. Here we report on the synthesis of germanene nanoflakes on Ag ML islands grown on Ag(111). The maximum achievable size is of the order of 30 nm, and germanene growth occurs due to the heavily oversaturated chemical potential for the Ge atoms confined on top of the Ag islands during growth. The nucleation of three-dimensional clusters, however, prevents the formation of larger germanene flakes.

Two-dimensional (2D) honeycomb lattices beyond graphene, such as germanene, appear very promising due to their outstanding electronic properties, such as the quantum spin Hall effects. While there have been many claims of germanene monolayers up to now, no experimental evidence of a honeycomb structure has been provided up to now for these grown monolayers. Using scanning tunneling microscopy (STM), surface X-ray diffraction (SXRD), and density functional theory, we have elucidated the Ge-induced (109×109)R±24.5° reconstruction on Ag(111). We demonstrate that a powerful algorithm combining SXRD with STM allows us to solve a giant surface reconstruction with more than a hundred atoms per unit cell. Its extensive unit cell indeed consists of 98 2-fold or 3-fold coordinated Ge atoms, forming a periodic arrangement of pentagons, hexagons, and heptagons, with the inclusion of six dispersed Ag atoms. By analogy, we show that the (77×77)R±19.1° reconstruction obtained by segregation of Ge through an epitaxial Ag/Ge(111) film possesses a similar structure, i.e., Ge pentagons/hexagons/heptagons with a few Ag atoms. Such an organization is more stable than that of pure Ge monolayers and can be assigned to the ground state of epitaxial germanene.

ADVERTISEMENT RETURN TO ISSUEPREVLetter to the EditorNEXTReply to the Comment on “The Ground State of Epitaxial Germanene on Ag(111)”Kai ZhangKai ZhangSorbonne Université, Centre National de la Recherche Scientifique, Institut des NanoSciences de Paris INSP, F-75005 Paris, FranceMore by Kai Zhang, Marie-Christine HanfMarie-Christine HanfUniversité de Haute Alsace, CNRS, IS2M UMR7361, F-68100 Mulhouse, FranceUniversité de Strasbourg, 67081 Strasbourg, FranceMore by Marie-Christine Hanfhttps://orcid.org/0000-0003-1820-504X, Romain BernardRomain BernardSorbonne Université, Centre National de la Recherche Scientifique, Institut des NanoSciences de Paris INSP, F-75005 Paris, FranceMore by Romain Bernard, Yves BorenszteinYves BorenszteinSorbonne Université, Centre National de la Recherche Scientifique, Institut des NanoSciences de Paris INSP, F-75005 Paris, FranceMore by Yves Borensztein, Hervé CruguelHervé CruguelSorbonne Université, Centre National de la Recherche Scientifique, Institut des NanoSciences de Paris INSP, F-75005 Paris, FranceMore by Hervé Cruguel, Andrea RestaAndrea RestaSynchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, FranceMore by Andrea Restahttps://orcid.org/0000-0002-0614-1192, Yves GarreauYves GarreauSynchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, FranceUniversité Paris Cité, Laboratoire Matériaux et Phénomènes Quantiques, CNRS, F-75013 Paris, FranceMore by Yves Garreau, Alina VladAlina VladSynchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, FranceMore by Alina Vlad, Alessandro CoatiAlessandro CoatiSynchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, FranceMore by Alessandro Coati, Davide SciaccaDavide SciaccaUniv. Lille, CNRS, Centrale Lille, Univ. Polytechnique Hauts-de-France Junia-ISEN, UMR 8520 - IEMN, F-59000 Lille, FranceMore by Davide Sciacca, Bruno GrandidierBruno GrandidierUniv. Lille, CNRS, Centrale Lille, Univ. Polytechnique Hauts-de-France Junia-ISEN, UMR 8520 - IEMN, F-59000 Lille, FranceMore by Bruno Grandidierhttps://orcid.org/0000-0001-6131-7309, Mickael DerivazMickael DerivazUniversité de Haute Alsace, CNRS, IS2M UMR7361, F-68100 Mulhouse, FranceUniversité de Strasbourg, 67081 Strasbourg, FranceMore by Mickael Derivaz, Carmelo PirriCarmelo PirriUniversité de Haute Alsace, CNRS, IS2M UMR7361, F-68100 Mulhouse, FranceUniversité de Strasbourg, 67081 Strasbourg, FranceMore by Carmelo Pirrihttps://orcid.org/0000-0002-3629-1044, Philippe SonnetPhilippe SonnetUniversité de Haute Alsace, CNRS, IS2M UMR7361, F-68100 Mulhouse, FranceUniversité de Strasbourg, 67081 Strasbourg, FranceMore by Philippe Sonnethttps://orcid.org/0000-0001-5891-5500, Régis StephanRégis StephanUniversité de Haute Alsace, CNRS, IS2M UMR7361, F-68100 Mulhouse, FranceUniversité de Strasbourg, 67081 Strasbourg, FranceMore by Régis Stephanhttps://orcid.org/0000-0003-0345-1387, and Geoffroy Prévot*Geoffroy PrévotSorbonne Université, Centre National de la Recherche Scientifique, Institut des NanoSciences de Paris INSP, F-75005 Paris, France*Email for G.P.: [email protected]More by Geoffroy PrévotCite this: ACS Nano 2023, 17, 22, 22149–22151Publication Date (Web):November 28, 2023Publication History Received22 September 2023Accepted2 November 2023Revised27 October 2023Published online28 November 2023Published inissue 28 November 2023https://doi.org/10.1021/acsnano.3c09178Copyright © Published 2023 by American Chemical SocietyRequest reuse permissions This publication is free to access through this site. Learn MoreArticle Views-Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertscloseSUBJECTS:Alloys,Density functional theory,Epitaxy,Layers,Scanning tunneling microscopy Get e-Alerts

Several studies have reported the possible growth of germanene on various metal surfaces. However, the exact structure of the layers formed upon evaporation at or above room temperature remains controversial. In particular, the layers obtained after Ge deposition on Al(111) have been either considered as honeycomb organization of Ge atoms on top of a nonreconstructed substrate, or as alloyed layers. Using quantitative measurements by surface x-ray diffraction compared to density functional theory calculations, we show that the (root 7 x root 7)R +/- 19.1 degrees reconstruction obtained after room temperature deposition is a mixed Ge-Al honeycomb layer, on top of an Al(111) plane, and not a pure germanene layer.

In the present study, we have combined several atomic-scale computational techniques [static lattice optimization, density functional theory (DFT), canonical Monte Carlo (MC), and Gibbs ensemble MC (GEMC)] with experiment in order to describe the adsorption of water in potassium-exchanged X-type faujasite. Indeed, by applying DFT calculations, we have evidenced a strongly heterogeneous adsorbent surface and classified the preferential adsorption sites at zero loading for water molecules. The sodalite cage was identified as the preferential location. Moreover, by applying the GEMC technique, we have successfully simulated the water adsorption isotherm in the K-X zeolite. Finally, through the canonical MC simulation, we have described the microscopic mechanisms of water adsorption within the K-X zeolite at various uptakes, ranging from low loading (8 H2O/unit cell) to saturation (240 H2O/unit cell). We have evidenced that at low loading, the sodalite cages host the major part of the adsorbed molecules, while at increasing hydration ratio, the water molecules locate more in supercages. At saturation, each sodalite cage accommodates more than three water molecules on average, whereas nearly 90% of water molecules are located within supercages. Finally, at any hydration ratio, the water molecules in supercages coordinate preferentially with potassium cations at crystallographic site III (or III') rather than at site II. Cations in site II start interacting with water molecules only at uptakes superior to 80 H2O molecules/unit cell, once all cations in site III (or III') are occupied by at least one water molecule.

Unlike silicene, for which the demonstration of its existence has been done through numerous independent studies, the possibility of growing epitaxial germanene remains highly controversial. It has been recently shown by scanning tunneling microscopy that the (3 x 3) surface reconstruction formed upon Ge deposition on Al(111) presents a honeycomb structure, and it was assigned to a pure germanene monolayer. Using quantitative measurements by surface X-ray diffraction compared to density functional theory calculations, we demonstrate that this Ge/Al(111) (3 x 3) reconstruction corresponds, in fact, to a mixed Ge--Al honeycomb layer on top of an alloyed interfacial layer. The model of a germanene monolayer on top of the Al(111) surface can be completely excluded.

The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It isimportant for fundamental studies not only in surface science but alsoin several applied domains including, for example, miniaturizedmolecular electronic or for the development of various devices suchas nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulatinglayer grown on a silicon surface via its epitaxy with CaF2. We showthat, following the formation of a wetting layer, the ensuing organizedunit cells are coupled to additional physisorbed CaF2molecules,periodically located in their surroundings. This configuration shapesthe formation of ribbons of stripes that functionalize the semi-conductor surface. The obtained assembly, having a monolayerthickness, reveals a surface gap energy of 3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of thisstructure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity(annealing, DFT +U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Ourfindings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfacessuch as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as aversatile surface platform for various atomic-scale studies of molecular devices.

Silicene and germanene freestanding layers are usually described as a honeycomb lattice formed by two hexagonal sub-lattices presenting a height difference, namely the layer buckling. In this work, first-principles calculations show that silicene and germanene can be rippled at 0 K with various wavelengths, without any compressive strain of the layer. For germanene, the height difference between two Ge atoms from the same sub-lattice can be as high as 4.7 for an undulation length of 81 . The deformations are related to slight (lower than 1.7°) bond angle modifications, and the energy cost is remarkably low, lying between 0.1 and 0.8 meV per atom. These undulations modify the electronic structure, opening a gap of 15 meV.

The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is important for fundamental studies not only in surface science but also in several applied domains including, for example, miniaturized molecular electronic or for the development of various devices such as nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ∼3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT + U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic-scale studies of molecular devices.

Our ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is not only important for fundamental studies in surface science, but also in several applied domains including for example miniaturized molecular electronic or for the development of various devices such as nanoscale bio-sensors or photovoltaic cells. Here, we provide atomic scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ~ 3.2 eV. The adsorption of iron-tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT+U and non-local van der Waals functionals) are employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layer on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripes structures, which lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic scale study of molecular devices.

The interaction of organic C-60 molecules with germanene grown on Al(1 1 1) is investigated by experimental tools and calculations. By mean of scanning tunneling microscopy, we show that a single but disordered C-60 layer is formed upon deposition in the monolayer range. Density functional theory calculations indicate that van der Waals and electrostatic interactions are present between the C-60 layer and the germanene, without formation of covalent bond. Moreover, the C-60 molecules are adsorbed without major crystallographic and charge modifications at the interface between germanene and the Al(1 1 1) substrate. The predicted charge transfer from the Al(1 1 1) substrate to the C-60 molecules is very small, which means that the germanene layer acts as an electronic buffer between the highly electron attractor C-60 molecules and the large electron reservoir Al(1 1 1). This leaves the C-60 layer quite uncharged, and so preserves its electron attractor properties for further layers grown on it, in the design of new molecular sensors.

The interaction of organic C60 molecules with germanene grown on Al(1 1 1) is investigated by experimental tools and calculations. By mean of scanning tunneling microscopy, we show that a single but disordered C60 layer is formed upon deposition in the monolayer range. Density functional theory calculations indicate that van der Waals and electrostatic interactions are present between the C60 layer and the germanene, without formation of covalent bond. Moreover, the C60 molecules are adsorbed without major crystallographic and charge modifications at the interface between germanene and the Al(1 1 1) substrate. The predicted charge transfer from the Al(1 1 1) substrate to the C60 molecules is very small, which means that the germanene layer acts as an electronic buffer between the highly electron attractor C60 molecules and the large electron reservoir Al(1 1 1). This leaves the C60 layer quite uncharged, and so preserves its electron attractor properties for further layers grown on it, in the design of new molecular sensors.

A combination of molecular simulation tools with the gravimetric experiments has been employed to explore the adsorption of dichlorinated aromatics in (EMT)-type zeolites at a microscopic scale. A suited combination of classical and quantum simulation tools provided a clear overall picture of the adsorption process, from both local and global points of view, well matching with the gravimetric measurement data. The adsorbate preferential locations, adsorbate/zeolite interaction nature and geometry, and the adsorption energy were extracted from density functional theory calculations. Furthermore, on the basis of classical force fields, the Gibbs ensemble Monte Carlo simulations made it possible to predict room temperature dichlorobenzene adsorption isotherms in the EMT -type zeolite in both purely siliceous and aluminosilicate forms. Finally, we accomplished a detailed analysis of the microscopic mechanism of the adsorption process, with a special highlight to understanding the interaction geometry of the molecule with the sodium cation, according to its crystallographic site. Thus, we could depict that adsorbates under study preferentially adsorb within the smaller cage, called hypocage. Then, the larger cages, designed as hypercages, start filling only once all hypocages are at least partially occupied.

A new germanene crystallographic structure is investigated by scanning tunnelling microscopy and density functional theory calculations. We found that germanene can crystallize in two stable but different structures when grown on Al(111) at the same temperature. These structures are evidenced in scanning tunnelling images by a honeycomb contrast and by a hexagonal contrast. These contrasts are relevant of a Ge network with one (hexagonal) or two (honeycomb) Ge atoms per unit cell shifted upward with respect to the other Ge atoms. These structures appear alternatively and can be turned on and off by a tip-induced process.

The strain dependence of benzene chemisorption on a silicene freestanding layer has been studied by means of density functional theory calculations. It appears that the molecule, which is adsorbed via a [4+2] pseudo-cycloaddition on the substrate, is more stable when adsorbed on strained than on unstrained silicene since the adsorption energy increases (in absolute value) with tensile or compressive strain. These results, which were not easily predictable, are interpreted in terms of strain-induced reinforcement of the Si–C bonds, formation of a pz-like atomic orbital at the silicene atoms, which augments the silicene reactivity and, for compressive or large tensile strains, increasing of the sp3 character of the Si–Si bonds.

Molecular simulations have been employed in order to explore at the microscopic scale the adsdrption of bis-chlorinated aromatics (1,2- and 1,3-dichlorobenzene) in Faujasite, a large pore openings zeolite. Both, the purely siliceous and the sodium cation exchanged forms of zeolite structures have been respectively considered, aiming to clearly determine the role of the charge compensating cation in the adsorption phenomenon of the investigated aromatics. A suited combination of classical and electronic structure simulation tools provided a clear overall picture of the adsorption process, from both local and global points of view, well matching with the accessible experimental data. The adsorbate preferential locations, adsorbate/zeolite interaction nature and geometry as well as the adsorption energy were extracted from Density Functional Theory calculations. Furthermore, on the basis of classical force fields, the Gibbs ensemble Monte Carlo simulations allowed predicting the room temperature (298 K) adsorption isotherms for the investigated molecules in Faujasite, within the purely siliceous and Na+ exchanged form, with mobile extra-framework cations upon the adsorption process. Finally, we accomplished a' detailed analysis of the microscopic mechanism in play along the whole adsorption process, with a special highlight to the understanding of the interaction geometry of the molecule with the sodium cation, in function of its crystallographic site. Location of the charge compensating cation has been found to influence the nature of interaction with the adsorbate molecule. (C) 2017 Elsevier Inc. All rights reserved.