I09-Surface and Interface Structural Analysis
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Paul
Ryan
,
Panukorn
Sombut
,
Ali
Rafsanjani-Abbasi
,
Chunlei
Wang
,
Fulden
Eratam
,
Francesco
Goto
,
Cesare
Franchini
,
Ulrike
Diebold
,
Matthias
Meier
,
David A.
Duncan
,
Gareth S.
Parkinson
Diamond Proposal Number(s):
[31726]
Open Access
Abstract: Water–solid interfaces pervade the natural environment and modern technology. On some surfaces, water–water interactions induce the formation of partially dissociated interfacial layers; understanding why is important to model processes in catalysis or mineralogy. The complexity of the partially dissociated structures often makes it difficult to probe them quantitatively. Here, we utilize normal incidence X-ray standing waves (NIXSW) to study the structure of partially dissociated water dimers (H2O–OH) at the α-Fe2O3(012) surface (also called the (11̅02) or “R-cut” surface): a system simple enough to be tractable yet complex enough to capture the essential physics. We find the H2O and terminal OH groups to be the same height above the surface within experimental error (1.45 ± 0.04 and 1.47 ± 0.02 Å, respectively), in line with DFT-based calculations that predict comparable Fe–O bond lengths for both water and OH species. This result is understood in the context of cooperative binding, where the formation of the H-bond between adsorbed H2O and OH induces the H2O to bind more strongly and the OH to bind more weakly compared to when these species are isolated on the surface. The surface OH formed by the liberated proton is found to be in plane with a bulk truncated (012) surface (−0.01 ± 0.02 Å). DFT calculations based on various functionals correctly model the cooperative effect but overestimate the water–surface interaction.
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Sep 2024
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I09-Surface and Interface Structural Analysis
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Benedikt P.
Klein
,
Matthew A.
Stoodley
,
Dylan B.
Morgan
,
Luke A.
Rochford
,
Leon B. S.
Williams
,
Paul T. P.
Ryan
,
Lars
Sattler
,
Sebastian M.
Weber
,
Gerhard
Hilt
,
Thomas J.
Liddy
,
Tien-Lin
Lee
,
Reinhard
Maurer
,
David A.
Duncan
Diamond Proposal Number(s):
[27138, 25379, 33709]
Open Access
Abstract: The role of the inorganic substrate termination, within the organic-inorganic interface, has been well studied for systems that contain strong localised bonding. However, how varying the substrate termination affects coordination to delocalised electronic states, like that found in aromatic molecules, is an open question. Azupyrene, a non-alternant polycyclic aromatic hydrocarbon, is known to bind strongly to metal surfaces through its delocalised π orbitals, thus yielding an ideal probe into delocalised surface-adsorbate interactions. Normal incidence X-ray standing wave (NIXSW) measurements and density functional theory calculations are reported for the adsorption of azupyrene on the (111), (110) and (100) surface facets of copper to investigate the dependence of the adsorption structure on the substrate termination. Structural models based on hybrid density functional theory calculations with non-local many-body dispersion yield excellent agreement with the experimental NIXSW results. No statistically significant difference in the azupyrene adsorption height was observed between the (111) and (100) surfaces. On the Cu(110) surface, the molecule was found to adsorb 0.06 ± 0.04 Å closer to the substrate than on the other surface facets. The most energetically favoured adsorption site on each surface, as determined by DFT, is subtly different, but in each case involved a configuration where the aromatic rings were centred above a hollow site, consistent with previous reports for the adsorption of small aromatic molecules on metal surfaces.
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Feb 2024
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I09-Surface and Interface Structural Analysis
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Aleksandr
Baklanov
,
Johannes T.
Kuchle
,
David A.
Duncan
,
Reinhard J.
Maurer
,
Martin
Schwarz
,
Eduardo Corral
Rascon
,
Ignacio
Piquero-Zulaica
,
Huynh Thien
Ngo
,
Alexander
Riss
,
Francesco
Allegretti
,
Willi
Auwärter
,
Paul T. P.
Ryan
Diamond Proposal Number(s):
[18874, 24276]
Abstract: We present a comprehensive, quantitative multimethod characterization of the geometric and electronic interfacial structure of zinc-porphine (Zn-P) on coinage metal supports, namely, Ag(111) and Cu(111). Complementary techniques including X-ray standing waves, X-ray photoelectron spectroscopy, scanning tunneling microscopy, bond-resolved atomic force microscopy, and density functional theory calculations reveal the molecular conformations, signal a temperature-dependence of element-specific adsorption heights, rule out a decisive role of the d10 nature of the Zn center for the adsorption configuration, and uncover a considerably increased Zn-P adsorption height on Ag(111) compared to Cu(111). Furthermore, a pronounced out-of-plane displacement of the Zn center upon water ligation is demonstrated, a manifestation of the surface trans-effect. This study thus sheds light on effects of temperature, chemical nature of the metal center, its ligation, and the coinage metal support on interfacial structure and molecular deformation of an archetypical surface-anchored metal-tetrapyrrole.
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Apr 2023
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I09-Surface and Interface Structural Analysis
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Johannes T.
Küchle
,
Aleksandr
Baklanov
,
Ari Paavo
Seitsonen
,
Paul
Ryan
,
Peter
Feulner
,
Prashanth
Pendem
,
Tien-Lin
Lee
,
Matthias
Muntwiler
,
Martin
Schwarz
,
Felix
Haag
,
Johannes V
Barth
,
Willi
Auwärter
,
David A.
Duncan
,
Francesco
Allegretti
Diamond Proposal Number(s):
[15804, 20771]
Open Access
Abstract: Silicene, the two-dimensional (2D) allotrope of silicon, is a promising material for electronics. So far, the most direct synthesis strategy has been to grow it epitaxially on metal surfaces; however, the effect of the strong silicon-metal interaction on the structure and electronic properties of the metal-supported silicene is generally poorly understood. In this work, we consider the 4×4-silicene monolayer grown on Ag(111), probably the most illustrious representative of the 2D silicon family, and show that our experimental results refute the common interpretation of this system as a simple buckled, honeycomb monolayer with a sharp interface to the Ag substrate. Instead, the presented analysis demonstrates the pervasive presence of a second silicon species, which we conclude to be a Si‑Ag alloy stacked between the 2D silicene and the silver substrate and scaffolding the 2D silicene layer. These findings question the current structural understanding of the silicene/Ag(111) interface and may raise expectations of analogous alloy systems in the stabilization of other 2D materials grown epitaxially on metal surfaces.
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Aug 2022
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I07-Surface & interface diffraction
I09-Surface and Interface Structural Analysis
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Philip J.
Mousley
,
Luke A.
Rochford
,
Paul T. P.
Ryan
,
Philip
Blowey
,
James
Lawrence
,
David A.
Duncan
,
Hadeel
Hussain
,
Billal
Sohail
,
Tien-Lin
Lee
,
Gavin R.
Bell
,
Giovanni
Costantini
,
Reinhard J.
Maurer
,
Christopher
Nicklin
,
D. Phil
Woodruff
Diamond Proposal Number(s):
[14884, 4884]
Open Access
Abstract: While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored.
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Apr 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[17261, 20785]
Open Access
Abstract: A quantitative structural investigation is reported, aimed at resolving the issue of whether substrate adatoms are incorporated into the monolayers formed by strong molecular electron acceptors deposited onto metallic electrodes. A combination of normal-incidence X-ray standing waves, low-energy electron diffraction, scanning tunnelling microscopy, and X-ray photoelectron spectroscopy measurements demonstrate that the systems TCNQ and F4TCNQ on Ag(100) lie at the boundary between these two possibilities and thus represent ideal model systems with which to study this effect. A room-temperature commensurate phase of adsorbed TCNQ is found not to involve Ag adatoms, but to adopt an inverted bowl configuration, long predicted but not previously identified experimentally. By contrast, a similar phase of adsorbed F4TCNQ does lead to Ag adatom incorporation in the overlayer, the cyano end groups of the molecule being twisted relative to the planar quinoid ring. Density functional theory (DFT) calculations show that this behavior is consistent with the adsorption energetics. Annealing of the commensurate TCNQ overlayer phase leads to an incommensurate phase that does appear to incorporate Ag adatoms. Our results indicate that the inclusion (or exclusion) of metal atoms into the organic monolayers is the result of both thermodynamic and kinetic factors.
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Mar 2022
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I09-Surface and Interface Structural Analysis
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Caio
Silva
,
Daniela
Dombrowski
,
Nicolae
Atodiresei
,
Wouter
Jolie
,
Ferdinand
Farwick Zum Hagen
,
Jiaqi
Cai
,
Paul
Ryan
,
Pardeep Kumar
Thakur
,
Vasile
Caciuc
,
Stefan
Bluegel
,
David Andrew
Duncan
,
Thomas
Michely
,
Tien-Lin
Lee
,
Carsten
Busse
Diamond Proposal Number(s):
[14799, 16710, 19801]
Open Access
Abstract: The lattice mismatch between a monolayer of MoS2 and its Au(111) substrate induces a moiré superstructure. The local variation of the registry between sulfur and gold atoms at the interface leads to a periodic pattern of strongly and weakly interacting regions. In consequence, also the electronic bands show a spatial variation. We use scanning tunneling microscopy and spectroscopy (STM/STS), x-ray photoelectron spectroscopy (XPS) and x-ray standing wave (XSW) for a determination of the geometric and electronic structure. The experimental results are corroborated by density functional theory (DFT). We obtain the geometric structure of the supercell with high precision, identify the fraction of interfacial atoms that are strongly interacting with the substrate, and analyze the variation of the electronic structure in dependence of the location within the moiré unit cell and the nature of the band.
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Jan 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[17635]
Open Access
Abstract: Using the chemically specific techniques of normal incidence X-ray standing waves and photoelectron diffraction, we have investigated the dissociative adsorption of formic acid on the Fe3O4(001) surface, specifically probing the local structures of both the adsorbed formate and resulting surface hydroxyl. Using model independent direct methods, we reinforce the observations of a previous surface X-ray diffraction study that the formate molecule adsorbs with both oxygens atop octahedrally coordinated surface Fe cations and that ∼60% of the formate is adsorbed in the so called tet site. We additionally determine, for the first time, that the surface hydroxyl species are found at the so called int site. This confirms previous DFT predictions and reinforces the pivotal role the surface hydroxyl plays in lifting the subsurface cation vacancy termination of the Fe3O4(001) surface.
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Dec 2021
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I09-Surface and Interface Structural Analysis
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Caio C.
Silva
,
Daniela
Dombrowski
,
Abdus
Samad
,
Jiaqi
Cai
,
Wouter
Jolie
,
Joshua
Hall
,
Paul
Ryan
,
Pardeep K.
Thakur
,
David A.
Duncan
,
Tien-Lin
Lee
,
Udo
Schwingenschlögl
,
Carsten
Busse
Diamond Proposal Number(s):
[14799, 16710, 19801]
Abstract: We determined the structure of epitaxial
2H-TaS2
on Au(111) using the method of x-ray standing waves (XSW), supported by density functional theory (DFT) calculations and scanning tunneling microscopy (STM). The lattice mismatch between substrate and overlayer gives rise to a moiré superstructure, which modulates the structural and electronic properties. For a specific registry (S atoms directly above Au substrate atoms), local covalentlike bonds form, whereas globally weak van der Waals bonding prevails. Still, the
TaS2
layer remains rather flat. Significant charge transfer from Au(111) into the conduction band of the two-dimensional material is found.
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Nov 2021
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I09-Surface and Interface Structural Analysis
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Peter
Knecht
,
Joachim
Reichert
,
Peter S.
Deimel
,
Peter
Feulner
,
Felix
Haag
,
Francesco
Allegretti
,
Manuela
Garnica
,
Martin
Schwarz
,
Willi
Auwärter
,
Paul T. P.
Ryan
,
Tien-Lin
Lee
,
David A.
Duncan
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Anthoula Chrysa
Papageorgiou
Diamond Proposal Number(s):
[24320]
Open Access
Abstract: We assess the crucial role of tetrapyrrole flexibility in the CO ligation to distinct Ru‐porphyrins supported on an atomistically well‐defined Ag(111) substrate. Our systematic real space visualisation and manipulation experiments with scanning tunnelling microscopy directly probe the ligation, while bond‐resolving atomic force microscopy and X‐ray standing waves measurements characterise the geometry, X‐ray and ultraviolet photoelectron spectroscopy the electronic structure, and temperature programmed desorption the binding strength. Density functional theory calculations provide additional insight into the functional interface. We unambiguously demonstrate that the substituents regulate the interfacial conformational adaptability, either promoting or obstructing the uptake of axial CO adducts.
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May 2021
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