I09-Surface and Interface Structural Analysis
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Pablo
Vezzoni Vicente
,
Tobias
Weiss
,
Dennis
Meier
,
Wenchao
Zhao
,
Birce Sena
Tömekçe
,
Marc
G. Cuxart
,
Benedikt P.
Klein
,
David A.
Duncan
,
Tien-Lin
Lee
,
Anthoula C.
Papageorgiou
,
Matthias
Muntwiler
,
Ari Paavo
Seitsonen
,
Willi
Auwärter
,
Peter
Feulner
,
Johannes V.
Barth
,
Francesco
Allegretti
Diamond Proposal Number(s):
[25907]
Abstract: In light of the recent research interest in low-dimensional bismuth structures as spin-active materials and topological insulators, we present a comprehensive characterization of the Bi/Au(111) interface. The nuanced evolution of Bi phases upon deposition in ultrahigh vacuum (UHV) on a Au(111) surface is investigated from semidisordered clusters to few-layer Bi(110) thin films. Particular attention is devoted to the high-coverage, submonolayer phases, commonly grouped under the (𝑃×√3) nomenclature. We bring forth a new model, refining the current understanding of the Bi/Au(111) interface and demonstrating the existence of submonolayer moiré superstructures, whose geometry and superperiodicity depend on their coverage. This tuneable periodicity paves the way for their use as tailored buffer and templating layers for epitaxial growth of thin films on Au(111). Finally, we clarify the growth mode of multilayer Bi(110) as bilayer-by-bilayer, allowing precise thickness control of anisotropically strained thin films. This holistic understanding of the structural properties of the material was enabled by the synergy of several experimental techniques, namely low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy and spectroscopy (STM, STS), and x-ray standing waves (XSW), further corroborated by density functional theory (DFT) simulations.
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Oct 2024
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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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I07-Surface & interface diffraction
I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[31429, 33153]
Open Access
Abstract: A structure determination of the commensurate phase formed by 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F4TCNQ) absorbed on Ag(111) is reported. Initial characterization was performed using low-energy electron diffraction and synchrotron radiation photoelectron spectroscopy, with quantitative structural data being provided by normal incident X-ray standing waves (NIXSW) and surface X-ray diffraction (SXRD). NIXSW data show the F4TCNQ molecule to adopt a “twisted” conformation on the surface, previously found to be associated with metal adatom incorporation into a 2d-metal–organic framework for F4TCNQ on Au(111), Ag(100), and Cu(111). SXRD results provide direct evidence of the presence of Ag adatoms that are found to occupy near-bridge or fcc hollow sites with respect to the underlying surface, at an adsorption height of 2.69 ± 0.10 Å. The results show a consistent pattern of behavior for F4TCNQ adsorption on the (111) surfaces of Cu, Ag, and Au.
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Jul 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[25379]
Open Access
Abstract: We report the quantitative adsorption structure of pristine graphene on Cu(111) determined using the normal incidence x-ray standing wave technique. The experiments constitute an important benchmark reference for the development of density functional theory approximations able to capture long-range dispersion interactions. Electronic structure calculations based on many-body dispersion-inclusive density functional theory are able to accurately predict the absolute measure and variation of adsorption height when the coexistence of multiple moiré superstructures is considered. This provides a structural model consistent with scanning probe microscopy results.
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May 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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P.
Ding
,
M.
Braim
,
A. L.
Hobson
,
L. A.
Rochford
,
P. T. P.
Ryan
,
D. A.
Duncan
,
T.-L.
Lee
,
H.
Hussain
,
G.
Costantini
,
M.
Yu
,
D. P.
Woodruff
Diamond Proposal Number(s):
[21622, 29928]
Open Access
Abstract: The results of a quantitative experimental structural investigation of the adsorption phases formed by 2,3,5,6-tetrafluoro-7,7′,8,8′-tetracyanoquinodimethane (F4TCNQ) on Cu(111) are reported. A particular objective was to establish whether Cu adatoms are incorporated into the molecular overlayer. A combination of normal incidence X-ray standing waves, low-energy electron diffraction, scanning tunneling microscopy, and X-ray photoelectron spectroscopy measurements, complemented by dispersion-inclusive density functional theory calculations, demonstrates that F4TCNQ on Cu(111) does cause Cu adatoms to be incorporated into the overlayer to form a two-dimensional metal–organic framework (2D-MOF). This conclusion is shown to be consistent with the behavior of F4TCNQ adsorption on other coinage metal surfaces, despite an earlier report concluding that the adsorption structure on Cu(111) is consistent with the absence of any substrate reconstruction.
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Oct 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[23730]
Open Access
Abstract: The study of surface-confined reactions provides a route towards characterising the mechanistic processes which underpin heterogeneous catalysis. On-surface reactions provide alternative pathways to solution phase synthesis, and can be studied by a range of techniques which can provide chemical and structural information. Importantly, these kinds of studies give us the insight required to potentially control the selectivity and efficiency of these reactions, as well as allowing for the design of molecular systems with specific functionalities. Porphyrin molecules are frequently selected as participants in these systems as they offer significant customisability, with respect to the reactivity of pendant groups and metal atoms which can be incorporated within the porphyrin macrocycle. Utilising the normal incidence x-ray standing wave (NIXSW) technique in conjunction with scanning probe methods and x-ray photoelectron spectroscopy (XPS) enables the generation of detailed models of on-surface systems, including the adsorption geometries of individual molecules. Here the NIXSW technique has been used to perform structural characterisation of three distinct phases of an on-surface reaction of tetraphenyl porphyrin (TPP) on Au(111); close-packed, diffuse and metalated. Using the chemical specificity of XPS and NIXSW we gain insight into chemical and structural changes exhibited by nitrogen atoms within the porphyrin macrocycle at several stages within the reaction process.
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Aug 2023
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30875, 31165, 29418]
Open Access
Abstract: The adsorption structure of iron phthalocyanine (FePc) and titanyl phthalocyanine (TiOPc) was studied by a combination of near edge X-ray absorption fine structure (NEXAFS) spectroscopy and normal incidence X-ray standing waves (NIXSW) technique. The FePc results demonstrate that the molecule adsorbs with the Fe metal centre at an adsorption height of 2.44 ± 0.09 Å, its macrocycle plane mostly parallel with the underlying surface and a single adsorption configuration. However, a small distortion of the isoindole groups, with respect to one another, is required to rationalise the results. The TiOPc results similarly indicate that the macrocycle plane is mostly parallel with the underlying surface up to thick multilayer films, yet, in the monolayer regime, the molecule must adsorb in multiple configurations. These configurations are nominally assigned to a mixture of adsorption configurations with some Ti=O bonds pointing towards the surface, and some pointing away. We determine that, in both configurations, the Ti metal centre sits at a similar adsorption height above the surface of 3.00 ± 0.20 Å.
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Jul 2023
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Yi-Ling
Chen
,
Jessica Soo Weei
Ng
,
Rosana
Ottakandathil Babu
,
Jeongmin
Woo
,
Janina
Nahler
,
Clare S.
Hardman
,
Prathiba
Kurupati
,
Lea
Nussbaum
,
Fei
Gao
,
Tao
Dong
,
Kristin
Ladell
,
David A.
Price
,
David A.
Duncan
,
David
Johnson
,
Uzi
Gileadi
,
Hashem
Koohy
,
Graham S.
Ogg
Abstract: Group A Streptococcus (GAS) infection is associated with multiple clinical sequelae, including different subtypes of psoriasis. Such post-streptococcal disorders have been long known but are largely unexplained. CD1a is expressed at constitutively high levels by Langerhans cells and presents lipid antigens to T cells, but the potential relevance to GAS infection has not been studied. Here, we investigated whether GAS-responsive CD1a-restricted T cells contribute to the pathogenesis of psoriasis. Healthy individuals had high frequencies of circulating and cutaneous GAS-responsive CD4+ and CD8+ T cells with rapid effector functions, including the production of interleukin-22 (IL-22). Human skin and blood single-cell CITE-seq analyses of IL-22–producing T cells showed a type 17 signature with proliferative potential, whereas IFN-γ–producing T cells displayed cytotoxic T lymphocyte characteristics. Furthermore, individuals with psoriasis had significantly higher frequencies of circulating GAS-reactive T cells, enriched for markers of activation, cytolytic potential, and tissue association. In addition to responding to GAS, subsets of expanded GAS-reactive T cell clones/lines were found to be autoreactive, which included the recognition of the self-lipid antigen lysophosphatidylcholine. CD8+ T cell clones/lines produced cytolytic mediators and lysed infected CD1a-expressing cells. Furthermore, we established cutaneous models of GAS infection in a humanized CD1a transgenic mouse model and identified enhanced and prolonged local and systemic inflammation, with resolution through a psoriasis-like phenotype. Together, these findings link GAS infection to the CD1a pathway and show that GAS infection promotes the proliferation and activation of CD1a-autoreactive T cells, with relevance to post-streptococcal disease, including the pathogenesis and treatment of psoriasis.
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Jun 2023
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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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