I09-Surface and Interface Structural Analysis
|
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.
|
Aug 2022
|
|
I07-Surface & interface diffraction
I09-Surface and Interface Structural Analysis
|
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.
|
Apr 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[17261, 20785]
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.
|
Mar 2022
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Jan 2022
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Dec 2021
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Nov 2021
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
May 2021
|
|
I09-Surface and Interface Structural Analysis
|
Peter
Knecht
,
Bodong
Zhang
,
Joachim
Reichert
,
David A.
Duncan
,
Martin
Schwarz
,
Felix
Haag
,
Paul
Ryan
,
Tien-Lin
Lee
,
Peter S.
Deimel
,
Peter
Feulner
,
Francesco
Allegretti
,
Willi
Auwärter
,
Guillaume
Médard
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Anthoula C.
Papageorgiou
Diamond Proposal Number(s):
[24320]
Abstract: The controlled arrangement of N-heterocyclic carbenes (NHCs) on solid surfaces is a current challenge of surface functionalization. We introduce a strategy of using Ru porphyrins in order to control both the orientation and lateral arrangement of NHCs on a planar surface. The coupling of the NHC to the Ru porphyrin is a facile process which takes place on the interface: we apply NHCs as functional, robust pillars on well-defined, preassembled Ru porphyrin monolayers on silver and characterize these interfaces with atomic precision via a battery of experimental techniques and theoretical considerations. The NHCs assemble at room temperature modularly and reversibly on the Ru porphyrin arrays. We demonstrate a selective and complete functionalization of the Ru centers. With its binding, the NHC modifies the interaction of the Ru porphyrin with the Ag surface, displacing the Ru atom by 1 Å away from the surface. This arrangement of NHCs allows us to address individual ligands by controlled manipulation with the tip of a scanning tunneling microscope, creating patterned structures on the nanometer scale.
|
Mar 2021
|
|
|
|
Open Access
Abstract: The adsorption configurations of a technologically relevant model organic adsorbate on the silicon (001) surface were studied using energy scanned X-ray photoelectron diffraction (PhD). Previous work has established the existence of an interesting vertically-aligned ("flagpole") configuration, where the acetophenone attaches to Si(001) via the acetyl group carbon and oxygen atoms. DFT calculations have predicted two energetically similar variants of this structure, where the phenyl ring is orientated parallel or perpendicular to the rows of silicon dimers on this reconstructed surface. However, previously published experimental measurements, including scanning tunnelling microscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure investigations were unable to distinguish between these two configurations. Here, we apply the unique experimental capabilities of the PhD technique to this system and demonstrate that the dominant adsorption configuration has the phenyl ring parallel to the dimer rows (the end-bridge structure). This information in turn facilitates the determination of the dominant reaction pathway for acetophenone on Si(001), which has remained elusive until now. Information about subtle preferences in reaction pathways that affect the alignment and orientation of organic adsorbates such as acetophenone on technologically-relevant semiconductor surfaces such as Si(001) is critical for the fabrication of future atomically-precise atomic and molecular-scale electronic devices utilising the organic-silicon interface, and this work demonstrates the unique and complementary capabilities of PhD for providing this information.
|
Feb 2021
|
|
I09-Surface and Interface Structural Analysis
|
Peter
Knecht
,
Paul T. P.
Ryan
,
David A.
Duncan
,
Li
Jiang
,
Joachim
Reichert
,
Peter S.
Deimel
,
Felix
Haag
,
Johannes T.
Kuchle
,
Francesco
Allegretti
,
Tien-Lin
Lee
,
Martin
Schwarz
,
Manuela
Garnica
,
Willi
Auwärter
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Anthoula C.
Papageorgiou
Diamond Proposal Number(s):
[24320, 17634]
Abstract: The adsorption and monolayer self-assembly of functional metal–organic blocks on solid surfaces are critical for the physicochemical properties of these low-dimensional materials. Although modern microscopy tools are very sensitive to the lateral arrangement of such blocks, they are still unable to offer directly the complete structural analysis especially for nonplanar molecules containing different atoms. Here, we apply a combinatorial approach for the characterization of such interfaces, which enables unexpected insights. An archetypal metalloporphyrin on a catalytically active surface as a function of its molecular coverage and substituent arrangement is characterized by low-energy electron diffraction, scanning probe microscopy, X-ray photoelectron spectroscopy, normal-incidence X-ray standing waves, and density functional theory. We look into Ru tetraphenyl porphyrin (Ru-TPP) on Ag(111), which is also converted into its planarized derivates via surface-assisted cyclodehydrogenation reactions. Depending on the arrangement of the phenyl substituents, the Ru atoms have distinct electronic structures and the porphyrin macrocycles adapt differently to the surface: saddle shape (pristine Ru-TPP) or bowl shape (planarized Ru-TPP derivates). In all cases, the Ru atom resides close to the surface (2.59/2.45 Å), preferably located at hollow sites and in the interface between the plane of the porphyrin macrocycle and the Ag surface. For the more flexible pristine Ru-TPP, we identify an additional self-assembled structure, allowing the molecular density of the self-assembled monolayer to be tuned within ∼20%. This precise analysis is central to harnessing the potential of metalloporphyrin/metal interfaces in functional systems.
|
Jan 2021
|
|
