|
|
Open Access
Abstract: Combined density functional theory (DFT) and X-ray standing wave (XSW) studies have previously provided evidence for the preferential adoption of an inverted conformation of 2H-TPP on Cu(111) in contrast to the saddle conformation usually favored by porphyrin molecules adsorbed on metals. We experimentally demonstrate, via X-ray photoelectron spectroscopy (XPS) analysis, that the binding energies of the aminic and iminic nitrogen species provide a spectral fingerprint for both inverted and saddle conformations, as predicted by DFT studies. Our complementary scanning tunneling microscopy (STM) characterization also reveals conversion from the saddle to inverted conformation at an elevated temperature for an analogous porphyrin species (Br2TPP).
|
May 2025
|
|
I06-Nanoscience (XPEEM)
I09-Surface and Interface Structural Analysis
|
Yiru
Zhu
,
Zhepeng
Zhang
,
Ye
Wang
,
Soumya
Sarkar
,
Yang
Li
,
Han
Yan
,
Larissa
Ishibe-Veiga
,
Anita
Bagri
,
Ziwei J.
Yang
,
Hugh
Ramsden
,
Goki
Eda
,
Robert L. Z.
Hoye
,
Yan
Wang
,
Manish
Chhowalla
Diamond Proposal Number(s):
[36685, 33391]
Open Access
Abstract: Chalcogen vacancy defects in monolayer transition metal dichalcogenides form in-gap states that can trap excitons, leading to defect-mediated photoluminescence (PL) emission. Here, we show that room-temperature (RT, 300 K) PL from sulfur vacancies in defective monolayer MoS2 is sensitive to doping from dielectric substrates such as SiO2 and HfO2. The defect-mediated PL is observed for monolayer MoS2 on untreated HfO2 but is quenched on untreated SiO2, which is attributed to electron doping of MoS2 on SiO2. Electron doping of MoS2 is confirmed by Raman and synchrotron X-ray photoelectron spectroscopy. Annealing of the SiO2 substrate modifies its surface states, which is reflected in the recovery of the defect-mediated PL emission. The role of substrate-induced doping on sulfur vacancy-mediated PL is further supported by gate-dependent PL measurements. Our results suggest that excess electrons fill the defect energy states from sulfur vacancies in MoS2, reducing the probability of photoexcited carrier occupation and subsequent defect-mediated emission.
|
Apr 2025
|
|
I09-Surface and Interface Structural Analysis
|
Jake M.
Seymour
,
Ekaterina
Gousseva
,
Lewis G.
Parker
,
Frances K.
Towers Tompkins
,
Richard M.
Fogarty
,
Lennart
Frankemoelle
,
Rebecca
Rowe
,
Coby J.
Clarke
,
David A.
Duncan
,
Robert G.
Palgrave
,
Roger A.
Bennett
,
Patricia A.
Hunt
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[20463]
Open Access
Abstract: Liquid-phase d10s2 post-transition metal anions, such as [SnCl3]−, appear in a range of applications with a focus on catalysis and material preparation. However, little is known about their electronic structure and how it relates to reactivity. Using X-ray photoelectron spectroscopy and ab initio calculations, we demonstrate that liquid-phase d10s2 post-transition metal anions can act as dual-mode Lewis bases, interacting through the metal center and/or the ligands, with the interaction mode depending on the identity of the Lewis acid/electron acceptor. The Lewis basicity of the metal donor atom is controlled mainly by the metal identity; the ligand can be used for fine-tuning. Changing the metal center has a strong effect on the ligand basicity. These findings provide insight into d10s2 post-transition metal anion electronic structure, which will enable better molecular-level design of catalytic systems.
|
Mar 2025
|
|
I15-1-X-ray Pair Distribution Function (XPDF)
|
Diamond Proposal Number(s):
[34748]
Abstract: We present a structural characterization of a low-transition-temperature mixture (LTTM), consisting of thymol and carvacrol, at an equimolar ratio. Carvacrol and thymol are natural regioisomers of terpenes. When combined at an equimolar ratio, they form a liquid mixture at room temperature, with supercooling capability and glass transition at ca. 210 K. Using small- and wide-angle X-ray scattering and molecular dynamics, we describe the structural complexity within this system. X-ray scattering reveals a low-Q peak at around 0.6 Å–1, indicating the existence of mesoscale structural heterogeneities, likely related to the segregation of polar moieties engaged in hydrogen bond (HB) interactions within an aromatic, apolar matrix. These polar interactions are predominantly a result of HBs involving thymol as the HB donor species. The liquid structure is also driven by O–H···π interactions, prevalently due to the ability of the carvacrol π-site to engage in this type of weak interaction as a HB acceptor. Besides, dispersive interactions affect the local arrangement of molecules, with a propensity of carvacrol rings to orient their first neighbors with a perpendicular orientation, while thymol tends to induce a closer approach of other thymol molecules with a preferential parallel alignment. Overall, we observed a complex structural arrangement driven by the interplay of both conventional and weak hydrogen bond interactions, with the aromatic nature of the compounds playing a pivotal role in shaping the system’s architecture. Carvacrol and thymol, despite being very similar compounds, are characterized by distinctly different behavior in terms of the interactions they engage in with their neighbors, likely due to the different steric hindrance experienced by their hydroxyl groups, which are close to either a small methyl or a bulky isopropyl group, respectively. Such observations can provide useful hints to develop new solvents with tailored properties.
|
Mar 2025
|
|
I11-High Resolution Powder Diffraction
|
Rachael
Hamp
,
Christoph G.
Salzmann
,
Zachary
Amato
,
Milz L.
Beaumont
,
Hannah E.
Chinnery
,
Peter
Fawdon
,
Thomas F.
Headen
,
Paul F.
Henry
,
Liam
Perera
,
Stephen P.
Thompson
,
Mark G.
Fox-Powell
Diamond Proposal Number(s):
[36314]
Open Access
Abstract: Sodium chloride (NaCl) plays an important role in geochemistry, biology, industry, and food production, and it is among the most common salts in the solar system. Here, we report the discovery of a metastable NaCl dihydrate formed through rapid freezing (101–102 K s–1) of a NaCl solution at ambient pressure. Using synchrotron X-ray and neutron powder diffraction, we show that it transforms irreversibly to hydrohalite and ice Ih above 190 K upon heating and propose it is structurally related to hydrohalite with a 3 × 1 × 3 supercell as its unit cell. Calorimetric analyses reveal that the new hydrate transforms to hydrohalite with a heat release of −3.47 ± 0.55 kJ mol–1. The identification of this new NaCl dihydrate on the surfaces of icy worlds such as the moons of Jupiter and Saturn could indicate regions of recent activity where subsurface brines have frozen rapidly, priority targets for upcoming planetary missions.
|
Dec 2024
|
|
I09-Surface and Interface Structural Analysis
|
Dennis
Meier
,
Peter
Knecht
,
Pablo
Vezzoni Vicente
,
Fulden
Eratam
,
Hongxiang
Xu
,
Tien-Lin
Lee
,
Alexander
Generalov
,
Alexander
Riss
,
Biao
Yang
,
Francesco
Allegretti
,
Peter
Feulner
,
Joachim
Reichert
,
Johannes V.
Barth
,
Ari Paavo
Seitsonen
,
David A.
Duncan
,
Anthoula C.
Papageorgiou
Diamond Proposal Number(s):
[30095]
Open Access
Abstract: Metalloporphyrins on interfaces offer a rich playground for functional materials and hence have been subjected to intense scrutiny over the past decades. As the same porphyrin macrocycle on the same surface may exhibit vastly different physicochemical properties depending on the metal center and its substituents, it is vital to have a thorough structural and chemical characterization of such systems. Here, we explore the distinctions arising from coverage and macrocycle substituents on the closely related ruthenium octaethyl porphyrin and ruthenium tetrabenzo porphyrin on Ag(111). Our investigation employs a multitechnique approach in ultrahigh vacuum, combining scanning tunneling microscopy, low-energy electron diffraction, photoelectron spectroscopy, normal incidence X-ray standing wave, and near-edge X-ray absorption fine structure, supported by density functional theory. This methodology allows for a thorough examination of the nuanced differences in the self-assembly, substrate modification, molecular conformation and adsorption height.
|
Dec 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[26045]
Open Access
Abstract: Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was employed to investigate the effect of applied potential on the interface of TiO2(110) with 0.1 M HCl. The study, which involved operando electrochemical characterization, enabled real-time monitoring and analysis of electrochemical processes. There is a significant influence on the interface composition; in particular, the surface Cl– surface coverage varies with electrochemical potential. Moreover, there appears to be a reaction of evolved Cl with adventitious carbon to form C–Cl and C–Cl2 species.
|
Nov 2024
|
|
|
|
Xiao
Wang
,
Jie
Zhang
,
Zhao
Pan
,
Dabiao
Lu
,
Maocai
Pi
,
Xubin
Ye
,
Cheng
Dong
,
Jie
Chen
,
Kai
Chen
,
Florin
Radu
,
Sonia
Francoual
,
Stefano
Agrestini
,
Zhiwei
Hu
,
Chun-Fu
Chang
,
Arata
Tanaka
,
Kazunari
Yamaura
,
Yao
Shen
,
Youwen
Long
Abstract: By means of X-ray absorption spectroscopic studies, both experimentally and theoretically, we investigated the magnetic properties of the transition-metal-only double perovskite oxide Mn2CoReO6, which experiences an antiferromagnetic transition at TN = 93 K, whereas it holds a considerable net moment at low temperature. Internal exchange fields against the applied magnetic field for all the transition metal ions were identified, providing a microscopic insight into the intrasite antiferromagnetic couplings. Nevertheless, parallelly oriented canted spins of the Mn, Co, and Re cations were observed. In particularly, the Mn and Co cations hold considerable canting moments, which can be ascribed to the competition between the ferromagnetic intersite and antiferromagnetic intrasite magnetic interactions. Moreover, a spin-valve-type magnetoresistance was observed below the TN. The concurrence of the magnetoresistance effect and the antiferromagnetic semiconductive nature make Mn2CoReO6 a promising candidate for high-speed and energy-saving spintronics applications.
|
Sep 2024
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Sep 2024
|
|
B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
|
F.
Bassato
,
S.
Mauri
,
L.
Braglia
,
A. Yu.
Petrov
,
E.
Dobovičnik
,
F.
Tavani
,
A.
Tofoni
,
P.
Ferrer
,
D.
Grinter
,
G.
Held
,
P.
D'Angelo
,
P.
Torelli
Diamond Proposal Number(s):
[33111]
Abstract: A-site doped SrTiO3 is considered as a promising substitute for traditional anodic metals in solid oxide fuel cells (SOFCs). In this study, we present the reactivity of La0.2Sr0.25Ca0.45TiO3 (LCSTO), La0.2Sr0.7TiO3 (LSTO), and SrTiO3 (STO) toward H2 by operando ambient pressure NEXAFS spectroscopy and theoretical spectra simulation with FDMNES code. The samples were synthesized by MBE (molecular beam epitaxy), hydrothermal, and modified-Pechini routes. We found that the reducibility of the samples depends not only on their stoichiometry but also on the morphology, which is determined by the synthetic method. The results of these experiments give insight into the reducibility of Ti4+ in perovskites as well as the opportunity to further optimize the synthesis of these materials to obtain the best performance for SOFC applications.
|
Aug 2024
|
|
