I05-ARPES
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Diamond Proposal Number(s):
[37658, 36215, 39549]
Open Access
Abstract: We report the electronic structure of monolayer CrSBr exfoliated onto mica template-stripped gold substrates. Angle-resolved photoemission spectroscopy reveals charge transfer from the substrate, populating the conduction band of monolayer CrSBr, accompanied by a pronounced reduction in the quasiparticle band gap. Furthermore, we observe two separate conduction bands that exhibit a splitting at the X point. This indicates a breaking of glide-mirror symmetry, which in the bulk or in a free-standing monolayer protects the band degeneracies at the Brillouin zone boundary. Our results demonstrate that ultraflat gold substrates do more than modify carrier densities and screening: they can lift symmetry-protected degeneracies and thus fundamentally reshape the band topology of 2D materials.
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Jan 2026
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E02-JEM ARM 300CF
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Evan David Innes
Tillotson
,
William
Thornley
,
William
Talbott
,
Alexander S.
Eggeman
,
Daria
Kriuchkova
,
Sam
Sullivan-Allsop
,
Matthew
Smith
,
Xuzhao
Liu
,
Ashley
Slattery
,
Pei Lay
Yap
,
Dusan
Losic
,
Zhun
Xu
,
Huan
Wang
,
Jim
Ciston
,
Alexander
Rakowski
,
Stephanie M.
Ribet
,
Benjamin H
Savitzky
,
Manfred Erwin
Schuster
,
Christopher S.
Allen
,
Danielle
Douglas-Henry
,
Valeria
Nicolosi
,
Andrew
Herzing
,
Jacques
O'Connell
,
Ezra J.
Olivier
,
Jan
Neethling
,
Yichao
Zou
,
Ercin Cagan
Duran
,
Rongsheng
Cai
,
Duc-The
Ngo
,
Roman
Gorbachev
,
Jonas
Haas
,
Michael
Schlegel
,
Jannik C.
Meyer
,
Alba
Centeno
,
Amaia
Pesquera
,
Amaia
Zurutuza
,
Sungsu
Kang
,
Jungwon
Park
,
Ivan
Erofeev
,
Utkur
Mirsaidov
,
Colin
Ophus
,
Christian
Rentenberger
,
Thomas
Waitz
,
Jani
Kotakoski
,
Abhijit
Roy
,
Raul
Arenal
,
Andrew
Pollard
,
Sarah
Haigh
Diamond Proposal Number(s):
[29951]
Open Access
Abstract: Standardisation of data collection and analysis is essential to enable commercialisation of 2D materials in a wide range of technologies. Selected area electron diffraction (SAED) in the transmission electron microscope (TEM) is one of the key methods for distinguishing monolayer from bilayer and few-layer graphene by comparing the 1st and 2nd order diffraction spot intensities. Yet there are many factors that can affect the reliability of data collection and interpretation, causing the measurement of monolayer samples to deviate from the literature boundary condition of I{-2110}/I{1-100}<1 for monolayer graphene. Here we present the results of a large interlaboratory SAED comparison study, where 15 international laboratories measured and analysed nominally identical samples of chemical vapour deposited (CVD) graphene. Large variations were observed in the measured ratios of diffraction spot intensities, with the largest variance associated with poor quality SAED data resulting from poor specimen handling and storage. To inform the reliable determination of monolayer thickness from SAED patterns we provide a description of best practice for specimen handling, TEM operation, data collection and analysis. This work was undertaken within VAMAS Technical Working Area (TWA) 41: Graphene and related 2D materials - Project 9, the results of which have been directly incorporated into ISO/TS 21356-2 for the characterisation of graphene sheets. We find that when this methodology is followed, monolayer graphene can be distinguished from bilayer or thicker material with high confidence where analysis of a single SAED pattern gives I{-2110}/I{1-100}<1.2, even in the absence of precise specimen tilting.
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Dec 2025
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I05-ARPES
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Diamond Proposal Number(s):
[34479, 33317, 35210]
Open Access
Abstract: Understanding the interface between metals and two-dimensional materials is critical for their application in electronics and for the development of metal-mediated exfoliation of large area monolayers. Studying the intricate interactions at the interface requires model systems that enable control of the roughness, purity, and crystallinity of the metal surface. Here, we use angle-resolved photoemission spectroscopy to investigate the layer-dependent electronic structure of WSe\textsubscript{2}~on template-stripped gold substrates fabricated using both silicon and mica templates, giving crystallographically disordered and Au(111) ordered surfaces, respectively, and contrast these findings with \textit{ab initio} predictions. We observe strong hybridization around the Brillouin zone centre at $\overline{\Gamma}$, indicating a covalent admixture in the gold-WSe\textsubscript{2}~interaction, and band shifts that suggest charge rearrangement at the Au(111) / WSe\textsubscript{2}~interface. Core-level spectroscopy shows a single chemical environment for the interfacial WSe\textsubscript{2}~layer on the template-stripped gold, distinct from the subsequent layers. These results reveal a mixture of van der Waals and covalent interactions, best described as a covalent-like quasi-bonding with intermediate interaction strength.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36085]
Open Access
Abstract: For establishing a fundamental understanding of the emerging properties of two-dimensional (2D) materials, a reliable determination of the crystallographic structure is essential, as we demonstrate in this work for the specific case of the quantum spin Hall insulator bismuthene. Diffraction-based methods are widely used for structure determination, however, they suffer from a fundamental shortcoming, the phase retrieval problem, that is the inability to directly measure the phase of scattered waves. The (normal incidence) X-ray standing wave (NIXSW) technique circumvents this problem by introducing a Bragg-generated X-ray standing wave field throughout the sample, relative to which any atomic species can be localized. In essence, a single NIXSW measurement captures the complex scattering factor (amplitude and phase) corresponding to one single Bragg reflection. Collecting data for multiple reflections enables a three-dimensional reconstruction of the scattering density as the Fourier sum of all measured scattering factors. Here, we utilize this technique to reveal the mechanism of a reversible switching process that has been reported for a 2D Bi layer recently (Tilgner et al., Nat. Commun. 16, 6171, 2025). In this prominent example, the Bi layer is confined between a 4H-SiC substrate and an epitaxial graphene layer, and can be reversibly switched between an electronically inactive precursor state and the bismuthene state. In our NIXSW imaging experiment, we clearly identify the change of the adsorption site of the Bi atoms, caused by H-saturation of one out of three Si dangling bonds per unit cell, as the key feature leading to the formation of the characteristic band structure of the 2D bismuthene honeycomb.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30105, 33391, 38086]
Open Access
Abstract: The clean and reliable transfer of two-dimensional (2D) materials is critical for preserving their intrinsic properties and enabling high-performance device applications. This study presents a method utilizing UV-ozone treated polydimethylsiloxane (UV-PDMS) as a transfer medium to achieve residue-free 2D materials. The UV-PDMS transfer method increases surface rigidity, reduces surface polymeric residues, and ensures intimate contact between 2D materials and target substrates. This is translated into cleaner samples as confirmed by atomic force microscopy (AFM), photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Field-effect transistors (FETs) based on monolayer MoS2 fabricated with UV-PDMS transferred method exhibit lower subthreshold swing, reduced hysteresis, and higher carrier mobility compared to devices fabricated with PDMS transfer. Additionally, vertical solar cells based on multilayer WSe2 prepared with UV-PDMS method demonstrate enhanced fill factor and power conversion efficiency.
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Sep 2025
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I05-ARPES
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Liam
Trzaska
,
Lei
Qiao
,
Matthew D.
Watson
,
Monica
Ciomaga Hatnean
,
Igor
Markovic
,
Edgar
Abarca Morales
,
Tommaso
Antonelli
,
Cephise
Cacho
,
Geetha
Balakrishnan
,
Wei
Ren
,
Silvia
Picozzi
,
Phil D. C.
King
Diamond Proposal Number(s):
[21986, 25564]
Open Access
Abstract: The recent discovery of the persistence of long-range magnetic order when van der Waals magnets are thinned towards monolayers provides a tunable platform for engineering of novel magnetic structures and devices. Here, we study the evolution of the electronic structure of CrGeTe3 as a function of surface electron doping. From angle-resolved photoemission, we observe spectroscopic fingerprints that this electron doping drives a marked increase in TC, reaching values more than double that of the undoped material, in agreement with recent studies using electrostatic gating. Together with density functional theory calculations and Monte Carlo simulations, we show that, surprisingly, the increased TC is mediated by the population of spin-minority Cr t2g states, forming a half-metallic 2D electron gas. This promotes a novel variant of double exchange, and unlocks a significant influence of Ge – which was previously thought to be electronically inert in this system – in mediating Cr-Cr exchange.
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Jan 2025
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NONE-No attached Diamond beamline
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Emily
Heppell
,
Ryuji
Fujita
,
Gautam
Gurung
,
Jheng-Cyuan
Lin
,
Andrew
May
,
Michael
Foerster
,
M. Waqas
Khaliq
,
Miguel Angel
Niño
,
Manuel
Valvidares
,
Javier
Herrero-Martin
,
Pierluigi
Gargiani
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Dirk
Backes
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Open Access
Abstract: The exploration of two-dimensional (2D) van der Waals ferromagnets has revealed intriguing magnetic properties with significant potential for spintronics applications. In this study, we examine the magnetic properties of Co-doped Fe5GeTe2 using X-ray photoemission electron microscopy (XPEEM) and X-ray magnetic circular dichroism (XMCD), complemented by density functional theory (DFT) calculations. Our XPEEM measurements reveal that the Curie temperature (TC) of a bilayer of (CoxFe1-x)5-δGeTe2 (with x = 0.28) reaches ∼300 K — a notable enhancement over most 2D ferromagnets in the ultrathin limit. Interestingly, the TC shows only a small dependence on film thickness (bulk TC ≈ 340 K), in line with the observed in-plane magnetic anisotropy and robust in-plane exchange coupling. XMCD measurements indicate that the spin moments for both Fe and Co are significantly reduced compared to the theoretical values. These insights highlight the potential of Co-doped Fe5GeTe2 for stable, high-temperature ferromagnetic applications in 2D materials.
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Dec 2024
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I05-ARPES
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Diamond Proposal Number(s):
[33317, 34489]
Open Access
Abstract: We present the evolution of the electronic structure of CrSBr from its antiferromagnetic ground state to the paramagnetic phase above TN = 132 K, in both experiment and theory. Low-temperature angle-resolved photoemission spectroscopy (ARPES) results are obtained using a novel method to overcome sample charging issues, revealing quasi-2D valence bands in the ground state. The results are very well reproduced by our calculations, which further identify certain bands at the X points to be exchange-split pairs of states with mainly Br and S character. By tracing band positions as a function of temperature, we show the splitting disappears above TN. The energy splitting is interpreted as an effective exchange splitting in individual layers in which the Cr moments all align, within the so-called A-type antiferromagnetic arrangement. Our results lay firm foundations for the interpretation of the many other intriguing physical and optical properties of CrSBr.
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Aug 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[24816]
Open Access
Abstract: Chemical exfoliation is an attractive approach for the synthesis of graphene due to low cost and simplicity. However, challenges still remain in the characterization of solution-processed graphene, in particular with atomic resolution. Through this work we demonstrate the X-ray pair distribution function as a novel approach to study the solution-processed graphene or other 2D materials with atomic resolution, directly in solution, produced by liquid-phase and electrochemical exfoliations. The results show the disappearance of long-range atomic correlations, in both cases, confirming the production of single and few-layer graphene. In addition, a considerable ring distortion has been observed as compared to graphite, irrespective of the solvent used: the normal surface angle to the sheet of the powder sample should be less than 6o, compatible with ripples formation observed in suspended graphene. We attribute this effect to the interaction of solvent molecules with the graphene nanosheets.
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Oct 2022
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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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