PGMweb: an online tool for visualizing the X-ray beam path through plane grating monochromators.

We present here a newly developed software tool (called PGMweb) for computing and simulating the X-ray beam path through a plane grating monochromator (PGM), a key component in soft X-ray beamlines at modern synchrotron and free-electron laser facilities. A historical overview of the development of PGMs is presented, with special attention dedicated to the collimated PGM optical scheme found at several X-ray facilities worldwide. The analytical expressions that fully describe the geometry of a PGM are derived and have been implemented as functions in a Python library (pyplanemono).

Boron-induced transformation of ultrathin Au films into two-dimensional metallic nanostructures.

The synthesis of large, freestanding, single-atom-thick two-dimensional (2D) metallic materials remains challenging due to the isotropic nature of metallic bonding. Here, we present a bottom-up approach for fabricating macroscopically large, nearly freestanding 2D gold (Au) monolayers, consisting of nanostructured patches. By forming Au monolayers on an Ir(111) substrate and embedding boron (B) atoms at the Au/Ir interface, we achieve suspended monoatomic Au sheets with hexagonal structures and triangular nanoscale patterns.

Surface polarization profile of ferroelectric thin films probed by X-ray standing waves and photoelectron spectroscopy.

Understanding the mechanisms underlying a stable polarization at the surface of ferroelectric thin films is of particular importance both from a fundamental point of view and to achieve control of the surface polarization itself. In this study, we demonstrate that the X-ray standing wave technique allows the surface polarization profile of a ferroelectric thin film, as opposed to the average film polarity, to be probed directly. The X-ray standing wave technique provides the average Ti and Ba atomic positions, along the out-of-plane direction, near the surface of three differently strained [Formula: see text] thin films.

Structure of Graphene Grown on Cu(111): X-Ray Standing Wave Measurement and Density Functional Theory Prediction.

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.

Probing the role of surface termination in the adsorption of azupyrene on copper.

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.

Achieving environmental stability in an atomically thin quantum spin Hall insulator via graphene intercalation.

Atomic monolayers on semiconductor surfaces represent an emerging class of functional quantum materials in the two-dimensional limit - ranging from superconductors and Mott insulators to ferroelectrics and quantum spin Hall insulators. Indenene, a triangular monolayer of indium with a gap of ~ 120 meV is a quantum spin Hall insulator whose micron-scale epitaxial growth on SiC(0001) makes it technologically relevant. However, its suitability for room-temperature spintronics is challenged by the instability of its topological character in air.

Combined Electrochemical, XPS, and STXM Study of Lithium Nitride as a Protective Coating for Lithium Metal and Lithium-Sulfur Batteries.

LiN is an excellent protective coating material for lithium electrodes with very high lithium-ion conductivity and low electronic conductivity, but the formation of stable and homogeneous coatings is technically very difficult. Here, we show that protective LiN coatings can be simply formed by the direct reaction of electrodeposited lithium electrodes with N gas, whereas using battery-grade lithium foil is problematic due to the presence of a native passivation layer that hampers that reaction. The protective LiN coating is effective at preventing lithium dendrite formation, as found from unidirectional plating and plating-stripping measurements in Li-Li cells.

Detailed Analysis of the Synthesis and Structure of MAX Phase (MoV)AlC and Its MXene Sibling (MoV)C.

MAX phases with the general formula are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of octahedra and the element depending on . While "211" MAXphases ( = 1) are very common, MAX phases with higher , especially ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the "514" MAX phase.

Emergent and robust ferromagnetic-insulating state in highly strained ferroelastic LaCoO thin films.

Transition metal oxides are promising candidates for the next generation of spintronic devices due to their fascinating properties that can be effectively engineered by strain, defects, and microstructure. An excellent example can be found in ferroelastic LaCoO with paramagnetism in bulk. In contrast, unexpected ferromagnetism is observed in tensile-strained LaCoO films, however, its origin remains controversial.

Band Alignments, Electronic Structure, and Core-Level Spectra of Bulk Molybdenum Dichalcogenides (MoS, MoSe, and MoTe).

A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS, MoSe, and MoTe are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX series as 5.

Computational Prediction and Experimental Realization of Earth-Abundant Transparent Conducting Oxide Ga-Doped ZnSbO.

Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the number of oxides that are transparent to visible light and have the metallic-like conductivity necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid density functional theory and defect chemistry analysis to demonstrate that tri-rutile zinc antimonate, ZnSbO, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high conductivity and transparency.

N-Heterocyclic Carbenes: Molecular Porters of Surface Mounted Ru-Porphyrins.

Ru-porphyrins act as convenient pedestals for the assembly of N-heterocyclic carbenes (NHCs) on solid surfaces. Upon deposition of a simple NHC ligand on a close packed Ru-porphyrin monolayer, an extraordinary phenomenon can be observed: Ru-porphyrin molecules are transferred from the silver surface to the next molecular layer. We have investigated the structural features and dynamics of this portering process and analysed the associated binding strengths and work function changes.

Complex Magnetic Order in Topochemically Reduced Rh(I)/Rh(III) LaMRhO (M = Co, Ni) Phases.

Topochemical reduction of the cation-disordered perovskite oxides LaCoRhO and LaNiRhO with Zr yields the partially anion-vacancy ordered phases LaCoRhO and LaNiRhO, respectively. Neutron diffraction and Hard X-ray photoelectron spectroscopy (HAXPES) measurements reveal that the anion-deficient phases contain Co/Ni and a 1:1 mixture of Rh and Rh cations within a disordered array of apex-linked MO square-planar and MO square-based pyramidal coordination sites. Neutron diffraction data indicate that LaCoRhO adopts a complex antiferromagnetic ground state, which is the sum of a C-type ordering (mM) of the -components of the Co spins and a G-type ordering (mΓ) of the -components of the Co spins.

Tackling Disorder in γ-Ga O.

Ga O and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga O offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga O presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure-electronic-structure relationship.

GeSe photovoltaics: doping, interfacial layer and devices.

Germanium selenide (GeSe) bulk crystals, thin films and solar cells are investigated with a focus on acceptor-doping with silver (Ag) and the use of an SbSe interfacial layer. The Ag-doping of GeSe occurred by a stoichiometric melt growth technique that created Ag-doped GeSe bulk crystals. A combination of capacitance voltage measurements, synchrotron radiation photoemission spectroscopy and surface space-charge calculations indicates that Ag-doping increases the hole density from 5.

Atomic-Site-Specific Surface Valence-Band Structure from X-Ray Standing-Wave Excited Photoemission.

X-ray standing-wave (XSW) excited photoelectron emission was used to measure the site-specific valence band (VB) for ½ monolayer (ML) Pt grown on a SrTiO_{3} (001) surface. The XSW induced modulations in the core level (CL), and VB photoemission from the surface and substrate atoms were monitored for three hkl substrate Bragg reflections. The XSW CL analysis shows the Pt to have a face-centered-cubic-like cube-on-cube epitaxy with the substrate.

Epitaxial SrTiO films with dielectric constants exceeding 25,000.

SignificanceSemiconductor interfaces are among the most important in use in modern technology. The properties they exhibit can either enable or disable the characteristics of the materials they connect for functional performance. While much is known about important junctions involving conventional semiconductors such as Si and GaAs, there are several unsolved mysteries surrounding interfaces between oxide semiconductors.

Cycle-Induced Interfacial Degradation and Transition-Metal Cross-Over in LiNiMnCoO-Graphite Cells.

Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNiMnCoO-graphite full cells over hundreds of cycles between fixed cell voltages (2.

Gently does it!: preparation of alkali metal-solid electrolyte interfaces for photoelectron spectroscopy.

The key charge transfer processes in electrochemical energy storage devices occur at electrode-electrolyte interfaces, which are typically buried, making it challenging to access their interfacial chemistry. In the case of Li-ion batteries, metallic Li electrodes hold promise for increasing energy and power densities and, when used in conjunction with solid electrolytes, the adverse safety implications associated with dendrite formation in organic liquid electrolytes can potentially be overcome. To better understand the stability of solid electrolytes when in contact with alkali metals and the reactions that occur, here we consider the deposition of thin (∼10 nm) alkali metal films onto solid electrolyte surfaces, where the metal is thin enough that X-ray photoelectron spectroscopy can probe the buried electrode-electrolyte interface.

Direct Experimental Evidence for Substrate Adatom Incorporation into a Molecular Overlayer.

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)-FTCNQ 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.

Thermodynamic Driving Forces for Substrate Atom Extraction by Adsorption of Strong Electron Acceptor Molecules.

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 FTCNQ 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.

Evidence of magnetism-induced topological protection in the axion insulator candidate EuSnP.

We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSnP, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSnP as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.