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Suspended graphene flakes are exposed simultaneously to fluorine and sulfur ions produced by the μ-wave plasma discharge of the SF 6 precursor gas. The microscopic and spectroscopic analyses, performed by Raman spectroscopy, scanning electron microscopy and photoelectron spectromicroscopy, show the homogeneity in functionalization yield over the graphene flakes with F and S atoms covalently bonded to the carbon lattice. This promising surface shows potential for several applications ranging from biomolecule immobilization to lithium battery and hydrogen storage devices. The present co-doping process is an optimal strategy to engineer the graphene surface with a concurrent hydrophobic character, thanks to the fluorine atoms, and a high affinity with metal nanoparticles due to the presence of sulfur atoms. [ABSTRACT FROM AUTHOR]

The scanning photoelectron microscope (SPEM), developed more than 30 years ago, has undergone numerous technical developments, providing an incredibly vast kind of feasible sample environments, which span from the traditional high spatial resolution core level based chemical analysis to insitu and operando complex experiments, including also electrochemical setups and operational electronic devices at various temperatures. Another important step ahead is overcoming the so-called pressure gap for operando studies, recently extended to near ambient values by building special environmental cells. Using recent results of conventional and unconventional experiments, obtained with SPEM at the ESCA Microscopy beamline at Elettra Sincrotrone Trieste the present review demonstrates the current potential of this type of photoelectron spectromicroscopy to explore the interfacial properties of functional materials with high spatial resolution. [Display omitted] [ABSTRACT FROM AUTHOR]

Synchrotron-based scanning photoelectron microscopy has opened unique opportunities for exploiting processes occurring at surfaces and interfaces, which control the properties of functional materials where issues of complexity at microscopic length scales should be faced and understood. The present article aims at demonstrating the present capabilities of this microscopic method to explore the surface composition of micro- and nano-structured materials, focused on cases relevant to catalysis. We report and discuss some recent results about the chemical state of supported PtRh alloy microparticles under oxidation conditions and the changes in the status of a Co/polypyrrole electrocatalyst due to ageing in the course of the oxygen reduction reaction. Monitoring the lateral inhomogeneity in the chemical state at sub-micrometer length scales by combining chemical imaging and micro-spectroscopy has provided comprehension of events occurring at the catalyst surface, which determine the performance of the morphologically complex catalytic systems. Ongoing efforts for development and implementing of new set-ups that allow working closer to the realistic conditions of catalytic reactions are also outlined and briefly discussed. [ABSTRACT FROM AUTHOR]

We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V2O3. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations. [ABSTRACT FROM AUTHOR]

Large surface area, 3D structured transparent electrodes with effective light management capability may represent a key component in the development of new generation optoelectronic and energy harvesting devices. We present an approach to obtain forest-like nanoporous/hierarchical Al-doped ZnO conducting layers with tunable transparency and light scattering properties, by means of room temperature Pulsed Laser Deposition in a mixed Ar:O 2 atmosphere. The composition of the background atmosphere during deposition can be varied to modify stoichiometry-related defects, and therefore achieve control of electrical and optical properties, while the total background pressure controls the material morphology at the nano- and mesoscale and thus the light scattering properties. This approach allows tuning electrical resistivity over a very wide range (10 − 1 − 10 6 Ω cm), both in the in-plane and cross-plane directions. Optical transparency and haze can also be tuned by varying the stoichiometry and thickness of the nano-forests. [ABSTRACT FROM AUTHOR]

[Display omitted] • Composite single crystals of (Fe,Ni) 4 Se 5 and Ti 3 Se 4 on bi-intercalated crystal (Fe,Ni) 0.25 TiSe 2 are grown. • The morphology of these composite crystals has been studied by SEM, AFM and SPEM. • The electronic structure of the inclusions (Fe,Ni) 4 Se 5 in coherent coupling with TiSe 2 was studied. • Mechanism for the formation of such composite crystals has been proposed. • Thermodynamic modeling of the Ti3Se4 and (Fe, Ni) 4Se5 inclusions stability in the composite has been performed. A nanocomposite material consisting of (Fe,Ni) 4 Se 5 and Ti 3 Se 4 nanocrystals coherently bounded with the (Fe,Ni) 0.25 TiSe 2 substrate was obtained during the synthesis of the (Fe, Ni) x TiSe 2 bi-intercalation compound from the mixture of Fe 0.25 TiSe 2 and Ni 0.25 TiSe 2. The morphology of these composite crystals has been studied using optical, scanning electron and atomic force microscopy. The electronic structure of the inclusions was studied using X-ray scanning photoelectron microscopy (SPEM). We have shown that (Fe,Ni) 4 Se 5 and Ti 3 Se 4 inclusions grow simultaneously with (Fe,Ni) x TiSe 2 substrate crystal on its (0 0 1) plane. The lateral growth of the (Fe,Ni) x TiSe 2 crystal is accompanied by the "capturing" of the (Fe,Ni) 4 Se 5 and Ti 3 Se 4 inclusions by the (Fe,Ni) 0.25 TiSe 2 substrate resulting in the formation of the composite crystal. [ABSTRACT FROM AUTHOR]

Nitrogen inclusion in vertically aligned carbon nanotubes (v-CNTs) was performed in situ and in ultra-high vacuum by nitrogen ion implantation and evaluated by X-ray photoelectron spectromicroscopy. The creation of defects induced by the ions drives the formation of different nitrogen species (pyridinic, pyrrolic, and graphitic) at the CNT surface. While nitrogen implantation in CNT sidewalls has results similar to implantation in graphene, where mainly nitrogen sp² bonding configuration occurs, we observed a different behaviour at the CNT tips, where nitrogen incorporation is also more efficient. A large amount of pyrrolic nitrogen is observed at the CNT tips compared to the amount at the CNT sidewalls for the same ion implantation parameters. This indicates a different reactivity of the CNT tips where the presence of natural defects may be involved in different nitrogen bonding formations between carbon and nitrogen with respect to the CNT sidewalls. [ABSTRACT FROM AUTHOR]

• Environmental cells for in-operando photoelectron spectroscopy and microscopy. • Advantages of using electron and photon transparent graphene membranes. • In-situ grafting of chemo-magnetic patterns and magnetic microscopy. Implementation of in-situ and operando experimental set-ups for bridging the pressure gap in characterization techniques based on monitoring of photoelectron emission has made significant achievements at several beamlines at Elettra synchrotron facility. These set-ups are now operational and have been successfully used to address unsolved issues exploring events occurring at solid–gas, solid–liquid and solid-solid interfaces of functional materials. The sections in the article communicate the research opportunities offered by the current set-ups at APE, BACH, ESCAmicroscopy and Nanospectroscopy beamlines and outline the next steps to overcome the present limits. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen inclusion in both chemical vapour deposition and exfoliated few-layer graphene flakes was performed by nitrogen ion implantation in ultra-high vacuum. Inclusion of up to ∼20 at.% nitrogen can be reached through this clean technique with absence of oxygen species in the final product, while maintaining a largely sp2-carbon network. The nitrogen inclusion was observed by scanning X-ray photoelectron microscopy (SPEM) with energy resolution of 0.2eV and spatial resolution of 10nm. SPEM can be used to follow the evolution of nitrogen species: pyridinic, graphitic, and pyrrolic, at different doping stages and annealing temperatures. Variations in the ratio between sp2 nitrogen species was observed for increasing treatment time; annealing results in quenching of the sp3 component, suggesting the graphitic nitrogen as the most thermal stable species. The occurrence of graphitic species together with the absence of pyrrolic is indicative of N-incorporation into a hexagonal graphene-based lattice. Ion irradiation followed by annealing performed in a controlled way is a promising strategy to fine control the nature of the nitrogen species grafted to the graphene while focusing on selected applications. [Copyright &y& Elsevier]

The morphology of the heterogeneous Cr x Ti 1-x Se 2 and Cr x Ti 1-x S 2 single crystals has been studied using X-ray scanning photoemission microscopy (SPEM) and angular resolved photoemission spectroscopy (ARPES). A direct method of SPEM provided us the insight into the origin of the blurred ARPES images for Cr 0.78 Ti 0.36 Se 2 single crystal. Using SPEM, we confirmed the formation of the CrSe 2 -based structural fragments inside the Cr x Ti 1-x Se 2 single crystals with x ≥ 0.75. The chemical composition of the forming structural fragments depends on the chalcogen (S, Se) forming the crystal lattice. [Display omitted] • Cr x Ti 1-x Ch 2 (Ch = S, Se) single crystals have been studied using SPEM • Structural fragments with different composition are formed in both Se and S systems • The fragments can be in coherent relation with each other • The fragments in Cr 0.78 Ti 0.36 Se 2 are TiSe 2 -based and CrSe 2 -based solid solutions • The fragments in Cr 0.34 Ti 0.66 S 2 are Cr x Ti 1-x+y S 2 -based solid solutions with different concentration y of superstoichiometric Ti [ABSTRACT FROM AUTHOR]

Abstract: Scanning photoelectron microscopy and impedance spectroscopy were used to study simultaneously the impact of NO gas on surface chemistry and the electrochemical response of electrolyte-supported (La1−xSrx)FeO3−δ (LSF) sensing layers in electrochemical NOx sensors, during high-temperature operation. Electrochemical model cells were fabricated by screen printing macro- and micro-patterned thin films on zirconia electrolyte. Cell bias, temperature and NO/O2 gas ratio were varied during the experiments. LSF/3YSZ sensing layers remained stable over a wide temperature-bias range in an oxygen-containing environment. LSF compositions with low strontium content (x=0.2) did not undergo any changes in their surface chemistry, while compositions with higher strontium level (x=0.4) showed partial reduction of surface iron at low oxygen chemical potential. Upon exposure to NO gas at low oxygen partial pressure, NO was observed to dissociate on the LSF surface and form chemisorbed O- and N-adatoms with strong interactions to surface iron or zirconium. Concentration and stability of these ad-complexes increased with the NO/O2 ratio, cathodic bias and decreasing temperature. At low NO level in the gas, NO was observed to interact preferentially with iron atoms at the LSF surface and the surface reaction was reversible. At high NO/O2 ratios and low temperatures, irreversible formation of surface ad-complexes was observed, with reduced iron and zirconium, and caused even new phase formation. Simultaneous assessment of surface chemistry and cell impedance demonstrated that modifications in surface chemistry directly affected the oxygen exchange rate in the cell. In the presence of NO, the sensing oxide resistance decreased for zero or small bias. For large bias, no additional decrease in cell resistance was observed beyond the corresponding intrinsic cell performance in oxygen. Under these conditions, again, the particular cell response depended on the strontium substitution level in LSF, favoring lower redox-stability and thus a more complicated cell response to NO gas for high strontium level. [Copyright &y& Elsevier]

Abstract: The existence and role of platinum oxide in the solid state electrode system Pt(O2)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate. [Copyright &y& Elsevier]

Abstract: In this work sintered thick microcrystalline films as well as micro and nanostructures of In2O3 have been studied. The results obtained by XPS microscopy show that the boundary regions of the microcrystalline films present a higher amount of oxygen, as well as a different O (1s) core level XPS spectrum with respect to the grains. CL images recorded at room temperature show that the emission is preferentially associated with the grain boundaries and the main emission band appeared at 1.9 eV in the recorded CL spectra. Core level and valence band spectromicroscopy measurements of the indium oxide arrows grown at the surface of the sintered InN revealed the incorporation of nitrogen, coming from the starting material. In these structures the N (1s) core level splits into two components, showing a higher amount of nitrogen in the pyramid surface than in the columns of the structures which correlates with an increase of CL intensity. [Copyright &y& Elsevier]

• Manganese vanadium sulfide-oxide (MVO) heterostructure thin film on graphite foil is deposited by one-step electrospray technique. • High spatially resolved synchrotron-based SPEM was used for chemical mapping on the cylindrical core-shell MVO heterostructures. • MVO heterostructure was able to host Li+ ions into its structure. Heterostructure based on metal sulfides and oxides nanomaterials can be relevant to the charge storage devices. Here, we show that Mn(CH 3 COO) 2 ·4H 2 O and VOSO 4 ·xH 2 O can react in ethanol/water droplets generated by an electric field assisted spray system, so that MnS x -VS x /Mn z V 2 O 5 heterostructures in the shape of nanometric cylindrical particles can be deposited on a graphite foil substrate. The composite material phases were detected by several microscopies and microscopic probes spectroscopies, i.e., micro-Raman and scanning X-ray photoemission microscopy. The nanometric cylindrical particles were relatively homogenously distributed throughout the film covering the graphite foil. Film thickness modulation on surface was calculated between 100 and 300 nm range. We show that the segregation of MnV-O and MnV-S relative abundance in the internal and external volume of the cylindrical nanoparticles respectively, can be exploited during faradaic and non-faradaic processes in charge/discharge. [ABSTRACT FROM AUTHOR]

Abstract: The surface chemistry of operating model SOFC cathodes with LSM catalyst and YSZ electrolyte was studied in-situ by photoelectron microscopy. The electrochemical activation of SOFC cathodes under cathodic biasing or polarization was explained by the finding that partially reduced manganese oxide species rapidly spread from the triple phase boundary over the electrolyte surface, thereby providing high electronic conductivity in the zirconia surface scale and promoting the direct incorporation of oxygen from the gas into the electrolyte. [Copyright &y& Elsevier]

Abstract: The surface segregation of Si used for doping of GaN films grown by metal-organic vapor phase epitaxy has been detected by spectro-microscopy. Facetted cracks with a threefold symmetry have been observed which extend over several micrometers. From local spectra, an enhanced Si segregation is deduced at the facets as compared to the flat surface. A scheme is presented which allows to extract quantitative information about the local surface concentrations for such facetted surface systems. Following to this scheme, Si coverages as high as approximately 4.5×1014 Siatoms/cm2 occur at the facets which clearly proves the segregation tendency of Si. [Copyright &y& Elsevier]

The growth mode of iron on Au(0 0 1) surface at room temperature has been studied by means of photoelectron spectroscopy and scanning photoemission microscopy. The analysis of Au4f core level shifts reveals the segregation of gold atoms during the growth, leading for high coverage to the floating of Au surface layer burying Fe thin film and AuFe interfacial alloy. The formation of such segregating layer is coherent with energetic criteria (low gold surface energy, negative interfacial mixing energy, size effect,…). The synergy between these effects may favour the intermixing at the interface and the gold segregation. Photoemission microscopy measurements have been carried out to characterize local morphological and compositional inhomogeneities. The growth proceeds via the segregation of small three-dimensional AuFe gold islands surrounded by a flat Fe/Au region. [Copyright &y& Elsevier]

Silicon nitride layers grown on Si (1 1 1) by atomic nitrogen exposure at elevated substrate temperatures have been investigated in situ by photoemission spectro-microsopy. From the X-ray photo emission spectra taken at various sample areas, the chemical composition of samples grown at 800 °C is found to be homogenous all over the surface, with a stoichiometry according to Si3N4. Due to attenuation of the photo electrons, the images also provide information about the morphology of the nitride films. For 800 °C, a smooth film is observed, whereas for growth temperatures exceeding 900 °C, an increased roughness is observed. [Copyright &y& Elsevier]

Here a sealing-style x-ray photoelectron spectroscopy study of the surface of a 1.0 wt. %Ni/TiO2 nanoparticle catalyst in a flowing mixture of CO and O2 at 1 bar was performed with a graphene membrane-sealed Si3N4 window-based miniature cell. We report the details on how a commercial Si3N4 window is modified before assembling a graphene membrane, how single-layer graphene membranes are transferred from their metal supports to the modified Si3N4 window, how a modified Si3N4 window covered with a double-layer graphene membrane is assembled onto a blank cell cap, how a nanoparticle catalyst is introduced to the cell cap and then the cell cap is installed onto a cell body to form a complete reaction cell, and how a complete cell is interfaced with a high vacuum chamber of an XPS system before an XPS study of 1.0 wt. %Ni/TiO2 catalyst surface in a flowing mixture for 0.2 bar CO and 0.8 bar O2 is performed. How the characterization of a catalyst using this type of graphene membrane-sealed Si3N4 window-based miniature cell is relevant to the finding of the actual surface chemistry of a catalyst during catalysis is discussed., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Bipolar plates, a critical component of proton exchange membrane fuel cell (PEMFC), are constructed out of alloys of Ti, Pt, Cr, or graphitic materials that have limitations. Electrical conductivity, cost, and corrosion resistance are among the critical considerations for bi-polar plate material. Graphene, which possesses impressive conductivity and toughness, is an attractive option as coating on metallic substrates of PEMFC bipolar plates. This study investigates corrosion resistance and its durability due to graphene developed by chemical vapor deposition on a pure Ni-Cu alloy and a commercial Ni-Cu alloy in 0.5 m H 2 SO 4 environment, with a view to exploring use of graphene coated Ni-Cu alloys for the construction of PEMFC bipolar plates. The graphene coating on the pure alloy shows remarkably superior corrosion resistance than the commercial alloy that is attributed to the former's ability to develop considerably defect-free graphene., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

Graphene coatings developed by chemical vapor deposition (CVD) that possess extraordinary/unique characteristics as barrier against aggressive environment can improve the corrosion resistance of Ni and Cu by up to two orders of magnitude. However, because of some compelling technical reasons, it has thus far been a nontrivial challenge to develop graphene coatings on the most commonly used engineering alloy, mild steel (MS). To circumvent the challenge simply by first electroplating MS with a Ni layer is attempted, and then developing CVD graphene over the Ni layer. However, this approach proved too simplistic and does not work. This necessitated an innovative surface modification of MS (based on basic metallurgical principles) that enabled successful CVD of graphene coating on MS. The graphene coating thus developed is demonstrated to improve the corrosion resistance of mild steel by two orders of magnitude in an aggressive chloride solution, through electrochemical testing. This improvement was not only sustained for the entire test duration of >1000 h; but there is a clear trend for the resistance to be possibly everlasting. The optimized surface modification that enabled development of CVD graphene coating on mild steel is generic in nature, and it should enable graphene coating on other alloy systems, which would otherwise not be possible., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

The catalytic behavior of Rh particles supported by three different materials (Rh, Au, and ZrO 2 ) in H 2 oxidation has been studied in situ by correlative photoemission electron microscopy (PEEM) and scanning photoemission electron microscopy (SPEM). Kinetic transitions between the inactive and active steady states were monitored, and self-sustaining oscillations on supported Rh particles were observed. Catalytic performance differed depending on the support and Rh particle size. Oscillations varied from particle size-independent (Rh/Rh) via size-dependent (Rh/ZrO 2 ) to fully inhibited (Rh/Au). For Rh/Au, the formation of a surface alloy induced such effects, whereas for Rh/ZrO 2 , the formation of substoichiometric Zr oxides on the Rh surface, enhanced oxygen bonding, Rh-oxidation, and hydrogen spillover onto the ZrO 2 support were held responsible. The experimental observations were complemented by micro-kinetic simulations, based on variations of hydrogen adsorption and oxygen binding. The results demonstrate how correlative in situ surface microscopy enables linking of the local structure, composition, and catalytic performance., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Improvements in sodium intercalation in sodium cathodes have been debated in recent years. In the present work, we delineate the significant effect of the carbon nanotubes (CNTs) and their weight percent in the intercalation capacity of the binder-free manganese vanadium oxide (MVO)-CNTs composite electrodes. The performance modification of the electrode is discussed taking into account the cathode electrolyte interphase (CEI) layer under optimal performance. We observe an intermittent distribution of the chemical phases on the CEI, formed on these electrodes after several cycles. The bulk and superficial structure of pristine and Na+ cycled electrodes were identified via micro-Raman scattering and Scanning X-ray Photoelectron Microscopy. We show that the inhomogeneous CEI layer distribution strongly depends on the CNTs weight percentage ratio in an electrode nano-composite. The capacity fading of MVO-CNTs appears to be associated with the dissolution of the Mn2O3 phase, leading to electrode deterioration. This effect is particularly observed in electrodes with low weight percentage of the CNTs in which the tubular topology of the CNTs are distorted due to the MVO decoration. These results can deepen the understanding of the CNTs role on the intercalation mechanism and capacity of the electrode, where there are variations in the mass ratio of CNTs and the active material., Competing Interests: The authors declare no conflicts of interest.

Understanding the chemical and electronic properties of point defects in two-dimensional materials, as well as their generation and passivation, is essential for the development of functional systems, spanning from next-generation optoelectronic devices to advanced catalysis. Here, we use synchrotron-based X-ray photoelectron spectroscopy (XPS) with submicron spatial resolution to create sulfur vacancies (SVs) in monolayer MoS 2 and monitor their chemical and electronic properties in situ during the defect creation process. X-ray irradiation leads to the emergence of a distinct Mo 3d spectral feature associated with undercoordinated Mo atoms. Real-time analysis of the evolution of this feature, along with the decrease of S content, reveals predominant monosulfur vacancy generation at low doses and preferential disulfur vacancy generation at high doses. Formation of these defects leads to a shift of the Fermi level toward the valence band (VB) edge, introduction of electronic states within the VB, and formation of lateral pn junctions. These findings are consistent with theoretical predictions that SVs serve as deep acceptors and are not responsible for the ubiquitous n-type conductivity of MoS 2 . In addition, we find that these defects are metastable upon short-term exposure to ambient air. By contrast, in situ oxygen exposure during XPS measurements enables passivation of SVs, resulting in partial elimination of undercoordinated Mo sites and reduction of SV-related states near the VB edge. Correlative Raman spectroscopy and photoluminescence measurements confirm our findings of localized SV generation and passivation, thereby demonstrating the connection between chemical, structural, and optoelectronic properties of SVs in MoS 2 .

Magnetic topological insulators (MTIs) have recently become a subject of poignant interest; among them, Z 2 topological insulators with magnetic moment ordering caused by embedded magnetic atoms attract special attention. In such systems, the case of magnetic anisotropy perpendicular to the surface that holds a topologically nontrivial surface state is the most intriguing one. Such materials demonstrate the quantum anomalous Hall effect, which manifests itself as chiral edge conduction channels that can be manipulated by switching the polarization of magnetic domains. In the present paper, we uncover the atomic structure of the bulk and the surface of Mn 0.06 Sb 1.22 Bi 0.78 Te 3.06 in conjunction with its electronic and magnetic properties; this material is characterized by naturally formed ferromagnetic layers inside the insulating matrix, where the Fermi level is tuned to the bulk band gap. We found that in such mixed crystals septuple layers (SLs) of Mn(Bi,Sb) 2 Te 4 form structures that feature three SLs, each of which is separated by two or three (Bi,Sb) 2 Te 3 quintuple layers (QLs); such a structure possesses ferromagnetic properties. The surface obtained by cleavage includes terraces with different terminations. Manganese atoms preferentially occupy the central positions in the SLs and in a very small proportion can appear in the QLs, as indirectly indicated by a reshaped Dirac cone.

As a semiconductor ferroelectric, GeTe has become a focus of renewed attention due to the recent discovery of giant Rashba splitting. It already has a wide range of applications, from thermoelectricity to data storage. Its stability in ambient air, as well as the structure and properties of an oxide layer, define the processing media for device production and operation. Here, we studied a reaction between the GeTe (111) surface and molecular oxygen for crystals having solely inversion domains. We evaluated the reaction kinetics both ex situ and in situ using NAP XPS. The structure of the oxide layer is extensively discussed, where, according to HAADF-STEM and STEM-EDX, nanoscale phase separation of GeO 2 and Te is observed, which is unusual for semiconductors. We believe that such behaviour is closely related to the ferroelectric properties and the domain structure of GeTe.

Herein, we report the microscopic and spectroscopic signatures of the hydrated V 2 O 5 phase, prepared from the α-V 2 O 5 powder, which was kept in deionized water inside an airtight glass container for approximately 2.5 years. The experimental results show an evolution of the V 4+ component in V 2p 3/2 core energy level spectra, and a peak corresponding to σ-OH - bond appeared in the valence band spectra in the hydrated V 2 O 5 powder sample due to the water intercalation. Vanadium metal oxide particles were found to be self-nucleated into micro/nanorods after a long period of exposure to an extremely humid environment. The distinct features in the spectra obtained with high-resolution transmission electron microscopy, micro-Raman scattering, and X-ray photoelectron spectroscopy confirmed the presence of structural water molecules for the first time in the long-aged naturally hydrated V 2 O 5 phase., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

We investigate the oxidation mechanism of the layered model system GeAs. In situ X-ray photoelectron spectroscopy experiments performed by irradiating an individual flake with synchrotron radiation in the presence of oxygen show that while As leaves the GeAs surface upon oxidation, a Ge-rich ultrathin oxide film is being formed in the topmost layer of the flake. We develop a theoretical model that supports the layer-by-layer oxidation of GeAs, with a logarithmic kinetics. Finally, assuming that the activation energy for the oxidation process changes linearly with coverage, we estimate that the activation energy for As oxidation is almost twice that for Ge at room temperature.

Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.

Catalytic hydrogen oxidation on a polycrystalline rhodium foil used as a surface structure library is studied by scanning photoelectron microscopy (SPEM) in the 10 -6 mbar pressure range, yielding spatially resolved X-ray photoemission spectroscopy (XPS) measurements. Here we report an observation of a previously unknown coexistence of four different states on adjacent differently oriented domains of the same Rh sample at the exactly same conditions. A catalytically active steady state, a catalytically inactive steady state and multifrequential oscillating states are simultaneously observed. Our results thus demonstrate the general possibility of multi-states in a catalytic reaction. This highly unusual behaviour is explained on the basis of peculiarities of the formation and depletion of subsurface oxygen on differently structured Rh surfaces. The experimental findings are supported by mean-field micro-kinetic modelling. The present observations raise the interdisciplinary question of how self-organising dynamic processes in a heterogeneous system are influenced by the permeability of the borders confining the adjacent regions., (© 2021. The Author(s).)

Graphene coating on the cobalt-chromium alloy was optimized and successfully carried out by a cold-wall chemical vapor deposition (CW-CVD) method. A uniform layer of graphene for a large area of the Co-Cr alloy (discs of 10 mm diameter) was confirmed by Raman mapping coated area and analyzing specific G and 2D bands; in particular, the intensity ratio and the number of layers were calculated. The effect of the CW-CVD process on the microstructure and the morphology of the Co-Cr surface was investigated by scanning X-ray photoelectron microscope (SPEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Nanoindentation and scratch tests were performed to determine mechanical properties of Co-Cr disks. The results of microbiological tests indicate that the studied Co-Cr alloys covered with a graphene layer did not show a pro-coagulant effect. The obtained results confirm the possibility of using the developed coating method in medical applications, in particular in the field of cardiovascular diseases.

Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H 2 oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H 2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.

Renewed interest in the ferroelectric semiconductor germanium telluride was recently triggered by the direct observation of a giant Rashba effect and a 30-year-old dream about a functional spin field-effect transistor. In this respect, all-electrical control of the spin texture in this material in combination with ferroelectric properties at the nanoscale would create advanced functionalities in spintronics and data information processing. Here, we investigate the atomic and electronic properties of GeTe bulk single crystals and their (111) surfaces. We succeeded in growing crystals possessing solely inversion domains of ∼10 nm thickness parallel to each other. Using HAADF-TEM we observe two types of domain boundaries, one of them being similar in structure to the van der Waals gap in layered materials. This structure is responsible for the formation of surface domains with preferential Te-termination (∼68%) as we determined using photoelectron diffraction and XPS. The lateral dimensions of the surface domains are in the range of ∼10-100 nm, and both Ge- and Te-terminations reveal no reconstruction. Using spin-ARPES we establish an intrinsic quantitative relationship between the spin polarization of pure bulk states and the relative contribution of different terminations, a result that is consistent with a reversal of the spin texture of the bulk Rashba bands for opposite configurations of the ferroelectric polarization within individual nanodomains. Our findings are important for potential applications of ferroelectric Rashba semiconductors in nonvolatile spintronic devices with advanced memory and computing capabilities at the nanoscale.

Multiphoton polymer cross-linking evolves as the core process behind high-resolution additive microfabrication with soft materials for implantable/wearable electronics, tissue engineering, microrobotics, biosensing, drug delivery, etc. Electrons and soft X-rays, in principle, can offer even higher resolution and printing rates. However, these powerful lithographic tools are difficult to apply to vacuum incompatible liquid precursor solutions used in continuous additive fabrication. In this work, using biocompatible hydrogel as a model soft material, we demonstrate high-resolution in-liquid polymer cross-linking using scanning electron and X-ray microscopes. The approach augments the existing solid-state electron/X-ray lithography and beam-induced deposition techniques with a wider class of possible chemical reactions, precursors, and functionalities. We discuss the focused beam cross-linking mechanism, the factors affecting the ultimate feature size, and layer-by-layer printing possibilities. The potential of this technology is demonstrated on a few practically important applications such as in-liquid encapsulation of nanoparticles for plasmonic sensing and interfacing of viable cells with hydrogel electrodes.

We combine spatially resolved scanning photoelectron spectroscopy with confocal Raman and optical microscopy to reveal how the oxidation of the buried graphene-Cu interface relates to the Cu crystallographic orientation. We analyze over 100 different graphene covered Cu (high and low index) orientations exposed to air for 2 years. Four general oxidation modes are observed that can be mapped as regions onto the polar plot of Cu surface orientations. These modes are (1) complete, (2) irregular, (3) inhibited, and (4) enhanced wrinkle interface oxidation. We present a comprehensive characterization of these modes, consider the underlying mechanisms, compare air and water mediated oxidation, and discuss this in the context of the diverse prior literature in this area. This understanding incorporates effects from across the wide parameter space of 2D material interface engineering, relevant to key challenges in their emerging applications, ranging from scalable transfer to electronic contacts, encapsulation, and corrosion protection., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

How a catalyst behaves microscopically under reaction conditions, and what kinds of active sites transiently exist on its surface, is still very much a mystery to the scientific community. Here we present an in situ study on the red-ox behaviour of copper in the model reaction of hydrogen oxidation. Direct imaging combined with on-line mass spectroscopy shows that activity emerges near a phase boundary, where complex spatio-temporal dynamics are induced by the competing action of simultaneously present oxidizing and reducing agents. Using a combination of in situ imaging with in situ X-ray absorption spectroscopy and scanning photoemission microscopy, we reveal the relation between chemical and morphological dynamics and demonstrate that a static picture of active sites is insufficient to describe catalytic function of redox-active metal catalysts. The observed oscillatory redox dynamics provide a unique insight on phase-cooperation and a convenient and general mechanism for constant re-generation of transient active sites.

We present an in-depth analysis of the surface band alignment and local potential distribution of InP nanowires containing a p-n junction using scanning probe and photoelectron microscopy techniques. The depletion region is localized to a 15 nm thin surface region by scanning tunneling spectroscopy and an electronic shift of up to 0.5 eV between the n- and p-doped nanowire segments was observed and confirmed by Kelvin probe force microscopy. Scanning photoelectron microscopy then allowed us to measure the intrinsic chemical shift of the In 3d, In 4d, and P 2p core level spectra along the nanowire and the effect of operating the nanowire diode in forward and reverse bias on these shifts. Thanks to the high-resolution techniques utilized, we observe fluctuations in the potential and chemical energy of the surface along the nanowire in great detail, exposing the sensitive nature of nanodevices to small scale structural variations.

Element clustering and structural features of liquid lead-bismuth eutectic (LBE) alloy have been investigated up to 720 °C by means of high temperature X-ray diffraction (HT-XRD), X-ray Photoemission Spectroscopy (XPS) and Scanning Photoemission Microscopy (SPEM) at the Elettra synchrotron in Trieste. The short-range order in liquid metal after melting corresponds to the cuboctahedral atomic arrangement and progressively evolves towards the icosahedral one as temperature increases. Such process, that involve a negative expansion of the alloy, is mainly connected to the reduction of atom distance in Pb-Pb pairs which takes place from 350 °C to 520 °C. On an atomic scale, it is observed a change of the relative number of Bi-Bi, Pb-Pb, and Pb-Bi pairs. The Pb-Bi pairs are detected only at a temperature above ~350 °C, and its fraction progressively increases, giving rise to a more homogeneous distribution of the elements. SPEM results showed evidence that the process of chemical homogenization on an atomic scale is preceded and accompanied by homogenization on micro-scale. Clusters rich of Bi and Pb, which are observed after melting, progressively dissolve as temperature increases: Only a few residuals remain at 350 °C, and no more clusters are detected a 520 °C.

We performed spatially resolved near-ambient-pressure photoemission spectromicroscopy on graphene-coated copper in operando under oxidation conditions in an oxygen atmosphere (0.1 mbar). We investigated regions with bare copper and areas covered with mono- and bi-layer graphene flakes, in isobaric and isothermal experiments. The key method in this work is the combination of spatial and chemical resolution of the scanning photoemission microscope operating in a near-ambient-pressure environment, thus allowing us to overcome both the material and pressure gap typical of standard ultrahigh-vacuum X-ray photoelectron spectroscopy (XPS) and to observe in operando the protection mechanism of graphene toward copper oxidation. The ability to perform spatially resolved XPS and imaging at high pressure allows for the first time a unique characterization of the oxidation phenomenon by means of photoelectron spectromicroscopy, pushing the limits of this technique from fundamental studies to real materials under working conditions. Although bare Cu oxidizes naturally at room temperature, our results demonstrate that such a graphene coating acts as an effective barrier to prevent copper oxidation at high temperatures (over 300 °C), until oxygen intercalation beneath graphene starts from boundaries and defects. We also show that bilayer flakes can protect at even higher temperatures. The protected metallic substrate, therefore, does not suffer corrosion, preserving its metallic characteristic, making this coating appealing for any application in an aggressive atmospheric environment at high temperatures.

Studying surface of catalyst nanoparticles in a flowing liquid is important for understanding the underlying mechanism of a reaction performed in liquid. We report the design of a reaction cell system of Si3N4 window covering the flowing liquid with an electron-transmissible membrane. By using metal nanoparticles as a catalyst dispersed in a solvent, examination of the surface of catalyst nanoparticles in a flowing liquid was demonstrated by observation of Ag 3d photoemission feature when a liquid containing Ag nanoparticles was flowing through this system.