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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.

We have investigated the electronic structure of protect annealed Pr1.3−xLa0.7CexCuO4 (x = 0.05) with small superconducting volume fraction by means of angle-resolved photoemission spectroscopy (AR...

International audience; Drug nanocarriers (NCs) with sizes usually below 200 nm are gaining increasing interest in the treatment of severe diseases such as cancer and infections. Characterization methods to investigate the morphology and physicochemical properties of multifunctional NCs are key in their optimization and in the study of their in vitro and in vivo fate. Whereas a variety of methods has been developed to characterize “bulk” NCs in suspension, the scope of this review is to describe the different approaches for the NC characterization on an individual basis, for which fewer techniques are available. The accent is put on methods devoid of labelling, which could lead to artefacts. For each characterization method, the principles and approaches to analyze the data are presented in an accessible manner. Aspects related to sample preparation to avoid artefacts are indicated, and emphasis is put on examples of applications. NC characterization on an individual basis allows gaining invaluable information in terms of quality control, on: i) NC localization and fate in biological samples; ii) NC morphology and crystallinity; iii) distribution of the NC components (drugs, shells), and iv) quantification of NCs’ chemical composition. The individual characterization approaches are expected to gain increasing interest in the near future.

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.

Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) millimeter-sized architecture without compromising its remarkable electrical, optical, and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining the state-of-the-art spectromicroscopy and imaging techniques. The connected and bicontinuous topology, without frayed borders and edges and with low density of crystalline defects, has been unveiled via helium ion, Raman, and transmission electron microscopies down to the atomic scale. Most importantly, nanoscanning photoemission unravels a 3D NPG structure with preserved 2D electronic density of states (Dirac cone like) throughout the porous sample. Furthermore, the high spatial resolution brings to light the interrelationship between the topology and the morphology in the wrinkled and highly bent regions, where distorted sp2 C bonds, associated with sp3-like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small-sized individual graphene sheets and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.

Suspended graphene is exposed to different fluorine-containing species produced by a plasma source fed with CF 4 precursor gas. We investigate the fluorination process by selecting two different kinetic energies for the ions striking the graphene surface. The chemical-bonding environment is discussed, and the control of the graphene-fluorination homogeneity is investigated at the individual graphene sheets. The modifications of the electronic and structural properties are examined by scanning photoelectron microscopy, micro-Raman analysis, and scanning electron microscopy. The results are compared with those obtained for supported graphene on copper. Suspended graphene provides a quasi-ideal model for investigating the intrinsic properties of irradiated carbon nano-systems while avoiding damage due to backscattered atoms and recoil due to a supporting substrate. [Figure not available: see fulltext.].

The novel approach was proposed for detailed high-resolution studies of morphology and physico-chemical properties concomitantly at one measurement spot of E. coli bacterial cells culture immobilized onto silicon wafer surface in UHV conditions applying PhotoEmission Electron Microscopy under Hg lamp irradiation. For the E. coli characterization scanning electron microscopy (electron beam) and X-ray photoelectron spectroscopy (X-ray tube radiation) were applied prior to PhotoEmission Electron Microscopy measurements. In spite of irradiation doses collected for the cell arrays we were successful in detection of high-resolution images even of single E. coli bacterium by PhotoEmission Electron Microscopy technique followed by detailed high-resolution morphology studies by scanning electron microscopy. These results revealed widespread stability of the E. coli membranes shape after the significant number of applied characterization techniques.

While many major strides have been made in the last three decades concerning the synthesis, characterisation and properties of individual nanoobjects, their technological uptake necessarily requires integration into devices. To achieve this, detailed characterization, design and control of the interface between nanoobjects and their environment is essential. Nanomaterials differ significantly from their bulk counterparts and one important aspect of this is their high surface to volume ratios. For this reason interface properties typically dominate the behavior of nanomaterials. As a consequence, one immediately faces the problem of designing and controlling surfaces and, in case of embedded or layered systems, interfaces on atomic scales.

© 2016 by the author. The understanding and control of early hydration of tricalcium silicate (C3S) is of great importance to cement science and concrete technology. However, traditional characterization methods are incapable of providing morphological and spectroscopic information about in situ hydration at the nanoscale. Using soft X-ray spectromicroscopy, we report the changes in morphology and molecular structure of C3S at an early stage of hydration. In situ C3S hydration in a wet cell, beginning with induction (~1 h) and acceleration (~4 h) periods of up to ~8 h, was studied and compared with ex situ measurements in the deceleration period after 15 h of curing. Analysis of the near-edge X-ray absorption fine structure showed that the Ca binding energy and energy splitting of C3S changed rapidly in the early age of hydration and exhibited values similar to calcium silicate hydrate (C-S-H). The formation of C-S-H nanoseeds in the C3S solution and the development of a fibrillar C-S-H morphology on the C3S surface were visualized. Following this, silicate polymerization accompanied by C-S-H precipitation produced chemical shifts in the peaks of the main Si K edge and in multiple scattering. However, the silicate polymerization process did not significantly affect the Ca binding energy of C-S-H.

Oxygen migration in tantalum oxide, a promising next-generation storage material, is studied using in-operando x-ray absorption spectromicroscopy and is used to microphysically describe accelerated evolution of conduction channel and device failure. The resulting ring-like patterns of oxygen concentration are modeled using thermophoretic forces and Fick diffusion, establishing the critical role of temperature-activated oxygen migration that has been under question lately., Comment: 7 pages, Advanced Materials (2016); updated abstract

Two powerful and complementary techniques for chemical characterisation of nanoscale systems are electron energy-loss spectroscopy in the scanning transmission electron microscope, and X-ray absorption spectroscopy in the scanning transmission X-ray microscope. A correlative approach to spectro-microscopy may not only bridge the gaps in spatial and spectral resolution which exist between the two instruments, but also offer unique opportunities for nanoscale characterisation. This review will discuss the similarities of the two spectroscopy techniques and the state of the art for each microscope. Case studies have been selected to illustrate the benefits and limitations of correlative electron and X-ray microscopy techniques. In situ techniques and radiation damage are also discussed.

Self-assembled colloidal crystals have attracted major attention because of their potential as low-cost three- dimensional (3D) photonic crystals. Although a high degree of perfection is crucial for the properties of these materials, little is known about their exact structure and internal defects. In this study, we use tomographic scanning transmission X-ray microscopy (STXM) to access the internal structure of self- assembled colloidal photonic crystals with high spatial resolution in three dimensions for the first time. The positions of individual particles of 236 nm in diameter are identified in three dimensions, and the local crystal structure is revealed. Through image analysis, structural defects, such as vacancies and stacking faults, are identified. Tomographic STXM is shown to be an attractive and complementary imaging tool for photonic materials and other strongly absorbing or scattering materials that cannot be characterized by either transmission or scanning electron microscopy or optical nanoscopy.

We present the first results from the upgraded version of the scanning photoemission spectromicroscope MAXIMUM, bared on synchrotron undulator fight and on a multilayer-coated Schwarzschild objective. The upgrade involved nearly all parts of the instrument, notably the beamline and the electron analysis system. Micro-images of Fresnel zone plates and of metal test patterns on semiconductor substrates reached a new record in lateral resolution, well beyond 0.1 micron. The first spectromicroscopy tests were also successfully performed on the new instrument, with analysis of f and d core levels in different systems.

Photonic crystals consisting of nano- to micrometer-sized building blocks, such as multiple sorts of colloids, have recently received widespread attention. It remains a challenge, however, to adequately probe the internal crystal structure and the corresponding deformations that inhibit the proper functioning of such materials. It is shown that scanning transmission X-ray microscopy (STXM) can directly reveal the local structure, orientations, and even deformations in polystyrene and silica colloidal crystals with 30-nm spatial resolution. Moreover, STXM is capable of imaging a diverse range of crystals, including those that are dry and inverted, and provides novel insights complementary to information obtained by benchmark confocal fluorescence and scanning electron microscopy techniques.

We have detected strong dichroism in the Ni ${L}_{2,3}$ x-ray absorption spectra of a monolayer NiO film. The dichroic signal appears to be very similar to the magnetic linear dichroism observed for thicker antiferromagnetic NiO films. Detailed analysis reveals, however, that the dichroism is caused by crystal-field effects in the monolayer film, which is a nontrivial effect because the high spin Ni ${3d}^{8}$ ground state is not split by low-symmetry crystal fields. We present a practical method for identifying the independent magnetic and crystal-field contributions to the linear dichroic signal in spectra of NiO films with arbitrary thicknesses and lattice strains. Our findings are also relevant for ${3d}^{5}$ and ${3d}^{3}$ systems such as ${\mathrm{LaFeO}}_{3},$ ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3},$ VO, ${\mathrm{LaCrO}}_{3},$ ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3},$ and ${\mathrm{Mn}}^{4+}$ thin films.

An important application of photoemission spectromicroscopy would be to measure heterostructures and semiconductor devices in cross section to directly determine band offsets and band bending. We present here studies of p-n GaAs homojunctions and Al/GaAs Schottky junctions fabricated by molecular-beam epitaxy. Our results suggest that a minimum experimental uncertainty of about 0.15 eV will effect band offset determination. In general, useful quantitative information on the junction electrostatics can be obtained provided that the experimental data are analyzed to substract the diffuse photon background and take into account the intensity profile of the photon spot.

We have measured the lateral homogeneity in Al/GaAs(0 0 1) Schottky barriers engineered for low barrier height through fabrication of a Si layer at the interface under As flux. We used a spectroscopic photo emission and low-energy electron microscope (SPELEEM) which combines a low-energy electron microscope with an imaging band pass filter to allow spatially resolved synchrotron radiation photoemission experiments. As-grown samples with a Si interlayer thickness of 0.5 and 3 monolayers appeared homogeneous within the spatial resolution of the SPELEEM (22 nm). Annealing an Al/Si(As)/GaAs(0 0 1) heterostructure for 10 min at 500 degrees C, however, caused inhomogeneous As outdiffusion which is correlated with a local As 3d core level shift of 0.3 eV. We suggest that the reported degradation of such engineered Schottky barriers might be correlated with laterally inhomogeneous As out-diffusion upon annealing.

Photoelectron spectromicroscopy, the combination of conventional photoelectron spectroscopy and high lateral resolution, is a novel technique that exploits the high brightness of the most recent synchrotron sources. We briefly review its main implementation modes and present some examples of applications, with particular emphasis on semiconductor interface research.

We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.

We have analyzed the surface of liquid Au-Si eutectic droplets with photoemission spectromicroscopy. The Si 2p core level of the droplets shifts 0.2 eV to lower kinetic energy with respect to the surrounding Au/Si(111)-6x6 phase. The integral intensity of the Si 2p peak is approximately equal on the liquid droplet and on the surrounding substrate indicating that the local Au/Si stoichiometry does not change. Since bulk Au-Si liquid is Au-rich, this indicates that the liquid surface has a higher Si content than the bulk. An additional shoulder in the Si 2p spectrum of the droplet develops at 1.3 eV lower kinetic energy.

Ballistic emission electron and X-ray photoelectron emission microscopy studies are presented for the sulfur-passivated Pt-GaP(001) buried metal-semiconductor interface. The topographic/ballistic images showed that the roughness of the metal-semiconductor samples after sulfur passivation and Pt deposition is higher than in the as-received substrate. The photoelectron emission microscope microimages showed a significant inhomogeneity as far as the interface chemical environment is concerned. The strongest inhomogeneity appeared to be related to the gallium, and these variations have a subtle effect on the P and Pt signals. These complementary techniques enabled us to correlate the surface topography and the interface transport variations, with the spatially resolved chemical information of the buried Pt-GaP metal-semiconductor interface. (C) 1998 Elsevier Science B.V. All rights reserved.

The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.