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This manuscript emphasizes the leading role of Raymond Castaing in the conception, realization, and use of three major families of scientific instruments for local analysis of matter. Starting from his early studies with his research director, Andre Guinier, on the visualization of the GP zones in metal alloys, Raymond Castaing has introduced different stages of innovation for the identification of the elements present in the smallest volume of material. These were successively the X-ray electron probe, the secondary ion mass spectrometry with his student Georges Slodzian, the electron energy-loss filtering with his student Lucien Henry. Besides his Ph.D. dissertation, a reference text on any aspect of electron beam induced X-ray microanalysis, Raymond Castaing has continuously published, over a period of three decades, his research in the successive issues of the Comptes rendus de l'Academie des sciences

This paper reviews the implementation of Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM), as an essential tool for advanced analytical studies, exhibiting a unique level of performance in terms of spatial resolution down to the interatomic distances for imaging and sensitivity down to the single atom for elemental identification. In terms of spectral resolution, it offers access with a resolution as good as a few meV, to a very broad spectral domain extending from tens of meV (in the IR) up to a few keV (in the X-ray). This new generation of instrument (EELS+(S)TEM) is now routinely used to investigate the structural, spectral, electronic and chemical properties of a wide range of materials and to broaden spectacularly the field of novel information which it provides. A first part of the paper describes the major progress in advanced instrumentation brought by the novel pieces of equipment (spectrometers, monochromators, aberration correctors and detectors) together with the newly elaborated tools for the acquisition and processing of huge data collections. The second part is devoted to the description of the information contained in a global EELS spectrum: (i) from the core-loss domain implying excitations from inner-shell atomic electrons and its application in elemental, chemical and electronic mapping; (ii) from the low-energy domain exhibiting individual or collective excitations of the valence and conduction electron gas, with its most recent developments in band gap mapping and nanoplasmonics; (iii) in the ultra-low energy domain, which is now in its infancy, the surface collective electron excitations, molecular bonds and the vibrations of phonons at surfaces and in the bulk of nanostructures. The third part is devoted to the exploration of unconventional domains of applications, which in many cases associate the EELS acquisition with the generation and the capture of other signals in various environments, in situ operation (temperature, pressure...), absorption or generation of photons (cathodoluminescence, X-ray emission), acquisition and handling of multidimension data (space, energy, momentum, time). In conclusion, EELS fifty years after its first recognition as a useful actor in the development and promotion of the analytical microscopy, has nowadays become an essential tool for the acquisition of many physical parameters with ultimate resolution, thus opening new routes in nanophysics to be explored.

This contribution aims at reporting, from the subjective point of view of a witness based in Orsay, the fundamental role of Ondrej Krivanek in the spectacular emergence of EELS (Electron Energy-Loss Spectroscopy) as a key tool in analytical electron microscopy. In this regard, he has successively designed and built while he was at Gatan, serial EELS spectrometers, parallel EELS spectrometers and post-column energy filters which have been fitted to many different (S)TEM columns installed around the world. More recently the implementation of monochromators on the NION dedicated STEM together with the realization and performance of aberration correctors (which lie out of the scope of the present review), have placed the most advanced instrumental tool in the hands of continuously increasing populations of users in many domains of materials science and in life sciences. Furthermore, the impact of Ondrej Krivanek has spread widely beyond his technical achievements into that of a highly respected organizer of workshops, bringing together at regular intervals, all the experts from around the world and building up a real community of scientists.

We report on a novel way of performing stimulated electron energy-loss and energy-gain spectroscopy (sEELS/sEEGS) experiments that does not require a pulsed gun. In this scheme, a regular scanning transmission electron microscope (STEM) equipped with a conventional continuous electron gun is fitted with a modified EELS detector and a light injector in the object chamber. The modification of the EELS detector allows one to expose the EELS camera during tunable time intervals that can be synchronized with nanosecond laser pulses hitting the sample, therefore allowing us to collect only those electrons that have interacted with the sample under light irradiation. Using ∼ 5 ns laser pulses of ∼ 2 eV photon energy on various plasmonic silver samples, we obtain evidence of sEELS/sEEGS through the emergence of up to two loss and gain peaks in the spectra at ± 2 and ± 4 eV. Because this approach does not involve any modification of the gun, our method retains the original performances of the microscope in terms of energy resolution and spectral imaging with and without light injection. Compared to pulsed-gun techniques, our method is mainly limited to a perturbative regime (typically no more that one gain event per incident electron), which allows us to observe resonant effects, in particular when the plasmon energy of a silver nanostructure matches the laser photon energy. In this situation, EELS and EEGS signals are enhanced in proportion to n + 1 and n, respectively, where n is the average plasmon population due to the external illumination. The n term is associated with stimulated loss and gain processes, and the term of 1 corresponds to conventional (spontaneous) loss. The EELS part of the spectrum is therefore an incoherent superposition of spontaneous and stimulated EEL events. This is confirmed by a proper quantum-mechanical description of the electron/light/plasmon system incorporating light–plasmon and plasmon–electron interactions, as well as inelastic plasmon decay.

In a transmission electron microscope, the incident electrons travelling through the specimen thin foil can lose energy in inelastic interaction processes with the target electrons. The analysis of these energy loss transfers, designed as Electron Energy Loss Spectroscopy, is thoroughly described in this review, written in 1984. Relying on the basics of inelastic scattering theory, two major families of excitations are accounted for: (i) the low energy loss region (in the few eV range) where collective excitations (plasmons) and interband transitions of the electrons gas in the valence and conduction bands are generated; (ii) the high energy loss region (from typically 50 to a few thousand eV) where inner shell excitations detected above a continuously decreasing background, correspond to the ionization of electrons initially on atomic core levels. The intensity of these characteristic signals gives access to quantitative measurements of the number of excited atoms while their fine structures can be related to local electronic states (valence, bonding, structural environment). After a rapid survey of the latest instrumental developments at the time of writing, the review is focused onto the impact of EELS as an analytical tool for elemental analysis with high spatial resolution, addressing major issues in detection limits, minimum detectable mass and mass fraction.

Since their first realization, electron microscopes have demonstrated their unique ability to map with highest spatial resolution (sub-atomic in most recent instruments) the position of atoms as a consequence of the strong scattering of the incident high energy electrons by the nuclei of the material under investigation. When interacting with the electron clouds either on atomic orbitals or delocalized over the specimen, the associated energy transfer, measured and analyzed as an energy loss (Electron Energy Loss Spectroscopy) gives access to analytical properties (atom identification, electron states symmetry and localization). In the moderate energy-loss domain (corresponding to an optical spectral domain from the infrared (IR) to the rather far ultra violet (UV), EELS spectra exhibit characteristic collective excitations of the rather-free electron gas, known as plasmons. Boundary conditions, such as surfaces and/or interfaces between metallic and dielectric media, generate localized surface charge oscillations, surface plasmons (SP), which are associated with confined electric fields. This domain of research has been extraordinarily revived over the past few years as a consequence of the burst of interest for structures and devices guiding, enhancing and controlling light at the sub-wavelength scale. The present review focuses on the study of these surface plasmons with an electron microscopy-based approach which associates spectroscopy and mapping at the level of a single and well-defined nano-object, typically at the nanometer scale i.e. much improved with respect to standard, and even near-field, optical techniques. After calling to mind some early studies, we will briefly mention a few basic aspects of the required instrumentation and associated theoretical tools to interpret the very rich data sets recorded with the latest generation of (Scanning)TEM microscopes. The following paragraphs will review in more detail the results obtained on simple planar and spherical surfaces (or interfaces), extending then to more complex geometries isolated and in interaction, thus establishing basic rules from the classical to the quantum domain. A few hints towards application domains and prospective fields rich of interest will finally be indicated, confirming the demonstrated key role of electron-beam nanoplasmonics, the more as an yet-enhanced energy resolution down to the 10meV comes on the verge of current access.

The electric field control of functional properties is a crucial goal in oxide-based electronics. Non-volatile switching between different resistivity or magnetic states in an oxide channel can be achieved through charge accumulation or depletion from an adjacent ferroelectric. However, the way in which charge distributes near the interface between the ferroelectric and the oxide remains poorly known, which limits our understanding of such switching effects. Here we use a first-of-a-kind combination of scanning transmission electron microscopy with electron energy loss spectroscopy, near-total-reflection hard X-ray photoemission spectroscopy, and ab-initio theory to address this issue. We achieve a direct, quantitative, atomic-scale characterization of the polarization-induced charge density changes at the interface between the ferroelectric BiFeO3 and the doped Mott insulator Ca1-xCexMnO3, thus providing insight on how interface-engineering can enhance these switching effects., Work supported by ERC Consolidator grant MINT (Contract No. 615759)

VO2 thin films grown on SiOx/Si substrates have been characterized at the sub-nanometer level by Cs-corrected scanning transmission electron microscopy along with electron energy loss spectroscopy. Reduced transitional regions of 2–3 nm thick were found at both the surface and the interface, where the vanadium valence progressively changes from +4 to +2. The formation of these nanometer-thick surficial and interfacial layers can be interpreted as a unique case of prewetting, and it explains the degradation of metal-to-insulator transition properties in VO2 thin films.

This dossier in Comptes rendus Physique is devoted to the most recent technologies and methodologies in electron microscopy available in 2014, which have provided this instrument with unique capabilities for atomic-level investigations in the domain of materials science. The present introduction provides some basic information required for an easier reading of the following manuscripts. It therefore focuses on column design, signal acquisition strategy, aberration correction, resolving power, in situ experiments and novel approaches, illustrated with a description of a few of their present and future fields of use.

Over the past ten years, Scanning Transmission Electron Microscopes (STEM) fitted with Electron Energy Loss Spectroscopy (EELS) and/or Cathodoluminescence (CL) spectroscopy have demonstrated to be essential tools for probing the optical properties of nano-objects at sub-wavelength scales. Thanks to the possibility of measuring them at a nanometer scale in parallel to the determination of the structure and morphology of the object of interest, new challenging experimental and theoretical horizons have been unveiled. As regards optical properties of metallic nanoparticles, surface plasmons have been mapped at a scale unimaginable only a few years ago, while the relationship between the energy levels and the size of semiconducting nanostructures a few atomic layers thick could directly be measured. This paper reviews some of these highly stimulating recent developments.

International audience

The microstructures of epitaxial polycrystalline VO2 thin films grown on (0 0 1) sapphire were investigated by means of X-ray diffraction, Cs-corrected scanning transmission electron microscopy (STEM), in both plane and transverse geometry, in relation to its metal–insulator transition (MIT) properties. It is shown that the epitaxial relationship between the thin film and the substrate can be defined as out-of-plane twofold twinning symmetry {0 2 0}M//(0 0 6)S (where subscripts “M” and “S” denote the monoclinic phase of VO2 and the sapphire α-Al2O3 substrate, respectively) with in-plane threefold twinning structure (2 0 0)M//{1 1 0}S. The origin of these twinning structures is discussed: the in-plane threefold twinning structure comes from the threefold symmetry of the Al2O3 (0 0 1) plane, and the twofold twinning symmetry is induced by the MIT phase transition. The STEM planar view observations of the thin film demonstrate the presence of elongated grains down to nanoscale, with a high density of twin boundaries (TB). These TB are highly orientated into two sets of families. STEM low-angle annular dark-field imaging and STEM dark-field atomic displacement measurements evidence very different strain behaviors for these two TB families. Most of the TB and some of the smaller grains with typical dimensions of only a couple of nanometers exhibit locally an enhanced tetragonality. They are proposed to act as nucleation centers during the MIT process and then to influence the dynamics of the transition.

International audience; Over the past two or three decades, nanoscience and nanotechnology have clearly established themselves as prominent domains in research in physics, not only because of the innovative concepts and properties that they display but also for their capacity to generate many important applications and commercial developments. As many of these new devices exhibit a range of properties (transport, optical, magnetic, catalysis) which are governed by local structural and electronic configurations, such as coordination and bonding at the atomic level, it is no surprise that new tools of investigation are constantly being developed for imaging, analyzing, understanding and controlling at the relevant scale. Among them, electron microscopy has recently demonstrated its ability to meet many of these requirements. In particular, Å-sized probes are nowadays generated by aberration correctors in a scanning transmission electron microscope (STEM) and they can investigate the electron excitation spectrum of the specimen (through electron energy-loss spectroscopy, EELS) with a typical energy resolution of 0.1–0.3 eV over a broad spectral band from the IR to the X ray domain. In the high energy range, characteristic signals due to the excitation of atomic core levels are quite useful because they identify the atoms in the analyzed volume (which can itself be as small as a single atom) and can therefore deliver atomically-resolved elemental maps. But the pixel-by-pixel recording of the fine structures beyond the characteristic threshold is much more informative and tells us how the excited atom is surrounded by its neighbors, what is its exact structural environment and its charge population. The present review focuses on this particularly exciting field, with a special interest in the types of information accessible and their signature. After summarizing the ingredients required for successful experiments (instrumental as well as theoretical), examples encountered in different situations, in particular in single layers of 2D materials and at the interfaces in oxide heterostructures, will demonstrate the present capabilities of this STEM-EELS technique.

In the scanning transmission electron microscope, multiple signals can be simultaneously collected, including the transmitted and scattered electron signals (bright field and annular dark field or Z-contrast images), along with spectroscopic signals such as inelastically scattered electrons and emitted photons. In the last few years, the successful development of aberration correctors for the electron microscope has transformed the field of electron microscopy, opening up new possibilities for correlating structure to functionality. Aberration correction not only allows for enhanced structural resolution with incident probes into the sub-Angstrom range, but can also provide greater probe currents to facilitate mapping of intrinsically weak spectroscopic signals at the nanoscale or even the atomic level. In this issue of MRS Bulletin, we illustrate the power of the new generation of electron microscopes with a combination of imaging and spectroscopy. We show the mapping of elemental distributions at atomic resolution and also the mapping of electronic and optical properties at unprecedented spatial resolution, with applications ranging from graphene to plasmonic nanostructures, and oxide interfaces to biology.

The vibrational excitations of nanostructures have been mapped using state-of-the-art electron microscopy. The results improve our understanding of these excitations, which will aid the design of nanostructures. See Letter p.529 The vibrational excitations of nanostructures have a fundamental effect on their suitability for various electronic, optical and thermal applications. Maureen Lagos and colleagues probe these excitations, using state-of-the-art electron microscopy to map the vibrational modes both at the surface and within the body of individual nanoparticles. Such information not only contributes to our knowledge of these fundamental vibrational modes, but will also be valuable for the design and optimization of nanostructures for practical use.

In order to understand the beneficial role of yttrium in the creep of alumina, Z-contrast high-angle annular dark field (HAADF) imaging in a scanning electron microscope was used to reveal the distribution of yttrium segregation in the core of intergranular dislocations, namely disconnections, in a rhombohedral twin in alumina. The defects accommodate the tilt deviation from twin orientation and present a large step height. In the undoped bicrystal the dislocations appear most often dissociated into partials that delimit grain boundary (GB) segments with alternating structure. In the doped bicrystal, a strong yttrium segregation appears along the step, extending over several planes normal to the twin plane. Yttrium is segregated to the faulted part of the defect. Moreover, it appears segregated to the partial disconnection cores. It does not simply adopt the alumina structure but forms a new structure close to a YAlO3 compound. The formation of an ordered compound at the GB dislocation core strongly supports the hypothesis that a reduced creep rate results from a decrease in dislocation mobility during GB sliding.

The challenging problem of mapping the chemical composition of cation columns in individual nanocrystals at atomic resolution is addressed by using a method based on aberration-corrected electron microscopy, core-loss electron energyloss spectroscopy, and simulations. The potential of this novel approach to provide unique structural information, which is the key to rationalizing macroscopic behavior, is illustrated with the analysis of ceria–zirconia mixed oxides, which are nanomaterials with substantial technological impact. Metal nanoparticles supported on this family of oxides are currently materials of interest as catalysts in a variety of chemical transformations in the area of environmental protection, such as low-temperature water-gas shift, selective oxidation of CO in the presence of large amounts of hydrogen, or three-way catalysis. Strong variations in the chemistry of ceria–zirconia mixed oxide catalysts have been observed after they have undergone redox cycles involving reduction treatments at high temperatures ( 1173 K) then oxidation at mild temperatures ( 823 K). In particular their reducibility is significantly enhanced after such aging treatments. Scanning transmission electron microscopy (STEM) techniques have provided crucial information to account for these changes in the redox behavior. High-resolution electron microscopy (HREM) combined with high-angle annular dark-field (HAADF) imaging and tomography have revealed the occurrence of a disorder–order transformation in the cationic sublattice of these oxides, which tend to rearrange into a distribution characteristic of the so called pyrochlore phase. This phase is an archetype structure for A2B2O7 (A= + 3 cation, B=+ 4 cation) compounds and can be considered a fluorite superstructure. The structural transformation takes place during the reduction step of the cycle, in which the fully reduced mixed oxide with Ce/Zr molar ratio 1:1 adopts the Ce2Zr2O7 stoichiometry. Nevertheless, HAADF studies have clearly shown that, in the case of ceria–zirconia mixed oxides, this cation-ordered arrangement is preserved even after full reoxidation, that is, in the oxide with Ce2Zr2O8 stoichiometry, whenever the oxidation temperature does not exceed 823 K. Electron-microscopy studies have also revealed another remarkable feature of the ceria–zirconia aged oxides with the pyrochlore-type cation sublattice: the occurrence of compositional heterogeneities at the nanometer scale. Taking these observations into account and also considering that the disorder–order transition may not be completed in the time scale and under the temperature conditions used in the redox-cycling treatments, the important question arises whether these heterogeneities are in fact occurring on a finer scale, that is, at the atomic level. Such heterogeneities, compatible with the HREM and HAADF observations, will strongly influence the details of the counterpart oxygen sublattice and, consequently, the chemical and catalytic response of these oxides. To date, the atomic-column by atomic-column compositional analysis of the oxidized pyrochlore required to justify such a possibility has not been accomplished. Herein, using the capabilities of an aberration-corrected Nion UltraSTEM microscope (operated at 100 kV) we not only provide the first direct chemical evidence of the cationic order present in the Ce2Zr2O8 oxidized pyrochlore but we also show how atomicresolution electron energy-loss spectroscopy (EELS) mapping, based on core–shell ionization, can be combined with EELS image simulation to detect quite subtle local deviations in the cation sublattice from the completely ordered structure. This information provides a much more accurate structural description of the active catalyst nanocrystals, which must be considered to model both their oxygen-exchange capabilities and, eventually, their catalytic performance. [*] Dr. S. Trasobares, Dr. M. L pez-Haro, Dr. J. A. Perez-Omil, Dr. J. J. Calvino Departamento de Ciencia de los Materiales e Ingenier a Metalfflrgica y Qu mica Inorg nica Facultad de Ciencias, Universidad de C diz Campus Rio San Pedro, 11510-Puerto Real, C diz (Spain) Fax: (+34)956-016286 E-mail: susana.trasobares@uca.es Homepage: http://www.uca.es/tem-uca

Aberration-corrected scanning transmission electron microscopes can now raster Angstrom-sized electron probes across cross-sectional foils with interfaces parallel to the incident beam. Bright and annular dark field images deliver views of the structural arrangement of the atomic columns across such interfaces. In parallel, electron energy-loss spectroscopy is efficient for recording the electronic response of the specimen with a high level of spatial and energy resolution. It thus provides maps, atomic column by atomic column, of the nature, and in some cases of the bonding state, of the atoms across artificially grown heterolayers for electronics, spintronics, and photonics components.

Here, we demonstrate that non-dipole allowed d-d excitations in NiO can be measured by electron energy loss spectroscopy (EELS) in transmission electron microscopes (TEM). Strong excitations from (3)A(2g) ground states to (3)T(1g) excited states are measured at 1.7 and 3 eV when transferred momentum are beyond 1.5 A(-1). We show that these d-d excitations can be collected with a nanometrical resolution in a dedicated scanning transmission electron microscope (STEM) by setting a good compromise between the convergence angle of the electron probe and the collected transferred momentum. This work opens new possibilities for the study of strongly correlated materials on a nanoscale.

Electromagnetic response of individual boron nitride nanotubes (BNNTs) has been studied by spatially resolved electron energy loss spectroscopy (EELS). We demonstrate how dedicated EELS methods using subnanometer electron probes permit the analysis of local dielectric properties of a material on a nanometer scale. The continuum dielectric model has been used to analyze the low-loss EEL spectra recorded from these tubes. Using this model, we demonstrate the weak influence of the out-of-plane contribution to the dielectric response of BNNTs. The optical gap, which can be deduced from the measurements, is found to be equal to 5.8 ± 0.2 eV, which is close to that of the hexagonal boron nitride. This value is found to be independent of the nanotubes configuration (diameter, helicity, number of walls, and interaction between the different walls).

We report on the synthesis of C-BN single-walled nanotubes made of BN nanodomains embedded into a graphene layer. The synthesis process consists of vaporizing, by a continuous CO2 laser, a target made of carbon and boron mixed with a Co/Ni catalyst under N2 atmosphere. High-resolution transmission electron microscopy (HRTEM) and nanoelectron energy loss spectroscopy (nanoEELS) provide direct evidence that boron and nitrogen co-segregate with respect to carbon and form nanodomains within the hexagonal lattice of the graphene layer in a sequential manner. A growth model is proposed to account for the observed C-BN self-organization and to explain how kinetics and local energetics at intermediate states can tailor ultimate single layer BN-C heterojunctions.

Preformed clusters carrying surfactant are used as primary blocks for the building of nanostructures. Self-assembly of silver atom based clusters, soft landed on a HOPG surface, generates a large variety of new architectures depending on the nature and on the concentration on the impurities. Fractal shapes fragmentated into multiple compact islands, and chainlike structures might be formed. A strong local enhancement of the silver atom mobility at the surface of islands is responsible for those morphology changes. ispartof: The European Physical Journal D vol:43 issue:1 pages:151-154 ispartof: location:SWEDEN, Goteborg status: published

We report on the direct synthesis of different kinds of BN-C multi-walled and single-walled nanotubes exhibiting a segregation between BN and C domains. Multi-walled BN-C nanotubes (MW-BN/C-NTs) were synthesized using the aerosol method whereas single-walled BN-C nanotubes (SW-BN/C-NTs) have been for the first time produced using a continuous CO 2 -laser vaporization process [S. Enouz et al., to be published]. Degrees of purity, homogeneity and yield have been estimated from a systematic inspection of the samples by scanning electron microscopy. Structure of these tubes and spatial distribution of C, B and N as well as their chemical environments have been inspected at the nanometer scale by combining high resolution transmission microscopy and nano-electron energy loss spectroscopy. These analyses provide clear evidence of new kinds of arrangements of C, B and N within the graphene layer, which are due to the segregation properties of h-BN and graphite. Thus, combining BN and C elements into nanotubular systems can open the way to a broad range of new nanodevices.

The deposition of preformed clusters on surfaces offers new possibilities to build complex artificial nanostructures, the shape of which depends on the cluster size. We describe routes for generating unusual polymorphic nanoislands, which constitute unique platforms for exploring instabilities. As coverage increases, the constraints accumulated in such nanostructures induce spectacular flattening collapse processes, which are not observed when the constraints are imposed by the substrate.

International audience; The exact perovskite structure has simple cubic symmetry and composition ABO3, where A is a relatively large cation and B a smaller one. The choices of A and B cations and the substitutions possible on either site generate a large variety of materials sharing the same base, with relatively small distortions of the size and shape of the cube. As in addition, these oxides often admit oxygen non stoichiometry with or without order to the amount of several per cent, they finally form a vast set of technologically relevant materials: conducting, insulating, ferroelectric, magnetic, superconducting,.... Heteroepitaxy of perovskite oxides allows one to construct atomically sharp interfaces between these materials and therefore to envisage a set of useful heterojunctions. The epitaxy has side effects that may also prove useful: (1) it forces a chemical neighbouring that would not occur naturally, creating a two-dimensional third material, and (2) it imposes a lateral strain. Both of these effects allow one to explore novel, sometimes unforeseen, properties with a strong two-dimensional character. This paper first reviews some of the knowledge that has been accumulated on {100} surfaces and interfaces of perovskites, with an emphasis on properties that could be used in future all-oxide microelectronics. It then exposes the case of the interface between the half-metal La2/3Sr1/3MnO3 and the insulator SrTiO3, which plays a key role in the magnetoresistance of magnetic tunnel junctions. It particularly presents thorough electron energy loss spectroscopy measurements that uncover the atomic scale structural and electronic properties of these objects.

In this study, we have investigated the mineralogy present on the scaphognatite of the Rimicaris exoculata shrimp collected at a Mid-Atlantic Ridge hydrothermal vent. The structure, morphology and impurities of the minerals were analyzed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The main minerals observed were clusters of iron oxides found attached to the bacterial cells present on the setae of the scaphognatite. Structural investigations based on high-resolution electron microscopy and electron diffraction affirm that these clusters are composed of two-line ferrihydrite. The EELS measurements demonstrate that the ferrihydrite is bearing a mixed valence iron distribution and P, Si, Ca, N and Ni ions at impurity levels. The stability of this uncommon phase is then discussed based on work previously reported in literature for analogous poorly ordered iron oxides.

We use High Resolution Electron Microscopy (HRTEM) together with Electron Energy Loss Spectroscopy (EELS) to analyze the crystallography and the chemical configuration of interfaces in a state- of-the-art La2/3Sr1/3MnO3/SrTiO3/La2/3Sr1/3MnO3 tunnel junction. EELS indicates that manganese ions keep their bulk valency up to the last atomic plane in contact with the insulator. Tunnel magnetoresistance however decreases with temperature faster than magnetisation in these samples. Quantitative HRTEM reveals some local departures from chemical abruptness at the interfaces, which could play a role in this decrease.

In this paper, we propose a numerical method which can routinely improve the energy resolution down to 0.2–0.3 eV of electron energy-loss spectra acquired in a transmission electron microscope. The method involves measurement of the point-spread function (PSF) corresponding to the spectrometer aberration and to the incident energy spread, and then an inversion of this PSF so as to restore the spectrum. The chosen algorithm is based on an iterative calculation of the maximum likelihood solution known to be very robust against small errors in the PSF used. Restorations have been performed on diamond and graphite C-K edges acquired with an initial energy resolution of around 1 eV. After reconstruction, the sharp core exciton lines become clearly visible for both compounds and the final energy resolution is estimated to be about 200–300 meV. In the case of graphite, restorations involving both energy resolution and angular resolution have been successfully conducted. Finally, restorations of Fe L2,3 and O-K edges measured for various iron oxides will be shown.

A magnetic tunnel junction consists of two ferromagnetic conducting electrodes separated by an insulating thin layer. The performance of such a system strikingly depends on the last conducting atomic layers in contact with the insulator. Consequently, the present paper reports a nanoscale electron energy loss spectroscopy (EELS) study, which has been performed across a couple of La0.66Sr0.33MnO3,/SrTiO3/La0.66Sr0.33MnO3 tunnel junctions with different barrier thickness es (1.5 nm and 5 nm respectively). It aims at determining not only the chemical composition in the interface areas, but also the effect of the neighbouring atoms on their electronic structure. Using recent improvements in the STEM-EELS data acquisition and processing techniques (systematic use of spectrum-line and spectrum-image modes, multivariate statistical analysis, 2D energy deconvolution schemes, etc.), the local chemical information is better extracted with shorter acquisition times, while the large increase of the data set contributes to validate the results. Within the accuracy level of these measurements, the elemental composition of the different phases remains stable up to the interfaces with no evidence of extra doping. Furthermore, weak changes on the Mn-2p edge fine structures (weak shift to lower energy loss values and extra splitting on the top of the Mn L3 line are observed on all the interfaces. They are interpreted as a consequence of a slight reduction of the local Mn valence likely accompanied by a strain induced change in local symmetry. The discussion is focussed on all spectral changes identified at a (sub)nanometer scale and their potential effects on the degradation of magnetic and transport properties measured, close to room temperature, at a macroscopic level.

We studied shape relaxation of nano-fractal islands, during annealing, after their growth from antimony cluster deposition on graphite surface. Annealing at 180°C shows evidence of an increase of the fractal branch width with time followed by branch fragmentation, without changing the fractal dimension. The time evolution of the width of the arm suggests the surface self-diffusion mechanism as the main relaxation process. With Monte Carlo simulations, we confirmed the observed behavior. Comparison is done with our previous results on fragmentation of nano-fractal silver islands when impurity added to the incident cluster promotes rapid fragmentation by surface self-diffusion enhancement [1].

Electron Energy-Loss Spectroscopy (EELS) is a very well adapted tool to study the dielectric response of nanotubes. Due to the ‘curved anisotropy’ of such nano-objects, the interpretation of the EEL spectra is far from being straightforward and an adapted theoretical framework is then required. In this contribution, we extend the continuum dielectric approach to hollow anisotropic cylindrical nanoparticles, showing that the energy-loss probability can be handled both analytically and numerically.

The decomposition process of melamine exposed to a high-energy electron beam has been investigated by monitoring the changes in the energy loss near edge structures (ELNES) using time-resolved elec...

To investigate the dielectric response of isolated single-walled carbon nanotubes, (SWCNTs), spatially resolved electron energy-loss spectroscopy measurements have been carried out using a scanning transmission electron microscope in a near-field geometry. Spectra have been compared with those acquired on multiwalled carbon nanotubes (MWCNTs) made of different numbers of layers, and with simulations performed within the framework of the continuum dielectric theory, taking into account the local anisotropic character of these nanostructures and adapted to the cylindrical geometry. Experimental data show a dispersion of mode energies as a function of the ratio of the internal and external diameters, as predicted by the continuum dielectric model. For thin MWCNTs, two polarization modes have been identified at 15 and 19 eV, indexed as tangential and radial surface-plasmon modes, respectively, resulting from the coupling of the two surface modes on the internal and external surfaces of the nanotubes. We finally show that the dielectric response of a SWCNT, displaying a single energy mode at 15 eV, can be understood in the dielectric model as the thin layer limit of surface-plasmon excitation of MWCNTs.

CNx thin films have been prepared by ion beam assisted deposition (IBAD) varying the C-atom to N-ion ratio during deposition. The layers were studied by means of TEM and EELS investigation, ERDA and AES depth profiling. The obtained films were amorphous. The incorporation probability of N into the films was found to depend on the N/C arrival ratio. Large amount of N incorporation was found above and small amount below a N/C arrival rate of 0.3. Due to intentional change in the N/C arrival rate, modulated structures have been produced. The N concentration in the individual layers of modulated samples was found to exhibit distinct values of approximately 5 and 20 at.%. The erosion rate of the various CNx layers upon Ar+-ion bombardment depends on their N content. The relative erosion rate of the samples containing nitrogen of 20 and of 5 at.% was found to be rrel=r20%/r5%=1.6 (1.2 keV, 83° angle of incidence. It was determined by XTEM and EELS that the origin of the TEM image contrast marking out the individual sublayers is mainly due to density variations in the modulated structure and partly due to thickness differences of the cross sectional TEM samples as a result of Ar+ ion milling of layers of various compositions.

A systematic study of the effect of different synthesis parameters on N incorporation into C nanotubes is presented. CNx nanotubes prepared by catalyzed pyrolysis of melamine exhibit a highly compartmentalized morphology with a remarkable periodicity structure along the nanotube axis. Spatially resolved electron energy loss spectroscopy (spectrum-imaging mode) indicates that the nanotubes are made of carbon and nitrogen, inhomogeneously distributed with an enrichment of carbon on the external surfaces. The evolution of the C-K-edge shape across the nanotube reveals a transition from a graphitic stacking on the outside to a disorganized-mixed type in the core of the nanotube. For the N-K edge, the situation is more complex. The fine structure of the N-K edge differs depending on the used catalyst, which indicates differences in the bonding configuration. When Ni is used as a catalyst, N replaces C in the graphitic structure whereas C–N pyridinic-like bonds are formed when the catalyst is Fe. The compartmen...

Nanocrystals of a new CN phase of presumably orthorhombic type embedded in an amorphous CN x (x matrix produced by magnetron sputtering have been identified. The evidence for the co-existence of different phases in the sample is first given by spatially resolved electron energy loss spectroscopy (EELS). A mathematical treatment of collections of EELS spectra applied to the core-edge fine structures (energy loss near edge fine structures (ELNES)) was used to isolate the characteristic signature of the different phases. Electron diffraction patterns and high-resolution transmission electron microscopy images (HRTEM) were then carried out from areas displaying the characteristic identified ELNES to confirm the identification of the structure and chemistry of these nanocrystals.

We have performed electrical transport experiments on individual carbon nanotubes (CNTs) in situ in a transmission electron microscope using the liquid-metal contact method (LMC method), which consists of immersing a CNT placed on the apex of a metallic tip into a drop of liquid mercury (Hg). In the literature, this method has been mostly employed without visualization (ex situ) to show the ballistic- and quantum-conductance properties of different kinds of CNTs. We show that on the one hand the in situ LMC method is well suited to create low-resistance contacts with the CNTs but on the other hand the ballistic and quantum conductance measured by the ex situ LMC method is likely to give false positives for three reasons: (a) the CNTs are likely to be removed from the tip surface through contact with the Hg, (b) occurring Hg-tip surface nanocontacts are likely to be mistaken for quantum-conductor CNTs, and (c) occurring Hg nanomenisci are likely to be mistaken for ballistic-conductor CNTs. These findings have strong consequences for the interpretation of previously reported works., Physical Review B, 91(19), 195431; 2014

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N2 discharge, was studied for postdeposition annealing temperatures TA up to 1000 °C. Films were grown at temperatures of 100 °C (amorphous structure) and 350 and 550 °C (fullerenelike structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure, and mechanical properties as a function of TA and annealing time. All properties investigated were found to be stable for annealing up to 300 °C for long times (>48 h). For higher TA, nitrogen is lost from the films and graphitization takes place. At TA = 500 °C the graphitization process takes up to 48 h while at TA = 900 °C it takes less than 2 min. A comparison on the evolution of x-ray photoelectron spectroscopy, electron energy loss spectroscopy and Raman spectra during annealing shows that for TA > 800 °C, preferentially pyridinelike N and –C≡N is lost from the films, mainly in the form of molecular N2 and C2N2, while N substituted in graphite is preserved the longest in the structure. Films deposited at the higher temperature exhibit better thermal stability, but annealing at temperatures a few hundred degrees Celsius above the deposition temperature for long times is always detrimental for the mechanical properties of the films.

The deposition of preformed clusters on surfaces has been established as a new way for growing nano-suctures on surfaces. It has been shown that supported island morphology relies on the dynamics of clusters, during the growth, giving rise to shapes from compact to ramified types. This paper identifies and discusses, in the case of antimony cluster deposits, several processes responsible for the non-equilibrium island shapes: limited kinetic cluster aggregation, size dependent coalescence, “wetting-like behavior” of antimony clusters on antimony islands. Using successive predetermined cluster sizes during the deposition process to synthesize polymorphic structure involves the interplay of those mechanisms.

Different spatially resolved electron energy-loss spectroscopy (EELS) experiments on individual nanotubes performed in the context of a scanning transmission electron microscope (STEM) are presented. The capabilities of EELS for probing the local anisotropy of the unoccupied electronic states are demonstrated and the effects of the graphite network curvature on the nature of the chemical bonding is investigated. The peculiarity of the valence electron excitation modes in carbon nanotubes due to the curved anisotropy is also pointed out through near-field EELS experiments.

Following the discovery of the fullerene molecules, multishell cage structures and nanotubes have been produced with carbon, boron nitride, and other planar uniaxial materials. These particles which are typically a few tens of nanometers in size, present a peculiar ‘in-shell’ anisotropy and a hollow inner cavity. We have developed a dielectric formalism for the resolution of Maxwell’s equations which takes into account these peculiarities. In the present contribution, we will emphasise the consequences of the anisotropy on the surface modes plasmon of nanoparticles.

The reversibility of metal–support interaction effects in NM/CeO2 catalysts (NM: Rh, Pt) is investigated using high-resolution electron microscopy and electron energy loss spectroscopy. Reoxidation treatments at 773 K followed by a mild reduction at 473 K are not effective in recovering ceria-based systems from the decorated or alloyed states observed upon high-temperature reduction (T red>973 K).

Mixed-phase WxMoyCzS2 nanotubes are generated when N2/H2S is passed over a preoxidized mixture of WC and MO2C, maintained at an elevated temperature.