electron energy loss spectroscopy (EELS)

Microstructural, δ(13)C isotope and C/N ratio investigations were conducted on excavated material from the black Younger Dryas boundary in Lommel, Belgium, aiming for a characterisation of the carbon content and structures. Cubic diamond nanoparticles are found in large numbers. The larger ones with diameters around or above 10 nm often exhibit single or multiple twins. The smaller ones around 5 nm in diameter are mostly defect-free. Also larger flake-like particles, around 100 nm in lateral dimension, with a cubic diamond structure are observed as well as large carbon onion structures. The combination of these characteristics does not yield unique evidence for an exogenic impact related to the investigated layer.

Doped metal oxides are plasmonic materials that boast both synthetic and postsynthetic spectral tunability. They have already enabled promising smart window and optoelectronic technologies and have been proposed for use in surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications. Herein, we report the first step toward realization of the former utilizing cubic F and Sn codoped In 2 O 3 nanocrystals (NCs) to couple to the C−H vibration of surface-bound oleate ligands. Electron energy loss spectroscopy is used to map the strong near-field enhancement around these NCs that enables localized surface plasmon resonance (LSPR) coupling between adjacent nanocrystals and LSPR-molecular vibration coupling. Fourier transform infrared spectroscopy measurements and finite element simulations are applied to observe and explain the nature of the coupling phenomena, specifically addressing coupling in mesoscale assembled films. The Fano line shape signatures of LSPR-coupled molecular vibrations are rationalized with two-port temporal coupled mode theory. With this combined theoretical and experimental approach, we describe the influence of coupling strength and relative detuning between the molecular vibration and LSPR on the enhancement factor and further explain the basis of the observed Fano line shape by deconvoluting the combined response of the LSPR and molecular vibration in transmission, absorption and reflection. This study therefore illustrates various factors involved in determining the LSPR−LSPR and LSPR−molecular vibration coupling for metal oxide materials and provides a fundamental basis for the design of sensing or SEIRA substrates.

Core and low energy electronic excitations have been studied in hexagonal boron nitride. Electron energy loss spectra have been measured using an electron microscope equipped with a monochro-mator and an in-column filter. Energy filtered diffraction patterns have been recorded and provide us with a global view of anisotropic effects in reciprocal space. From combined angular and energy resolved measurements, we analyze the symmetry of the losses as a function of the energy transferred to the material. As an example we show how easily the core loss spectra at the K edges of boron and nitrogen can be measured and imaged. Low losses associated to interband and/or plasmon excitations are also measured and discussed from ab initio calculations. This electronic inelastic scattering technique is shown to provide results comparable to those obtained from non resonant X-ray inelastic scattering. Both techniques are complementary: X-ray scattering is more accurate at large q wave vector whereas electron spectroscopy is more accurate at low q and is an attractive tool to study excitonic effects, which are inaccessible by optical techniques. Furthermore the method is fast and local, at a nanoscale level, and is very promising for studying two dimensional materials and related heterostructures.

Auger electron (AES), electron energy loss (EELS) and X-ray photoelectron spectroscopy (XPS) were used to identify the reaction products at the fibre-matrix interface in SiC nicalon fibre-LAS (Li2O, Al2O3, SiO2) or LAS + Nb2O5 glass matrix composites. Chemical bonding of the different elements was investigated by AES using sputter-depth profiling on fibres extracted from two matrices by etching in hydrofluoric acid. The chemistry of the silicium was studied by EELS in nicalon-LAS + Nb2O5 composite cross-sections. XPS was performed on fibres extracted from the nicalon-LAS + Nb2O5 composite to confirm EELS and AES results. These investigations show that in both composites the reaction scale at the fibre-matrix interface consists of a carbon layer next to the matrix and of a silicate phase rich in oxygen which contains carbon, probably in the form of a silicon oxycarbide, and which is located between the carbon layer and the fibre core.

The thermal behaviour of [Ba(C2H6O2)4][Sn(C2H4O2)3] used as a BaSnO3 precursor, and its phase evolution during thermal decomposition are described. The initially formed transient barium tin oxycarbonate phase disintegrates into BaCO3 and SnO2, reacting subsequently to BaSnO3. The existence of the intermediate oxycarbonate phase is evidenced by Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD) and electron energy loss spectroscopy (EELS (ELNES)) investigations.

The low loss (i.e. the valence band) portion of transmission electron energy loss spectroscopy (EELS) spectrum comprises of very high signal (as well as high signal to noise ratio for many excitations) with rich information embedded in it about electronic and optical properties of solids. There are, however, clear interpretation problems in low loss EELS owing to the complexity of electronic transitions in multi-component systems (e.g. high T c oxides) and the perennial multiple scattering which masks real information, and considerable deconvolution (often dicy) is necessary before useful information can be obtained. This paper briefly reviews the relevant aspects of low loss EELS in the context of electronic structure and spectral excitations in oxide superconductors. Particular attention is paid to the details of various corrections and deconvolution procedures, illustrated with examples of oxide superconductors. It is shown that a prudent combination of careful experiments, appropriate deconvolution procedures and conservative interpretation are key to successful application of this technique. This review argues that low loss EELS is a viable technique even for complex oxides as in superconductors.

Because of the large energy separation between O-K and Mo-L2,3 edges, extracting precise and reliable chemical information from core-loss EELS analyze of molybdenum oxides has always been a challenge. In this regard Mo-M2,3 edges represents an interesting alternative as they are situated close to the O-K edges. They should allow thus the extraction of a wealth of chemical information from the same spectra. However the main difficulty to overcome in order to work properly with these edges is the delayed maxima of the Mo-M4,5 edges which hinders the automated background subtraction with the usual inverse power low function. In this study we propose another background subtraction method specifically designed to overcome this obstacle and we apply it to the study of MoO3 and MoO2. We are able to show that quantitative chemical information can be precisely and accurately determined from the joined analyze of O-K and Mo-M2,3 edges. In particular k-factors are derived as a function of the integration window width and standard errors close to 2% are reported. The possibility to discriminate the two oxides thanks to chemical shifts and energy-loss near-edge structures is also investigated and discussed. Furthermore the M3/M2 ratios are derived and are found to be strongly dependent on the local chemical environment. This result is confirmed by multiplet calculations for which the crystal field parameters have been determined by ab initio calculations. The whole methodology as well as the conclusions presented in this paper should be easily transposable to any transitions metal oxides of the 4d family. This work should open a new and easier way regarding the quantitative EELS analyses of these compounds.

Hydrogenated amorphous carbon thin films (a:C-H) are very promising materials for numerous applications. The growing of relevance of a:C-H is mainly due to the long-term stability of their outstanding properties. For improving their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, electron energy-loss spectroscopy (EELS), developed in a transmission electron microscope (TEM), was the technique of choice to extract such kind of quantitative information on these materials. Other optical techniques, as Raman spectroscopy, are now clearly favored by the scientific community. However, they still lack of

Experimental and theoretical studies of the linear and nonlinear optical susceptibilities for single crystals of potassium titanyl phosphate KTiOPO₄ are reported. The state-of-the-art full potential linear augmented plane wave method, based on the density functional theory, was applied for the theoretical investigation. The calculated direct energy band gap at Γ, using the Engel-Vosko exchange correlation functional, is found to be 3.1 eV. This is in excellent agreement with the band gap obtained from the experimental optical absorption spectra (3.2 eV). We have calculated the complex dielectric susceptibility ε(ω)dispersion, its zero-frequency limit ε₁(0) and the birefringence of KTiOPO₄. The calculated birefringence at the zero-frequency limit Δn(0) is equal to about 0.07 and Δn(ω) at 1.165 eV (λ = 1064 nm) is 0.074. We also report calculations of the complex second-order optical susceptibility dispersions for the principal tensor components: χ₁₁₃((2))(ω), χ₂₃₂((2))(ω), χ₃₁₁((2))(ω), χ₃₂₂((2))(ω), and χ₃₃₃((2))(ω). The intra- and interband contributions to these susceptibilities are evaluated. The calculated total second order susceptibility tensor components |χ(ijk)((2))(ω)| at λ = 1064 nm for all the five tensor components are compared with those obtained from our measurements performed by nanosecond Nd:YAG laser at the fundamental wavelength (λ = 1064 nm). Our calculations show reasonably good agreement with our experimental nonlinear optical data and the results obtained by other authors. The calculated the microscopic second order hyperpolarizability, β₃₃₃, vector component along the dipole moment direction for the dominant component χ₃₃₃((2))(ω) is found to be 31.6 × 10⁻³⁰ esu, at λ = 1064 nm.

Due to their large specific surface and their abundance, micro and nano particles play an important role in the transport of micropollutants in the environment. Natural particles are usually composed of a mixture of inorganic amorphous or crystalline material (mainly FeOOH, Fe(x)Oy, Mn(x)Oy and clays) and organic material (humics and polysaccharides). They all tend to occur as very small particles (1-1,000 nm in diameter). Most natural amorphous particles are unstable and tend to transform with time towards more crystalline forms, either by aging or possibly, by dissolution and re-crystallization. Such transformations affect the fate of sorbed micropollutants and the scavenging properties are therefore changed. As these entities are sensitive to dehydration (aggregation, changes in the morphology), it is highly important to observe their morphology in their natural environment and understand their composition at the scale of the individual particles. Also for the understanding and o...

One-dimensional wires are known to be inherently unstable at finite temperature. Here, we show that long-range order of atomic Au double chains adsorbed on a Si(553) surface is not only stabilized by interaction with the substrate, but spontaneous self-healing of structural defects is actually enforced by the adsorption of atomic species such as Au or H. This is true even for random adsorbate distribution. Combining atomistic models within density functional theory with low energy electron diffraction and high-resolution electron energy loss spectroscopy, we demonstrate that this apparently counterintuitive behavior is mainly caused by adsorption-induced band filling of modified surface bands, i.e., by the strong electronic correlation throughout the whole terrace. Although adsorption preferably occurs at the step edge, it enhances the dimerization and the stiffness of the Au dimers. Thus, the intertwinement of quasi-1D properties with delocalized 2D effects enforces the atomic wire order. The reduction of size and dimensionality of metallic objects gives rise to peculiar physical properties such as quantization of conductance, spin-charge separation, charge and spin density waves, and Luttinger liquid behavior [1-5], which are subject of fundamental studies on low-dimensional physics. Unfortunately, free-standing metallic wires cannot be realized due to their inherent instability [5]. This problem can be partially circumvented by the formation of self-assembled, metallic atomic chains on stepped semiconductor surfaces such as Ge and Si, which are regarded as the low-end limit for long-range ordered nano-structures [6-15]. Several realizations of such wire systems have been reported [11,16-21]. While structural embedding is a prerequisite for the realization of 1D wires, the coupling to higher dimensions implies an intricate balance between preservation and destruction of typical 1D instabilities [22]. On the other hand, the coupling to higher dimensions can be exploited to tune wire properties such as morphology and conductivity. Here, we demonstrate a quite unique and unexpected example thereof: the enhanced and even enforced order of atomic chains by random adsorption of atoms, as a new mechanism of crossover between 1D and 2D properties. This behavior is in striking contrast to previously investigated adsorbates, which adsorb at random for low concentrations and thus introduce disorder. While an increased order might be expected if the adsorbates build patterns with the same periodicity of existing structures on the surface, it appears counterintuitive as a consequence of randomly distributed adatoms. Among the metallic wires grown on regularly stepped surfaces, the Si(553)-Au is one of the most studied systems, due to its relatively high stability, and because of a long-standing debate concerning its exact atomic structure [11,18,19,23-27]. It is commonly accepted that the system features a Si honeycomb and a Au double chain on each terrace. The Au chain is dimerized (even in the absence of adsorbates), which leads to a ×2 periodicity along the terraces. Several attempts to tune the conductivity of this system by deposition of oxygen [28,29] or hydrogen [30-32] are available in the literature. They demonstrate an intricate scenario with adsorbate specific modifications of the electronic structure. Generally, different adsorption sites of similar energy are available on the surface, leading to a random adsorbate distribution and a complex modification of the electronic structure. In this Letter, we demonstrate the improvement of the dimerized Au chain order simply by adsorption of small amounts of surplus Au, or of atomic H at room temperature. Since these adsorbates, as shown in the following, adsorb at random sites, this effect does not depend on the formation of ordered adsorbate arrays. Density functional theory (DFT) calculations show that the observed behavior stems from the coupling of the 1D atomic chains to higher dimensions. The electronic structure is modified by the effective electron donation from the adsorbates. The latter affects nonlocally the atomic arrangement of the whole terrace, demonstrating the extreme electronic correlation in this quasi-1D system. The rearranged structure is by far less PHYSICAL REVIEW LETTERS 126, 106101 (2021)

The large-scale production of graphene and reduced-graphene oxide (rGO) requires low-cost and eco-friendly synthesis methods. We employed a new, simple, cost-effective pyrolytic method to synthetize oxidized-graphenic nanoplatelets (OGNP) using bamboo pyroligneous acid (BPA) as a source. Thorough analyses via high-resolution transmission electron microscopy and electron energy-loss spectroscopy provides a complete structural and chemical description at the local scale of these samples. In particular, we found that at the highest carbonization temperature the OGNP-BPA are mainly in a sp2 bonding configuration (sp2 fraction of 87%). To determine the electrical properties of single nanoplatelets, these were contacted by Pt nanowires deposited through focused-ion-beam-induced deposition techniques. Increased conductivity by two orders of magnitude is observed as oxygen content decreases from 17% to 5%, reaching a value of 2.3 × 103 S m−1 at the lowest oxygen content. Temperature-dependent conductivity reveals a semiconductor transport behavior, described by the Mott three-dimensional variable range hopping mechanism. From the localization length, we estimate a band-gap value of 0.22(2) eV for an oxygen content of 5%. This investigation demonstrates the great potential of the OGNP-BPA for technological applications, given that their structural and electrical behavior is similar to the highly reduced rGO sheets obtained by more sophisticated conventional synthesis methods.

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.

Indium tin oxide (ITO) is a semiconducting material combining high conductivity and high transparency in the visible range. It is the most widely used transparent conducting oxide in applications such as flat panel displays. In this work, ITO thin films were deposited by pulsed laser deposition (PLD) onto transparent glass substrates. The substrate temperature and oxygen pressure during deposition were controlled to generate a variety of microstructures and electro-optical properties. Similar film thicknesses were used to avoid any change of carrier concentration. The dielectric function and complex refractive index were derived using spectroscopic ellipsometry and electron energy loss spectroscopy.

The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB2 (60:40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiBxCy) or mixed binary (TiB2 and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K- and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiBxCy compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiBxCy phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.

Dielectric properties of α-MoO3 are investigated by a combination of valence electron-energy loss spectroscopy and ab initio calculation at the random phase approximation level with the inclusion of local-field effects (LFE). A meticulous comparison between experimental and calculated spectra is performed in order to interpret calculated dielectric properties. The dielectric function of MoO3 has been obtained along the three axes and the importance of LFE has been shown. In particular, taking into account LFE is shown to be essential to describe properly the intensity and position of the Mo-N2,3 edges as well as the low energy part of the spectrum. A detailed study of the energy-loss function in connection with the dielectric response function also shows that the strong anisotropy of the energy-loss function of α-MoO3 is driven by an anisotropic influence of LFE. These LFE significantly dampen a large peak in ε2, but only along the [010] direction. Thanks to a detailed analysis at specific k-points of the orbitals involved in this transition, the origin of this peak has not only been evidenced but a connection between the inhomogeneity of the electron density and the anisotropic influence of local-field effects has also been established. More specifically, this anisotropy is governed by a strongly inhomogeneous spatial distribution of the empty states. This depletion of the empty states is localized around the terminal oxygens and accentuates the electron inhomogeneity.

These studies have utilized a range of state-of-the-art surface techniques to gain insight into the mechanism of action of a new technology for dentin hypersensitivity relief based upon arginine and calcium carbonate and, in particular, to address important questions regarding the nature and extent of dentin tubule occlusion. Confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) have been used to assess tubule occlusion. Energy dispersive x-ray (EDX) and electron spectroscopy for chemical analysis (ESCA) have been used to identify the composition of the dentin plug. CLSM has also been used to compare the mechanism of action of the toothpaste and the desensitizing prophylaxis paste, to address whether both the arginine and the calcium carbonate components are essential to occlusion, to identify the location of the arginine within the occluded dentin, and to demonstrate resistance of the occlusion to acid challenge. Hydraulic ...