Electron Energy Loss Spectroscopy Techniques Research Articles

Association of iron oligomeric species with natural organic matter: a combined EELS and Mössbauer investigation

The nature of the interaction between iron oxyhydroxide compounds and natural organic matter (NOM) may take various forms and is still a matter of debate. It is an important field to understand, especially for water treatment applications and for the knowledge of iron transport in the environment. The nature of association reached between iron oligomeric species and NOM is here investigated using Mossbauer spectroscopy and electron energy-loss spectroscopy (EELS) at the Fe-L3 edge. Raw water NOM taken from Moselle River (France), natural humic substances extracted from the riverine suspended matter, and a synthesized humic-like substance, are coagulated with iron nitrate according to a jar-test procedure. The results from Mossbauer spectroscopy indicate that Fe is present in an octahedral coordination environment, which is consistent with prior X-ray absorption spectroscopy reported in the literature. The areas beneath the peaks (Fe L3 edge) and the peak shapes of EELS spectra differ according to the origin of the organic matter, suggesting that various types of Fe populations can be distinguished using the EELS technique. Combining the selectivity of both Mossbauer spectroscopy for identifying trace, poorly crystalline Fe solids, oxidation state and of EELS for being able to characterize the population of Fe based on L-edge spectra, appears promising for characterizing Fe in systems containing NOM.

Analytical TEM study of CVD diamond growth on TiO2 sol–gel layers

The early growth stages of chemical vapor deposition (CVD) diamond on a sol–gel TiO2 film with buried ultra dispersed diamond seeds (UDD) have been studied. In order to investigate the diamond growth mechanism and understand the role of the TiO2 layer in the growth process, high resolution transmission electron microscopy (HRTEM), energy-filtered TEM and electron energy loss spectroscopy (EELS) techniques were applied to cross sectional diamond film samples.We find evidence for the formation of TiC crystallites inside the TiO2 layer at different diamond growth stages. However, there is no evidence that diamond nucleation starts from these crystallites. Carbon diffusion into the TiO2 layer and the chemical bonding state of carbon (sp2/sp3) were both extensively investigated. We provide evidence that carbon diffuses through the TiO2 layer and that the diamond seeds partially convert to amorphous carbon during growth. This carbon diffusion and diamond to amorphous carbon conversion make the seed areas below the TiO2 layer grow and bend the TiO2 layer upwards to form the nucleation center of the diamond film. In some of the protuberances a core of diamond seed remains, covered by amorphous carbon. It is however unlikely that the remaining seeds are still active during the growth process.

Ion beam sputter-deposition of LiCoO2 films

LiCoO2 films, 200nm in thickness, are produced by ion beam sputter-deposition. The structural, electrical and electrochemical properties of the films are studied by means of X-ray diffraction (XRD), electrical direct-current-measurements, and electron energy loss spectroscopy (EELS). The influence of preparation parameters like substrate temperature or oxygen partial pressure, are explored. While an oxygen deficiency was observed in films sputtered under pure argon atmosphere, the oxygen content of the thin films increases, significantly, in case of films sputtered under addition of O2. At substrate temperatures below 300°C, XRD measurements reveal a lattice structure similar to the low-temperature-phase, while the formation of the high-temperature-phase is clearly observed at temperatures above 500°C and an Argon/Oxygen ratio of 3/2. Furthermore, the EELS technique is demonstrated to be a sensitive tool to characterize the lithiation state of the sputter-deposited thin films.

From electron energy-loss spectroscopy to multi-dimensional and multi-signal electron microscopy

This review intends to illustrate how electron energy-loss spectroscopy (EELS) techniques in the electron microscope column have evolved over the past 60 years. Beginning as a physicist tool to measure basic excitations in solid thin foils, EELS techniques have gradually become essential for analytical purposes, nowadays pushed to the identification of individual atoms and their bonding states. The intimate combination of highly performing techniques with quite efficient computational tools for data processing and ab initio modeling has opened the way to a broad range of novel imaging modes with potential impact on many different fields. The combination of Angström-level spatial resolution with an energy resolution down to a few tenths of an electron volt in the core-loss spectral domain has paved the way to atomic-resolved elemental and bonding maps across interfaces and nanostructures. In the low-energy range, improved energy resolution has been quite efficient in recording surface plasmon maps and from them electromagnetic maps across the visible electron microscopy (EM) domain, thus bringing a new view to nanophotonics studies. Recently, spectrum imaging of the emitted photons under the primary electron beam and the spectacular introduction of time-resolved techniques down to the femtosecond time domain, have become innovative keys for the development and use of a brand new multi-dimensional and multi-signal electron microscopy.

Local order of Ca in a CaF2–Al2O3–SiO2 glass by electron energy-loss spectroscopy

Local order of Ca in a CaF2–Al2O3–SiO2 glass is studied using electron energy loss spectroscopy technique. The energy shift of ionization threshold in the Ca L2,3 and the differences in the near-edge structure of the Ca M2,3 edge between the glasses with and without F suggest the local ordering of F around Ca in the F-containing aluminosilicate glass. The local order phenomenon requires the clustering of Ca–F. Therefore, the transparent fluorinated calcium aluminosilicate glass is not structurally and compositionally homogeneous at nanometer scale.

Application of Electron Energy-Loss Spectroscopy (EELS) and Energy-Filtered Transmission Electron Microscopy (EFTEM) to the Study of Mineral Transformation Associated with Microbial Fe-Reduction of Magnetite

AbstractElectron energy-loss spectroscopy (EELS), energy-filtered transmission electron microscopy (EFTEM), and high-resolution transmission electron microscopy (HRTEM) have been applied in mineralogy and materials research to determine the oxidation states of various metals at high spatial resolution. Such information is critical in understanding the kinetics and mechanisms of mineral–microbe interactions. To date, the aforementioned techniques have not been applied widely in the study of such interactions. In the present study, the three techniques above were employed to investigate mineral transformations associated with microbial Fe(III) reduction in magnetite. Shewanella putrefaciens strain CN32, a dissimilatory metal-reducing bacterium, was incubated with magnetite as the sole electron acceptor and lactate as the electron donor for 14 days under anoxic conditions in bicarbonate buffer. The extent of bioreduction was determined by wet chemistry and mineral solids were investigated by HRTEM, EFTEM, and EELS. Magnetite was partially reduced and biogenic siderite formed. The elemental maps of Fe, O, and C and red-green-blue (RGB) composite map for residual magnetite and newly formed siderite were contrasted by the EFTEM technique. The HRTEM revealed nm-sized magnetite crystals coating bacterial cells. The Fe oxidation state in residual magnetite and biogenic siderite was determined using the EELS technique (the integral ratio of L3 to L2). The integral ratio of L3 to L2 for magnetite (6.29) and siderite (2.71) corresponded to 71% of Fe(III) in magnetite, and 24% of Fe(III) in siderite, respectively. A chemical shift (~1.9 eV) in the Fe-L3 edge of magnetite and siderite indicated a difference in the oxidation state of Fe between these two minerals. Furthermore, the EELS images of magnetite (709 eV) and siderite (707 eV) were extracted from the electron energy-loss spectra collected, ranging from 675 to 755 eV, displaying different oxidation states of Fe in the magnetite and siderite phases. The results demonstrate that EELS is a powerful technique for studying the Fe oxidation-state change as a result of microbial interaction with Fe-containing minerals.

Transmission electron microscopy analysis of octanethiol-coated Cu powders

In this study, microstructures of Cu powders coated with octanethiol were analyzed using (scanning) transmission electron microscopy. Moreover, aging process of the octanethiol-coated layer as time passes by was analyzed using the electron energy loss spectroscopy technique. The octanethiol layer coated on the surface of Cu powders was kept until it was exposed to air for around 30 days. As days passes by, the coating layer had been decomposed and then a Cu(2)O layer was formed on the surface of powders.

Magnetic Nanoparticles-Templated Assembly of Protein Subunits: A New Platform for Carbohydrate-Based MRI Nanoprobes

A new approach for the preparation of carbohydrate-coated magnetic nanoparticles is reported. In a first step, we show that the pH-driven assembly-disassembly natural process that occurs in apoferritin protein is effective for the encapsulation of maghemite nanoparticles of different sizes: 4 and 6 nm. In a second step, we demonstrate that the presence of functional amine groups in the outer shell of apoferritin allows functionalization with two carbohydrates, N-acetyl-D-glucosamine and d-mannose. High-resolution electron microscopy (HREM), high angle annular dark field scanning electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and SQUID technique have been used to characterize the magnetic samples, termed herein Apomaghemites. The in vivo magnetic resonance imaging (MRI) studies showed the efficiency in contrasting images for these samples; that is, the r(2) NMR relaxivities are comparable with Endorem (a commercial superparamagnetic MRI contrast agent). The r(2) relaxivity values as well as the pre-contrast and post-contrast T(2)*-weighted images suggested that our systems could be used as perspective superparamagnetic contrast agents for magnetic resonance imaging (MRI). The carbohydrate-functionalized Apomaghemite nanoparticles retained their recognition abilities, as demonstrated by the strong affinity with their corresponding carbohydrate-binding lectins.

Process-Induced Damage Characterization of Patterned Low-κ Film Using Electron Energy Loss Spectroscopy Technique

A patterned low dielectric constant (κ) film composed of a porous Si–O–C layer (p-SiOC) and a Cu interconnect is characterized by electron energy loss spectroscopy (EELS) with transmission electron microscopy. The relative thickness distribution map is obtained by the valence EELS (VEELS) log-ratio technique with nanometer scale resolution. Two regions with depleted carbon composition and varied relative thickness are found in the p-SiOC layer near the side wall of Cu lines, which are ascribed to the process-induced damage. They cannot be identified only by the conventional elemental mapping obtained by the core EELS (CEELS). Since the VEELS log-ratio technique is convenient to perform, this should be a useful method to routinely characterize the process-induced damage of the patterned low-κ films with Cu interconnects for advanced integration devices.

Scaling Dopant States in a Semiconducting Nanostructure by Chemically Resolved Electron Energy-Loss Spectroscopy: A Case Study on Co-Doped ZnO

Dilute dopant introduces foreign states to the electronic structures of host semiconductors and imparts intriguing properties to the materials. Identifying and positioning the dopant states are of crucial importance for seeking the underlying mechanism in the doped systems. However, such determination has still been challenging, particularly for individual nanostructured materials, due to the lack of the spectroscopic probe that possesses both nanometer spatial resolution and chemical resolution. Here, we shall demonstrate the successful scaling of dopant states of individual semiconducting nanostructures by chemically resolved electron energy-loss spectroscopy (EELS), taking the individual Co-doped ZnO nanorods as an example. Guided by the Co dopant spatial distribution mapped by the core-loss EELS technique, chemical resolution is achieved in the accumulated valence electron energy-loss spectra. Three Co dopant states are successfully identified and positioned in the host ZnO bands. Furthermore, the electron extension degrees of the Co dopant states are assessed on the basis of the multiple-atom effect. The above experimental inputs optimize the density functional theoretical calculations, which generates the corrected full electronic structures of (Zn,Co)O dilute magnetic semiconductors. These results give a carrier-mediated interpretation for the room-temperature ferromagnetism of Co-doped ZnO nanostructures based on a recent theory.

Adhesion and the cold welding of gold-silver thin films

This paper presents the results of a combined experimental and theoretical study of adhesion in cold-welded Au–Ag interfaces that are relevant to the fabrication of organic electronic structures. Focused ion beam /transmission electron microscopy and electron energy loss spectroscopy techniques are used to reveal interfacial impurities associated with the cold welding of nanoscale Au and Ag thin films. A theoretical model is also developed and used to predict the contact profiles around impurities between cold-welded thin films. The model is shown to provide new insights into how adhesion affects the surface contacts that occur during cold welding. The implications of the results are then discussed for the design of cold-welding processes.

Low-energy vibrational excitation cross section of multilayers of CO molecules on graphite using electron scattering

This paper presents a low-energy study of the vibrational excitation cross section of 50 layers of CO molecules on graphite at 23 K using the electron energy loss spectroscopy technique. The vibrational excitation cross section or the excitation curve is presented for two different scattering angles. The results show an energy dependence of the vibrational excitation cross section, at both angles, which indicates the formation of negative ion resonance in this adsorbed phase of CO on graphite. The data show an oscillatory structure in the region between 0.5 and 3 eV that is associated with the excitation of the 2Π state.

Radiation damage in zircon by high-energy electron beams

Radiation damage induced by high-energy (200 keV) electron irradiation in zircon has been studied thoroughly using imaging, diffraction, and electron energy-loss spectroscopy techniques in transmission electron microscopy. Both structural and compositional changes during the damage were measured using the above techniques in real time. It was found that the damage was mainly caused by the preferential sputtering of O. The loss of O occurred initially within small sporadic regions with dimension of several nanometers, resulting in the direct transformation of zircon into ZrxSiy. These isolated patches gradually connect each other and eventually cover the whole area of the electron beam. These differ from the previous observations either in the self-irradiated natural and synthetic zircon or in ion-beam irradiated thin zircon specimen.

Deposit of glass fragments during femtosecond laser penetrating keratoplasty

To evaluate femtosecond laser interaction with the applanation lens during pre-programmed penetrating keratoplasty corneal cuts. Three different-shaped penetrating keratoplasty dissections were performed on edematous corneas from bank eyes using a clinical femtosecond laser system (Intralase FS60) with energies higher than 2 microJ, and the "depth into glass" parameter at 50 microm, which is defined as the length over which the laser interacts with the glass of the applanation cone in contact with the cornea. Additional full-thickness corneal incisions were obtained with an experimental laser source with technical characteristics similar to the clinical laser. Following cutting, tissue sections were examined by optical microscopy (OM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). After the procedure, the cones were examined by optical and scanning electron microscopy (SEM). A control was obtained by repeating the procedures and stopping the laser at the cornea-lens interface. OM and TEM analysis of the tissue showed the presence of solid particles of a maximum dimension of 1.5 mum on the epithelium and the anterior stroma, regardless of the laser system used to cut. The EELS technique revealed their composition as silicon dioxide. We believe that the fragments originate from the applanation cone, which is machined by the laser interacting with the glass in contact with cornea. This is consistent with the structures observed on the lens by OM and SEM. Radial and circumferential tracks on the surface of the lens are visible, corresponding to the laser path in penetrating keratoplasty protocols. No particles were found in the control samples. When performing penetrating keratoplasty corneal cuts by infra-red femtosecond laser, the applanation lens in contact with the cornea is machined by the laser depending on the system parameters. As a consequence, microscopic glass fragments are created, which may remain in the tissue. This unwanted effect can be avoided by stopping the procedure at the lens-cornea interface.

Synthesis of visible light-active nanostructured TiOx (x < 2) photocatalysts in a flame aerosol reactor

Titanium dioxide is a wide band gap (3.2eV) semiconductor which is photo-active when irradiated with UV light. For wider scale use of TiO2 as a photocatalyst, its activity needs to be extended to the visible light region (constituting 45% of total incident solar energy). A diffusion flame aerosol reactor (FLAR) with an oxygen lean environment in the particle formation zone has been used to synthesize oxygen deficient titanium suboxide (TiOx with x<2) nanoparticles. Using a standard-based electron energy loss spectroscopy (EELS) technique, the non-stoichiometry (x in TiOx) in the flame synthesized particles has been quantified with high accuracy (uncertainty less than 3%). Under an oxygen lean environment in the particle formation zone, the non-stoichiometry in the TiOx particles is a function of the flame temperature. The value of x in the flame synthesized TiOx nanoparticles is in the range of 1.88<x<1.94. Diffuse reflectance spectra confirmed that the oxygen deficient TiOx particles absorbed visible light. Visible light activity of the TiOx particles is demonstrated by photocatalytic degradation of methyl orange solution under visible light illumination.

Synthesis and Structural Characterizations of Multi-Crystalline La0.5Ba0.5MnO3 Nanowires: A "Multi-Nuclei" Growth Mode

Multi-crystalline La0.5Ba0.5MnO3 Nanowires have been synthesized with cationic surfactant at 220 degrees C. The structure, composition and physical property of the as-prepared nanowires have been characterized by a series of techniques including XRD, SEM, HRTEM, electron energy-loss spectroscopy (EELS) and magnetic measurements. It is found that the La0.5Ba0.5MnO3 nanowire has the typical cubic perovskite structure, each nanowire is composed of many small crystalline grains with different orientations. Valance state of manganese ion in La0.5Ba0.5MnO3 nanowires is determined by EELS technique. A "multi-nuclei" growth mode is proposed based on the microstructure analysis. The temperature dependence of magnetization has been briefly discussed.

Coordination and optical attenuation of TiO 2–SiO 2 glass by electron energy loss spectroscopy

Electron energy loss spectroscopy (EELS) techniques have been applied to investigate both the coordination and optical attenuation of TiO 2–SiO 2 glass. The coordination was determined from the electron energy loss near edge fine structure (ELNES) of Ti L 2,3-edges, and the results show that Ti ions substitute for Si ions in the tetrahedral coordinated sites. The optical attenuation of the glass was obtained from low energy loss of EELS data through Kramers–Kronig analysis, and the results show that Ti-doped silica has an absorption edge near 4.0 eV.

Actual constitution of the mixed oxide promoter in a Rh/Ce1−xPrxO2−y/Al2O3 catalyst. Evolution throughout the preparation steps

AbstractThe evolution of the ceria‐praseodymia mixed oxide promoter throughout the successive steps involved in the preparation of a 3% Rh/25% Ce0.8Pr0.2O2−x/Al2O3–3.5% SiO2 catalyst is studied with the help of X‐ray diffraction (XRD), spatially resolved electron energy loss spectroscopy (EELS), XPS, and thermal programed desorption (TPD) techniques. Incipient wetness impregnation has been used to obtain the appropriate loading of this promoter. As revealed by XRD, EELS, and XPS data, the alumina‐supported CeO2PrO2−x mixed oxide sample consisted of a bimodal distribution of the particles of the promoter. XRD shows two fluorite‐like phases: cerium‐rich particles with a mean crystallite size greater than 6 nm and smaller praseodymium‐rich crystals, about 3.5 nm size. Surface Ce/Pr ratio obtained by XPS was consistent with a higher dispersion of the praseodymium‐rich oxide particles. The final Rh catalyst was prepared in a second step, by impregnation of the CePrOx/Al2O3 system with an acidic solution of Rh(NO3)3. The low pH of this solution is responsible for further modifications of the lanthanide oxides distribution. Thus, there is a redispersion of the praseodymium‐rich phase, which is evidenced by EELS and XPS data. Likewise, CO2 desorption from samples exposed to the atmosphere is consistent with an enhanced basicity of the sample due to the increase of Pr3+ content at the surface of the catalyst. The observed changes on the nanostructure of the mixed oxide promoter can be attributable to a partial dissolution of the oxide, selectively leaching Pr3+ cations from the lattice, which are finally deposited as small particles after the drying steps of the preparation. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Examining manganese dioxide electrode in KOH electrolyte using TEM technique

The manganese dioxide/zinc cell in an alkaline potassium hydroxide electrolyte is a widely studied system. However, most of this work has focused on additives to manganese dioxide (MnO2) in order to make this cell rechargeable. To the best of my knowledge, no work has been done so far on the discharge–charge mechanism using microscopic techniques. Hence, with an aim to understand the redox mechanism, the MnO2 cathodes are characterized by transmission electron microscopy (TEM), energy dispersive spectrum analysis (EDS), electron energy loss spectroscopy (EELS) and secondary ion mass spectrometry (SIMS) techniques. The results suggest that the electrode reaction of MnO2 in this electrolyte is potassium (K+) insertion or surface film formation on the surface in addition to the usual protonation i.e. H+ insertion during discharge process.

Bonding characteristics at the Ni-alumina composite interface via STEM-based EELS technique

Bonding characteristics of the metal and ceramic interfaces are significant to understand toughening mechanisms and design metal-ceramic composites. The Ni/alumina composite has been prepared by hot press-sintering of Ni-coated alumina powders and the bonding characteristics at the Ni-alumina composite interface have been studied by use of transmission electron microscopy (TEM)-based electron energy loss spectroscopy (EELS) techniques. From Al L2,3, Ni L2,3, and O K-edge EELS spectrum obtained, it can be reasoned that the interface in the Ni/alumina composite mainly consists of aluminum-terminated alumina and metallic Ni, and the bonding between them is primarily nonreactive with a nonionic ?Ni?Ni?Al?O?linkage, rather than by chemical bonding with Ni?O bonds from ?Ni?Ni?Ni?O?Al?O? or chemical reaction forming spinel interphases.