Electron Energy Loss Fine Structure Research Articles

Revealing Spatial Distribution of Al-Coordinated Species in a Phase-Separated Aluminosilicate Glass by STEM-EELS.

Structure determination of glass remains an important issue in glass science. The electron microscope with its high spatial resolution and versatile functions has been widely applied to observe phase separation and structural heterogeneity in glass. While elemental analysis such as energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) may provide local compositional information with nanometer-scale resolution, structural information in a glass network cannot be directly obtained. Here, a novel way to probe local coordination is employed using electron energy loss fine structure (ELNES) in the scanning transmission electron microscope (STEM). The method is demonstrated in a phase-separated aluminosilicate glass with multiple Al-coordinated species. With the support of ab initio calculation, two exciton-like peaks in the Al L2,3-edge at around 77 and 80 eV are attributed to 4-fold and 5,6-fold Al excitations, respectively. Mapping of the relative intensity ratio for two peaks in a phase-separated microstructure reveals a heterogeneous distribution of highly coordinated Al species in real space. The finding is in agreement with previous MD simulation that 5- and 6-fold Al species are favored to form in the Al-rich phase. This work has demonstrated that complex network structure within the phase-separated region can now be studied via STEM-EELS.

Changes in the chemical compound and local atomic structure of ultrathin surface layers of Fe due to implantation of argon and oxygen ions

In this work, we consider the effect of irradiation in Ar+ → O+ and O+ → Ar+ sequences on changes in the chemical compound, type of chemical bond and the local atomic structure of ultrathin (~20 nm) iron surface layers. Investigation of the chemical compound and the type of chemical bond of the ion-modified surface was carried out by the XPS (X-ray photoelectron spectroscopy) and Auger electron spectroscopy. The study of changes in the local atomic structure was carried out by an XAFS-like method — electron energy loss fine structure (EELFS) spectroscopy. The parameters of the local atomic environment of oxygen and iron — partial interatomic distances, dispersion parameters, and coordination numbers — were obtained by analyzing atomic pair correlation functions. Analysis of experimental data showed that the two-stage irradiation of iron significantly changes the chemical compound and local atomic structure of the initial surface. This leads to formation of an oxide layer of greater depth than in the case of irradiation with only oxygen ions.

Characterization of thin carbon films formed on the iron surface by magnetron sputtering with ion-beam mixing

The chemical composition, interatomic chemical bonds, and specific features of the atomic structure of nanosized carbon films on the surface of iron, which were prepared by magnetron sputtering before and after ion-beam mixing, have been investigated using X-ray photoelectron spectroscopy, X-ray diffraction analysis, extended electron energy loss fine structure spectroscopy, and Raman spectroscopy. It has been found that, in the ion-beam mixing region, there are structural inhomogeneities and nonstoichiometric iron carbides. The parameters of the local atomic structure of an ultrathin surface layer and the “carbon film–metal” transition region have been determined.

Al grain boundary segregations in doped intermetallic NiAl and their effect on brittleness at room temperature

The nature of intermetallic NiAl brittleness is investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and electron energy-loss fine structure (EELFS) means. It is found that the reason for this phenomenon is the ordering of intermetallic NiAl, accompanied by the formation of aluminum structural segregations at grain boundaries. Doping with 0.1 wt % La transforms the atomic and electronic structures of grain boundaries, eliminating NiAl intergranular fracturing at room temperature. Doping is accompanied by Fermi level shifts and an increase in conduction electron density neff. These factors are responsible for the lower covalence of interatomic bonds in pure intermetallic NiAl. The effect A1 segregations have on the critical deformation of the generating grain boundary fracture in NiAl is discussed.

Single molecular spectroscopy: identification of individual fullerene molecules.

We report the molecule-by-molecule spectroscopy of individual fullerenes by means of electron spectroscopy based on scanning transmission electron microscopy. Electron energy-loss fine structure analysis of carbon 1s absorption spectra is used to discriminate carbon allotropes with known symmetries. C(60) and C(70) molecules randomly stored inside carbon nanotubes are successfully identified at a single-molecular basis. We show that a single molecule impurity is detectable, allowing the recognition of an unexpected contaminant molecule with a different symmetry. Molecules inside carbon nanotubes thus preserve their intact molecular symmetry. In contrast, molecules anchored at or sandwiched between atomic BN layers show spectral modifications possibly due to a largely degraded structural symmetry. Moreover, by comparing the spectrum from a single C(60) molecule and its molecular crystal, we find hints of the influence of solid-state effects on its electronic structure.

Interface composition between Fe3O4 nanoparticles and GaAs for spintronic applications

Recent interest in spintronic applications has necessitated the study of magnetic materials in contact with semiconductor substrates; importantly, the structure and composition of these interfaces can influence both device functionality and the magnetic properties. Nanoscale ferromagnet/semiconductor structures are of particular interest. In this study, the interface structure between a monolayer of ferromagnetic magnetite (Fe3O4) nanoparticles and a GaAs substrate was studied using cross-sectional transmission electron microscopy techniques. It was found that a continuous amorphous oxide interface layer separates the nanoparticles from the GaAs substrate, and that iron diffused into the interface layer forming a compositional gradient. Electron energy-loss near-edge fine structures of the O K absorption edge revealed that the amorphous oxide is composed of γ-Fe2O3 directly underneath the Fe3O4 nanoparticles, followed by a solid solution of Ga2O3 and FeO and mostly Ga2O3 when approaching the buckled oxide/substrate interface. Real-space density functional theory calculations of the dynamical form factor confirmed the experimental observations. The implication of the findings on the optimization of these structures for spin injection is discussed.

Theoretical ELNES fingerprints of BC2N polytypes

Electron energy-loss near-edge fine structures are calculated for sp3-bonded BC2N polytypes to provide theoretical fingerprints for characterization. The calculation is based on an ab initio plane wave pseudopotential method from density functional theory. The core–hole effect is included, and the transition matrix element is explicitly evaluated. Spectral features that can be used to distinguish the different structures are identified and discussed.

Electron-impact excitation of internal atomic layers of a substance in the formation of extended fine structures of electron emission spectra

The formalism of collision theory was used to describe the formation of extended electron energy loss fine structures taking into account multipolarity of the electron-impact excitation of internal atomic layers, and the formation of extended secondary electron fine structures taking into account the first and second order nonradiative relaxation of excited state of the electronic subsystem of a sample. The extended electron energy loss fine structures, extended secondary electron fine structures, and corresponding oscillating parts were obtained in the experiments. The experimental and calculated data showed good agreement.

ELNES for boron, carbon, and nitrogen K-edges with different chemical environments in layered materials studied by density functional theory

Electron energy-loss near-edge fine structures (ELNES) were calculated for graphene, doped graphene, a hexagonal BN monolayer, and a hexagonal BC₂N layer using an ab initio pseudopotential plane wave method including the core-hole effect. Spectral features that can be used to distinguish different chemical environments are identified. The spectral features are closely related to the atomic species and arrangement. The connection between chemical environments and fine structures is discussed.

ELNES study of chemical solution deposited [formula omitted] Ruddlesden–Popper films: Experiment and simulation

This article analyzes electron energy-loss near-edge fine structures of the SrO(SrTiO3)n=1 Ruddlesden–Popper system and of the parent compounds SrTiO3 and SrO by comparison with first principles calculations. For that, the fine structures of chemical solution deposited Ruddlesden–Popper films have been experimentally recorded by means of transmission electron microscopy. Moreover, density of states computations using an all-electron density-functional code have been performed. It is shown that the appearance and shape of the experimental O–K and Ti–L2,3 fine structure features result from the crystallography-dependent electronic structure of the investigated oxides, which display technologically interesting dielectric as well as lattice–structural properties.

Spectroscopy of extended electron energy loss fine structures for quantitative analysis of the local atomic structure in ultrathin oxide films on the surface of 3d-metals

The work presents the theoretical description of formation processes of extended electron energy loss fine structure (EELFS) spectra. Simple analytical formulas are obtained to calculate EELFS spectra. Methods are proposed to compute amplitudes and intensities of electronic transitions of different multipolarity in electron-impact excitation of the inner shell of an atom. The corresponding test calculations are performed. We present experimental M 2,3 EELFS spectra of 3d-metals obtained from clean surfaces of Fe, Ni, and Cu and ultrathin stoichiometric oxide films of Fe2O3, NiO, and CuO as well as K EELFS spectra of oxygen from thin stoichiometric oxide films. Techniques are proposed to extract normalized oscillating parts from experimental EELFS data based on the use of calculated intensities of the corresponding electronic transitions. Atomic pair correlation functions are obtained for the objects under study from experimental EELFS data with regard to multipolarity of electron impact excitation of the atomic inner shell. Experimental results correspond well to known crystallographic data (partial interatomic distances, coordination numbers, and Debye-Waller factors).

The Theory and Interpretation of Electron Energy Loss Near-Edge Fine Structure

Electron energy loss fine structure near the threshold of inner-shell edges can potentially give valuable information on bonding on an atomic scale. To use near-edge structure it is essential to understand what factors influence both the occupied and unoccupied local density of states in the material of interest. Different techniques of electronic structure theory are suitable for metals, semiconductors, and ionic materials, although some methods can be applied to a wide range of systems. To extract quantitative information on bonding it is important to avoid those edges that are strongly affected by the presence of the core hole such as cations in ionic materials.

Investigations of SiC semiconductor nanoinclusions formed by sequential ion implantation and annealing in thermally oxidized Si

AbstractThe methods of X‐ray photoelectron and extended electron energy loss fine structure (EELFS) spectroscopy were used for the investigation of phase composition and structure of SiO2 layer implanted sequentially by Si+ (energy of 100 keV, dose of 7 × 1016 cm−2) and C+ (energy of 50 keV, dose of 7 × 1016 cm−2) ions and postannealed at 1000 or 1100 °C (2 h). The SiSi and SiC bonds in carbide (SiC) nanoinclusions and CC bonds of sp3 type in carbon inclusions are identified. The concentration of dangling bonds significantly decreases with elevation of annealing temperature. The distribution of SiC nanoinclusions at 1100 °C annealing corresponds to the distribution of implanted atoms, whereas sp3‐C phase is distributed nearly homogeneously over the implanted layer. The ratio of SiC to sp3‐C quantities is lower when intermediate annealing at 1100 °C is provided after Si+ implantation. The local atomic structure near the surface is determined from the EELFS. The experimental results demonstrate the physical basis of white photoluminescence, originating from the SiC nanocrystals, diamond‐like carbon particles, matrix, and interfacial defects. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of Channeling on Core-Loss Electron Energy Loss Fine Structure

Effects of Channeling on Core-Loss Electron Energy Loss Fine Structure

Radial Distribution Function Analyses of Amorphous Carbon Films Containing Silicon and Hydrogen by Energy-Filtered Diffraction and EXELFS

Short-range order in amorphous materials is most commonly characterized with the use of radial distribution functions (RDFs). Two analytical electron microscopy methods were used in this study to measure RDFs from amorphous carbon films containing different levels of silicon and hydrogen (Si-aC:H): energy-filtered convergent-beam electron diffraction (EFCBED) and extended electron energy-loss fine structure (EXELFS) analyses. The films were deposited in an industrial-scale system onto a thin adhesive titanium layer on silicon substrates by reactive sputtering of carbon with a feed gas of tetramethyl silane (TMS) and argon, to produce a series of films with different Si and H contents (Si/C = 0, 0.04, 0.10, and 0.18).

Characterization of Ambient Airborne Particles by Energy-Filtered Transmission Electron Microscopy

This article demonstrates that energy-filtered trairsmission electron microscop, (EFTEM) can be a valuable tool for the identification and analysis of nanometer-sized airborne particles. Ambient airborne particulate matter (PM) samples collected at Lexington, Kentucky were investigated using EFTEEM in combination with electron energy-loss spectroscopy (EELS), energg-dispersive Xray spectroscopy (EDS), selected area electron diffraction(SAED), and high-resolution transmission electron microscopy (HARTEM). EFTEM provides a fast and convenient way to map the distribution of carbonaceous aggregates, which cnstitute a significant fraction of the samples. Sulfur-bearing particles are common in the submicron inorganic fraction. Sulfur elemental maps were obtained from some sulfur-beariang particles, and the oxidation state of sulfur was revealed to be primarily S(VI) as sulfate from the electron energy-loss near-edge fine structures of the sulfur L-edge. Other types of inorganic particles, such as silicon-bearin...

Reply to “Comment on ‘Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminoborosilicate glasses containing gadolinium’ by M. Qian, H. Li, L. Li and D.M. Strachan [J. Non-Cryst. Solids 328 (2003) 90

The nature of ^*-band, near 188-194 eV, from B K EELS spectra of borate minerals and boron containing glasses has been well documented. The ban results rom teh transition of B 1s to P ^* in B with sp hybridization. Similarly, the higher energy broad band is attributed to the transition from B 1s to P in B Radiation effects on B04 conversion to Bo3 was also studied in details for crystalline solids by Sauer et al.

Comment on ‘Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminosilicate glasses containing gadolinium’ by M. Qian, H. Li, L. Li and D.M. Strachan [J. Non-Cryst. Solids 328 (2003) 90

Comment on ‘Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminosilicate glasses containing gadolinium’ by M. Qian, H. Li, L. Li and D.M. Strachan [J. Non-Cryst. Solids 328 (2003) 90

Radial distribution function analyses of amorphous carbon thin films containing various levels of silicon and hydrogen

Short-range order in amorphous carbon thin films containing silicon and hydrogen (Si-aC:H) was characterized using radial distribution functions (RDFs). RDFs describe the average number of neighbors located a distance r away from an arbitrary atom in the sample. Two methods in the transmission electron microscope (TEM) were used in this study to obtain RDFs: energy-filtered convergent-beam electron diffraction (EFCBED) and extended electron energy-loss fine structure (EXELFS) analyses. Four Si-aC:H film samples were prepared in cross section for TEM using a focused ion beam system. Both EFCBED and EXELFS techniques were used to study the same samples. RDF interpretation included estimation and comparison of near-neighbor distances, average bond angles, and coordination numbers as a function of sample composition. Key RDF characteristics were correlated to thin film material properties.

Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminoborosilicate glasses containing gadolinium

Electron energy loss boron K-edge spectra of gadolinium-bearing sodium aluminoborosilicate glasses were acquired. Extended electron energy loss fine structure studies were performed in both extended and near edge region. Using Gd-metaborate, GdB 3O 6, as a model, we fitted the experimental B K-edge spectra of the glasses containing 30 and 47 mass% Gd 2O 3 in r-space with a non-linear least-square fitting method. Based on the results obtained from the current study, the majority of borate units appear to react with Gd cations and the local environment of Gd cations resembles that of the Gd-metaborate structure. Therefore, a distorted Gd-metaborate-like local atomic structure is proposed, in which each Gd cation is stabilized by one tetragonal BO 4 unit and two trigonal BO 3 units. The similarity of the chemical environment between the two high Gd-bearing glasses implies that the local Gd-metal borate environment, 1BO 4:Gd:2BO 3, is stable. When the Gd to B ratio in the glasses exceeded 1 to 3 ratio, according to the model, excess Gd cations should form bonds with silicate units. The modeling results are further supported by the energy loss near edge spectra data and previously results obtained from Raman and laser fluorescence deduced phonon side band studies.