Energy-loss Near-edge Fine Structure Research Articles

The effect of nanometre-scale kinetic competition on the phase selection in Zr/Si superstructure

Nano structured coating system demonstrates outstanding performance stemming from unique structure evolution. Zr/Si coating was proposed as an ideal candidate for the protection of Zr alloy cladding. However, the phase selection remains a challenge to coordinate the complex requirement under the service and accident conditions of reactor core. In this work, a phase selection mechanism for amorphous Zr-Si-O (abbr. ZSO) was elucidated by the competitive consumption of Zr layer by silicidation and oxidation, which was also scale-dependent. The energy-loss near-edge fine structure and nanoindentation were also employed to characterize the unique scale effect in the two processes. Both the oxides kinetics and elastic modulus gain indicated an immediate passivation process under the subcritical condition after the in situ phase selection of the amorphous ZSO. Ab initio molecular dynamics (AIMD) was performed to disclose the origination of depressed O migration in ZSO. The multilayer structure also shows accident tolerance potential. The interfacial phase selection provided a strategy to regulate mesoscale structure originating from nanomter interface and meets the diversified requirement for “structure-performance relationship” under the service and accident conditions.

Electron energy loss spectroscopy of K0.7Fe1.7Se2 superconductor

Electronic structure and microstructure of ternary selenide superconductor K0.7Fe1.7Se2 have been investigated by transmission electron microscopy (TEM) and energy band structure calculations. Electron energy-loss spectroscopy (EELS) was performed to study K0.7Fe1.7Se2 experimentally. The individual inter-bands transitions were identified through the comparison between the energy loss peak positions with the partial density of states (PDOS) obtained by first principle calculation. The electron energy-loss near-edge fine structure (ELNES) were analyzed, the core-hole effect was found to play a key role in the simulation of ELNES. The results can present some insight into the interaction between superconductivity and electronic structure in this group of iron-related superconductor.

A hyperspectral unmixing framework for energy-loss near-edge structure analysis

Extracting different spectral components and their corresponding concentrations from spectrum images is one of the key challenges for electron energy-loss spectroscopy analysis due to the large amount of data, differing spectral features and low signal-to-noise ratio. Here, an open-source software framework of hyperspectral unmixing for energy-loss near-edge fine structure analysis is proposed. This software determines the number of independent spectral components, the signature of each spectral component and the abundance of each spectral component in each pixel, without reference spectrum or prior knowledge of the datasets. This approach should be suitable for automated materials and chemical analysis.

Zero Cu valence and superconductivity in high-quality CuxBi2Se3 crystal

In this work, the role of Cu dopants in the development of superconductivity in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ is investigated. A series of $\mathrm{C}{\mathrm{u}}_{x}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ ($x=0--0.3$) crystals is grown using the Bridgman method and electrochemical techniques. Based on the observable lattice increases along the $c$ axis, the existence of Cu atoms intercalated in the van der Waals (vdW) gaps in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ is verified by x-ray diffraction, scanning electron microsopy--energy dispersive spectroscopy, and transmission electron microscopy analysis. Furthermore, the chemical state of the Cu is found to be zero valence by characterization of the x-ray photoelectron and Auger electron spectra. The absence of $\mathrm{C}{\mathrm{u}}^{1+}$ and $\mathrm{C}{\mathrm{u}}^{2+}$ in the electron energy-loss spectroscopy near-edge fine structure is confirmed as well. Meanwhile, our Raman data also show the same result: the intercalation of Cu in the vdW gap which weakens the binding of the quintuple layers in the $\mathrm{C}{\mathrm{u}}_{0.1}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ crystal. The electric resistance and magnetic susceptibility show a superconducting transition near 3--3.4 K in the series of Cu-doped $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. A sharp superconducting transition with the highest value of ${T}_{C}=3.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the largest magnetic shielding fraction of 84% is observed in the optimized 10% Cu-doped $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. These results imply that the formation of superconducting quasiparticles is not related to the charge transfer of Cu, but is supported by the internal stress of Cu intercalated in the van der Waals gap. The superconducting transition observed in the specific heat implies that the superconductivity in $\mathrm{C}{\mathrm{u}}_{x}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ is unconventional.

Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond.

In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.

Towards atomically resolved EELS elemental and fine structure mapping via multi-frame and energy-offset correction spectroscopy

Electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy are two of the most common means for chemical analysis in the scanning transmission electron microscope. The marked progress of the instrumentation hardware has made chemical analysis at atomic resolution readily possible nowadays. However, the acquisition and interpretation of atomically resolved spectra can still be problematic due to image distortions and poor signal-to-noise ratio of the spectra, especially for investigation of energy-loss near-edge fine structures. By combining multi-frame spectrum imaging and automatic energy-offset correction, we developed a spectrum imaging technique implemented into customized DigitalMicrograph scripts for suppressing image distortions and improving the signal-to-noise ratio. With practical examples, i.e. SrTiO3 bulk material and Sr-doped La2CuO4 superlattices, we demonstrate the improvement of elemental mapping and the EELS spectrum quality, which opens up new possibilities for atomically resolved EELS fine structure mapping.

Atomic signatures of local environment from core-level spectroscopy inβ−Ga2O3

We present a joint theoretical and experimental study on core-level excitations from the oxygen $K$ edge of $\beta$-Ga$_2$O$_3$. A detailed analysis of the electronic structure reveals the importance of O-Ga hybridization effects in the conduction region. The spectrum from O 1$s$ core electrons is dominated by excitonic effects, which overall redshift the absorption onset by 0.5 eV, and significantly redistribute the intensity to lower energies. Analysis of the spectra obtained within many-body perturbation theory reveals atomic fingerprints of the inequivalent O atoms. From the comparison of energy-loss near-edge fine-structure (ELNES) spectra computed with respect to different crystal planes, with measurements recorded under the corresponding diffraction conditions, we show how the spectral contributions of specific O atoms can be enhanced while quenching others. These results suggest ELNES, combined with ab initio many-body theory, as a very powerful technique to characterize complex systems, with sensitivity to individual atomic species and to their local environment.

Effects of inverse degree on electronic structure and electron energy-loss spectrum in zinc ferrites

Abstract First-principles calculations were performed to study the effects of inverse degree in zinc ferrite on electronic structure and properties. The electron energy-loss near-edge fine structure (ELNES) were simulated, and the splitting of peak and intensities of the oxygen K-edges can be used to identify the inversion of zinc ferrite. More Fe 3+ transferring from the octahedral sites to the tetrahedral sites lead to the changing of the ligand shells surrounding the absorbing atom, accounting for the observed changing in ELNES. The standard criterion for determining the reversal extent of the cations in zinc ferrite by ELNES was given.

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.

Toward deep blue nano hope diamonds: heavily boron-doped diamond nanoparticles.

The production of boron-doped diamond nanoparticles enables the application of this material for a broad range of fields, such as electrochemistry, thermal management, and fundamental superconductivity research. Here we present the production of highly boron-doped diamond nanoparticles using boron-doped CVD diamond films as a starting material. In a multistep milling process followed by purification and surface oxidation we obtained diamond nanoparticles of 10-60 nm with a boron content of approximately 2.3 × 10(21) cm(-3). Aberration-corrected HRTEM reveals the presence of defects within individual diamond grains, as well as a very thin nondiamond carbon layer at the particle surface. The boron K-edge electron energy-loss near-edge fine structure demonstrates that the B atoms are tetrahedrally embedded into the diamond lattice. The boron-doped diamond nanoparticles have been used to nucleate growth of a boron-doped diamond film by CVD that does not contain an insulating seeding layer.

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.

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.

Electron beam-induced oxygen desorption in [formula omitted]-LiAlO 2

Effects of electron irradiation damage in γ -LiAlO 2 were analysed using energy loss near edge fine structure (ELNES) of the O K-edge. Simulations of the O K-fine structure by means of a density functional theory (DFT) code show that under the electron beam γ -LiAlO 2 undergoes the following transformation: LiAlO 2→ LiAl 5O 8→ Al 2O 3. O K-edge spectra, which were recorded during this decomposition process, contain an additional peak at 531 eV. This peak can be attributed to a π ∗ -transition, which is observed for molecular oxygen O 2. This result suggests that the electron beam-induced LiAlO 2 decomposition occurs through the loss of O 2.

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.

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.

Martensitic transformation ofNi2FeGaferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy

The structural properties of ${\text{Ni}}_{2}\text{FeGa}$ Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the ${\text{Ni}}_{2}\text{FeGa}$ alloy was annealed into a well-defined $L{2}_{1}$ structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the $⟨110⟩$ or $⟨100⟩$ directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature $({M}_{s},\ensuremath{\sim}142\text{ }\text{K})$, the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the $⟨100⟩$ direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a $5M$ modulation structure along the $⟨110⟩$ directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to $spd$ orbital hybridization among the Ni-Fe-Ga atoms.

EELS Investigations of Different Niobium Oxide Phases

Electron energy loss spectra in conjunction with near-edge fine structures of purely stoichiometric niobium monoxide (NbO) and niobium pentoxide (Nb2O5) reference materials were recorded. The structures of the niobium oxide reference materials were checked by selected area electron diffraction to ensure a proper assignment of the fine structures. NbO and Nb2O5 show clearly different energy loss near-edge fine structures of the Nb-M4,5 and -M2,3 edges and of the O-K edge, reflecting the specific local environments of the ionized atoms. To distinguish the two oxides in a quantitative manner, the intensities under the Nb-M4,5 as well as Nb-M2,3 edges and the O-K edge were measured and their ratios calculated. k-factors were also derived from these measurements.

Scanning transmission electron microscopy investigations of interfacial layers in HfO2 gate stacks

Electron energy-loss spectroscopy combined with high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy was used to investigate the chemistry of interfacial layers in HfO2 gate stacks capped with polycrystalline Si gate electrodes. To interpret the energy-loss near-edge fine structure (ELNES) obtained from the interfacial layers, reference spectra were obtained from single crystal hafnium silicate (HfSiO4), monoclinic HfO2 powder, and amorphous SiO2. No bulk-like silicate bonding could be detected in the ELNES of Si L2,3 and O K edges recorded from layers at the Si substrate interface. Compared to bulk SiO2, the interfacial ELNES showed additional features that were caused by overlap of signals from Si, HfO2, and SiO2, despite a relatively small electron probe size of ∼3Å. HAADF showed that interfacial roughness caused the projected thickness of nominally pure SiO2 (within the detection limit of the method) to be as small as ∼5Å in many locations.

Energy-loss near-edge fine structures of iron nanoparticles

Body centered cubic (bcc) Fe nanoparticles were fabricated by in situ decomposition of iron fluoride films in a transmission electron microscope. Electron energy-loss near edge structure (ELNES) was used to characterize this exposure process. In particular, the L 3/L 2 white-line intensity ratio (WLR) was used to monitor the iron valence state during exposure, and as an indicator of other properties of the iron nanoparticles. Iron nanoparticles with sizes between 2 and 20 nm exhibit a constant WLR, whose value is same as that for a continuous bcc iron film, suggesting little or no dependence of the local magnetic moment or structure on the particle size. A broad but prominent peak which occurs 40 eV after the L 3-ionization threshold in the iron fluoride, is absent for a metallic iron film but reappears when the iron is converted to an oxide. Long-range ferromagnetic coupling was observed in samples densely populated with iron nanoparticles. Because there is little interaction between particles and the supporting carbon substrate, these samples provide an ideal model system for studying the influence of particle size and interparticle distance on magnetic properties.

Theoretical electron energy-loss spectroscopy and its application in materials research

Electron energy-loss near-edge fine structure (ELNES) of group-III nitrides is calculated using a pseudopotential plan wave method within the framework of density functional theory. Core-hole effect and supercell size influence are investigated. Based on our present and earlier work, a comprehensive understanding of theoretical ELNES application in materials research is demonstrated: interpreting experimental spectra, predicating theoretical reference spectra when reliable experimental spectra are not available, identifying ELNES-structure correlation and estimating the reliability of experimental spectra.