Quantitative Electron Energy Loss Spectroscopy Research Articles

Discovery of Real-Space Topological Ferroelectricity in Metallic Transition Metal Phosphides.

Ferroelectric metals-with coexisting ferroelectricity and structural asymmetry-challenge traditional perceptions because free electrons screen electrostatic forces between ions, the driving force of breaking the spatial inversion symmetry. Despite ferroelectric metals having been unveiled one after another, topologically switchable polar objects with metallicity have never been identified so far. Here, the discovery of real-space topological ferroelectricity in metallic and non-centrosymmetric Ni2 P is reported. Protected by the rotation-inversion symmetry operation, it is found that the balanced polarity of alternately stacked polyhedra couples intimately with elemental valence states, which are verified using quantitative electron energy-loss spectroscopy. First-principles calculations reveal that an applied in-plane compressive strain creates a tunable bilinear double-well potential and reverses the polyhedral polarity on a unit-cell scale. The dual roles of nickel cations, including polar displacement inside polyhedral cages and a 3D bonding network, facilitate the coexistence of topological polarity with metallicity. In addition, the switchable in-plane polyhedral polarity gives rise to a spin-orbit-coupling-induced spin texture with large momentum-dependent spin splitting. These findings point out a new direction for exploring valence-polarity-spin correlative interactions via topological ferroelectricity in metallic systems with structural asymmetry.

HRTEM and EELS investigations of flame-formed soot nanostructure

High resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) were applied to soot probed along a premixed methane flame from the inception phase up to the burnout region in order to follow the transformations of soot nanostructures. The nascent methane soot presented the predominance of large coalesced disordered structures in comparison to young, intermediate and mature soot presenting spherule aggregates. Quantitative structural information describing the shape, size and orientation of sp2-bonded (aromatic) layers and their distribution inside the carbon particle were obtained by HRTEM image analysis. A moderate structural improvement in terms of a better stacking of longer and more planar layers along with the tortuosity fringe decrease was observed along the methane flame. EELS was instead used to provide quantitative information about the relative concentrations of sp3 and sp2 hybridized carbon. It is the first time that quantitative EELS is applied to soot from the inception to maturation along a premixed laminar flame. The aromatic content for the nascent soot resulted to be rather high (84%) indicating the predominant aromatic character of soot precursors. The steep increase of sp2 content from 84 to 94% in the passage from nascent to young soot was noteworthy. The similar sp2 content (94–96%) as well as the invariance of fringe length of young, intermediate and mature soot testified that most of the structural changes occurred at the inception, after then methane soot did not undergo a significant nanostructural restructuring, possibly because of the less reactive environment generated from methane combustion.

Lifshitz analysis of dispersion forces based on quantitative reflection electron energy loss spectroscopy

HypothesisThe energy loss experienced by an electron while moving through a solid is determined by the optical properties of the surrounding. Hence, quantitative Reflection Electron Energy Loss Spectroscopy (REELS) should allow the determination of optical data required for the calculation of Hamaker coefficients using Lifshitz theory. This approach might improve the accuracy of calculated Hamaker coefficients and should also enable to harness the unique capabilities of REELS to analyse nanostructured surfaces and thin-films with great spatial resolution and surface sensitivity. ExperimentsREELS spectra of a survey of insulating polymers and of metal-like Ti0.23Al0.32N0.44 (TiAlN) were measured, the complex dielectric functions determined and the corresponding Hamaker coefficients across vacuum and water calculated. The sensitivity of the quantification procedure towards typical systematic errors was investigated. For polystyrene the results were comparatively analysed using vacuum ultraviolet spectroscopy (VUV). FindingsThe accuracy especially of the non-retarded vacuum Hamaker constants of the polymers was increased when compared to VUV reflectance spectroscopy due to the higher spectral range of REELS. Furthermore, a new correction procedure for the intricate case of unresolved inelastic losses in the REELS spectrum, such as encountered in the case of TiAlN, could be developed using spectroscopic ellipsometry as a complementary mean.

(Invited) In Situ Electrochemical STEM As a Platform for Interpreting Electrochemical Phenomena

In situ electrochemical STEM (ec-STEM) is a multi-modal characterization technique that allows for the direct interpretation of nanoscale mechanisms and kinetics during electrochemical operation. The major advantage of this method is the ability to perform quantitative electrochemical measurements while simultaneously characterizing nanoscale structural and chemical changes that occur at site-specific electrode/electrolyte interfaces using high spatial resolution imaging, spectroscopy, and/or diffraction; all within a scanning transmission electron microscope (STEM). ec-STEM is being used for battery research by studying the formation mechanisms of the solid electrolyte interphase (SEI) and growth mechanisms of lithium metal dendrites within an organic electrolyte (1.2M LiPF6 EC:DMC). The initial stage of lithium metal dendrite nucleation and growth is observed on the surface and edge of the glassy carbon working electrode during cyclic voltammetry experiments below -3.0V vs. Ptpseudo reference electrode. The Li dendrites grow with a globular morphology during a sequence of bursts, whereby newly formed lithium metal deposits are passivated by the SEI followed by additional growth events associated with localized regions of SEI breakdown. Electron energy loss spectroscopy (EELS) confirms that the deposits are lithium metal with surfaces composed of inorganic compounds commonly found in the SEI. The EEL spectra reveal a Li metal plasmon peak at 7.5eV and a characteristic LiF spectral feature on the Li K-edge at 55eV. Furthermore, a framework for obtaining and analyzing quantitative EELS measurements is demonstrated to directly determine the oxidation state of battery electrodes (LiMn2O4 and Li4Ti5O12) using the “white-lines” of the L2,3 core loss ionization edges of Mn and Ti. By simultaneously acquiring low-loss and core-loss EEL spectra, plural scattering effects caused by scattering through the electrolyte can be removed to quantify the oxidation state of Mn and Ti using the white-line intensity ratio method. RF magnetron sputtering was used to deposit a thin layer of LiMn2O4, a commonly used battery cathode material, directly onto the silicon nitride membrane of the ec-STEM cell. Simultaneous low-loss and core-loss EEL spectra are acquired with and without the presence of dimethyl carbonate (DMC) in the liquid cell (Figure 3c). The low-loss portion of the EEL spectra confirms the presence of the DMC within the liquid cell and aides in the quantification of fluid layer thickness. If the fluid layer thickness is small, it is possible to extract and analyze the Mn L2,3-edge for quantification of the Mn oxidation state using the “white-line” intensity ratio method. Mixed Mn3+/4+ oxidation is measured in the as-deposited LiMn2O4, which shifts to a lower oxidation state when DMC is present in the cell, suggesting that LiMn2O4 may be prone to electron beam induced chemical reduction when immersed in a battery electrolyte during in situ ec-STEM experiments. The information obtained from these studies can help provide a deeper understanding of how batteries function at the nanoscale. Research supported by the Fluid Interface Reactions Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the Department of Energy’s Office of Basic Energy Sciences Division and by the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Quantitative Electron Energy Loss Spectroscopy (EELS) Analysis of Flowable CVD Oxide for Shallow Trench Isolation of finFET Integration

Journal Article Quantitative Electron Energy Loss Spectroscopy (EELS) Analysis of Flowable CVD Oxide for Shallow Trench Isolation of finFET Integration Get access J Li, J Li IBM Research, Albany, NY 12203 Email: juntaoli@us.ibm.com, Tel: (518) 292-7419 Search for other works by this author on: Oxford Academic Google Scholar J Bruley, J Bruley IBM Research, Yorktown Heights, NY 10598 Search for other works by this author on: Oxford Academic Google Scholar R Conti, R Conti IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar M Belyansky, M Belyansky IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar S Metha, S Metha IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar J Strane, J Strane IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar L Tai, L Tai IBM Systems, Hopewell Junction, NY 12533 Search for other works by this author on: Oxford Academic Google Scholar L Jiang, L Jiang IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar J Demarest, J Demarest IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar J Gaudiello, J Gaudiello IBM Research, Albany, NY 12203 Search for other works by this author on: Oxford Academic Google Scholar ... Show more Y Zhu, Y Zhu IBM Research, Yorktown Heights, NY 10598 Search for other works by this author on: Oxford Academic Google Scholar A Grill A Grill IBM Research, Yorktown Heights, NY 10598 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 1462–1463, https://doi.org/10.1017/S1431927617007978 Published: 04 August 2017

Robust theoretical modelling of core ionisation edges for quantitative electron energy loss spectroscopy of B- and N-doped graphene

Electron energy loss spectroscopy (EELS) is a powerful tool for understanding the chemical structure of materials down to the atomic level, but challenges remain in accurately and quantitatively modelling the response. We compare comprehensive theoretical density functional theory (DFT) calculations of 1s core-level EEL K-edge spectra of pure, B-doped and N-doped graphene with and without a core-hole to previously published atomic-resolution experimental electron microscopy data. The ground state approximation is found in this specific system to perform consistently better than the frozen core-hole approximation. The impact of including or excluding a core-hole on the resultant theoretical band structures, densities of states, electron densities and EEL spectra were all thoroughly examined and compared. It is concluded that the frozen core-hole approximation exaggerates the effects of the core-hole in graphene and should be discarded in favour of the ground state approximation. These results are interpreted as an indicator of the overriding need for theorists to embrace many-body effects in the pursuit of accuracy in theoretical spectroscopy instead of a system-tailored approach whose approximations are selected empirically.

Nanoscale Investigation of the Degradation Mechanism of a Historical Chrome Yellow Paint by Quantitative Electron Energy Loss spectroscopy Mapping of Chromium Species

Getting the picture: The investigation of 100 year old chrome yellow paint by transmission electron microscopy and spectroscopy has led to the identification of four types of core-shell particles. This nanoscale investigation has allowed a mechanism to be proposed for the darkening of some bright yellow colors in Van Gogh's paintings (e.g. in Falling leaves (Les Alyscamps), 1888).

Nanoscale Investigation of the Degradation Mechanism of a Historical Chrome Yellow Paint by Quantitative Electron Energy Loss spectroscopy Mapping of Chromium Species

Nanoscale Investigation of the Degradation Mechanism of a Historical Chrome Yellow Paint by Quantitative Electron Energy Loss spectroscopy Mapping of Chromium Species

Method for local temperature measurement in a nanoreactor for in situ high-resolution electron microscopy

In situ high-resolution transmission electron microscopy (TEM) of solids under reactive gas conditions can be facilitated by microelectromechanical system devices called nanoreactors. These nanoreactors are windowed cells containing nanoliter volumes of gas at ambient pressures and elevated temperatures. However, due to the high spatial confinement of the reaction environment, traditional methods for measuring process parameters, such as the local temperature, are difficult to apply. To address this issue, we devise an electron energy loss spectroscopy (EELS) method that probes the local temperature of the reaction volume under inspection by the electron beam. The local gas density, as measured using quantitative EELS, is combined with the inherent relation between gas density and temperature, as described by the ideal gas law, to obtain the local temperature. Using this method we determined the temperature gradient in a nanoreactor in situ, while the average, global temperature was monitored by a traditional measurement of the electrical resistivity of the heater. The local gas temperatures had a maximum of 56 °C deviation from the global heater values under the applied conditions. The local temperatures, obtained with the proposed method, are in good agreement with predictions from an analytical model.

Chemisorption-Isotherm Measurements at Electrode Surfaces by Quantitative High-Resolution Electron Energy Loss Spectroscopy

The chemisorption isotherm of benzoquinone at a well-defined Pd(100) surface was obtained by quantitative high-resolution electron energy loss spectroscopy (HREELS). Extraction of surface-coverage information from HREELS required the normalization of integrated peak intensities to compensate for differences in the backscattered electron flux brought about by the organic adlayer. A common procedure rests on a match of the elastic-peak heights, but it fails for organic adsorbates since those introduce surface roughness that result in a higher stream of inelastically scattered electrons. A more accurate method is based on the equalization of the incident electron beam currents. This is attained only when the background intensities integrated over a peak-free spectral region are set equal to one another. The HREELS-generated isotherm was compared with that acquired by thin-layer electrochemical measurements; excellent agreement was observed.

Structural Analysis of Longitudinal Si–C–N Precipitates in Multicrystalline Silicon

During crystallization of multicrystalline silicon, carbon-rich liquid-solid phase-boundary layers appear, resulting in precipitation of n-type conductive Si-C-N filaments. We present an in-depth structural analysis of distinct types of filaments to support modeling of their growth. Phase-contrast microtomography down to the submicron level is used to study morphology and seeding of precipitates while still embedded in fully functional solar cell samples. A detailed transmission electron microscopy analysis and a quantitative electron energy loss spectroscopy analysis are presented, based on tomography-assisted target preparation.

Enhanced absorption in ultrathin Si by NiSi2 nanoparticles

Various forms of Si including amorphous Si (a-Si) are important photovoltaic (PV) materials. However, in order to improve the cost-to-performance aspects of Si solar cells, such as by enabling ultrathin (<500 nm) Si solar technology, new strategies are required to improve optical absorption within Si, which is a relatively poor absorber of light in the visible solar spectrum. In this study, the authors demonstrate a potential approach to enhance optical absorption in ultrathin a-Si films by embedding nickel di-silicide (NiSi2) nanoparticles (NPs). The Ni silicide NPs were engineered inside 50 nm thick a-Si by thermal annealing of co-deposited Ni and Si thin films on Si and quartz substrates. A quantitative electron energy-loss spectroscopy analysis was used to accurately determine the composition of silicide NPs. From broadband absorption optical studies, integrated optical absorption was found to increase by ~85% in the visible solar range (350–750 nm) and by ~150% in the infrared range (750–3000 nm) for the NiSi2 NP incorporated amorphous Si films. Optical modeling captured the absorption behavior of NP embedded a-Si thin films, thus suggesting an efficient route to design new photo-absorber NPs for future Si based PV devices.

Distinguishing the core from the shell in MnO x/MnO y and FeO x/MnO x core/shell nanoparticles through quantitative electron energy loss spectroscopy (EELS) analysis

The structural and chemical characterization of inverted bi-magnetic MnO x (antiferromagnetic)/MnO y (ferrimagnetic) and FeO x (soft-ferrimagnetic)/MnO x (hard-ferrimagnetic) core/shell nanoparticles has been carried out by means of scanning transmission electron microscopy with electron energy loss spectroscopy analysis, (S)TEM-EELS. Quantitative EELS was applied to assess the local composition of the nanoparticles by evaluating the local Mn oxidation state based on the Mn L 3/L 2 peak intensity ratio and the Mn L 3 peak onset. The analysis allows to unambiguously distinguish the core from the shell and to determine the nature of the involved manganese oxides in both cases. The results evidence that the structure of the nanoparticles is, in fact, more complex than the one designed by the synthesis parameters.

Quantitative chemical analysis of ocular melanosomes in stained and non-stained tissues

Energy-filtered Analytical Electron Microscopy (AEM) was used to image the ultrastructure and determine quantitatively the chemical composition of rat melanosomes of the choroid and the Retinal Pigment Epithelium (RPE). For the first time, the effect of staining in elemental analysis of melanosomes was investigated. Detection limits and accuracies of the applied methods were determined.Compared to previous work applying only quantitative Energy Dispersive X-ray microanalysis (EDX) in the TEM (Eibl, O., et al., 2006. Micron 37, 262), here we present a combined quantitative EDX and Electron Energy Loss Spectroscopy (EELS) analysis, including N. This yields the fraction of eumelanin and pheomelanin in melanosomes by the S/N mole fraction ratio. Melanosomes of the sepia ink sac, used as eumelanin standard, showed an S/N mole fraction ratio of <0.004. Thus, they consist primarily of eumelanin as reported by degradation analysis. In contrast, melanosomes of the rats contained mixed melanin with significant amounts of pheomelanin (S/N 0.02) in the RPE and the choroid. Consistent with the previous publication, it was shown that oxygen mole fractions are especially large in melanosomes (7–10at.%) compared to other cell compartments, e.g. 2–4at.% oxygen in the cytoplasm. In the melanosomes of non-stained tissue, the oxygen mole fraction clearly correlated with the Ca mole fraction.EDX spectra used for quantitative analysis had about 15,000 net counts under the oxygen peak, which is necessary to obtain (i) a small statistical error for oxygen and (ii) optimum minimum detectable mole fractions for S, Ca and transition metals. The precise determination of the oxygen mole fraction in melanosomes is important for understanding metabolism. Therefore, a detailed analysis was carried out on the possible errors affecting quantification.While O, S, and N mole fractions yielded similar results in stained and non-stained ocular melanosomes of rats, transition metals can only be determined reliably in non-stained tissues. High-precision EDX analysis of melanosomes yielded minimum detectable mole fractions of less than 0.04at.% for Cu and Zn, these elements were present in melanosomes with mole fractions of about 0.3at.% and 0.1at.%, respectively. Zn is of great importance for metabolism and for age related macular degeneration. Its mole fraction in melanosomes of rats is large enough to be detected and to be quantitatively analyzed by EDX spectroscopy. Ultrastructural information can now be correlated to the elemental composition. This is important to better understand the physical and chemical properties of melanosomal metabolism and turnover.

Characterization of nickel silicides using EELS‐based methods

The characterization of Ni-silicides using electron energy loss spectroscopy (EELS) based methods is discussed. A series of Ni-silicide phases is examined: Ni₃Si, Ni₃₁Si₁₂, Ni₂Si, NiSi and NiSi₂. The composition of these phases is determined by quantitative core-loss EELS. A study of the low loss part of the EELS spectrum shows that both the energy and the shape of the plasmon peak are characteristic for each phase. Examination of the Ni-L edge energy loss near edge structure (ELNES) shows that the ratio and the sum of the L₂ and L₃ white line intensities are also characteristic for each phase. The sum of the white line intensities is used to determine the trend in electron occupation of the 3d states of the phases. The dependence of the plasmon energy on the electron occupation of the 3d states is demonstrated.

Chemical analysis of nickel silicides with high spatial resolution by combined EDS, EELS and ELNES

The purpose of this study is to develop methodologies for the characterization of Ni-silicides by analytical TEM techniques. The measurements are performed in STEM mode to allow a good spatial resolution. Initial examination of the Ni-silicide phases is done by energy-dispersive X-ray spectroscopy (EDS). It is shown that quantification results with high accuracy and precision are obtained when a Ni-silicide reference layer is used as a standard, and an absorption correction is applied to the data. The EDS quantification results are then used as a reference for the quantitative electron energy-loss spectroscopy (EELS) analysis. It is shown that EELS analysis yields quantification results with high accuracy and precision, when the EELS data are treated with a model based approach. The EELS analysis is combined with a study of the Ni-L2,3 near-edge structure (ELNES). The ELNES of the phases can be distinguished either visually or by calculating the branching ratio from the spectra with the model based approach. This paper shows that the different Ni-silicide phases can be distinguished with these EELS based methods. The accuracy and precision of the EDS and EELS results are compared.

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part II: Quantification

A comprehensive electron energy-loss spectroscopy (EELS) study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. Part II of this work is devoted to quantitative EELS by means of experimental k-factors derived from the intensity ratio of the O-K edge and the Nb-M4,5 or Nb-M2,3 edges for all three stable Nb-oxides. The precision and accuracy of the quantification are investigated with respect to the influence of intensity-measurement energy windows, background subtraction, and sample thickness. Integration-window widths allowing optimum accuracy are determined. Owing to background-subtraction errors, the Nb-M4,5 edges rather than Nb-M2,3 are preferred for quantification. Different approaches are applied to improve the precision with regard to thickness-related errors. Thus, a precision up to +/-1.5% is achieved by averaging spectra from all three reference oxides to determine a k-factor using Nb-M4,5. Using the experimental k-factor, the determination of atomic concentration ratios CNb/CO in the range of 0.4 (Nb2O5) to 1 (NbO) was found to be possible with an accuracy of 0.6% (relative deviation between measured and nominal composition), whereas ratios of calculated partial ionization cross sections lead to less accurate results.

Local valence and magnetic characteristics ofLa2NiMnO6

Epitaxial thin films of ordered double perovskite ${\text{La}}_{2}{\text{NiMnO}}_{6}$ have been studied by a combination of high-resolution scanning transmission electron microscopy, quantitative electron energy loss spectroscopy, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD) spectroscopy. Our results show the nominal oxidation states of Ni and Mn ions to be ${\text{Ni}}^{2+}$ and ${\text{Mn}}^{4+}$ thus the ferromagnetism in ground state is mainly due to ${\text{Ni}}^{2+}{\text{-O-Mn}}^{4+}$ superexchange interactions. In addition, short-range ferromagnetic correlations are observed above the Curie temperature $({T}_{C}\ensuremath{\sim}280\text{ }\text{K})$ from XMCD measurement, which are likely induced by antisite defects against long-range ordering of the Ni/Mn sublattice. The XMCD results also demonstrate that the ${\text{Ni}}^{2+}$ and ${\text{Mn}}^{4+}$ ions are ferromagnetically aligned but exhibit large differences in the spin and orbital contributions to their effective magnetic moments.

Kinetic measurements from in situ TEM observations

Environmental transmission or scanning transmission electron microscope is ideally suited to observe gas solid interactions at nanoscale. It is shown that the time and temperature resolved data, obtained from in situ observations, can be used to obtain reaction rates and understand the kinetics of the processes. Low or high magnification images provide the change in length, area or volume with time at constant temperature and pressure conditions during nitridation of Cu-Cr thin films, deposition of Au particles, growth of Si nanowire and carbon nanotubes. Effect of electron beam is estimated by making observations with and without constant electron beam exposure. Quantitative electron energy loss spectroscopy is employed to measure the reduction rate of Ce(+4) in pure ceria, mixed oxides (ceria-zirconia) and catalyst (Rh-ceria-zirconia) powders.

3D morphology of the human hepatic ferritin mineral core: New evidence for a subunit structure revealed by single particle analysis of HAADF-STEM images

Ferritin, the major iron storage protein, has dual functions; it sequesters redox activity of intracellular iron and facilitates iron turn-over. Here we present high angle annular dark field (HAADF) images from individual hepatic ferritin cores within tissue sections, these images were obtained using spherical aberration corrected scanning transmission electron microscopy (STEM) under controlled electron fluence. HAADF images of the cores suggest a cubic morphology and a polycrystalline (ferrihydrite) subunit structure that is not evident in equivalent bright field images. By calibrating contrast levels in the HAADF images using quantitative electron energy loss spectroscopy, we have estimated the absolute iron content in any one core, and produced a three dimensional reconstruction of the average core morphology. The core is composed of up to eight subunits, consistent with the eight channels in the protein shell that deliver iron to the central cavity. We find no evidence of a crystallographic orientation relationship between core subunits. Our results confirm that the ferritin protein shell acts as a template for core morphology and within the core, small (∼2 nm), surface-disordered ferrihydrite subunits connect to leave a low density centre and a high surface area that would allow rapid turn-over of iron in biological systems.